Megabenthic invertebrate diversity in Mediterranean trawlable soft bottoms: a synthesis of current knowledge

Abstract

Mediterranean bottom trawling is generally characterised by a highly diversified mixed catch, composed of fish, cephalopods,crustaceans, and other megabenthic invertebrates. Although management of Mediterranean trawling requires a multispecies approach on a community basis, this does not seem to be the case in the relevant literature. Herein, we present an extensive review ofthe existing knowledge on megabenthic invertebrate communities, focusing on the trawlable bottoms. A total of 207 publicationsfrom 1930 to the early 2021 was collected and classified into seven research areas. Research effort on soft bottom megabenthicinvertebrates of trawlable grounds was higher for the Western Mediterranean and the depth zone of 50-200 m. Overall, 1,797 taxawere reported belonging to different taxonomic groups, the most diverse of which were Mollusca, Crustacea, Polychaeta, andPorifera. Among the reported taxa, 43 species are alien to the Mediterranean Sea, and 42 are included in the lists of threatened/ endangered and protected species under the Barcelona and Bern Conventions. The Western Mediterranean and the Aegean Sea werethe ecoregions with the highest number of megabenthic invertebrate species reported from trawlable grounds. All Mediterraneanecoregions were grouped according to their megabenthic fauna at a similarity level of 27%. The present work compiles the knownscattered information, highlights knowledge gaps, and underlines the need for time series data on the megabenthic communitiesof the Mediterranean fishing grounds.

Sponge Community Patterns in Mesophotic and Deep-Sea Habitats in the Aegean and Ionian Seas

“…Species richness did not differ statistically significantly between the subareas, but GLM ANOVA showed a clear distinction between the five depth zones for both ecoregions, with the number of species decreasing with depth. This is in agreement with previous studies, both those concerning sponges [76] and those regarding generally megabenthic invertebrates [26]. As expected, species with large body size and massive growth forms dominated in most depth zones.…”

“…These authors reported notable sponge and anthozoan populations in this subarea using ROV. The higher megabenthic diversity (including sponges) of the Aegean over the Ionian Sea was recently highlighted in a review about megabenthic invertebrates from trawlable soft bottoms [26].…”

“…The Mediterranean basin is home to around 10% of the world's sponge species [25]. Sponges account for around 6% of the recorded invertebrate diversity in the Mediterranean [23] and 14.4% of the megabenthic invertebrate taxa reported as trawl bycatch from the Mediterranean soft-bottom grounds [26]. Even though in recent years the importance of sponges in deep-water Mediterranean ecosystems has been recognized, and sponge dominated deep-sea habitats are considered remarkable [1,27], the impacts of direct and indirect anthropogenic activities, such as bottom trawling and global climate change, on deep-sea sponge ecosystems have not yet been extensively studied [28,29].…”

Ecosystem-based assessment of a widespread Mediterranean marine habitat: The Coastal Detrital Bottoms, with a special focus on epibenthic assemblages

“…In the Mediterranean Sea, CDB are one of the most widespread ecosystems between 30 and 100 m depth, corresponding to the upper part of the circalittoral zone (Peŕès and Picard, 1964;Peŕès, 1967), and house a high alpha species diversity (Stamouli et al, 2022). Besides a mineral component (typically coarse sand with a variable proportion of finer particles), these bottoms contain significant quantities of recent organogenic and bioclastic sediments (remains from hard bottoms, shell debris, bryozoans or calcified macro-algae), either autogenous or imported from adjacent ecosystems (e.g., coralligenous reefs, photophilic rocky reefs, seagrass meadows).…”

“…Important ecological functions and ecosystem services, up to now poorly assessed, are provided by CDB (Ballesteros, 1994;Barbera et al, 2003): (i) primary production (Basso, 2012;Basso et al, 2012); (ii) key habitat and trophic resources for invertebrates and fish; (iii) breeding, spawning and nursery grounds for fish and crustaceans including species of fishery interest, sometimes close to the deep limit of the Posidonia oceanica (L.) Delile meadow (e.g., Mullidae, Sparidae, Scorpaenidae, Palinurus elephas (Fabricius, 1787)) (Harmelin and Harmelin-Vivien, 1976;Verlaque, 1990;Kamenos et al, 2004;Soykan et al, 2010); (iv) fishing ground for trawlers and artisanal fishers (Stamouli et al, 2022); (v) long term carbon sink (Basso, 2012;Basso et al, 2012;Savini et al, 2012;Burrows et al, 2014;Watanabe et al, 2020); (vi) recycling of necromass (e.g., rhizomes and dead Posidonia oceanica leaves and drift macroalgae) (Boudouresque et al, 2016); (vii) exportation and settlement of larvae towards or from adjacent ecosystems (source-sink hypothesis; Levin and Dayton, 2009). In addition, CDB host numerous protected species and other species of conservation interest (Astruch et al, 2012;Joher et al, 2015;Astruch et al, 2019): e.g., the fan shell Pinna nobilis L. 1758 (annexe II Berne convention and UICN Red list: critically endangered), the red coralline alga Lithothamnion corallioides (Annexe 5 of the HD: species of interest with regulation of its exploitation), and several Fucales (Annexe 2 of the Barcelona convention), among others.…”