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Tropical Coral Reef Environment Rhythmicity and
Techniques for Inducing Captive Coral Spawning
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Steve Tyree Reef Breeder
October 1992
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Modern captive coral reef aquaria ecosystems have attained the capability
for supporting the long term healthy maintenance of many tropical reef
corals. The stimulation of asexual reproduction has also occurred for many
species and captive propagation is proceeding slowly. Asexual reproductive
methods include fragmentation, budding, fission and colonial proliferation.
The corals currently being asexually propagated consist of numerous soft
species (Orders Actiniana, Corallimorpharia, Zoanthiniaria and the entire
Subclass of Octocorallia) and a few stony corals (Order Scleractinia).
When these captive ecosystems are combined with simulated natural environment
parameter variances, some stony and soft corals have been stimulated
to spawn by utilizing sexual reproductive methods. Examples of these methods
are brooded planulae, massive broadcast egg and sperm release, egg
and sperm bundles or planulae bundle releases. This article contains a
review of coral reef ecosystem parameter research and describes successful
captive spawning induction techniques. Speculation on the application of
this research in alternative spawning methodology will also be presented.
An extensive literature cited listing provides references to important
data and details the location of additional scientific breeding information.
A glossary of scientific terms is included to help define some of
the more complex words.
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Natural Coral Reef Ecosystem Parameter Variances
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On a natural marine reef many environmental variables have the potential
for affecting the spawning behavior of coral reef species. Juvenile scleractinian
coral recruitment on the Great Barrier Reef has been documented
to have seasonal peaks and annual fluctuations which are greatest during
the local spring-summer (Oct to Feb) season. The percentage of coral recruitments
occurring there in spring-summer can be 89%, in summer-winter
(Feb to Jan) 8% and in winter-spring (Jun to Oct) 3% (Wallace, 1985). The
periodicity in the breeding patterns for marine species can be analyzed
as three distinct rhythms. The annual rhythm determines the length of the
breeding season and can vary amongst speciations. Temperature is probably
the most important seasonality inducer and breeding seasons can extend all
year or be as short as a couple of annual days. Within the breeding season
a monthly rhythm can exist for the maximum and minimum spawning periods.
This periodicity could be induced by tides, moon luminance or biological
inbreed factors. Recent studies have shown that moon luminance may be the
most dominate environmental monthly rhythmic trigger. The daily rhythm is
established when marine species actually release gametes. Certain repeatable
patterns suggest that each species has an optimum daily time for releasing
(Korringa, 1947). The simulation of annual sea temperature variations,
monthly lunar or tidal cycles and annual diel light cycles for the
Great Barrier Reef, might induce a synchronous mass spawning event in a
captive tropical reef ecosystem. Sea water temperature patterns in that
region may influence gametogenic cycles and lunar brightness might possibly
induce lunar periodicity in spawning (Babcock et al., 1986).
Some of the following parameters have been empirically employed to induce
corals to sexually spawn in captivity by duplicating their natural rhythmicity.
These parameters are all described with reference to their value in
inducing captive spawning only. Information detailing the routine healthy
maintenance of reef species can be found in more species specific articles.
Always use caution when changing any parameter in your captive reef
and use the suggested guidelines or establish safer variances while constantly
monitoring the condition of your specimens. The exact duplication
of natural parameters might have negative implications towards the healthy
maintenance of captive reef species. The longer photoperiod and higher
temperatures which occur during the summer months can put severe stress
on the corals and possibly cause bleaching (Yap et al., 1992). Winters
seasonally low temperatures and shorter photoperiods can depress coral
growth (Kojis, 1986b). Reef flat tidal variations can cause incredible
daily extremes in temperature, luminance and salinity.
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Sunlight Diel Time or Photoperiod
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This parameter represents the total length of time that the ecosystems
main lighting is at full intensity. The period or "cycle" time for daylight
reef lighting should vary in an annual natural rhythm that corresponds
to a natural reefs daylight variances. These variances are relative
to the tropical reefs latitudinal location. An example of natural reef
annual photoperiod periodicity can be found on the eastern side of Cangaluyan
Island, Pangasinian, Philippines (16 deg 22 min N) (120 deg 00 min
E). Highest recorded value of mean day length in 1983 was 12.97 hours and
the lowest was 11.22 hours (Yap et al., 1992). The suggested reef ecosystem
range is 10 hour cycle times during winter and up to 13 hours during
summer which is separate from the twilight or moonlight periods. On the
Great Barrier Reef the seasonally increasing photoperiod reached 11.2 to
11.4 hours when oocytes increased in size and started proliferating in
Acropora palifera (Kojis, 1986b). Captive ecosystem coral sexual spawns
have been reported to occur with photoperiods of 11 to 12 hours. The maximum
suggested rate of photoperiod change is 1 hour per month with 30 minute
diel length shifts recommended for stability. This sunlight luminance
is normally reproduced utilizing metal halide bulbs or VHO florescent tubes
with high color temperature values greater than 5000 degrees kelvin.
The heat generated from metal halide bulbs must be dissipated if the longer
photoperiods which exist during summer are to be duplicated. This thermal
influence needs to be considered when annual temperature rhythmicity
is determined.
Most annually spawning coral develop and release gametes during the late
spring or early summer season. One possible seasonal limiting factor might
be the energy requirements for planula production which are supported by
translocation of products from algal photosynthesis (Rinkevich, 1989). The
longer diel times which persist in the summer months probably cause an increase
in the creation of algal photosynthesis nutrient products (Tomascik
and Sander, 1987). These nutrients appear to be consumed more rapidly during
planulae production. This could lead to the hypothesis that longer
diel times might always be beneficial for stimulating gamete production
and for inducing monthly planulae brooding corals to spawn more regularly.
Suspended particulate matter can limit the amount of surface illumination
which penetrates local sea water over a natural reef. This lower light intensity
value has been shown to affect coral growth rates (Tomascik and
Sander, 1985). Captive coral reef ecosystems require special design, regular
maintenance and adequate filtration to limit suspended particulate
matter and to prevent microalgae overgrowths from adversely affecting the
captive corals. Micro and macro algaes can overgrow certain areas of a
coral colony and restrict the amount of illumination the coral receives.
The captive reefs support and maintenance systems must be operating superbly
if maximum diel times of 12 to 13 hours are to be achieved without
possible blooming hair algae growths. A very abundant growth of coralline
algaes will help prevent microalgae blooms from inhibiting the maximum
attained photoperiod.
Every coral species specimen requires a specific light intensity and wave
length for an exact duplication of its natural environment. The main difficulty
with this duplication attempt is that these natural ecosystem
lighting specifications are never completely known by the reef breeder.
Soft and hard corals can modify their light gathering capabilities by morphological
changes in growth, algal symbionts population changes and daily
physical form manipulation in orientation, expansion or extension. This
capability has probably evolved due to the dynamic nature of the coral
reef environment and can be utilized in a captive reef ecosystem if the
specimen is properly acclimated.
