Preliminary assessment of structural and functional variations in macrobenthic assemblages impacted by mechanical harvesting of bivalves in the Southern Adriatic Sea
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Dipartimento di Biologia, Università di Padova, Via Ugo Bassi, 58/B, Padova, PD - 35131, Italia
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URL Bari, CoNISMa, P.le Flaminio, 9, Roma, RM - 00165, Italia
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DICATECh, Politecnico di Bari, Via Orabona, 4, Bari, BA - 70125, Italia
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OGS - Sezione di Oceanografia, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Borgo Grotta Gigante, 42/C, Sgonico, TS - 34010, Italia
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Dipartimento di Bioscienze, Biotecnologie e Ambiente, Università di Bari, Via Orabona, 4, Bari, BA - 70125, Italia
The harvesting of commercial bivalves through hydraulic dredges represents a critical disturbance for macrobenthic communities inhabiting shallow soft bottoms. However, the ecological responses of these communities are shaped by cumulative impacts, including fishing and environmental stressors. This contribution presents preliminary results on temporal variations in the functional diversity and traits occurrences in benthic assemblages impacted by the clam fishery (Chamelea gallina) in the Southern Adriatic Sea during the period 2019-2022. Biological data were collected through monitoring surveys conducted in two areas characterized by different fishing effort intensity levels (Lesina high and Barletta low). Standardized abundance data (N/100m2) for 51 species were used to perform a Biological Trait Analysis. Eleven traits (6 response and 5 effect on the environment), encompassing 42 categories, were assigned to each species using a fuzzy coding approach (scores 0–3 based on affinity). Functional Dispersion index (FDis) and Community Weighted Mean (CWM) were calculated, and temporal and spatial differences were tested using univariate non-parametric test (Kruskall-Wallis test) and a multivariate ordination method (Principal Coordinate Analysis, PCoA) based on Gower’s similarity matrix calculated on CWM values. Significant temporal increase and decrease in median FDis values, calculated for response traits, were observed in Barletta and Lesina, respectively (p<0.05). In both areas, response traits showed increased occurrence in tube-protected, medium-sized organisms with intermediate longevity (3–6-years) between 2019 and 2022, while effect traits showed an increase in endofauna species and suspension and deposit feeders. PCoA plot showed greater variability in Lesina than in Barletta for all considered traits during the investigated period. C. gallina abundance showed a strong decrease in Barletta, while remaining constant in Lesina. Overall, site-specific fishing efforts patterns seem to interact with several environmental stressors (e.g sedimentation processes, warmer waters, hydrological changes), driving shift in the functional composition expressed by the investigated benthic assemblages.
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