No Abstract available

In 1999, the Long Island Sound lobster fishery suffered a significant mortality event, following 2 years of smaller, more localized, die-offs. A national research initiative investigating the potential cause(s) of the mortalities was undertaken under the auspices of the Steering Committee for Lobster Disease Research, a subcommittee of the Atlantic States Marine Fisheries Commission's Lobster Management Board. More than 20 research efforts investigated the effects of anthropogenic and environmental stressors and disease on lobsters over a 3-year period. The findings of the collective projects were synthesized and presented publicly in October 2004. Lobsters, at an all-time high abundance, and possibly already infected with parasitic amoebae, Neoparamoeba pemaquidensis, were subjected to sustained, stressful environmental conditions, driven by above average water temperature. Physiologically weakened and unable to fend off disease (paramoebiasis), many lobsters died.

Hemocytes from the American lobster (Homarus americanus) were exposed to several receptor-independent and -dependent putative NADPH oxidase stimulators. This stimulation should result in the generation of cytotoxic reactive oxygen species (ROS) that are used by the cells to control infections by destroying ingested microorganisms. Superoxide (O₂⁻) and hypocholorous acid (HOCl) were quantified by the use of chemiluminescent probes. Only phorbol myristate acetate (PMA), of all the stimuli tested, produced a strong ROS response, which was characterized primarily by the generation of a ~20-fold increase in HOCl. Unstimulated cells produced small O₂⁻ and HOCl peaks. Exposure of the cells to arachidonic acid, zymosan, Bacillus subtilis, conA, laminarin and E. coli lipopolysaccharide failed to stimulate net O₂⁻ generation. However, most of these agents as well as PMA caused the time to peak O₂⁻ production to be significantly reduced. The significance of this apparent kinetic shift (KS) in the O₂⁻ is unknown. The results suggest that, although lobster hemocytes in vitro do not respond to a number of known ROS elicitors, PMA will stimulate a large HOCl response presumably involving the typical pathway of protein kinase C activation, translocation of cytosolic NADPH oxidase components to the site of enzyme assembly and cellular activation.

A significant mortality of the American lobster (Homarus americanus) in western Long Island Sound in 1999 seriously impacted the harvest of this species. Whereas the exact cause or causes of the mortality are still not precisely known, dead and dying lobsters in the initial phase of the die-off were diagnosed with infections with paramoeba, a newly recognized disease condition of lobsters. Because the immune system represents the first line of defense against disease-causing agents and is one of the most sensitive systems to environmental stressors, this study is aimed at the development of new assays to quantify the immune system of lobsters. Flow cytometry allowed the discrimination of different populations of hemocytes based on their relative size and complexity. Also using flow cytometry, natural killer (NK) cell-like activity and its stimulation by human recombinant interleukin 2 (IL-2) are described for the first time in lobsters, as is the expression of TLR2, a pattern recognition receptor, on granular hemocytes. Apoptosis is also measured for the first time in lobster hemocytes in higher proportion in nongranular hemocytes than in granular hemocytes. Also shown is the fact that circulating hemocytes fail to proliferate on stimulation, suggesting that they are terminally differentiated and originate from a separate hematopoietic organ. Overall, several new assays are developed to allow the quantitative evaluation of disease-relevant immune functions for future use in health assessment of the American lobster.

The fixed phagocytes are noncirculating cells in the digestive gland (hepatopancreas) of the American lobster (Homarus americanus) and other decapod crustaceans. They are attached to the outer walls of the terminal hepatic arterioles and lie in the hemal spaces, where they are bathed in blood; they remove foreign particles from the blood as it circulates through the digestive gland. This study has developed and adapted methods for the in vivo assessment of the activity of the fixed phagocytes of lobsters by measuring the uptake of foreign particles from the blood. After fluorescent microspheres were injected into the blood, samples of the digestive gland were excised, arterioles were prepared for microscopy, confocal laser scanning micrographs were collected and microspheres and cells were counted. These methods may be used in larger-scale studies to assess the state of activity of this important part of the immune system of lobsters, and to compare immune activity in lobsters exposed to various environmental and anthropogenic stresses.

