Magic nights of coral spawning

by    Carin    24th October 2016
1 Ben Mueller (2)
Coral spawning – diving in a 'snow storm' by Benjamin Mueller
2 Paul SElvaggio (2)
A corals love night, full moon over the Riviera Maya, Mexico by Paul Selvaggio
3 Ben Mueller (7)
Massive coral setting for spawning by Benjamin Mueller
4 Ben Mueller (8)
Same coral releasing egg-and-sperm bundles by Benjamin Mueller
5 Ben Mueller (5)
Male coral releasing milky clouds of sperm by Benjamin Mueller
6 Paul SElvaggio (1)
Close-up of spawning brain coral by Paul Selvaggio
7 Ben Mueller (4)
Spawning christmastree worms by Benjamin Mueller
8 Paul SElvaggio (3)
Collecting coral gametes with nets during night dive Paul Selvaggio
9 Paul SElvaggio (4)
Fertilization work during this year's sexual coral restoration workshop at Curacao by Paul Selvaggio

On
certain nights, around full moon, corals have their tryst of love.
Diving on such a night is a lifetime experience and this is not
overstated at all! Starting your dive, you are immediately aware of
the crackling and rustling all around you. The reef bursts with
activity, its origin somehow not detectable yet, but there is
something in the wind―or
rather in the water. It's gonna be a special night, the night of a
coral mass spawning event; and many other creatures will join in.

Let's
talk about coral sex!

Most
stony corals―corals
that build up the reef themselves with their calcareous
structures―have
developed a special strategy.
Synchronized almost to the minute, corals of a certain species
release their eggs and sperm into the water column where
fertilization can take place. Led by the annual temperature profile
to choose the right month, by the lunar cycle to appoint for the day,
and by sunset time to pinpoint the hour, corals know exactly when
it's time to start their lovegame.

Some
coral species are hermaphrodites―having both sexes―and release
eggs-and-sperm bundles. When the bundles are visible at each polyp's
mouth, the coral prepares for spawning: they set. Then, sometimes the
whole colony 'plops' out the tiny, pinkish, round bundles all
together (spawning video Montastrea annularis). For a moment they hang
in the water, perfectly forming the shape of the coral before they
start to drift away. Other corals are either female or male and they
release egg-bundles or streaky clouds of sperm that turn the water
milky (spawning video Porites sp).

Often,
several coral species spawn in concert, filling the water with
gametes till you feel like diving within a snowstorm. And corals are
not the only ones! Many other reef creatures take their chance to
join the spawning night, such as sea fens, gorgonians, brittle stars,
christmastree worms, and many more. The reason for that, as Sir
Attenbourough repeatedly likes to emphasize in the famous Blue Planet
series, is 'safety in numbers'. And this is a very thoughtful
precaution! Predators, little swirling creatures like worms,
crabs, shrimp, or fish, occupy the water to
take part in the generously laid banquet and to get their piece of
the high-protein goodies!

Not
everywhere, coral spawning still happens. When corals suffer from
stress―and being stressed out
is a not uncommon state for corals these days―they are likely to
stop their reproduction (coral reefs are dying
and are vulnerable to climate change). In other areas corals may still spawn, but
there are factors that prevent the corals' enormous investment in
offspring to pay off. The reasons are manifold: there may be too few
colonies, too far apart to let fertilization of the gametes happen;
water quality may be poor and coral larvae cannot develop; coral reef
degradation and algae overgrowth may not spare the tiny coral larvae
a place to settle and grow into a new coral colony. Times are rough
for tiny coral babies (...and corals are important for survival of
our planet
).

Part
of SECORE International's work is to raise sexually derived coral
offspring where nature cannot carry out its duty on its own anymore.
Especially when corals still spawn, but the number of new coral
recruits is very low to non-existing. During night dives, we collect
the coral gametes with nets (e.g. in Mexico) or, in the case of male
corals releasing clouds of sperm, with syringes. We bring the gametes
to the laboratory and let them fertilize. The delicate larvae are
raised in various set ups, from perfectly-cared for, numerous, small
bins for coral reproduction research to big bulk containers with
thousands of larvae to study and apply restoration approaches. Like
any living being, corals need to grow and reproduce. SECORE is giving
them a helping hand in doing so (SECORE's work).

SECORE.org

photos
by Benjamin Mueller (CARMABI)
and Paul Selvaggio (Pittsburgh Zoo & PPG Aquarium)

Written by
Carin
Date
24th October 2016
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