Last updated on October 23, 2019
Disruption is not a good thing for the web of life. It often leads to extinction.
One of the Earths most spectacular events occurs just once a year, though the timing varies depending on the reef location, is coral spawning. The phenomenon is brought about by the lunar cycle as well as water temperatures just right, which triggers the coral reef colonies to release their eggs and sperm into the ocean simultaneously. These events allow for genetic mixing and dispersal over large swathes of the surface of the sea.
NOAA explains the role of the gamete (either a sperm or an egg):
In ways that scientists still do not fully understand, mature corals release their gametes all at the same time. This synchrony is crucial, because the gametes of most coral species are viable for only a few hours. The “blizzard” makes it more likely that fertilization will occur.
The gametes, full of fatty substances called lipids, rise slowly to the ocean surface, where the process of fertilization begins.
When a coral egg and sperm join together as an embryo, they develop into a coral larva, called a planula. Planulae float in the ocean, some for days and some for weeks, before dropping to the ocean floor. Then, depending on seafloor conditions, the planulae may attach to the substrate and grow into a new coral colony at the slow rate of about .4 inches a year.
Most corals are hermaphrodites releasing a “bundle” composed of both eggs and sperm, some corals colonies though, have separate male and female corals. In either case, a mix of “smoky white clouds of sperm” and eggs float to the surface during the spawning. Once the egg reaches the surface, it breaks open and mixes with the sperm. Fertilization occurs during this small sliver of time, so synchronicity is critical to the survival of the species.
Climate change is impacting the coral reef ability to sustain their populations a Tel Aviv University study found.
A new Tel Aviv University study finds that the highly synchronized, iconic spawning events of certain reef-building corals in the Gulf of Eilat/Aqaba, Red Sea, have completely changed over time and lost their vital synchrony, dramatically reducing chances of successful fertilization.
According to the research, led by Prof. Yossi Loya and PhD candidate Tom Shlesinger of TAU's School of Zoology and published in Science on September 6, the breakdown in coral spawning synchrony has led to a dearth of new recruits and stagnant aging populations, creating circumstances for extinction.
“Although it appeared that the overall state of the coral reefs at Eilat was quite good and every year we found many new corals recruiting to the reefs, for those species that are suffering from the breakdown in spawning synchrony, there was a clear lack of recruitment of new juvenile generations, meaning that some species that currently appear to be abundant may actually be nearing extinction through reproductive failure,” says Shlesinger.
“Several possible mechanisms may be driving the breakdown in spawning synchrony that we found,” Prof. Loya concludes. “For example, temperature has a strong influence on coral reproductive cycles. In our study region, temperatures are rising fast, at a rate of 0.31 degrees Celsius per decade, and we suggest that the breakdown in spawning synchrony reported here may reflect a potential sublethal effect of ocean warming. Another plausible mechanism may be related to endocrine (hormonal) disrupting pollutants, which are accumulating in marine environments as a result of ongoing human activities that involve pollution.”
“Regardless of the exact cause leading to these declines in spawning synchrony, our findings serve as a timely wake-up call to start considering these subtler challenges to coral survival, which are very likely also impacting additional species in other regions,” says Shlesinger. “On a positive note, identifying early-warning signs of such reproductive mismatches will contribute to directing our future research and conservation efforts toward the very species that are at potential risk of decline, long before they even display any visible signs of stress or mortality.”
Coral reefs are already extremely stressed due to our greenhouse gas emissions that heat the planet. Marine heatwaves result in mass bleaching events, infectious disease outbreaks and ocean acidification.
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