Western Long Island Sound (LIS) lobsters collected by trawl surveys, lobstermen and coastal residents during 2000 to 2002 were identified histologically as infected with a parasome-containing amoeba. Primers to conserved SSU rRNA sequences of parasome-containing amoebae and their nonparasome-containing relatives were used to amplify overlapping SSU rRNA fragments of the presumptive parasite from gill, antenna, antennal gland and ventral nerve cord of infected lobsters. The consensus sequence constructed from these fragments had 98% or greater nucleotide sequence identity with SSU rRNA gene sequences of strains of Neoparamoeba pemaquidensis and associated with high confidence in distance- and parsimony-based phylogenetic analyses with strains of Neoparamoeba pemaquidensis and not members of the family Paramoebidae, e.g., Paramoeba eilhardi. Primers designed to SSU rRNA sequences of the lobster amoeba and other paramoebid/vexilliferid amoebae were used in a nested polymerase chain reaction (PCR) protocol to test DNA extracted from formalin-fixed paraffin-embedded tissues of lobsters collected during the 1999 die-off, when this amoeba initially was identified by light and electron microscopy and reported to be a paramoeba of the genera Paramoeba or Neoparamoeba (Mullen et al. 2004). All sequences amplified from 1999 lobsters, with the exception of one, had 98% to 99% identity to each other, and the 1999 PCR product consensus had 98% identity to Neoparamoeba pemaquidensis strains CCAP 1560/4 (AF371969.1) and 1560/5 (AF371970.1). Molecular characterization of the amoeba from western LIS lobsters by direct amplification circumvents a collective inability to culture the organism in vitro, provides insight into the molecular epidemiology of neoparamoebiasis in American lobster, and allows for PCR-based detection of infected lobsters for future research and diagnostics.

Some Neoparamoeba strains are pathogens of fish and invertebrates and were implicated in lobster mortality in Long Island Sound in recent years. To better understand the dynamics of these pathogens and their potential linkages to the mortality of marine animals, the capability to specifically detect and accurately quantify these parasites in the environment and in affected organisms is essential. Molecular markers such as mitochondrial cytochrome b (cob) can be powerful tools. In this study, we isolated cob from N. aestuarina and developed species-specific primers. Sequence analysis showed that this gene was A/T rich. Variable regions were identified and used to develop a species-specific primer set for real-time quantitative PCR (RTQ-PCR). This primer set was demonstrated to be specific (with no cross-reaction to N. pemaquidensis and other protists) and sensitive (with a detection limit of 1 cell/30 mL). Further, the quantitative capability of the RTQ-PCR system was verified by a strong correlation between the threshold cycle number and the logarithmic-transformed cob copy number used in the amplification. Using the established RTQ-PCR assay, we estimated that each N. aestuarina cell contained approximately 707 ± 63 copies of cob. This assay was applied to Lugol-fixed water samples collected from Long Island Sound during August 2002 to September 2003, which showed no detectable N. aestuarina. The cob primer set developed will be useful for future environmental detection of N. aestuarina and provides a basis from which cob gene probes for other Neoparamoeba and Paramoeba species can be developed.

Epizootic shell disease in the American lobster is an important factor affecting lobster fisheries in and around the Long Island Sound. It is a strictly dermal disease, because no correlation was observed between occurrence of epizootic shell disease and hemolymph infection. The culturability of bacteria from lesions was variable and averaged around 1.1%. The lesions contained two to four orders of magnitude more bacteria than healthy carapace surfaces of the same animal. Chitinoclastic bacteria comprised a very small fraction of bacteria present in the lesions, suggesting that their role in epizootic shell disease may be limited. Phylogenetic analysis of bacteria isolated from the lesions showed no typical bacterial pathogens of lobsters such as Aerococcus viridans or Vibrio fluvialis. Moreover, bacteria commonly associated with shell disease of other Crustacea or other forms of shell disease of the American lobster were not found. Two common groups of bacteria were isolated from lesions of all lobsters used in this research: one belonging to a species complex affiliated with the Flavobacteriaceae family and the second belonging to a series of closely related if not identical strains of Pseudoalteromonas gracilis. Bacteria isolated from only a few lobsters were related to Shewanella frigidimarina, Alteromonas arctica, Vibrio lentus, Shewanella fidelia, Pseudoalteromonas tunicata and Vibrio spp. Based on the analyses of culturable isolates, overall microbial communities found in lesions of lobsters from eastern Long Island Sound and Buzzards Bay appear to be similar to each other.

