Investigating the outcomes of a threatened gorgonian in situ transplantation: Survival and microbiome diversity in Paramuricea clavata (Risso, 1827)

International audienc

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

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

Species identification of fish shoals using coupled split-beam and multibeam echosounders and two scuba-diving observational methods

Species identification remains crucial for interpreting acoustic backscatter delivered by active acoustic meth-odologies. The study took place in a Marine Protected Area where highly restricted areas were present such as no take zones. We used an innovative methodology coupling split-beam and multibeam echosounders to detect and classify monospecific fish shoals (i.e. schools or aggregations). Species identifications were realised by under-water visual censuses made by scientific divers. Two experimental protocols, where the divers gave the identi-fications instantaneously thanks to a communication wireframe, were tested: three roving scuba divers locating the shoals or a towed scuba diver directly behind the vessel. Energy responses, 3-D morphological, shape indexes and spatial descriptive variables of multiple independent samples of 4 observed fish species shoals (Atherina sp., Boops boops, Chromis chromis and Spicara maena) were calculated from the acoustic data. According to their behaviour and feeding strategy, significant differences in the acoustic variables were found between species. The combined use of acoustic data from both echosounders significantly improved the fish species classification. They were well discriminated using a Linear Discriminant Analysis (LDA), including for B. boops, C. chromis and S. maena, which were all observed in aggregations. Finally, we used this LDA model to allocate species to un-known shoals monitored by acoustics methods in the studied site, highlighting the interest of our methodology to predict bentho-pelagic and pelagic fish distributions in shallow waters. We suggest that these acoustic methods to discriminate fish species could provide valuable insights for marine management and decision-making

Results of univariate PERMANOVAs comparing fish assemblage structure between forest and barren.

<p>Results of univariate PERMANOVAs comparing fish assemblage structure between forest and barren.</p

Abundance and Diversity of Crypto- and Necto-Benthic Coastal Fish Are Higher in Marine Forests than in Structurally Less Complex Macroalgal Assemblages - Fig 5

<p><b>Fish assemblage structure compared among habitats and regions-times, in terms of (A) presence / absence, (B) densities, and (C) biomasses of all crypto- and necto- benthic fish.</b> Principal coordinates analyses (PCoA) were built using dissimilarities among centroids of each levels of the combined factor habitat X locality-protection (region-time), which were computed using Jaccard dissimilarity for presence / absence data and Bray-Curtis dissimilarity for both square root transformed densities and biomass data. First two axes (MDS 1 and 2) are plotted and percentages of explained variance are indicated within brackets. Labels refer to the 4 locality-protection levels (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.g002" target="_blank">Fig 2</a>). Modified from Thiriet <i>et al</i>. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.ref030" target="_blank">30</a>].</p

Location of the sampling sites.

<p>Green filled arrows indicate forest sites, red filled arrows indicate barren sites, orange filled arrows indicate turf sites. Localities 'L1' and 'L3' were within the Marine Protected Areas (MPA) Scandola Marine Reserve and Norte de Menorca Marine Reserve, respectively. Dotted lines indicate MPA boundaries. Localities 'L2' and 'L4' were both outside MPAs. See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.s004" target="_blank">S2 Table</a> for geographical coordinates of all sites. Public domain source of backgrounds maps: OpenStreetMap contributors, available under ODbL licence at <a href="http://www.openstreetmap.org/" target="_blank">http://www.openstreetmap.org/</a>. Figure modified from Thiriet <i>et al</i>. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.ref030" target="_blank">30</a>].</p

Univariate descriptors of fish assemblage structure compared among habitats and regions-times.

<p>Mean values (+/- SE) of the number of taxa (observed per site), the total density and the total biomass of all fish, only crypto-benthic fish and only necto-benthic fish, for each habitat x locality-protection (region-time) level combination. Modified from Thiriet <i>et al</i>. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.ref030" target="_blank">30</a>].</p

Groups of fish sharing the same density variations across habitats and regions-times.

<p>Mean standardized density (+/-SE) indicates variations of every fish taxon on a common scale even if their respective absolute densities may be different. NBJ: early juveniles of necto-benthic species sampled by EASV, while late juveniles and (sub-)adults were sampled by UVC. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.t003" target="_blank">Table 3</a> for detailed information about body-size and absolute densities of each fish taxon. Modified from Thiriet <i>et al</i>. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.ref030" target="_blank">30</a>].</p

Four habitat types in North-Western Mediterranean subtidal rocky reefs.

<p>(A) forest formed by the locally threatened species <i>Cystoseira brachycarpa</i> var. <i>balearica</i>, and 3 habitat types that may replace lost <i>Cystoseira</i> forests: (B) shrubs formed by Dictyotales and Sphacelariales, (C) turf formed by articulated corallinales, and (D) barren characterized by the absence of erect macrophytes. Upper panel: schematic representations of the habitat structure provided by the dominant macrophytes. Habitat complexity decreases from A to D. Lower panel: pictures taken in Corsica during summer 2011, at 8 m depth. Foregrounds span around 2 m width. Modified from Thiriet <i>et al</i>. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164121#pone.0164121.ref030" target="_blank">30</a>].</p

Results of multivariate PERMANOVAs comparing fish assemblage structure between forest and barren.

<p>Results of multivariate PERMANOVAs comparing fish assemblage structure between forest and barren.</p