Herbivory by the Caribbean king crab on coral patch reefs

Caribbean coral reefs are increasingly dominated by macroalgae instead of corals due to several factors, including the decline of herbivores. Yet, virtually unknown is the role of crustacean macrograzers on coral reef macroalgae. We examined the effect of grazing by the Caribbean king crab (Mithrax spinosissimus) on coral patch reef algal communities in the Florida Keys, Florida (USA), by: (1) measuring crab selectivity and consumption of macroalgae, (2) estimating crab density, and (3) comparing the effect of crab herbivory to that of fishes. Mithrax prefers fleshy macroalgae, but it also consumes relatively unpalatable calcareous algae. Per capita grazing rates by Mithrax exceed those of most herbivorous fish, but Mithrax often occurs at low densities on reefs and its foraging activities are reduced in predator-rich environments. Therefore, the effects of grazing by Mithrax tend to be localized and when at low density contribute primarily to spatial heterogeneity in coral reef macroalgal communities.     

Patterns of growth and triacylglycerol content in snow crab Chionoecetes opilio (Brachyura: Majidae) zoeal stages reared in the laboratory

Snow carb Chionoecetes opilio zoea I and zoea II larvae, hatched from females in a controlled mating experiment, were reared in the laboratory at 10.1 °C and 28.0 salinity, to resolve the patterns of growth (dry weight [DW]) and change in energy reserves (triacylglycerols [TAG]) within a given moult cycle. The patterns of growth and change in TAG reserves were similar in each zoeal stage. Following hatching or a moult, the zoeae entered a phase of rapid size increase, i.e. high daily growth rates (5.5 to 12.8% DWd^-1), for 1/3 to 2/5 of the duration of the moult cycle. During the same period, the zoeae accumulated TAG reserves until a maximum (TAG DW^-1) was reached at the end of the phase of rapid growth. The period of high growth rates and of TAG accumulation is interpreted as the required time for the zoeae to reach a point in development [i.e. point of reserves saturation (PRS); Anger and Dawirs (1981)] where sufficient growth and energy reserves allow moulting to the next stage. Following the phase of rapid growth and TAG accumulation, the zoeae entered a phase of low daily growth rates (0 to 1% DWd^-1) during which the TAG reserves decreased to a minimum at the end of the phase. Prior to, and during the moult to zoea II, a phase of negative growth was observed in the zoea I larvae. We conclude that measurement of zoeal size and TAG content, along with morphometric criteria (e.g. epidermal retraction), can be used to assess growth and nutritional condition of C. opilio zoeal stages from the sea.     

Feeding,growth, and survival of Engraulis mordax larvae reared in the laboratory

Methods are described for the successful rearing of northern anchovy larvae (Engraulis mordax Girard) on cultured foods. Larvae were fed successively on the unarmored dinoflagellate Gymnodinium splendens, the veliger of the gastropod Bulla gouldiana, and nauplii of the brine shrimp Artemia salina. Rearing containers ranging in capacity from 4.5 to 510 l were tested; the smaller ones were found to be most useful for laboratory experimentation. Irreversible starvation occurred when E. mordax were denied food for more than 1.5 days after yolk absorption. Growth rates of larval anchovies fed different diets were compared. Larvae fed G. splendens grew for 1 week at the same rate as animals fed wild plankton, but did not maintain this rate. Laboratory survival of E. mordax larvae on a diet of G. splendens alone, did not differ significantly when veligers supplemented the diet. However, when G. splendens and veligers were fed simultaneously to E. mordax larvae, growth rate was greatly improved, although still not matching the growth attained on a diet of wild plankton. Length (L) versus weight (W) analyses were made for all larvae at all diets. The results showed that weight could be calculated most accurately from length by the relationship log W=3.3237 log L-3.8205, regardless of diet.     

Larval development of the hermit crab Clibanarius albidigitus (Crustacea: Anomura: Diogenidae) reared under laboratory conditions

The larval development of Clibanarius albidigitus Nobili is described and illustrated from laboratory-reared specimens. At 30°C, this species passes through four zoeal stages before molting to the megalopa. Of the 120 individual larvae reared, survival was high, with 88% reaching the megalopal stage. Zoeal stage durations varied from 3 to 18 d. Rearing was terminated after 45 d, and at that time no megalopae had molted to the firstcrab stage. Among known larvae of Clibanarius species, C. albidigitus is immediately distinguished by the presence of dorsomedial and dorsolateral carapace keels.     

