Schooling behavior of Antarctic krill (Euphausia superba) in laboratory aquaria: Reactions to chemical and visual stimuli

Antarctic krill,Euphausia superba, often exhibit abnormal behavior in laboratory aquaria, usually hovering in a stationary position, unresponsive to most external stimuli. In the austral summer of 1985–1986 at Palmer Station on Anvers Island, Antarctica, we provided laboratory conditions which inducedE. superba to school in large aquaria. Captive krill swam horizontally and exhibited the full spectrum of behaviors normally displayed while schooling at sea. Schooling krill avoided visually contrasting stimuli, with avoidance distances correlated with stimulus size. Schools responded in qualitatively different ways to presentations of food, chemical compounds, and abrupt increases in light intensity. We describe the conditions necessary for aquarium schooling and discuss the importance of an appropriate social environment for displays of escape, avoidance, and feeding behaviors and of positional preference within the school.     

Feeding preferences of periwinkles among four species ofFucus

A widely accepted view of intertidal community organizatiton in the NW Atlantic proposes that fucoid vegetation is maintained by the actions of predators which remove species competitively superior toFucus species. Herbivory is an important component of these predatory interactions, but has been studied largely with reference to the interaction betweenF. vesiculosus andLittorina littorea. There are many species of fucoids and herbivorous invertebrates on the shores of the NW Atlantic and this paper reports field and laboratory experiments performed in 1987 (in or near Halifax, Canada) on the effects of grazing by three species ofLittorina on adults and juveniles of four species ofFucus. In laboratory experiments, portions ofFucus species were presented singly (no choice) or together (multiple choice) to single species ofLittorina. AdultF. distichus was grazed to only a small extent.F. evanescens andF. vesiculosus adult tissues were heavily grazed in most laboratory experiments.F. spiralis adults were heavily grazed in no choice experiments, but were grazed only slightly in multiple choice tests. When adult fucoid tissues were exposed to a mixed suite of grazers in the field, onlyF. vesiculosus was grazed heavily. Tests done on adult tissues showed clearly thatFucus species are highly variable in their vunerability to grazers. Moreover, we found variability among periwinkle species in grazing rates on adultFucus. We also found a great disparity in the feeding rates of different periwinkle species on juveniles ofFucus. Therefore, it is not possible to extrapolate from a single periwinkle species/single fucoid species interaction when attempting to identify vegetation structuring processes.     

A molecular genetic analysis of social structure, dispersal, and interpack relationships of the African wild dog (Lycaon pictus )

The African wild dog is a highly social, pack-living predator of the African woodland and savannah. The archetypal wild dog pack consists of a single dominant breeding pair, their offspring, and non-breeding adults who are either offspring or siblings of one of the breeding pair. Non-breeding adults cooperate in hunting, provisioning and the protection of young. From these observations follows the prediction that the genetic structure of wild dogs packs should resemble that of a multigenerational family, with all same-sexed adults and offspring within a pack related as sibs or half-sibs. Additionally, a higher kinship between females from neighboring packs should be evident if females tend to have small dispersal distances relative to males. We test these predictions through analysis of mitochondrial DNA control region sequences and 14 microsatellite loci in nine wild dog packs from Kruger National Park, Republic of South Africa. We show that as predicted, African wild dog packs generally consist of an unrelated alpha male and female, subdominant close relatives, and offspring of the breeding pair. Sub-dominant wild dogs occasionally reproduce but their offspring rarely survive to 1 year of age. Relatedness influences the timing and location of dispersal events as dispersal events frequently coincide with a change in pack dominance hierarchy and dispersers often move to areas with a high proportion of close relatives. Received: 22 February 1996 / Accepted after revision: 16 November 1996     