Epizootic shell disease is responsible for great economic losses in the commercial lobster fishing industry in the northeastern United States. Histologic examination of the carapace from affected American lobsters showed the disease is primarily caused by bacteria invading the carapace from the surface of the shell. The carapace itself appears normal in areas that are not eroded and there seems to be an appropriate inflammatory response mounted by the lobsters' hemocytes and tissues to the erosive lesions.

Shell disease is a problem affecting lobsters in eastern Long Island Sound causing disfiguration of the shell, decreasing the lobsters' value, and whereas mild and medium levels of the disease are not lethal, ultimately, severe cases result in mortality. Levels of the molting hormone, ecdysone, were quantitated, using a radioimmunoassay (RIA), in hemolymph of animals exhibiting shell disease. Our results indicate that levels of ecdysone were increased in the hemolymph of shell-diseased lobsters, with a medium level of expression of the disease to 89 ± 32 ng/mL (n = 76), whereas unaffected, presumably healthy ones had 57 ± 16 ng/mL (n = 210). In 7 of 10 months of the year shell-diseased animals had higher ecdysone levels in their hemolymph than unaffected animals. In addition, ecdysone levels were abnormally high, 165 ± 53 ng/mL (n = 5), in shell-diseased ovigerous lobsters, whereas normal unaffected ovigerous ones had low levels of this hormone, 13 ± 4 ng/mL (n = 7). These results indicate that shell disease may induce lobsters to alter the systemic levels of ecdysone, possibly serving as a defensive measure, allowing the animals to ward off the effects of shell disease through induced molting.

Two groups of lobsters were maintained for 31 days at temperatures environmentally realistic for Long Island Sound to investigate the effects of prolonged thermal stress on the physiology of lobsters. One group was held at 16°C, representative of late spring (controls), and the other group at 23°C, representative of late summer/early fall (treatments). In vivo hemolymph pH and samples for serum chemistry analysis were taken before and after temperature exposure. Hemolymph samples were taken before, during and after temperature exposure to investigate effects on hemocyte phagocytic activity assay and total hemocyte counts. Treatment lobsters developed a significant pH acidosis. Other serum index changes included marked hyperchloremia and hyperproteinemia. Phagocytic activity of hemocytes was significantly depressed (~60%) in treatment lobsters after 14 days and remained so until the end of the experiment. Similarly, total hemocyte counts increased strongly in the thermal stress group after 14 days, and remained so until the end of the experiment. Results suggest that late summer temperatures in the bottom waters of Long Island Sound may have profound deleterious effects on the physiology of lobsters. Recent changes in water temperature regimes in the bottom waters of Long Island Sound suggest that it may in the long term become inhospitable for lobster survival.

A flow-through experimental system was designed to simulate habitat conditions encountered by American lobsters (Homarus americanus) during an eutrophication-driven mass mortality in the Long Island Sound during 1999. Seawater for the system was chemically conditioned through gas exchange and the addition of inorganic salts, resulting in simultaneous control of multiple environmental variables including: temperature (±0.5°C), dissolved oxygen (±0.3 mg L⁻¹), sulfide (±1 μM) and ammonium (±3 μM). The system consisted of eight gas-tight, 280-L tanks, each capable of accommodating 22 lobsters, supplied with 0.4 L min⁻¹ animal⁻¹ of conditioned seawater. Outflows were fitted with ozone and ultraviolet sterilization so that lobsters could be exposed to infectious pathogens in varying doses to study effects of habitat on disease resistance, without contaminating the environment. Shelters are supplied in excess and lobsters utilizing them may be monitored to observe behavioral and physiologic responses without opening the tanks. With minimal alterations this system design can be applied to species with diverse structural requirements and to a wide range of ecologic issues including growth, survival and disease resistance under simulated habitat conditions.

