No barrier to emergence of bathyal king crabs on the Antarctic shelf

Cold-water conditions have excluded durophagous (skeleton-breaking) predators from the Antarctic seafloor for millions of years. Rapidly warming seas off the western Antarctic Peninsula (WAP) could now facilitate their return to the continental shelf, with profound consequences for the endemic fauna. Among the likely first arrivals are king crabs (Lithodidae), which were discovered recently on the adjacent continental slope. During the austral summer of 2010-2011, we used underwater imagery to survey a slope-dwelling population of the lithodid Paralomis birsteini off Marguerite Bay, WAP for environmental or trophic impediments to shoreward expansion. The average density was ~4.5 ind·1000m-2 within a depth-range of 1100-1500 m (overall observed depth-range 841–2266 m). Evidence of juveniles, molting, and precopulatory behavior suggested a reproductively viable population on the slope. At the time of the survey, there was no thermal barrier to prevent the lithodids from expanding upward and emerging on the outer shelf (400–500 m depth); however, near-surface temperatures remained too cold for them to survive in shallow, coastal environments (<200 m). Ambient salinity, composition of the substrate, and the depth-distribution of potential predators likewise indicated no barriers to expansion onto the outer shelf. Primary food resources for lithodids—echinoderms and mollusks—were abundant on the upper slope (500–800 m) and outer shelf. At present rates of warming, lithodids should emerge in outer-shelf environments within several decades. As sea temperatures continue to rise, they will likely play an increasingly important trophic role in subtidal communities closer to shore

Duration of the pre-settlement period of the mangrove crab Ucides cordatus (decapoda:Ocypodidae) under laboratory conditions

The goal of the present study was to determine the most appropriate time to release the immatures of Ucides cordatus (Linnaeus) produced in the laboratory into the natural environments. Specifically, the time when the megalopae sought the mangrove sediment to excavate the burrows was determined, as well as the time necessary for their metamorphosis into the first juvenile stage. Results indicated that the megalopae of U. cordatus reared in the laboratory took three to ten days (median = 6) after their molt to excavated burrows in the sediment. The average time for the megalopae to molt into juveniles was 12.6 days (SD = 2.3).<br>O estágio de desenvolvimento em que se encontram as formas jovens de caranguejo produzidas em laboratório, no momento da sua liberação para o ambiente, é um fator chave para o sucesso dos trabalhos de repovoamento. O presente trabalho teve como objetivo determinar a idade mais adequada das formas jovens de U. cordatus, produzidas em laboratório, para sua liberação no ambiente natural. Especificamente, o momento em que as megalopas procuram o sedimento de mangue para escavar tocas foi determinado, assim como o tempo que demoram até realizarem a metamorfose para o primeiro estágio juvenil. O experimento indicou que as megalopas de U. cordatus produzidas em laboratório levam de 3 a 10 dias (mediana = 6) após a metamorfose até escavarem tocas no sedimento. O tempo médio que as megalopas levaram até realizar a metamorfose para o primeiro estágio juvenil foi de 12,6 dias (desvio padrão = 2,33)