Assessing Risks to Biodiversity from Future Landscape Change

We examined the impacts of possible future land development patterns on the biodiversity of a landscape. Our landscape data included a remote sensing derived map of the current habitat of the study area and six maps of future habitat distributions resulting from different land development scenarios. Our species data included lists of all bird, mammal, reptile, and amphibian species in the study area, their habitat associations, and area requirements for each. We estimated the area requirements using home ranges, sampled population densities, or genetic area requirements that incorporate dispersal distances. Our measures of biodiversity were species richness and habitat abundance. We calculated habitat abundance in two ways. First, we computed the total habitat area for each species in each landscape. Second, we calculated the number of habitat units for each species in each landscape by dividing the size of each habitat patch in the landscape by the area requirement and summing over all patches. Species richness was based on presence of habitat. Species became extinct in the landscape if they had no habitat area or no habitat units, respectively. We then computed ratios of habitat abundance in each future landscape to habitat abundance in the present for each species. We also computed the ratio of future to present species richness. We then calculated summary statistics across all species. Species richness changed little from present to future. There were distinctly greater risks to habitat abundance in landscapes that extrapolated from present trends or zoning patterns, however, as opposed to landscapes in which land development activities followed more constrained patterns. These results were stable when tested using Monte Carlo simulations and sensitivity tests on the area requirements. We conclude that this methodology can begin to discriminate the effects of potential changes in land development on vertebrate biodiversity.     

Influence of body size on the uptake,depuration, and bioaccumulation of polychlorinated biphenyl congeners by Baltic Sea blue mussels,Mytilus edulis

The present study was designed to examine the influence of body size on the bioaccumulation of polychlorinated biphenyl (PCB) congeners by Baltic Sea blue mussels, Mytilus edulis L. This was done, firstly, by establishing the relationship (as a power function: PCB tissue conc = a tissue dry wt^b) between tissue concentration and body weight for seven PCB congeners (International Union of Pure and Applied Chemistry No. 52, 101, 105, 118, 138, 153, and 180) in field sampled mussels; and, secondly, by assessing the influence of body weight on the uptake clearance coefficients, the depuration rate coefficients and the calculated bioaccumulation factors (BAFs) of three ¹⁴C-labelled PCB congeners (IUPAC No. 31, 49, 153) in mechanistic kinetic experiments. Both the background tissue concentrations of PCB 138, PCB 153 and PCB 180 and the predicted BAF values in the kinetic experiments correlated negatively with body weight (b=-0.17 and-0.31, respectively). Of the two kinetic rate coefficients examined, only the uptake clearance rate showed weight dependency (b=-0.32, i.e. negative correlation with body weight), whereas depuration rates were unaffectd by body weight. Uptake clearance rates and BAFs adjusted for body weight increased with the octanol/water partition coefficient (K_ow) of the congener, whereas depuration rates dectreased with K_ow. These observations suggest that size-dependent bioaccumulation of hydrophobic organic contaminants (HOCs) in suspension-feeding bivalves is driven by size-related differences in uptake rate, although several other mechanisms may also affect bioaccumulation in natural mussel beds (e.g. sizerelated differences in lipid content, production, and contaminant exposure). From an ecotoxicological perspective size-dependent bioaccumulation implies not only that variability due to body size differences has to be dealt with in experimental designs, but also that several ecological factors such as size-specific predation and shifts in population structure may affect HOC cycling by dense populations of bivalve suspensionfeeders.     

Age-related settlement success by cyprids of the barnacleBalanus amphitrite,with special reference to consumption of cyprid storage protein

