Effect of Paramuricea clavata (Risso, 1826) "forest" on the benthic populations of Tremiti Islands Effetto "foresta" di Paramuricea clavata (Risso, 1826) sui popolamenti bentonici delle Isole Tremiti

Mediterranean coralligenous habitats are biogenic reefs characterised by high species diversity and built mainly by encrusting calcareous red algae, growing in dim light conditions. The global climate change and several human activities may threaten species living in these habitats, especially some of those that are considered particularly relevant in structuring and in maintaining the complexity and diversity of the benthic assemblages. Among them, the red gorgonian, Paramuricea clavata (Risso, 1826), which can form dense populations, in the last decades showed worrying mass mortality events. Understand the role of this “animal forests” in the coralligenous assemblages is of fundamental importance in order to design appropriate monitoring programs and conservation policies, especially in the marine protected areas. For this purpose, benthic assemblages were studied in presence and absence of red gorgonians at two sites at the Tremiti islands. Overall, the benthic assemblages significantly differed among sites, nevertheless in both places, clear differences between assemblages associated and not associated to the gorgonian forests were found. In particular, encrusting corallinered algae were significantly more abundant in the gorgonian understories at both sites. This result indicates that the gorgonians may promote the development of calcareous algae, which are the main builders of the coralligenous habitats. Moreover species diversity resulted higher in the assemblages associated to the gorgonians. The present study highlights the role of Paramuricea clavata as a relevant ecosystem engineer in the coralligenous habitats.

Effect of multiple sources of disturbance on rocky benthic assemblages in some localities of Salento, Apulia

The first part of my work consisted in samplings conduced in nine different localities of the salento peninsula and Apulia (Italy): Costa Merlata (BR), Punta Penne (BR), Santa Cesarea terme (LE), Santa Caterina (LE), Torre Inserraglio (LE), Torre Guaceto (BR), Porto Cesareo (LE), Otranto (LE), Isole Tremiti (FG). I collected data of species percentage covering from the infralittoral rocky zone, using squares of 50x50 cm. We considered 3 sites for location and 10 replicates for each site, which has been taken randomly. Then I took other data about the same places, collected in some years, and I combined them together, to do a spatial analysis. So I started from a data set of 1896 samples but I decided not to consider time as a factor because I have reason to think that in this period of time anthropogenic stressors and their effects (if present), didn’t change considerably. The response variable I’ve analysed is the covering percentage of an amount of 243 species (subsequently merged into 32 functional groups), including seaweeds, invertebrates, sediment and rock. 2 After the sampling, I have been spent a period of two months at the Hopkins Marine Station of Stanford University, in Monterey (California,USA), at Fiorenza Micheli's laboratory. I've been carried out statistical analysis on my data set, using the software PRIMER 6. My explorative analysis starts with a nMDS in PRIMER 6, considering the original data matrix without, for the moment, the effect of stressors. What comes out is a good separation between localities and it confirms the result of ANOSIM analysis conduced on the original data matrix. What is possible to ensure is that there is not a separation led by a geographic pattern, but there should be something else that leads the differences. Is clear the presence of at least three groups: one composed by Porto cesareo, Torre Guaceto and Isole tremiti (the only marine protected areas considered in this work); another one by Otranto, and the last one by the rest of little, impacted localities. Inside the localities that include MPA(Marine Protected Areas), is also possible to observe a sort of grouping between protected and controlled areas. What comes out from SIMPER analysis is that the most of the species involved in leading differences between populations are not rare species, like: Cystoseira spp., Mytilus sp. and ECR. Moreover I assigned discrete values (0,1,2) of each stressor to all the sites I considered, in relation to the intensity with which the anthropogenic factor affect the localities. 3 Then I tried to estabilish if there were some significant interactions between stressors: by using Spearman rank correlation and Spearman tables of significance, and taking into account 17 grades of freedom, the outcome shows some significant stressors interactions. Then I built a nMDS considering the stressors as response variable. The result was positive: localities are well separeted by stressors. Consequently I related the matrix with 'localities and species' with the 'localities and stressors' one. Stressors combination explains with a good significance level the variability inside my populations. I tried with all the possible data transformations (none, square root, fourth root, log (X+1), P/A), but the fourth root seemed to be the best one, with the highest level of significativity, meaning that also rare species can influence the result. The challenge will be to characterize better which kind of stressors (including also natural ones), act on the ecosystem; and give them a quantitative and more accurate values, trying to understand how they interact (in an additive or non-additive way).

Effects of Paramuricea clavata (Risso, 1826) (Anthozoa: Plexauridae) forests on settlement of benthic species: an experimental approach

