Variation in long black-spined urchins

Graduate Student: Xueying Shirley Han

Understanding the mechanisms that influence species' distributions and abundances is a central goal of ecology. Many factors, both biological and physical, have been shown to control where a species can live and how abundant it can become. Shirley is interested in understanding the spatial patterns of abundance of the tropical sea urchin Diadema savignyi. Sea urchins are important herbivores in both temperate and tropical systems. In coral reef ecosystems, sea urchins (along with herbivorous fishes) have been suggested as important organisms in the prevention of coral to macroalgal dominated phase shifts.


Working on the island of Moorea, Shirley found that the long, black-spined urchins occur in two variations - either as solitary and cryptic individuals or as part of a larger aggregation. She was interested in understanding the mechanisms that control the spatial patterns of abundance in these sea urchins. Specifically, Shirley looked at variation in death rates, recruitment rates, the abundance of things that eat sea urchins and how complex the habitat was as possible explanations for why certain areas have more urchins than others. Shirley's final goal will be to test whether these two abundance patterns, occurring either as individuals or in groups, are actually two stable, alternative population states.

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