Relative Susceptibility of Penaeus aztecus to Baculovirus penaei

Experimental infections of wild juvenile Penueus azrecus with Baculovinrs penuei (BP) demonstrate similar levels of prevalence as found in the natural environment. Moreover, neither postlarvae nor juveniles of P. setiferus , which rarely exhibit natural infections in the Gulf of Mexico, developed experimental patent infections using routine methods. Six other crustaceans, two of which were penaeids and none of which is a known host, did not develop experimental patent infections either.     

The lake at Llandrindod Wells—a restoration comedy?

• 1. The lake at Llandrindod Wells, Wales, UK, is a typical urban shallow lake. Created in the 19th century for amenity, it has a long history of management for various, often conflicting, purposes. After the 1950s, the once clear water became turbid with phytoplankton, and aquatic plants became very scarce.
• 2. The most likely reason for this was introduction of common carp, for angling, into a fish community that contained no piscivores. Mobilization of phosphorus from the sediments by activities of the fish led to severe internal phosphorus loading, culminating ultimately in a requirement to close the lake, temporarily in summer, to water contact activities, because of a risk of toxic cyanophyte blooms.
• 3. The lake‐owners decided to restore the lake to greater amenity and conservation value by biomanipulation of the fish community and associated works. The restoration was successful in restoring clear water and plant communities, but because of the nature of the plants reintroduced, there were new problems of dense plant growth. Ownership of the lake then changed and, in a somewhat confused situation, the lake has been returned to a carp fishery.
• 4. Documents on the history of management of the lake, and available limnological data, are reviewed in relation to a general strategy for lake restoration and general lessons are drawn for future restoration projects.

Copyright © 2002 John Wiley & Sons, Ltd.     

A rapid,non-destructive method for sampling castrating parasites in endangered bivalve molluscs

1. Bivalves are important ecosystem engineers, and there is emerging evidence that many species are afflicted with castrating parasites. Understanding the prevalence of these largely overlooked parasites is crucial in understanding the fundamental biology of bivalves, informing conservation efforts, and providing a wider understanding of host–parasite dynamics.
2. Current techniques to assess the presence of parasites are destructive, making them untenable for endangered or protected populations. This article presents a non-destructive method of sampling bivalve molluscs (Anodonta anatina) to detect castrating trematodes. Gonadal fluid is removed with a hypodermic needle from bivalves in situ and analysed in a laboratory setting without removing the mollusc from the field; this sampling mechanism has previously been shown not to harm the mollusc.
3. A single 50 μl sample is sufficient to detect both the presence and developmental stage of the trematode with greater than 95% reliability, with all but the lightest infections visible. We recommend that this technique should be used to enhance knowledge on host–parasite dynamics in bivalves, and inform sensible conservation for threatened species.

     

Adding value to live, commercial size soft-shell clams (Mya arenaria L.) in Maine, USA: results from repeated, small-scale, field impoundment trials

The soft-shell clam (Mya arenaria L.) fishery in the state of Maine, USA, is worth $5–10 million annually and is primarily based on the sale of live individuals. More than 80% of the catch is sold for the “steamer clam” market that is highly seasonal due to supply and demand. Prices paid to harvesters for live clams throughout the year increases by as much as 70% during a 4-month period between early spring and late summer. If clams harvested in the spring could be held until late summer, a value-added product could be developed in this fishery. From April to August 1996, at an intertidal and subtidal location in eastern Maine, I tested whether it was biologically feasible to impound commercially harvested clams (shell LENGTH=44–75 mm) at densities between 720 and 850/m² using cages and nets (1.12 m²) to protect animals from predators. Survival was 91.7% (n=12) and 91.6% (n=6) at the intertidal and subtidal site, respectively. There was no discernible shell growth during this period and there was no difference between initial and final clam weights. The methodology was transferred to commercial harvesters in two Maine communities: Wiscasset (1997 and 1998) and Perry (2000). Impounded clams ( =21.8 kg/cage; n=18) lost, on average, 5 kg/cage in 1997 and 1998, whereas no significant net loss in wet weight occurred in cages deployed in 2000 ( =23.2 kg/cage; n=3). Differing harvesting and handling methods of individual clammers, prior to impounding clams, likely explains the variation in weight lost during the impounding periods. The difference in price per live kilogram between the beginning of the impounding period and the August sale date resulted in an average gain of $13.60/cage for clammers in 1997 and 1998 and $57.73/cage in 2000. Simple culture techniques can be used to increase the value of the live harvest of soft-shell clams along the coast of Maine. Clam impoundments may be a way for communities that co-manage the public clam resource with the state's marine resource agency to generate funds to pay for traditional management schemes, as well as enhancement programs that employ hatchery-reared juveniles. In addition, an indirect benefit of clam impoundments might be to create spawner sanctuaries since animals are impounded during the time when gamete release occurs.     

