Feeding ecology of littoral Gobiid and Blennioid fishes of the Banyuls area (Mediterranean Sea). III. Seasonal variations
C. Dieter Zander, Thomas Hagemann

The quantitative analysis of small-sized fish assemblages is still in an early phase. This is especially true in rocky habitats where commercial fishing gear is ineffective. In 1979 and 1984, underwater investigations were made to get density and biomass data of small littoral fish. Three habitats were chosen: Overhanging rocks in 9-12 m depth, an adjoining fine sand bottom in 12-13 m, and a coarse sand bottom in 6-7 m. The most conspicuous fish species were: Tripterygion delaisi, T. melanurus, Parablennius gattorugine, P. rouxi and Gobius auratus among the rocks, Pomatoschistus bathi, Gobius auratus and G. geniporus on the sand bottoms. The densities of the fish assemblages increased in all habitats during summer. Biomass was highest in the rocky habitat in spring (1.3 g m-2) whereas the soft bottoms reached at most 0.4 (fine sand) or 0.3 g m-2 (coarse sand) in summer. While the biannual T. delaisi and the annual P. bathi were of greater importance in spring, the biomasses of P. rouxi, G. auratus and G. geniporus increased in summer. Polychaetes were the dominant prey in both grazers as well as pickers on the rocks in spring. They were replaced by algae or crustaceans respectively, in summer. On the sand bottoms mainly mysids and fish larvae were fed on in spring, diverse benthic crustaceans in summer. Ingestion rates were 11.2 (spring) or 8.1 mg m-2 (summer) on the rocks, but only 2.8 or 1.9 mg m-2 on the soft bottoms. When the consumption efficiency (CIP) is estimated, 10% of the mobile fauna and 0.5% of the periphyton production was consumed on the rocks. The same index for the coarse sand fishes was 14%. The calculation of consumption efficiencies may indicate whether the habitat offers sufficient food for the predators or whether other habitats are necessary to complete the food requirements.

Keywords: feeding ecology, Gobiids, Blennioids, littoral fishes, seasonality, Mediterranean.
Contents of this volume Sci. Mar. 53(2-3) : 441-449 Back PDF
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