MSc student Clayton Manning (@claytongmanning) is studying how different habitat, prey, and predator variables affect the abundance and size distributions of seahorses in Australia. He is teasing out which variables are most important among different seagrass beds, and within a single seagrass bed.
Targeted fishing, incidental capture, and habitat degradation have led to the decline of seahorse populations around the world. Of these three pressures, the effect of habitat degradation on seahorse populations is the least understood. This makes it difficult for conservationists to accurately assess the status of seahorse populations or make appropriate action plans for their conservation.
Clayton's work will help conservationists and resource managers around the world to make better decisions about how to manage seahorse populations and shallow seas habitats.
(Banner photo: Guylian Seahorses of the World)
Seahorses are cryptic, sedentary fish that live in a diverse range of habitats - including seagrasses, coral, macroalgae and mangroves - but we are largely unaware of what it is about specific seagrass beds or coral reefs that support either large or small numbers of seahorses. This limits the ability of conservationists to accurately assess seahorse conservation status or make appropriate action plans. Pinpointing how different elements of habitat affect seahorse populations will better equip conservationists to inform management decisions.
First things first - seahorses must avoid predation. Although seahorses are not particularly appetizing because of their strong, bony frame, some opportunistic fish and octopus are known to feed on seahorses (especially juveniles) when they're hungry. The pressure is great enough that seahorses spend a considerable amount of time hiding, often camouflaged with their background. You will rarely find a seahorse swimming in the open for this reason.
If not preyed upon, seahorses must then be able to eat the small crustacean prey that they love (amphipods, copepods, isopods, decapods). Although you will find many of these critters on any seagrass leaf you look at, the amount and suite of prey vary between and within habitats. Making things even more confusing (and fun), prey also vary according to other habitat characteristics such as complexity, substrate type, depth, patch size and patch connectivity.
The objective of my thesis is to disentangle which of these three variables - predator abundance, prey availability, and patch characteristics - are most important when it comes to seahorse abundance and population dynamics. My research will be co-supervised by Dr. David Harasti - a research scientist with the New South Wales government. He has over 15 years of experience working with Hippocampus whitei, the seahorse species I will work with. My fieldwork will be spent searching for and comparing the seahorse populations and habitat characteristics we find between different seagrass (Posodonia) beds, and between different soft coral (Dendronephthya australis) patches along the southern shore of Port Stephens, NSW, Australia.
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