Characterizing bubble penetration from a falling stream

The depth that bubbles will penetrate a receiving pool before rising due to buoyancy forces is an important phenomena in designing Low Head Oxygenator (LHO) devices, particularly in an indoor application where the available elevation between the top of the fish tank water column and the inside ceiling height is limited. The relationship between bubble loss and LHO geometry is unclear. If the submergence of the LHO is less than the bubble penetration depth, excessive escape of bubbles can increase operating costs substantially. A series of physical experiments were conducted using an elevated bucket with a single orifice to create a falling stream into a receiving pool. The primary variables of hydraulic head, hole diameter and fall height were varied over a practical range for such applications. Videotaping was used to analyze bubble penetration. Regression equations were developed to predict both bubble penetration and standard deviation associated with a specific set of operating conditions. The standard deviation regression equation can be used to predict the statistical variation in bubble penetration depth. Bubble penetration depth decreased as fall height was increased and became stable at a fall height of 50 cm. Bubble penetration increased as hole diameter was increased at all fall heights and hydraulic heads. An example is provided of how to predict bubble penetration depth to meet some user defined statistical confidence for maximum bubble penetration.     

Disentangling the drivers of β diversity along latitudinal and elevational gradients

Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (β diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in β diversity caused simply by changes in the sizes of species pools. For example, forest inventories sampled along latitudinal and elevational gradients show the well-documented pattern that β diversity is higher in the tropics and at low elevations. However, after correcting for variation in pooled species richness (γ diversity), these differences in β diversity disappear. Therefore, there is no need to invoke differences in the mechanisms of community assembly in temperate versus tropical systems to explain these global-scale patterns of β diversity.     

Potential host ranges of three Asian larval parasitoids of Drosophila suzukii

Asobara japonica (Hymenoptera: Braconidae), Ganaspis brasiliensis and Leptopilina japonica (Hymenoptera: Figitidae) are Asian larval parasitoids of spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae). This study evaluated these parasitoids’ capacity to attack and develop from 24 non-target drosophilid species. Results showed that all three parasitoids were able to parasitize host larvae of multiple non-target species in artificial diet; A. japonica developed from 19 tested host species, regardless of the phylogenetic position of the host species, L. japonica developed from 11 tested species; and G. brasiliensis developed from only four of the exposed species. Success rate of parasitism (i.e., the probability that an adult wasp successfully emerged from a parasitized host) by the two figitid parasitoids was low in hosts other than the three species in the melanogaster group (D. melanogaster, D. simulans, and D. suzukii). The failure of the figitids to develop in most of the tested host species appears to correspond with more frequent encapsulation of the parasitoids by the hosts. The results indicate that G. brasiliensis is the most host specific to D. suzukii, L. japonica attacks mainly species in the melanogaster group and A. japonica is a generalist, at least physiologically. Overall, the developmental time of the parasitoids increased with the host’s developmental time. The body size of female A. japonica (as a model species) was positively related to host size, and mature egg load of female wasps increased with female body size. We discuss the use of these parasitoids for classical biological control of D. suzukii.