Thermosensitivity of the lobster, Homarus americanus, as determined by cardiac assay

8 Pages·2000·3.7 MB·

by  S H Jury

Reference: Biol. Bull. 199: 2?7-264. (December 2000)
Homarus
Thermosensitivity of the Lobster,
americanus, as Determined by Cardiac Assay
STEVEN H. JURY* AND WINSOR H. WATSON 111
Zoology Department and Centerfor Marine Biology, University ofNew Hampshire.
Durham, New Hampshire 03824
Abstract. It is generally accepted that crustaceans detect, Introduction
and respond to, changes in water temperature, yet few
studies have directly addressed their thermosensitivity. In Temperature is one of the most important and pervasive
this investigation a cardiac assay was used as an indicator environmental influences on the American lobster, Homa-
that lobsters (Hoinarus americantts) sensed a change in rus americanus (Cobb and Phillips, 1980; Aiken and
temperature. The typical cardiac response of lobsters to a Waddy, 1986; Factor. 1995). It is generally accepted that
1-min application=ofa thermal stimulus, either warmer (;; = (loMccoLmeoetsoeryanadctiWviiltdyerin.t1hi9s58s:peRceiyesnoilsdtsemapnedraCtausrteerldienp,en1d9e7n9t;
19) or colder (n 17) than the holding temperature of 15
Haakonsen and Anoruo. 1994) and that it carries out sea-
C, consisted ofa short bradycardia (39.5 8.0 s) followed
sonal inshore to offshore migrations to gain the develop-
by a prolonged tachycardia (188.2 10.7 s). Lobsters mental benefitsofwarmercoastal temperatures in the spring
exposed to a range ofrates oftemperature change (0.7, 1.4, and summer(Cooperand Uzmann, 1971; Pezzack and Dug-
2.6, 5.0 C/min) responded in a dose-dependent manner, gan, 1986; Karnofsky el al.. 1989; Haakonsen and Anoruo,
with fewer lobsters responding at slower rates of tempera- 1994; Factor, 1995; Watson elal, 1999). Laboratory studies
ture change. The locationoftemperature receptorscould not have demonstrated that H. americanus has a thermal pref-
be determined, but lesioning ofthe cardioregulatory nerves erence ofabout 16 C (Reynolds and Casterlin. 1979; Cros-
eliminated the cardiac response. Although the absolute de- sin et al., 1998). and it has been proposed that behavioral
tection threshold is not known, it is conservatively esti- thermoregulation may allow members of the species to
mated that lobsters can detect temperature changes of occupy thermal niches which maximize their metabolic or
greater than 1 C, and probably as small as 0.15 C. A behavioral efficiency. The behavioral responses of lobsters
comparison of winter and summer lobsters, both held at 15 to thermal gradients suggest they have some mechanism to
C for more than 4 weeks, revealed that although their sense temperature so that they may effectively respond to
responses to temperature changes were similar, winter lob- the thermal properties of their environment.
sters (n - 18) had a significantly lower baseline heart rate Thermosensitivity in lobsters may be mediatedby distinct
(34.8 4.4 bpm) and a shorter duration cardiac response thermoreceptors or thermosensitive neurons as in some
(174 s) than summer lobsters (n = 18: 49.9 5.0 bpm, and other invertebrates (Prosser and Nelson, 1981; Mori and
320 s respectively). This suggests that some temperature- Ohshima, 1995). Although behavioral studies strongly sug-
independent seasonal modulation ofcardiac activity may be gest that H. americanus can sense temperature (Reynolds
and Casterlin. 1979; Crossin etal., 1998), to our knowledge
occurring.
