PRIMARY RESEARCH PAPER

Fight or flight: an investigation of aggressive behaviorand predator avoidance in two populations of blue crabs(Callinectes sapidus Rathbun) in New Jersey

Jessica M. Reichmuth • James MacDonald •

Jonathan Ramirez • Judith S. Weis

Received: 14 April 2010 / Revised: 13 July 2010 / Accepted: 30 August 2010

� Springer Science+Business Media B.V. 2010

Abstract Recent literature has suggested aggres-

sion may be context dependent. The purpose of this

investigation was to examine aggressive and predator

avoidance behaviors in juvenile blue crabs of two

populations. Furthermore, we wanted to determine

whether aggression persisted into the adult stages.

Juvenile blue crabs collected from an impacted

estuary, the Hackensack Meadowlands (HM), were

found to attack a threatening stimulus significantly

more often (70%) than conspecifics from a less

impacted estuary (Tuckerton—TK). TK juveniles

responded significantly more often with a flight

(*35%) or mixed response (*30%). Additionally,

HM juveniles were significantly more successful than

TK juveniles at avoiding an adult blue crab predator

when sandy substrate was present in laboratory

experiments. However, the video clarity made it

impossible to determine which interactions were

allowing survival. To determine if ‘‘aggression’’

exhibited by the HM juveniles was the reason for

their enhanced survival, follow-up predator avoid-

ance experiments were conducted without substrate

and videotaped. The results of these experiments

suggest that aggression per se is not the reason since

aggressive juveniles were no more successful than

non-aggressive individuals. The aggressive behavior

exhibited by HM juveniles continues into the adult

stages. This behavior may be important to recognize

when estimating population size as well as local

fishery efforts.

Keywords Aggression � Behavior � Blue crab �Callinectes sapidus � Predator avoidance

Introduction

An organism’s propensity for aggression may affect

interactions between individuals. This propensity for

aggression may also help determine its foraging

success (e.g., subduing resisting prey and pressing

attacks) or defending other items such as mates or

refuge, from other individuals (Kaiser et al., 1990).

Aggression has been widely observed in many types

of invertebrates. For example, larger and more

aggressive wild octopuses (Abdopsus aculeatus

d’Orbigny) were more successful at gaining time to

successfully mate with females (Huffard et al., 2010).

Handling editor: L.B. Kats

J. M. Reichmuth � J. Ramirez � J. S. Weis

Department of Biological Sciences, Rutgers, The State

University of New Jersey, 195 University Avenue,

Newark, NJ 07102, USA

J. MacDonald

New York Sea Grant, c/o NYS DEC, 47-40 21st Street,

Long Island City, NY 11101, USA

J. M. Reichmuth (&)

Department of Biology, Augusta State University,

2500 Walton Way, Augusta, GA 30904, USA

e-mail: jreichmuth02@gmail.com

123

Hydrobiologia

DOI 10.1007/s10750-010-0460-z

Other examples of aggression have been observed

with reef-building corals (Romano, 1990), ants

(Vasquez & Silverman, 2008), sea urchins (Shulman,

1990), crayfish (Graham & Heberholz, 2009), and

crabs (Huntingford et al., 1995).

Crustaceans are good models for observing aggres-

sive and/or agonistic behavior for a number of

reasons: ease of accessibility, known physiology,

size, and social behavior (Kravitz & Huber, 2003).

Both adult and juvenile blue crabs are known to be

aggressive, especially toward conspecifics (Moksnes

et al., 1997; Clark et al., 1999a). Such encounters can

leave a crab injured or missing appendages. Because

of such an alteration, an individual can have a

presumed competitive and/or energetic disadvantage

as well as increased predation risk (Juanes & Smith,

1995). The blue crab’s most formidable defensive (or

offensive) weapons are its sharp, strong chelae. How

an individual uses these weapons may affect its

prospects for survival in an encounter with a predator

or conspecific competitor. Jachowski (1974) offered

the first experimental study of agonistic behavior by

C. sapidus. He suggested that agonistic encounters

with other individuals were highly dependent on the

presence of food or a potential mate. More recent

literature (e.g., Nye, 1989; Wolcott & Hines, 1989,

1990; Clark et al., 1999b) has focused on aggressive

behavior associated with foraging activities and has

shown agonistic activity occurring simultaneously

with periods of feeding. Not only did the presence of

conspecifics interfere with feeding and foraging, but

some adult crabs spent up to 40% of their time

engaged in agonistic activities (Clark et al., 1999a, b).

Studies using telemetry supported the idea that the

frequency and nature of interactions occurring

between C. sapidus conspecifics are dependent on

the density of crabs in a specific area at one time and,

as a result, have important implications for fisheries

management. A field study found an increase of

agonistic behavior in crabs when using certain kinds

of commercial crab pots (Vasquez-Archdale et al.,

2003). Since crab pots are sometimes used in

population estimates, it is possible that agonistic

behaviors may affect the likelihood of crabs entering

the pot and thus impact the count.

Aggressive behavior has been correlated with

boldness and reactive behavior, which has implica-

tions for predator avoidance behavior. Individuals

that are more reactive in the presence of a predator

potentially increase the chance of being eaten (Sih

et al., 2004a, b). However, other studies have

suggested that the increase of aggression/agonistic

behavior toward a predator can increase the chance of

survival (Whitehouse, 1997; Reany & Backwell,

2007). Juvenile C. sapidus normally avoid predation

by fleeing and/or by burying themselves in the

sediment. Some juveniles will even stand their

ground and use their chelae for defense, an aggressive

act that is more characteristic of larger adults.

Recent animal behavior research has focused on

differences among individuals in a species and

classifying the ‘‘behavioral syndrome’’ of a popula-

tion (Sih et al., 2004a, b). The most common of

these behavioral types are aggression and the shy-

bold regime, which have been investigated mostly in

vertebrates, such as fish (e.g., Coleman & Wilson,

1998; Ward et al., 2004). The behavior of brachyu-

ran crabs has also been widely studied (e.g., Hazlett,

1971, 1972; Jachowski, 1974; Crane, 1975), but not

necessarily in this context. Just as in other animal

populations, aggressive and defensive responses can

vary across a population as well as between

populations, and could impact predator avoidance

abilities. Recently, aggression and bold behavior

have been correlated with the success of an invasive

crayfish, Pacifcastacus leniusculus Dana (Pintor

et al., 2008). In another study, risk-taking behavior

predicted aggression and mating success in the

fiddler crab, Uca mjoebergi Rathbun (Reany &

Backwell, 2007).

The blue crab is a swimming decapod that is

estuarine dependent and widely distributed from

Nova Scotia to northern Argentina. They inhabit

estuaries and near shore coastal waters to depths of at

least 36 m and are a year-long resident of New Jersey

estuaries (Norse, 1977). This species is not only

important ecologically, but economically as well. The

Chesapeake Bay produces approximately 13,000 MT

of crabs a year, but in the northern Atlantic states the

crab provides access to a localized fishery (Jop et al.,

1997). Blue crabs are part of a predatory guild that

structures the dynamics of estuarine soft bottom

communities, which makes them important in the

estuarine food web. They are not only predators, but

also scavengers, and are themselves sometimes prey

for fishes and carnivorous crabs, especially as juve-

niles (Virnstein, 1979; Nelson, 1981; Edwards et al.,

1982; Hines et al., 1990).

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In this investigation of aggression, we compared

juveniles of two populations for their response to a

threatening stimulus and their predator avoidance

abilities. One population was from the Hackensack

Meadowlands (HM), an estuarine system with a long

history of impact, and the other from a less impacted

site in southeastern NJ, Tuckerton (TK). We hypoth-

esized that if one population of juvenile blue crabs

was more aggressive/reactive, this would give an

advantage with a predator. We also examined the

tendency of adult crabs from the same two systems to

enter crab pots. We expected that aggressive indi-

viduals, once inside a pot, would keep other crabs out

of the baited pot.

Materials and methods

Study sites

Hackensack Meadowlands (HM)

The HM is an impacted brackish marsh in northeast

New Jersey, encompassing approximately 83 km2 in

Bergen and Hudson counties (Fig. 1). This area is one

of the largest wetland ecosystems in the Hudson-

Raritan Estuary and is the largest contiguous open

space in the New York metropolitan area. The

wetlands are important to many estuarine bird and

fish species.

74°0'W

74°0'W

75°0'W

75°0'W

41°0'N 41°0'N

40°0'N 40°0'N

39°0'N 39°0'N

0 50 100 sretemoliK52

Newark Bay New York City

Hudson River

Great Bay

TKMullica River Little Egg Harbor

Raritan Bay

Hackensack River

HM

Delaware Bay

PA

DE

NY

Fig. 1 Map of study

locations: the Hackensack

Meadowlands (HM) in

northeastern NJ

(40�4205500N, 74�604200W)

and Tuckerton (TK) in

southeastern NJ

(39�360500N, 74�2001700W)

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123

Tuckerton (TK)

The Mullica River-Great Bay estuary comprised

225 km2 of salt marsh and 145 km2 of shallow

estuarine waters. The surrounding area is protected

by the Edwin B. Forsythe National Wildlife Refuge

and the Great Bay Wildlife Management Area

(Fig. 1). The system is less impacted and has been

designated as the Jacques Cousteau National Estua-

rine Research Reserve (NERR). TK is about 160 km

south of HM.

Experimental design

Crabs were collected from various sites within HM

and TK using a seine net and otter trawl and brought

back to the laboratory. They were kept in aerated

tanks with a sand depth of 1 cm and artificial

seawater (Instant Ocean�) at their native salinity

(HM: 15 psu; TK: 30 psu). A 14/10 light cycle was

kept throughout the field season. TK crabs were fed

with a diet of ribbed mussels (Geukensia demissa

Dillwyn) and Atlantic menhaden (Brevoortia tyran-

nus Latrobe) collected from TK, while HM crabs

were fed with a diet of menhaden and mummichogs

collected from HM; all crabs were fed three times a

week after which the water was changed. Intermolt

crabs were acclimated to laboratory conditions for

48 h prior to the beginning of experimentation.

Response to a threatening stimulus

Crabs [HM: mean carapace width, CW = 52 ±

4.8 mm; N = 41; TK: mean CW = 48 ± 5.3 mm

(SE), N = 58] were constrained inside a small,

inverted opaque container positioned. This container

was positioned at one end inside a 38-l aquarium with

a depth of 5-cm artificial sea water (salinity of

22 psu; no substrate). Each crab was allowed to

acclimate for 10 min. Substrate was not used so that

specific behaviors could be isolated. The aquarium

was covered on three sides with opaque, non-

reflective paper to restrict the crab’s peripheral vision

and prevent it from reacting to its own reflection or

movement outside the aquarium. The top two-thirds

of the remaining side were covered as well for the

same reason; the bottom third was left clear for

observation.

An individual crab, from either HM or TK, was

isolated in the opaque container. Once isolated, a

stimulus consisting of a black rubber stopper 44-mm

diameter attached to a dowel 54 cm in length was

slowly lowered into the other end of the aquarium.

After 10 min, the opaque container was slowly

removed. The stopper was slowly pushed toward

the crab by an investigator who stood beyond the

opaque side of the aquarium. No part of this

researcher ever appeared directly over the aquarium.

A second observer, stationed several feet back from

the aquarium to avoid provoking a reaction from the

crab, recorded the nature of the crab’s reaction.

Three response types were recorded. A ‘‘flee’’

reaction was defined as the crab quickly moving away

from the stopper, and ‘‘attack’’ was a lunge toward it.

A ‘‘mixed’’ response was a lunge toward the stopper

immediately followed by a quick retreat to the

opposite end of the tank. If the crab was facing away

from the stimulus, especially active, or moved

immediately across the aquarium before the stimulus

was activated, then the trial was discontinued. The

observer recording the reaction was blind to the

population of crab being tested. Statistical analyses

were conducted using Statistix 7.0 and GraphPad

Prism 4.0 software. Differences in the responses to

the stimulus were analyzed using v2 tests.

Survival with an adult blue crab predator

with substrate

Adult blue crab predators from these two sites were

highly variable in their time to capture juvenile blue

crabs (Reichmuth et al., 2009). To best determine the

exact vulnerability of the juveniles, we set up an

experiment to determine which juveniles were more

likely to be captured.

In this experimental set-up, one adult predator and

two juveniles from each population were used. The

experiment was conducted in a 76-l aquarium with

*35 mm sand covering the bottom and salinity of

22 psu, which is similar to field conditions. The

aquarium was covered with opaque paper on all four

sides so that the crabs did not get distracted by

outside movement or reflections. The four juveniles

(mean CW: HM = 32 ± 2.8 mm, N = 110; TK =

35 ± 2.6 mm (SE), N = 110) were added to the

aquarium and allowed to acclimate for 1 h; sizes and

sexes were noted and recorded. Swimming paddles

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123

on juvenile crabs from one population were marked

with a black Sharpie� in order to determine the

survivors; each population was marked in alternate

trials.

After the juvenile’s acclimation period, one adult

crab that had been food deprived for 48 h (male or

female, mean CW: HM = 101 ± 8.2 mm, TK = 94 ±

7.4 mm) was added. Adults were usually 80–100 mm

larger than the juveniles. Preliminary studies deter-

mined sex of the predator was not a factor in the

observed differences of survivorship. All trials were

recorded using a closed circuit digital camera

(Ikegami Tsushinki Co. Ltd) with a 7.5–75-mm lens

(Canon) and digital disk recorder (Panasonic, Model

WJ-HD 309). The experiment ended once two

juveniles were consumed. The number and identity

(which population) of juveniles consumed was also

recorded, and data were analyzed using v2 tests.

Survival with a predator without substrate

Baseline threatening stimulus test In the video from

the previous experiment, it was often impossible to

view the interactions between the juvenile(s) and

adults clearly. In order to closely observe the

interactions, we designed a follow-up experiment

without substrate.

