ALBERT

Description: Latitudinal declines of species richness from the tropics to the poles represent a general spatial pattern of diversity on land. For the marine realm, the generality of this pattern has frequently been questioned. