Seasonal movement of the American horseshoe crab \u3cem\u3eLimulus polyphemus\u3c/em\u3e in a semi-enclosed bay on Cape Cod, Massachusetts (USA) as determined by acoustic telemetry

American horseshoe crabs Limulus polyphemus were tracked using acoustic telemetry and traditional tagging in a semi-enclosed bay on Cape Cod (Pleasant Bay), Massachusetts, USA, to determine seasonal movement patterns. Fifty-five actively spawning females were fitted with transmitters in 2008 and 2009 and were tracked using acoustic telemetry from May 2008 through July 2010. Fifteen crabs with transmitters also had archive depth-temperature tags attached. In addition, over 2000 spawning crabs (males and females) were tagged with US Fish and Wildlife (USFWS) button tags over the same period. Ninety-one percent of the crabs with transmitters were detected during this study. In the spring, crabs were primarily located in the northern section of the bay near spawning beaches, whereas in the fall crabs moved towards the deeper portions of the bay, and some may have overwintered in the bay. There was evidence that a majority (58%−71%) of the females with transmitters spawned in two sequential seasons. One archive tag was recovered resulting in a year-long continuous record of depth and temperature data that, when integrated with telemetry data, indicated that the crab overwintered in the bay. The live recapture rate of crabs with USFWS button tags was 11%, with all re-sighted crabs except one observed inside Pleasant Bay. Eighty-three percent of recaptures were found within 2.5km of the tagging location, and 51% were observed at the same beach where they were tagged. This study provides further evidence that horseshoe crabs in Pleasant Bay may be philopatric to this embayment

Growth rates of planktonic and newly settled American lobsters \u3cem\u3eHomarusamericanus\u3c/em\u3e

Growth rates, as estimated by the RNA:DNA ratio, were determined for planktonic postlarvae and for recaptured and wild newly settled benthic stages (fifth and sixth instars) of the American lobster Homarus americanus. The mean growth rate of planktonic postlarvae in 1994 was 0.522 ± 0.247 mg protein d-1. This was significantly higher than planktonic growth rates observed in 1991 (0.449 ± 0.121 mg protein d-1) but not in 1992 (0.460 ± 0.144 mg protein d-1). The percentage of poorly nourished planktonic postlarvae, those with growth rates \u3c0.220 mg protein d-1, ranged from 3 to 13% in 1991, 1992 and 1994 and was similar to that observed in previous years (1988 to 1990). Newly settled lobsters had significantly lower mean growth rates (0.223 ± 0.180 mg protein d-1) than planktonic postlarvae. Recaptured lobsters originating from wild stock had significantly higher growth rates than those originating from laboratory stock (0.281 ± 0.176 vs 0.085 ± 0.078 mg protein d-1, respectively). Laboratory rearing effects (lowered growth rates) appeared to persist even after 1 wk in the field. The differences in the growth rates between planktonic and benthic phase lobsters may be evidence of a trade-off between slow growth due to decreased food ingestion and potential increased vulnerability to predation when actively foraging

Influence of size and delayed settlement on the recapture rate of newly settled American lobsters \u3cem\u3eHomarus americanus\u3c/em\u3e

Postlarval American lobsters Homarus americanus exhibit variation in size at settlement and timing of settlement but it is not known if this variability influences future survival. The ability to track the fate of individual newly settled lobsters has become possible with the advent of micro-wire tags. In this study micro-wire tags were used to identify individual postlarval and fifth instar lobsters that were released into the field and then recaptured 1 wk later. The influence of size at settlement and timing of settlement on subsequent recapture rate were determined. The overall recapture rate for tagged postlarvae and fifth instars was approximately 15%. Larger sized postlarvae and fifth instar lobsters were recaptured significantly more frequently than their smaller counterparts. There was no difference in recapture rate for postlarvae that delayed settlement, as compared to those that settled at the normal time. Differences in recapture rates between large- and small-sized newly settled lobsters might be associated with emigration, behavioral interactions, or differential survival

Effects of Open Marsh Water Management on Numbers of Larval Salt Marsh Mosquitoes