only one study has addressed how neurons respond to
changes in temperature in this species. In that study, firing
ofcells associated with thoracic ganglia connectives gener-
ally showed no spontaneous activity below 14 C, but most
became spontaneously active above this temperature. Inter-
R*Perceesievnetda2d2drMeassr:chCa1r9i9b9b;eaancceMpatreidne14RAeusgeuasrtch20C0e0n.ter. Tequesta, FL estingly, these cells "cycle reversibly from silent to contin-
33469. E-mail: [email protected] uously active to bursting and back as the temperature is
257
258 S. H. JURY AND W. H. WATSON III
increased and decreased" (Konishi and Kravitz, 1978). converter (model #2991) to record heart rate (Dyer and
Other than these cells, which may or may not play a role in Uglow, 1970). Because the impedance recording technique
thermally guided behaviors, we know little about the loca- can be sensitive to temperature, the method was verified by
tion ofputative thermoreceptors, or the mechanisms used to using a second pair of electrodes and a Grass model 7D
detect temperature, in lobsters and most other crustaceans polygraph to simultaneously monitor the electrical activity
(Dorai Raj and Murray. 1962; Ache, 1982). associated with lobster heart contractions (see Watson and
In situations where the precise receptors have not been Wyse, 1978; Watson, 1980). External temperature was re-
identified, or are not readily accessible to electrophysiolog- corded using a small (3 mm X 1 mm) thermistor (C & B
ical investigation, cardiac assays are a valuable tool for Sciences/iWorx, Inc., Dover, NH) placed on the dorsal
preliminary investigations of sensory capabilities (Larimer, carapace. The thermistor was calibrated weekly over the
1964; Offutt, 1970; Florey and Kriebel. 1974; Dufort. range of temperatures used in the experiments. The time
1997). For example, many crustaceans exhibit a drop in constant ofthe thermistorwas 2.0 s (time to achieve 67% of
heart rate in response to novel stimuli (Maynard, 1960; the final response). The absolute resolution ofthe thermistor
Larimer, 1964; McMahon and Wilkens, 1972; DeWachter was 0.15 C, but it could accurately detect changes in
and McMahon, 1996). This cardiac response has been used temperature as small as 0.01 C. However, because of
to measure the ability of H. americanus to detect sound turbulent mixing within the recording chamber, the slight
(Offutt, 1970) and salinity (Dufort, 1997). Although a num- time delay due to the time constant of the thermistor (Fig.
ber of studies have addressed the effect of temperature on 1 ). and the unknown location of temperature-sensitive neu-
decapod heart rates at time scales ranging from hours to ral elements relative to the location ofthe thermistor, it was
days (Ahsanullah and Newell. 1971; Florey and Kriebel, not possible to assess the thermal detection threshold with
1974; DeFur and Magnum, 1979; DeWachter and McMa- great accuracy. All temperatures presented are those re-
hon. 1996; DeWachter and Wilkens. 1996; Hokkanen and corded by the externally located thermistorabove the dorsal
Demont. 1997). few have characterized the initial response carapace. These should be interpreted conservatively, in the
(i.e., <5 min.) to brief changes in water temperature. The context of the methods used and the unknown location of
present study used a cardiac assay to demonstrate that the sensory receptors.
American lobsters are consistently capable of sensing in-
creases or decreases in temperature that are greater than 1 Experimental chamber
C. The typical response elicited by both cold and warm
stimuli was a brief slowing of the heart rate, followed by After insertion of the electrodes, lobsters were placed in
prolonged cardioacceleration. Winter and summer lobsters a recording chamber consisting of an 18-cm-diameter PVC
responded somewhat differently to thermal stimuli, suggest- pipe covered on the top and bottom by perforated plates
ing some type of seasonal temperature-independent modu- through which seawater (temperature 15 1 C) continu-
lation of their responsiveness to thermal stimuli. ously flowed (Fig. 1). This arrangement kept lobsters rela-
tively immobile and ensured that changes in temperature
Materials and Methods within the recording chamber were rapid and relatively
Animals homogeneous. The chamberwas placed in an acrylic plastic
insert (30 X 30 X 30 cm) that was immersed in a temper-
mm
Adult (82-92 carapace length), intermolt lobsters ature-controlled 120-1 aquarium (the ambient bath). Ambi-
were held at 15 1 C (salinity 30 1 ppt) for more than ent seawater was continuously pumped (2 1/min) from the
4 weeks prior to use, and experiments were initiated at this aquarium through the recording chamber, into the insert,
temperature. All lobsters were captured from coastal New and back to the aquarium. Thermal stimuli were delivered
Hampshire waters, and experiments were conducted at the by switching the source of seawater from the ambient bath
University of New Hampshire, Durham, New Hampshire. to the stimulus bath. This switching was accomplished by
Experiments were carried out in both summer and winter turning a stopcock and was considered the initiation of the
under ambient light conditions. In the summer, the thermo=- stimulus (see arrows in Fig. 2). The stimulus bath was filled
sensitivity of 18 lobsters was determined (cold stimuli, n from the ambient bath to minimize novel chamber chemo-
9; warm stimuli, n = 9); in the winter, lobsters kept at the sensory cues (Fig. 1) and brought to the appropriate exper-
same temperature ( 15 C) as summer lobsters were used in imental temperature using aquarium heaters or cooling
identical experiments (cold stimuli, n = 8; warm stimuli, ;; coils. The recordingchamberwascovered with black plastic
= 10). to minimize visual disturbance, and the lobster was left in
the experimental apparatus overnight before an experiment.
