Abstract
Spatial configuration of habitat types in multihabitat seascapes influence ecological function through links of biotic and abiotic processes. These connections, for example export of organic matter or fishes as mobile links, define ecosystem functionality across broader spatial scales. Herbivory is an important ecological process linked to ecosystem resilience, but it is not clear how herbivory relates to seascape configuration. We studied how herbivory and bioerosion by 3 species of parrotfish were distributed in a multi-habitat tropical seascape in the Western Indian Ocean (WIO). We surveyed the abundance of three species with different life histories—Leptoscarus vaigiensis (seagrass species), Scarus ghobban (juvenile-seagrass/adults-reefs) and Scarus rubroviolaceus (reef species) —in seagrass meadows and on reefs and recorded their selectivity of feeding substrate in the two habitats. Herbivory rates for L. vaigiensis and S. ghobban and bioerosion for S. rubroviolaceus were then modelled using bite rates for different size classes and abundance and biomass data along seascape gradients (distance to alternative habitat types such as land, mangrove and seagrass). Bioerosion by S. rubroviolaceus was greatest on reefs far from seagrass meadows, while herbivory rates by S. ghobban on reefs displayed the opposite pattern. Herbivory in seagrass meadows was greatest in meadows close to shore, where L. vaigiensis targeted seagrass leaves and S. ghobban the epiphytes growing on them. Our study shows that ecological functions performed by fish are not equally distributed in the seascape and are influenced by fish life history and the spatial configuration of habitats in the seascape. This has implications for the resilience of the system, in terms of spatial heterogeneity of herbivory and bioerosion and should be considered in marine spatial planning and fisheries management.
Highlights
Herbivory is a key ecological process in coral reef and seagrass ecosystems, with the potential to shape benthic community composition and primary productivity [1,2,3,4,5,6]
All S. ghobban fish observed in the seagrass meadows were juvenile, except on one occasion when a group of larger individuals (
Densities of both S. ghobban and L. vaigiensis were highly variable among seagrass meadows, with S. ghobban being slightly more numerous at all sites compared to L. vaigiensis (1.7 ± 0.43 and 1.6 ± 0.27 ind m−2 respectively, Appendix B, Figure A3)
Summary
Herbivory is a key ecological process in coral reef and seagrass ecosystems, with the potential to shape benthic community composition and primary productivity [1,2,3,4,5,6]. In these systems, macro herbivores such as fish and sea urchins are the main herbivores based on their abundance and functional diversity [7,8,9]. Proximity to mangroves seems to have less effect on parrotfish grazing rates on the epilithic algal matrix (EAM) on Indo-Pacific reefs [22,23]
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