ICES Journal of Marine Science, 55: 289–298. 1998
The western Pacific brachyuran (Hemigrapsus sanguineus:
Grapsidae), in its new habitat along the Atlantic coast of the
United States: geographic distribution and ecology
John J. McDermott
McDermott, J. J. 1998. The western Pacific brachyuran (Hemigrapsus sanguineus:
Grapsidae), in its new habitat along the Atlantic coast of the United States: geographic
distribution and ecology. – ICES Journal of Marine Science, 55: 289–298.
The Asian shore crab, Hemigrapsus sanguineus (de Haan, 1853), discovered on the
coast of New Jersey in 1988, is now known to be distributed in the western Atlantic
from Massachusetts (south of Boston) to Oregon Inlet, North Carolina. Living in the
mid to upper rocky intertidal zone, it exploits a niche mostly unoccupied by native
brachyurans. In the northern part of its range there is some mid-intertidal overlap with
the green crab, Carcinus maenas. In North Carolina H. sanguineus becomes sympatric
in the high intertidal with another grapsid, the wharf crab, Armases cinereum.
Distributional evidence indicates that H. sanguineus was probably introduced via
ballast water at one or more major shipping centres south of Cape Cod (i.e. the New
York Bight, Delaware Bay, Chesapeake Bay), perhaps in the early 1980s. Its present
latitudinal range in the western Atlantic is only about one-fifth of that in the western
Pacific. H. sanguineus is now the most abundant brachyuran at the intertidal
monitoring site in southern New Jersey, and apparently in some areas of Long Island
Sound to the north. In New Jersey, crabs range in carapace width from 2.3 to 43.9 mm.
The breeding season is from late April through September, and recruitment to the
intertidal population begins in June and continues through the fall and winter. Some
crabs become subtidal, particularly during the winter months, as evidenced by the
growth of bryozoans, mussels and barnacles on their carapaces. There is no evidence
in this population of parasitism with metacercariae, nemerteans, rhizocephalans or
bopyrid and entoniscid isopods.
1998 International Council for the Exploration of the Sea
Key words: crustacea, rocky intertidal, salinity tolerance, morphometrics.
Received 30 January 1997; accepted 13 August 1997.
J. J. McDermott: Department of Biology, Franklin and Marshall College, Lancaster,
Pennsylvania 17604-3003, USA: tel: +1 717 2914110; fax: +1 717 3994548; e-mail:
[email protected].
Introduction
A single ovigerous specimen of the Pacific grapsid crab,
Hemigrapsus sanguineus, was discovered in southern
New Jersey in 1988 (Williams and McDermott, 1990). It
was found in the high intertidal region of a rock-fill at
the southern end of the Townsends Inlet Bridge in Cape
May County (390706
N, 744300
W) (Fig. 1). Subsequent observations in 1990 revealed males, ovigerous
crabs and young-of-year crabs (y.o.y.) living at this site
(McDermott, 1991a). H. sanguineus was occupying
an upper intertidal niche previously unexploited by
decapods on the New Jersey coast.
In the western Pacific H. sanguineus ranges from ]20
to 50N latitude (Fig. 2), including Hong Kong and
Taiwan, the Chinese and Korean coasts, all of Japan
1054–3139/98/020289+10 $25.00/0/jm970273
from the Ryukyu Islands in the south to Hokkaido, and
as far north as Sakhalin Island in Russia (Shen, 1932;
Sakai, 1976; Gamo and Muraoka, 1977; Kikuchi et al.,
1981; Takahashi et al., 1985; Fukui, 1988; Fukui et al.,
1989; Hwang et al., 1993). This distribution is latitudinally equivalent to a western Atlantic range from the
Gulf of St Lawrence to Cuba. Sakai (1976) described
H. sanguineus as one of the commonest crabs of Japan,
as also may be inferred from the hundreds utilized in the
comprehesnive biological studies of Fukui (1988). In
Japan the species is most abundant on rocky beaches in
the upper and middle intertidal zones of open coasts and
the lower reaches of estuaries (Sakai, 1976; Kikuchi
et al., 1981; Fukui, 1988).
One of the most important methods for the dissemination of non-indigenous species is the discharge of
1998 International Council for the Exploration of the Sea
290
John J. McDermott
50°
S
Russia
40°
HO
30° N
Korea
HU
SU
Pacific
Ocean
K
20°
China
140° E
T
HK
120°
Figure 1. Distribution of Hemigrapsus sanguineus along the
New Jersey coast. Key to locations: BI=Barnegat Inlet;
CI=Corsons Inlet; CM=Cape May Harbor; CP=Cape May
Point; GB=Great Bay area; GE=Great Egg Harbor area;
HI=Hereford Inlet; MI=Manasquan Inlet; SH=Sandy Hook;
SR=Shark River Inlet; TI=Townsends Inlet (site of first crab
reported in the United States in 1988). See text for details.
ballast water by ocean-going vessels in foreign ports
(Carlton, 1985; Carlton and Geller, 1993). It is likely
that H. sanguineus was introduced into the western
Atlantic in this way (Williams and McDermott, 1990;
Carlton and Geller, 1993).