Juvenile crabs were pre-screened for aggressive

tendencies. One juvenile crab [HM, mean CW =

28 ± 2.9 mm; TK, mean CW = 31 mm ± 2.3 mm

(SE)] from either population was placed in an

opaque rectangular Nalgene� container (dimensions:

L = 23 cm, W = 13.5 cm, H = 13.5 cm). The con-

tainer did not have substrate, but had a water depth of

4 cm. Individual crabs were allowed to acclimate for

30 min before testing. Each crab was tested three

times using a similar threatening stimulus: a #2

stopper (diameter: 2 cm) attached to a wooden dowel

(length: 52.5 cm) with a 10-min rest period between

tests. Responses were recorded as in the previous

section. The crab was classified as either ‘‘aggres-

sive,’’ ‘‘non-aggressive,’’ or ‘‘mixed’’ as a result of

the responses from this baseline test. Only TK

juveniles were used for this experiment, and by

doing this, we were able to isolate aggressive

behavior as a factor in avoiding predators. After this

classification, they were used in the following

experiment.

Predator avoidance

This predator avoidance experimental set-up is sim-

ilar to the experiment described earlier. The set-up

used a 76-l aquarium, but without sand to allow better

visual observations of behavioral interactions. Addi-

tionally, white paper was placed underneath the

aquarium to further enhance visibility when using the

low-light digital recorder. This set-up does not

simulate field conditions, but was necessary in order

to visualize the interactions between the predator and

the prey.

Two juveniles were used in each experiment in

one of the following combinations: one aggres-

sive ? one non-aggressive, one aggressive ? one

mixed, or one non-aggressive ? one mixed. All trials

were recorded using a closed circuit digital camera

(Ikegami Tsushinki Co. Ltd) with a 7.5–75-mm lens

(Canon) and digital disk recorder (Panasonic, Model

WJ-HD 309). The juveniles were marked with a

Sharpie� in order to distinguish them on the video

and allowed to acclimate to the tank for 1 h. After the

acclimation period, an adult male blue crab that had

been food deprived for 48 h was introduced to the

tank. The experiment ended after 48 h. The first

juvenile to be consumed and any other interactions

with the predator were recorded and analyzed using

v2 tests.

Adult crab pot experiment

To test if aggression continued into the adult stages,

which could ultimately affect entry into crab traps,

adults from both populations were pre-screened for

aggressive behavior. Adult blue crabs [HM: mean

CW = 118 mm ± 9.2 mm; TK: mean CW = 96 ±

8.7 mm (SE)] from either population were isolated in

a Nalgene� container (dimensions: L = 20 cm,

W = 21.5 cm, H = 6.5 cm) for 15 min. After the

acclimation period, a hand was passed over the

container. If the crab lunged, the individual was

classified as aggressive; if it did not, it was classified

as non-aggressive.

Crab pot experiments were conducted outdoors in a

large circular tank (diameter: 1.7 m; height: 1.5 m).

The tank had a sand depth of 1 cm and water depth of

0.5 m. Five adult crabs that had food deprived for

48 h were placed in the tank simultaneously and

allowed to acclimate for 30 min. Only crabs from one

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population were used in each trial (HM: N = 11 trials;

TK: N = 9 trials). After acclimation, one commercial

crab pot (dimensions: 1.0 m 9 1.3 m 9 0.75 m) with

bait (Atlantic menhaden, B. tyrannus) was placed on

the bottom of the tank. Crabs were checked after 24

and 48 h. After 48 h, the experiment ended and crab

positions within the tank and pot were recorded. The

number of crabs that had entered the pot at 24 and

48 h were analyzed using Student’s t tests.

Results

Response to a threatening stimulus

In 99 trials, HM juveniles attacked a threatening

stimulus significantly more often than TK juveniles

(v2 = 8.45, df = 2, P B 0.015; Fig. 2); TK juveniles

either fled or gave a mixed response significantly

more often than HM juveniles.

Survival with a predator

In 45 trials, HM juveniles were significantly more

successful at avoiding being eaten by an adult than TK

juveniles (v2 = 10.06, df = 1, P B 0.002; Fig. 3).

Even though these experiments were recorded, it

was not possible to see the actual details of the

interactions between the juveniles and adult predator

due to the sandy substrate. Some flees and other

interactions between juveniles and the adult were

observed, but even though the juveniles were marked

it was hard to determine which population they were

from on the video recording.

Survival with a predator without substrate

In 11 trials, aggressive juveniles were no better at

avoiding an adult predator than non-aggressive ones

(v2 = 0.69, df = 2, P B 0.708; Fig. 3). All juveniles

in this study were from TK and only two trials were

conducted with a mixed response crab.

Video observations indicated that when aggressive

crabs often exhibited a threat posture with their claws

extended. In these occurrences, they were likely to be

captured by the adult, which was much larger and not

daunted by the threat display. Only in one trial did

this allow survival: the adult stopped pursuit of the

aggressive juvenile and pursued the non-aggressive

one until it was cornered. The videos indicated that,

in general, fleeing to the opposite end of the tank was

the best strategy for survival; this was true for all

three behavioral types.