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Twilight Period
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This parameter is equivalent to the length of time in which the sun is
setting or rising on the horizon. During this period a twilight or low
light intensity value occurs for a short duration. Many coral and fish
species use the night twilight intensity value as a triggering device for
spawning activity. The majority of spawn releases in captive reef aquaria
have occurred during the last few minutes of night twilight and for a few
minutes afterward. On natural reefs scientist use hours from sunset as a
standard spawn time measure and this should equate with hours from start
of twilight for a captive ecosystem. During mass synchronous spawnings of
scleractinian corals on the Great Barrier Reef, most releases of gametes
begin after sunset. Species spawn during specific time frames which range
from 10 minutes after sunset to 4 hours after sunset (Babcock et al.,
1986). The onset of darkness might be the last forcing function which induces
spawning after other seasonal and monthly triggers have occurred.
Captive Reef ecosystems will operate more naturally if these twilight
periods are simulated and the suggested range is 30 minutes to 2 hours for
this intermediate light intensity. The authors reef contains corals and
fish which spawn quite regularly and the fish do benefit from extending
the night time twilight. This extended period permits the fish to spend
more time in the prespawning ritual dance and might possibly provide extra
coral bundle setting time. The morning twilight period is 30-60 minutes
and the evening twilight period is extended for 60-120 minutes. Twilight
can be reproduced with actinic florescents or a dimmer daylight configuration
that allows the observation of gamete releases. Spawn releases which
occur near the full moon and after the twilight period can be observed if
the simulated peak moonlight has enough luminance, otherwise occasional
searches with a flashlight will have to be performed.
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Moon Light Intensity
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The reflected light intensity from the moons surface experiences a periodic
phase which is approximately 29.5 days long. The full moons position
in our sky is 180 degrees out of phase with the sun and when the sun sets
the moon rises with its luminance at maximum intensity. The new moon is in
phase with the sun and rises in conjunction. At first and last quarter the
moon is 90 degrees out of phase with the sun and will remain in the sky
for half the night. The moon intensity from new to full, if measured as
total photons received during the night, rises slowly initially and then
slopes upward very quickly as the brighter moon remains in the night sky
longer. This positional periodicity helps define the full phase period
and might have contributed to the synchronous spawning behavior. Moonlight
intensity rises more linearly if brightness is measured as the maximum
attained daily value instead of total quantity of photons received during
the night.
The maximum full moon intensity should be a factor of the particular ecosystems
twilight and also prevent local ambient nite light from affecting
the new moon phase. A suggested full moon maximum would be equivalent to
twilight or down to 1/2 or 1/4 luminance of twilight. A background new
moon ambient luminance should exist since corals usually receive starlight
at night. Moon light can be reproduced with 15-25 watt incandescent bulbs
positioned over the top of the reef. Moonlight luminance on an natural
reef is a very small fraction of maximum daylight luminance. Night irradiance
measurements show the following. Full moon PPFD or photosynthetic
photon-flux density was 0.01 micro E / m(squared)s while midday readings
showed 2,000 micro E / m(squared)s (Jokiel et al., 1985).
A scientific review detailed the reproductive traits for 210 of the 600
known species of scleractinian corals. Most species were hermaphroditic
broadcast spawners (131), while some were hermaphroditic brooders (11) and
gonochoristic brooders (7) and a few gonochoristic broadcasters were also
studied. Broadcast spawners outnumbered brooders in the pacific regions
and the Red Sea. Brooding appears to be the dominate form of reproduction
from the caribbean. Nocturnal illumination might be the fine tuning or
forcing function for determining the daily rhythm or timing of spawning.
Differences in timing among allopatric populations of species may represent
adaptations to local environmental parameters and cues which could
also raise questions concerning taxonomy based on morphological characteristics
alone. Over 80 % of spawns occurred following the full moon while
less than 15 % followed the new moon phase (Richmond and Hunter, 1990).
An extensive amount of research has analyzed moon luminance periodicity
and its contribution to lunar spawning synchronicity. Data extracts will
be included below and have been combined into 5 different groups. The
Great Barrier Reef, The Red Sea, The Hawaiian Islands, The Caribbean and
the Authors Captive Reef Ecosystem.
- The Great Barrier Reef -
Research locations on the Great Barrier Reef included Magnetic Island
(19 deg 10 min S) (146 deg 52 min E), Orpheus Island (18 deg 36 min S)
(146 deg 29 min E), Big Broadhurst Reef and Bowden Reef (~19 deg S), Lizard
Island (~15 deg S) and Heron Island. Mass synchronous spawning in
October and November from 1984 to 1987 for 16 species of soft coral (Alcyoniidae
Family) at Magnetic Island was observed 2 to 5 days following
the full moon. Spawning occurred at Orpheus Island in November and December
(Alino and Coll, 1989). Spawning in 1983 was observed on Big
Broadhurst, Bowden Reef and Lizard Island to occur 5 to 6 days following
the seasonal full moon. At Magnetic and Orpheus Island spawning was 3
to 5 days following the full moon (Babcock et al., 1986). In 1981 mass
spawning occurred in mid-october and mid-november 5 to 8 days after the
full moon at Magnetic Island. Spawning was observed again in november 4
to 5 days after the full moon. Acroporid and Faviid species were seen to
release spawns from 2000-2330 during the night. Spawns in 1982 were also
seen at Orpheus Island and Bowden Reef in early December from 4 to 5 days
following the full moon (Harrison et al., 1984). The species Goniastrea
australensis spawned at Heron Island between day 3 and 4 following the
full moon during research conducted from 1977 to 1980. Spawning occurred
from 1600-1800 during neap low tides (Kojis and Quinn, 1981).
One reason for synchronous lunar spawning was speculated to be the reduction
in the ability of would-be predators to consume all the reproductive products
from the spawning coral colonies (Alino and Coll, 1989).
It appears that the seasonal warming spring water started the maturing
of gonads in these great barrier reef corals. A large study of 105 species
found that 87 of them spawned within 3 to 6 nights following the
seasonal full moon. One mass spawning occurred on the inshore reefs in
october and this was followed by the off shore reefs which spawned in
november (Babcock et al., 1986).
- The Red Sea -
The soft coral Parerythropodium fulvum fulvum was found to have two
distinct lunar spawning rhythms. Shallow water (3 - 5 m) coral spawned
between the full moon and last quarter. Deeper reef zone (27 - 30 m)
coral spawned between the new moon and first quarter. The reproductive
period for this surface brooding egg developer was from the end of june
through the beginning of august (Benayahu and Loya, 1983). The planula
brooding coral Stylophora pistillata was studied at a latitude of 30 deg
N in the Gulf of Eilat. Planulae shedding occurred from december through
july during all 8 moon phases. The annual temperature range was 20 C to
26 C. This same species was found to exhibit year long planulation with
lunar periodicity at 7.5 deg N in a annual temperature range of 27 C to
28 C (Rinkevich and Loya, 1979). Spawning on the Red Sea was discovered
to exhibit some lunar periodicity however spawning seasons, months and
lunar phases varied. The development of these traits have been attributed
to temporal reproductive isolation. The reproductive season was 3 to 4
months long and spawning occurred generally twice annually for 2 to 6
nights. Most gonads started development in january and february and actual
spawning releases occurred in may, june, july and august (Shlesinger,
1985).
- The Hawaiian Islands -
Three species of Acropora were studied on the French Frigate Shoals and
A. valida spawned in 1989 right after a new moon. A. humilis was observed
to spawn during the moons first quarter. A. cytherea in okinawa spawned 1
to 2 days after the late spring full moon. On Johnston Atoll the coral was
seen to spawn 5 to 6 nights after the may 31 full moon in 1988 (Kenyon,
1992).