Recording oftemperature and heart aciivit\ Lobsters are much more sensitive to stimuli if allowed to
Small wire electrodes were inserted through the dorsal recover from electrode insertion and become accustomed to
carapace above the heart and used with a UFI impedance the recording chamber (Larimer. 1964; Dufort, 1997).
THF.RMOSHNS1TIVITY OF LOBSTERS 259
A. orcold) were tested on the following day. A 25% change in
Heat/Cool Stopcock Animal heart rate bradycardia (decrease) or tachycardia (in-
Chamber Heart crease) was used as an indicator that lobsters sensed a
i Electrodes change in water temperature (Offutt, 1970; Dufort. 1997).
All records were digitized using a MacLab system (C & B
Sciences/iWorx. Inc.) and were analyzed to determine the
following: (1) delay to a response: (2) duration of brady-
cardia, tachycardia, or both: (3) heart rate (bpm) during
bradycardia: and (4) heart rate (bpm) during tachycardia. In
Stimulus ^V Ambient Balh addition, thermosensitivity thresholds were estimated from
Bath Pumps
the water temperature measured above the dorsal carapace
c. at the time of the initial cardiac response. Controls were
conducted before any thermal stimuli were applied; the
same protocol described above was followed, but without
changing the temperature in the stimulus bath.
Localization ofpunitive temperature receptors
In an attempt to localize regions with putative tempera-
=
ture receptors, lobsters missing antennae (n 4) or missing
=
antennae and antennules (n 4) were tested for a response
to a temperature change of +2.5 C/min. Antennae or
23456
50 100 150 200 250 -1 1 antennules were removed bilaterally at their base, the
Time (s) Time (s) wounds were sealed with wax to prevent blood loss, and the
lobsters were allowed more than 24 h to recover.
Figure 1. Experimental apparatus used to record lobster cardiac re-
sponses to changes in temperature. (A) Seawater (I? C> flows continu-
ously from the ambient bath into the animal chamber through perforated
plates located above and below the lobster(direction offlow indicatedby
darkarrows). Heartrate isrecordedbefore,during,andafterexposure toa
temperature stimulus. Switching the stopcock changes the source ofsea-
waterfrom the ambient bathtoseawaterfrom the stimulus bath (direction
offlow indicatedby white arrows). A thermistoron thedorsal carapace is
used to monitor temperature during each trial. (B) Rates of temperature
change in a typical experiment in response to I min stimuli (turned on al
time = andoffatarrow)of 0.7. 1.4.2.6.and5.0 C warmerorcolder
tehxapnostehde atombaiesntteptecmhpaenragteurien.t(eCm)peTriamtuerecoonfstant2ofCthe(dtohtetremdisltinoer).whTehne -20-10 10 20Ti3m0e40 50 60 70 80 90
estimated time to achieve 67% offinal temperature is 2.0 s. (s)
The following day, after basal heart rate was measured
for at least 30 min, each animal was exposed for 1 min to a
warm or cold stimulus that changed the temperature in the
recording chamber at a rate of 0.7 C/min. This was
followed by stimuli delivered at targeted rates of 1.5
C/min, 2.5 C/min. and 5.0 C/min for 1 min. Tem- 12
perature was allowed to return to ambient (Fig. 2) between Time (s)
each treatment. Treatments were separated by at least 30
min. The temperature in the recording chamber was moni- TheFitgoupretr2a.ce sThyopiwcsalthecartydpiiaccalrersepsopnosnesetotoaach+a1n.g4e Cin/mtienmpsetriamtuulrues.:(tAh)e
