Juv Dungeness lab study_10 Sept05

Growth of juvenile Dungeness Crabs (Cancer magister) reared in a laboratory from Southeastern Alaska

Mistee VinzantUniversity of Alaska Southeast

August 2005ABSTRACT

The Dungeness crab (Cancer magister), harvested throughout its range from California to Unalaska Island, express a complex life cycle with multiple planktonic stages. The transition from the planktonic larval stage to a benthic life style may be the most vulnerable point in its life history; however, little is known about early life stages in Alaska. To see if local growth patterns apply to other regions within the Pacific Northwest, juveniles were observed within a live holding tank from October 2004 to August 2005. 500 Dungeness megalopae from Bartlett Cove were collected from 3 battery-operated light traps that were attached to a public dock in October 2004. Megalopae were transported to the UAS Marine Lab to observe growth behavior of the juveniles. Size data from these lab-reared juveniles showed that the average CW for J1 instars were 6.59 mm (length: width ratio = 0.98), J2 instars were 9.17 mm (length: width ratio = 0.79), J3 instars were 11.65 mm (length: width ratio = 0.79), J4 instars were 13.04 mm (length: width ratio = 0.77)., and J5 instars were 12.64 (length:width ratio = 0.75). Not all of the juveniles reached the J5 growth stage by the end of the study. On the other hand, YOY juveniles ranged in size from 5.9 to 13.4mm CW, which represented approximately the first three instars. 1+ juveniles ranged from 9.7 to 15.23mm CW and mostly represented J3 and J4 instars. The year-class sizes found in this study are significantly smaller and younger than what has been known to occur in lower latitudes. These findings have significance in the ability to back calculate the age of field caught juveniles and can be used to predict juvenile and adult growth patterns for the fisheries in Southeastern Alaska.

INTRODUCTIONThe Dungeness crab (Cancer magister) is a soft bottom Cancrid that is sport and

commercially harvested throughout most of its range, from Southern California to Unalaska Island (Jensen and Armstrong, 1987; Iribarne et al., 1995). Sport and commercial harvest of Dungeness crab is productive in Southeastern Alaska, and the overall 2001-2002 commercial harvest in Southeastern Alaska was 4.1 million pounds worth nearly $7.4 million (Rumble and Bishop, 2002). Juvenile/adult growth rates are not well known and are variable in Alaska; however, the study of larval and juvenile transport is vital to predict Dungeness crab recruitment patters for the fisheries in Southeastern Alaska.

The Dungeness is a meroplanktonic, benthic crustacean that expresses a broadcast reproductive stragtey. Larvae are released around near-shore areas and hatch between January and June, depending upon latitude (Shirely et al., 1987; Reilly, 1983; Hobbs and Botsford, 1992). Dungeness crab larvae are independent and become planktotropic with teleplanic dispersal (i.e., the larvae are able to swim as plankton in the water column for more than 2 months). The larvae molt 5 times (5 zoeal stages and 1 megalopal stage) in the plankton before they metamorphose to a non-swimming juvenile stage and settle to the benthos in near-shore areas.

Glacier Bay National Park and Preserve (GBNPP) serves as the largest functional marine reserve in the United States. As a marine reserve, GBNPP has to sustain and protect the productivity of marine organisms through the increase of abundance and biodiversity (O’Clair et al., 1988). In order to meet conservational needs and marine reserve criteria, GBNPP has been closed to the commercial harvest of Dungeness crab and red king crab (Paralithodes camtschatucus) since 1999. Bartlett Cove in GBNPP may serve as an important nursery ground for the recruitment and development of juvenile Dungeness crabs. The rate of growth during juvenile development was measured in a laboratory setting and was compared to patterns from other regions in the Pacific Northwest. Since GBNPP is glacially active with cold water temperatures, it is predicted that growth of laboratory-reared juveniles will be considerably smaller and slower than warmer regions throughout the geographic range of the Dungeness crab.

METHODSDuring a low tide in October 2004, 500 Dungeness crab megalopae were

collected from 3 submerged light traps at a public dock in Bartlett Cove (Figure 1). The light traps were plastic, translucent 5-gallon containers with 4 funnels (one on each side with a 10mm diameter). The funnels allowed large brachyuran larvae to enter, while excluding unsolicited fish and other species that were attracted to the lights. The traps were battery operated with 2 Princeton Tec Attitude fluorescent, high intensity-dive lights (6 LED for each trap) to attract surface oriented plankton through vertical migrations. Each light trap contained a removable PVC pipe with 250 um mesh on the bottom to trap megalopae. For all tidal variations, the traps were tied to the public dock and were held in place by weights on the bottom and floats to keep the traps upright within one meter from the surface.

