Stephen Sulkin

Laboratory study of survival and duration of individual zoeal stages as a function of temperature in the brachyuran crab Cancer magister

Larvae were hatched from ovigerous Dungeness crabs, Cancer magister, collected from Puget Sound Basin, Washington, USA, in April, 1986, and the effects of temperature on rates of survival and development were studied for each of the five zoeal stages both in small batch-culture and in individual culture. Culture method had little effect on the results at 10°, 15°, and 20°C. Increased mortality was measured at all stages at 20°C, with 100% mortality occurring during the terminal fifth stage. Fifth stage larvae may also show higher mortality at 15°C than at 10°C. Stage duration varied inversely with temperature at all stages, although differences between 10° and 15°C were greater than between 15° and 20°C. The results indicate that survival and stage duration are independent of the values for the previous and subsequent stages, that variability among larvae in instar duration increases with temperature, and that the terminal fifth zoeal stage is the most sensitive to temperature stress. Duration of a late zoeal instar is not related to its earlier development rate nor can early development rates be used to predict whether individual zoeae will successfully develop to the megalopa. Measurements of megalopa dry weights indicate no differences due either to previous culture temperatures or to total time to the megalopa. Predictive models of larval transport that require estimates of larval duration should account for both changes in temperature response that can affect individual stage duration, and variability among individuals in stage duration that can influence the degree of larval dispersion.

Influence of temperature on larval development of four co-occurring species of the brachyuran genus Cancer

Effects of temperature on zoeal development of Cancer productus, C. oregonensis, and C. gracilis collected from Puget Sound, Washington, USA, were determined and compared with published data on C. magister. Survival through zoeal development, mortality per individual zoeal instar, instar duration, and megalopa weight were determined for zoeae of each species raised in the laboratory at 10, 15, and 20°C. In contrast to larvae of C. magister, the larvae of both C. productus and C. gracilis survived to the megalopa at 20°C. Larvae of C. oregonensis, however, died by Zoeal Stage 3 at 20°C. Individual instar mortality rates varied as a function of temperature among species, reflecting different patterns of thermal tolerance through ontogeny. Zoeal duration varied inversely with temperature, although differences between 10 and 15°C were far greater than those between 15 and 20°C in each species. Duration of individual zoeal instars varied as a function of temperature and species. Megalopa weight was significantly reduced at 20°C in C. productus and C. gracilis, although no differences were measured between 10 and 15°C in any of the four species. Although literature reports indicate that reproductive output varies directly with adult size in these Cancer species, the larval traits measured here varied independent of body size.

Protists and detrital particles as prey for the first larval stage of the brachyuran crab, Hemigrapsus oregonensis

Abstract Newly-hatched larvae of the brachyuran crab, Hemigrapsus oregonensis, were raised in the laboratory on an autotrophic dinoflagellate (Prorocentrum micans), a heterotrophic dinoflagellate (Noctiluca milaris), a green alga (Dunaliella tertiolecta), an unfed control, and a fed control of Artemia sp. nauplii. Larvae also were fed preparations of seagrass detritus that had been cultured both to promote microbial colonization and to discourage it. Detrital diets were used both alone and in combination with sub-optimal applications of Artemia sp. nauplii. Larvae raised on P. micans showed survival to zoeal stage II equal to those raised on the Artemia sp. nauplii control, although development was delayed. Larvae raised on N. milaris showed substantial (34.7%) survival to zoeal stage II; however survival was lower and development slower than for Artemia sp. nauplii-fed larvae. Survival on D. tertiolecta was less than 3%. Larvae fed microbially-enriched detritus showed a delay in mortality as compared to unfed controls. No larvae fed solely on detritus survived to zoeal stage II. When larvae were fed a sub-optimal diet of Artemia nauplii, supplemented by detrital particles, survival to zoeal stage II increased, although not to the level shown by Artemia-fed larvae in optimal application. Development was not accelerated over the sub-optimal diet in either treatment. The potential for larval crabs to utilize a wide variety of potential prey immediately upon hatching is significant given their susceptibility to early starvation. Such omnivory also suggests a trophic link between carbon sources of the microbial loop and crab larvae.

