Marco Abbiati

Genetic structuring of the temperate gorgonian coral (Corallium rubrum) across the western Mediterranean Sea revealed by microsatellites and nuclear sequences

In the past decades, anthropogenic disturbance has increased in marine costal habitats, leading to dramatic shifts in population size structure of various marine species. In the temperate region, the gorgonian coral (Corallium rubrum) is one of the major disturbed species, mostly owing to the exploitation of its red skeleton for jewellery purposes. Red coral is a gonocoric species inhabiting subtidal rocky habitats in the Mediterranean and neighbouring Atlantic coasts. In order to investigate the spatial genetic structuring of C. rubrum, five microsatellite markers and the ribosomal internal transcribed spacer 1 (ITS‐1) sequences were analysed in 11 samples from the northwestern Mediterranean Sea. Phylogenetic reconstructions obtained from ITS‐1 sequences analysis showed that samples from Minorca and Sardinia islands were the most divergent while the three samples from the Tuscan archipelago (Argentario, Giannutri and Elba) appeared genetically homogeneous. Both markers revealed a strong structuring over large spatial scales (though to a different extent) with no isolation by distance pattern. Microsatellite‐based FST estimates appeared much smaller than ITS‐based estimates and not significantly correlated, likely due to microsatellite allele size homoplasy typical of these highly polymorphic loci. Our study shows that the absence of clear patterns of genetic structuring over large spatial scales together with strong genetic structuring should be interpreted with caution because such patterns may hide underlying small‐scale genetic structuring. Our results further confirm that effective larval dispersal in red coral is highly restricted in the northwestern Mediterranean Sea, suggesting that an increase of anthropogenic disturbance could aggravate the disappearance of red coral, not only along the Mediterranean coasts but also, and with more intensity, in the main Mediterranean islands.

Phylogeography of the common ragworm Hediste diversicolor (Polychaeta: Nereididae) reveals cryptic diversity and multiple colonization events across its distribution

Previous studies on the common ragworm Hediste diversicolor (Polychaeta: Nereididae) revealed a marked genetic fragmentation across its distribution and the occurrence of sibling taxa in the Baltic Sea. These results suggested that the phylogeographic patterns of H. diversicolor could reflect interactions between cryptic differentiation and multiple colonization events. This study aims to describe the large‐scale genetic structuring of H. diversicolor and to trace the phylogeographic origins of the genetic types described in the Baltic Sea. Samples of H. diversicolor (2 < n < 28) were collected at 16 locations across the NE Atlantic coasts of Europe and Morocco and in the Mediterranean, Black and Caspian Seas and sequenced at two mitochondrial gene fragments (COI and cytb, 345 and 290 bp, respectively). Bayesian analyses revealed deep phylogeographic splits yielding three main clades corresponding to populations (i) from the NE Atlantic coasts (from Germany to Morocco) and from part of the Western Mediterranean, (ii) from the Mediterranean Sea, and (iii) from the Black and Caspian Seas. These clades are further divided in well‐supported subclades including populations from different regions of NE Atlantic and Mediterranean (i.e. Portugal/Morocco, Western Mediterranean, Adriatic Sea). The Baltic Sea comprises three sympatric lineages sharing a common evolutionary history with populations from NE Atlantic, Western Mediterranean and Black/Caspian Seas, respectively. Hence, the current patterns of genetic structuring of H. diversicolor appear as the result of allopatric isolation, multiple colonization events and possible adaptation to local environmental conditions.

Allozyme evidence of genetic differentiation between populations of Hediste diversicolor (Polychaeta: Nereididae) from the Western Mediterranean

The occurrence of genetic differentiation among western Mediterranean Hediste diversicolor (Polychaeta: Nereididae) populations was assessed by allozyme electrophoresis on cellulose acetate. Seventeen loci were analysed in four populations. The level of the genetic variability was markedly low (mean H L range: 0.014–0.034), but comparable to that of other brackish water nereidids. The values of Nei genetic distance index (D) confirm the existence of genetic differentiation between the geographically isolated populations at Venice, Elba, Navicelli and Serchio D range: 0.128–0.356). However, the two samples from Serchio and Navicelli, ~15 km apart, were not genetically different (D=0·00005). The level of genetic differentiation in H. diversicolor populations followed the isolation-by-distance model. Reduced gene flow among H. diversicolor populations may be explained by its limited dispersal capacity and the eco-physiological barriers that occur between different brackish habitats.

