Abstract
The effects of and the interplay between natural and anthropogenic influences on the composition of benthic communities over long time spans are poorly understood. Based on a 160-cm-long sediment core collected at 44 m water depth in the NE Adriatic Sea (Brijuni Islands, Croatia), we document changes in molluscan communities since the Holocene transgression ~11,000 years ago and assess how they were shaped by environmental changes. We find that (1) a transgressive lag deposit with a mixture of terrestrial and marine species contains abundant seagrass-associated gastropods and epifaunal suspension-feeding bivalves, (2) the maximum-flooding phase captures the establishment of epifaunal bivalve-dominated biostromes in the photic zone, and (3) the highstand phase is characterized by increasing infaunal suspension feeders and declining seagrass-dwellers in bryozoan-molluscan muddy sands. Changes in the community composition between the transgressive and the highstand phase can be explained by rising sea level, reduced light penetration, and increase in turbidity, as documented by the gradual up-core shift from coarse molluscan skeletal gravel with seagrass-associated molluscs to bryozoan sandy muds. In the uppermost 20 cm (median age <200 years), however, epifaunal and grazing species decline and deposit-feeding and chemosymbiotic species increase in abundance. These changes concur with rising concentrations of nitrogen and organic pollutants due to the impact of eutrophication, pollution, and trawling in the 20th century. The late highstand benthic assemblages with abundant bryozoans, high molluscan diversity, and abundance of soft-bottom epi- and infaunal filter feeders and herbivores represent the circalittoral baseline community largely unaffected by anthropogenic impacts.
Highlights
Investigations on modern marine ecosystem responses to natural and anthropogenic changes are typically limited to annual or decadal time scales
Our analyses show that the sediment cores collected at 44 m water depth from the Brijuni Islands reach back to the Holocene transgression about 11,000 years ago
They capture the transgressive phase coupled with shoreface erosion and reworking, followed by the establishment of epifaunal bivalve-dominated biostromes during the late transgressive/early highstand transition, by the shift to low-energy bryozoan-dominated biostromes during the highstand phase, and by strong environmental changes triggered by human impact mainly during the last century
Summary
Investigations on modern marine ecosystem responses to natural and anthropogenic changes are typically limited to annual or decadal time scales. The northern Adriatic Sea is a prime example of an ecosystem strongly affected by centuries of human pressure (Barmawidjaja et al, 1995; Gallmetzer et al, 2017; Huntley and Scarponi, 2015; Kowalewski et al, 2015; Lotze et al, 2011; Mautner et al, 2018; Scarponi et al, 2017a) This semi-enclosed shallow basin with high riverine input, extensive soft bottoms, susceptibility to seasonal water-column stratification, and propensity to eutrophication due to high primary production in its western part is classified as sensitive (Stachowitsch, 1984) and is considered one of the most degraded marine ecosystems worldwide (Lotze et al, 2006).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