Individual growth and size-selective mortality of larval turbot (Scophthalmus maximus) reared in enclosures

Larval turbot (Scophthalmus maximus) were reared in a large marine enclosure and in plastic bags in southern Norway. Samples of larvae in the enclosure were taken during the first 12 d of life to estimate individual body growth based on back calculations from daily growth rings on their otoliths. Size selective mortality was documented for these larvae in the predator-free enclosure. Starvation in the laboratory occurred on the seventh day. In the enclosure, a mortality rate of 18.1% d^-1 prevailed. Our data indicates that the survivors beyond the starvation period are larger by 0.18 mm on average. This result is important with regard to the question of whether starvation is an important mechanism for larval mortality in the sea. A possible means of estimating the relative effects of starvation versus predation based on these results and the backcalculation technique is suggested.     

Digestive enzymes in the ontogenetic stages of the southern king crab, Lithodes santolla

The early ontogenetic stages of the sub-Antarctic king crab Lithodes santolla were analyzed for the presence and activities of a set of important digestive enzymes. The eggs and non-feeding larvae (zoea I-III, megalopa) showed high activities of esterases, phosphatases, and exopeptidases indicating the enzymatic ability to utilize endogeneous yolk reserves. SDS-PAGE showed a continuous decrease of proteins or proteids in the range of 59–81 kDa during ontogenetic development from the eggs through the zoeal stages to the first juvenile crab stage, CI. This reduction reflects the degradation of storage compounds during lecithotrophic larval development. Activities of the endopeptidases, trypsin and chymotrypsin, were low in eggs and larvae but increased significantly in the first juvenile crab stage. These enzymes typically facilitate the first steps of proteolysis in the extra-cellular spaces of the midgut gland and in the stomach. Their scarcity indicates that the larvae of L. santolla are physiologically not prepared to digest external food. This ability seems to appear first in the CI stage. Extracts of juvenile midgut glands and the gastric fluids of adults showed high activities of a variety of digestive enzymes including phosphatases, carbohydrases, as well as endo- and exopeptidases. High activities of digestive enzymes in adults may compensate for scarce food supply and rate-limiting low temperatures in the predominantly sub-Antarctic habitats of L. santolla.     

Effects of non-circadian light/dark cycles on the growth and moulting of Palaemon elegans reared in the laboratory

The growth and moulting of Palaemon elegans Rathke has been compared under a circadian (12 h light: 12 h dark) and two non-circadian (8 h light:8 h dark and random light:dark) light/dark cycles. In prawns reared individually from hatching to the late juvenile phase, growth, measured as increase in total length, was significantly retarded in the non-circadian regimes, during zoeal, post-larval and early juvenile development. This effect was primarily the result of reduced increments at moulting in the non-circadian regimes. Growth of prawns reared from hatching to the post-larval phase, measured as wet and dry weights, was similarly reduced in a non-circadian regime. These effects support the hypothesis that the integrity of an animal's physiology is partially dependent on maintaining, through the action of daily environmental cycles, correct timing relationships between its oscillating sub-systems.     

Food and feeding habits of the king crab Paralithodes camtschatica near Kodiak Island,Alaska

Stomach contents from 809 king crabs, Paralithodes camtschatica (Tilesius), from 6 areas near Kodiak Island, Alaska, and 9 sampling periods (1978–1979) were exammed quantitatively; 713 (88%) contained food. Mollusca (mainly the bivalves Nuculana spp., Nucula tenuis, and Macoma spp.) and Crustacea (mainly barnacles) were the dominant food groups in terms of percentage wet weight and frequency of occurrence; fishes were the next most important group of prey. No significant differences in feeding between sexes occurred; however, significant differences were apparent in the quantity of food consumed from different sampling periods, areas, depths, size groups, and crab molt-classes. Consumption was greater in spring and summer and in offshore locations at depths of 126 to 150 m. In addition, king crabs <140 mm carapace length (CL) consumed more food than crabs 140 mm CL. Adult, newshell (individuals that molted during the last molting period) females greater than 95 mm CL, and newshell males greater than 100 mm CL, each contained more food than did juvenile, newshell females <120 mm CL.Contribution No. 449, Institute of Marine Science, University of Alaska, Fairbanks, Alaska 99701, USA     

Growth and reproduction ofCaprella danilevskii (Crustacea: Amphipoda) reared in the laboratory

