Seabird influence on ecological processes in coastal marine ecosystems: an overlooked role?

Coastal marine ecosystems and especially transitional environments host a large variety of birds, functioning as nesting sites for resident species and corridors for migratory ones. Seabirds activity may trigger movement of nutrients and organic matter between coastal boundaries, affecting their availability and processing. Consequently seabirds are often labelled as biotic vectors. While attention has been focused on the study of biodiversity level and migratory patterns of avifauna, there is little information on the effects of seabirds on ecological features (i.e. trophic status, biodiversity level, food web patterns, transfer of contaminants) in coastal marine ecosystems. To address these knowledge gaps, in this presentation we will firstly review the available information on the role of seabird derived-subsidies (i.e. nutrients) in coastal marine ecosystems and then we will present a case study from a Mediterranean transitional environment (Marinello ponds, Sicily, Italy). This area may be considered a field laboratory where to study the ecological role of seabirds due to the presence of several small (1-2 ha) and adjoining ponds that differ strongly in the amount of subsidies they receive from seabird guano. We will summarize data on trophic condition, benthic biodiversity, isotopically constructed-food webs and trace element contamination and biomagnification. The results provide evidence of the important ecological role of seabirds in driving ecosystem structure and functioning; indeed the pond affected by gull guano showed a higher trophic status and trace element contamination, lower biodiversity of benthic communities and simpler food webs. This overall picture highlights that avifauna may exert a noteworthy, though so far neglected, ecological role in coastal marine ecosystems, and especially in transitional environments, deserving more attention.