A study on the coral species Pocillopora damicornis verified that lunar
periodicity was occurring for this monthly planula brooder. Two distinct
types of P. damicornis were analyzed. Type Y spawned synced to the full
moon while Type B synced to new moon phases. The corals were subjected to
constant full moon luminance, constant new moon luminance and a 15 day
shifted lunar cycle. The corals responded quickly to the shifted cycle
experiment. The reproductive output was reduced during the constant new
and full moon experiments. The following table combines results from both
coral types.
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| constant full shifted constant new
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larvae |
produced | 15,400 23,100 11,300
--------------|-------------------------------------------------------
mean planulae |
settled on | 7.30 52.00 35.50
aquaria wall |
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Type Y was able to sync into the shifted phase in 3 to 4 cycles while
type B could accomplish this shift in 2 to 3 cycles. Type B spawning went
into a unsynced rhythm very quickly in a constant full moon while type Y
held sync for 3 or 4 phases till going unsynced. Both types went into
very little productive output after only 2 phases of new moon treatment.
Type Y was able to increase an unsynced production in 3 to 4 phases. In
nature type B will reduce its monthly planulae output during heavy cloud
cover periods. Type Y has shown an ability to sync into a new rhythm without
an apparent external sync.
This study concluded that the mechanisms behind these observed phenomenon
in corals (as in most other species) is a mystery. They also noted that
the rather dramatic biological response to changes in the monthly cycle of
night irradiance demonstrates that subtle modulation of the natural photic
environment is an extremely important environmental factor. One explanation
for this phenomenon was that a regulatory process in corals involves
the photo chemical control of a substance that influences early gametogenesis.
Another possibility was that extremely low rates of photosynthesis
by zooxanthellae on moonlit nights might influence metabolism and hence
influence reproduction in corals. Species could posses neurologically
linked photoreceptors that have not yet been described (Jokiel et al.,
1985).
Two species of Pocillopora were also researched in the eastern pacific.
P. damicornis spawned after the new moon and P. elegans spawned after the
full moon (Glynn et al., 1991).
A study in Hawaii and Enewetak was performed on 19 species. Coral species
Pocillopora damicornis spawned after a full moon in Hawaii but spawned
after a new moon at Enewetak. In Australia this species only planulated
after the new moon from december to april and after the full moon from
july to august. In Palau the coral was a new moon spawner. The following
table lists percentage spawning for some species during the 4 lunar phases
(Stimson, 1978).
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species |new (1-7)|first (8-14)|full (15-12)|last (22-28)
-------------------|---------|------------|------------|------------
Pocillopora jun-jul| 55 % | 29 % | 1 % | 0 %
verrucosa jan | 16 % | 53 % | 0 % | 0 %
-------------------|---------|------------|------------|------------
Pocillopora jun-jul| 65 % | 12 % | 0 % | 38 %
damicornis jan | 57 % | 100 % | 0 % | 8 %
-------------------|---------|------------|------------|------------
Pocillopora jun-jul| 60 % | 5 % | 0 % | 0 %
elegans jan | 0 % | 40 % | 0 % | 0 %
-------------------|---------|------------|------------|------------
Seriatopora jun-jul| 54 % | 43 % | 27 % | 0 %
hystrix jan | 0 % | --- | 0 % | 13 %
-------------------|---------|------------|------------|------------
Acropora jun-jul| 40 % | 0 % | 0 % | 0 %
humilis jan | 0 % | 0 % | 0 % | 0 %
-------------------|---------|------------|------------|------------
Acropora jun-jul| 0 % | 8 % | 0 % | 0 %
striata jan | 29 % | 33 % | 0 % | 0 %
-------------------|---------|------------|------------|------------
Acropora jun-jul| 12 % | 20 % | 0 % | 0 %
corymbosa jan | 0 % | 0 % | 0 % | 0 %
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- The Caribbean -
In the shallow waters of the Atlantic coast of Panama, 11 species of
scleractinian coral were studied at a latitude of 9 deg N. Spawning
periodicity for 7 broadcast corals was from august to september which
happened to be a period of declining temperatures. Annual sea temperatures
vary from 26.5 C to 29 C and initiation of gametogenesis might be
caused by rising temperature in spring. The remaining studied species
were year long planula brooding spawners. Of the four planulae brooders
only Favia fragum showed lunar periodicity in release rhythm. Planula
size for F. fragum exhibited a lunar development rhythm which is listed
below (Soong, 1991).
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lunar day | 24 25 26 30 5 8 10
------------|-----------------------------------
size in mm | .55 .60 .67 .72 .81 .83 .86
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The coral species Favia fragum, a year long planulae brooder, was studied
to determine if lunar periodicity existed in development of spermatozoa,
ovaries and embryo. Lunar periodicity was found during oogenesis
by determining that maximum size was reached from 8 to 18 days following
the new moon. It appears that several months are required for oocytes to
attain maximum size and only a few are fertilized every month. Spermatogenesis
was also found to have lunar periodicity by developing tails from
day 10 to 18. Embryogenesis first started from day 16 to 17 with the appearance
of embryos which developed into brooded planulae. Peak release
of fully developed planulae occurred from day 9 to 11. The timing of ovulation
and spawning events were more closely synchronized with the lunar
cycle than the timing of planulation. Ovulation occurs over at most 2 to
3 day period, while planulation occurs over more than a week. This study
suggested that the lunar forces are acting to synchronize the spawning
event and that the planulae begin to dribble out about 3 weeks later as
they mature (Szmant-Froelich et al., 1985).
A study of Caribbean corals was performed to determine lunar periodicity.
Most corals observed spawned in the July to September period.
Diploria strigosa was observed spawning 7 nights following the July/
August 1985 full moon. Preparation for spawning for Acropora cervicornis
on night 6 after the August 1984 full moon and 7 to 8 days after the
July/August 1985 full moon. Several colonies of Montastrea annularis
spawned in the laboratory 8 days after the September 1984 full moon.
The D. strigosa released large bundles 2-4 mm in diameter of gametes by
individual polyps at around 2100 h. Mycetophyllia ferox brooded planula
only during the winter season (January to April). Favia fragum displayed
embryogenic cycles all year long. This study demonstrates that Caribbean
Reef corals do have well-defined seasonal patterns of sexual reproduction
(Szmant, 1986).
The caribbean broadcast spawning reef corals Montastrea annularis and
M. cavernosa were studied at Puerto Rico. M. annularis is hermaphroditic
while M. cavernosa is gonochoric. Speculation was made that planulating
coral are opportunistic and short lived corals, while broadcast spawners
are longer lived. Oogenesis in M. annularis begins in early summer and is
completed in less than 4 months. While in M. cavernosa oogenesis occurs
throughout most of the year. The spermatogenic period of M. annularis is
also shorter than M. cavernosa. Both species spawned 1 week after the full
moon in august. Annual temperature range is 3 to 4 C. Spawning in Puerto
Rico occurs in the warmest months of year while the photoperiod is decreasing.
Spawning might be uniform from Bermuda to Panama which could
contradict the Great Barrier Reef latitudinal spawning variations (Szmant,
1991).
