Bathymetric segregation of sea urchins on reefs of the Canarian Archipelago: Role of flow-induced forces |
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| Authors: | F Tuya J Cisneros-Aguirre L Ortega-Borges RJ Haroun |
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| Institution: | aSchool of Natural Sciences, Center for Ecosystem Management, Edith Cowan University, Joondalup Drive, 6027 Joondalup, WA, Australia;bBIOGES, Department of Biology, Marine Sciences Faculty, Campus Tafira, University of Las Palmas de Gran Canaria, 35017 Las Palmas de G.C., Canary Islands, Spain;cDepartment of Physics, Marine Sciences Faculty, Campus Tafira, University of Las Palmas de Gran Canaria, 35017 Las Palmas de G.C., Canary Islands, Spain |
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| Abstract: | We examined whether adults of three species of sea urchins species (Diadema antillarum, Arbacia lixula, and Paracentrotus lividus) exhibit a consistent depth-dependent partitioning pattern on rocky reefs of the Canarian Archipelago (eastern Atlantic). Hydrodynamic experiments were carried out to quantify the resistance to flow-induced dislodgement in these three species. We tested the model that different morphology can result in habitat partitioning among these sea urchins. Abundances of D. antillarum increased with depth. In contrast, A. lixula and P. lividus showed the opposite zonation pattern, coexisting in high abundances in the shallowest depths (<5 m), and occurring in low densities in the deepest part of reefs (>7 m). Both A. lixula and P. lividus had greater adhesion-surface to body-height ratios than D. antillarum. Similarly, A. lixula and P. lividus showed a greater ability to resist flow-induced dislodgement compared with D. antillarum. The mean “velocity of dislodgement” was  300% and 50% greater for A. lixula and P. lividus, respectively, relative to D. antillarum, for any particular size. As a result, A. lixula and P. lividus are better fitted to life in high-flow environments than D. antillarum. We conclude that the risk of dislodgement by water motion likely play a relevant role in the vertical distribution patterns of these sea urchins in the eastern Atlantic. |
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| Keywords: | sea urchin vertical distribution water movement spatial patterns waves Canary Islands |
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