Substrate Characteristics, Fish Grazing, and Epibenthic Reef Assemblages off Hawaii
Authors: Hixon, Mark A.; Brostoff, William N.
Source: Bulletin of Marine Science, Volume 37, Number 1, July 1985 , pp. 200-213(14)
Abstract:Potentially important determinants of whether artificial reefs or settling plates will support relatively “natural” epibenthic communities are the surface texture (smooth or rough), chemical composition, and small-scale relief (flat or irregular) of the chosen substrate. Holding texture constant, this study investigated the effects of the latter two characteristics upon subtidal epibenthic reef assemblages which developed under several fish-grazing treatments in situ off Oahu, Hawaii. Some 1,200 settling surfaces were sampled without replacement during the yearlong course of the experiment.With relief held constant, we tested the hypothesis regarding chemical composition that a nontoxic artificial substrate (polyvinyl-chloride plastic) would support the same assemblages as the natural substrate in our reef-crest system (dead coral rock). Comparisons of invertebrate abundance, detritus and sediment load, algal biomass, coverage, diversity, and species composition usually supported this hypothesis. However, several significant differences were evident, especially at high grazing intensities. These were apparently due to the relative softness and porosity of the coral.With chemical composition held constant, we tested two independent hypotheses regarding small-scale relief by comparing assemblages that developed on flatly-cut coral-rock plates versus unaltered, irregularly-contoured pieces of coral rock. The first prediction, that irregular natural coral would support greater benthic diversity than flat coral only at low grazing intensities, was based on the hypothesis that natural coral provides only spatial heterogeneity allowing enhanced microhabitat partitioning among potentially competing benthic species. This hypothesis was rejected. The second prediction, that natural coral would support greater diversity only at high grazing intensities, was based on the hypothesis that natural coral provides only refuges from predation. This hypothesis was supported.Previous research has shown that rough surface texture is important for enhancing benthic settlement on artificial substrates. Our findings additionally suggest that, for artificial reefs designed to provide a food source for fishes, an irregular substrate may provide refuges for settling benthic organisms. Such refuges may prevent colonizing fishes from overgrazing early successional benthic assemblages, thus allowing the establishment and persistence of a diverse and sustainable food source.
Document Type: Research article
Publication date: 1985-07-01
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