Tropical Coastal Habitats as Surrogates of Fish Community Structure, Grazing, and Fisheries Value

Abstract

Abstract. Habitat maps are frequently invoked as surrogates of biodiversity to aid the design of networks of marine reserves. Maps are used to maximize habitat heterogeneity in reserves because this is likely to maximize the number of species protected. However, the technique's efficacy is limited by intra-habitat variability in the species present and their abundances. Although communities are expected to vary among patches of the same habitat, this variability is poorly documented and rarely incorporated into reserve planning. To examine intra-habitat variability in coral-reef fishes, we generated a data set from eight tropical coastal habitats and six islands in the Bahamian archipelago using underwater visual censuses. Firstly, we provide further support for habitat heterogeneity as a surrogate of biodiversity as each predefined habitat type supported a distinct assemblage of fishes. Intrahabitat variability in fish community structure at scales of hundreds of kilometers (among islands) was significant in at least 75% of the habitats studied, depending on whether presence/absence, density, or biomass data were used. Intra-habitat variability was positively correlated with the mean number of species in that habitat when density and biomass data were used. Such relationships provide a proxy for the assessment of intra-habitat variability when detailed quantitative data are scarce. Intra-habitat variability was examined in more detail for one habitat (forereefs visually dominated by Montastraea corals). Variability in community structure among islands was driven by small, demersal families (e.g., territorial pomacentrid and labrid fishes). Finally, we examined the ecological and economic significance of intra-habitat variability in fish assemblages on Montastraea reefs by identifying how this variability affects the composition and abundances of fishes in different functional groups, the key ecosystem process of parrotfish grazing, and the ecosystem service of value of commercially important finfish. There were significant differences in a range of functional groups and grazing, but not fisheries value. Variability at the scale of tens of kilometers (among reefs around an island) was less than that among islands. Caribbean marine reserves should be replicated at scales of hundreds of kilometers, particularly for species-rich habitats, to capture important intra-habitat variability in community structure, function, and an ecosystem process.

Complex reef architecture supports more small-bodied fishes and longer food chains on Caribbean reefs

“…This may be a consequence of increases in the home range size with increasing body size, as larger Caribbean reef fishes tend to also increase in mobility (Kramer and Chapman 1999), and are therefore less likely to be associated with specific attributes of individual coral colonies. The reduction in dependence on reef complexity of large-bodied fishes suggests that factors such as the availability of prey (Hixon and Beets 1993) and/or reef conditions at larger scales (e.g., the effect of protection at Marine Reserve scales; Kramer and Chapman 1999) or connectivity to adjacent habitats (Mumby et al 2004, Harborne et al 2008) may be stronger influences on the abundance of these adult fishes. The increase in mean trophic level with 'coral cover-complexity', in addition to the strong and positive influence of Montastraea on highertrophic level (especially carnivorous) fish, suggests that reefs with greater architectural complexity support longer food chains with more predator-dominated fish communities compared to flatter reefs with lower coral cover.…”

Revealing the regime of shallow coral reefs at patch scale by continuous spatial modeling

“…However, it is obvious that a continuous approach is better suited for describing natural pattern-process interactions that are emerging from a range of gradients and resources (Austin, 2007). The continuously ranging approach provides insights into the spatial modeling of species diversity (Harborne et al, 2008;Mellin et al, 2009) and can successfully map the variations in ecological processes by means of appropriate indicators such as the functional index (Borja et al, 2000),…”

Habitat-associated intraspecific variation in behavior and stress responses in a demersal coral reef fish

“…Habitats exhibiting a high degree of spatial complexity or microhabitat variety frequently support a wider diversity -and often greater abundance -of species (Luckhurst & Luckhurst 1978, Roberts & Ormond 1987, Harborne et al 2008, DeRaedemaecker et al 2010. What is less commonly recognized, however, is that heterogeneity in habitat conditions can also shape the behavior and physiology of animals in ways that affect how they cope with different ecological demands.…”