- The Authors Captive Reef Ecosystem -
A lunar time scale experiment was conducted on the authors reef and the
full moon periodicity was shortened to a 15 day cycle instead of the normal
29.5 days. This experiment attempted to produce a synchronous mass
spawn within a 3 month test period but was not successful. While this
experiment was running an annual broadcast egg spawner released eggs and 2
brooders released planulae bundles. The egg broadcaster was a branching
Euphyllia ancora coral that released eggs after an artificial new moon on
July 8 1992. Planulae bundles of green and brown color were also released
during this experiment. The events are listed below.
June 6 1992 new moon
June 9 green planulae bundle released
June 11 brown planulae bundle released
June 14 1992 full moon
June 21 1992 new moon
June 29 1992 full moon
July 6 1992 new moon July 8 approximately 100 eggs broadcast
July 9 approximately 200 eggs broadcast
July 9 green planulae bundle released
July 10 approximately 1500 eggs broadcast
July 11 approximately 50 eggs broadcast
July 11 brown planulae bundle released
July 14 1992 full moon
July 21 1992 new moon July 21 approximately 250 eggs broadcast
July 22 approximately 1000 eggs broadcast
July 23 approximately 250 eggs broadcast
July 24 approximately 200 eggs broadcast
July 25 1992 constant full moon interruption till august 4.
August 5 1992 new moon August 9 approximately 100 eggs broadcast.
The above recordings illustrate that the monthly planulae brooders were
probably not able to produce mature planulae in half normal time. The
annual egg broadcaster released eggs after the new moon on July 6 and 15
days later after the July 21 new moon. This demonstrates that once the
eggs are mature the spawning release will sync into the lunar phase even
if this phase is twice as fast. This experiment shows the importance of
using a rhythmic moon luminance in the spawning induction of captive
corals. Since most spawns occur following the full moon and new moon, it
appears that the actual triggers may be the lowering of luminance intensity
from full and the increasing luminance from new. The authors reef
ecosystem is currently synced into a natural 29.5 day lunar rhythm.
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Moon Rise and Set Times
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This parameter represents the rise and set time of the moon for any
specific day of the monthly cycle. Calculating rise and set times for exact
geographical reef locations requires algorithmic computer power for
accuracy, however some published marine tables are available. Astronomical
software programs could be combined with computer control to automatically
raise and lower the proper moon luminance at specific calculated times.
Integrating a moon control system can be very beneficial for inducing
spawning but fortunately less complicated methods are possible. The authors
moon control system requires the manual linear setting of luminance values
which are based on average total photons received per night. This has
stimulated Euphyllia ancora, Trachyphyllia geoffroyi, Gorgonian sp., Turbinaria
turbinata, Actinodiscus sp. and other corals to naturally spawn via
planulae or coral egg releases. The table below lists the authors monthly
linear moon luminance values for an entire cycle. Note - full moon intensity
is approximately half twilight intensity.
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day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
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value.00 .01 .02 .04 .07 .11 .16 .22 .28 .36 .44 .54 .64 .74 .86 1.0
phasenew first full
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day 17 18 19 20 21 22 23 24 25 26 27 28 29 30
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value.86 .74 .64 .54 .44 .36 .28 .22 .16 .11 .07 .04 .02 .01
phase last
--------------------------------------------------------------------
Interruptions of moonlight regularly occur due to cloud weather patterns
which vary nightly and hourly. This has led scientists to speculate that
lunar rise and set times could be significant in the development of synchronous
monthly spawning rhythms (Oliver, 1992). This potential ability to
sync with rise and set times might find substantiation in a scientific
study performed on Pocillopora damicornis coral. The coral was researched
at Enewetak Marshall Islands (11 deg 26 min N) (162 deg 24 min E) and Kaneoke
Bay Hawaii (21 deg 60 min N) (157 deg 47 min W). Three distinct lunar
rhythms were discovered and determination if these were due to geographic
phenomena or isolated phase shifting was attempted. Planula releases that
occurred in outdoor aquaria stayed in sync with the natural undisturbed
specimens on the reef. The species in Enewetak released planula following
the new moon with peak releases occurring seven days after full. In Kaneoke
Bay two distinct planula lunar release periods were found. One group
released between the full moon phase and third quarter, while the second
group preferred to release between the first quarter and the full moon.
The mean water temperature in hawaii was 25.0 C (77.0 F) with an annual
range of 7.7 C and the study sites were in shallow water. A mean temperature
of 27.9 C (82.2 F) with an annual range of 4.8 C occurred in the
deeper waters at Enewetak. One hypothesis for the shifted lunar spawning
phase was the possibility that geographically separated populations
through natural selection had modified their timing of peak planula release
to coincide with optimum local environmental conditions. A second
hypothesis was concerned with the possibility that these coral were actually
composed of three distinct species of Pocillopora. The ability to synchronize
planulae release on any phase of the moon was certainly demonstrated
(Richmond and Jokiel, 1984).
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Water Temperature
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This parameter represents the average daily water temperature and usually
varies in a seasonal rhythm. Daily temperature fluctuations in a captive
reef ecosystem should be kept to a minimum. Water on a natural reef is
warmer during the local summer period and cooler during the local winter
period and some reef locations experience very large annual temperature
extremes. These variations in temperature were researched in three scientific
studies and data from this research is listed below. Note - Some
values were interpreted from graphs.
Annual temperatures on Curacao Netherlands Antilles (12 deg 30 min N).
(Van Moorsel, G.W.N.M., 1983).
1979 jan feb mar apr may jun jul aug sep oct nov dec
C 26.6 26.4 26.3 26.5 26.8 28.1 27.6 27.7 28.6 28.5 28.7 27.4
1980 jan feb mar apr may jun jul aug sep oct nov dec
C 26.8 26.7 25.4 26.5 27.4 27.0 26.8 27.8 28.5 29.0 28.2 27.2
1981 jan feb mar apr
C 27.2 27.0 26.6 27.5
Maximum and minimum temperature examples for the eastern side of Canga-
luyan Island, Pangasinan, Philippines (16 deg 22 min N) (120 deg 0 min E)
(Yap et al., 1992).
Highest maximum daily temperature 33 C (91.4 F) jul-oct 1983
Lowest maximum daily temperature 29 C (84.2 F) jan-feb 1984
Highest minimum daily temperature 31 C (87.8 F) apr-jun 1984
Lowest minimum daily temperature 24 C (75.2 F) dec 83 - jan 1984
Maximum temperatures
1983 July/Apr Sep/Oct Dec/Jan Feb/Mar Apr/May 1984
33 33 29.7 31.6 32 C
Minimum temperatures
1983 July/Apr Sep/Oct Dec/Jan Feb/Mar Apr/May 1984
28 26.8 23.9 25.8 31 C
Barbados seasonal temperature extremes, 26.2 C(79.2 F) - 29.5 C(85.1 F)
(13 deg 10 min N) (Tomascik and Sander, 1985).
When seasonal temperature variations have wide extremes, corals appear
to spawn within certain thermal parameters. Temperatures coinciding with
tropical coral spawning were researched and data extracts from four of
these studies is listed below.