Figure 1: Collection site. Dungeness megalopae were gathered in Bartlett Cove in Glacier Bay National Park.

Live megalopae were transported and acclimated to a tank that provided a constant flow of ambient sea water and temperature at the UAS Marine Lab. To ensure that a constant food supply was available, all juveniles were fed more than they could eat once a week (most juveniles seemed to prefer salmon over herring). Juveniles were lumped together according to similar age and date of molt within plastic Gladware® containers. To minimize potential competition and stress, each plastic container housed no more than 5 juveniles. However, since cannibalism was more prevalent with older instars, juveniles at the J4 stage were kept alone in seperate containers. Information was gathered on the growth and age of all molts including a size frequency for each growth

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interval. When a crab molted, the new carapace width (CW) and length (CL) were recorded, as well as the time interval between growth stages. An ocular micrometer from a dissecting microscope was used to measure the change in carapace size. Measurements of CW included the 10th anterolateral spines and CL was measured from the longest point between the eye orbits to the posterior end of the carapace. In order to determine the mean carapace size and intermolt duration, data were exported and graphed in Excel. Comparisons of growth and frequency patterns were then produced with similar data from warmer regions around California and Washington States.

RESULTSCrab-size data from Bartlett Cove Dungeness crabs showed that the average CW

and CL for J1 instars were 6.59mmand 6.43mmrespectively; 9.17mm CW and 8.02mm CL for J2 instars; 11.65mm CW and 9.24mm CL for J3 instars; 13.04mm CW and 10.09mm CL for J4 instars; and 12.64mm CW and 9.54mm CL for J5 instars. On the other hand, YOY juveniles ranged in size from 5.9 to 13.4 mm (CW) and 5.8 to 13.2 mm (CL), which represented approximately the first three instars (Table 1). However, not all 1+ juveniles reached the J5 growth stage by the end of the study in August. The collected megalopae settled within 16 days of the study in late October. After the megalopae settled, molt intervals between J1 and J2 crabs ranged up to 18 weeks and up to 16 weeks between J2 and J3 crabs (Figure 2). J1 and J2 instars also appeared more circular in shape than the later ovoid instars (Figure 4). However, there was a noticeable size difference between the “early” instars. The morphological changes for each instar are represented and verified by the spacing in the carapace length:width ratios (Figure 3). The demonstrated mean length:width ratios for J1 instars were 0.98, 0.88 for J2 instars, and 0.79 for J3 instars, 0.77 for J4 instars, and 0.75 for J5 instars.

Size frequencies were noticeably different between “early” instars. J1 instars molted between mid October to early November (16 days), with the highest molt frequency in late October (Figure 5). J2 instars molted between late December - late January, with the peak in late December and mid January. J3 instars had longer molt durations than earlier crabs, late March - mid July. J5 instars should continue to molt for another 4 weeks. A relationship between molt frequency and temperature was also observed. The frequency of individual molts slowed down as the ambient seawater temperature decreased over the winter months (Figure 6). Molting did not take place when the tank seawater was the coldest (~4 oC). However, molting did take place in temperatures ranging between 5-9 oC.

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Table 1: Dungeness crab. Average carapace size of juveniles crabs up to the fourth instar (J4).

  J1 Instar J2 Instar J3 Instar J4 Instar J5 InstarCarapace Width (mm)          

Mean SD 6.59 0.36 9.17 0.38 11.65 ± 1.01 13.04 ± 0.94 12.64 ± 0.25

Maximum 8.2 9.9 14.04 14.34 12.84

Minimum 5.9 8.2 9.7 11.25 12.36

(N) 96 68 30 11 3

Carapace Length (mm)          

Mean SD 6.43 0.31 8.02 0.64 9.24 ± 0.61 10.09 ± 0.59 9.54 ± 0.10

Maximum 7.1 9.5 11.04 10.99 9.6

Minimum 5.8 7.3 8.25 8.85 9.42

(N) 96 68 30 11 3

Length:Width Ratio          

Mean 0.98 0.88 0.79 0.77 0.75

Molt Interval          

Range 18 Oct.-04 Nov. 26 Dec.-03 Feb. 19 Jan.-02 July N/A N/A

Days 17 38 163 N/A N/A

Average Molt Interval          

Range 20-28 Oct. 01-14 Jan. 09 March-19 June N/A N/A

Days 8 23 98 N/A N/A

0

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Date of Molt

Freq

uenc

y

J1 Instar, n=96J2 Instar, n=68J3 Instar, n=30J4 Instar, n=11J5 Instar, n=3

Figure 2: Dungeness crab. Number of molts for the first five instars from laboratory-reared juveniles.

