Ocean Warming Impacts on Physiology of Brittle Stars

The echinoderm fauna found in the rocky intertidal and shallow subtidal coasts around Sydney is extremely diverse.  Most are quite familiar with the star fish and sea urchins, but often over looked are their cousins, the brittle stars.

Despite their anonymity, they are one of the most abundant invertebrates and are important components of the ecosystem, serving as major transferrers of energy between levels of the food chain.  They get their name “brittle star” from their habit of breaking off an arm, called autotomy, whenever threatened or attacked by a predator.  The arm wriggles after detachment attracting the attention of the predator while allowing the rest of the brittle star to escape and regrow its lost arm; this phenomenon is termed sub-lethal predation.

Brittle stars are often sensitive to environmental changes and are employed as bioindicators of ecosystem health.  One of the variables of most concern is ocean warming; as temperature increases, so does the metabolism of the brittle star.  This places stress on the animal and increases its energy expenditures for normal behavior, leaving less energy available for other processes including reproduction and arm regeneration.  Not only does this have negative implications for the brittle star, but also for those species that rely on them as a food source, causing negative repercussions up the food chain. For eastern Australia this is particularly important to understand because the ocean in this region is warming more quickly than elsewhere due to climate change induced changes in ocean currents.

There are several aims of the present study.  Firstly, to compare the current incidence of sub-lethal predation in brittle stars from Little Bay with that of a study conducted 15 years ago to see if predation pressure has changed.  Secondly, assess the effects of elevated temperature on the metabolism and arm regeneration rates.  As many species are already living at the limits of their thermotolerance and will be unable to acclimate to further temperature increases, it is important to understand how even small changes will affect the diverse fauna of Sydney in the near future.

This research is a collaboration between Professor Ana Christensen Lamar University, Beaumont, TX and Professor Maria Byrne at the University of Sydney and the research on the impact of ocean warming on the physiology of the brittle stars is being conducted at the Sydney Institute of Marine Science.