tored with the dorsally located thermistor, and the actual lower trace is a plot ofthe temperature change during the 60-s trial. The
mean rates achieved were 0.72 0.04. 1.37 0.06. 2.61 dark closed arrow shows when the stimulus flow was turned on. and the
0.10. and 4.95 0.16 C/min. Thus, the average maximum whiteopenarrowshowswhenitwasturnedoff.(B)Anenlargementofthe
warm stimuli after 60 s were 15.7. 16.4. 17.6. and 20.0 C, hiahliahtedareafrom(A),showing thetimecourseofthebradycardiaand
and the maximum cold stimuli were 14.3. 13.6. 12.4. and associatedtemperaturechange.Notethattherapidresponsemaybearesult
ofthecombinationofthelocationofthethermistorrelative tothe location
10.0 C. oftheunknown temperature sensitivereceptorsandthe slightdelaydueto
Which stimulus (warm orcold) wastested on the firstday thetimeconstantofthethermistor.Therewasnoresponsetocontrolswhen
was assigned randomly, and the other set of stimuli (warm the flow was switched but the temperature was not changed.
260 S. H, JURY AND W. H. WATSON III
To determine whether changes in cardiac activity were 0.50
mediated by the cardioregulatory nerves, responses to ther-
mal stimuli were measured before and afternerve lesions (n
= 5). Changes in heart rate were initially recorded in
response to thermal stimuli of +1.5 C/min and -1.5 C/
min. Then the cardioregulatory nerves were cut. and lob-
sters were allowed at least 2 days to recover. Finally their
cardiac responses were measured again in response to the
same stimuli that were applied before the lesions. Lesions
were made as described in Guirguis and Wilkens (1995). A
small (3-cnr) rectangular piece of dorsal carapace just
above the heart was removed, and superficial cuts were
made with fine scissors through the connective tissue along
the border of the opening. The shell was then replaced and
fastened in place with tape. Sham-operated control animals
=
(/; 4) were treated in the same mannerexcept that no cuts
were made in the connective tissue.
Statistical analysis
Throughout the text, variation is presented as standard
error ofthe mean (i.e.. mean SEM). A P value of <0.05
was considered to be significant for all statistical tests.
Results
Typical response to a change in temperature
The typical cardiac response to both warm and cold 1.0 2.0 3.0 4.0 5.0
stimuli consisted of a short bradycardia (39.5 8.0 s). Rate of Change (C/min)
followed by a significantly (paired t test) longertachycardia
(w1e8r8e.2simil1a0r.7ins;reFisgp.on2s).eItnogbeontehrawl,archman(nge=s i1n9)heaarntdaccotlidvit(ny TheFigtuhrerem3a.l dReetescptoinosnesthtroesthhoelrdm,alorstitmhueliaamtoduinftferoefnttreamtpeseroaftcuhraengceh.an(gAe)
- 17) stimuli. Although the intensity and duration of car- required to elicit a cardiac response, was similareven when hot and cold
diac responses were similar for all temperatures tested stimuli were applied at different rates. (B) When thermal stimuli were
(ANOVA, P > 0.05). some lobsters did not respond to appliedatslowratesofchange,thedelaytorespondwaslonger,especially
slowerrates ofchange (0.7 and 1.4 C/min). whereas almost tinhetrhmealcassteimouflicoaplpdlisetidmualti.fas(tC)anAdlstlhoowugrhatelsobosftecrhsanrgees,posnodemdeasinmiimlaalrslyditdo
all lobsters responded to the maximum rate of change (5.0 not respond at all to slow rates ofchange, while all animals responded to
C/min; Fig. 3). There was no cardiac response in control hisiher rates ol chansic.
