***The following is a guest post from Stanford University PhD student Tom Hata. In his research of biomechanics, Tom has been forced to develop novel methods for measuring ocean flows in the field on an almost microscopic level. We hope to get more updates from Tom as he continues his research on coral larvae in the Great Barrier Reef.***
Last November, I was fortunate to witness one of nature’s great annual events: the mass coral spawning on Australia’s Great Barrier Reef. Specifically, I spent two weeks on the remote Lizard Island, located near the northern extreme of the Great Barrier Reef in a joint project between members of Stanford University, Macquarie University, and James Cook University. Coral reefs worldwide are threatened by a suite of rapidly changing environmental factors (global climate change, ocean acidification, and rising sea levels), so a great deal of attention has been turned toward understanding what it takes to maintain a healthy reef and promote recovery in a degraded one.
My research focuses on better understanding a fundamental and crucial step of a coral colony’s life cycle — the initial settlement of coral larvae onto the reef. This is of course a difficult subject to study because larvae are so small (roughly ranging between 0.1 mm to 1 mm) in such a vast ocean, but my colleagues and I addressed this matter by borrowing techniques from the realm of engineering.
First, we wanted to know what the world “looked” like to a larva. As they are such weak swimmers relative to their environment, coral larvae are mostly dependent on ambient water motion to transport them to their eventual homes. To map the flow environment across parts of the reef, we illuminated the water with a plane of laser light and filmed particles as they floated by. This technique is also known as Particle Image Velocimetry (PIV).
Next, we needed a way to observe how coral larvae behaved in these flows. We accomplished this by collecting the larvae of Isopora cuneata, a brooding coral species. Unlike broadcast spawners that iconically release their gametes into the water during the mass spawning, brooders retain their eggs within the adult colony and directly release their developed larvae into the water. We then put these larvae in a flume, or water race track, to measure their settlement behaviors in a variety of flow conditions. This project is still ongoing, but early results are promising in better understanding the underlying mechanisms of successful coral larval settlement.
Tags: biometrics, coral, coral larvae, coral reef, Great barrier reef, Lizard Island, ocean conservation