In some of the trials, juvenile–juvenile interactions

sometimes promoted survival of the more aggressive

individual. In two trials, the aggressive crab ‘‘bul-

lied’’ the other crab into the area of the tank where

the adult was, resulting in capture. In one case, the

aggressive individual held its ground in an area of the

tank and the other crab was forced to another area of

the tank where the adult was, and was captured. In

Fig. 2 Percentage of responses to a threatening stimulus by

HM and TK juvenile blue crabs

Fig. 3 Percentage of HM and TK juvenile blue crabs that

successfully avoided an adult blue crab predator with substrate

and percentage of aggressive, non-aggressive and mixed

individuals that successfully avoided an adult blue crab

predator

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another case, however, a scuffle between juveniles

alerted the adult and the aggressive individual was

captured.

Adult crab pot experiment

Significantly more TK crabs entered the crab pot than

HM crabs after 24 h (t = 7.51, df = 18, P [ 0.001;

Fig. 4). The same result was true after 48 h. Aggres-

sive crabs in the pot killed and sometimes cannibal-

ized other crabs that entered the pot in many HM

trials. If this occurred, no other crabs entered the pot.

In contrast, individuals did not prevent other crabs

from entering the pot and cannibalism did not occur

in all TK trials.

Discussion

Ecology and behavior

Hackensack Meadowlands (HM) juveniles showed

significantly more attacks in response to a threatening

stimulus than TK conspecifics. Additionally, HM

juveniles were better at avoiding predation. Blue

crabs are known to show a range of agonistic

behavior ranging from displays, fending, and striking

(Clark et al., 1999a; Hines, 2007). These behavioral

differences have implications for survival. The find-

ing that HM juveniles survived longer in the presence

of a predator was unexpected. It is unlikely that the

HM crabs survived longer because they were unpal-

atable. If that had been the case, they would have

been killed and not consumed. The parameters of the

predator avoidance experiment with substrate gives

the juveniles many options to escape the predator;

these options include fleeing and then rapidly burying

themselves, fighting back while staying buried or

standing ground to offer resistance. With the sand in

the aquarium, it was impossible to observe the actual

interactions between the adult and juveniles.

However, it seems that this suite of behaviors in

conjunction with the substrate allowed HM juve-

niles to successfully avoid predators. Furthermore,

there is limited area in which to flee in the aquarium

and it is unclear how these results apply to the open

estuary.

To test whether it is indeed the aggressive

tendencies that confer an advantage in dealing with

a predator, we conducted the experiment without

substrate. This experimental set-up allowed us clear

observations of the interactions between the juveniles

and adult predator. Using only TK crabs, we could

separate the role of aggression from any other

behaviors unique to HM crabs that might have

promoted their survival. The results indicate that it

is not aggressive behavior per se that protects the

crabs since aggressive and non-aggressive individuals

were equally likely to be captured. However, the

most common scenario preceding capture was dis-

playing and standing ground, a type of aggressive

behavior that is not useful when the predator is much

larger. Yet, it may be more useful under competitive

circumstances with other individuals of a comparable

size. Since these experiments only used TK juveniles,

the data can only provide insight into whether or not

aggression per se increases the survival of these

individuals. It appears that other behaviors of HM

juveniles must be responsible for their superior

predator avoidance ability.

Interactions of the aggressive juveniles with the

other juvenile in the tank were also relevant. In

several trials, the aggressive juvenile bullied the other

juvenile to the area of the tank where the adult was

present; however, the aggressive individual was not

necessarily the survivor in the trials in which this type

of interaction occurred. This suggests the existence of

a tradeoff to aggressive behavior. For example,

aggressive individuals may be better at holding

ground or defending their space/refuge against other

juveniles. On the other hand, their aggression might

put them at risk from an undeterred larger predator.

Fig. 4 Mean number of crabs entering a baited crab pot after

24 and 48 h respectively; error bar represents one ± standard

error

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At the same time, the juvenile crabs that were most

aggressive toward the stopper did not always show an

aggressive posture (i.e., bold behavior) toward the

predator suggesting that this behavior may be context

dependent. Similar results were found in sunfish.

Individuals were classified as bold when approaching

a meter stick, but the same bold individual did not

inspect a novel food source (Coleman & Wilson,

1998). The behavioral plasticity observed in the

predator avoidance experiments is adaptive to the

circumstances. Additional studies will be needed to

ascertain exactly what aspects of behavior are most

closely associated with the survival of HM juveniles,

since increased propensity for aggression per se is not

the critical factor.

Adult blue crabs are responsible for 75–97% of

mortality in juvenile blue crabs within Chesapeake

Bay (Hines & Ruiz, 1995). In the Gulf of Mexico,

this value ranges from 85 to 91% (Heck & Coen,

1995); in New Jersey, mortality ranges from 10 to

45% (Wilson et al., 1990a, b). However, in a previous

study, HM adults were found to be poor predators on

juvenile blue crabs under laboratory conditions, and

few crab parts were found in stomach contents of

field-collected individuals (Reichmuth et al., 2009).