Caprella danilevskii Czerniavski, an epifaunal amphipod crustacean, was successfully reared for two generations under laboratory conditions. Amphipods were maintained in pairs or fours in a Petri dish. Temperature and photoperiod were maintained at 20°C, and 14 h light: 10 h dark, respectively. Colonies of the diatomCylindrotheca closterium (Ehrenberg) Reumann and Lewin were provided as food source. The red algaGelidium amansii (Lamouroux) Lamouroux was used to provide an attachment substrate for the caprellids. Juveniles that emerged from the brood pouch were described as instar I. Subsequent instars were identified by molts. Juveniles molted successively at 2.5 to 6.5 d intervals. The body length of males at each instar increased exponentially, while that of females followed a sigmoid curve. A different pattern of flagellar segment addition in the antenna I of males and females was revealed. At the age of 20.8 d, females reached instar VII, and produced their first embryos. After 5.1 d, juveniles emerged from the brood pouch. On average, females produced 5.4 clutches successively at 5.0 d intervals. The number of offspring per spawning increased from 6.3 at instar VII to 22.0 at instar XII. The total number of offspring was 69.0 for a female throughout her life span.     

Effect of temperature and salinity on larval development of southern king crab (Lithodes antarcticus)

Larvae of Lithodes antarcticus Jacquinot were reared in October, 1981 from hatching to the glaucothoe stage at 16 temperature/salinity combinations (5.5°; 7.5°; 9.5° and 13.5°C; 26, 29, 32 and 35 S) to determine optimal environmental conditions for larval development. The highest survival percentage was obtained in the culture at 7.5°C and diminished according to temperature increase or decrease. High temperature cultures significantly shorten the larval life duration, but produce large mortalities. At 5.5°C mortality occurred almost exclusively during the moult to glaucothoe stage. Higher survival percentages were obtained as salinity was increased. In the lowest salinity culture (26 S) no zoea reached the post-larvae stage at culture temperatures. The best T/S combination was obtained at 7.5°C and 35 S, with a survival percentage of 29%. The shortest zoeal developments were obtained at 32 S in all culture temperatures. Salinity also affects larvae coloration: there is a pigment concentration on erythrophores, which causes a color decrease.     

Life history of a free-living marine nematode Daptonema normandicum reared in laboratory

Life history of a free-living meiobenthic nematode Daptonema normandicum (DeMan, 1890) was studied in the laboratory. Live specimens were primarily collected from the sewage outlet site near the mouth of the Mandovi estuary, Goa This species was the most dominant (> 67%) among the meiobenthic nematodes. Vertically, nematode abundance was highest at the surface sediment and correlated with the organic carbon and sediment chlorophyll-a. Considering their dominance in the meiofauna, attempts were made to rear D. normandicum in laboratory. Salinity of the culture medium was maintained at 14 to 17 PSU (same as the collection site). All the culture experiments were conducted in semisolid nutrient agar media at 27 +/- 2 degrees C temperature for 12 hr dark: 12 hr light conditions. The food consists primarily of an unidentified bacterium and mixed algae, but diatom and ciliates were also observed in culture. Females produced first batch of eggs at the age of 23 days. Gravid female normally carry 8-10 eggs. Embryonic development is completed in -72 hr and entire life cycle (egg to adult) was completed in 22-24 days. Average size of juveniles at the hatching was 0.189 mm. Young individuals attains a maximum size of 1.23 mm (male) and 1.04 mm (female) in -21-23 days. Growth, in terms of length was augmented upto 23rd day and ceased thereafter. The daily growth increment for the first 5 days was 0.01-0.04 mm which increased upto 0.05-0.08 mm d(-1) during the maturation (10-18 days). Male : female ratio was 1:2. In this laboratory study, we provided information on the embryonic development, the life cycle and ecology Our results demonstrated that D. normandicum can be reared successfully under the controlled conditions, suggesting possible use of this species in toxicological and aquaculture studies. The culture method described is very handy and can be applicable for rearing other meiobenthic species particularly the nematodes with comparable feeding habits.     