Newly molted (0-d-old) cyprids of the barnacleBalanus amphitrite Darwin were prevented from settling for 0 to 14 d at four different temperatures (25, 20, 15 and 5°C treatments). The effect on settlement success of prolonging the cyprid lifetime was evaluated using a nitrilocellulose membrane assay. In addition, protein extract prepared from these cyprids was analyzed using gel electrophoresis to characterize the effect of age on protein content and composition. Settlement success was significantly affected for larvae aged at 25 (P < 0.001), 20 (P < 0.001) and 15°C (P < 0.05), while differences in settlement success between age groups was negligible at 5°C (P = 0.09). Settlement success of cyprids increased with time for up to 3 d (P < 0.001, Phase 1), following which settlement success significantly declined (P < 0.001, Phase 11). Temperature had no significant effect on settlement in Phase I (P = 0.17), but did enhance the decline in settlement success with age during Phase II (P < 0.001). Gel electrophoresis revealed a significant decline in the quantity of the cyprid storage protein CMP (Cyprid Major Protein) with increasing age at 25, 20 and 15°C, but CMP levels remained constant at 5°C. These results suggest that, upon molting to the cyprid stage, larvae may still require a settlement-competence attainment period. This may be achieved by CMP utilization during Phase I, depletion of which during Phase II may be responsible for reduction in settlement success with cyprid age such that remaining CMP stores can no longer support the production of adult structures following settlement.     

Genetic differentiation in three Sepia species (Mollusca: Cephalopoda) from Galician waters (north-west Iberian Peninsula)

The systematics of the genus Sepia is not yet clear. Morphological evidence has led to S. officinalis Linnaeus, 1758 being considered as belonging to the subgenus Sepia sensu stricto, and S. orbignyana Férussac, 1826 and S. elegans Blainville, 1827 as belonging to the subgenus Rhombosepion. Samples of 30 individuals of S. officinalis and S. orbignyana from both sides of an oceanographic boundary off the north-west Iberian Peninsula, and a sample of S. elegans from the northern side, were collected in 1993–1994. Allozyme electrophoresis for 32 presumptive loci revealed low levels of genetic variability for the three Sepia species (mean expected heterozygosity estimates were <0.052). No significant differences in allozyme frequencies were detected among populations of either S. officinalis or S. orbignyana. The genetic identities (I) of S. officinalis and S. orbignyana (I=0.12) and of S. elegans (I=0.13) were significantly different from that of S. orbignyana and S. elegans (I=0.49). The former are typical of values for confamilial genera, and a new generic status is proposed for the latter two species, which become Rhombosepion orbignyana (Férussac, 1826) and R. elegans (Blainville, 1827).     

Form and feeding mechanism of a living Planctosphaera pelagica (phylum Hemichordata)

We describe aspects of the anatomy and suspension-feeding mechanism of a single Planctosphaera pelagica captured from the plankton in June 1992 off Bermuda in the western Atlantic. We also describe several unusual features of the larva, including its occurrence in surface waters, unusually large size, and limited swimming ability. Our account of the form and feeding behavior of P. pelagica is the first based on observations of a specimen captured and observed alive. Our limited observations suggest that the planctosphaera may use a suspension-feeding mechanism much like that of the other feeding deuterostome larvae (the pluteus and bipinnaria larvae of echinoderms and the tornaria larva of enteropneust hemichordates) known to capture food particles using a single ciliated band. Although we could not observe cilia directly, the movement of dye streams and food particles and the structure of the ciliated band suggest that some particles may be captured at the ciliated band by the reversal of ciliary beat. The planctosphaera possesses many prominent mucous glands near the food grooves. This suggests an important role of mucus in the biology of the larva, but we were not able to observe directly any role of mucus in particle capture.     

The influence of pH and household plumbing on water lead concentration

The water lead concentrations measured in the homes of children who were part of the Edinburgh Lead study are related to the characteristics of the water supply and the household plumbing. At the time of the study one of the City of Edinburgh's two water supplies was lime treated to reduce plumbosolvency but in the second supply this treatment had not yet become effective. This allows us to estimate the extent to which this type of water treatment reduces water lead concentrations, in houses with lead plumbing, to comply with existing and proposed limits for lead in water. The kitchen cold water was supplied from a lead storage tank in 69 (15%) of the houses. These houses had the highest lead concentrations and water treTo whom correrspondence should be addressed.