Impacts of Increasing Temperature on the Metabolism of Confined and Freely Moving American Lobsters (Homarus americanus).

AbstractGulf of Maine waters are warming rapidly, prompting a reevaluation of how commercially important marine species will respond. The goal of this study was to determine the respiratory, cardiac, and locomotory responses of American lobsters (Homarus americanus) to increasing water temperatures and to compare these to similar published studies. First, we measured the heart rate and ventilation rate of 10 lobsters that were confined in a temperature-controlled chamber while exposing them to gradually warming temperatures from 16 to 30 °C over 7 h. Both heart rate and ventilation rate increased along with the temperature up to a break point, with the mean heart rate peaking at 26.5 ± 1.6 °C, while the ventilation rate peaked at 27.4 ± 0.8 °C. In a subset of these trials (n = 5), oxygen consumption was also monitored and peaked at similar temperatures. In a second experiment, both the heart rate and activity of five lobsters were monitored with custom-built dataloggers while they moved freely in a large tank, while the temperature was increased from 18 to 29 °C over 24 h. The heart rate of these lobsters also increased with temperature, but their initial heart rates were lower than we recorded from confined lobsters. Finally, we confirmed that the low heart rates of the freely moving lobsters were due to the methods used by comparing heart rate data from eight lobsters collected using both methods with each individual animal. Thus, while our overall results are consistent with data from previous studies, they also show that the methods used in studies of physiological and behavioral responses to warming temperatures can impact the results obtained.

Biochemical changes throughout early- and middle-stages of embryogenesis in lobsters (Homarus americanus) under different thermal regimes.

Most marine crustacean eggs contain the full complement of nutritional resources required to fuel their growth and development. Given the propensity of many ovigerous (egg-bearing) American lobsters (Homarus americanus) to undergo seasonal inshore-to-offshore migrations, thereby potentially exposing their eggs to varying thermal regimes, the goal of this study was to determine the impact of water temperature on egg quality over their course of development. This was accomplished by documenting changes in total lipids, proteins, and size (volume) of eggs subjected to one of three thermal regimes: inshore, offshore, and constant (16 °C) conditions. Total egg lipids showed a marked decrease over time, while protein levels increased over the same period. Although there were no significant differences in total lipids, proteins, or egg sizes between eggs exposed to inshore and offshore temperatures, they differed from values for eggs exposed to a constant temperature, which also hatched almost three months sooner. This is most likely due to the fact that eggs held at a constant temperature did not experience a period of slow development during the colder months from November to March that are important for synchronizing egg hatch and may be compromised by elevated seawater temperatures.

Influence of natural inshore and offshore thermal regimes on egg development and time of hatch in American lobsters, Homarus americanus.

Some egg-bearing (ovigerous) American lobsters (Homarus americanus) make seasonal inshore-to-offshore movements, subjecting their eggs to different thermal regimes than those of eggs carried by lobsters that do not make these movements. Our goal was to determine if differences in thermal regimes influence the rate of egg development and the subsequent time of hatch. We subjected ovigerous lobsters to typical inshore or offshore water temperatures from September to August in the laboratory (n=8 inshore and 8 offshore, each year) and in the field (n=8 each, inshore and offshore), over 2 successive years. Although the rate of egg development did not differ significantly between treatments in the fall (P∼0.570), eggs exposed to inshore thermal regimes developed faster in the spring (P<0.001). "Inshore" eggs hatched about 30 days earlier (mean=26 June) than "offshore" eggs (mean=27 July), and their time of development from the onset of eyespot to hatch was significantly shorter (inshore=287±11 days vs. offshore: 311.5±7.5 days, P=0.034). Associated growing degree-days (GDD) did not differ significantly between inshore and offshore thermal treatments (P=0.061). However, eggs retained by lobsters exposed to offshore thermal regimes accumulated more GDD in the winter than did eggs carried by inshore lobsters, while eggs exposed to inshore temperatures acquired them more rapidly in the spring. Results suggest that seasonal movements of ovigerous lobsters influence the time and location of hatching, and thus the transport and recruitment of larvae to coastal and offshore locations.

A noninvasive method for in situ determination of mating success in female American lobsters (Homarus americanus).

Despite being one of the most productive fisheries in the Northwest Atlantic, much remains unknown about the natural reproductive dynamics of American lobsters. Recent work in exploited crustacean populations (crabs and lobsters) suggests that there are circumstances where mature females are unable to achieve their full reproductive potential due to sperm limitation. To examine this possibility in different regions of the American lobster fishery, a reliable and noninvasive method was developed for sampling large numbers of female lobsters at sea. This method involves inserting a blunt-tipped needle into the female's seminal receptacle to determine the presence or absence of a sperm plug and to withdraw a sample that can be examined for the presence of sperm. A series of control studies were conducted at the dock and in the laboratory to test the reliability of this technique. These efforts entailed sampling 294 female lobsters to confirm that the presence of a sperm plug was a reliable indicator of sperm within the receptacle and thus, mating. This paper details the methodology and the results obtained from a subset of the total females sampled. Of the 230 female lobsters sampled from George's Bank and Cape Ann, MA (size range = 71-145 mm in carapace length), 90.3% were positive for sperm. Potential explanations for the absence of sperm in some females include: immaturity (lack of physiological maturity), breakdown of the sperm plug after being used to fertilize a clutch of eggs, and lack of mating activity. The surveys indicate that this technique for examining the mating success of female lobsters is a reliable proxy that can be used in the field to document reproductive activity in natural populations.