ProblemThe issue of the present and past roles of sea turtles in ecosystems is underlined as one of the global research priorities for sea turtle management and conservation in the 21st century (Hamann et al. 2010). Sea turtles act at multiple levels, as predators, prey, competitors, substrate for epibionts, hosts of parasites and pathogens, nutrient transporters and modifiers of habitats (Bjorndal 2003;Bjorndal & Jackson 2003). Knowledge on the role of sea turtles in the ecosystems they utilize is necessary for our ability to predict how natural and anthropogenic-driven environmental changes can affect their populations in order to make informed management decisions (Bjorndal 2003).Loggerhead sea turtle, Caretta caretta (Linnaeus, 1758) is an endangered (IUCN 2009), large, long-lived top predator in marine ecosystems, with a complex life history characterised by switching between different habitats AbstractMolluscs are a diverse and ubiquitous group of organisms which contribute to the formation of biogenic sediments and are one of the major prey taxa for the neritic-stage loggerhead sea turtles (Caretta caretta) worldwide. Here we investigated to what degree molluscs contribute to the diet of individual turtles, and what role the feeding strategy of loggerheads might play in bioturbation, one of the key processes in nutrient transport in marine ecosystems. We performed a detailed analysis of benthic molluscs from the digestive tracts of 62 loggerhead sea turtles (curved carapace length: 25.0-85.4 cm) found in the Northern Adriatic Sea. From 50 of the turtles that contained benthic molluscs, we identified 87 species representing 40 families and three classes (Gastropoda, Bivalvia and Scaphopoda), including 72 new dietary records for loggerhead turtle. Most of the identified molluscs were small-sized species (shell length £ 3 cm) and were often found in a subfossil condition. Their intake may be considered a byproduct of infaunal mining, while larger molluscs were mainly found crushed into smaller fragments. Through such foraging behaviour loggerheads actively rework sediments, increase the surface area of shells and the rate of shells disintegration, acting as bioturbators in this system. We conservatively estimate that loggerheads in the neritic zone of the Adriatic Sea bioturbate about 33 tonnes of mollusc shells per year, and hypothesize about the possible effects of bioturbation reduction on environmental changes in the Northern Adriatic ecosystem.

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The corallivorous gastropod Coralliophila meyendorffi (family Coralliophilidae) is a well-known predator of the coral Cladocora caespitosa, particularly in the eastern Adriatic Sea, where population outbreaks can drastically reduce coral cover. Coralliophila meyendorffi ranges in size from 5 to 40 mm in shell total length, and smaller specimens are often found living with the coral C. caespitosa. Specimens of C. meyendorffi feed exclusively on live coral tissue, stripping it from the calcium carbonate skeleton. Recent outbreaks of the gastropod C. meyendorffi have caused considerable damage on a C. caespitosa bank in Veliko Jezero (the Mljet National Park, eastern Adriatic Sea). The bank occurs at depths between 6 and 18 m, covering a 65  m2 area. During summer of 2010, a substantial outbreak affected about 5%t of the coral colonies. The gastropods were highly aggregated in sheltered areas of the coral bank (up to 41 specimens/dm2) with smaller clusters (from 8 to 12 specimens/dm2) on coral colonies that were influenced by strong bottom currents (up to 1.23 ms−1).

The institute in Rovinj was founded in 1891 as the field station of the Berhn Aquarium.