Larval mortality during export to the sea in the fiddler crab Uca minax

Dense populations of the fiddler crab Uca minax (Le Conte 1855) are common along tidally influenced freshwater rivers and streams >50 km from the sea. Adults do not migrate from inland sites to release larvae, but instead release them directly into an environment where the zoeae cannot survive. Laboratory salinity tolerance experiments were used to determine how long larvae from the inland-most population of U. minax along the Pee Dee River, South Carolina, USA can survive zero salinity compared to larvae from a brackish water population (salinity 5) near the mouth of Winyah Bay in the same estuary. Larvae from the brackish water population were also exposed to a salinity of 5 and their survival tracked. These experiments were conducted from May to August 2004 and 2005. To determine if inland larvae suffered significant mortality in transit due to salinity stress, current profiles were measured in the field and used to model the time taken by a larva using ebb-tide transport to travel to permissive salinities. The laboratory tolerance experiments showed that larvae from the inland freshwater population had LT50’s of 4–5 days at 0 salinity, which were significantly longer than those of the brackish water zoeae (2–3 days). Zoeae from the brackish water population survived for at least one larval molt at a salinity of 5 with LT 50’s of ∼12 days. Estimated travel times to reach permissive salinities from the inland-most population based on current profiles were 3–5 days for larvae using night-time only ebb-tide transport and 1.5–2.5 days for those using ebb-tide transport both day and night. Previously published field data indicate that U. minax larvae do use both day- and night-time ebb-tide transport, and are found in high densities in the water column during the day. These results lead to the conclusion that U. minax stage I zoeae do not undergo significant salinity-induced mortality during their 50+ km trip to the sea.     

The effects of partial mortality on the fecundity of three common Caribbean corals

The recent intensification of human disturbances in the Caribbean has increased the prevalence of partial mortality on coral colonies. Partial mortality can change colony size by directly shrinking colonies or by splitting colonies into fragments. A reduction in colony size can also adversely affect fecundity and fitness as internal resources shift away from reproduction toward colony maintenance. This study aimed to determine whether three Caribbean coral species, Siderastrea siderea, Montastraea faveolata, and Diploria strigosa, along the reef tract in Puerto Morelos, Mexico (20^o52′N, 86^o51′W), continued to dedicate resources to reproduction when colonies were fragmented to pre-maturation size. Contrary to expectations, eggs were found in colonies that were smaller than the maturation size and had been subjected to partial mortality. The continued dedication of resources toward reproduction, even in the smallest colonies, suggests that resource trade-offs away from reproduction are not as rigid as previously suggested in stressed corals.     

Morphological and functional development of larval and juvenile Limanda yokohamae (Pisces: Pleuronectidae) reared in the laboratory

Morphological and behavioural aspects in larval development need to be studied in detail to understand the early life history better, and to gain a comprehensive knowledge on early life stages for fish species important in aquaculture and fisheries. In the present study, larvae of Limanda yokohamae (Günther) were reared to observe their behavioural development, and to obtain specimens for studying the morphological features and the intestinal development at Ohno, Hiroshima, Japan, in 1987. Swimming activity was monitored at several larval stages, and swimming speed was recorded until settlement and after-feeding behaviour was initiated. A slight increment of swimming speed was observed with larval growth. Larvae changed their swimming behaviour from surface waters to the bottom of the rearing tank when their eyes began to move. Morphological development of pigmentation patterns, fin development, squamation and the development of the digestive tract were described and illustrated in detail to characterize development stages, especially those relating to metamorphosis. During metamorphosis, growth ceased and rapid changes in allometric growth were accompanied by differentiation of the digestive tract. After metamorphosis there was steady growth, allometric growth achieved a constant value, and both the scales and digestive organs were fully formed. Metamorphosis was therefore a crucial developmental milestone, including a critical phase during which survival potential was lowered.     

Influence of limited starvation periods on growth and elemental composition (C,N,H) of Carcinus maenas (Decapoda: Portunidae) larvae reared in the laboratory

Zoea-1 larvae of Carcinus maenas L. (Decapoda: Brachyura: Portunidae) were from Helgoland in March 1984 and reared in the laboratory at 18°C through ecdysis. Dry weight (DW) and elemental composition of carbon (C), nitrogen (N), and hydrogen (H) were analyzed in newly hatched zoea-1, after different initial starvation periods, and in newly moulted zoea-2. Continually starved zoea-1 lost biomass and energy steadily, and logarithmic functions show best fit of empirical and predicted data. Biomass and energy equivalents of newly moulted zoea-2 are significantly correlated with starvation periods in the zoea-1, showing lower values with longer initial starvation. After about 25 to 34% individual biomass and energy losses, larvae exceed the point-of-noreturn (PNR), and do not recover or moult to the zoea-2, even if re-fed. When starvation ceases before the PNR, larvae moult to the zoea-2, and develop with lower average growth rates (AGR) after prolonged periods of initial food deprivation. The later larvae were re-fed, the less absolute amounts of DW, C, H, and individual energy, but more DW-related energy equivalents and N accumulated during subsequent feeding towards ecdysis. It is suggested that lipid, rather than protein, is the main source of energy controlling the maintenance of larval moult cycles. After lipid reserves are depleted, zoea-1 larvae live on body protein, and lose the ability to absorb and restore sufficient lipid if re-fed later than the PNR.Contribution to research project An-145/1-1 granted by the Deutsche Forschungsgemeinschaft (DFG)     