The objective of this work is to determine whether increased (but environmentally realistic) temperature, hypoxia, sulfide and ammonium, alone or in combination, can increase susceptibility of lobsters to microbial infection. Lobsters from eastern Long Island Sound (LIS) were injected with Aerococcus viridans var homari, a pathogen that causes a disease known as gaffkemia. Injected animals (and controls) were placed in a flow-through seawater-system with mechanisms for control of temperature, dissolved oxygen, sulfide and ammonium levels as well as disinfection of effluent. Exposure variables included 0.1 mL injections of A. viridans at doses of 1 × 10³ and 1 × 10⁶; dissolved oxygen at 2.5–6.3 mg L⁻¹; sulfide at 0–21 μM; ammonium at 0–80 μM and temperatures at 14.5 and 19.5°C. The criterion for stressor effect was the time at 50% survival in each set of 15 to 22 lobsters per treatment variable. Also, at regular time intervals, lobster hemolymph and hepatopancreas tissues were analyzed for bacterial levels. When lobsters were held under normoxic conditions at 19.5°C, rates of death from gaffkemia were accelerated in the presence of sulfide above 4 μ M. When lobsters were subjected to moderate hypoxia (3 mg L⁻¹), death rates were accelerated regardless of the presence of sulfide. Exposure to ammonium up to a level of 80 μ M had no effect on death rates. Bacterial counts were similar in lobsters regardless of exposure to stressors. The geometric median count in the hemolymph for all lobsters infected beyond 3 days was 7.7 × 10⁸ ml⁻¹ (maximum raw value 1.6 × 10⁹ ml⁻¹) and that for hepatopancreas was 7.7 × 10⁷ g⁻¹ (maximum raw value 1.1 × 10⁹ g⁻¹). Our work showed that, at 19.5°C (a peak, summer, bottom-water temperature routinely found in Long Island Sound), relatively moderate levels of hypoxia as well as sulfide in the absence of hypoxia may accelerate deaths in lobsters that are infected with a pathogenic bacterium. Because eutrophication may lead to hypoxia and increased sulfide levels, policies that reduce eutrophication may improve lobster health.

A lobster die-off significantly reduced the 1999 fall landings in western Long Island Sound. The die-off corresponded in time with the application of pesticides for the control of mosquitoes that carried West Nile virus, a new emerging disease in North America at the time. To determine the possible implication of pesticide application as a direct cause or contributing factor in the die-off, we studied the effects of experimental exposure to resmethrin on the health of lobsters. Lobsters (Homarus americanus) were exposed in 80-L tanks, and the direct toxicity as well as sublethal effects on the immune and endocrine system were determined. The 96-h LC₅₀ for resmethrin on single exposure was greater than 1 μg/L, the highest concentration tested in our experiments, whereas the 14-day LC₅₀ was 0.75 μg/L. Phagocytosis was significantly decreased 5 days after a single exposure to initial water concentrations of 1 and 0.1 μg/L, as well as after weekly exposure to 0.1 μg/L (week 3 and 4) and 0.01 μg/L (week 4). Cell counts varied widely and inconsistently upon exposure to resmethrin. Evaluation of phagocytosis is a sensitive indicator of subtle sublethal effects of resmethrin. Crustacean hyperglycemic hormone (CHH), a potential stress-related hormone in lobsters, was measured in the hemolymph of the chronically-exposed animals. Significant increases in CHH concentrations were observed after 4 wk of exposure to 0.1 μg/L. Whereas it is yet unknown if the concentrations at which toxicity was documented were ever encountered by lobsters in Long Island Sound during the 1999 die off, exposure resulting in the modulation of their immunology and physiology could likely have contributed to increasing lobster susceptibility to infectious diseases.

