Sherry L. Tamone

Changes in Embryonic Development and Hatching in Chionoecetes opilio (Snow Crab) With Variation in Incubation Temperature

Water temperature affects the distribution, movement, and reproductive potential of female snow crab, Chionoecetes opilio. Ovigerous females of C. opilio from the eastern Bering Sea were held at five temperatures (−1, 0, 1, 3, and 6 °C) in the laboratory while their embryos developed from gastrula to hatching. The duration of incubation increased by 105 d (30%) with decreasing temperature; however, a switch to a 2-year duration of embryo incubation was not observed. For females held at 6, 3, and 1 °C, their embryos underwent a short period of diapause late in development; no diapause was observed for embryos of females held at 0 or −1 °C. Successful extrusion of a subsequent clutch and hatch timing comparable with that observed in the eastern Bering Sea indicated that temperatures of 0 to 3 °C may be optimal for multiparous female reproduction. We demonstrated that a switch from 1-year to 2-year reproduction cannot be triggered by changing the thermal regime after several months of embryonic development. The timing of female movement from colder to warmer waters may be important for maintaining population reproductive potential during the recent phase of warming and contraction of cold-water biomes in the Bering Sea.

Effect of Eyestalk-Ablation on Circulating Ecdysteroids in Hemolymph of Snow Crabs, Chionoecetes opilio: Physiological Evidence for a Terminal Molt

Abstract Bering Sea snow crabs (Chionoecetes opilio) are a commercially important crab harvested in the Bering Sea. Optimal management of this species requires an understanding of the biology of this crab that is currently incomplete. Fisheries managers apply a continuous growth model in their management of snow crab, which assumes that male crabs increase in size throughout their lifespan. Male snow crabs undergo a morphometric molt that leads to a disproportionate increase in chelae size and it is still debated whether this molt is associated with a terminal molt. This study was conducted to determine whether adult male C. opilio are anecdysic. Using current knowledge of the hormonal regulation of crustacean growth, snow crab physiology was manipulated to induce an increase in molting hormones (ecdysteroids). Since female snow crabs are known to undergo a terminal molt after attaining reproductive maturity, we compared ecdysteroid levels in eyestalk-ablated terminally molted females, small-clawed males and large-clawed males. Snow crabs were collected from the Bering Sea and maintained in circulating seawater at approximately 6°C. Animals were either eyestalk-ablated or left intact. Ecdysteroid levels in hemolymph were quantified using an enzyme-linked immunosorbant assay (ELISA). Circulating ecdysteroids were significantly higher in small-clawed male crabs when compared to large-clawed males or terminally molted females. Eyestalk-ablation increased circulating ecdysteroids in small-clawed males, but had no significant effect on circulating ecdysteroids in large-clawed males or in terminally molted females.

The relationship between circulating ecdysteroids and chela allometry in male tanner crabs: Evidence for a terminal molt in the genus Chionoecetes

Abstract Whether male Tanner crabs, Chionoecetes bairdi, undergo a terminal molt associated with a change in claw allometry has long been debated. We measured molting hormone levels in captured male C. bairdi to assess the potential for molting. We plotted a frequency histogram of chela height to carapace width ratios and found a bimodal distribution of crabs with a ratio of approximately 0.18 separating the two modes. Male crabs with a ratio less than 0.18 were classified as “small-clawed” (SC) while crabs with a ratio greater than 0.18 were classified as “large-clawed” (LC). Circulating molting hormones between SC and LC crabs were compared. Significantly lower ecdysteroid levels were found in LC crabs, indicating that this morphotype had negligible potential for molting. Circulating ecdysteroids were measured in SC males of different shell conditions (soft, new, old, and very old) and no significant differences were found. This research suggests that the molt to LC morphology is a terminal molt. The results from this study have important implications for fisheries management because sub-legal LC males will not recruit into the fishery and removal of larger males may have long term effects on population size structure.

Comparison of first year growth among field, hatchery- and laboratory-raised juvenile red king crab, Paralithodes camtschaticus (Tilesius, 1815), in Alaska

In an effort to better understand juvenile growth in the first year and to determine potential effects of hatchery larval rearing, we compared growth of juvenile red king crab, Paralithodes camtschaticus (Tilesius, 1815), in the field and under laboratory-rearing conditions. Glaucothoe were obtained from the Alutiiq Pride Shellfish Hatchery and field; once molted to first stage juveniles, both sets were raised individually in the laboratory under ambient conditions (hereafter called hatchery/laboratory-reared and wild/laboratory-reared, respectively) and measured at each molt. Field-surveyed juveniles were observed and measured monthly in the intertidal in Juneau, AK, USA. Size, molt interval, cumulative molt interval, and molt increment did not differ significantly between hatchery/laboratory-reared and wild/laboratory-reared crab or between male and female crab over one year. Crab reached an average size ± SD of 13.6 ± 2.1 mm CL after 10-11 molts/year with 24% average molt increment at ambient temperatures. Carapace lengths of hatchery/laboratory-reared, wild/laboratory-reared, and field-surveyed juveniles were not significantly different in five of eight months from January through August, with small differences in January, February, and May, likely resulting from differences in hatch timing. Spine lengths differed from January through March but not from April through August. Spine lengths of hatchery/laboratory-reared crab were significantly larger than field-surveyed crab from January through March. Wild/laboratory-reared crab had significantly longer spine lengths than field-surveyed crab in February and March. In conclusion, growth did not differ significantly among juveniles reared in the laboratory and from the field.