trials (H = 36). where temperature was not changed but
ambient water was pumped through the chamber from the
stimulus bath (Fig. 4). to 0.79 C. There were no significant differences (un-
paired t test) between the sexes in the temperature change
Sensitivity to warm and cult/ stimuli at initial response; when lobsters responded, they exhib-
Lobsters were extremely sensitive to both warm and ited comparable thresholds, at all measured rates of
cold stimuli (Fig. 3). For example, when subjected to a change (Fig. 3. Kruskal-Wallis test). The average tem-
+2.6 C/min stimulus, lobsters responded after just perature-detection threshold, for all trials in which ani-
3.8 0.5 s, when the temperature in the chamber had mals responded, was 0.15 0.03 C. This is considered
changed by only 0.09 0.04 C. Lobsters exposed to the to be only an estimate because of the inherent time
-2.6 C/min stimulus responded after a drop of only constant and resolution of the thermistor, the How of
0.13 0.09 C. and the latency to respond (4.6 1.8 s) water in the chamber, and the location of the thermistor
was not significantly different (paired t test) than during relative to the still unknown location of the receptors
a warm stimulus (Fig. 3). mediating the response. Nonetheless, this assay demon-
Temperature change measured al the initiation of a strates that lobsters are sensitive to very small changes in
cardiac response by individual lobsters ranged from 0.01 temperature.
THERMOSENSITIVITY OF LOBSTERS 261
A.
D
response latency
S
bradycardia
D
tachycardia
0)
50 100 150 200 250 300 350
Time
(s)
80 -
262 S. H. JURY AND W. H. WATSON III
and 0.6 C (Ehn and Tichy. 19%). Studies ofthermorecep- cardiovascular function of lobsters (Mercaldo-Allen and
tion in aquatic species are fewer, but are consistent with our Thurberg. 1987: McMahon. 1995: Whiteley et <//., 1995;
findings. For example. Forward (1990) found that crab DeWachter and McMahon. 1996). brief decreases in heart
larvae (Rhithropanopeus Imrrinii and Neopanope sayi) as- rate following acute temperature changes are also common
cend or descend in a water column in response to absolute in lobsters and many crustaceans (McMahon and Wilkens.
temperature changes of0.29-0.49 C, as long as the rate of 1972; McMahon. 1995; DeWachter and McMahon. 1996).
change is fast enough (0.06-0.24 C/min, depending on It is unlikely that these acute responses are due to a direct
larval stage and species). Thus, the American lobster is impact of temperature on the heart for the following rea-
probably not unusual in its ability todetect small changes in sons: ( 1 ) lobsters with cut cardioregulatory nerves do not
temperature, although the extent to which this level of change their heart rate in response to acute temperature
thermosensitivity exists in other crustaceans remains to be changes; (2) QM values for heart rates of intact lobsters
,
investigated. generally range from 1.5 to 2.5 (Mercaldo-Allen and Thur-
Although several behavioral studies indicate that crusta- berg. 1987; Schreiber et /., 1998), but excised lobster
ceans are quite sensitive to changes in temperature, little is hearts are not very sensitive to changes in temperature over
known about thermosensitivity in this large group of pri- the range of 12 to 19 C, and they generally have lower QM1
marily aquatic invertebrates. A study of the thermal sensi- values than intact lobsters overthe same range (Schreiberet
tivity of the dactyl receptors of Cancer imtewuirhts, C. i//.. 1998; Jury, unpublished data); (3) the initiation of a
antlwnvi. and Panidinis iiiterntptus strongly suggests that cardiac response is immediate and robust, and the response
they possess a thermal sensory system capable of integrat- extends well beyond the duration ofa temperature stimulus
ing temperature information for use in thermally cued be- (Fig. 2): and (4) the response is similar (i.e., bradycardia
havior (Cook, 1984). However, the actual thermoreceptors followed by tachycardia) whether warm or cool stimuli are
have not been identified in these species. In lobsters, a applied (Fig. 3). Therefore, although temperature can have
number ofneurons change their rate offiring in response to a long-term, direct influence on heart rate and cause release
shifts in temperature, but it is not clear if these cells are of modulatory substances from the pericardia! organs of
actually serving the function ofthermoreceptors. Forexam- lobsters (Kuramoto and Tani, 1994), all current data
ple, intracellular recordings from cells of the thoracic gan- strongly suggest that in lobsters some type of thermosensi-
glia connectives ofH. americanus show firing patterns that tive mechanism senses a change in temperature, and this
reversibly change from silent to continuously active to leads to a change in heart rate through activation of inhib-
bursting over the range of 10-17 "C (Konishi and Kravitz, itory or excitatory cardioregulatory nerves.