Methoprene was a constituent of the pesticide cocktail applied to the Western Long Island Sound (WLIS) watershed area during the summer of 1999. Subsequently, the seasonal lobster catches from the WLIS have decreased dramatically. We have been engaged in ongoing studies of the effects of methoprene on larval, juvenile and adult lobsters. Most recently, we found that Stage IV larvae exposed to 50 ppb methoprene experience >90% mortality rate after 3 days. Bioaccumulation studies on adult lobsters showed that methoprene concentrated against the gradient of the surrounding seawater (50 ppb) in hepatopancreas (1.55 ppm), gonad (5.18 ppm), epithelial tissue (6.17 ppm) and, most significantly, the eyestalks (28.83 ppm). Exposure to methoprene altered the expression of the stress proteins and the pattern of ubiquitinylation of cytosolic proteins by Day 1 Stage I larvae and by epithelial tissue of postmolt juvenile lobsters. Postmolt juvenile animals also demonstrated an altered pattern of protein phosphorylation in their epithelial tissues following methoprene exposure, indicating that it may interfere with cell signaling pathways. Increasing concentrations of methoprene were associated with increasing chitoproteins in the microsomal fractions of Day 1 Stage I larvae, suggesting that methoprene may compromise the exocytosis of shell matrix precursors from the epithelial cells. Methoprene did not, however, alter the activity of chitin synthase in these larvae. Although it is likely that a combination of harmful events and exposures led to the reduced lobster population in WLIS, methoprene may have contributed to the decline both by direct toxic effects and by disrupting homeostatic processes.

Acute toxicity and immune response, combined with temperature stress effects, were evaluated in larval and juvenile American lobsters (Homarus americanus) exposed to malathion, resmethrin and methoprene. These pesticides were used to control West Nile virus in New York in 1999, the same year the American lobster population collapsed in western Long Island Sound (LIS). Whereas the suite of pesticides used for mosquito control changed in subsequent years, a field study was also conducted to determine pesticide concentrations in surface waters on Long Island and in LIS after operational applications. The commercial formulations used in 2002 and 2003—Scourge, Anvil and Altosid—contain the active ingredients resmethrin, sumithrin and methoprene, respectively. Concentrations of the synergist piperonyl butoxide (PBO) were also measured as a proxy for pesticide exposure. Acute mortality in Stage I-II larval lobsters demonstrated that they are extremely sensitive to continuous resmethrin exposure. Resmethrin LC50s for larval lobsters determined under flow-through conditions varied from 0.26–0.95 μg L⁻¹ in 48- and 96-h experiments at 16°C, respectively. Increased temperature (24°C) did not significantly alter resmethrin toxicity. Malathion and methoprene were less toxic than resmethrin. The 48-h LC50 for malathion was 3.7 μg L⁻¹ and methoprene showed no toxicity at the highest (10 μg L⁻¹) concentration tested. Phenoloxidase activity was used as a measure of immune response for juvenile lobsters exposed to sublethal pesticide concentrations. In continuous exposures to sublethal doses of resmethrin (0.03 μg L⁻¹) or malathion (1 μg L⁻¹) for 7 d at 16 or 22°C, temperature had a significant effect on phenoloxidase activity (P ≤ 0.006) whereas pesticide exposure did not (P = 0.880). The analytical methods developed using high performance liquid chromatography coupled to time-of-flight mass spectroscopy (LC-TOF-MS) provided high sensitivity with mass detection limits of 0.1–0.3 ng L⁻¹. Pesticide levels were often detected in the ng L⁻¹ range in Long Island surface waters and western LIS (except in open waters), but rarely at concentrations found to be toxic in flow-through laboratory exposures, even immediately after spray events.

