Long-term trends (1989-2013) in the seabird community breeding in the lagoon of Venice (Italy)

The community of seabirds breeding in the lagoon of Venice, one of the largest around the Mediterranean, was monitored over the 1989-2013 period. Six species have been recorded (Larus michahellis, Chroicocephalus ridibundus, Larus melanocephalus, Sternula albifrons, Sterna hirundo, Sterna sandvicensis). Over the study period, 346 colonies were surveyed; they were located on saltmarsh islets, dredge islands and other artificial sites, in descending order of importance. Beaches were used only at the beginning of the survey. About 4,900 pairs bred in the 2009-2013 years. The community has been always dominated by L. michahellis; in the 2009-2013, this species and S. sandvicensis comprised about 70% of the total. The longterm trends show moderate increase in the size of the whole community. Contrasting trends were observed in different species, with L. michahellis, S. albifrons and S. sandvicensis stable or increasing, whereas C. ridibundus and S. hirundo were declining. The number of pairs nesting on artificial sites increased over the last 15 years, while those on saltmarsh islets decreased correspondingly. This was possibly a response to the increase of mean sea level and storminess observed in the last twenty-five years. S. albifrons and S. sandvicensis populations reached national importance; the population of the latter species is noteworthy at a Mediterranean level.