engleski

Loggerhead sea turtles as bioturbators in marine ecosystems

The northern Adriatic Sea is one of the most important foraging habitats for loggerhead sea turtle (Caretta caretta) in the Mediterranean. Its shallow continental shelf, favorable sea temperatures and rich benthic communities constitute feeding areas for loggerheads in neritic stage. While searching for prey, loggerheads actively dig and mine through the seafloor, ingest seafloor sediments and mix substrate. The sea floor of the Adriatic shelf is covered by muddy and sandy sediments of terrigenous origin and inorganic remains of benthic organisms, like shells of bivalves and gastropods. In order to examine ecological role of loggerheads in nutrient mixing and cycling in marine ecosystem, we qualitatively and quantitatively analyzed mollusk component in the diet of 50 loggerhead turtles (mean CCLn-t: 42.5 cm, SD: 11.7) found dead in the northern Adriatic Sea (Slovenia and Croatia) in 2001-2004. We preformed detailed identification and quantification of bivalve and gastropod fragments and sub-fossil shells. In total, we recorded 99 mollusc taxa. Most taxa belonged to gastropods (55) and bivalves (41), which were found in 88% of analyzed turtles. Majority of identified gastropod and bivalve species were small (shell length < 2 cm) and of sub-fossil origin. Due to the small size and low energetic value, shells of these species (e.g. Bittium reticulatum, Turritela communis, Corbula gibba) most likely do not present selected prey of loggerheads, and were probably eaten incidentally while digging through benthic sediments. By such feeding strategy, loggerheads actively mix sediments, enable aeration and contribute in nutrient cycling. Large proportion of sub-fossil shells found in our samples emphasizes the role of loggerheads as bioturbators in marine ecosystems.

sea turtles; ecological role; marine ecosystems; feeding ecology

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