CIRCULATING ECDYSTEROID CONCENTRATIONS IN ALASKAN DUNGENESS CRAB (CANCER MAGISTER)

Abstract The currently accepted reproductive cycle of Alaskan female Dungeness crab (Cancer magister) is that females molt and mate during summer and fall, extrude eggs in the fall, and incubate eggs through the winter until larval hatching in May and June. In this cycle, molting and mating are coincident with ovarian maturation. In this study, we quantified circulating concentrations of hemolymph ecdysteroids (molting hormones) in laboratory and field sampled crabs using an enzyme-linked immunosorbent assay (ELISA), for molt status assessment of individuals. Captive female crabs from southeastern Alaska (mean CW = 134.8 mm; n = 48) had a typical crustacean molt cycle profile of circulating ecdysteroids. Concentrations of ecdysteroids were low during intermolt (20.3 ± 0.7 ng/ml), maximal during premolt (1886.5 ± 186.2 ng/ml) 15 days before ecdysis and precipitously declined to low levels (< 90 ng/ml) 5 days prior to ecdysis. The duration of premolt was 150 days. Crabs held in captivity either molted (67%), extruded eggs (7%), or demonstrated no reproductive or molting activity (26%). Peak molting occurred in November for crabs held in the laboratory. Most (98%) of the female crabs sampled (n = 579) in Port Frederick, Alaska during the expected premolt period (May-July), had intermolt ecdysteroid concentrations. The capability to predict ecdysis 150 days prior to ecdysis by measuring ecdysteroid concentrations provides a useful tool to assess the molt status and timing of ecdysis in Alaskan Dungeness crab populations.

Linking Insects with Crustacea: Physiology of the Pancrustacea: An Introduction to the Symposium

Insects and crustaceans represent critical, dominant animal groups (by biomass and species number) in terrestrial and aquatic systems, respectively. Insects (hexapods) and crustaceans are historically grouped under separate taxonomic classes within the Phylum Arthropoda, and the research communities studying hexapods and crustaceans are quite distinct. More recently, the hexapods have been shown to be evolutionarily derived from basal crustaceans, and the clade Pancrustacea recognizes this relationship. This recent evolutionary perspective, and the fact that the Society for Integrative and Comparative Biology has strong communities in both invertebrate biology and insect physiology, provides the motivation for this symposium. Speakers in this symposium were selected because of their expertise in a particular field of insect or crustacean physiology, and paired in such a way as to provide a comparative view of the state of the current research in their respective fields. Presenters discussed what aspects of the physiological system are clearly conserved across insects and crustaceans and how cross-talk between researchers utilizing insects and crustaceans can fertilize understanding of such conserved systems. Speakers were also asked to identify strategies that would enable improved understanding of the evolution of physiological systems of the terrestrial insects from the aquatic crustaceans. The following collection of articles describes multiple recent advances in our understanding of Pancrustacean physiology.

Relationship of molting, gonadosomatic index, and methyl farnesoate in male snow crab (Chionoecetes opilio) from the eastern Bering Sea

Snow crabs, Chionoecetes opilio (Fabricius, 1788), have a complex mating system, and understanding their reproductive physiology is paramount to crab fishery management. Mating and molting are inextricably linked, so the energetically demanding molting process may compromise male mating potential for some period prior to and after the molt. Recently molted, new-shell males are targeted preferentially during the commercially valuable eastern Bering Sea (EBS) fishery. Old-shell males, or males that have not molted within the last year, are not as visually appealing, but may have greater reproductive capacity and can contribute disproportionately to the genetic stock. We measured a crustacean reproductive hormone, methyl farnesoate (MF), and reproductive fitness, using gonadosomatic index (GSI) as a proxy, in EBS male snow crab to determine differences in reproductive potential between adolescents and adults. We compared these reproductive indices in new- and old-shell males as a broad estimate of the effect of molting biology on reproduction. Circulating MF was significantly higher in new-shell adolescent males compared to old-shell adolescent males and old-shell adult males, suggesting a juvenilizing rather than gonadotropic role for MF in C. opilio. New-shell males had a significantly lower GSI compared to old-shell males for both adolescent and adult males. The lower GSI measured in new-shell adults compared to the significantly higher GSI levels measured in old-shell adults suggests that new-shell males harvested during the commercial fishery lack the reproductive capacity of the old-shelled adults and therefore may not be contributing equally to the population.

PUBLICATION IN THE JOURNAL OF CRUSTACEAN BIOLOGY

(FRS, correspondence: jcb@whidbey.com) General Editor, P.O. Box 1569, Langley, Washington 98260, U.S.A.; (STA) P.O. Box 14-901, Kilbirnie, Wellington, New Zealand; (KAC) Department of Integrative Biology, Brigham Young University, Provo, Utah 84602-5181, U.S.A.; (FG) Biologia Animale e Genetica, Università degli Studi di Firenze, Via Romana 17, I-50125, Firenze, Italy; (MJG) Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan; (KLL) CGS, Division of Natural Science, Boston University, Boston, Massachusetts 02215, U.S.A.; (GP) Museum Victoria, G.P.O. Box 666, Melbourne, Victoria 3001, Australia; (DCR) EcoAnalysts, Inc., 707 Dead Cat Alley, Woodland, California 95695, U.S.A.; (GS) Humboldt-Universität zu Belin, Institut für Biologie/ Vergleichende Zoologie, Philippstraße 13, D-10115 Berlin, Germany; (TS) U.S. Fish and Wildlife Service, 620 S. Walker St., Bloomington, Indiana 47403-2121, U.S.A.; (ST) Department of Biology, University of Alaska Southeast, 11120 Glacier Highway, Juneau, Alaska 99801, U.S.A.; (MW) Department of Biology, Texas A&M University, College Station, Texas 77843, U.S.A.