1978). This is within the normal ecological range for this Lobsters do not appear to have seasonal differences in
species, and while it is unknown what physiological or their ability lo detect temperature. However, winter lobsters
motor output results from this neuronal property, the corre- have lower basal heart rates and respond to temperature
spondence to the behaviorally determined preferred temper- somewhat differently than summer lobsters. These differ-
ature ( 16 "C; Crossin ettil.. 1998) forthis species is intrigu- ences suggest the presence of some type of seasonal mod-
ing. In the spiny lobster, Puniilinix japonicns, ligamental ulation of the lobster cardiovascular system, similar to the
nerves innervating the pericardia! organ have also been actions of thyroid hormones in frogs (Miller and Mizell.
reported to increase their firing in response to cold stimu- 1972). Biogenic amines, such as serotonin and octopamine.
lation (Kuramoto and Tani. 1994). Once again, temperature have been shown to increase cardiac output. Seasonal
stimuli were shown to have a direct physiological effect in changes in circulating levels of these, or similar, neuro-
viim. but it is unknown how. orif. thiseffect isrelatedtothe modulators might increase basal heart rates in the summer
existence of thermoreceptors or behavioral thermoregula- or alter how the heart responds to input from cardioregula-
tion. Ablation studies indicate that lobsters missing anten- tory nerves (Fingerman et a/.. 1994; Wood et ai. 1995;
nae or antennules respond to temperature just like intact Weiger, 1997). This type ofseasonal modulation is likely to
animals, suggesting that while these appendages may or influence responses to a variety of stimuli, in addition to
may not contain thermosensitive elements, they are not temperature. The precise mechanisms underlying these sea-
necessary in order for lobsters to exhibit a cardiac response sonal changes in the cardiovascular system ot crustaceans
to temperature. Thus, while localisation of receptors and remain to be resolved. A recent study of blue crabs, Culli-
mechanisms of thermoreception are beginning to be eluci- ncctcx scipitliis, which documented seasonal differences in
dated in some invertebrates (Mori and Ohshima. 1995; their behavioral responses to injected biogenic amines and
Komatsu el ai. 1996: McCleskey, 1997), it remains unclear proctolin (Wood et <//., 1995), suggests that seasonal vari-
exactly where and how crustaceans are sensing temperature ability in theexpressionofreceptors may be the mechanism.
(Ache. 1982). The rate of temperature change may be an important
Although gradual changes in temperature have a pro- variable in detection of thermal shifts in the environment.
found, well-documented inlHicnce on the metabolism and The lobsters in this study responded to rates as low as 0.7
THERMOSENSITIVITY OF LOBSTERS 263
C/min. and there was no statistically significant difference ofenvironmental stimuli (Offutt. 1970: Florey and Kriebel.
between the thermal-detection thresholds obtained over the 1974); thus, the sensitivity of lobsters to temperature may
range of rates tested. We did not attempt to determine the have been enhanced in ourexperiments. In contrast, lobsters
slowest rate ofchange they were able to detect, but we did that are not given time to recover from handling have high
find that some lobsters did not respond at all to the slower basal heart rates and often do not exhibit typical responses
rates of change used in our experiments (0.7-1.4 ~C/min). to environmental stimuli. Thus, although lobsters in their
Florey and Kriebel ( 1974) found that in Cancerspecies, the natural habitat can probably sense very small changes in
rate of change must be greater than 0.33 C/min to "avoid water temperature, these thermal stimuli may not always
hysteresis effects." This is interpreted as meaning that acute lead to the types ofcardiac responses observed in quiescent
bradycardias or tachycardias were seen at rates of change laboratory animals. This hypothesis is being tested by re-
faster than this, but only long-term changes in heart rate cording from freely moving lobsters subjected to acute
were observed at slower rates. Crab larvae (R. hurrisii) changes in temperature as they move spontaneously through
descend in the water column when the temperature is ele- thermal gradients.
