Simulated effects of seagrass loss and restoration on settlement and recruitment of blue crab postlarvae and juveniles in the York River, Chesapeake Bay

Seagrass meadows provide important settlement habitat, food and refuge for postlarvae and young juveniles of the blue crab, Callinectes sapidus. In the York River, Chesapeake Bay, area] cover and distribution of seagrass beds has declined historically. Beds which existed 12-25 km upriver from the mouth disappeared and have not recovered. A model for planktonic postlarval behavior, coupled with a 3-dimensional hydrodynamic transport model for the York River, was used to investigate potential effects of the decline in seagrass abundance, and hypothetical restoration, on blue crab settlement and recruitment to the benthos, both in seagrass and to unvegetated bottom. Effects of habitat loss were investigated in model simulations using two historic patterns of seagrass cover (ca. 1965 and ca. 1996), five patterns with intermediate loss of cover, and three settlement rates. Declines of crab settlement in seagrass

Joint effects of larval dispersal, population regulation, marine reserve design, and exploitation on production and recruitment in the Caribbean spiny lobster

A spatially explicit population-dynamics model for the Caribbean spiny lobster (Panulirus argus) in Exuma Sound Bahamas, was used to investigate the joint effects of marine reserve design and larval dispersal via hydrodynamic currents on an exploited benthic invertebrate. The effects of three hydrodynamic scenarios tone diffusion-only and two advection-diffusion cases), one exploitation level, and 28 reserve configurations (7 sizes x 4 locations) on catch and larval production were simulated. The diffusion-only scenario represented the condition in which settlement did not vary substantially over broad spatial scales; in contrast, the advection-diffusion scenarios represented realistic hydrodynamic patterns and :introduced broad spatial variation. Both advection-diffusion scenarios were based on empirical measurements of near-surface flow in Exuma Sound. Catches were sensitive to interactions between reserve configuration and pattern of larval dispersal. A given reserve configuration led to enhancement or decline in catch, depending on the hydrodynamic scenario, reserve size, and reserve location. Larval production increased linearly with reserve size, when size was expressed as the population fraction initially protected by the reserve, but when reserve size was expressed as the fraction of coastline protected, larval production decreased for some reserve configurations under the two advection-diffusion hydrodynamic scenarios. Use of a simple reserve-design rule (e.g., protect 20% of a coast) would in the latter cases, lead to a false sense of security, thereby endangering-not protecting-exploited stocks. The optimal design of marine reserves therefore requires attention to the joint effects of larval dispersal, reserve location, and reserve size on fishery yield and recruitment

Partitioning loss rates of early juvenile blue crabs from seagrass habitats into mortality and emigration

