ALBERT

Description: The epibacterial chemical defense of the marine sponge Suberites domuncula was explored by screening sponge extract, sponge primmorph (3-D aggregates containing proliferating cells) extract and sponge-associated as well as primmorph-associated bacteria for antibacterial activity. 16S rDNA sequencing revealed that the antimicrobially active bacteria belonged to the a- and γ-subdivisions of Proteobacteria ( α-Proteobacterium MBIC 3368, Idiomarina sp. and Pseudomonas sp., respectively). Moreover, a recombinant perforin-like protein was cloned from S. domuncula that displayed strong antibacterial activity. Based on these observations, it is proposed that the sponge may be provided with a direct (by producing antibacterial metabolites) as well as an indirect (with the help of associated bacteria) epibacterial defense.

Description: There is mounting molecular evidence that bacteria belonging to the phylum Planctomycetes are abundant in marine sponges including members of the genus Aplysina. In an attempt to culture planctomycete bacteria from Aplysina sponges, 116 bacterial strains were isolated on selective oligotrophic media. Screening of the strain collection by fluorescence in situ hybridization with the planctomycete-specific probe Pla46 yielded 3 positive candidates. Nearly complete sequencing of the respective 16S rRNA genes revealed that the isolates were affiliated with 2 distinct clusters of the genus Pirellula: 1 isolate was obtained from a Mediterranean sponge, 1 from a Caribbean sponge and a third from Caribbean seawater. To our knowledge this is the first report of cultured Planctomycetes from marine sponges. The isolates grew slowly on oligotrophic media and failed to grow on nutrient-rich media. Pirellula sp. Strain 797 was pink-pigmented while the other 2 isolates, 16 and 81, were non-pigmented. Transmission electron microscopy revealed a pear- or droplet-shaped cell morphology that is characteristic of the genus Pirellula. The application of strain-specific oligonucleotide probes to sponge tissue cryosections showed that the isolates contribute only a minor fraction to the total microbial community that is associated with Aplysina spp. sponges

Description: Somatic growth and nucleic acid content were studied in North Sea houting Coregonus oxyrhinchus larvae fed exclusively on dry diets at 2 temperatures (8.4 and 17.5°C) during a 32 d rearing experiment. The higher temperature enhanced growth significantly. Mean dry weights at the end of the experiment were 3.6 mg (SD = 1.07, range 1.4 to 5.7 mg) and 31.5 mg (SD = 21.9, range 3.6 to 96.0 mg), and mean standard lengths were 17.7 ± mm (SD = 1.6, range 11.8 to 19.6 mm) and 25.5 mm (SD = 4.2, range 17.0 to 35 mm), respectively. Significant responses to temperature were also found in the nucleic acids. However, these differences were not as remarkable and gave indications that differences in protein growth between treatments was based on protein biosynthesis being driven by the activity of the ribosomes, rather than their number. The use of the degree-day approach to normalize the data clearly showed the temperature-dependence of somatic growth. Only small differences in growth and nucleic acid content were observed in the comparable range of the first 280 degree-days in fed fish. In non-fed fish, the starving potential was very similar (approx. 350 degree-days). Shifts in growth pattern from predominantly hyperplasia to predominantly hypertrophy were detected, with ongoing growth at both temperatures.

Description: Pelagic and demersal juvenile Baltic cod Gadus morhua L. were collected on the slope and the top of Rønne bank in the Baltic Sea during 2 cruises in November and December 1998. The objective of this study was to evaluate distinct changes in otolith increment width observed in demersal juveniles by comparison with laboratory-reared individuals, and to investigate the factors determining variation in these increments. The different increment-width patterns were identified with a method based on the widths of consecutive increments. Otolith increment widths of juvenile cod were found to be highly variable within and between individuals, in both the experimental and the field samples. The first change in increment pattern observed in the field samples was related to settling. The formation periodicity of increments within the different pattern intervals was confirmed with a growth model based on otolith growth rates of juvenile cod reared in the laboratory under different conditions. In this model, otolith growth rate was expressed as a function of rearing temperature and fish dry weight. Otolith growth of the field samples was calculated using ambient temperatures obtained from a 3D-circulation model. The best fit to observed otolith growth rates was obtained under the assumption that fish on the slope performed daily vertical migrations between the warm surface layer and the cold bottom layer. The data suggested that fish stayed in the surface layer during the first increment-pattern interval, performed vertical migrations during the second interval, and stayed in association with the seafloor in the subsequent interval, corresponding to the time after the breakdown of the thermocline.

