Hospital ultrasound used to peek at coral eggs without cutting the coral

Scientists scanned living corals underwater for developing eggs, a possible alternative to cutting samples. Whether it predicts spawning is still being tested.

Scientists at Coral Spawning International (CSI) have used a hospital ultrasound platform, Canon's Aplio i700, to scan living corals for developing eggs while the animals stayed submerged. The work is part of Canon EMEA's World Unseen initiative. Canon calls it a world first, though that claim is the company's own.

The team scanned six species of large polyp stony coral from Australia, the Caribbean and Indonesia. The corals sat in shallow seawater tanks, and the high- and ultra-high-frequency probes were gel-coated and sheathed. Until now, checking reproductive status meant breaking off a branch or cutting into the coral to look for gametes. Eggs can be as small as 300 microns, according to CSI co-founder Jamie Craggs. For one species, Trachyphyllia geoffroyi, the team fragmented the coral and compared the tissue with macro photographs. Craggs said this confirmed that egg development was visible on the scans.

This matters because reefs cover about 1% of the ocean yet shelter at least a quarter of marine life, and they underpin fisheries and coastal protection. Sexual breeding adds genetic diversity that coral gardening, which clones fragments, cannot. But it depends on catching colonies at the right moment, which in the wild may come once a year. A scan that shows when a colony is ripe, without damaging it, could make breeding programmes less wasteful and more reliable. It could also make it easier to track how stressors such as bleaching affect egg production. Australian Institute of Marine Science researchers found 21% fewer eggs in one common branching coral after the severe 2020 bleaching, but had to dissect samples to count them.

The key test is still ahead. Over the next six months the corals will be isolated daily and their gamete release times recorded, then matched to scan dates to see whether scans predict spawning. Only T. geoffroyi has been checked against the cut-and-look method, and the results are not yet peer reviewed.

Source: New Atlas