On the Biology of Submarine Caves with Sulphur Springs: Appraisal of 13 C/ 12 C Ratios as a Guide to Trophic Relations

Submarine caves with sulphurous springs at Cape Palinuro, Campania, Italy, have a richer fauna than expected from the known oligotrophic nature of the cave habitat. Warm water containing sulphide issues from springs and rises above the cooler ambient sea-water with a sharp thermocline/chemocline between. The warm water then escapes from the caves mixed with cooler sea-water, probably inducing an inflow of ambient sea-water. Bacterial mats, often dominated by large species of attached bacteria resembling Beggiatoa , line the upper parts of the inner caves and act as primary producers, fixing CO 2 by means of the autotrophic enzyme ribulosebisphosphate carboxylase. Many of the animals in the innermost parts of the caves live close to the chemocline or just below, where they would experience fall-out of bacterial organic matter, and some carry filamentous bacteria on their tubes and hard parts. Dominant members of the community include sponges, cnidarians, and tubicolous polychaetes.

Comparing efficacy of different taxonomic resolutions and surrogates in detecting changes in soft bottom assemblages due to coastal defence structures

Sandy shores on the West coast of the North Adriatic Sea are extensively protected by different types of defence structures to prevent coastal erosion. Coastal defence schemes modify the hydrodynamic regime, the sediment structure and composition thus affecting the benthic assemblages. This study examines the effectiveness in detecting changes in soft bottom assemblages caused by coastal defence structures by using different levels of taxonomic resolution, polychaetes and/or bivalves as surrogates and different data transformations. A synoptic analyses of three datasets of subtidal benthic macrofauna used in studies aimed at assessing the impact of breakwaters along the North Adriatic coast has been done. Analyses of similarities and correlations between distance matrices were done using matrices with different levels of taxonomic resolution, and with polychaetes or bivalves data alone. Lentidium mediterraneum was the most abundant species in all datasets. Its abundance was not consistently related to the presence of defence structures. Moreover, distribution patterns of L. mediterraneum were masking the structure of the whole macrofaunal assemblages. Removal of L. mediterraneum from the datasets allowed the detection of changes in benthic assemblages due to coastal defences. Analyses on different levels of taxonomic resolution showed that the level of family maintained sufficient information to detect the impacts of coastal defence structures on benthic assemblages. Moreover, the outcomes depended on the transformation used. Patterns of distribution of bivalves, used as surrogates, showed low correlations with the patterns of the total macrofaunal species assemblages. Patterns of polychaetes, if identified to the species or genus level showed higher correlations with the whole dataset. However, the identification of polychaetes to species and genus level is as costly as the identification of all macrobenthic taxa at family level. This study provided additional evidences that taxonomic sufficiency is a useful tool in environmental monitoring, also in investigations on the impacts of coastal defence structures on subtidal macrofauna. The use of coarser taxonomic level, being time-efficient, would allow improving sampling designs of monitoring programs by increasing replication in space and time and by allowing long term monitoring studies.

Effects of an artificial protection structure on the sandy shore macrofaunal community: the special case of Lido di Dante (Northern Adriatic Sea)

This study analysed the benthic compartment at Lido di Dante (Northern Adriatic Sea, Italy) within the frame of an integrated European project (DELOS), which aimed to identify, describe and quantify the effects of the Low Crested Structures (LCS) on the beach environment of many European coastlines. Both macrofaunal benthic communities and sediment characteristics were analysed in a sandy beach protected by a LCS parallel to the shoreline and laterally connected to land by two groynes, which have been responsible for changes of hydrodynamic patterns. A first survey (2001) focused on three exposure levels with respect to wave action. A higher species richness and a different community structure were found in the sheltered site as compared to the exposed and partially exposed sites. In addition, changes in sediment variables were found according to the exposure levels. A second survey (2002) assessed the combined effects of exposure and depth on both benthic communities and sediment variables. Our results suggest that both exposure and depth interact on measured biotic and abiotic variables. Species richness, community structure and size-classes distribution of the macrofauna, as well as the sediment composition, showed the greatest differences among the shallowest exposed zone and the deepest sheltered ones. On the contrary no difference at all occurred between the shallowest sheltered zone and the deepest exposed ones.