Open marsh water management (OMWM) is a commonly used approach to manage salt marsh mosquitoes than can obviate the need for pesticide application and at the same time, partially restore natural functions of grid-ditched marshes. OMWM includes a variety of hydrologic manipulations, often tailored to the specific conditions on individual marshes, so the overall effectiveness of this approach is difficult to assess. Here, we report the results of controlled field trials to assess the effects of two approaches to OMWM on larval mosquito production at National Wildlife Refuges (NWR). A traditional OMWM approach, using pond construction and radial ditches was used at Edwin B. Forsythe NWR in New Jersey, and a ditch-plugging approach was used at Parker River NWR in Massachusetts. Mosquito larvae were sampled from randomly placed stations on paired treatment and control marshes at each refuge. The proportion of sampling stations that were wet declined after OMWM at the Forsythe site, but not at the Parker River site. The proportion of samples with larvae present and mean larval densities, declined significantly at the treatment sites on both refuges relative to the control marshes. Percentage of control for the 2 yr posttreatment, compared with the 2 yr pretreatment, was \u3e90% at both treatment sites

Influence of coded micro-wire tags on postlarval lobster (Homarus americanus) behavior

The influence of coded micro-wire tags on postlarval lobster behavior was investigated in a simulated cobble environment. Newly settled postlarvae were divided into two treatment groups, tagged and untagged. Seven behavioral categories were identified and the proportion of time spent in each for each treatment was evaluated. We observed no difference in the proportion of time spent in any of the behaviors between tagged and untagged postlarvae. We conclude that the presence of micro-wire tags does not influence behavior of newly settled lobsters

Behavioral interactions of postlarval and fifth instar lobsters (Homarus americanus) in a simulated. Cobble environment

Behavioral interactions among newly settled postlarval and fifth instar lobsters in a simulated cobble environment were quantified. Seven behavioral categories were identified and the proportion of time spent in each was evaluated. Transition matrices for three general behavior categories were evaluated for the postlarval and fifth instar. Postlarval and fifth instar lobsters displayed different behavioral patterns. Postlarvae spent a large proportion of time walking on the sand substrate and excavating shelters, whereas fifth instar lobsters spent the majority of time excavating and sitting in shelters. Agonistic interactions between early benthic stage lobsters were similar to those described for older juvenile and adult lobsters. Dominance hierarchies, burrow invasion and eviction of subdominant individuals were observed in both the postlarval and fifth instar

Power analysis to determine sample size for monitoring vegetation change in salt marsh habitats

Numerous initiatives are underway throughout New England and elsewhere to quantify salt marsh vegetation change, mostly in response to habitat restoration, sea level rise, and nutrient enrichment. To detect temporal changes in vegetation at a marsh or to compare vegetation among different marshes with a degree of statistical certainty an adequate sample size is required. Based on sampling 1 m2 vegetation plots from 11 New England salt marsh data sets, we conducted a power analysis to determine the minimum number of samples that were necessary to detect change between vegetation communities. Statistical power was determined for sample sizes of 5, 10, 15, and 20 vegetation plots at an alpha level of 0.05. Detection of subtle differences between vegetation data sets (e.g., comparing vegetation in the same marsh over two consecutive years) can be accomplished using a sample size of 20 plots with a reasonable probability of detecting a difference when one truly exists. With a lower sample size, and thus lower power, there is an increased probability of not detecting a difference when one exists (e.g., Type II error). However, if investigators expect to detect major changes in vegetation (e.g., such as those between an un-impacted and a highly impacted marsh) then a sample size of 5, 10, or 15 plots may be appropriate while still maintaining adequate power. Due to the relative ease of collecting vegetation data, we suggest a minimum sample size of 20 randomly located 1 m2 plots when developing monitoring designs to detect vegetation community change of salt marshes. The sample size of 20 plots per New England salt marsh is appropriate regardless of marsh size or permanency (permanent or non-permanent) of the plots. © 2007 Springer Science+Business Media, Inc

Influence of settlement time and size on postsettlement growth in the American lobster (Homarus americanus)

We investigated the size and timing of settlement of postlarval (fourth instar) American lobster (Homarus americanus) and the size attained by the end of the first growing season. Mean size and duration of benthic instars (IV-XI) were obtained from a field growth experiment. Lobsters settling in early- and mid-season were larger at each instar and had different growth profiles than late-season settlers. In particular, the rate of growth at the fifth and sixth instar transition was greater for early- and mid-season settlers than for late-season settlers. Postlarvae settling early reached the ninth instar sooner than mid- or late-season settlers. Estimates of size and intermolt duration of each instar for early- and late-season postlarvae were applied to planktonic postlarval data (1988-1995) to estimate growth trajectories during the first year. For all years, postlarvae present early in the season were 30-50% larger (carapace length) and two or three instars further developed than late settlers by the end of the growing season. Estimates of size attained by the end of the 1994 growing season matched field-collected benthic size frequency data for this same year. Although initial carapace length at settlement was important, the timing of settlement was more influential on the size attained by the end of the first growing season