Fecundity and spawning of the Atlantic horseshoe crab, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Marine Ecology 27 (2006): 54-65, doi:10.1111/j.1439-0485.2005.00053.x.This study provided the first comprehensive analysis of Atlantic horseshoe crab (Limulus polyphemus) fecundity. Limulus appear to be determinate spawners, maturing all their eggs for the breeding season before spawning begins. On average, larger females held a larger number of eggs (63,500) than smaller females (14,500). By the end of the breeding season there was an average of 11,600 mature eggs female-1 left undeposited, regardless of female size. Larger females laid a higher percentage of the eggs they contained. Thus they not only contain more eggs, but are more effective at laying them as well. Size of spawning females ranged from about 185-300 mm prosomal width, with by far the highest concentration in the mid-size ranges. Although on an individual basis large females carry and lay the greatest number of eggs, mid-size crabs as a group contributed more to the horseshoe crab population in Pleasant Bay because they were more plentiful (net fecundity was highest for mid-size crabs). These results have implications for the management of this important species, which is harvested for bait, scientific, and biomedical uses. Incorporation of these results into models and other management tools can help predict growth rates, effects of size-selective harvest, reproductive value, and stable stage distribution of populations.This project was partially funded by MIT Sea Grant 8247-5

A Method to Quantitatively Sample Nekton in Salt‐Marsh Ditches and Small Tidal Creeks

We designed a novel gear to quantitatively sample nekton (free-swimming fish and crustaceans) from salt-marsh ditches and small tidal creeks. This gear, the ditch net, is portable and inexpensive to manufacture, and many replicate samples can be simultaneously collected. The ditch net can sample ditches and tidal creeks as narrow as 25 cm and up to 1 m wide (or wider if the design is modified). The net is suspended between four stakes and covers a 1-m length of ditch bottom. To sample nekton, the mesh doors on both ends of the ditch net are raised, thus enclosing a known area of water and trapping nekton within the net. Catch efficiency of the ditch net was comparable with the actual density of fish traversing the ditch as estimated from video data. Recovery efficiency of the gear was high (99%), indicating that fish rarely escape after the net is triggered. A power analysis indicated that a sample size of 20 provided good power (\u3e0.80 at an alpha level of 0.05) to detect temporal or site differences in nekton community composition. © Copyright by the American Fisheries Society 2010

Neuronal regeneration in C. elegans requires subcellular calcium release by ryanodine receptor channels and can be enhanced by optogenetic stimulation

Regulated calcium signals play conserved instructive roles in neuronal repair, but how localized calcium stores are differentially mobilized, or might be directly manipulated, to stimulate regeneration within native contexts is poorly understood. We find here that localized calcium release from the endoplasmic reticulum via ryanodine receptor (RyR) channels is critical in stimulating initial regeneration following traumatic cellular damage in vivo. Using laser axotomy of single neurons in Caenorhabditis elegans, we find that mutation of unc-68/RyR greatly impedes both outgrowth and guidance of the regenerating neuron. Performing extended in vivo calcium imaging, we measure subcellular calcium signals within the immediate vicinity of the regenerating axon end that are sustained for hours following axotomy and completely eliminated within unc-68/RyR mutants. Finally, using a novel optogenetic approach to periodically photo-stimulate the axotomized neuron, we can enhance its regeneration. The enhanced outgrowth depends on both amplitude and temporal pattern of excitation and can be blocked by disruption of UNC-68/RyR. This demonstrates the exciting potential of emerging optogenetic technology to beneficially manipulate cell physiology in the context of neuronal regeneration and indicates a link to the underlying cellular calcium signal. Taken as a whole, our findings define a specific localized calcium signal mediated by RyR channel activity that stimulates regenerative outgrowth, which may be dynamically manipulated for beneficial neurotherapeutic effects