vated at rates ranging from 0.07 to 0.24 C/min. and they
ascend when the temperature decreases at rates of 0.06 to Acknowledgments
0.1 C/min. However, "the average absolute amounts of
temperature change needed to evoke a response was inde- We thank the following people for helping to make this
pendent of the rate of change at rates above threshold and project possible: HeatherJury. Chris Dufort. Jim Newcomb.
ranged from 0.29 to 0.49 C" (Forward. 1990). Seasonal Paul Bartell, Christina Rockel. and Glen Crossin. Special
changes in water temperature in some lobster habitats (e.g., thanks to Dan O'Grady for conducting the cardioregulatory
coastal New Hampshire) can range from to 25 C. but nerve lesion experiments: Hunt Howell at the UNH Coastal
rates ofchange may be too slow to directly stimulate puta- Marine Lab forsupplying animals: Rich Langan at the UNH
tive lobster thermoreceptors. However, tidal changes or Jackson Estuarine Lab for housing animals; Dan Reves for
thermoclines may change fast enough to be detected. We drawings; and Cliff Bredneberg and Ashish More ofC & B
have measured rates oftemperature change as high as 0.33 Sciences. Inc.. for technical assistance. This work was sup-
C/min in the Great Bay estuary, although average rates are ported by USDA (Hatch) and NOAA (Sea Grant) grants to
about 0.004 C/min (based upon hourly Licor CTD read- WHW and by UNH Graduate student enhancement and
ings, R. Langan, University of New Hampshire. Durham, Center for Marine Biology Grants to SHJ. This study was
unpublished data). Some studies have also found lobsters to part ofthe doctoral dissertation research ofSHJ. This manu-
aggregate at thermoclines (Ennis. 1984: Estrella and Mor- script was greatly improved by the comments of three
rissey. 1997). Movement of a lobster (or an appendage) anonymous reviewers. This is contribution #355 ot the
within a thermally heterogeneous habitat may increase the UNH Center for Marine Biology Series.
realized rate of change to the point at which temperatures
fall within the detection range. In addition, movement of Literature Cited
water (i.e.. a current) past a stationary or moving lobster
could also increase the rate of change if the water was Ache,B.\V. 1982. Chemoreception and thermoreception.Chapter8. pp.
390-391. in D. Bliss, ed.. The Biolo^ "t Crustacea. Neurohioloxy:
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tions, the combination of mobility and sensitivity to small Ahsanullah.M.,and R.C.Newell. 1971. Factorsaffectingtheheartrate
temperature changes may provide lobsters with sufficient oftheshorecrabCarcinusinaenas(L). Coiti[>. Biochcm. Pliysiol. 39A:
information to behaviorally thermoregulate in their natural 277-287.
habitat in the same manner observed in small thermal gra- Aiken. D. E., and S. L. \Vaddy. 198f>. Environmental influence on
recruitment ofthe American lobster. Hoinarimamericanus: aperspec-
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selection (Reynolds and Casterlin, 1979: Crossin et ul.. thermo- and hygroreceptors.Annw. Rev. Entomol. 30: 273-295.
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assay is useful for determining an animal's ability to sense California. Santa Barbara. 140 pp.
small changes in temperature, it is not known whether Cooper, R. A., and J. R. Uzmann. 1971. Migrations and growth of
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held for more than12 h in a state of "sensory deprivation" lobster (Honuiru\ americanus). J. E.\p. Biol. 201: 365-374.
have been reported to be much more responsive to a variety deFur. P. L.. and C. P. Magnum. 1979. The effects ofenvironmental
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