The cellular features of mercury and selenium accumulation has been studied by transmission electron microscopy and x-ray microprobe analysis in the liver of striped dolphins. Mercury and selenium occurred as dense intracellular granules, located mainly within the liver macrophages (Kupffer cells). Granules were composed of 150 A spherical particles showing the same electron diffraction pattern and x-ray spectrum as mercuric selenide. The role of macrophages in mercuric selenide granule production and storage is discussed.

In exploring a substratum, Balanus amphitrite amphitrite Darwin (Crustacea: Cirripedia) cyprids deposit ‘footprints’ of antennular secretion. The results of in vitro settlement assays suggest that in addition to serving as a temporary adhesive, the secretion acts as a pheromone, in that its presence induces the settlement of conspecific cyprids. This result is in accord with a previous study on Balanus balanoides (L.)(=Semibalanus balanoides). In settlement assays, the pheromone is likely to contribute to an observed positive linear relationship between settlement and cyprid density. The density effect should thus be an important consideration in the design of barnacle settlement assays. In the field, cyprid searching behaviour may render a surface more attractive to settlement by cypris larvae.

Six species of dinoflagellates were investigated for their responsiveness to the indoleamine melatonin (and its homologue 5-methoxytryptamine), the vertebrate hormone for circadian rhythm regulation. Five species were observed forming pellicle cysts in response to 5-methoxytryptamine at concentrations around 10−6M. Cells of Oxyrrhis marina were observed retracting from the theca, part of the responsive pathway to indoleamine, but the resulting naked cells were unable to form a new cell wall and lysed.

The effects of environmental temperature on haemocyte antibacterial activity were investigated for the shore crab, Carcinus maenas. Haemocyte lysate supernatants (HLS), prepared from groups of five animals (sampled at monthly intervals over one year and covering a range of temperatures) were assayed for their ability to reduce viable counts of the marine bacterium Psychrobacter immobilis NQMB 308 during 4 h incubation. Parallel measurements were made of HLS protein concentration, total haemocyte count and ambient aquarium sea-water temperature. Despite wide variation in the values derived for each parameter, the results show that powerful antibacterial activity was present in HLS for all months except February and August, when respective aquarium water temperatures were at their lowest and highest for the year. This emphasizes the importance of environmental factors in immune capability: a phenomenon of significance not only to commercial shellfish culture but also for the use of immune parameters as biomarkers of environmental disturbance.

The tenacity of cypris larvae of the barnacles (Crustacea: Cirripedia) Balanus perforatus (Bruguiere) and Elminius modestus Darwin was measured on multispecies biofilms developed under contrasting shear regimes. For both species, relatively thin, dense biofilms associated with high shear (83 s-1) afforded increased tenacity over relatively thick, less dense films associated with low shear (15 s-1). Although both species showed reduced tenacity on low-shear films compared to high-shear films, E. modestus cyprids attached as strongly to low-shear films as they did to unfilmed surfaces. Balanus perforatus cyprids, however, attached less strongly to low-shear films than to unfilmed surfaces. The results show that B. perforatus and E. modestus may appreciate differences in bacterial communi-ties grown under different shear conditions and highlight the potential for biofilms as one of the many cues to barnacle settlement.

Rates of decrease in epifluorescence-detectable bacteria in preserved sea-water samples changed significantly with temperature. This apparent cell loss was substantial even in preserved samples stored in a refrigerator, decreasing exponentially with time, with 56% apparent cell loss after 99 days’ storage. Storage at room temperature resulted in the greatest decrease in detectable cells, with 73% apparent cell loss after the same storage period. No significant difference was found between storage in two different containers. The apparent cell loss can be modelled in order to calculate the original cell numbers with confidence. However, models produced from one set of samples cannot be applied to the data from another.