Determining how post-settlement processes modify patterns of settlement is vital in understanding the spatial and temporal patterns of recruitment variability of species with open populations. Generally, either single components of post-settlement loss (mortality or emigration) are examined at a time, or else the total loss is examined without discrimination of mortality and emigration components. The role of mortality in the loss of early juvenile blue crabs, Callinectes sapidus, has been addressed in a few studies; however, the relative contribution of emigration has received little attention. We conducted mark-recapture experiments to examine the relative contribution of mortality and emigration to total loss rates of early juvenile blue crabs from seagrass habitats. Loss was partitioned into emigration and mortality components using a modified version of Jackson\u27s (1939) square-within-a-square method. The field experiments assessed the effects of two size classes of early instars (J1-J2, J3-J5), two densities of juveniles (low: 16 m(-2), high: 64 m(-2)), and time of day (day, night) on loss rates. In general, total loss rates of experimental juveniles and colonization rates by unmarked juveniles were extremely high (range = 10-57 crabs m(-2)/6 h and 17-51 crabs m(-2)/6 h for loss and colonization, respectively). Total loss rates were higher at night than during the day, suggesting that juveniles (or potentially their predators) exhibit increased nocturnal activity. While colonization rates did not differ by time of day, J3-J5 juveniles demonstrated higher rates of colonization than J1-J2 crabs. Overall, there was high variability in both mortality and emigration, particularly for emigration. Average probabilities of mortality across all treatment combinations ranged from 0.25-0.67/6 h, while probabilities of emigration ranged from 0.29-0.72/6 h. Although mean mortality rates were greater than emigration rates in most treatments, the proportion of experimental trials in which crab loss from seagrass due to mortality was greater than losses due to emigration was not significantly different from 50%. Thus, mortality and emigration appear to contribute equally to juvenile loss in seagrass habitats. The difference in magnitude (absolute amount of loss) between mean emigration and mean mortality varied between size classes, such that differences between emigration and mortality were relatively small for J1-J2 crabs, but much larger for J3-J5 crabs. Further, mortality rates were density-dependent for J3-J5 juvenile stages but not for J1-J2 crabs, whereas emigration was inversely density-dependent among J3-J5 stages but not for J1-J2 instars. The co-dependency of mortality and emigration suggests that the loss term (emigration or mortality) which has the relatively stronger contribution to total loss may dictate the patterns of loss under different conditions. For older juveniles (J3-J5), emigration may only have a large impact on juvenile loss where densities are low, since the contribution of mortality appears to be much greater than emigration at high densities. The size-specific pattern of density-dependent mortality supports the notion of an ontogenetic habitat shift by early juvenile blue crabs from seagrass to unvegetated habitats, since larger individuals may experience increased mortality at high densities within seagrass beds. Qualitative comparisons between this study and a concurrent study of planktonic emigration of J1-J5 blue crabs (Blackmon and Eggleston, 2001) suggests that benthic emigration among J1-J2 blue crabs was greater than planktonic emigration; for J3-J5 stages benthic and planktonic emigration were nearly equal. This study demonstrates the potentially large role of emigration in recruitment processes and patterns of early juvenile blue crabs, and illustrates how juvenile size, juvenile density, and time of day can affect mortality and emigration rates as well as total loss and colonization. The components of population loss can have very different impacts at the population level on multiple spatial scales, which highlights the need to separate population loss into emigration and mortality

Spatial dynamics and value of a marine protected area and corridor for the blue crab spawning stock in Chesapeake Bay

In lower Chesapeake Bay, a 172,235 ha marine protected area and corridor (MPAC) was recently established to protect blue crab adult females either en route to or at the spawning grounds during the reproductive period. The MPAC was justified due to a recent substantial decline in spawning stock biomass. It was situated in waters deeper than 10 in throughout the lower bay due to the high abundances of adult females in this zone, and it was an expansion of a historical spawning sanctuary near the bay mouth to include northward extensions (upper and lower MPACs). We examined spatial dynamics of the blue crab spawning stock in relation to the MPAC through analyses of trawl Survey data (abundances of adult females and egg-bearing females from 1989-1997 and 1995-1997, respectively) partitioned by water depth, time (month and year), and spatial zone (upper MPAC, lower MPAC, MPAC Historical Sanctuary) during the reproductive period (June-September). Adult female abundance peaked at 6-14 m water depths. Consequently, nearly half of all adult females in the lower bay were deeper than 10 in, and therefore protected by the MPAC during the reproductive period, whereas the historical sanctuary protected about 1/3 that of the MPAC. All MPAC segments were utilized by adult females at different times of the spawning season, without consistent use of any particular segment. In contrast, abundance patterns of egg-bearing females were consistent and did not differ by developmental stage of the eggs. Peak abundances of egg-bearing females shifted from the northern to southern portions of the MPAC as the spawning season progressed. Differences in distribution of adult females and egg-bearing females demonstrated the importance of the expanded MPAC to the conservation of the spawning stock, which requires an extensive area to cover seasonal and yearly alterations in distribution. The expanded MPAC is much more effective than the historical sanctuary at protecting a consistent fraction of the blue crab spawning stock over the full spawning season and every year. Both the lower MPAC and historical sanctuary contained high abundances of adult females and egg-bearing females, and these segments therefore potentially function as corridors and spawning grounds. In contrast, whereas adult females were equally abundant in all MPAC segments, egg-bearing females were rarely common in the upper MPAC segment. Hence, the upper MPAC serves primarily as a corridor for females migrating to spawn or hatch their egg masses in the lower MPAC and historical sanctuary. The MPAC protects a major fraction of the spawning stock and spawning grounds both seasonally and yearly, and it encompasses a dispersal corridor for adult females in the deeper waters of Chesapeake Bay. The MPAC therefore serves as a foundation for long-term protection of the blue crab spawning stock, and should be utilized concurrently with complementary management measures to conserve the blue crab population in Chesapeake Bay. Furthermore, the MPAC for the blue crab in Chesapeake Bay may serve as a model system for investigating the value of marine protected areas for exploited marine populations with ontogenetically disjunct stages in the life cycle that encompass diverse habitats