0.65

0.70

0.75

0.80

0.85

0.90

0.95

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1.15

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Leng

th:W

idth

Rat

io

J1 Instar, n=96J2 Instar, n=68J3 Instar, n=30J4 Instar, n=11J5 Instar, n=3

Figure 3: Dungeness crab. Length:width vs. width ratios in for the first five instars from laboratory-reared juveniles.

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Figure 4: General overlay on the morphological changes (size and shape) between “early” instars.

0

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5 6 7 8 9 10 11 12 13 14 15

Carapace Width (mm)

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J1 Instar, n=96"J2 Instar, n=68"J3 Instar, n=30"J4 Instar, n=11"J5 Instar, n=3

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9

9/20/2004 11/9/2004 12/29/2004 2/17/2005 4/8/2005 5/28/2005

DateTe

mpe

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)

Figure 5: Dungeness crab. Size-frequency distributions Figure 6: Dungeness crab. Temperature of ambient of carapace width (mm) for juvenile instars. seawater for the duration of the study.

DISCUSSIONTemperature strongly affects Dungeness crab juvenile growth rates (Gutermuth

and Armstrong, 1989; Gunderson et al., 1990). Kondzela and Shirley (1993) observed a difference between Dungeness crabs from California and Southeastern Alaska waters with respect to megalopal/J1 instar timing of settlement and carapace size. There are differences in the timing of larval and juvenile stages for California, Washington, and Alaska (Table 2). Larval and juvenile life stage durations increase and growth rates decrease in higher latitudes. The data presented in this paper confirms that there is a difference in life stage durations and carapace size throughout the distribution of the Dungeness crab.

Table 2: Dungeness crab. Differences in growth and peak durations for various life stages (Puget Sound typically experiences colder inland water temperatures than Grays Harbor and was included to illustrate the effect temperature has on life stage durations).

Life Stage San Francisco Bay, CA Grays Harbor, WA Puget Sound, WA Southeastern AlaskaEgg Hatch January (1) January-February (3) January- February (3) May-June (7)

Zoeal ( I - IV) January-April (1) February-April (3) February-April (3) May-September (7)

Megalopae April (2) April (4) July (6) September-October (8)

Settlement May (2) May (4) August (6) September-October (8)

0+ Juvenile (CW) 7-58.6 mm (2) 11-54 mm (5) 5-30 mm (6) 6-9 mm (9)

1+ Juvenile (CW) 72-111 mm (2) 55-100 mm (5) 35-104 mm (6) 10-20 mm (9)

(1) Reilly, 1983; (2) Collier, 1983; (3) Hobbs and Botsford, 1992; (4) Stevens and Armstrong, 1985; (5) Armstrong Gunderson, 1985; (6) Dinnel et al., 1993; (7) Shirley et al., 1987; (8) G. Eckert, unpublished data; (9) M. Vinzant, unpublished data.

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J1 J2

J3

The settlement of larvae to J1 juveniles marked the beginning of the second pulse of settlement that typically occurs between September-October in Bartlett Cove (Eckert, unpublished data). Early settlers in the intertidal typically have a larger advantage over late settlers (Dinnel et al., 1993). Several studies from the Puget Sound area have suggested multiple molting pulses, or cohorts, of juveniles can occur from differences in hatch and settlement time (Dinnel et al., 1993; McMillan et al., 1995). Early settlers have an advantage because they experience more time for growth and development, move to the subtidal before the winter season, and contribute to the local fishery quicker than late settlers. (Dinnel et al., 1993). Settlement patterns of juvenile Dungeness crabs observed in Bartlett Cove may indicate that the second pulse of larvae are indeed late settlers and require an extended duration in the intertidal in order to develop and prepare for the migration to deeper water.