In the fall of 1999 the lobster population of western Long Island Sound (WLIS) experienced a massive die-off (LoBue et al. 2003). In fact, the lobster populations in WLIS still have not recovered as of this writing (Benway et al. 2004). Factors suspected of playing roles in this mortality event include water temperature, hypoxia and a neoparameoba. The overall objective of this study is to obtain an understanding of bottom water chemical conditions in WLIS, and their potential influence on benthic community structure and lobster health. Beginning in May 2002, water samples were collected within 5.0 cm and at 1.0 m above the bottom at 12 selected stations in WLIS and analyzed for dissolved NH4, H2S and O2. Grab samples for benthic community determination and sediment-profile images were simultaneously obtained with the water samples at 6 of the 12 stations. The data collected provide an accurate field record of the apparent levels of dissolved oxygen in the sediments of western Long Island Sound, as reflected in apparent redox depths (as recorded in sediment-profile images) and the amount of ammonia, hydrogen sulfide and oxygen present in the bottom waters, over a period critical to the LIS lobster fishery. Levels of dissolved oxygen in actual (within 5 cm) bottom waters of WLIS remain low throughout the summer and fall, despite the increase in dissolved oxygen recorded in the fall in waters 1 m above the bottom. Dissolved sulfide and ammonia concentrations in bottom waters of WLIS increased during spring and fall. These chemicals have been shown by other researchers to be physiologic stressors on lobsters and other marine life that live within benthic environments (Knezovich et al. 1996, Lianso 1991, McMahon & Wilkens 1975, Shumway & Scott 1983, Theede et al. 1969, Vargo & Sastry 1978, Vismann 1990, Wang & Widdows 1991). Given that the lobster die-off of 1999 began in late summer to early fall, it is hypothesized that ammonia and sulfide released from the sediments during that time may have played a role in weakening the lobsters. A comparison of water quality and temperature data from this study with that collected by the CT DEP at certain stations in WLIS during 1999 revealed some similarities and further strengthens the argument that environmental stressors played a role in the lobster mortality event of 1999.

We examined the accumulation of manganese (Mn) in gill tissues of chemically naïve lobsters held in situ at six sites in Long Island Sound (LIS) for up to six weeks to evaluate the possible contribution of eutrophication-driven habitat quality factors to the 1999 mass mortality of American lobsters (Homarus americanus). These western LIS lobster habitats experience seasonal hypoxia, which results in redox-mobilized Mn being transferred to and deposited on the tissues of the lobsters. Manganese accumulated in gill tissue of lobsters throughout the study, but rates were highest at western and southern LIS sites, ranging from 3.4–0.8 μ g/g/d (~16 μg/g initial). The Baden-Eriksson observation that Mn accumulation in Norway lobsters (Nephrops norvegicus) is associated with ecosystem hypoxia is confirmed and extended to H. americanus. It seems likely that, after accounting for molting frequency, certain critical values may be applied to other lobster habitats of the NE US shelf. If a high proportion of lobsters in autumn have gill Mn concentrations exceeding 30 μg/g, then the habitats are likely experiencing some reduced oxygen levels. Manganese concentrations above 100 μg/g suggest exposure to conditions with the potential for lobster mortality should the temperatures of bottom waters become elevated, and gill concentrations above some higher level (perhaps 300 μg/g) indicate the most severe habitat conditions with a strong potential for hypoxia stress.

Lobsters from eastern Long Island Sound (LIS) were exposed to laboratory conditions designed to simulate the habitat in western LIS during the 1999 mass mortality. Elsewhere (Robohm et al. 2005) we have shown that hypoxia and concomitant biogeochemical conditions increase the susceptibility of lobsters to a common pathogen at normal summer temperatures. Here we report that in otherwise favorable conditions, high temperature (24°C) alone had no lethal effect on disease-free eastern LIS lobsters for weeks. However, at this temperature, moderate hypoxia (<2.5 mg/L dissolved oxygen) was lethal to half of a group (n = 20) of lobsters in about 5 days. Addition of sulfide and ammonium to levels reported for LIS (5.5 μM sulfide and 17 μM ammonium) decreased the LT₅₀ to 3.3 days. Higher sulfide concentrations decreased the LT₅₀ significantly. We conclude that lobster survival times are greatly diminished by hypoxia, sulfide and ammonium at high temperature. Because seasonal hypoxia with the production of sulfide and ammonium is an annual occurrence due to cultural eutrophication in western LIS, the results imply that habitat conditions could have been sufficient to account for the observed mortalities in the warm summer of 1999.