Rationale: Coralligenous habitat is considered the second most important subtidal “hot spot” of species diversity in the Mediterranean Sea after the Posidonia oceanica meadows. It can be defined as a typical Mediterranean biogenic hard bottom, mainly produced by the accumulation of calcareous encrusting algae that, together with other builder organisms, form a multidimensional framework with a high micro-spatial variability. The development of this habitat depends on physical factors (i.e. light, hydrodynamism, nutrients, etc.), but also biologic interactions can play a relevant role in structuring the benthic assemblages. This great environmental heterogeneity allows several different assemblages to coexist in a reduced space. One of the most beautiful is that characterised by the Mediterranean gorgonian Paramuricea clavata (Risso, 1826) that can contribute to above 40% of total biomass of the community and brings significant structural complexity into the coralligenous habitat. In sites moderately exposed to waves and currents, P. clavata can form high-density populations (up to 60 colonies m-2) between 20 – 70 m in depth. Being a suspension feeder, where it forms dense populations, P. clavata plays a significant role in transferring energy from planktonic to benthic system. The effects of the branched colonies of P. clavata could be comparable to those of the forests on land. They can affect the micro scale hydrodynamism and light, promoting or inhibiting the growth of other species. Unfortunately, gorgonians are threatened by several anthropogenic disturbance factors (i.e. fishing, pollution, tourism) and by climatic anomalies, linked to the global changes, that are responsible of thermal stress, development of mucilage and enhanced pathogens activity, leading to mass mortality events in last decades. Till now, the possible effects of gorgonian forest loss are largely unknown. Our goal was to analyse the ecological role of these sea fan forests on the coralligenous benthic assemblages. Experimental setup and main results: The influence of P. clavata in the settlement and recruitment of epibenthic organisms was analysed by a field experiment carried out in two randomly selected places: Tavolara island and Portofino promontory. The experiment consisted in recreate the presence and absence of the gorgonian forest on recruitment panels, arranged in four plots per type (forested and non-forested), interspersed each other, and deployed at the same depth. On every forested panel 3 gorgonian colonies about 20 cm height were grafted with the use of Eppendorf tubes and epoxy resin bicomponent simulating a density of 190 sea fans per m-2. This density corresponds to a mean biomass of 825 g DW m-2,3 which is of the same order of magnitude of the natural high-density populations. After about 4 months, the panels were collected and analysed in laboratory in order to estimate the percent cover of all the species that have colonized the substrata. The gorgonian forest effects were tested by multivariate and univariate permutational analyses of the variance (PERMANOVA). Recruited assemblages largely differed between the two study sites, probably due to different environmental conditions including water quality and turbidity. On overall, the presence of P. clavata reduced the settlement and recruitment of several algae: the shadow caused by the gorgonian might reduce light availability and therefore their growth. This effect might be greater in places where the waters are on average more clear, since at Portofino it is less visible and could be masked by the high turbidity of the water. The same pattern was registered for forams, more abundant outside gorgonian forest, probably linked with algal distribution, shadowing effect or alimentary competition. The last one hypothesis could be valid also for serpulids polychaetes that growth mainly on non-forested panels. An opposite trend, was showed by a species of bryozoan and by an hydroid that is facilitated by the presence of P. clavata, probably because it attenuates irradiance level and hydrodynamism. Species diversity was significantly reduced by the presence of P. clavata forests at both sites. This seems in contrast with what we expected, but the result may be influenced by the large algal component on non-forested panels. The analysis confirmed the presence of differences in the species diversity among plots and between sites respectively due to natural high variability of the coralligenous system and to different local environment conditions. The reduction of species diversity due to the presence of gorgonians appeared related to a worst evenness rather than to less species richness. With our experiment it is demonstrated that the presence of P. clavata forests can significantly alter local coralligenous assemblages patterns, promoting or inhibiting the recruitment of some species, modifying trophic relationships and adding heterogeneity and complexity to the habitat. Moreover, P. clavata could have a stabilising effect on the coralligenous assemblages.

Genetic variability and structuring of deep Corallium rubrum (Linnaeus, 1758) populations

ABSTRACT Given the decline of shallow-water red coral populations resulting from over-exploitation and mass mortality events, deeper populations below 50 metres depth (mesophotic populations) are currently the most harvested; unfortunately, very little is known about their biology and ecology. The persistence of these populations is tightly linked to their adult density, reproductive success, larval dispersal and recruitment. Moreover, for their conservation, it is paramount understand processes such as connectivity within and among populations. Here, for the first time, genetic variability and structuring of Corallium rubrum populations collected in the Tyrrhenian Sea ranging from 58 to 118 metres were analyzed using ten microsatellite loci and two mitochondrial markers (mtMSH and MtC). The aims of the work were 1) to examine patterns of genetic diversity within each geographic area (Elba, Ischia and Praiano) and 2) to define population structuring at different spatial scales (from tens of metres to hundreds of kilometres). Based on microsatellite data set, significant deviations from Hardy-Weinberg equilibrium due to elevated heterozygote deficiencies were detected in all samples, probably related to the presence of null alleles and/or inbreeding, as was previously observed in shallow-water populations. Moreover, significant levels of genetic differentiation were observed at all spatial scale, suggesting a recent isolation of populations. Biological factors which act at small spatial scale and/or abiotic factors at larger scale (e.g. summer gyres or absence of suitable substrata for settlement) could determine this genetic isolation. Using mitochondrial markers, significant differences were found only at wider scale (between Tuscany and Campania regions). These results could be related to the different mutation rate of the molecular makers or to the occurrence of some historical links within regions. A significant isolation by distance pattern was then observed using both data sets, confirming the restricted larval dispersal capability of the species. Therefore, the hypothesis that deeper populations may act as a source of larvae helping recovery of threatened shallow-water populations is not proved. Conservation strategies have to take into account these results, and management plans of deep and currently harvested populations have to be defined at a regional or sub regional level, similarly to shallow-water populations. Nevertheless, further investigations should be needed to understand better the genetic structuring of this species in the mesophotic zone, e.g. extending studies to other Mediterranean deep-water populations.