The concept of biological control methods in aquaculture

Microbial techniques of biocontrol using the interaction ofmicroorganisms to repress the growth of deleterious bacteria andviruses were developed. The bacterial strain used in this work alsoimproved the growth of fishes and crustaceans. Using the conceptandprocedures of the biocontrol method described here, the aquacultureproduction became stable and evenincreased.     

Highly contrasted population genetic structures in a host–parasite pair in the Caribbean Sea

Evolution and population genetic structure of marine species across the Caribbean Sea are shaped by two complex factors: the geological history and the present pattern of marine currents. Characterizing and comparing the genetic structures of codistributed species, such as host–parasite associations, allow discriminating the relative importance of environmental factors and life history traits that influenced gene flow and demographic events. Using microsatellite and Cytochrome Oxidase I markers, we investigated if a host–parasite pair (the heart urchin Meoma ventricosa and its parasitic pea crab Dissodactylus primitivus) exhibits comparable population genetic structures in the Caribbean Sea and how the observed patterns match connectivity regions from predictive models and other taxa. Highly contrasting patterns were found: the host showed genetic homogeneity across the whole studied area, whereas the parasite displayed significant differentiation at regional and local scales. The genetic diversity of the parasitic crabs (both in microsatellites and COI) was distributed in two main groups, Panama–Jamaica–St Croix on the one hand, and the South‐Eastern Caribbean on the other. At a smaller geographical scale, Panamanian and Jamaican parasite populations were genetically more similar, while more genetic differentiation was found within the Lesser Antilles. Both species showed a signature of population expansion during the Quaternary. Some results match predictive models or data from previous studies (e.g., the Western‐Eastern dichotomy in the parasite) while others do not (e.g., genetic differentiation within the Lesser Antilles). The sharp dissimilarity of genetic structure of these codistributed species outlines the importance of population expansion events and/or contrasted patterns of gene flow. This might be linked to differences in several life history traits such as fecundity (higher for the host), swimming capacity of larval stages (higher for the parasite), and habitat availability (higher for the host).     

Modelling the biological invasion of Carcinus maenas (the European green crab)

This paper proposes a system of integro-difference equations to model the spread of Carcinus maenas, commonly called the European green crab, that causes severe damage to coastal ecosystems. A model with juvenile and adult classes is first studied. Here, standard theory of monotone operators for integro-difference equations can be applied and yields explicit formulas for the asymptotic spreading speeds of the juvenile and adult crabs. A second model including an infected class is considered by introducing a castrating parasite Sacculina carcini as a biological control agent. The dynamics are complicated and simulations reveal the occurrence of periodic solutions and stacked fronts. In this case, only conjectures can be made for the asymptotic spreading speeds because of the lack of mathematical theory for non-monotone operators. This paper also emphasizes the need for mathematical studies of non-monotone operators in heterogeneous environments and the existence of stacked front solutions in biological invasion models.     

Diet of Anguilla mossambica (Teleostei,Anguillidae) elvers in the Sundays River,Eastern Cape,South Africa

The southern African crab Hymenosoma orbiculare was recently split into five distinct species, of which three are estuarine/coastal and have peripatric distributions that are linked to temperature-defined marine bioregions. This suggests that the species’ ranges may be limited by physiological adaptations to their thermal environment. We explored this hypothesis by rearing the larvae of the warm-temperate lineage of H. orbiculare and the warm-temperate/subtropical H. longicrure at a range of water temperatures, and found clear temperature-dependent differences in the duration of larval development. Our study contributes to the growing body of evidence that stresses the importance of adaptation to regional environmental conditions, rather than physical dispersal barriers on their own, in limiting the mixing of marine species between temperature-defined biogeographic regions.     

Temporal variation in abundance of the egg predator Carcinonemertes epialti (Nemertea) and its effect on egg mortality of its host,the shore crab,Hemigrapsus oregonensis

An outbreak of the nemertean, Carcinonemertes epialti, was observed on Hemigrapsus oregonensis during October, 1982 at Campbell Cove, Bodega Harbor, California. Mean worm intensity (296 worms/crab) was the highest recorded for this nemertean egg predator on H. oregonensis. During the outbreak, male crabs were found to harbor more worms than both non-ovigerous and ovigerous females. Crab egg mortality was substantial; 83% of the ovigerous females experienced 75–100% brood mortality. The seasonal peak in worm abundance coincided with the seasonal low in crab reproduction at this locality. A method for estimating the impact of C. epialti on H. oregonensis natality was developed using crab size and fecundity, and worm prevalence and intensity. For a non-outbreak sampling period, a mean of 5.6% egg mortality was experienced by infested crabs for the period selected. Thus, brood mortality during the outbreak was much greater than that experienced at non-outbreak periods. Heavy fishing pressure on some commercially important crab species has been suggested as a possible factor inducing worm outbreaks and facilitating their continued persistence. These observations suggest that fisheries are not necessarily responsible for the outbreaks of nemerteans on commercially important crab species. However, fishing pressure may still be a sufficient condition to promote nemertean outbreaks.     