In this paper the current geographic distribution of
H. sanguineus in the western Atlantic is presented
together with morphometric data and intertidal
ecological associations of the New Jersey population.
Materials and methods
Townsends and Hereford Inlets (THI) are at the north
and south ends, respectively, of an 11.3 km long sandy
barrier beach on the Cape May peninsula (Fig. 1). They
provided a composite monitoring site for monthly
sampling of crabs between May 1990 and October 1994,
and periodically from 1995 to 1997. Crabs were obtained
by hand from beneath overturned rocks. Other brachyurans found among the rocks with or near H. sanguineus
were collected and measured, and at Townsends Inlet a
0
1000
km
Figure 2. Geographic distribution of the Asiatic crab Hemigrapsus sanguineus in the western Pacific Ocean from Sakhalin
Island, Russia (S) to Hong Kong (HK). It is found along the
mainland, around the Japanese islands of Hokkaido (HO),
Honshu (HU), Kyushu (K) and Shikoku (SU), as well as the
Ryukyu Islands to the south, and the island of Taiwan (T). See
text for details.
checklist of other animals and algae was compiled. Air
and water temperatures, salinity (hydrometer method),
and general weather conditions were recorded at least
monthly at the monitoring site and during collections at
other sites. The mean tide range at Townsends Inlet is
approximately 122 to 152 cm, reaching 198 cm on spring
tides. Between 1991 to 1995 other locations were visited
in New Jersey and most coastal states between Maine
and North Carolina, in search of additional populations
of H. sanguineus.
Each animal was sexed and if ovigerous this was
recorded. The carapace width (CW) and length (CL) of
larger crabs were measured to the nearest 0.1 mm with
vernier calipers. Very small crabs were measured with a
calibrated ocular micrometer under a dissecting microscope. When subsequently mentioned in this paper crab
size refers to CW. The wet weight of freshly collected
crabs was determined to 0.01 g on a top-loading balance,
or for minute specimens, on an analytical balance to
0.001 g.
Results
Geographic distribution in the western Atlantic
Soon after the initial collections of H. sanguineus
at Townsends Inlet in 1990 (McDermott, 1991a),
The western Pacific brachyuran, Hemigrapsus sanguineus
43°
41°
Figure 3. Geographic distribution of Hemigrapsus sanguineus in
the western Atlantic Ocean from Massachusetts to North
Carolina, as of 1996. Key to general locations marked with
black circles: 1=Cape Cod Bay (south of Boston) and the
Cape Cod Canal; 2=Rhode Island and the south coast of
Massachusetts, namely Buzzards Bay and Woods Hole;
3=Long Island Sound, from eastern New York (Bronx) and the
south shore of Connecticut; 4=South shore of Long Island
(western end) and the New York harbours; 5=all along the
New Jersey coast; 6=Cape Henlopen and Indian River Bay,
Delaware; 7=Chesapeake Bay, Virginia; 8=Oregon Inlet,
North Carolina. Long Island, New York is located between
locations 3 and 4. See text for details.
specimens were found 11 km to the south in rocky
locations on both sides of Hereford Inlet (Fig. 1).
Subsequently crabs were collected or reports were
received of crabs from two additional locations to the
south (includes Delaware Bay) and eight locations
northward to Sandy Hook at the entrance to the harbours of New York City. Thus, by 1992 H. sanguineus
had populated sites along the whole coast of New Jersey,
a distance of approximately 200 km.
North of New Jersey, the species was found in 1992 at
Woods Hole, Massachusetts, while south of New Jersey,
crabs were collected in Indian River Bay, Delaware in
1992, and at Cape Charles, Virginia in the Chesapeake
Bay in 1993 (McDermott, 1992, 1995). Therefore, by
1993 the range of H. sanguineus extended at least from
southern New England to Chesapeake Bay (Fig. 3).
Prior to 1994, the only report of H. sanguineus in the
United States was of a few specimens picked from a
291
clump of blue mussels in Cape May Harbor in January
or February 1990 (McDermott, 1991a). However, from
1994 onwards, reports of crabs being found in rocky
intertidal situations became increasingly frequent (some
taken subtidally in seines or with SCUBA) in the areas
around Delaware, New York, Connecticut, Rhode
Island and Massachusetts (Fig. 3). Many of these
reports coincided with a press release from Franklin and
Marshall College, and with the publication of a brief
article in Discover magazine (vol. 15, no. 11, pp. 20 & 22,
1994). These reports included records from 3 locations
on the south shore of Long Island, and 13 locations
along the north shore of Long Island Sound from
Bronx, New York to Narrow River, Rhode Island. P.
