Predators structure fish communities in Posidonia oceanica meadows: meta-analysis of available data across the Mediterranean basin

Posidonia oceanica meadows are thought to provide refuge for prey species, which suggests that fish communities are organized according to the abundance and behavior of predators. We collected published research on fish assemblages associated with P. oceanica meadows in the Mediterranean Sea and performed a meta-analysis to test hypotheses regarding the drivers of community structure. In 14 studies documenting the relative abundance of fish species, 112 taxa within a depth range of 1-40 m were reported at local P. oceanica meadows. Sampling method had the most significant effect on community abundance. Total predator abundance and abundance of resident predators each had a significant effect on the prey fish community. A higher abundance of resident predator species such as Scorpaena notata and Zosterisessor ophiocephalus was associated with a lower abundance of small Symphodus spp., Chromis chromis, and Gobiidae, and overall lower prey species richness. Fish communities in P. oceanica meadows are, therefore, in part organized in response to the presence and abundance of piscivorous species, which reduces the value of seagrass as a refuge habitat for potential prey species. For more robust estimates of the habitat value of P. oceanica, a concerted international, collaborative research effort that applies uniform, non-destructive sampling methods, such as visual census or stereo-videography within and outside meadows, is needed.