Mediterranean populations of the bivalve Arca noae were found to be specifically fouled by the demosponge Crambe crambe. The surface of the shells forms spines which favour settlement of the sponge larvae. The reproductive strategy of this symbiotic sponge contrasts with other Mediterranean sponges, which produce numerous small larvae, while Crambe crambe produces relatively small numbers of quite large larvae containing secondary metabolites. The selective shell fouling of Arca noae suggests that this is behavioural farming of a chemically defended sponge by a bivalve which does not sequester or synthesize de novo metabolites. Some of the observed benefits of this symbiosis are the enhanced survival of the bivalve, and the sponge being able to live in a site free of competitors. This mutual symbiosis is optional for the sponge but essential for the bivalve, since the fouled bivalves can use the secondary metabolites produced by the sponge to deter predators. We tested the effects of sponge epibiosis on predator preferences. Feeding trials were carried out on the starfish Marthasterias glacialis and the snail Hexaplex trunculus in Hornillo Bay, SE Spain. When A. noae fouled by the sponge Crambe crambe were offered to starfish and snails, they survived significantly more than unfouled bivalves. Field studies in the Mar Menor lagoon indicate that the aposymbiotic populations of A. noae have disappeared from this hypersaline lagoon due to the biological invasion by the non-native snail Hexaplex trunculus. This symbiotic relationship was also effective against octopus. Aposymbiotic bivalves were rapidly eaten when presented to octopuses, while fouled bivalves were consistently rejected.

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The gilthead sea bream (Sparus aurata L.) is one of the most important marine fish species produced in southern European countries. Over the last two decades, microsatellites have become a powerful tool for DNA studies of fish populations, making it possible to establish existing genealogical relationships between individuals and to perform reliable estimates of genetic parameters. In the present study, a total of 7959 fish (494 breeders and 7465 fry) were genotyped using two rounds of multiplex reactions with four microsatellite markers each. Offspring were assigned based on the Mendelian exclusion principles, using FAP program. Genealogical information was successfully obtained for more than 83 % of the progeny. Heritability estimates were close to 0.40 in all cases and for all considered traits. The lowest value was for the length at first age (350 ± 6 dph) and the highest for the length at the second age (500 ± 7 dph). The heritabilities for the first and the second weight were similar although somewhat higher for the second age, but not significant. The highest genetic correlations were found between weight and length at the same age and the lowest between weight and length at different ages. Based on the results of this study, it seems reasonable to expect that the implementation of a breeding program for improved growth in this population of gilthead sea bream will offer comparable & Tiago Fernandes