Dargel (pers. comm. 1994), a fishing boat captain at
Milford, Connecticut, revealed that he had been collecting Hemigrapsus since 1993, as fish bait for tautog
(Tautoga onitis). In Massachusetts, new reports of the
crab were received from Buzzards Bay (West Island,
about 16 km from Woods Hole), and from north of
Cape Cod at the east end of the Cape Cod Canal and
in Green Harbor, about 46 km north of the Canal
entrance. In October 1995, however, H. sanguineus
was not recovered at the following locations north of
Green Harbor: Magnolia Harbor on Cape Ann,
Massachusetts, Odiorne Point State Park, New
Hampshire, and York Harbor, Maine, i.e. sites ranging
as far as 182 km north of the Cape Cod Canal. In late
June 1996, C. Wright (pers. comm.) also searched for
this species at three locations approximately 20 km
north of Green Harbor and found none. He also found
no specimens in the Pleasant Bay region at the ‘‘elbow’’
of Cape Cod, approximately 45 km east of the Cape
Cod Canal.
In August 1995, I searched southward for H.
sanguineus in North Carolina (Fig. 3), and at Oregon
Inlet (Pamlico Sound) during 20 min collecting five H.
sanguineus and two specimens of a potential competitor,
Armases cinereum (Bosc, 1802) (formerly Sesarma
cinereum, see Abele 1992), in the upper intertidal.
Thus, between 1988 and 1995, personal collecting and
reports from correspondents revealed the existence of H.
sanguineus over a 800 km extent of the Atlantic coast,
between latitude 36N in North Carolina and latitude
42N in Massachusetts, but not north of Boston. This
known range encompasses three major estuaries:
Pamlico Sound; Chesapeake Bay; and Raritan–
New York Bays, as well as sites in Delaware and
Massachusetts. By 1996 I had collected a total of 1200
crabs in New Jersey and the other four states. These
ranged from 2.3 to 43.9 mm CW, the extremes of this
size range representing early y.o.y. and a male that may
have passed its terminal anecdysis. At the THI site 1101
crabs were collected from 1988 to 1996. The majority
came from Townsends Inlet (954 or 86.6%). The smaller
numbers of crabs recorded from other locations may
292
John J. McDermott
several crabs escaped. Another indication of abundance
was the increased occurrence of molted exoskeletons
found in the field. In October 1996 I noted for the first
time several exoskeletons along the tide line of a sandy
beach at the THI site where in years past the only
common brachyuran exoskeletons belonged to Cancer
irroratus and the strictly subtidal Ovalipes ocellatus.
Fishermen at Townsends Inlet are now using Hemigrapsus as bait. Previously, fishermen collected Carcinus or
xanthids for bait from the lower intertidal rocks at low
water or dug for fiddler crabs (Uca spp.) in an adjacent
marsh. Now they often collect Hemigrapsus from
underneath the higher intertidal rocks.
Mean water temperature °C
30
20
10
0
J
F
M A M
J J A
Months
S
O
N
D
Figure 4. Mean monthly surface water temperatures and ranges
(C) determined at various tidal stages from 1988 to 1996 at the
Townsends–Hereford Inlets (THI) monitoring site in New
Jersey, based on 253 recordings.
simply reflect the relatively cursory search that was made
at these sites, but it may be noted that suitable rockyshore habitats are increasingly common northward from
New Jersey, and increasingly rare southward from New
Jersey.
Studies of New Jersey populations
Ecology and population structure
At the THI monitoring site (Fig. 1), water temperatures
(1989 to 1995) ranged from 0.8 to 26.7C (Fig. 4), and air
temperatures ranged from 2.7 to 35.0C. Salinities (at
HW3 h) during the same period ranged from 29.5 to
33.6‰ (n=74). Crabs were relatively inactive during low
temperatures from December through February, seeking
shelter from freezing air temperatures deep among the
rocks or subtidally. Even at air and water temperatures
below 5C, some crabs were found under intertidal rocks
in January, February and March. The lowest air and
water temperatures at which crabs were collected during
these months were 5.5 and 3.8C, respectively, on 30
January 1996, 0.6 and 0.8C on 2 February 1992, and 3.5
and 3.0C on 20 March 1993.
By 1994 the population of H. sanguineus had
increased greatly at the THI monitoring site relative to
the 1990 collections. This was particularly noticeable for
y.o.y. crabs seen in late summer and fall collections. On
30 January 1996 from beneath a triangular rock covering 0.18 m2 of relatively flat, solid surface in the middle
intertidal, 56 crabs (28 males, 3.5 to 14.0 mm, mean
7.232.54 mm; 28 females, 4.2 to 14.7 mm, mean
6.732.56; at least 46 were y.o.y.) were collected. This
represents 320 crabs m 2, a minimum value because
Intertidal associates
At Townsends Inlet crabs were collected from the southern end of the bridge spanning the Inlet, and at Hereford
Inlet from underneath rocks at both sides of a bridge
and from a rocky jetty extending into the surf. In the
warmer months they were generally captured in the
upper to middle intertidal zone, which had a heavy
growth of the brown alga, Fucus vesiculosus, large
numbers of acorn barnacles, Semibalanus balanoides,
and some blue mussels, Mytilus edulis. Most of
the mussel population, however, was in the deeper
intertidal.
