Condition, feeding and reproductive potential of white seabream Diplodus sargus as indicators of habitat quality and the effect of reserve protection in the northwestern Mediterranean

Individuals of white seabream Diplodus sargus collected from rocky and sandy coastal areas in the northwestern Mediterranean were examined to evaluate habitat influences on their condition, feeding and reproductive potential. To determine the potential effectiveness of a marine protected area, we quantified the consequences of the Marine Reserve of Banyuls-Cerbere (situated on the rocky coast) on condition, feeding and reproduction. Measures of condition (weight at length, liver size and lipid content in muscle and liver), feeding potential (digestive tract weight) and reproductive potential (gonad weight) were compared between substrate type, bathymetric zone, level of protection, sexes and maturity stages. The study reveals differences in the condition of white seabream between adjacent habitats. During the juvenile phase, fish condition was generally higher in the unprotected rocky coast than in the unprotected sandy coast. In addition, post-spawners were better conditioned within the rocky areas of the reserve than in adjacent unprotected rocky areas. At the Banyuls-Cerb6re Marine Reserve, the reproductive potential of male spawners decreased with depth, but the condition of spawners followed the opposite trend. However, we did not find any significant effect of protection on feeding or reproductive potential. With the exception of the liver index, condition did not differ significantly between sexes and maturity stages. For a given body weight, livers of female spawners were significantly bigger than those of male spawners and postspawners. In addition, feeding potential of post-spawners was better than that of spawners. Condition indices were independent of fish size, but there was a positive relationship between the reproductive potential and length of male spawners. Because condition is presumed important to growth, survival and recruitment, and because reproductive potential is presumed important to recruitment, we hypothesize that: (1) unprotected rocky areas may potentially contribute more to production of white seabream than the unprotected sandy coasts and are therefore, potential essential fish habitats for this species; and (2) the marine reserve might offer increased production for white seabream, providing long-term benefits to the local fishery of this species.