Twenty seagrass meadows from inside Marine Protected Areas (3 MPAs Reserva Marina del Freu de sa Dragonera, Reserva Marina de la Badia de Palma, Reserva Marina del Migjorn de Mallorca) and at varying distances from anthropogenic activity hubs such as harbours and marinas were studied along the southern coast of Mallorca, Balearic Islands, Spain. A total of 4 ecological surveys and one hydro-acoustic survey were carried out to collect data on seagrass habitat structure and complexity and fish communities associated with this habitat. Estimates of recreational fishing pressure, anchoring pressure and water quality were used to examine the influence of anthropogenic pressures on seagrass habitat structure. We found a significant negative association between anchoring pressure and seagrass patch size suggesting that high anchoring pressure results in smaller and more fragmented meadows. Water nutrient concentration (represented by the δ15N in seagrass leaves) also affected seagrass and fish species living in this habitat. High nutrient concentrations resulted in seagrass meadows of low shoot density and shoot biomass, which were favoured by populations of Diplodus annularis, but not by Symphodus ocellatus. The annular seabream (D. annularis) is a resident fish species of Posidonia oceanica and a species of socio-economic importance to the Mallorcan recreational fishery. Therefore, further studies into how seagrass habitat structure affects D. annularis population structure (density and biomass), growth and body condition were carried out. Body condition was higher at higher shoot density and lower conspecific density suggesting that release from competition among conspecifics for resources might influence D. annularis body condition. The mean daily growth for juveniles during the early settlement phase in seagrass (30 days post-settlement) was higher for juveniles in areas with low shoot density, high predator & conspecific density, high water nutrient content, and high recreational fishing pressure. Variation in seascape composition can affect access to food resources and/or predators, possibly influencing post-settlement growth and mortality, and subsequently adult population structure. Understanding how the surrounding seascape affects individual-based measures of habitat quality, like condition or growth, provides useful information regarding optimal fish habitat.