Gastric processing and evacuation during emersion in the red rock crab, Cancer productus

The passage of a radio-opaque meal was followed through the digestive system of the red rock crab, Cancer productus, using a fluoroscope. When the crabs were maintained in seawater, the food was apparent in the foregut as soon as the animals had fed. Release of food from the foregut was routinely slow and digesta appeared in the midgut only in small amounts at any one time. The foregut was emptied between 24 and 36 h, digesta was cleared from the midgut region at 36 h and by 48 h only a small amount of residual digesta was left in the posterior part of the hindgut. Contractions of the cardiac region of the foregut were somewhat sporadic and ranged between 6 and 11 min^-1. Contractions of the pyloric region were more stable, varying between 45-65 min^-1. In both cases, there was no change in rate during 18 h period in seawater. When crabs were subjected to both short- and long-term aerial exposure, release of food from the foregut was halted for the first 4-6 h of emersion. Although, small amounts of digesta appeared in the midgut and hindgut, there was no significant change in the amount in each region during emersion. There was a trend towards a depression of cardiac stomach contraction rates, but this was only significant in 3 h postprandial crabs during short-term emersion. A pronounced decrease in pyloric stomach contraction rate was maintained for the duration of the aerial exposure. When crabs were returned to seawater, contraction rates took 3-5 h to return to normal, but no significant change in gastric evacuation was observed during this period. During re-immersion, over 65% of the animals regurgitated the stomach contents. This regurgitation may act as a protective mechanism to avoid digestion and the subsequent specific dynamic action. The decrease in gastric processing in C. productus is probably part of an overall metabolic depression occurring during emersion.     

The genetic variability of the red king crab, <Emphasis Type="Italic">Paralithodes camtschatica</Emphasis> (Tilesius, 1815) (Anomura,Lithodidae) introduced into the Barents Sea compared with samples from the Bering Sea and Kamchatka region using eleven microsatellite loci

The intentional introduction of red king crab, Paralithodes camtschatica (Tilesius, 1815) in the Barents Sea represent one of a few successful cases and one that now supports a commercial fishery. Introductions of alien species into new environments are often associated with genetic bottlenecks, which cause a reduction in the genetic variation, and this could be important for the spreading potential of the species in the Atlantic Ocean. Red king crab samples collected in the Varangerfjord located on the Barents Sea (northern Norway) were compared with reference crab samples collected from the Bering Sea and Kamchatka regions in the Pacific Ocean. All samples were screened for eleven microsatellite loci, based on the development of species-specific primers. The observed number of alleles per locus was similar, and no reduction in genetic variation, including gene diversity and allelic richness, was detected between the Varangerfjord sample and the reference sample from Okhotsk Sea near Kamchatka, indicating no genetic bottlenecking at least for the microsatellite loci investigated. The same results were found in comparison with the sample from Bering Sea. The level of genetic differentiation among the samples, measured as overall F _ST across all loci, was relatively low (0.0238) with a range of 0.0035–0.1000 for the various loci investigated. The largest pairwise F _ST values were found between the Bering Sea and Varangerfjord/Barents Sea samples, with a value of 0.0194 across all loci tested. The lowest value (0.0101) was found between the Varangerfjord and Kamchatka samples. Genetic differentiation based on exact tests on allele frequencies revealed highly significant differences between all pairwise comparisons. The high level of genetic variation found in the Varangerfjord/Barents Sea sample could be of significance with respect to further spreading of the species to other regions in the North Atlantic Ocean.     

Reduced byssal thread production and movement by the intertidal mussel<Emphasis Type="Italic"> Hormomya mutabilis</Emphasis> in response to effluent from predators

Laboratory experiments were carried out to investigate byssal thread production by the intertidal mytilid mussel Hormomya mutabilis in response to effluent from the predatory crab Eriphia smithii and the starfish Coscinasterias acutispina. During the early period of the experiment, large H. mutabilis exposed to crab effluent produced a significantly smaller number of functional byssal threads than mussels in crab-free water. No significant difference in the diameter of threads produced in the two treatments was detected. The number of functional byssal threads produced by small H. mutabilis exposed to crab effluent did not differ significantly from that of mussels in crab-free water. However, small H. mutabilis exposed to crab effluent tended to discard fewer byssal bundles, that is, they shifted their attaching sites less frequently than similar mussels in crab-free water. In the presence of waterborne cues from the crab, H. mutabilis tended to reduce both the secretion of byssal threads and movement across the substratum. No significant differences in behaviour were observed between large mussels exposed to effluent from the starfish and those unexposed. The adaptive significance of the responses shown by H. mutabilis is discussed in terms of protection against predators differing in foraging behaviour. Electronic Publication     

High production of cold-tolerant chitinases on shrimp wastes in bench-top bioreactor by the Antarctic fungus Lecanicillium muscarium CCFEE 5003: Bioprocess optimization and characterization of two main enzymes

The Antarctic fungus Lecanicillium muscarium CCFEE-5003 was preliminary cultivated in shaken flasks to check its chitinase production on rough shrimp and crab wastes. Production on shrimp shells was much higher than that on crab shells (104.6 ± 9.3 and 48.6 ± 3.1 U/L, respectively). For possible industrial applications, bioprocess optimization was studied on shrimp shells in bioreactor using RSM to state best conditions of pH and substrate concentration. Optimization improved the production by 137% (243.6 ± 17.3). Two chitinolytic enzymes (CHI1 and CHI2) were purified and characterized. CHI1 (MW ca. 61 kDa) showed optima at pH 5.5 and 45 °C while CHI2 (MW ca. 25 kDa) optima were at pH 4.5 and 40 °C. Both enzymes maintained high activity levels at 5 °C and were inhibited by Fe⁺⁺, Hg⁺⁺ and Cu⁺⁺. CHI2 was strongly allosamidin-sensitive. Both proteins were N-acetyl-hexosaminidases (E.C. 3.2.1.52) but showed different roles in chitin hydrolysis: CHI1 could be defined as “chitobiase” while CHI2 revealed a main “eso-chitinase” activity.