Analyses of time series data for bottom or near bottom temperatures for 50 stations distributed throughout Long Island Sound reveal distinctive features of the bottom water temperature history during the lobster mortality event of 1999. These include: temperatures that exceeded 23.5°C in shallow, well-mixed areas; markedly higher temperatures, in general, in those areas with water column depth <20 m; basin-averaged bottom temperatures that were the highest for the decade during the months of July and August; and a rapid increase in bottom temperatures in late August caused by the vertical mixing of warm surface waters during a strong wind event. Results indicate that anomalies in the local surface heat flux made an important contribution to bottom temperature anomalies.

In 1999, the massive die-off of the American lobster (Homarus americanus) populations in western Long Island Sound (LIS) caused complete collapse of the commercial lobster fishery. Reestablishment of a commercial fishery in western LIS requires, in part, knowledge of lobster populations that provide larvae to western LIS. To address this issue, larvae collected from sites within LIS were assigned to egg-bearing female lobsters by comparison of microsatellite allele frequencies. Egg-bearing female lobsters were collected from three sites within LIS and from a site in the Hudson Canyon (Crivello et al. 2005). Tissue samples were collected from female lobsters in spring, summer, and fall of 2001, and lobster larvae were collected in late summer of 2001 and 2002 from five sites within LIS. Differences in microsatellite allele frequencies were used to assign larvae to female lobster populations by a Bayesian and neural network approach. Larval assignments indicated that a high percentage (35% to 45%) of the larvae collected in the eastern or central LIS originated in female lobsters collected in the Hudson Canyon. In contrast, very few larvae collected in western LIS originated from females in western LIS (<30%) and the overall contribution of western female lobsters to the collected larvae was very low. The relative contribution of all sampled female lobsters to collected larvae was greatest from the Hudson Canyon area (35%), followed by central LIS (25%), eastern LIS (20%), western LIS (13%) and the Stratford Shoals area (7%). These results are discussed in context of reestablishment of a lobster commercial fishery in western LIS.

The genetic population structure of the American lobster (Homarus americanus) was examined in populations collected in Long Island Sound (LIS) and the Hudson Canyon of the Northeastern United States with recently developed microsatellite DNA loci probes. Pereiopods, a thoracic appendage used for movement, feeding and defense, were collected from egg-bearing female lobsters from three sites within LIS—an eastern, central and western site—and from sites within the Hudson Canyon. Genomic DNA was isolated from each pereiopod and examined for nine microsatellite loci. Microsatellite allele frequencies, corrected for the presence of null alleles, were used to determine genetic differences between sampled groups. In agreement with earlier studies that used mitochondrial DNA and allozyme markers, there was little genetic differentiation between eastern and central LIS sites and the Hudson Canyon site. However, the genetic differences between western LIS populations and other sampled populations were 10 times higher. These were greater differences than could be attributed to geographical separation. These differences may have arisen as a result of the massive lobster die-off that occurred in 1998/1999 in western LIS.