Poor prey capture by adults, combined with effective

predator avoidance by juveniles, suggests that less

cannibalism may be occurring within the Meadow-

lands, which should allow larger numbers of juve-

niles to survive. If this is the case, juvenile blue crabs

may be overcrowded in a degraded, patchy habitat.

Studies have shown that increased agonistic encoun-

ters occur in populations of blue crabs in crowded

conditions (Mansour & Lipcius, 1991; Clark et al.,

2000, 1999a, b), and this may be one reason why HM

juveniles showed increased aggression. Funnel-web

spiders (Agelenopsis aperta) were highly aggressive

under low food availability conditions (Maupin &

Riechert, 2001). Furthermore, adult blue crabs were

found to exhibit increased agonism under varying

food availability (Mansour & Lipcius, 1991). In these

situations, resources are limited and competition is

increased, which favors aggressive individuals (Sih

et al., 2004a, b). Increased aggression may also be a

response to greater predation risk in the environment,

as has been seen in populations of various species

(spiders: Whitehouse, 1997; fiddler crabs: Reany &

Backwell, 2007). However, this does not appear

likely within the Meadowlands since a major predator

of juvenile blue crabs—adult blue crabs—are poor

predators and eat few juveniles (Reichmuth et al.,

2009). Whether predation by other species is greater

at HM than TK is not known.

However, another possible reason for altered

aggressive behavior is effects of contaminants. The

altered feeding behavior of adult HM blue crabs

(Reichmuth et al., 2009) is related to the environment

(Windham et al., 2004). When exposed to ‘‘clean

food’’ or a less impacted environment for 8 weeks,

HM adults predatory behavior improved and became

similar in behavior to crabs from TK, suggesting that

contaminants are the cause for the decreased preda-

tory behavior observed in HM adults (Reichmuth,

2009; Reichmuth et al., 2010).

Ecology of crab pots

The results of the crab pot experiment suggest that

HM crabs remain aggressive into the adult life stages.

Aggressive behavior can have serious implications on

the ecology of an organism if the individuals are

aggressive in novel or inappropriate situations (Sih

et al., 2004a, b). In our initial collections of juveniles

from HM, we put them in containers together, and by

the time we returned to the laboratory in under an

hour many had been killed by others, unlike TK

crabs. This experience prompted the current behav-

ioral studies.

A few of the crab pot trials with HM crabs resulted

in a crab being killed and eaten. The other crabs may

not have entered the trap due to the scent of the

injured conspecifics. Field experiments using crab

pots baited with an injured blue crab caught fewer

crabs than traps baited with menhaden (Ferner et al.,

2005). Another study using odor plumes containing

metabolites of injured crabs found crabs reduced their

foraging behavior and movement (Moir & Weiss-

burg, 2008). It is possible that metabolites released

from the injured crab in our mesocosm acted as a

deterrent.

Our results have important implication for popu-

lation surveys, suggesting caution when using crab

pots in population estimates. These results suggest an

apparent difference in the propensity for individual

crabs to enter the pot, which could also affect local

fisheries. When we used crab pots in the Meadow-

lands, few crabs were caught, and on occasion, an

inhabitant would be dead or severely damaged. Using

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the same effort in TK, many more crabs were caught

(personal observation) without damage to the inhab-

itants. The poor field catch with baited crab traps is

not an accurate representation of the blue crab

abundance within the Meadowlands since other

fishing techniques (seines and trawls) were far more

successful. A survey using only trapping as a

technique might result in severe undercounting if

behavior is not taken into account.

Conclusion

Hackensack Meadowlands juveniles were more

aggressive when threatened with a stimulus and were

also significantly better than crabs from the less

impacted site (Tuckerton) at avoiding predators.

However, it appears that aggressive behavior itself

does not confer an advantage with a larger predator,

but rather it may be more important in interactions

with similar-sized conspecifics in gaining refuge or

protecting a prime habitat patch. Aggressive behavior

also reduced the rate in which crabs entered baited

traps, which may have implications in using this

method for population counts or a localized fishery.

Acknowledgments This research was funded in part by

grants from the Rutgers University Marine Field Station

Graduate Student Research Fund and the Meadowlands

Environmental Research Institute (MERI). The authors would

like to thank B. Bragin (New Jersey Meadowlands

Commission) and J. Grzyb (MERI) for their help with

collection and boat time on the Hackensack River as well as

Dr. T. Glover for statistical assistance. We would also like to

thank the many undergraduate and high school students who

helped with collecting and maintaining specimens,

experimental set-up, and data collection in the lab.

References

Clark, M. C., T. G. Wolcott, D. L. Wolcott & A. H. Hines,

1999a. Intraspecific interference among foraging blue

crabs Callinectes sapidus: interactive effects of predator

density and prey patch distribution. Marine Ecology

Progress Series 178: 69–78.

Clark, M. C., T. G. Wolcott, D. L. Wolcott & A. H. Hines,

1999b. Foraging and agonistic activity co-occur in free-

ranging blue crabs (Callinectes sapidus): observations of

animals by ultrasonic telemetry. Journal of Experimental

Marine Biology and Ecology 233: 143–160.