Gonad maturation of Goniastrea australenis at Heron Island on the Great
Barrier Reef may be influenced by the spring temperature rise beginning
in september. Final ripening occurred when a minimum temperature of
approximately 23 C (73.4 F) to 24 C (75.2 F) was reached. At nearby Lord
Howe Island the rapid spring temperature rise begins in november and the
23 to 24 C gradient is not reached until January. This could explain why
spawning of this species occurs 2 months later at Lord Howe Island (Kojis
and Quinn, 1981).
The coral Pocillopora damicornis was studied in Hawaii and the best
reproductive temperature was found to be 26 to 27 C (78.8 to 80.6 F). The
maximum reproduction rate occurred within 1 degree C of 26.5 C. The coral
was able to maintain a high growth rate in the 24 to 29 degree C range,
with rates changing by less than 10 % with a 1 degree C difference in
temperature. The high reproductive rate changed drastically with a 1 degree
difference in the temperature range of 26 - 27 degree C. Summer temperature
was always above 26 C (Jokiel and Guinther, 1978a).
Sexual reproductive spawning in Hawaii of various Acropora sp. occurred
at a temperature of 29.5 degrees Centigrade (85.1 F)(Kenyon, 1992).
The Great Barrier Reef undergoes a rapid rise in temperature which occurs
in the local spring from august to september. Mass spawnings happen from
mid-october to early december. The possible importance of temperature in
determining timing of the spawning season is supported by the differences
in the month of spawning at the inshore and offshore reefs. On 1982 at
Magnetic Island, spawning happened during early november while spawning at
Big Broadhurst Reef, Orpheus Island occurred one month later in early
december. The shallow water at Magnetic Island warms faster and gonads
mature quicker. The following charts list temperature data from these sites.
(Babcock et al., 1986).
Palm Island jan feb mar apr may jun jul aug sep oct nov dec
1979-1984 30.3 30.6 30.2 28.8 27.1 24.8 23.0 23.4 25.1 27.1 28.8 29.2
2-5m depth spawning occurred in november at 28.3 C
Magnetic 25.1 28.2 29.6
Island spawning occurred in october at 27.4 C
jan apr sep oct nov
1980 21.5 22.0 24.0 26.7 28.0 spawning 27.3 C
1981 22.0 23.8 24.6 24.5 28.0 spawning 26.5 and 29.0 C
1982 21.0 21.5 22.2 24.5 27.0 spawning 27 C
1983 21.3 21.5 24.0 28.0 29.0 spawning 28.4 C
Temperatures and photoperiods follow annual patterns that vary relative
to latitudinal location. These geo-indexed parameters might be the
controlling factors in spawning pattern variances. Latitudinal seasonal
variations have been studied and data from three of these studies was
extracted and listed below.
The following chart compares annual temperature variations to latitudinal
locations (Richmond and Hunter, 1990).
|-----------------------------------------------------------------------|
|parameter |Central|Caribbean|Hawaii|Red Sea|Okinawa|Great Barrier|
|description |Pacific| | | | |Reef-Magnetic|
| | Guam | Barbados| Oahu | Eilat | | Island |
|----------------|-------|---------|------|-------|-------|-------------|
|annual variation| | | | | | |
|in sea water | 2.2 | 3.2 | 4.0 | 6.0 | 9.8 | 12.0 |
|temperature | | | | | | |
|----------------|-------|---------|------|-------|-------|-------------|
|percentage of | | | | | | |
|coral spawning | 18% | 26% | 29% | 20% | 65% | 88% |
|in same month | | | | | | |
|and lunar phase | | | | | | |
|----------------|-------|---------|------|-------|-------|-------------|
|latitude degrees|13 deg | 13 deg |21 deg|30 deg |26 deg | 19 deg |
|latitude minutes|30 min | 10 min |30 min|00 min |30 min | 00 min |
|----------------|-------|---------|------|-------|-------|-------------|
|depth of site |> 10 m | > 10 m |> 10 m|> 10 m |> 10 m | * < 10 m |
|-----------------------------------------------------------------------|
Temperature variation in the above chart is in degrees centigrade.
Degree of synchrony among species may be related to sea water temperature
ranges in each region and the trend is for decreasing synchrony as the
annual variations in temperature get smaller. This correlates with
tighter interspecific synchrony with increased seasonal temperature range.
This could establish an order of importance for the parameters causing
synchronicity in mass spawning to be: temperature (seasonal cue),
photoperiod (stimulate photosynthesis) and moon luminance (monthly sync).
The coral Pocillopora damicornis was studied at Rottnest Island near
Western Australia which is the southern limit of its distribution. The
findings from this study were compared to studies performed on this
species at other geographical locations. The seasonality in planulation
is primarily mediated by variations in sea temperature. The local variation
in sea temperatures were greater than 10 degrees C. Planulation
only occurred at maximum water temperature of 25 to 26 C. This species
in Hawaii was found to have a year round planulation with optimum
development of planulae occurring at 26 to 27 degrees C. The temperature
annual range at the Hawaii location was 7.7 degrees C. On Lizard Island
of the Great Barrier Reef the annual temperature range is 4 degrees C,
which provides a less marked seasonal variation in temperature. A
substantial seasonal component was found in the abundance of planulae, due
to the planulation rate being minimum at minimum temperature ranges. At
Enewetak on the Marshall Islands seasonal temperature varies only 4.8
degrees C. Year round planulation occurs with a fecundity rate doubled
during summer as compared to winter. This means that environmental
parameters don't fully explain the latitudinal variation in planulation
for this species, due to the Lizard Island findings. At non-optimum
temperatures the period of gametogenesis may be increased, planulation may
shift or production can be ceased and reabsorption of gametes may ensue
(Stoddart and Black, 1985).
The coral Acropora palifera, a planulae producer, was studied at three
different locations. The latitudinal coordinates of the locations were
all south of the equator and are listed below (Kojis, 1986b).
Lizard Island Great Barrier Reef Lat 14 degrees 40 minutes
Salamaua/Busama near Lae, Papua New Guinea Lat 7 degrees 4 minutes
Heron Island Great Barrier Reef Lat 23 degrees 27 minutes (Kojis, 1986a)
The intent of the study was to determine how sea temperatures which vary
inversely with latitude, affect the spawning procedures of this coral.
The mean temperature and annual range are listed below.
----------------|--------------|-------------------|------------------|
measurement | Salamaua | Lizard Island | Heron Island |
----------------|--------------|-------------------|------------------|
mean surface | | | |
temperature | 29.5 C | 26.5 C | 24.5 C |
----------------|--------------|-------------------|------------------|
annual range of| | | |
monthly mean | 3.5 C | 5 C | 6 C |
water temps | | | |
----------------|--------------|-------------------|------------------|
latitude | 7 deg 4 min S| 14 deg 40 min S | 23 deg 27 min S |
| low latitude | mid latitude | high latitude |
----------------|--------------|-------------------|------------------|
breeding | year round | year round | once in spring |
| monthly | monthly | yearly |
----------------|--------------|-------------------|------------------|
fecund percent | 50 % shift | 50 % shift | 100 % |
----------------|--------------|-------------------|------------------|
minimum temp | > 24 C | | breed at 24 C Two|
| | | months before max|
----------------|--------------|-------------------|------------------|
-------------|-----------------------------------------------------------
monthly temp|jan feb mar apr may jun jul aug sep oct nov dec
-------------|-----------------------------------------------------------
Heron island |27.2 27.2 27.2 26.0 24.5 22.8 22.2 21.8 21.7 23.2 25.0 26.7
Lizard Island|29.1 29.0 28.9 27.2 26.0 25.5 24.1 24.5 25.0 25.5 26.8 28.0
Salamaua |31.2 31.9 30.5 30.8 27.7 29.6 28.4 28.6 28.0 28.7 31.1 31.0
-------------|-----------------------------------------------------------
note - Heron island temps averaged over 12 years. 1966-1977
Lizard island temps averaged over 9 years. 1974-1982
(Kojis, 1986b)
The monthly temperature table shows that the coolest months were july to
september. The rising temperature gradient occurred from october to december.
