engleski

Top-down regulation of fish communities in the shallow infralittoral of the Croatian Adriatic

A fundamental paradigm of community ecology of the shallow infralittoral is that the most important factor limiting animal populations is the shelter from predators provided by three dimensional structure. However, that structure can also provide ambushing cover for resident predators. Thus the value and role of structured habitat could vary depending on the density of predators and their mode of predation. Our objectives were to assess the direct negative effect of predation by mesopredators on the regulation of prey fish populations, the direct negative effect of top predators on mesopredators, and the indirect positive effect of top predators on prey populations. We used methods of experimental fishing (with hook, bait, and long lines) and fish traps to estimate the relative population abundance of prey, meso- and top predators inside and outside of marine protected areas on the Croatian coast, at several benthic habitats including Posidonia oceanica, unconsolidated sediment, rock, and macroalgae. We found that populations of large predators and small prey species were larger within marine protected areas than outside them, and prey species occurred inside and outside P. oceanica meadows. Outside marine protected areas, top predator populations were very small, and mesopredator populations were larger, showing “mesopredator release”. Outside marine protected areas, small prey species were caught mostly outside of seagrass meadows or at their margins, perhaps due to avoidance of the resident mesopredators using seagrass as ambushing cover. We conclude that top-down effects are important in structuring fish communities in the shallow infralittoral, and the importance of three dimensional structure may vary with the abundance of predator populations and the local fishing pressure.

Marine Protected Areas; experimental fishing; Posidonia oceanica; predator; prey

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