Potential bottom-up control of blue crab distribution at various spatial scales

Top-down (i.e., predation), bottom-up (i.e., food availability), and physical factors may influence blue crab (Callinectes sapidus) distribution. To assess the role of bottom-up and physical process in blue crab distributions, we concurrently measured density of the blue crab (Callinectes sapidus), density of its principal prey, the Baltic clam (Macoma balthica), and physical characteristics in mud and sand habitats spanning various spatial scales (1-10 km and 10-50 km) in the York River, Chesapeake Bay. Clam and crab densities were intermediate in mud, low in downriver sand, and high in upriver sand. Clam and crab densities were not correlated in mud. whereas in sand, they were significantly and positively correlated at both the local scale (I km) and at the broadest spatial scale (10-50 km). Crab density also correlated with salinity at the broad spatial scale. After removing the effect of salinity, crab density remained significantly correlated with clam density. Using a hydrodynamic model for the York River, potential transport of clams from downriver coves was primarily to upriver habitats, but transport of crabs was mainly to downriver seagrass habitats. At the local scale, upriver zones where crab and clams were abundant, crab density was highly correlated (r(2) = 0.93) with clam density, but not with salinity, suggesting that the distribution of blue crabs was driven mostly by their primary food item-clams. The collective findings are consistent with the hypotheses that crab density is driven by both food availability and salinity at broad spatial scales (10-50 km), whereas food availability is a primary control at smaller spatial scales (1-10 km). Bottom-up control of upper trophic levels may be distinctive; thus far, in marine and freshwater systems, bottom-up control has not been demonstrated to filter from basal to upper trophic levels. Furthermore, unvegetated habitats where food, such as clams, is abundant may be important in the population dynamics of the blue crab, even in systems where seagrass beds are common

Connectivity and resilience of coral reef metapopulations in marine protected areas : matching empirical efforts to predictive needs

© 2009 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Coral Reefs 28 (2009): 327-337, doi:10.1007/s00338-009-0466-z.Design and decision-making for marine protected areas (MPAs) on coral reefs require prediction of MPA effects with population models. Modeling of MPAs has shown how the persistence of metapopulations in systems of MPAs depends on the size and spacing of MPAs, and levels of fishing outside the MPAs. However, the pattern of demographic connectivity produced by larval dispersal is a key uncertainty in those modeling studies. The information required to assess population persistence is a dispersal matrix containing the fraction of larvae traveling to each location from each location, not just the current number of larvae exchanged among locations. Recent metapopulation modeling research with hypothetical dispersal matrices has shown how the spatial scale of dispersal, degree of advection versus diffusion, total larval output, and temporal and spatial variability in dispersal influence population persistence. Recent empirical studies using population genetics, parentage analysis, and geochemical and artificial marks in calcified structures have improved the understanding of dispersal. However, many such studies report current self-recruitment (locally produced settlement/settlement from elsewhere), which is not as directly useful as local retention (locally produced settlement/total locally released), which is a component of the dispersal matrix. Modeling of biophysical circulation with larval particle tracking can provide the required elements of dispersal matrices and assess their sensitivity to flows and larval behavior, but it requires more assumptions than direct empirical methods. To make rapid progress in understanding the scales and patterns of connectivity, greater communication between empiricists and population modelers will be needed. Empiricists need to focus more on identifying the characteristics of the dispersal matrix, while population modelers need to track and assimilate evolving empirical results.Work by CB Paris was supported by the National Science Foundation grant NSF-OCE 0550732. Work by M-A Coffroth and SR Thorrold was supported by the National Science Foundation grant NSF-OCE 0424688. Work by TL Shearer was supported by an International Cooperative Biodiversity Group grant R21 TW006662-01 from the Fogarty International Center at the National Institutes of Health

