@article {469,
	title = {emporal variability in abundance of the sea urchins Paracentrotus lividus and Arbacia lixula in the northwestern Mediterranean: comparison between a marine reserve and an unprotected area},
	journal = {Marine Ecology Progress Series},
	volume = {168},
	year = {1998},
	abstract = {<p>Sea urchin populations were monitored in the Medes Islands Marine  Reserve (NW Mediterranean) and an adjacent unprotected area in order to  (1) describe temporal variability in abundance and population  size-structure of sea urchins within each area (from 1991 to 1997), and  (2) to compare these areas to investigate the role of fish predation  level in determining sea urchin population structure over time (from  1995 to 1997). Abundance of the sea urchin Paracentrotus lividus  (Lamarck) was monitored at 7 sites (4 inside and 3 outside the reserve),  and 2 distinct habitats (fields of big boulders and vertical walls). P.  lividus exhibited signficant variability in density over time on  boulders, both inslde and outside the reserve, whereas its density dld  not vary significantly on vertical walls. P hvjdus populations differed  significantly in size-structure across sites, varying from unimodal to  blmodal among sltes and years. Density and mean size of P. lividus were  not significantly different between the protected and the unprotected  area in either of the 2 habitats. Abundance of the sea urchin Arbaca  lixula (L) was monitored from 1995 to 1997 on vertical walls and  boulders (4 sites inside and 3 sites outside the reserve). Density of A.  lixula differed slgnlficantly over time on boulders, but it did not on  walls. On vertlcal walls, density and mean slze of A. lixula were not  significantly different between areas in both habitats. This study shows  that in the Medes Islands region, sea urchins exhibit striking  short-term fluctuations in abundance, which can lead to  misinterpretation of larger-scale temporal patterns. The comparison  between the protected and the unprotected area does not support the  hypothesis of fish predation as the most. important factor affecting P.  lividus populations in the Medes Islands, as patterns of lower sea  urchin density relative to the unprotected area nearby were not  maintained over time. These facts indicate that factors other than fish  predation are very important in determining sea urchin population  structure in the northwestern Mediterranean.</p>},
	keywords = {Arbacia lixula, comparison, density, echinoderm, fish, habitat, island, marine protected area, marine reserve, Medes, Mediterranean sea, Paracentrotus lividus, population, predation, protected area, r{\^o}le, sea urchin, size, Spain, temporal heterogeneity, unprotected area, western Mediterranean},
	author = {E. Sala and J. Garrabou and R. Coma and V. Alva and M. Zabala and B. Hereu and M. Ribes}
}