Intraspecific Morphological Variability in Megalopae of Three Sympatric Species of the Genus Cancer (Brachyura: Cancridae)

ABSTRACT Selected morphological traits were documented for megalopae of Cancer magister, C. oregonensis,and C. productus collected at three sites within the Puget Sound basin and at two offshore sites in the eastern Pacific Ocean. Variation in selected traits was compared among species, among individuals within species, and among regions sampled. Traits selected for measurement were those proposed in the literature as diagnostic for identification of species of Cancer. For each of three species of Cancer collected, substantial intraspecific variability in size and appendage setation was documented. Although individual megalopae differed in selected morphological traits from published reports, published values were within the range of those measured in the present study. Significant differences among regions were determined for size and setation in C. magister, with the clearest differences being those between megalopae collected offshore and within the Puget Sound basin. Results indicate that megalopae of C. magister can be separated from those of C. productus and C. oregonensis by size alone, but that the latter two species cannot be separated with certainty on the basis of features described in the literature as diagnostic. Differences between offshore and inland water populations of megalopae of C. magister may reflect hydrographic features of the region and the megalopas site of origin. Variability in morphological traits must be included in any analysis of factors for species identification and may contribute to analysis of broader ecological issues.

Larval development of the crabCancer magister in temperature regimes simulating outer-coast and inland-water habitats

Postlarval megalopae of the Dungeness crabCancer magister inhabiting offshore coastal waters along the west toast of North America are larger and settle earlier than do those occupying the inland waters of the Puget Sound basin (Washington, USA, and British Columbia, Canada). The Puget Sound habitat is characterized by low initial temperatures that steadily increase during the course of zoeal development, while offshore temperatures are more moderate and stable. Larvae were raised in the laboratory from hatching to megalopa in three temperature treatments: (1) constant 10 °C (CO), (2) a regime that temporally simulated temperatures found off the central California coast during the larval season (CA); and (3) a regime simulating temperatures found within the Puget Sound basin (PS). Zoeal duration was 44% longer in the PS treatment than in the other two, at least partially accounting for observed differentes between outer-toast and inland-water settlement times. Although differentes were measured in megalopal weights and carapace lengths among treatments, results do not explain differences in megalopal size observed between outer-toast and inland-water individuals. Survival to megalopa was highest in the PS treatment, with the difference due to significantly lower mortality than in CO and CA treatments during the terminal zoeal stage. Daily instantaneous mortality rates were lower in the PS than in CO or CA treatments, indicating Chat extended larval duration will not necessarily result in reduced settlement success.

Effects of seismic energy releases on the survival and development of zoeal larvae of dungeness crab (Cancer magister)

In blind, controlled field experiments, early Stage II zoeae of Dungeness crab (Cancer magister DANA) were exposed to sounds from single discharges of a 13·8-litre array of seven air guns. Their survival and development were followed during subsequent laboratory culture. Immediate mortality was low (0 to 2%) and showed no significant difference between control and exposed larvae (α > 0·05). Across all treatments and blocks of the experiment, survival to the molt to Stage III averaged 88·8%. The conditional Stage IV survival rate averaged 69·8%. The times to the molts to Stage III and Stage IV averaged 14·4 and 34·9 days, respectively. For immediate and long-term survival and time to molt, the field experiment revealed no statistically significant (α > 0·05) effects on zoeae for exposures as close as I m from the array, nor for mean sound pressure as high as 231 dB re 1 μPa and cumulative energy density up to 251 J/M2. Post hoc power calculations showed that any reduction in zoeal survival as a result of sound exposure was less than 7% for survival to Stage III and less than 12% for Stage IV conditional survival (1-β = 0·90, α = 0·05 one-tailed). The sound exposures in our study were at the maximum levels likely to be experienced by a zoea during an actual survey.

Increasing Diversity in the Marine Sciences Through the Minorities in Marine Science Undergraduate Program

The Minorities in Marine Science Undergraduate Program (MIMSUP) is an academic program at Western Washington Universitys Shannon Point Marine Center (SPMC) that seeks to increase the representation of minority individuals in the marine sciences. For the past 13 years, groups of students have spent two 10-week quarters at SPMC studying marine science, doing independent research, and developing the skills needed for success as marine scientists/educators. Program elements include formal coursework in marine science, supervised independent research, training in up-to-date field and laboratory investigative techniques, experience developing scientific and personal job-related skills, and introduction to the career options open to marine scientists. Results indicate that the program is impacting the career paths of student participants; program alumni seek advanced education and pursue careers in the marine and environmental sciences. MIMSUP introduces underrepresented students to the marine sciences, helps them develop greater confidence in their potential, and prepares them for successful careers in this field.