Growth and average growth rates of tanner crab zoeae collected from the plankton

Growth of the two zoeal stages of Tanner crabs, Chionoecetes bairdi and C. opilio, was estimated by changes in total dry weight of individuals sampled from plankton of the southeastern Bering Sea during the springs of 1977, 1978, 1980 and 1981. Since the age of larvae within a stage cannot be determined, approximate beginning and end weights of each stage were used. Epidermal retraction, conspicuous under low magnification of a dissecting microscope, was used to identify larvae presumed to be in advanced stages of growth (biomass) for their respective larval stage. This assumption was corroborated by holding retracted larvae that subsequently molted on board ship, by comparison of dry weight measurements from extensive field sampling, and by the low proportion of larvae showing such conspicuous retraction. An exponential growth model was used to calculate the average daily growth rate based on estimates of stage duration in the field. The adequacy of this model for describing the average rate, rather than the pattern, of growth is discussed. Carbon-specific rates of respiration from discrete measurements and of growth averaged for each zoeal stage indicate average net growth efficiencies comparable to laboratory results for other species. The method used to estimate growth should be applicable to other larval decapods and offers the advantage of estimating this parameter from data gathered from natural populations.Contribution No. 652 of the School of Fisheries, University of Washington     

Abundance,breeding and growth of the crab Scylla serrata in two South African estuaries

Populations of the crab Scylla serrata (Forskal) were studied in two South African estuaries from 1971 until 1974. One estuary was open to the sea, the other was closed by a sandbar. Population density in the closed estuary was estimated by means of mark-release-recapture data from tagged crabs. The population of S. serrata was estimated as 1 crab/124m² and the production at 3.4 g/m²/annum. Catch per unit effort data from the closed estuary indicated a natural mortality of 41% in the crabs' second year and 60% in the third. Growth was studied in both estuaries by means of size-frequency analysis and from tagging returns. Growth was rapid in the first 12 to 15 months, when the crabs attained a carapace width of 80 to 160 mm. Thereafter growth slowed, and after 3 years crabs were between 140 and 180 mm in carapace width. Females mated in summer at a carapace width of 103 to 148 mm, males at 141 to 166 mm. After mating, females migrated out of both estuaries into the sea.     

Larval development of the spider crab Pisoides edwardsi (Decapoda,Brachyura) under laboratory conditions

Larvae of Pisoides edwardsi (Bell, 1835) have been reared in the laboratory at 2 different temperatures (13.8° and 18.5°C), from hatching to megalops stage. The two zoeal stages and the megalops, as well as the setation of the functional appendages are described and illustrated. The main characteristics useful to differentiate the larvae of P. edwardsi from those of Libidoclaea granaria, the other Chilean species belonging to the same sub-family, are discussed. Data on duration of zoeal development, length of moulting intervals, and mortality at the 2 test temperatures, are also given.This study was financially supported, in part, by the Chilean Ministry of Agriculture.     

Reproduction,growth and mortality of the holothurian Cucumaria pseudocurata

Certain phases of the ecology of a sea cucumber (Cucumaria pseudocurata Deichmann, 1938) population at Shell Beach, Sonoma County, California (USA), were investigated. The sea cucumber is a brooder, lays large (1 mm diameter) yolky eggs, which undergo direct development. It forms large aggregations in the rocky intertidal zone, extending from the lower boundary of the Mytilus californianus beds to about zero tide-level. The gonad cycle was followed from September, 1970 to January, 1972. Spawning occurred in January, 1971 and January, 1972. The holothurians produce from 1 to as many as 340 eggs, depending on the size of the individual; they completely spawn-out in a few days. Hatching takes place about 1 month after egg laying. The main sources of mortality are predation by the sea star Pycnopodia helianthoides and wave action. Survival of the young is negatively correlated with density of the aggregation. C. pseudocurata increases in weight 10 to 30 fold in the first year, but much more slowly in later years. Individuals live perhaps 5 years or more, and do not become reproductive until about the third year. Dispersal is accomplished by the young being washed away to a suitable new habitat. The upper range of the intertidal distribution is determined by exposure to air, and the lower range by P. helianthoides predation.Contribution No. 1 of the Bodega Marine Sciences Association.