Other animals and plants making up the intertidal
community at Townsends Inlet are listed in Table 1.
These include eight other species of brachyurans, of
which the xanthids Panopeus herbstii and Dyspanopeus
sayi and the portunid Carcinus maenas are dominant.
Except for Carcinus, which encroaches somewhat into
the upper intertidal Hemigrapsus habitat, all the other
brachyurans inhabit the lower third of the intertidal and
shallow subtidal zones. At low tide periods Hemigrapsus
moves to lower levels to feed, and at these times has been
found under the rocks together with Carcinus and
Panopeus. The numbers and size ranges of all the
sympatric brachyurans encountered at Townsend Inlet
are given in Table 2.
No attempts were made to collect crabs subtidally.
However, in spring intertidal collections from the THI
site and Great Egg Harbor Inlet, 34 crabs had attached
epifaunal species that indicated subtidal excursions during the preceding winter. The encrusting cheilostome
bryozoan, Conopeum tenuissimum, a normally free-living
species found abundantly in New Jersey (pers. obs.) and
elsewhere along the coast (Dudley, 1973a,b), was found
on the carapaces of 15 crabs. The encrusting ctenostome
bryozoan, Alcyonidium sp., covered the carapace of
another. Eleven crabs collected in late March and April
of 1993 and 1994, harbored many minute spat (]1 mm
or less in length) of Mytilus edulis, attached to hairs at
the base of the legs. Three crabs had byssus threads
(from larger mussels) attached to their carapaces. Four
crabs collected in April, May and June harbored
The western Pacific brachyuran, Hemigrapsus sanguineus
Table 1. Flora and fauna associated with Hemigrapsus sanguineus in the rocky intertidal of Townsends Inlet, New Jersey.
Species within major taxa are listed alphabetically.
Species
Chlorophyta
Bryopsis plumosa
Cladophora sp.
Codium fragile
Enteromorpha spp.*
Ulva lactuca*
Phaeophyta
Chorda sp.
Fucus vesiculosus*
Punctaria latifolia
Scytosiphon lomentaria
Rhodophyta
Agardhiella tenera
Ceramium sp.
Polysiphonia spp.
Porphyra sp.
Cnidaria
Haliplanella luciae
Metridium senile
Obelia sp.
Nemertea
Lineus socialis
Bryozoa
Alcyonidium polyoum†
Amathia vidovici
Conopeum tenuissimum§
Schizoporella unicornis
Polychaeta
Glycera sp.
Hydroides dianthus
Lepidonotus squamatus
Nereis succinea
Spirorbis violaceus
Species
Gastropoda
Doridella obscura
Littorina littorea*
Urosalpinx cinerea
Bivalvia
Anomia simplex
Crassostrea virginica
Mytilus edulis*
Petricola pholadiformis
Cirripedia
Balanus eburneus
Balanus improvisus
Semibalanus balanoides*
Isopoda
Sphaeroma quadridentata
Amphipoda
Gammarus palustris
Hyale plumulosa*
Unciola dissimilis
Decapoda
Cancer irroratus
Carcinus maenas*
Cronius ruber
Eurypanopeus depressus*
Libinia emarginata
Dyspanopeus sayi*
Pagurus longicarpus
Panopeus herbstii*
Uca pugnax
Echinodermata
Asterias forbesi
*Common.
†Found on carapace of C. irroratus and H. sanguineus.
§Found on carapace and legs of H. sanguineus.
barnacles, two hosting Balanus improvisus, one Semibalanus balanoides, and one an unidentified Balanus.
None of these spring-collected crabs was near terminal
molt; thus they presumably had acquired their subtidal
epifauna during the winter, and would lose it in their
first summer edysis in the intertidal. Although epifauna
were not usually found at other times of the year, a very
large (43.9 mm) male, collected in July 1992 at Sandy
Hook harbored 6 barnacles (three immature Chelonibia
patula and two B. improvisus), and 11 other mature
individuals collected in July, September and October,
when crabs would not be expected to be subtidal,
harbored evidence of subtidal epifauna. Nine carried the
remains of byssus threads from mature mussels that
were formerly attached to the crabs’ carapaces. Obviously, these crabs had spent time among mussels near
the subtidal level. A large 38.9 mm male crab collected
September 1994 from the jetty at Hereford Inlet had two
293
living Balanus improvisus attached, and must have spent
some time subtidally (either in the winter, if it had not
molted since then, or more recently during the spring or
summer). An even larger male (40.5 mm) hosting 38
S. balanoides was collected using SCUBA in June 1996
from among boulders of the Shark River Inlet jetty.
