Exploring decadal changes in macrobenthic assemblages of shallowest soft bottoms impacted by clam fishery in the northern Gargano (Southern Adriatic Sea)

Francesca Pia De Luca
1*
Daniela Cascione
2
Pasquale Ricci
1,3
Giulia Cipriano
1,4
Angelica Catacchio
1
Francesco Mastrototaro
1,4
Roberto Carlucci
1,4
1
ULR Bari, Consorzio Nazionale Interuniversitario per le Scienze del Mare - CoNISMa, Piazzale Flaminio, 9, Roma, RM - 00196, Italia
2
DICATECh, Politecnico di Bari, Via Edoardo Orabona, 4, Bari, BA - 70125, Italia
3
Dipartimento di Biologia, Università di Padova, Via Ugo Bassi, 58/B, Padova, PD - 35121, Italia
4
Dipartimento di Bioscienze, Biotecnologie e Ambiente - DBBA, Università degli studi di Bari "Aldo Moro", Via Edoardo Orabona, 4, Bari, BA - 70125, Italia

This study explores the decadal changes in soft-bottom macrobenthic assemblages in two southern Adriatic areas, Lesina and Varano, respectively characterized by high and occasional impact of fishing dredging, targeting Chamelea gallina. The biological data analysed were obtained from monitoring surveys conducted in the winters of 2013 and 2022 in 45 sampling stations to assess the status of the C. gallina stock and associated assemblage. Standardized abundance data (N/100m2) of collected benthic species were analyzed using Shannon's and Pielou's diversity indices, and testing differences through the non-parametric Kruskal-Wallis test. A multivariate analysis was performed on fourth-root transformed data for 53 species using a Bray-Curtis similarity matrix. Permutational analysis of variance (PERMANOVA) and principal coordinate analysis (PCoA) were performed to explore the structure of macrobenthic assemblages according to two fixed factors (Year and Area, both with 2 levels). Significant decreases in median values of both diversity indices were observed in Varano in 2022 compared to 2013 (p<0.001), while no significant differences were detected in Lesina. PERMANOVA showed significant differences in the structure of benthic assemblages for both Year and Area factors (p<0.001). PCoA showed a clear separation between areas in each year with 41.4% and 12.6% of total explained variance by the first and second axes, respectively. The species more correlated to Varano in 2013 (Glycimeris pilosa, Ophiura albida, Bolinus brandaris, Macropodia longirostris) were replaced by Echinocardium cordatum, Dosinia lupinus, Mactra stultorum in 2022. In Lesina, Astropecten spp., Diogenes pugilator, Polybius depurator were correlated to stations in 2013, while several polychaetes (Owenia fusiformis, Hyalinoecia tubicola) and the bivalve Peronidia albicans increased in 2022. Fishing dredge pressure has decreased in time due to national regulations introduced in 2017, which affected the structure of benthic assemblages. However, observed changes, especially in the less fishing-impacted Varano area, highlighted impacts due to other environmental stressors.

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