Habitat correlates of the distribution and biomass of Seychelles' reef fishes

Abstract

SynopsisRelationships between quantitative measures of habitat type and the biomass of Chaetodon, Scarus and Parupeneus species were investigated across 35 reef sites in the Inner Seychelles Group. Multiple regression was used to determine the proportion of variance in biomass between sites which could be explained by depth, exposure, vertical relief, topographic complexity, live coral cover, coral rubble cover, rock cover, sand cover, underlying carbonate substrate, underlying sand substrate, underlying rock substrate and an index of fishing intensity. A significant proportion of the variance in biomass was explained by habitat variables and the index of fishing intensity for 7 of 12 Chaetodon species (23-52% of variance explained), 3 of 6 Parupeneus species (33-40%), and 10 of 13 Scarus species (1446%). Within genera, different groups of habitat variables explained the variance in biomass for different species and, of the variables studied, only the proportion of underlying sand substrate failed to explain a significant proportion of the variance in biomass for any species. Quantitative relationships between the biomass of Chaetodon and habitat were often in accordance with those suggested by previous studies of their ecology, life-history and distribution at other Indo-Pacific locations. However, the habitat associations of the Parupeneus and some Scarus species have not been studied at other locations and clearly warrant further investigation. It was concluded that habitat was an important determinant of the distribution of many Seychelles reef fishes, but that the habitat variables examined were rarely the most important determinant of biomass. However, the inclusion of a procedure to collect habitat data provided a useful means by which to reduce the unexplained variance associated with visual census biomass estimates and therefore improves the possibility of elucidating the effects of other factors on the biomass of Seychelles reef fishes.

Community structure and biogeography of shore fishes in the Gulf of Aqaba, Red Sea

“…This strong relationship has been shown in several studies of corallivorous fishes (Bouchon-Navaro et al 1985;Jennings et al 1996;Öhman and Rajasuriya 1998), Chaetodontidae in general (Bell et al 1985;Bouchon-Navaro and Bouchon 1989) and the complete fish community in regard to abundance, species richness and diversity (Bell and Galzin 1984;Carpenter et al 1981;Harmelin-Vivien 1989;Chabanet et al 1997;Adjeroud et al 1998). An experimental disturbance of hard corals resulted in a significant reduction in abundance of chaetodontid fishes (Lewis 1997).…”

“…The discrepancy between the different studies may have several reasons. Jennings et al (1996) stated that "resident obligate corallivores will be absent if sites without coral cover are included, but this does not suggest that coral cover limits abundance in areas where coral is present". Jones and Syms (1998) discussed this problem in more detail and conclude that these discrepancies between studies are due to different ranges of observed coral cover.…”

Species-area relationships for coral reef fish assemblages of St. Croix, US Virgin Islands

“…Because of the quadratic forms of the independent variables, non-linear relationships were examined. Multiple forward stepwise regression works by sequentially adding habitat variables to the regression equation only if there is significant improvement to the coefficient of determination (Jennings et al 1996). Plots of residuals versus predicted values of log 10 (species richness) were done following the analysis in order to test for normality, linearity and homoscedasticity (Tabachnick & Fidell 1996).…”

Effects of habitat complexity on Caribbean marine fish assemblages

“…Thus, a systematic approach that simultaneously examines as many complexity variables as possible to determine which are the most important factors is needed. For this study, 5 main habitat-complexity variables recurring in the literature were identified: (1) topographic complexity or rugosity of the substrate (Risk 1972, Luckhurst & Luckhurst 1978, Roberts & Ormond 1987, Jennings et al 1996, Chabanet et al 1997, Ohman & Rajasuriya 1998, (2) substratum diversity (Roberts & Ormond 1987, Ohman & Rajasuriya 1998, (3) variety of refuge hole sizes (Roberts & Ormond 1987), (4) vertical relief or height of substrate architecture (Luckhurst & Luckhurst 1978, Molles 1978) and (5) percentage hard substrate (Cohen et al 1993, Guidetti 2000, Khalaf & Kochzius 2002. The effects of each of these variables on the local fish assemblage were tested in a field experiment, and this study is one of the first experimental attempts to simultaneously compare the effects of all these habitat complexity variables.…”