Nearly all the crabs (>1000) from New Jersey
were examined for the externae of rhizocephalan
barnacles, and prior to preservation they were examined
internally for evidence of these barnacles, as well as
for parasitic isopods (Bopyridae and Entoniscidae),
metacercariae of digenetic trematodes, and nemerteans
(e.g., Carcinonemertes spp.). All crabs were negative.
Size distribution and morphometric relations
Males were more abundant and tended to be larger than
females (Fig. 5). The largest male was a specimen
collected at Sandy Hook (CW 43.9 mm, CL 36.2 mm).
Its dirty eroded exoskeleton and the presence of barnacles on the carapace and legs indicate that it had
probably reached its terminal molt. The largest New
Jersey female collected so far is the original ovigerous
specimen (35.8 mm) discovered in Townsends Inlet.
The linear relationships between CW and CL are
similar for each sex, CW being the larger dimension for
both males and females over the whole size range
represented (Fig. 6). Males are heavier than females at
equivalent CW (Fig. 7). The smallest male and female
crabs (<3 mm) weighed <0.010 g, while the largest male
(43.9 mm) and female (31.1 mm) weighed 39.0 g and
10.3 g, respectively. A weight was not recorded for the
35.8 mm ovigerous female collected in 1988, but employing the equation in Figure 6, it probably weighed ]18 g.
It is not surprising that females weigh less than males at
equivalent CW because their chelipeds are much smaller.
Recruitment
In New Jersey, ovigerous H. sanguineus occur from
late April through September. Females may become
ovigerous at ]12.0 mm, and at least two broods of
embryos are produced in a season. Large crabs may
produce broods of >40 000 (McDermott, 1991a, 1992).
Recruitment of new crabs begins as early as June, and
continues throughout the summer into the fall and
winter (Fig. 8). The peak of crabs <10 mm in March–
April represents the previous year’s recruitment, and this
is followed in June by a new cohort of crabs <6 mm. By
September–October this cohort is represented by the
peak in crabs <10 mm.
Discussion
Introduction and spread of H. sanguineus
There will never be satisfactory evidence to pinpoint the
precise site(s) of introduction of H. sanguineus into the
294
John J. McDermott
Table 2. Numbers and carapace widths (mm) of brachyurans other than H. sanguineus collected in the
intertidal zone at Townsends Inlet, New Jersey (1990–1994).
Species
Eurypanopeus depressus
Dyspanopeus sayi
Panopeus herbstii
Carcinus maenas
Cronius ruber†
Cancer irroratus
Libinia emarginata
Uca pugnax
n
Males
Means.d.
15
73
131
36
1
11
16.1 4.2
13.5 3.9
15.9 5.7
16.211.4
27.5
50.422.3
Range
n
Females
Means.d.
Range
Total
10.0–22.0
7.3–24.7
4.0–32.6
5.9–67.3
18
18
73
45
14.0 2.7
10.1 2.9
15.4 4.1
17.911.8
7.8–19.9
4.5–17.6
7.2–23.3
6.3–50.3
33
90
204
81
14.5–104.4
8
1
2
37.410.6
49.2
12.7 1.3
25.4–53.0
19
1
2
11.8–13.6
†Juvenile male (carapace length 16.6 mm) collected 20 October 1992 in a torpid condition (air
temperature 5.5C); only second record for this portunid in New Jersey (Williams, 1984).
60
Male
n = 649
40
Frequency
20
0
Female
n = 528
20
40
60
0
10
20
30
40
Carapace width (1.0 mm classes)
50
Figure 5. Frequency distribution of 1.0 mm CW classes of male
and female Hemigrapsus sanguineus randomly collected from all
locations in New Jersey (Sandy Hook south to Hereford Inlet),
based on 74 individual collections 1988 to 1996. Most crabs
(1102 of 1177=93.6%) were from the Townsends Inlet–
Hereford Inlet area in the southern part of the state. Male–
female sex ratio 1.23.
Atlantic Ocean, but it may have been near the site of
the first discovery in 1988. For more than thirty years
prior to 1988 I had been collecting marine coastal fauna
in New Jersey, and had this species been there at its
present abundance it would have been detected. The size
of the first recorded specimen, found along the coast of
southern New Jersey in September 1988, indicates that it
was approximately three-years-old when collected (cf.
Fukui, 1988), and thus it could have been in Atlantic
waters at least since the mid-1980s. The fact that this
large female was ovigerous presupposes the presence of
at least one male at the site in 1988.
It was not until 1994 that I began to receive reports
and inquiries about this species from other states. R.
