In situ visual surveys using a hierarchical sampling design were carried out at 36 sublittoral rocky locations along the central-east Atlantic Canarian Archipelago to find relationships among (1) benthic primary producers, (2) the demographic structure of the herbivorous sea urchin Diadema antillarum Phillipi and (3) the trophic structure of coastal fish communities. Our correlation approach displayed a relationship between the lack of large macroinvertebrate-eating predatory fish and the increase in density of sea urchins, in addition to a decrease in fish richness. In contrast, increases in fast-growing plankton-feeding fish species were detected. The size structure of D. antillarum is dominated by small-to-intermediate sized sea urchins in environments with a high density of individuals, whereas low sea urchin density locations are characterized by the dominance of large sized individuals. The physical complexity of the substrate seems to play an important role in determining the local patchiness of D. antillarum. Finally, a non-linear decrease in the percentage of fleshy macroalgal cover with increasing density of D. antillarum was observed. We therefore propose D. antillarum as a key herbivorous species, which plays an important role in determining the structure of shallow, hard-substratum, infralittoral benthic communities throughout the Canary Islands. KEY WORDS: Urchin-fish interactions · Trophic cascades · Diadema antillarum · Sea urchins · Fish assemblages · Macroalgae · Canary Islands Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 278: [157][158][159][160][161][162][163][164][165][166][167][168][169] 2004 tourist industry and the increased demand of fishery resources (Bortone et al. 1991, Falcón et al. 1996. However, no empirical evidence of the effect of these disturbances is available, as there are no data on the nearshore fish populations during the predevelopment era of the 1960s (Falcón et al. 1996). Personal observations and several local studies have suggested that the long-spined sea urchin Diadema antillarum Philippi has experienced a significant increase in abundance throughout the central-east Atlantic (FAO fisheries region #34) in the last decades (Casañas et al. 1998, Alves et al. 2001, Tuya et al. 2004b. Although D. antillarum has been extensively studied in the western Atlantic, where it has a great impact on benthic community structure (e.g. Sammarco et al. 1974, Carpenter 1981, Lessios 1988, little research has been undertaken in the eastern Atlantic to link the demographic structure of this echinoid species with the abundance and biomass of rocky-reef fish assemblages in the Canarian Archipelago. Moreover, no study has addressed the above along with the coastal trophic cascades within this area (Pinnegar et al. 2000).The general aim of this study was therefore to determine whether there is an association between the structure of Diadema antillarum populations and the community structure of macroalgae and fish. This potenti...

Wild fish were counted in 4 depth-related strata (bottom, midwater, cage and surface) around 3 floating sea-cage fish farms (Altea, Campello, Guardamar) along the Spanish coastline and 2 farms (Los Cristianos, San Andrés) in the Canary Islands. Almost 200 000 wild fish belonging to 53 species were seen; representatives of Sparidae (8 species), Carangidae (6 species), Mugilidae (5 species) and Chondrichthyid rays (7 species) were commonly observed. At all 5 farms, 1 to 3 taxa accounted for > 74% of the abundance and > 94% of the biomass of aggregated wild fish. Abundances (5.7 to 162 times) and biomasses (42 to 1728 times) of wild fish were higher in the cage stratum at the 3 Mediterranean farms than at the bottom. In contrast, abundances and biomasses of wild fish at the Canary Island farms were highest at the bottom at San Andrés and highest at the surface at Los Cristianos. Large differences in the sizes of associated fish existed among farms, with low percentages of fish > 20 cm total length at Guardamar, Los Cristianos and San Andrés (11 to 25%) compared to Altea and Campello (81 to 95%). However, the greatest proportions of large fish were present in the cage stratum at each of the 5 farms. This variability suggests that assemblage structure and aggregated biomass of wild fish at farms cannot be predicted prior to their installation, causing uncertainty in modelling of nutrient dispersal. Further, the sedimentation 'footprint' of temperate seacage fish farms may vary depending on (1) the species and biomass of associated wild fish, and (2) where these fish are distributed in the water column. As wild fish consume lost feed and assimilate nutrients, we suggest that coastal managers prohibit fishing of large planktivorous species at farms to fully harness their ability to ameliorate benthic impacts.

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