Ecology – Urchin Population Dynamics
Photo Credit: Josh Smith
In kelp forest ecosystems around the world, outbreaks in populations of herbivorous sea urchins have led to phase shifts across many spatial and temporal scales (Pearse 2006, Baskett and Salomon 2010, Fagerli et al. 2015). For example, outbreaks of urchins along the Norwegian coast have resulted in a large extension of barren grounds northward into Russian waters that have persisted for over 40 years (Sivertsen 1997). Consequently, biological diversity and productivity associated with kelp forests declined (Christie et al. 2003). Similar dynamics have been noted in Nova Scotia in the Northwest Atlantic, along the Northwest coast of North America from Alaska to Mexico, and in Tasmania in the Southwest Pacific (Filbee-Dexter and Scheibling 2014, Ling et al. 2015). Kelp provides essential habitat, structure, and food for many species of both economic and ecological interest. Therefore, the loss of kelp due to destructive grazing can have devastating effects that permeate throughout the ecosystem.
A large-scale ecological shift is occurring along the central coast of California. Seemingly uncontrolled populations of important purple sea urchin (Strongylocentrotus purpuratus) grazers have shifted a once continuous kelp forest landscape to a patchwork mosaic of urchin barrens and kelp forests. Until now, mosaic patchiness in the distribution of barren areas within a kelp forest that is attributed to sea urchin grazing has not been recorded along the central coast of California. Therefore, there is impending need for a long-term sea urchin settlement monitoring program to track sea urchin population dynamics through time.
Through the integration of community and institutional outreach, analysis of juvenile urchin samples collected along coastal wharfs, and use of current population statistics, the CEnCal Network for Sea Urchin Settlement Program (CENSUS) is tracking and quantifying the patterns of dispersal for this dynamic and influential kelp forest species.
References:
Baskett, M. L., & Salomon, A. K. (2010). Recruitment facilitation can drive alternative states on temperate reefs. Ecology, 91(6), 1763–1773. http://doi.org/10.1890/09-0515.1
Christie H, Jorgensen NM, Norderhaug KM, Waage- Nielsen E. (2003). Species distribution and habitat exploitation of fauna associated with kelp (Laminaria hyperborea) along the Norwegian coast. J Mar Biol Assoc UK 83: 687−699
Fagerli, C. W., Stadniczeñko, S. G., Pedersen, M. F., Christie, H., Fredriksen, S., & Norderhaug, K. M. (2015). Population dynamics of Strongylocentrotus droebachiensis in kelp forests and barren grounds in Norway. Marine Biology, 162(6), 1215–1226. http://doi.org/10.1007/s00227-015-2663-3
Filbee-Dexter, K., & Scheibling, R. E. (2014). Sea urchin barrens as alternative stable states of collapsed kelp ecosystems. Marine Ecology Progress Series, 495, 1–25. http://doi.org/10.3354/meps10573
Ling SD, Scheibling RE, Rassweiler A, Johnson CR, Shears N, Connell SD, Salomon AK, Norderhaug KM, Pérez-Matus A, Hernández JC, Clemente S, Blamey LK, Hereu B, Ballesteros E, Sala E, Garrabou J, Cerbrian E, Zabala M, Fujita D, Johnson LE. (2015). Global regime shift dynamics of catastrophic sea urchin overgrazing. Phil Trans B370:20130269
Pearse J. S. Ecological role of purple sea urchins. Science 314, 940–941 (2006).
Sivertsen K. (1997). Geographic and environmental factors affecting the distribution of kelp beds and barren grounds and changes in biota associated with kelp re – duction at sites along the Norwegian coast. Can J Fish Aquat Sci 54: 2872−2887