The effect of epibenthic predators and macroalgal cover on the benthic macroinvertebrate community of a shallow lagoon in the Bay of Cádiz (SW Spain)

Abstract

Three field predator exclusion experiments were conducted in 1992 on a lagoonal muddy pan of the Bay of Cadiz to measure the effects of large epibenthic predators (fish and crustacean decapods) on the benthic macroinvertebrate community at different periods of the year (May–June, August–September, November–December). At the end of each field experiment (30–31 days), benthic macrofaunal communities within exclosures and control plots (three replicates for each treatment) were compared. There were no considerable exclosure artifacts in all three experiments, but a great heterogenity in the spatial macrofaunal distribution was observed especially in the late autumn experiment. No systematic change in overall faunal characteristics was observed with the exclusion of epibenthic predators, except significantly greater mean individual sizes (all experiments) and lower total densities (June and December) within exclosures. For several benthic species, a statistically detectable increased density and larger mean individual size were also observed within exclosures in May–June and August–September experiments but not in December, probably related to the higher predatory activity during the warm season. Conversely, the amphipod Microdeutopus gryllotalpa showed lower density but also larger mean size when epibenthic predators were excluded. An algal cover (Ulva) was present at three field experiments and had a mixed effect on the density of benthic macrofauna. Some epifaunal species (or epifaunal stages) were positively affected by the algal biomass, while some infaunal species were negatively affected.