Latitudes from 23 to 14 degrees have sea temperature conditions that
vary annually and this might have caused local marine species to develop
distinctive breeding seasons. Some species do not follow this pattern and
this could be due to species-specific breeding temperature requirements.
The following hypothesis was supported by the findings of this study.
"Seasonal variations in sea temperature caused seasonal breeding in marine
animals. The length of the breeding season of a species will be longer in
lower latitudes than in higher ones and that where annual temperature
conditions are nearly unvarying, breeding will be year round" (Kojis, 1986b).
A new hypothesis was devised in the study. In high latitude regions the
marine species evolve a history strategy that limits the amount of energy
they allocate to reproduction, so that more energy can be allocated to
growth. The single annual reproductive cycle and accompanying production
of fewer planulae, along with the larger size of colonies at Salamaua appears
to support this supposition. The justification for additional allocation of
resources to growth is due to the lower temperature and shorter
photoperiod which slows growth, development and gamete maturation in the
winter season. The planulae on Heron Island were retained for 4.5 months
while those at Salamaua which were fewer and smaller were retained for 2.5
months. This meant that less effort was put into reproduction by the
Salamaua corals on average but more spawns occurred year round. Large seasonal
temperature extremes might influence the timing of reproduction. If the
temperature patterns are small or unstable, photoperiod might become the
main factor for establishing the timing of reproduction (Kojis, 1986b).
The average seasonal temperature periodicity reported in the preceding
scientific studies was 76.8 F to 85.8 F or 24.9 C to 29.9 C. Average spawning
occurrence range was 77 F to 78.8 F or 25 C to 26 C, however three
single species studied reported average spawning temperatures of 83.1 F or
28.4 C. The average mean yearly temperature for the three latitudes of 7,
14 and 23 degrees was 80.3 F or 26.8 C. Spawning induction should occur in
a captive aquaria in the 77 F (25 C) to 79 F (26 C) degree range, however
the peak summer temperature could be as high as 79 F (26.1 C) to 81 F (27.
2 C). The suggested maximum annual rhythm is 75 F (23.9 C) to 80 F (26.7
C) for a reef which is operating exceptionally well. Higher temperatures
might be required for certain geographically located species which only
spawn at temperatures exceeding 80 F (26.7 C). The latitudinal location
and depth specifications for a naturally developed specimen is very
important for ecosystem duplication. If a mass synchronous spawning event is
desired than the wide temperature rhythms which occur at high latitudes
should be duplicated. Monthly spawning with less synchronicity requires a
narrow rhythm with a higher temperature average that is equivalent to the
environmental specifications which occur at lower latitudes. Please exercise
caution when using reef ecosystem temperatures that exceed 79 F or
26 C.
-------------------------------------------------------------------------
Salinity Trends
-------------------------------------------------------------------------
This parameter represents local salinity trends which occur in certain
natural reef locations. An example of these trends was recorded during a
scientific study conducted on Barbados in the West Indies. The findings
will be listed below.
Monthly Salinity and Temperature Rhythms. Salinity in ppt. Temp in C.
|-----------------------------------------------------------------------|
|start 1982 |June July Aug Sep Oct Nov Dec Jan Feb Mar Apr May |
|-----------|-----------------------------------------------------------|
|location 1 | |
|salinity |29.3 29.9 30.4 32.0 32.0 32.2 33.7 33.3 33.1 32.4 31.8 30.7|
|temperature|28.3 28.5 28.7 29.3 29.9 30.2 28.8 27.9 28.1 27.3 27.3 28.3|
|-----------------------------------------------------------------------|
|location 2 | |
|salinity |31.2 32.1 31.3 32.2 31.2 34.5 34.2 35.2 35.5 34.1 33.7 33.3|
|temperature|27.6 27.7 28.6 28.0 28.5 29.2 28.8 27.8 27.2 26.2 26.3 27.0|
|-----------------------------------------------------------------------|
|location 3 | |
|salinity |32.2 31.8 30.9 32.2 31.8 34.5 34.2 35.2 35.4 34.2 33.5 33.0|
|temperature|27.6 27.6 28.5 27.7 28.5 29.2 28.8 27.8 27.3 26.3 26.4 27.0|
|-----------------------------------------------------------------------|
Highest temperatures occurred from september through november. They
then sloped downward until the march through april cold period. The
highest salinities occurred around january and then the value declined
until june and july.
All three locations were studied and the average number of male and
female gonads per 0.25 cm squared of Porites porites tissue represented
the productive activity or Gonad Index. The peak months of activity
occurred from november through january. The following table column
values are defined as follows. Gonad Index as described above. Temp in
degrees Centigrade. Salinity in ppt. SPM (suspended particulate matter)
in mg per liter. Chla (chlorophyll a) in mg per meter cubed. PEN (percentage
of surface illumination) in percentage (Tomascik and Sander, 1987).
|-----------------------------------------------------------------------|
| |Gonad Index Temp Salinity SPM Chla PEN |
|------------------|----------------------------------------------------|
|location 1 | |
|average value | 5.48 28.56 32.3 7.32 0.895 28.82 |
|standard deviation| 5.22 1.11 1.7 2.86 0.406 11.84 |
|sample size | 137 57 56 46 46 28 |
|------------------|----------------------------------------------------|
|location 2 | |
|average value | 6.26 27.89 33.5 5.94 0.799 34.52 |
|standard deviation| 6.65 0.94 1.1 3.41 0.470 7.32 |
|sample size | 119 57 54 44 46 28 |
|------------------|----------------------------------------------------|
|location 3 | |
|average value | 8.85 27.82 33.4 5.21 0.546 40.45 |
|standard deviation| 8.51 0.91 1.2 3.29 0.270 8.43 |
|sample size | 110 57 56 44 46 28 |
|-----------------------------------------------------------------------|
The Gonad Index increase from location 1 to 2 was 12.5 % and from
location 1 to 3 was 38.1 %. This difference between the three sites
might be due to genetic variability or the different environmental
parameters recorded (Tomascik and Sander, 1987).
Annual synchronous spawning events which only occur during a few days are
occasionally subjected to the environmental parameter extremes which can
occur in a natural reef ecosystem. An example affecting buoyant propagules
from epidemic spawning corals occurred at Magnetic Island in November 1981.
A heavy rain squall coincided with the spawning and propagules on the surface
were probably destroyed by reduced salinity. This negated the reproductive
effort of these coral for an entire year (Harrison et al., 1984).
