New Insights into a Mediterranean Sea Benthic Habitat: High Diversity of Epiphytic Bryozoan Assemblages on Phyllophora crispa (Rhodophyta) Mats

Abstract

With its geographically isolated location and geological history, the Mediterranean Sea harbors well-known biodiversity hotspots, such as Posidonia oceanica seagrass meadows. Recently, long-living mats formed by the fleshy red alga Phyllophora crispa have been described to be associated with a high diversity of sessile invertebrates in the Tyrrhenian Sea. One of the key taxa among these sessile invertebrates are bryozoans: their abundance, diversity, and spatial distribution in P. crispa mats represent a gap in scientific knowledge. Thus, we conducted a pilot study on bryozoan assemblages associated with P. crispa mats around Giglio Island (Tuscan Archipelago, Italy) in 2018, followed by a comparative study on four sites distributed around the island in the subsequent year, 2019. We compared these findings to bryozoan abundance and diversity on P. oceanica shoots and leaves during the second expedition. The findings revealed more than 46 families, with a significantly higher number of taxa identified in P. crispa mats (33) than in P. oceanica meadows (29). The Shannon diversity index was similar between P. crispa and P. oceanica shoots, while Pielou’s evenness index was lower in P. crispa mats. The most abundant families reported across all habitats were Crisiidae, Aetidae, and Lichenoporidae; but the most abundant family on P. crispa was Chlidoniidae (Chlidonia pyriformis). The assemblages associated with P. crispa differed among sites, with higher abundances but lower diversity on the exposed southernmost site. The total bryozoan abundance was significantly higher on P. crispa (average 2.83 × 106 ± 1.99 × 106 colonies per m2 seafloor) compared to P. oceanica meadows (average 0.54 × 106 ± 0.34 × 106 colonies per m2 seafloor). Our results show a high diversity of bryozoans on P. crispa thalli compared to P. oceanica meadows, which was consistent throughout the study. These findings confirm the value of the red alga-generated habitat for associated bryozoans and may have implications for future biodiversity assessments and conservation measures.

The Bryozoan Margaretta cereoides as Habitat-Former in the Coralligenous of Marzamemi (SE Sicily, Mediterranean Sea)

“…An amount of 41 bryozoan and 5 serpulid species (with 220 colonies and 58 specimens) were present on further algae, largely represented by fronds of Phyllophora crispa. Whereas no data is available for epibionts on F. petiolata, extensive surveys on epibionts growing on P. crispa from several samples collected in different sites and seasons around the Giglio Island (Tuscany Archipelago, NE Tyrrhenian Sea) allowed (Rossbach et al, 2022 [47]) to recognize a number of bryozoan species belonging to 43 different families and ( [47] and Rossbach et al, 2021 [48]) to list 9 serpulid taxa, roughly comparable to figures observed in the present study. As far as we know, together with the record of 54 bryozoan epibiont species on 100 fronds of the large-sized Laminaria rodriguezii Bornet, 1888 (colonisable surface of ca.…”

“…Indeed, few studies have been so far devoted at investigating epibiont communities on habitat-forming bryozoans in general, unlike for other taxa, especially P. oceanica (e.g., Mazzella et al, 1989 [64]; Nesti et al, 2009 [65]; Di Martino and Taylor, 2014 [66] for a review about bryozoan epibionts), some fleshy algae (e.g., [47,50]; Di Geronimo et al, 1990 [67]) and reef-forming organisms, including coralligenous algae and mesophotic benthic animals (e.g., [24] Harmelin, 2017 [68]; Giampaoletti et al, 2020 [69]; Pica et al, 2022 [70], focusing particularly on bryozoans). In European seas, the most investigated species is possibly F. foliacea.…”