Clarke (pers. comm.) first found Hemigrapsus at Pelham
Bay Park, Bronx, New York in September 1994, a
location he had collected 13 times since 1987 without
previously finding Hemigrapsus. This suggests that the
species may have secondarily colonized Pelham Bay,
probably from the south. B. Whitman reported to me in
July 1996 that Hemigrapsus in western Long Island
Sound was then about five times more abundant than
when she first reported its presence in 1994. This plus my
own evidence of rapidly increasing abundance at THI
suggests that the successful introduction of H. sanguineus into the western Atlantic dates to the early
1980s.
The species may be extending its distribution both
north and south. The present known distribution of
H. sanguineus along the Atlantic coast from below Cape
Ann, Massachusetts to Oregon Inlet, North Carolina
(]36 to 42N, or 6 of latitude), a distance of approximately 800 km, is about one-fifth of its latitudinal distribution in the Pacific (]22 to 50N, a distance of
3700 km).
Documentation of the southern range limit of H.
sanguineus in the Atlantic is somewhat tentative. In
addition to myself, G. Ruiz (pers. comm. December
1995) has found the species at Oregon Inlet, NC (36N
latitude, its known southern limit), but not near
Beaufort, NC approximately 160 km to the southwest.
R. Dimock (pers. comm. December 1995), who has
taught a summer course in invertebrate zoology at the
Duke Marine Laboratory in several recent years, also
has not seen H. sanguineus in the Beaufort area. In April
1996 I also failed to find it in an intertidal rock-fill at
Beaufort.
Temperature doubtless influences the present distribution of H. sanguineus in the Pacific, and will probably
influence its final geographic distribution in the Atlantic.
The temperature range encompassing the overall distribution of the crab in the Pacific is similar to the
temperature range in the western Atlantic from Maine to
The western Pacific brachyuran, Hemigrapsus sanguineus
40
2
2
R = 0.999
1
30
log Weight (g)
Carapace length (mm)
y = 0.19332 + 0.86824x
n = 605
20
2
R = 0.996
R2 = 0.996
0
–1
10
Male
0
y = –3.5067 + 3.1320x
n = 224
y = –3.4266 + 3.0150x
n = 162
295
10
20
30
Carapace width (mm)
40
50
–2
0.4
0.6
0.8
1.0
1.2
1.4
log Carapace width (mm)
1.6
1.8
Figure 7. Relationship of log wet weight to log carapace width
for male (open squares) and female (closed squares) Hemigrapsus sanguineus collected in New Jersey from 1991 to 1996.
Ovigerous crabs not included. The slopes for males and females
are significantly different (ANCOVA, F=33.84, p=c0.0001).
40
Carapace length (mm)
y = 0.22805 + 0.84948x
n = 481
R2 = 0.998
30
20
10
Female
0
10
20
30
Carapace width (mm)
40
not inhibit expansion further to the north. New Jersey is
at about the same latitude (39 to 41N) as northern
Honshu in Japan, which is about 640 km north of
Tanabe Bay, but over 1100 km south of the northern
known limit of H. sanguineus at Sakhalin Island in
Russia (]50N). Takahashi et al. (1985) studied a large
reproducing population of H. sanguineus from Oshoro
Bay in western Hokkaido at ]43N, which is equivalent
to the latitude of southern Maine. Water temperatures in
Oshoro Bay during the winter of 1984 (January to
March) were below 5C, which is equivalent to surface
water temperatures at the same latitude in the Gulf of
Maine (Bigelow, 1928). Intertidal and near subtidal
temperatures in both locations would be even lower.
50
Figure 6. Relationship of carapace length to carapace width for
male and female Hemigrapsus sanguineus collected in New
Jersey from 1988 to 1996.
Florida. Tanabe Bay in Japan, where Fukui (1988)
collected very large numbers of crabs, is at ]3240N, a
latitude corresponding to the southern coast of North
Carolina (Cape Fear). Fukui (1993) showed that the
mean monthly water temperatures in the Bay ranged
from 14C in February to 27C in August. These upper
temperature extremes exceed those at THI, suggesting a
strong potential for extension of the crab’s range southward in the Atlantic if favourable rocky habitats are
available.
Winter water temperatures experienced by crab
populations north of its present Atlantic range should
Interaction with Atlantic brachyurans
Competition from established intertidal species of
brachyurans is another factor that may affect the final
Atlantic distribution of H. sanguineus. Xanthid crabs
mostly inhabit the lower intertidal and subtidal levels;
even though they also wander into the mid-intertidal,
it is improbable that the xanthids will outcompete
Hemigrapsus in the latter’s preferred habitat, and vice
versa. However, Carcinus maenas, itself introduced from
the eastern north Atlantic (Williams, 1984), is a relatively cold water, essentially intertidal species that could
be a major competitor of Hemigrapsus. The southern
limit of C. maenas is Virginia (Williams, 1984), but New
Jersey seems to be a transition zone between a marked
northern abundance and a distinct reduction to the
south. In New Jersey Carcinus does not normally occupy
the upper intertidal zone preferred by H. sanguineus, but
296
John J. McDermott
30
there is distinct overlapping of the two species in the
mid-intertidal. North of New Jersey Carcinus seems to
be well represented in the upper intertidal (pers. comm.:
R. Clarke, crabs in western Long Island Sound; C.
Boyko, Rhode Island; C. Wright, north of the Cape Cod
Canal). Evidently both young and adult Hemigrapsus
are sharing and possibly competing for living space with
Carcinus in New England waters. Both species are
omnivorous (pers. obs. on H. sanguineus; Ropes, 1968,
1989 for Carcinus), but their food preferences and
different capabilities for opening shelled prey (e.g.
barnacles and mussels) have yet to be compared.
These factors may eventually determine the long-term
compatibility or incompatibility of the two species.
In warmer Atlantic waters there may also be competition for Hemigrapsus from native species of its own
family, the Grapsidae. From New Jersey northward the
only native grapsid crab is Sesarma reticulatum (Say,
1817), a rather sluggish species that lives in intertidal
muddy burrows generally at the edges of saltmarshes
(pers. ob.; Williams, 1984). This habitat is distinct
from that of H. sanguineus. South of New Jersey
H. sanguineus overlaps with Armases cinereum, a swiftly
moving grapsid found in the supralittoral zone of
marshes, on wharves and rocky jetties from Chesapeake
Bay to Mexico (Williams, 1984). Although in 1995 I
found both H. sanguineus and A. cinereum in the upper
rocky intertidal at Oregon Inlet, my experience with
A. cinereum is that it is usually more terrestrially oriented than H. sanguineus; moreover, A. cinereum is
endowed with adaptations that suggest a supralittoral
existence (Gray, 1957; Bliss, 1968; Horn, 1968). Nevertheless, there is habitat overlap, and it remains to be
determined how much competition occurs.
Within the potential southern range of H. sanguineus
another species of high intertidal, grapsid crab could
become a competitor. The mottled shore crab Pachygrapsus transversus (Gibbes, 1850), a species inhabiting
rocky areas as well as other habitats, is distributed from
North Carolina to South America as well as in other
areas around the world (Williams, 1984). I have found
it to be common under intertidal rocks in Bermuda
(McDermott, 1991b), and it is abundant on the
sabellariid reefs of eastern Florida (Gore et al., 1978).
Studies of salinity tolerance, such as those of Kurata
(1962) and Watanabe (1982) plus preliminary experiments of my own, indicate that the mesohaline parts of
mid-Atlantic estuaries should also be vulnerable
to invasion by H. sanguineus, so competition from
Jan/Feb
n = 77
20
10
0
20
Mar/Apr
n = 153
10
0
20
May/Jun
n = 246
Percent frequency
10
0
Jul/Aug
n = 260
10
0
20
Sep/Oct
n = 389
10
0
Nov/Dec
n = 42
20
10
0
8
16
24
32
40
Carapace width (2.0 mm classes)
48
Figure 8. Frequency distribution of 2.0 mm carapace width
(CW) classes for combined male and female Hemigrapsus
sanguineus, randomly collected in New Jersey from 1988
to 1996, plotted in 2-month intervals to show trends in
the recruitment of young-of-year cohort represented by
crabs<10 mm in CW.
The western Pacific brachyuran, Hemigrapsus sanguineus
estuarine grapsids and other crabs is a factor to consider
as well. In Japan, H. sanguineus is known to overlap
with other grapsids in the lower parts of estuaries, but its
penetration into the upper reaches may be limited partially by the presence of at least four sympatric estuarine
grapsids (Kikuchi et al., 1981). In the mid-Atlantic
states, the only potential estuarine grapsid competitor
for H. sanguineus is Armases cinereum. The osmoregulatory capability of this species is probably very similar
to that of H. sanguineus; Seiple (1979) recorded it in
water from 0 to 34‰. However estuarine competition
between these species may be minimal because of A.
cinereum’s supralittoral preferences. North of New
Jersey, H. sanguineus may have estuarine competition
from Carcinus maenas, since the green crab has a similar
tolerance from brackish water (Williams, 1984) in
addition to its intertidal habitat overlap.
Other intertidal associates and parasitism
Rocky intertidal locations in the western Atlantic provide varied, abundant and renewable sources of food for
H. sanguineus. Evidence from stomach and faecal analyses and laboratory observations show that crabs feed
on diatoms, green algae, Mytilus edulis, Semibalanus
balanoides, amphipods and isopods (McDermott,
unpublished).
Although it is likely that epifaunal species occur on
H. sanguineus in the western Pacific, I have not seen
references to their occurrence. The epifauna reported
here suggest that some crabs spend time subtidally,
especially during the winter. Epifauna, particularly the
barnacles and encrusting bryozoans, may prove useful in
the future as biological tags for distinguishing different
populations of H. sanguineus in the western Atlantic.