One scientific study recorded annual rainfall and temperature at four
locations in the central american region. Costa Rica (lat 8 deg 43 min N)
(long 83 deg 52 min), Panama Gulf of Chirigui (lat 7 deg 49 min N) (long
81 deg 45 min), Panama Gulf of Panama (lat 8 deg 38 min N) (long 79 deg
4 min) and Galapagos Island (lat 0 deg 35 min S) (long 90 deg 17 min).
In the table that follows temp is in degrees centigrade and ppt is
precipitation in parts per thousand. Note - values were interpreted from
graphs (Glynn et al., 1991).
-----------|-----------------------------------------------------------
location |jan feb mar apr may jun jul aug sep oct nov dec
-----------|-----------------------------------------------------------
Costa Rica |
ppt | 0 0 5 15 115 220 215 190 240 245 100 15
temp |28.2 28.5 28.8 29.1 28.7 28.5 28.5 28.4 28.3 28.0 27.9 28.0
-----------|-----------------------------------------------------------
Panama-Gulf|
of Chirigui|
ppt | 30 35 50 100 205 250 210 290 295 415 250 105
temp |28.6 28.7 29.0 29.0 28.7 28.4 28.4 28.5 28.2 27.9 28.0 28.2
-----------|-----------------------------------------------------------
Panama-Gulf|
of Panama |
ppt | 25 10 5 65 220 190 195 205 200 305 280 130
temp |26.2 24.9 24.2 25.8 28.4 29.0 28.8 28.9 29.0 28.8 28.5 28.2
-----------|-----------------------------------------------------------
Galapagos |
Island |
ppt | 35 15 60 60 50 45 15 5 5 7 7 30
temp |24.7 25.1 25.2 25.3 24.4 23.2 22.8 21.7 22.0 22.3 22.9 23.4
-----------|-----------------------------------------------------------
Some natural reef locations do experience seasonally rhythmic salinity
variations which are primarily due to freshwater rainfall which occurs
during the local rainy seasons. The value of this salinity parameter for
the induction of spawning in a captive reef ecosystem has yet to be
determined.
-------------------------------------------------------------------------
Local Hydrodynamics
-------------------------------------------------------------------------
This parameter represents local current strengths and how they induce
morphological changes in coral growth. These ecomorphs might have
relevance in the development of spawning induction procedures. An experiment
conducted in Hawaii was run to determine the effects water motion
variability would have on different types of stony corals. Three coral species
were utilized with each reaching maximum abundance in specific water
current environments. Pocillopora meandrina (high wave energy), P.
damicornis (L.) (semiprotected reefs) and Montipora verrucosa (Lamarck) (calm
environments). The results from this experiment will be summarized here
for analysis by reef breeders who are experimenting with water current
values.
|-----------------------------------------------------------------------|
| | water motion measured (diffusion factor) |
| Environment | n mean +-S.D. Range |
|--------------------------|--------------------------------------------|
|Montipora verrucosa zone | 61 2.4 +- 1.19 1.5 - 6.7 |
|Pocillopora damicornis zon|e 34 4.3 +- 1.35 2.3 - 6.6 |
|Pocillopora meandrina zone| 30 15.0 +- 6.69 4.9 - 27.1 |
|-----------------------------------------------------------------------|
Results of Laboratory Water Motion Study (Jokiel, 1978b)
|-----------------------------------------------------------------------|
| parameter measured | relative water motion treatment |
| | low(L) medium(M) high(H) |
|---------------------------------|-------------------------------------|
|water motion energy transfer rate| 0 0.05 0.33 |
|(agitator horsepower in aquarium)| |
|mean temperature. n=41. (C+-S.D.)| 24.0 +-0.8 24.0 +-0.8 24.3 +-0.9 |
|mean measured water motion n=15 | 1.7 +-0.3 5.4 +-1.9 7.4 +-2.3 |
| (diffusion factor +- S.D.) | |
|median measured water motion n=15| 1.7 4.7 6.6 |
| (diffusion factor) | |
|coral reproduction (new colonies | 13 178 237 |
| per aquarium)| |
|median size of new colonies | 1 2 3 |
| (number of polyps) | |
|median linear growth of colonies | |
| Pocillopora meandrina (mm) | 0 1.1 1.3 |
| Pocillopora damicornis (mm) | 0.5 1.8 2.8 |
| Montipora verrucosa (mm) | 2.9 3.5 4.4 |
|mortality as estimated total | |
| percentage of tissue loss | |
| Pocillopora meandrina (mm) | 40 5 5 |
| Pocillopora damicornis (mm) | 0 0 15 |
| Montipora verrucosa (mm) | 0 0 0 |
|-----------------------------------------------------------------------|
The calm water coral M. verrucosa achieved a high growth rate in low
water motion treatment and continued to benefit from increased water
current. The study did suggest that a certain saturation level exists
for each particular species that is relative to each specimens prior
environmental growth exposure. The moderate water coral P. damicornis
did achieve better growth with stronger water motion but a saturation
point does exist where growth rate will slow until damage results to
coral tissue from storm type currents. The turbulent water coral P.
meandrina probably has a growth rate which peaks at currents twice as
high as was simulated in the experiment (Jokiel, 1978b).
Corals undergo morphological adaptations to differing hydrodynamic
environments. An example would be the P. meandrina from the study above which
has developed skeletal projections called verrucae which provide a drag on
the water and slow the current flow near the coral surface tissue. These
adaptations were observed for two species of Acropora coral which were
located at Heron Island Reef in the Great Barrier reef. Five distinct forms
or "ecomorphs" were verified for the hermatypic planulae brooding corals
A. cuneata and A. palifera. The names used to describe these ecomorphs,
(inner reef flat, outer reef flat, crest, slope and lagoon), were derived
from the corals dominate geographical domain (Kojis, 1986a). Coral branch
thickness may also be related to local hydrodynamic environmental
parameters. Thick branched specimens which are transferred from strong current
to calm current, experience a high initial mortality rate but will eventually grow
thinner branches. The initial mortality rate could be attributed to respiratory
shock due to a skeletal growth which is not efficiently designed for calm water
environments. When thinner branched corals are transferred to strong current,
thicker branches grow in response to current divergence (Jokiel, 1978b). Some
species of coral have the ability to survive and propagate in areas that inhibit
normal growth rates. Asexual reproductive processes are the dominate modes
used to propagate these coral species in areas which are environmentally
marginal for growth. High wave energy is one example of an inhibiting
parameter (Richmond and Hunter, 1990). Reef currents with velocities of 4 to 5
cm per second, might be strong enough to passively disperse propagules
released from polyp ball methods of reproduction (Sammarco, 1982).
Many captive reef engineers are utilizing wave motion generators to provide
a pulsating or rhythmic motion to their reef. This improves the operation of
the corals respiratory system and will keep ecosystem water flowing around
the coral. This current will promote the transfer of nutrients,
waste products and dissolved gases between the coral and water interface.
