Breakdown of spawning synchrony silently threatens coral survival in red sea reefs

Changes to the environmental conditions that underpin the reproductive success of some corals may be causing their highly synchronized mass-spawning strategy to break down, a new study finds. This desynchronization – a previously unnoticed threat – could drive aging coral populations to extinction. When the water temperature and the moon align just so each year, entire colonies of coral reef release millions of tiny eggs and sperm into the ocean. Like cherry blossoms in a stiff breeze, the brightly colored gametes drift together in quantities so vast they can occasionally be seen from space. Because gametes only survive for a few hours, their highly synchronized release is crucial to ensuring successful fertilization. Previous studies have suggested that the synchronicity of coral reproduction relies on various environmental cues working in unison to determine the exact moment of spawning. Assuming these features are stable and consistent, researchers interested in threats to corals have focused on more observable damages, like bleaching events. However, given that changes associated with a changing climate are greatly contributing to mass mortality events worldwide, researchers have wondered if corals, too, are affected by these. Tom Shlesinger and Yossi Loya observed annual coral spawning events from the Red Sea’s most abundant coral species and found that several have shifted the timing of spawning events. According to the authors, some species have experienced a complete breakdown in their reproductive synchrony, spawning in different months year to year, and even across several days within each month, severely reducing gamete fertilization potential. Findings from other reef communities indicate that reproductive asynchrony is likely occurring in different parts of the world as well, Shlesinger and Loya suggest. “[The authors] warn that coral populations around the globe might still appear healthy, while suffering silently from these reproductive struggles,” write Nichole Fogarty and Kristin Marhaver in a related Perspective.

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