The importance of predation by horseshoe crabs, Limulus polyphemus, to an intertidal sand flat community

Horseshoe crabs, Limulus polyphemus (L.), are abundant in the lower Delaware Bay during their spring spawning activity. The impact of predation on the benthic community of intertidal flats in the vicinity of breeding beaches was investigated using exclosures and enclosures. In 1978 and 1979, protected sediments contained significantly more individuals, biomass and species per core than unprotected sediments. In 1978, the bivalves Gemma gemma, Mulinia lateralis, and Mya arenaria were significantly more numerous within cages. At that time, unprotected sediments contained very few Mya or Mulinia over 4 mm, suggesting that predators “cropped off” these species as they attained a larger size. Changes in the benthic community were evident when the population of Limulus was at or near maximum. Alternative explanations for the changes seen in the exclusion experiment, including sedimentary modifications and the effects of alternative predators (crabs, fish, and shorebirds), were rejected. Sedimentary modifications were not observed, while the effects of predators besides Limulus were minor

Horseshoe Crab Research in Urban Estuaries: Challenges and Opportunities

Horseshoe crabs rely on estuaries for food resources, places to spawn and for larvae and juveniles to develop and grow. Many of these estuaries are becoming increasingly urbanized and dominated by human activity. An urban estuary is characterized by armored shorelines, high nutrient loads, large fluctuations in algal and bacteria populations, increased levels of pollutants like heavy metals and pesticides, and seasonally low oxygen levels and pH. While urban estuaries are challenging for horseshoe crab survival and to researchers trying to study them, there are also opportunities for involving the public in research and increasing public awareness of the importance of the conservation and survival of horseshoe crabs. Two recent studies in New York and Connecticut have involved citizen scientists to tag and gather valuable data on horseshoe crab population dynamics. It has been discovered that there is very low recruitment of new adults into the two urban estuaries studied and that spawning populations of horseshoe crabs are relatively low when compared to less disturbed more rural estuaries

Prosomal-width-to-weight relationships in American horseshoe crabs (Limulus polyphemus): examining conversion factors used to estimate landings

Horseshoe crabs (Limulus polyphemus) are valued by many stakeholders, including the commercial fishing industry, biomedical companies, and environmental interest groups. We designed a study to test the accuracy of the conversion factors that were used by NOAA Fisheries and state agencies to estimate horseshoe crab landings before mandatory reporting that began in 1998. Our results indicate that the NOAA Fisheries conversion factor consistently overestimates the weight of male horseshoe crabs, particularly those from New England populations. Because of the inaccuracy of this and other conversion factors, states are now mandated to report the number (not biomass) and sex of landed horseshoe crabs. However, accurate estimates of biomass are still necessary for use in prediction models that are being developed to better manage the horseshoe crab fishery. We recommend that managers use the conversion factors presented in this study to convert current landing data from numbers to biomass of harvested horseshoe crabs for future assessments

Assessment of sampling methods to estimate horseshoe crab (Limulus polyphemus L.) egg density in Delaware Bay

Each spring horseshoe crabs (Limulus polyphemus L.) emerge from Delaware Bay to spawn and deposit their eggs on the foreshore of sandy beaches (Shuster and Botton, 1985; Smith et al., 2002a). From mid-May to early June, migratory shorebirds stopover in Delaware Bay and forage heavily on horseshoe crab eggs that have been transported up onto the beach (Botton et al., 1994; Burger et al., 1997; Tsipoura and Burger, 1999). Thus, estimating the quantity of horseshoe crab eggs in Delaware Bay beaches can be useful for monitoring spawning activity and assessing the amount of forage available to migratory shorebirds

Place attachment in deprived neighbourhoods: The impacts of population turnover and social mix

This paper examines the determinants of individual place attachment, focussing in particular on differences between deprived and others neighbourhoods, and on the impacts of population turnover and social mix. It uses a multi-level modelling approach to take account of both individual- and neighbourhood-level determinants. Data are drawn from a large sample government survey, the Citizenship Survey 2005, to which a variety of neighbourhood-level data have been attached. The paper argues that attachment is significantly lower in more deprived neighbourhoods primarily because these areas have weaker social cohesion but that, in other respects, the drivers of attachment are the same. Turnover has modest direct impacts on attachment through its effect on social cohesion. Social mix has very limited impacts on attachment and the effects vary between social groups. In general, higher status or more dominant groups appear less tolerant of social mix

CXCR2 and CXCL4 regulate survival and self-renewal of hematopoietic stem/progenitor cells

The regulation of hematopoietic stem cell (HSC) survival and self-renewal within the bone marrow (BM) niche is not well understood. We therefore investigated global transcriptomic profiling of normal human hematopoietic stem/progenitor cells, revealing that several chemokine ligands (CXCL1-4, CXCL6, CXCL10, CXCL11, CXCL13) were up-regulated in human quiescent CD34+Hoescht-Pyronin Y- and primitive CD34+38-, as compared to proliferating CD34+Hoechst+Pyronin Y+ and CD34+38+ stem/progenitor cells. This suggested that chemokines may play an important role in the homeostasis of HSCs. In human CD34+ hematopoietic cells, knock-down of CXCL4 or pharmacological inhibition of the chemokine receptor CXCR2, significantly decreased cell viability and colony forming cell (CFC) potential. Studies on Cxcr2-/- mice demonstrated enhanced BM and spleen cellularity, with significantly increased numbers of HSC, hematopoietic progenitor cell (HPC)-1, HPC-2 and Lin-Sca-1+c-Kit+ sub-populations. Cxcr2-/- stem/progenitor cells showed reduced self-renewal capacity as measured in serial transplantation assays. Parallel studies on Cxcl4 demonstrated reduced numbers of CFC in primary and secondary assays following knock-down in murine c-Kit+ cells and Cxcl4-/- mice showed a decrease in HSC and reduced self-renewal capacity after secondary transplantation. These data demonstrate that the CXCR2 network and CXCL4 play a role in the maintenance of normal hematopoietic stem/progenitor cell fates, including survival and self-renewal

Megakaryocytes possess a functional intrinsic apoptosis pathway that must be restrained to survive and produce platelets

Deletion of Bak and Bax, the effectors of mitochondrial apoptosis, does not affect platelet production, however, loss of prosurvival Bcl-xL results in megakaryocyte apoptosis and failure of platelet shedding