Antiinflammatory Therapy with Canakinumab for Atherosclerotic Disease

Background: Experimental and clinical data suggest that reducing inflammation without affecting lipid levels may reduce the risk of cardiovascular disease. Yet, the inflammatory hypothesis of atherothrombosis has remained unproved. Methods: We conducted a randomized, double-blind trial of canakinumab, a therapeutic monoclonal antibody targeting interleukin-1β, involving 10,061 patients with previous myocardial infarction and a high-sensitivity C-reactive protein level of 2 mg or more per liter. The trial compared three doses of canakinumab (50 mg, 150 mg, and 300 mg, administered subcutaneously every 3 months) with placebo. The primary efficacy end point was nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death. RESULTS: At 48 months, the median reduction from baseline in the high-sensitivity C-reactive protein level was 26 percentage points greater in the group that received the 50-mg dose of canakinumab, 37 percentage points greater in the 150-mg group, and 41 percentage points greater in the 300-mg group than in the placebo group. Canakinumab did not reduce lipid levels from baseline. At a median follow-up of 3.7 years, the incidence rate for the primary end point was 4.50 events per 100 person-years in the placebo group, 4.11 events per 100 person-years in the 50-mg group, 3.86 events per 100 person-years in the 150-mg group, and 3.90 events per 100 person-years in the 300-mg group. The hazard ratios as compared with placebo were as follows: in the 50-mg group, 0.93 (95% confidence interval [CI], 0.80 to 1.07; P = 0.30); in the 150-mg group, 0.85 (95% CI, 0.74 to 0.98; P = 0.021); and in the 300-mg group, 0.86 (95% CI, 0.75 to 0.99; P = 0.031). The 150-mg dose, but not the other doses, met the prespecified multiplicity-adjusted threshold for statistical significance for the primary end point and the secondary end point that additionally included hospitalization for unstable angina that led to urgent revascularization (hazard ratio vs. placebo, 0.83; 95% CI, 0.73 to 0.95; P = 0.005). Canakinumab was associated with a higher incidence of fatal infection than was placebo. There was no significant difference in all-cause mortality (hazard ratio for all canakinumab doses vs. placebo, 0.94; 95% CI, 0.83 to 1.06; P = 0.31). Conclusions: Antiinflammatory therapy targeting the interleukin-1β innate immunity pathway with canakinumab at a dose of 150 mg every 3 months led to a significantly lower rate of recurrent cardiovascular events than placebo, independent of lipid-level lowering. (Funded by Novartis; CANTOS ClinicalTrials.gov number, NCT01327846.

Concurrent decline of the spawning stock, recruitment, larval abundance, and size of the blue crab Callinectes sapidus in Chesapeake Bay

Conservation of exploited marine populations requires knowledge of interannual variation in the characteristics of and relationships between the spawning stock and recruitment, which determine Population resilience and persistence. We examined relationships between spawning stock abundance, postlarval recruitment, larval abundance, and female size of the blue crab in Chesapeake Bay, both within the Spawning grounds over a 13 yr interval (1988 to 2000) and within lower-bay tributaries over 20 yr (1979 to 1998). Our findings establish that there has been a concurrent, persistent and substantial reduction in the spawning stock, recruitment, larval abundance, and female size, Specifically, in 1992 to 2000: (1) spawning stock abundance declined by 81 female size by 8%, and spawning stock biomass by 84%; (2) mean size at maturity (L) diminished by 9%; (3) larval abundance and postlarval recruitment were lower by approximately 1 order of magnitude compared with earlier years. The decrease in these variables was rapid, occurring over 1 to 2 yr, and therefore indicative of a phase shift in the Spawning stock and recruitment, rather than a progressive diminution, We propose that the initial descent resulted from poor recruitment in 1991, despite high spawning stock and larval abundance, and that the poor recruitment in 1991, in concert with high fishing and natural mortality, subsequently led to a diminished spawning stock in 1992 and thereafter, We further suggest that the Spawning stock, larval abundance, and recruitment are unlikely to rebound to former high levels without significant reductions in fishing and natural mortality along with enhanced environmental conditions conducive to successful recruitment. The key consequences of a diminished spawning stock and recruitment are a heightened probability of recruitment failure and reduced resilience to demographic and environmental stochasticity. In addition, the relationships between spawning stock abundance (SSA) and larval abundance, SSA and postlarval recruitment, and SSA and female size were positive and significant. The demonstration of a concurrent decrease and significant association between spawning stock abundance and recruitment, larval abundance and female size is unique for the blue crab and for marine invertebrates in general, and indicates an urgent need to conserve the Spawning stock for long-term sustainable exploitation and population persistence