No abstract

Although ascidians form a conspicuous part of sessile assemblages in the Caribbean, no specialized inventories have been developed in Venezuela, except for a list of 15 species reported from Margarita Island (1984). Here we present the results of a taxonomic workshop held in the Universidad de Oriente, Boca del Rio, Margarita Island during April 20-25 of 2009, sponsored by the NaGISA-Caribbean Sea program. La Restinga National park was surveyed and we found 29 species belonging to 19 genera and 10 families. The most abundant colonial species were Clavelina oblonga, Aplidium accarense, Polyclinum constellatum, Distaplia bermudensis, Symplegma rubra, S. brakenhielmi, Botrylloides nigrum and Ecteinascidia turbinata. Among the solitary ascidians Phallusia nigra, Ascidia curvata, Microcosmus exasperatus, Styela canopus, Styela sp.1 and Styela sp. 2 were the most abundant. The ascidian diversity in this lagoon is one of the highest for similar habitats in the Caribbean and seven species are new registers for Venezuela (Ascidia curvata, Ecteinascidia styeloides, Aplidium accarense, Distaplia stylifera, Trididemnum orbiculatum, Symplegma rubra, and S. brakenhielmi). One point of concern for the conservation of la Restinga National Park is the presence of possible introduced species, and some management procedures are suggested.

Resource-monopolization theory predicts the adoption of a solitary habit in species using scarce, discrete, and small refuges. Life-history theory suggests that temporarily stable parental dwellings favor extended parental care in species that brood embryos. We tested these two predictions with the symbiotic crab Tunicotheres moseri. This species exhibits abbreviated development and inhabits the atrial chamber of the scarce, structurally simple, long-lived, and relatively small ascidian Phalusia nigra in the Caribbean. These host characteristics should favor a solitary habit and extended parental care (EPC) in T. moseri. As predicted, males and females of T. moseri inhabited ascidians solitarily with greater frequency than expected by chance alone. The male-female association pattern and reverse sexual dimorphism (males < females) additionally suggests a promiscuous "pure-search" mating system in T. moseri. Also in agreement with theoretical considerations, T. moseri displays EPC; in addition to embryos, females naturally retain larval stages, megalopae, and juveniles within their brooding pouches. This is the first record of EPC in a symbiotic crab and the second confirmed record of EPC in a marine brachyuran crab. This study supports predictions central to resource-monopolization and life-history theories.

Charybdis hellerii is one of several poorly known non-indigenous crabs in the Caribbean. In this study we report on the reproductive dynamic of a shallow subtidal population that invaded Isla Margarita, Venezuela, south-eastern Caribbean Sea . 15 years ago and has persisted in the region up to date. Male and female crabs, both large and small, were found year-round at the study site. The size-frequency distribution indicated a lifespan of 2-3 years. Charybdis hellerii reproduces continuously but with very low intensity during the year. Small individuals (,25 mm carapace length) were uncommon and intermittently found during the study period. Sex-ratio varied between 0.1 and 0.65 (mean + SD ¼ of 0.46 + 0.14) and did not differ significantly from 1:1 ratio during most of the year. The size of the smallest brooding female was 36.81 mm carapace width (CW). Behavioural size at first maturity (movable abdomen) in males and females was estimated to be 22.39 mm CW (confidence limits: 18.35-24.72) and 37.43 mm CW (35.55-39.09), respectively. Reproductive output, estimated as the ratio of embryo to female body dry mass, varied between 0.052 and 0.084 (0.07 + 0.008). Also, reproductive output was sizedependent with large females allocating proportionally less resources to egg production than small females. The reproductive schedule here reported for C. hellerii disagrees with the generalized idea of exotic populations 'thriving' in an environment free of natural enemies (e.g. predators, competitors and diseases).

Crabs from the Mithrax-Mithraculus species complex are known for their diversity of lifestyles, habitats, and coloration. This group includes small, colourful, symbiotic species and much larger, reef-dwelling crabs targeted by fishermen. The evolutionary relationships between the species within this complex are not well-defined. Previous studies based upon morphological characters have proposed the separation of this complex into two genera (Mithrax and Mithraculus), but cladistic analyses based upon larval characters do not support this division. A molecular phylogeny of the group may help to resolve this longstanding taxonomic question and shed light on the ecological conditions driving the diversity of these crabs. Using a 550-bp alignment of the 16S rRNA mitochondrial DNA segment we examined the phylogenetic relationships between 8 species within the Mithrax-Mithraculus complex native to the Caribbean. The resulting phylogeny indicates that this complex is paraphyletic, as it includes the genus Microphrys. The analyses revealed a well-supported, monophyletic group containing four species of Mithraculus (M. cinctimanus, M. coryphe, M. sculptus and M. forceps) and supported one pair of sister species from the genus Mithrax (M. caribbaeus and M. spinosissimus). No complete segregation of species, according to genera, was evident, however, from tree topologies. Bayesian-factor analyses revealed strong support for the unconstrained tree instead of alternative trees in which monophyly of the two genera was forced. Thus, the present molecular phylogeny does not support the separation of the species within this complex into the genera Mithrax and Mithraculus. A review of the literature demonstrated considerable phenotypic variation within monophyletic clades in this group.