ZOEAL DEVELOPMENT OF PALAPEDIA INTEGRA (DECAPODA: BRACHYURA: XANTHIDAE) REARED IN THE LABORATORY

Abstract Ovigerous crabs of the xanthid Palapedia integra were collected in South Korean waters, and their larvae were reared in the laboratory. Four zoeal stages are described and illustrated. The durations of zoeal stages I–IV were 4, 4, 4, and 6 days, respectively. Morphological characteristics of the first zoeal stage are compared with those of Palapedia valentini in the Kraussiinae and to other brachyuran species. The first zoea of P. integra is significantly different from that of P. valentini in having 3+4 setae on the endopod of the maxilla. Based on zoeal morphology, it is suggested that P. integra may not belong in the genus Palapedia.

EFFECTS OF PRIOR EXPOSURE TO PETROLEUM HYDROCARBON CONTAMINATION DURING BROODING ON THE SUBSEQUENT LARVAL DEVELOPMENT OF THE BRACHYURAN CRAB HEMIGRAPSUS OREGONENSIS

Larvae of the brachyuran crab Hemigrapsus oregonensis were raised in the laboratory from broods obtained from egg-bearing females collected at a site previously contaminated by a spill of crude petroleum hydrocarbons and from a site not recently contaminated. Larvae from both sites were raised throughout development on 2 diets of the rotifer Brachionus plicatilis, one in which the rotifer was cultured on the green alga Dunaliella tertiolecta, the other cultured on the brown alga Isochrysis galbana. Percentage mortality per stage for larvae from the contaminated site was equal to or lower than for larvae from the clean site. There was no difference in duration of zoeal development nor for megalopal weight for larvae from either site on either diet. Larvae raised on rotifers fed Dunaliella showed higher mortality during the fifth zoeal stage, longer zoeal duration for stages II-V, and lower megalopal weight than did those raised on rotifers fed Isochrysis. Results indicate that previous exposure to petroleum hydrocarbon contamination during brooding has no effect on subsequent zoeal development when larvae are not directly exposed to contamination. Differences in larval response to diet demonstrate that the nutritional value of heterotrophic prey will depend upon what the prey has previously fed upon, either in the laboratory or in nature. Marine organisms may be exposed to petroleum hydrocarbon contamination in coastal waters due to transport, exploration and development of petroleum resources, and episodes of mechanical and industrial failure (Burger and Gochfeld, 1992). Crabs that occupy shallow subtidal and intertidal habitats may be particularly susceptible to hydrocarbon exposure due to their sedentary life style that includes burrowing into the mud or hid

EFFECT OF STARVATION ON MEGALOPAL DEVELOPMENT IN THE BRACHYURAN CRAB HEMIGRAPSUS OREGONENSIS

The effect of starvation imposed at regular time intervals upon megalopal survival and duration was measured in the brachyuran crab Hemigrapsus oregonensis. Treatments included a fed control, starvation imposed after 5 days of feeding, starvation imposed after 10 days of feeding, and a total starvation control. Survival to metamorphosis did not occur in the Starvation Control. Survival measured 38% in the Day 5 treatment, and 85% and 80% in the Day 10 and Fed Control treatments, respectively. Time to metamorphosis was the same for surviving megalopae in all treatments. Feeding early during the megalopal instar appears sufficient to support successful metamorphosis in a substantial number of individuals, although the point beyond which feeding is no longer essential varies among individuals. Freedom from the need to satisfy metabolic or specific nutritional requirements during the latter part of megalopal development may permit the megalopa to adapt more effectively to the needs of the transition from the pelagic larva to the benthic adult. The megalopal stage of brachyuran crabs possesses traits that reflect its role in transition from the pelagic habitat of the zoea to the benthic habitat typical of most adults. Such traits may be morphological, physiological, and behavioral. Morphological traits are obvious, such as possession of adultlike thoracic appendages adapted for walking as well as specialized abdominal appendages that permit swimming. A number of authors have speculated that behaviorally mediated vertical distribution patterns of meg