Utilization Of Marsh And Seagrass Habitats By Early Stages Of Callinectes-aapidus - A Latitudinal Perspective

Seagrass beds and marshes have been identified as important nurseries for the blue crab, Callinectes sapidus. This nursery paradigm is based on blue crab abundance data from trawl, seine and drop-net sampling that has revealed greater abundances in these habitats than in adjacent unvegetated areas. Recently, more quantitative and intensive sampling in seagrass beds and marshes over broad latitudinal scales, combined with manipulative experiments, indicate that the same habitat may vary in utilization on regional scales. Mechanisms accounting for enhanced abundances in these nursery habitats have not been elucidated from a latitudinal perspective. Regional comparisons of blue crab catch data regressed on habitat area were not significant whereas similar comparisons within the Gulf region showed a significant positive relationship of crab harvest with total vegetated area. Thus, the quantity of habitat may be important over small latitudinal scales but other factors could affect population abundances across broad latitudinal distances. Latitudinal differences in habitat use may result from alternate modes of settlement via megalopae or recruitment by juveniles, active or passive habitat selection, post-settlement mortality and food quality and quantity. Tidal regimes and coastal morphology in relation to physical processes may influence the accessibility of important habitats by settling or recruiting individuals and thus be equally important. These factors are reviewed in an attempt to understand regional differences in the patterns of C. sapidus abundance

Utilization Of A Seagrass Meadow And Tidal Marsh Creek By Blue Crabs Callinectes-sapidus II. Spatial And Temporal Patterns Of Molting

Blue crabs were collected weekly from a lower Chesapeake Bay seagrass meadow and adjacent tidal marsh creek over 2 months (July-August 1987) and molt staged. Molting activity, determined from a total of I ,220 crabs, was greater in the grassbed than in the marsh creek, and greater for small crabs and females. The difference between the two habitats in molting activity decreased from the first to the second month of sampling, possibly in response to seasonal decline in seagrass biomass. The proportion of small (\u3c70 mm) females in both habitats was greatest on full moons. There was a lunar rhythm of molting activity by large crabs (2:70 mm), with peak molting activity on fuIl moons. SmaIl crabs demonstrated a similar, but nonsignificant rhythm of molting. We suggest that blue crabs approaching ecdysis aggregate in seagrass meadows, taking advantage of the refuge from predation that this structurally complex habitat affords. Lunar rhythmicity of molting activity may further reduce predation mortality through a dilution effect

Settlement indices for blue crab megalopae in the York River, Virginia: Temporal relationships and statistical efficiency

The efficacy of artificial settlement substrates in quantifying relative rates of settlement of blue crab, Callinectes sapidus, postlarvae (megalopae) was examined. The technique has been widely used to assess settlement at local (Chesapeake Bay) and broad geographic scales (Atlantic and Gulf Coasts). This analysis examined differences in settlement between two configurations of substrates and two depths of deployment, in relation to lunar day, month, year and hours of flood tide occurring at night. Substrates were deployed daily for four years (1989-1992) during the settlement season (July-November) in the York River, Virginia. Settlement did not differ between substrate configurations (flat and cylindrical) deployed at the same location in the water column. Substrates deployed at the bottom of the water column had higher settlement than substrates at the surface, except during the last lunar month sampled (approximately November), when settlement was higher at the surface. There was a semilunar periodicity in settlement with high settlement following the new and full moon phases. Settlement varied annually and with lunar month. Statistical efficiency was achieved with a minimum of three or four replicate substrates. Cylindrical artificial settlement substrates are efficient, reliable and capable of detecting temporal patterns in settlement

Daily, Monthly And Annual Settlement-Patterns By Callinectes-sapidus And Neopanope-sayi Megalopae On Artificial Collectors Deployed In The York River, Virginia - 1985-1988

Daily, monthly and annual settlement of dominant brachyuran megalopae on six replicate artificial settlement substrates (collectors) was examined at one site in the York River, Virginia, from mid-July or early August to early December during 1985-1988. Callinectes sapidus Rathbun, an exported estuarine species, and Neopanope sayi (Smith), a retained estuarine species, were the numerically dominant colonizers of collectors. C. sapidus settlement was highly episodic (l-3-day duration) and significantly associated with the full moon period (lunar day 15-22). The temporal mean of settlement for C. sapidus each year fell within a 12-day period (24 September-6 October) over the 4 years. C. sapidus megalopae settled over a broad range of temperatures (7-3 1°C)extending into the fall months when resident predators become inactive or migrate to deeper water. In contrast, N. sayi settled throughout the lunar month with no significant lunar or tidal periodicity. Settlement by N. sayi occurred over a narrower temperature range (12-31°q than that for C. sapidus, and mean annual settlement for N. sayi occurred earlier within a 12-day period from 9-21 September. A behavioral and physiological mechanism is invoked to explain the observed pattern of C. sapidus settlement. We postulate that synchrony in settlement over a broad temperature range may reduce predation in C. sapidus