Description: At Hydrate Ridge (HR), Cascadia convergent margin, surface sediments contain massive gas hydrates formed from methane that ascends together with fluids along faults from deeper reservoirs. Anaerobic oxidation of methane (AOM), mediated by a microbial consortium of archaea and sulfate-reducing bacteria, generates high concentrations of hydrogen sulfide in the surface sediments. The production of sulfide supports chemosynthetic communities that gain energy from sulfide oxidation. Depending on fluid flow, the surface communities are dominated either by the filamentous sulfur bacteria Beggiatoa (high advective flow), the clam Calyptogena (low advective flow), or the bivalve Acharax (diffusive flow). We analyzed surface sediments (0 to 10 cm) populated by chemosynthetic communities for AOM, sulfate reduction (SR) and the distribution of the microbial consortium mediating AOM. Highest AOM rates were found at the Beggiatoa field with an average rate of 99 mmol m-2 d-1 integrated over 0 to 10 cm. These rates are among the highest AOM rates ever observed in methane-bearing marine sediments. At the Calyptogena field, AOM rates were lower (56 mmol m-2 d-1). At the Acharax field, methane oxidation was extremely low (2.1 mmol m-2 d-1) and was probably due to aerobic methane oxidation. SR was fueled largely by methane at flow-impacted sites, but exceeded AOM in some cases, most likely due to sediment heterogeneity. At the Acharax field, SR was decoupled from methane oxidation and showed low activity. Aggregates of the AOM consortium were abundant at the fluid-impacted sites (between 5.1 × 1012 and 7.9 × 1012 aggregates m-2) but showed low numbers at the Acharax field (0.4 × 1012 aggregates m-2). A transport-reaction model was applied to estimate AOM at Beggiatoa fields. The model agreed with the measured depth integrated AOM rates and the vertical distribution. AOM represents an important methane sink in the surface sediments of HR, consuming between 50 and 100% of the methane transported by advection.

Description: The accuracy of species-specific phytoplankton growth rates estimated by cell cycle analysis was tested with the dinoflagellate Prorocentrum minimum (Pav.) Sch. under conditions of altered nitrogen and phosphorus availability. Reduced nutrient availability caused major changes in the duration of cell cycle phases. At the nutrient level of complete f/2 media, the length of the combination of S, G2, and M phases was about 8 h at growth rates of 0.53 to 0.56 d-' A decrease in ~ 0 ,o~r N-O3 concentration extended the S+G2+M phase to about 15.5 to 17.7 h at growth rates ranging from 0.41 to 0.30 d-' Changes in phase durations dld not significantly affect growth rate estimates. In addition, a minimum growth rate, calculated from the maximum values on phase fraction curves, was shown to be usable as an error detector in some cases. Results support the validity of cell cycle analysis to measure in situ growth rates.

Description: Although the 'intermediate disturbance hypothesis' (IDH) was originally postulated for marine hard-bottom communities, it has rarely been tested for this community type. We experimentally examined the effects of ambient plus artificially enhanced UV-B radiation (eUV-BR) along an intensity gradient on the abundance of individual species, species composition, and diversity of a macrobenthic community in the western Baltic, Germany. Plots were either exposed each day for 0.5, 1, 2, 4, and 8 h to the maximum expected future UV-BR or were left untreated (= ambient irradiance). Species recruitment and succession on artificial substrata were followed for 5 mo. Transient unimodal patterns for species richness and diversity H' were produced along the UV-BR gradient early in succession. The density of the competitively superior mussel Mytilus edulis and the abundance of the foliose green alga Ulvopsis grevillei were positively related to UV-BR exposure; suggesting conditions different from those predicted by the IDH-generated unimodal patterns. Protective shading of substratum by U. grevillei and the resultant mitigation of the UV-BR impact for succeeding colonizers may be important in this context. Species composition differed persistently among eUV-BR treatments. In contrast to mussels and U. grevillei, the abundance of red algae was adversely affected by eUV-BR along the disturbance gradient. Our results suggest that expected future UV-BR levels will have limited influence on the diversity of shallow-water macrobenthic fouling assemblages in the western Baltic, whereas their species composition may be affected over longer periods.

Description: Dilution experiments were used to examine growth and grazing mortality rates among Prochlorococcus and Synechococcus populations in the Sargasso Sea and California Current. In these experiments, deviation from linearity in the relationship between dilution and net growth rate was significant in a large number of cases. An alternative, more conservative approach for estimating growth and grazing mortality rates (independent of the shape of this relationship) was therefore employed. Growth rates estimated by this approach ranged from 0.32 to 0.76 and 0.37 to 0.67 d-1 for Prochlorococcus and Synechococcus, respectively. Grazing mortality rates ranged from 0.25 to 0.85 and 0.13 to 0.51 d-1, respectively. Cell-cycle-based growth rate estimates were consistent with these dilution-based rates. Nutrient amendment had little affect on picocyanobacterial growth rates, but did stimulate grazing mortality (and in some cases changed the apparent functional response of the grazer community) in a number of experiments. We hypothesize that improved food quality in nutrient-replete picoplankton cells may be responsible for these changes. Diel patterns of picocyanobacterial abundance in the Sargasso Sea experiments suggest that grazing activity varied strongly over the diel cycle, with low grazing activity during the first half of the light period. Growth rate and abundance were not positively correlated among or within picocyanobacterial groups, as might be expected if physiologically mediated controls were the dominant forces regulating these populations.