In Japan, both male and female H. sanguineus are
parasitized by the rhizocephalan barnacle Sacculina
sp. at rates ranging from <1 to ]70% (Fukui, 1988;
Takahashi and Matsuura, 1994). Sacculina was not
found in the New Jersey population. Because H.
sanguineus presumably arrived in the Atlantic in its
planktonic larval state, the immigrants would not be
expected to have harboured invasive stages of Sacculina.
It remains to be seen, however, whether this or other
Pacific parasites of H. sanguineus eventually reach
Atlantic shores, or if any of the Atlantic’s native
parasites eventually exploit this new potential host.
Recruitment and population density
Fukui’s (1988) study on the life history of H. sanguineus
involved extensive collections (May 1981 to September
1982) on the coast of Tanabe Bay in southern Honshu.
Fukui found recruitment in Tanabe Bay from May
through the summer and into the winter; this corresponds closely to the recruitment period in New Jersey.
297
Locations harbouring crabs in New Jersey and elsewhere
to the south were covered with rocks, concrete fragments
and other fill having dimensions similar to those at
Fukui’s site in Japan. Fukui evidently was sampling a
very large population: he measured 13 695 specimens
from 16 collections, and the numbers per collection
ranged from 477 to 1556. In contrast, my monthly
collections at THI were much smaller: initially the crabs
were not abundant and difficult to collect, and through
most of my study period I was, in addition, being careful
not to overcollect. However, Fukui’s maximum
recorded densities of slightly more than 100 crabs m 2
are only about one-third of my single estimate of
320 crabs m 2 recorded from Townsends Inlet in 1996.
At Oshoro Bay in western Hokkaido, located at ]43N
and 1100 km north of Tanabe Bay, the maximum
density recorded by Takahashi et al. (1985) was
]55 crabs/m 2. Thus the population density of H.
sanguineus in New Jersey is at least up to the levels found
in Japanese waters.
Acknowledgements
I am grateful to the following individuals from Franklin
and Marshall College for their help during these studies:
J. L. Richardson (reviewing the manuscript); D. E.
Lofsvold, M. C. Shearer, and J. D. Williams (statistical
assistance); V. C. Abraham, J. P. Bernardi, G. J.
Cavanaugh, Jr, C. K. Cortese, R. A. Fluck, J. H.
Gillman, N. A. Lissy, T. L. Maccagnan, C. R. Shearer,
Jr, B. M. Sigman, and M. L. Stoklosa (field and laboratory assistance). A. J. Bejda and A. Phelan, of the
National Marine Fisheries Service, Highlands, NJ,
kindly directed me to a suitable collecting location.
For critical reviews of the manuscript, I thank J. N.
Kraeuter, Haskin Shellfish Research Laboratory,
Rutgers the State University of New Jersey, and
T. Takahashi, Department of Fisheries, Kyushu
University, Japan. I appreciate the combined efforts of
S. Green, A. B. Williams and M. Zehe, Smithsonian
Institution, for providing me with a translation of a
critical Japanese paper. Institutional grants from
Franklin and Marshall partially supported this study. I
am particularly in debt to the following for providing me
with geographical information, measurements or specimens of H. sanguineus: K. W. Able, Rutgers University
Marine Field Station, Tuckerton, NJ, K. Becker,
Rutgers University, Piscataway, NJ (SCUBA samples),
M. L. Botton, Fordham University, New York, NY
(SCUBA samples), C. Boyko, University of Rhode
Island, Kingston, J. T. Carlton, Williams College,
Mystic, CT, R. D. Clarke, Sarah Lawrence College,
Bronxville, NY, R. Dimock, Wake Forest University,
Winston-Salem, NC, D. R. Franz, Brooklyn College,
Brooklyn, NY, P. Dargel, Milford, CT, R. E. Knowlton,
George Washington University, Washington, D.C.,
298
John J. McDermott
A. M. Kuris, University of California, Santa Barbara,
K. T. Lee, Connecticut College, New London, G. M.
Ruiz, Smithsonian Environmental Center, Edgewater,
MD, K. Soltesz, Reed Wildlife Sanctuary, Rye, NY, A.
Starner, Thomas Jefferson High School for Science and
Technology, Alexandria, VA, F. W. Steimle, National
Marine Fisheries Service, Highlands, NJ, A. Totah, Jr,
Nature Center of Cape May, NJ, S. Tuleveck, Stockton
College, Pomona, NJ, M. Tyrrell, Stonehill College,
North Easton, MA, J. G. Walls, TFH Publications,
Neptune, NJ, B. Whitman, Terramor Marine Biology
Program, Monroe, CT, J. D. Williams, University of
Rhode Island, Kingston, C. Wright, Concord, NH.
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