ABSTRACT1. Natural populations of Mediterranean commercial sponges have declined substantially over recent decades. 2. The present study explored the distribution of genetic diversity of the endangered bath sponge Spongia lamella along the western Mediterranean and the Portuguese coast.3. Seven microsatellite markers were used to genotype 231 individuals scattered over nine populations. Basic genetic descriptors and population genetic analyses based on F ST test, analyses of the molecular variance (AMOVA), Bayesian clustering, dissimilarity analysis of principal components, and demographic analyses were performed.4. Genetic differentiation between populations was large and highly significant (global F ST = 0.236, P < 0.001). AMOVA and Bayesian analyses showed genetic differentiation among the Atlantic, Balearic, and North Mediterranean areas (F CT = 0.129, P = 0.003).5. Restricted gene flow owing to short-distance larval dispersal and hydrographical barriers may be playing an important role in genetic differentiation.6. Recent bottlenecks were also detected for most populations of this sponge. 7. The high levels of inbreeding, sub-structuring, and modest levels of genetic diversity that characterized populations of S. lamella (mean value of genetic diversity 0.512), may compromise its long-term survival. Only one population, from the Gibraltar Strait, presented high levels of genetic diversity (Ceuta, genetic diversity = 0.657), indicating a hotspot of genetic diversity for this species with special relevance for its conservation.8. Disease outbreaks and overexploitation may be the most important causes of genetic diversity impoverishment of S. lamella.9. Future conservation guidelines should focus on preserving genetic diversity within genetically impoverished populations by limiting exploitation, and increasing population size. Transplanting specimens from areas with high values of genetic diversity to areas with low diversity values or to areas that have recently experienced demographic declines could reverse the local and global recession of this species.

The intra-specific diversity in secondary metabolites can provide crucial information for understanding species ecology and evolution but has received limited attention in marine chemical ecology. The complex nature of diversity is partially responsible for the lack of studies, which often target a narrow number of major compounds. Here, we investigated the intra-specific chemical diversity of the Mediterranean sponge Spongia lamella. The chemical profiles of seven populations spreading over 1200 km in the Western Mediterranean were obtained by a straightforward SPE-HPLC-DAD-ELSD process whereas the identity of compounds was assessed by comparison between HPLC-MS spectra and literature data. Chemical diversity calculated by richness and Shannon indexes differed significantly between sponge populations but not at a larger regional scale. We used factor analysis, analysis of variance, and regression analysis to examine the chemical variability of this sponge at local and regional scales, to establish general patterns of variation in chemical diversity. The abundance of some metabolites varied significantly between sponge populations. Despite these significant differences between populations, we found a clear pattern of increasing chemical dissimilarity with increasing geographic distance. Additional large spatial scale studies on the chemical diversity of marine organisms will validate the universality or exclusivity of this pattern.

The abundance of the bath sponge Spongia agaricina has decreased drastically in recent years and it is now considered an endangered species under Annex 3 of Bern and Barcelona conventions. We describe eight microsatellite markers and present data on their allelic variation and utility as high resolution genetic markers. We analyzed 36 individuals from two populations and found that the number of alleles per locus ranged between 1 and 7. Observed heterozygosity ranged from 0 to 0.72. We found deviations from Hardy-Weinberg expectations for some loci. We exclusively detected null alleles for those loci that deviated from Hardy-Weinberg expectations. Also, distributions of allele frequencies differed significantly between the two populations, making them suitable for population genetic analyses.

While marine organisms such as bivalves, seagrasses and macroalgae are commonly used as biomonitors for the environment pollution assessment, widely distributed sponges received little attention as potential helpful species for monitoring programmes. In this study, the trace element and radionuclide bioaccumulation and retention capacities of some marine sponges were estimated in a species-comparative study using radiotracers technique. Six Mediterranean species were exposed to background dissolved concentrations of (110m)Ag, (241)Am, (109)Cd, (60)Co, (134)Cs, (54)Mn, (75)Se and (65)Zn allowing the assessment of the uptake and depuration kinetics for selected elements. Globally, massive demosponges Agelas oroides, Chondrosia reniformis and Ircinia variabilis displayed higher concentration factor (CF) than the erectile ones (Acanthella acuta, Cymbaxinella damicornis, Cymbaxinella verrucosa) at the end of exposure, suggesting that the morphology is a key factor in the metal bioaccumulation efficiency. Considering this observation, two exceptions were noted: (1) A. acuta reached the highest CF for (110m)Ag and strongly retained the accumulated metal without significant Ag loss when placed in depuration conditions and (2) C. reniformis did not accumulate Se as much as A. oroides and I. variabilis. These results suggest that peculiar metal uptake properties in sponges could be driven by specific metabolites or contrasting biosilification processes between species, respectively. This study demonstrated that sponges could be considered as valuable candidate for biomonitoring metal contamination but also that there is a need to experimentally highlight metal-dependant characteristic among species.

Marine sponges can host in their tissues abundant and diverse bacterial communities. Lack of truly quantitative data on bacterial abundance and dynamics limits our understanding of the organization and functioning of these endobiotic communities. In this technical note, we describe a quantitative polymerase chain reaction approach to quantify the relative abundance of multiple clades of three major sponge-associated bacterial phyla: Chloroflexi, Acidobacteria, and Actinobacteria. To test our approach we used the Mediterranean sponges Spongia lamella and Aplysina aerophoba. We designed five out of the six primer sets used in our study. We tested the new primer sets for specificity and optimized their conditions. Our preliminary data showed that Spongia lamella had larger bacterial abundance than Aplysina aerophoba, except for one clade of Chloroflexi. The two Chloroflexi clades investigated in our study amplified a fraction of the Chloroflexi present in Spongia lamella and most of what is present in Aplysina aerophoba, suggesting a more diverse Chloroflexi population in Spongia lamella than in Aplysina aerophoba. This quantitative technique has a great potential to provide a rapid and robust assessment of sponge microbial target and could contribute to deciphering the complexity of these largely unknown host-symbiont interactions.