Existing long-term monitoring data and studies initiated in response to the 1999 lobster die-off in Long Island Sound were examined to determine long-term trends that might clarify causes of the die-off. Data examined included a 28-y time series of commercial lobster-trap catch (harvest and discard) sea-sampling, a 20-y time series of research trawl survey indices, a 13-y time series of bottom water temperature, 3 y of mark-recapture data and 1 y of a research trap survey. Movement information was gathered from the recapture of 2,309 lobsters at large within the Sound for more than 30 days (average days at large = 177). Only 9% of the recaptured lobsters traveled more than 10 km from their release point and 1.3% traveled more than 20 km. Based on the recaptures reported over 3 y, it appears that most lobsters remain resident in the Sound and do not travel extensive distances. The eastern portion of Long Island Sound contained the majority of lobsters that moved greater distances. Abundance of lobsters by size class taken in the trawl survey showed a rise in overall abundance during the 1990s due to a substantial increase in the abundance of pre-recruit and recruit size lobsters (<82 mm CL). Following the die-off, abundance of all size classes declined sharply. The increase and decrease in abundance of the sublegal size classes were negatively correlated with mean summer bottom water temperature. Following the die-off, the percentage of females that were egg-bearing in catches from the western Narrows, the area hardest hit by the die-off, was significantly lower compared with the rest of the Sound. It appears that egg-bearing females were most vulnerable to mortality factors causing the die-off, and/or these factors may have limited their ability to carry eggs. Observed mortality in the commercial catch in the western Sound also correlated with mean summer bottom water temperature over 8 y bridging the die-off (1996–2003). Multiple factors probably played a role in the higher-than-normal mortality recorded in 1999, however, the long-term monitoring data examined here implicate increased bottom water temperatures as a significant contributing factor.

A phased approach was taken for applying previously developed numerical models to address quantitatively whether application of 4 pesticides (i.e., methoprene, malathion, resmethrin and sumithrin) to combat mosquitoes carrying West Nile virus could alone have caused the massive die-off of lobster observed in western Long Island Sound during 1999. Model results show that even with an overly conservative model input assumption (i.e., that the entire mass of pesticides applied in the watershed reached the open waters of Long Island Sound without any attenuation or decay in either the watershed or the Sound) the calculated 24-h average ambient levels of methoprene in the Sound were less than 0.0005 μg/L and well below the lowest reported ecologic endpoint of lobster stress (i.e., 2.8 μg/L stage 2 larvae LC50). Under the assumed conservative model loadings, results for malathion were highest in the East River (maximum 24-h average = 10.3 μg/L) and were much lower in the western Sound area of the lobster die-off. These levels are below the lowest reported ecologic endpoint of lobster stress (i.e., 4.1 μg/L larvae LC50). Model calculations for resmethrin and sumithrin were compared with ecologic endpoints for lobster stress measured for resmethrin. The lowest reported ecologic endpoints reported for resmethrin were 0.01 μg/L and 0.095 μg/L for reduction in adult phagocytosis after weekly exposure and larval 96-h LC50, respectively. Calculated resmethrin levels on a 24-h average basis were as high a 0.225 μg/L, but were significantly lower in western Long Island Sound. For sumithrin, the maximum calculated 24-h average concentration, 0.151, occurred in Eastchester Bay in near surface waters. The calculated levels of neither resmethrin nor sumithrin reached the LC50 value for adult lobsters of >1 μg/L. Malathion, resmethrin and sumithrin were also modeled with a less conservative and more realistic set of assumptions that included decay of the pesticide within the receiving water. Based on a 24-h average malathion concentrations calculated by the model were <1 μg/L in near bottom waters throughout Long Island Sound and probably did not represent a stress to the lobsters. Calculated resmethrin levels throughout near bottom waters of Long Island Sound were <0.005 μg/L and, therefore, did not represent a stress to lobsters. Calculated sumithrin concentrations in near bottom waters were as high as 0.08 μg/L in portions of western Long Island Sound. Assuming that resmethrin endpoints are applicable to sumithrin, it is unlikely that sumithrin could have caused mortality in adult lobsters, however, we cannot fully rule out the possibility that sumithrin may have been a stressor at sublethal levels.

Results for hindcast simulations are presented for the transient concentration distributions in Long Island Sound for the pesticides malathion, resmethrin and sumithrin for the period August 1, 1999 through October 19, 1999. The high resolution of the simulations provide information concerning the detailed spatial patterns in time varying concentration distributions that are dependent on the distribution of pesticide loadings around the perimeter of the basin. Plume concentrations attenuate very rapidly with distance from the coast to below 0.001 μg/L; high concentrations are detected only in confined coastal embayments and regions immediately adjacent to the coast. The decay rates used in the simulations have a strong influence on the concentration fields. Concentrations in plumes for pesticides dispersing into the western Sound from the East River also attenuate rapidly with distance from the East River.