Clark, M. C., T. G. Wolcott, D. L. Wolcott & A. H. Hines,

2000. Foraging behavior of an estuarine predator, the blue

crab Callinectes sapidus in a patchy environment.

Ecography 23: 21–31.

Coleman, K. & D. S. Wilson, 1998. Shyness and boldness in

pumpkinseed sunfish: individual differences are context-

specific. Animal Behavior 56: 927–936.

Crane, J., 1975. Fiddler Crabs of the World. Princeton

University Press, Princeton.

Edwards, D. C., D. O. Conover & F. Sutter III, 1982. Mobile

predators and the structure of marine intertidal commu-

nities. Ecology 63: 1175–1180.

Ferner, M. C., D. L. Smee & Y. P. Chang, 2005. Cannibalistic

crabs respond to the scent of injured conspecifics: danger

or dinner? Marine Ecology Progress Series 300: 193–200.

Graham, M. E. & J. Heberholz, 2009. Stability of dominance

relationships in crayfish depends on social context.

Animal Behavior 77: 195–199.

Hazlett, B. A., 1971. Interspecific fighting in three species of

brachyuran crabs from Hawaii. Crustaceana 20: 308–314.

Hazlett, B. A., 1972. Response to agonistic postures by the

spider crab Microphyrys bicornutus. Marine Behavioral

Physiology 1: 85–92.

Heck, J. L. Jr., & L. D. Coen, 1995. Predation and the abun-

dance of juvenile blue crabs: a comparison of selected east

and Gulf coast (USA) studies. Bulletin of Marine Science

57: 877–883.

Hines, A. H., 2007. Ecology of juvenile and adult blue crabs. In

Kennedy, V. S. & L. E. Cronin (eds), The Blue Crab,

Callinectes sapidus. Maryland Sea Grant College, College

Park, MD: 565–654.

Hines, A. H., A. M. Haddon & L. A. Wiechert, 1990. Guild

structure and foraging impact of blue crabs and epibenthic

fish in a subestuary of Chesapeake Bay. Marine Ecology

Progress Series 67: 105–126.

Hines, A. H. & G. M. Ruiz, 1995. Temporal variation in

juvenile blue crab mortality: nearshore shallows and

cannibalism in Chesapeake Bay. Bulletin of Marine

Science 57: 884–901.

Huffard, C. L., R. L. Caldwell & F. Boneka, 2010. Male–male

and male–female aggression may influence mating asso-

ciations in wild octopuses (Abdopus aculeatus). Journal of

Comparative Psychology 124: 38–46.

Huntingford, F. A., A. C. Taylor, I. P. Smith & K. E. Thorpe,

1995. Behavioural and physiological studies of aggression

in swimming crabs. Journal of Experimental Marine

Biology and Ecology 233: 143–160.

Jachowski, R. L., 1974. Agonistic behavior of the blue crab,

Callinectus sapidus Rathbun. Bulletin of Marine Science

6: 232–253.

Jop, K. M., R. C. Biever, J. R. Hoberg & S. P. Shepherd, 1997.

Analysis of metals in blue crabs, Callinectes sapidus,

from two Connecticut estuaries. Bulletin of Environmen-

tal Contamination and Toxicology 58: 311–317.

Juanes, F. & L. D. Smith, 1995. The ecological consequences

of limb damage and loss in decapod crustaceans: a review

and prospectus. Journal of Experimental Marine Biology

and Ecology 93: 197–223.

Kaiser, M. J., R. N. Hughes & D. G. Reid, 1990. Chelal

morphometry, prey-size selection and aggressive compe-

tition in green and red forms of Carcinus maenas (L.).

Journal of Experimental Marine Biology and Ecology

140: 121–134.

Hydrobiologia

123

Kravitz, E. A. & R. Huber, 2003. Aggression in invertebrates.

Current Opinion in Neurobiology 13: 736–743.

Mansour, R. A. & R. N. Lipcius, 1991. Density-dependent

foraging and mutual interference in blue crabs preying

upon infaunal clams. Marine Ecology Progress Series 72:

236–249.

Maupin, J. L. & S. E. Riechert, 2001. Superfluous killing in

spiders: a consequence of adaptation to food-limited

environments? Behavioral Ecology 12: 569–576.

Moir, F. & M. J. Weissburg, 2008. Cautious cannibals:

behavioral responses of juvenile and adult blue crabs to

the odor of injured conspecifics. Journal of Experimental

Marine Biology and Ecology. doi:10.1016/j.jembe.2008.

10.026.

Moksnes, P. O., R. N. Lipcius, L. Pihl & J. Montfrans, 1997.

Cannibal-prey dynamics in young juveniles and post lar-

vae of the blue crab. Journal of Experimental Marine

Biology and Ecology 215: 157–187.