In this study, growth patterns of juvenile Dungeness crabs were measured to investigate possible relationships between larval settlement and molt frequency in order to stage field caught juveniles (back-calculate when they settled), as well as to predict juvenile and adult recruitment patterns for the fisheries in Southeast Alaska. It was expected that juvenile Dungeness crabs from Bartlett Cove would experience slower growth rates and longer molt intervals, as well as late settlement, compared to warmer regions around the Pacific Northwest. The data indicate that this may be the case since the average water temperature in Bartlett Cove is substantially lower (3-10 oC; H. Herter unpublished data) than UAS marine lab (4-9 oC; M. Vinzant unpublished data), and Puget Sound (7-10 oC; Dinnel et al., 1993).

ACKNOWLEDGEMENTSThis project was sponsored by the University of Alaska Southeast and was

performed to meet required criteria for an undergraduate research course. Computers and equipment was provided by the University of Alaska Southeast, Juneau Campus. The support and assistance from G. L. Eckert, R. F. Vinzant, and several other University of Alaska facility and students made this project possible. I thank them for their assistance.

REFERENCESArmstrong D., and Gunderson D. 1985. The role of estuaries in Dungeness crab early life history: a case

study in Grays Harbor, Washington. In: Proceedings of the Symposium on Dungeness Crab Biology and Management. Alaska Sea Grant Report No. 85-3. 145-170.

Collier P. 1983. Movement and growth of post-larval Dungeness crabs, Cancer magister, in the San Francisco area. In: In: Life history, environment, and mariculture studies of the Dungeness crab, Cancer magister, with emphasis on the central California fishery resource. Fish Bull 172: 125-134.

Dinnel P., Armstrong D., and McMillan R. 1993. Evidence for multiple recruitment-cohorts of Puget Sound Dungeness crab, Cancer magister. Marine Biology. 115: 53-63.

Gunderson D., Armstrong D., Shi Y., and NcConnaughey R. 1990. Patterns of estuarine use by juvenile English sole (Parphrys vetulus) and Dungeness crab (Cancer magister). Estuaries. 13(1): 59-71.

Gutermuth F., and Armstrong D. 1989. Temperature-dependent metabolic response of juvenile Dungeness crab Cancer magister Dana: ecological implications for estuarine and coastal populations. J. Exp. Mar. Biol. Ecol. 126: 135-144.

Hobbs R. C., and Botsford L. W. 1992. Diel vertical migration and timing of metamorphosis of larvae of the Dungeness crab Cancer magister. Marine Biology. 112. 417-428.

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Iribarne O., Armstrong D., and Fernandez M. 1995. Environmental impact of intertidal juvenile Dungeness crab habitat enhancement: effects on bivalves and crab foraging rate. J. Exp. Mar. Bio. Eco. 192: 173-194.

Jensen G., and Armstrong D. 1987. Range extensions of some northeastern Pacific decapoda. Crustaceana. 52: 215-217.

Kondzela C., and Shirley T. 1993. Survival, feeding, and growth of juvenile Dungeness crabs from Southeastern Alaska reared at different temperatures. Journal of Crustacean Biology. 13(1): 25-35.

McMillan R. O., Armstrong D. A., and Dinnel P. A. 1995. Comparison of intertidal habitat use and growth rates of two northern Puget Sound cohorts of 0+ age Dungeness crab, Cancer magister. Estuaries. 18 (2): 390-398.

O’Clair C., Stone R., and Freese L. 1988. Movements and habitat use of Dungeness crabs and the Glacier Bay fishery. Proceedings of the Second Glacier Bay Science Symposium. U.S. Department of the Interior. National Park Service. Alaska Regional Office. Anchorage, Alaska.

Reilly P. 1983. Dynamics of Dungeness crab, Cancer magister, larvae off central and northern California. In: Life history, environment, and mariculture studies of the Dungeness crab, Cancer magister, with emphasis on the central California fishery resource. Fish Bull 172: 57-84.

Rumble J., and Bishop G. 2002. Report to the Board of Fisheries, Southeast Alaska Dungeness crab fishery. Alaska Department of Fish and Game. Juneau, Alaska. Regional Information Report No. 1J02-45.

Shirley S. M., Shirley T. C., and Rice S. D. 1987. Latitudinal variation in the Dungeness crab, Cancer magister: zoeal morphology explained by incubation temperature. Mar. Bio. 95: 371-376.

Stevens B., and Armstrong D. 1985. Ecology, growth, and population dynamics of juvenile Dungeness crab, Cancer magister Dana, in Grays Harbor, Washington, 1980-1981. In: Proceedings of the Symposium on Dungeness Crab Biology and Management. Alaska Sea Grant Report No. 85-3. 119-134.

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