Abundance and Diversity of Crypto- and Necto-Benthic Coastal Fish Are Higher in Marine Forests than in Structurally Less Complex Macroalgal Assemblages

Abstract

In Mediterranean subtidal rocky reefs, Cystoseira spp. (Phaeophyceae) form dense canopies up to 1 m high. Such habitats, called ‘Cystoseira forests’, are regressing across the entire Mediterranean Sea due to multiple anthropogenic stressors, as are other large brown algae forests worldwide. Cystoseira forests are being replaced by structurally less complex habitats, but little information is available regarding the potential difference in the structure and composition of fish assemblages between these habitats. To fill this void, we compared necto-benthic (NB) and crypto-benthic (CB) fish assemblage structures between Cystoseira forests and two habitats usually replacing the forests (turf and barren), in two sampling regions (Corsica and Menorca). We sampled NB fish using Underwater Visual Census (UVC) and CB fish using Enclosed Anaesthetic Station Vacuuming (EASV), since UVC is known to underestimate the diversity and density of the ‘hard to spot’ CB fish. We found that both taxonomic diversity and total density of NB and CB fish were highest in Cystoseira forests and lowest in barrens, while turfs, that could be sampled only at Menorca, showed intermediate values. Conversely, total biomass of NB and CB fish did not differ between habitats because the larger average size of fish in barrens (and turfs) compensated for their lower densities. The NB families Labridae and Serranidae, and the CB families Blenniidae, Cliniidae, Gobiidae, Trypterigiidae and Scorpaenidae, were more abundant in forests. The NB taxa Diplodus spp. and Thalassoma pavo were more abundant in barrens. Our study highlights the importance of using EASV for sampling CB fish, and shows that Cystoseira forests support rich and diversified fish assemblages. This evidence suggests that the ongoing loss of Cystoseira forests may impair coastal fish assemblages and related goods and services to humans, and stresses the need to implement strategies for the successful conservation and/or recovery of marine forests.

Exploring the relationships between marine protected areas and invasive fish in the world's most invaded sea

“…Cryptobenthic species (belonging to Blenniidae, Gobiidae, and Tripterygiidae) were excluded from the analyses as their probability of detection is strongly affected by the percentage coverage and type of algae on the rocky substrate (Thiriet et al. ), which is highly variable across the Mediterranean Sea (Sala et al. ).…”

“…We also assigned fish species to five functional groups based on published data on diet and trophic level and recent references (Guidetti et al 2014, Froese andPauly 2016): planktivores, detrivores, herbivores, low/medium-level predators, and high-level predators. Cryptobenthic species (belonging to Blenniidae, Gobiidae, and Tripterygiidae) were excluded from the analyses as their probability of detection is strongly affected by the percentage coverage and type of algae on the rocky substrate (Thiriet et al 2016), which is highly variable across the Mediterranean Sea .…”

“…The biomass of each herbivore species was plotted as a vector, and the percent cover of barren per site was overlaid as bubble value (with size proportional to the cover of barren). The relationship between barrens and native fishes belonging to the genus Symphodus, which are associated with algal cover (Chemin ee et al 2013, Thiriet et al 2016, was explored using linear regression.…”

Comparing sessile benthos on shallow artificial versus natural hard substrates in the Eastern Mediterranean Sea

“…These species can modify the community structure (Benedetti-Cecchi et al, 2001;Maggi et al, 2009) by providing new habitat and shelter (Boudouresque, 1971;Cheminée et al, 2017) and facilitating the establishment of propagules and larvae Bulleri, et al, 2009). In addition to the increase of habitat complexity, they constitute an important source of primary production, supporting rich vagile biota, such as fish (Thiriet et al, 2016;Cheminée et al, 2017).…”

A quantitative assessment of the diel influence on the cryptobenthic fish assemblage of the shallow Mediterranean infralittoral zone

“…These fishes by definition have an intimate association with the benthos and provide important food web links between the benthos and nekton communities of coral reefs, with their quantitative significance resulting from their exceptional growth rates and mortality (Goatley et al 2016). Most quantitative ecological studies that differentially have targeted microhabitats of cryptobenthic fishes have been performed in coral reef and seagrass meadow ecosystems (Depczynski and Bellwood 2003, Ahmadia et al 2012, Tornabene et al 2013), a few in south temperate reefs (Prochazka 1998, Willis andAnderson 2003), and only a few in northeastern Atlantic (Beldade and Goncalves 2007) and Mediterranean warm temperate reefs (Kovačić et al 2012, Glavičić et al 2016, Thiriet et al 2016. Mainly on the basis of these studies, cryptobenthic reef fishes are now considered to play a globally significant role in temperate and tropical reefs: they are numerically dominant across different cryptic microhabitats, they may serve as a key trophodynamic component between open water and seafloor habitats, and ecologically highly differentiated species assemblages evolve rapidly in different microhabitats and regions and hence may serve as sensitive environmental indicators (Goatley and Brandl 2017).…”