As long as an increased water flow is under the saturation point for a
particular coral, the respiration will be accelerated contributing to
healthness and enhancing the ability to develop gametes. The utilization of
this parameter in a captive reef ecosystem can become extremely complex
when individual specimen morphological adaptation requirements are
factored into the system setup. Active water flow needs to exist in any captive
system but the saturation point and specific demands of each coral should
be considered when locating each specimen within the ecosystem. Further
research is required for determination of the value of water current parameters
as well as wave generated rhythmicity for the induction of spawning
in a captive reef ecosystem. The author has recently upgraded his 180 gallon
reef with elevated pvc matrixes which have 1200-2000 liters per hour
submersible water pumps forcing current through holes drilled strategically
in the matrix.
-------------------------------------------------------------------------
Local Tidal Variations
-------------------------------------------------------------------------
This parameter represents tidewater level changes and associated current
movements. The Great Barrier Reef synchronous mass spawns occur during
neap tides which begin after the full and new moons and continue until
the third and first quarter moons respectively. An extended slack current
period results from the relative small difference in high and low tidal
water heights. One reason for this spawning evolutionary trait might be
the increased fertilization potential for released gametes (Alino and Coll,
1989)(Babcock et al., 1986)(Kojis and Quinn, 1981). Coral egg or planulae
sexual spawns have been observed in the authors reef during slack current
periods (Trachyphyllia geoffroyi) and high current periods (Euphyllia
ancora, Gorgonian sp., Turbinaria turbinata and Actinodiscus sp.). When
these occurrences are considered along with other aquaria spawning reports,
the deduction that tidal current rhythms might be coincidental or ancillary
to spawning synchronicity, gains substantiation.
Further evidence against tidal factors influencing synchronous spawning
was documented in an experiment which utilized Pocillopora damicornis
coral specimens. Planulae release from this coral in a captive aquaria
without tidal influences, stayed in periodicity with field specimens. The
rhythmic patterns in the aquaria were more regular and intense than the field
corals due to the more moderate physical environment which existed in the
laboratory. A severe rainstorm on 14 December 1980 killed exposed corals
and caused slightly submerged coral to experience low salinity. This
resulted in the continual aborting of developing planulae and a low rate of
reproduction to occur for several months in the field specimens. The
laboratory coral ecosystem was cycled with sea water collected from deeper
regions and spawning periodicity was not adversely affected. These corals
also received normal sun and moon luminance and after 16 months the
laboratory corals continued to reproduce synchronously with the reef-flat
corals. This experiment probably eliminated futher consideration of
tide-related physical effects on monthly synchronous spawning (Jokiel et al.,
1985).
-------------------------------------------------------------------------
Fluctuations in Reef Chemistry
-------------------------------------------------------------------------
These parameters represent chemical measurements that many captive reef
owners perform routinely. Variances can occur hourly, daily or weekly and
are kept within an established acceptable range. The importance that any
annual rhythmic parameter variance would have for the induction of coral
spawning has yet to be determined. They are listed here for completeness
in environment parameter research. Dissolved Oxygen, Dissolved Carbon
Dioxide, Alkalinity and Hardness, Carbonate Hardness, PH, Redox Potential
and Calcium Concentration. These values might not require annual rhythmic
variance and it would be practical to experiment with the more relevant
parameters discussed previously. Please consult reef aquaria literature
for suggested acceptable levels and ranges for these chemical parameters.
-------------------------------------------------------------------------
Alternate Strategy for Applying Environmental Rhythmicity
-------------------------------------------------------------------------
Rhythmicity in moon phase luminance appears to be the most important
environmental monthly spawning synchronizer. The natural 29.5 day
periodicity for this parameter should be artificially simulated in captive reef
ecosystems. The main annual spawning season inducer appears to be
temperature variances. As the annual variation increases, the spawning season
will shorten for monthly brooding species whose minimum gonad development
temperatures are not attained. One methodology for inducing spawning
entails keeping the annual temperature constant and above the minimum gonad
maturation range. This would prevent the annual egg broadcasters from
releasing eggs synchronously on the same lunar cycle and the normal spawning
month should occur annually due to gonad maturation development
requirements. Monthly brooders will start to release planulae based on the lunar
periodicity of the ecosystem. Brooding fecundity might be increased if
the photoperiod is kept at a summer length for the entire year. The reef
breeder should employ a different strategy to stimulate spawning which
only occurs during a brief annual period. The utilization of photoperiod
periodicity might be combined with annual temperature variances for the
development of this mass spawning event. The resulting pollution from such
an event should be considered before an attempt is made.
=========================================================================
Tropical Coral Reef Environment Rhythmicity and
Techniques for Inducing Captive Coral Spawning
October 1992
Author - Steve Tyree [Reef Breeder and Computer Support Specialist]
=========================================================================
Literature Cited
Alino P.M. and J.C. Coll (1989): Observations of the Synchronized Mass
Spawning and Postsettlement Activity of Octocorals on the Great Barr-
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Wallace and B.L. Willis (1986): Synchronous spawnings of 105 Sclerac-
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379-394
Benayahu Y. and Y. Loya (1983): Surface Brooding in the Red Sea Soft
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Glynn P. W., N. J. Gassman, C. M. Eakin, J. Cortes, D.B. Smith and H. M.
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Oliver J. K. (1992): Personal correspondence via computer mail.
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waii. Bull. Mar. Sci. 34(2):280-287
Richmond R. H. and C. L. Hunter (1990): Review - Reproduction and re-
cruitment of corals: comparisons among the Caribbean, the Tropical
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Glossary of Terms
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allopatric - originating in or occupying different geographical areas.
asexual - designating or of reproduction without union of male and female
germ cells: budding, fission are types of asexual reproduction.
broadcast - to cast or scatter eggs and sperm over an area for fertiliza-
tion and distribution.
brooding - developing eggs within the body cavity or on external surface.
diel - see photoperiod.
embryogenic- the formation and development of the embryo.
fecundity - fertile, productive, prolific.
gametes - a reproductive cell that is haploid and can unite with another
gamete to form the cell that develops into a new organism.
gametogenic - process of consecutive cell divisions and differentiation
by which mature eggs or sperm are developed.
gonads - an organ in animals that produces reproductive cells; esp., an
ovary or testis.
gonochoric - separate sexes, male reproductive organs in one individual
and the female organs in another.
haploid - an organism or cell having only one complete set of chromo-
somes ordinarily half the normal diploid number.
hermaphroditic - animal with sexual organs of both male (testes) and fe-
male (ovaries).
hermatypic - see hermaphroditic.
hydrodynamic - having to do with the motion and action of water and other
liquids; dynamics of liquids.
morphological - form and structure, as of an organism, regarded as whole.
oocytes - an egg that has not yet undergone maturation.
oogenesis - the process by which the ovum is formed in preparation for
its development.
photoperiod - the number of daylight hours best suited to the growth and
maturation of an organism.
planulae - the ciliate, free-swimming larva of a coelenterate.
propagules - a structure that propagates an organism.
sexual - designating or of reproduction by the union of male and female
germ cells.
testes - male sex glands which secrete spermatozoa.
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Reef Breeding Conversion Equations
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Fahrenheit to Celsius
C = (5/9)*(F-32)
Celsius to Fahrenheit
F = (C*(9/5))+32
Liters to US Gallons
G = L/3.8
US Gallons to Liters
L = G*3.8
PPM to ml/liter to mg/liter
mg/liter = ml/liter =~ PPM
Liter to ml
1 ml = L/1000
ml to microliter
1 microliter = 1000 ml
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