A few nights after the full moon, something begins to spawn...and no, we don’t mean werewolves! It’s coral spawning season. This weekend, corals across the Great Barrier Reef will release their reproductive bundles into the water column in a spectacular, synchronised event. For the Reef Catchments team, it’s one of the busiest and most exciting times of the year.
As a partner in the Boats4Corals project, Reef Catchments works alongside the Australian Institute of Marine Science (AIMS), local tourism operators, and Traditional Owners to collect coral spawn and release the larvae into reef areas that receive less natural larval inflow and are slower to recover from impacts.
The preparation for this year’s spawning has already begun. Last week, the Boats4Corals team inspected 12 sites around the Whitsundays for their readiness to spawn, referred to as gravid coral checks.
During gravid coral checks, teams assess several factors to determine whether a site is suitable for coral spawn slick collections. Key considerations include the extent and diversity of hard coral coverage, the presence and development stage of coral eggs, and whether the area is protected or has any environmental or physical barriers that might inhibit slick formation. These elements help the team evaluate the site's potential for successful collection and monitoring.
To answer these last two questions, the team take small samples of coral and look at the skeleton*. Egg bundles are visible as tiny spheres, often in groups, and the developmental stage of the eggs can be inferred by their colour. Generally, eggs start out as white and become pink as they mature.
The team sampled 370 hard coral colonies over two days, approximately two thirds of which had eggs. They have used the data to narrow down their target sites for spawn collection in a fortnight, having identified a subset of sites which are expected to be productive.
Ultimately the amount of spawn the team are able to collect is very strongly influenced by the weather on the night. However, Reef Catchments state that the extensive presence of developed eggs throughout the Whitsunday islands is a promising sign for this year’s fieldwork!
*Please note it is illegal to sample corals without a permit.
Pictured: Lisa McMullen – Daydream Island Living Reef, credit Reef Catchments
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