Nelson, W. G., 1981. Experimental studies of decapod and fish

predation on seagrass macrobenthos. Marine Ecology

Progress Series 5: 141–149.

Norse, E. A., 1977. Aspects of the zoogeographic distribution

of Callinectes (Brachyuran: Portunidae). Bulletin of

Marine Science 27: 440–447.

Nye, L. A., 1989. Variation in feeding behavior of blue crabs

(Callinectes sapidus Rathbun) measured by ultrasonic

biotelemetry. M.Sc. thesis, North Carolina State Univer-

sity, Raleigh: 82 pp.

Pintor, L. M., A. Sih & M. L. Bauer, 2008. Differences in

aggression, activity and boldness between native an

introduced populations of an invasive crayfish. Oikos 117:

1629–1636.

Reany, L. T. & P. R. Y. Backwell, 2007. Risk-taking behavior

predicts aggression and mating success in a fiddler crab.

Behavioral Ecology 18: 521–525.

Reichmuth, J. M., 2009. Behavioral ecology and population

genetics in two populations of blue crabs Callinectes sa-pidus (Rathbun) in New Jersey. Ph.D. Thesis, Rutgers,

The State University of New Jersey: 125 pp.

Reichmuth, J. M., R. Roudez, T. Glover & J. S. Weis, 2009.

Differences in prey capture behavior in populations of

blue crab (Callinectes sapidus Rathbun) from contami-

nated and clean estuaries in New Jersey. Estuaries and

Coasts 32: 298–308.

Reichmuth, J. M., P. Weis & J. S. Weis, 2010. Bioaccumula-

tion and depuration of metals in blue crabs (Callinectessapidus Rathbun) from a contaminated and clean estuary.

Environmental Pollution 158: 361–368.

Romano, S. L., 1990. Long-term effects of interspecific

aggression on growth of the reef-building corals

Cyphastrea ocellina (Dana) and Pocillopora damicomis

(Linnaeus). Journal of Experimental Marine Biology and

Ecology 140: 135–146.

Shulman, M. J., 1990. Aggression among sea urchins on

Caribbean coral reefs. Journal of Experimental Marine

Biology and Ecology 140: 197–207.

Sih, A., A. Bell & C. J. Johnson, 2004a. Behavioral syndromes:

an ecological and evolutionary overview. Trends in

Ecology and Evolution 19: 372–378.

Sih, A., A. Bell, C. J. Johnson & R. E. Ziemba, 2004b.

Behavioral syndromes: an integrative overview. Quarterly

Review of Biology 79: 241–277.

Vasquez-Archdale, M., K. Anraku, T. Yamamoto & N. Hig-

ashitani, 2003. Behavior of the Japanese rock crab ‘Ishi-

gani’ Charybdis japonica towards two collapsible baited

pots: evaluation of capture effectiveness. Fisheries Sci-

ence 69: 785–791.

Vasquez, G. M. & J. Silverman, 2008. Intraspecific aggression

and colony fusion in the Argentine ant. Animal Behavior

75: 583–593.

Virnstein, R. W., 1979. Predation of estuarine infauna:

response patterns of component species. Estuaries 2:

69–86.

Ward, A. J. W., P. Thomas, P. J. B. Hart & J. Krause, 2004.

Correlates of boldness in the three-spined stickleback

(Gasterosteus aculeatus). Behavioral and Ecological

Sociobiology 55: 561–568.

Wilson, K. A., K. W. Able & K. L. Heck Jr., 1990a. Predation

rates on juvenile blue crabs in estuarine nursery habitats:

evidence for the importance of macroalgae (Ulva lactuca).

Marine Ecology Progress Series 48: 243–251.

Wilson, K. A., K. W. Able & K. L. Heck Jr., 1990b. Habitat

use by juvenile blue crabs: a comparison among habitats

in southern New Jersey. Bulletin of Marine Science 46:

105–114.

Whitehouse, M. E. A., 1997. The benefits of stealing from a

predator: foraging rates, predation risk, and intraspecific

aggression in the kleptoparasitic spider Argyrodes antip-odiana. Behavioral Ecology 8: 665–667.

Wolcott, T. G. & A. H. Hines, 1989. Ultrasonic biotelemetry of

muscle activity from free-ranging marine animals: a new

method for studying foraging by blue crabs (Callinectessapidus). Biological Bulletin 176: 50–56.

Wolcott, T. G. & A. H. Hines, 1990. Ultrasonic telemetry of

small-scale movements and microhabitat selection by

molting blue crabs (Callinectes sapidus). Bulletin of

Marine Science 46: 83–94.

Windham, L., J. S. Weis & P. Weis, 2004. Metal dynamics of

plant litter of Spartina alterniflora and Phragmites aus-tralis in metal-contaminated salt marshes. Part 1. Patterns

of decomposition and metal uptake. Environmental Tox-

icology and Chemistry 23: 1520–1528.

Hydrobiologia

123