Predation on postlarvae and juveniles of the shore crab Carcinus maenas: importance of shelter, size and cannibalism

Settlement and early juvenile stages are considered a bottleneck in the Life history of many epibenthic organisms because of high predation mortality. Nursery habitats may play an important role in mitigating settlement and post-settlement mortality by providing refuge from predation. We examined these relationships in postlarvae and early juvenile stages of the shore crab Carcinus maenas L. in laboratory and field tethering experiments. We studied habitat and size related habitat mortality using postlarvae and young juvenile crabs as prey, and various predators, including juvenile conspecifics, in several habitats common in shallow (0 to 1 m) soft bottom nursery areas on the Swedish west coast. Settling mortality was high in open sand (80 to 90%), whereas a significant habitat refuge was obtained in mussel beds, eelgrass and filamentous green algae, the latter yielding the lowest mortality (13 to 14%). Small differences in structural complexity of ephemeral macroalgae dramatically affected predation mortality of first instar crabs, with a significant refuge obtained only in algae of medium complexity. Predation rate on tethered crabs in the field was high (52 to 67%) only on the smallest crabs (\u3c5 mm carapace width, CW), which obtained a significant refuge in the eelgrass habitat compared to open sand. Mortality for larger crabs (5 to 25 mm CW) was low (\u3c10%) and similar in sand and eelgrass habitats. Our results indicate that predation is an important process that can create a bottleneck for juvenile shore crab populations during settlement and early juvenile stages, mediated by the availability of nursery habitats. Postlarvae obtained refuge from predation in several different habitats, suggesting that the recruitment of juvenile shore crabs will be less affected by temporal and spatial variation of any single habitat type. The strong size refuge for crabs larger than 4 mm CW indicates that key predators are small. We suggest that cannibalistic juveniles, which caused predation rates similar to or higher than all other investigated predators, are dominant predators on settling postlarvae and young juvenile crabs in nursery areas. We further propose that habitat- and size-specific predation by small epibenthic predators are an important selective force in habitat selection by postlarvae and ontogenetic shifts in habitat use by juveniles

Immunotherapy of Crohn's disease.

Although the initiating events of Crohn's disease are unknown, models of experimental colitis have provided new insights in the immunologically mediated pathways of mucosal inflammation. In Crohn's disease activated mucosal T lymphocytes produce proinflammatory cytokines within the mucosal compartment. With this understanding, there has been a shift in past years from the use of unspecific anti-inflammatory agents (corticosteroids, aminosalicylates) to the use of immunomodulatory drugs (azathioprine, methotrexate). Moreover, novel strategies have been designed for specific targets in Crohn's disease, in particular T lymphocytes and cytokines. In an open label study treatment of steroid-refractory Crohn's disease with anti- CD4+ antibodies was well tolerated and showed clinical benefit. However, a sustained depletion of the CD4+ cells precluded further clinical trials. In controlled clinical studies, anti-tumour necrosis factor (TNF-alpha) antibodies induced complete remissions and few side effects were observed. One study suggested efficacy in active Crohn's disease of recombinant interleukin-10. Long term treatment studies will have to answer questions about the indications for use, benefit and toxicity. Altogether, these results hold promise for future management of Crohn's disease, where disease-modifying interventions and strategies that effectively maintain disease remission will play a key role

A Preliminary Study of Predation on Blue Crabs by Three Fish Predators in a Seagrass Bed

This report serves as a preliminary assessment of potential feeding impacts on blue crab prey inhabiting a seagrass bed in the York River by three species of recreationally and commercially important fish (striped bass, croaker, and red drum). We also provide an historic perspective indicating possible changes in relative abundance of these predatory fish between the period 1978-1980 and 1998. In no way do we intend for this report to reflect an accurate, bay-wide assessment of these relationships; the extremely limited temporal and spatial scope of this effort precludes such conclusions. However, this report supports the contention that habitat-specific predation impacts on juvenile crabs inhabiting seagrass beds that serve as nurseries for blue crabs may be important to consider when examining sources of natural crab mortality. Definitive conclusions regarding such impacts await more comprehensive research efforts targeting these relationships at the appropriate bay-wide scale. Finally, it is important to recognize that mortality impacts on blue crab populations stem from a combination of causes. Natural mortality via predation (which is difficult to control) apparently impacts crabs less than 75 mm (3 inches) in carapace width (Moody, 1994; Smith, 1995), whereas those individuals larger than 75 mm likely experience heaviest mortality from commercial and recreational fisheries (which can be controlled through effective management policy)