Exploring the causes of spatial variation in an assemblage of benthic invertebrates from a submarine cave with sulphur springs

Abstract In this study we tested possible explanations concerning the spatial distribution of organisms in a submarine cave (Snow Hall, Grotta Azzurra Cave) influenced by sulphur-water springs. The major goals of the study were: (1) to determine whether the effects on other invertebrates due to the removal of sponges were consistent across positions in the Snow Hall; (2) to contrast the performance of two sponges and one cnidarian in different sites within the Azzurra Cave and, in the case of the cnidarian, also in other caves not affected by sulphurous activity, and (3) to examine patterns of colonisation of cleared surfaces at different distances from the entrance of the Snow Hall and at different distances from the boundary between sea and sulphur water. The removal of the massive sponge Geodia cydonium from the vault significantly increased the abundance of other invertebrates and patterns were consistent across positions; in contrast, the removal of the smaller sponge Petrosia ficiformis from the sides of the Snow Hall had little effect. Patterns of growth of Geodia cydonium did not differ among positions, nor among replicated areas within positions, while significant differences among replicated areas within each of the two sides of the Snow Hall occurred for Petrosia ficiformis . Patterns of mortality of the cnidarian Astroides calycularis differed largely among areas within sites, and a trend toward a greater mortality in the inner part of the Snow Hall was evident. Early patterns of colonisation were very patchy, and neither position nor the distance from the boundary affected the abundance of recruits in cleared plots. Several potential processes that might have determined the observed results are discussed. The need for further experiments involving comparisons between the Snow Hall and other caves not influenced by thermal springs is also stressed.

Quantifying spatial genetic structuring in mesophotic populations of the precious coral Corallium rubrum.

While shallow water red coral populations have been overharvested in the past, nowadays, commercial harvesting shifted its pressure on mesophotic organisms. An understanding of red coral population structure, particularly larval dispersal patterns and connectivity among harvested populations is paramount to the viability of the species. In order to determine patterns of genetic spatial structuring of deep water Corallium rubrum populations, for the first time, colonies found between 58–118 m depth within the Tyrrhenian Sea were collected and analyzed. Ten microsatellite loci and two regions of mitochondrial DNA (mtMSH and mtC) were used to quantify patterns of genetic diversity within populations and to define population structuring at spatial scales from tens of metres to hundreds of kilometres. Microsatellites showed heterozygote deficiencies in all populations. Significant levels of genetic differentiation were observed at all investigated spatial scales, suggesting that populations are likely to be isolated. This differentiation may by the results of biological interactions, occurring within a small spatial scale and/or abiotic factors acting at a larger scale. Mitochondrial markers revealed significant genetic structuring at spatial scales greater then 100 km showing the occurrence of a barrier to gene flow between northern and southern Tyrrhenian populations. These findings provide support for the establishment of marine protected areas in the deep sea and off-shore reefs, in order to effectively maintain genetic diversity of mesophotic red coral populations.

Genetic population structure of Neanthes succinea (Polychaeta: Nereididae)

Two samples of Neanthes succinea (Frey & Leuckart 1847) from the Mediterranean Sea were investigated. Twenty-one loci were analysed; seven of them were polymorphic in both populations. The level of heterozygosity was 2.2% and 4.4% in populations from the Tyrrhenian and Adriatic coasts respectively. The value of Neis genetic identity index (1=0.965), together with the mean F(IT) (=0.350), shows that the samples can be considered reproductively isolated populations. F-statistics indicate that ME-1 is the discriminant locus between populations.

Spatial variability in the distribution of sponges and cnidarians in a sublittoral marine cave with sulphur-water springs

The distribution of sponges (Aplysilla sulfurea, Geodia cydonium and Petrosia ficiformis) and cnidarians (Astroides calycularis, Caryophyllia inornata and Leptosammia pruvoti) was investigated in a sublittoral cave with sulphur water springs from May 1993 to February 1994 at Capo Palinuro, on the south-western coast of Italy. Multi-factorial sampling designs were used to address: (1) the distribution and abundance of sponges and cnidarians on the vault and the sides of the cave at different distances from the entrance; (2) the distribution of cnidarians on the vault of the cave with respect to the type of substratum (sponges vs others) and distance from the entrance; and (3) whether abundances were correlated with the distance from the sulphur boundary and how this relationships changed moving from the outer to the inner part of the cave. All the sources of variation included in the study affected to some degree the distribution of organisms but patterns were not consistent among species. The abundance of A. calycularis decreased proceeding from the outer to the inner part of the cave, while the reverse was observed for L. pruvoti. Differences also occurred between the vault and the sides, A. calycularis and G. cydonium being completely absent on the vertical walls. Both A. calycularis and L. pruvoti were less abundant on sponges than on other types of substratum, but patterns changed in relation to the distance from the entrance. The abundance of L. pruvoti decreased close to the sulphur boundary, while the percentage cover of A. calycularis increased, but only at outer positions. Strong variability also occurred at the spatial scale of a few metres (between replicated areas) often overriding other patterns of distribution. Results have been discussed in terms of variability in the physico-chemical environment and in the outcome of interspecific interactions.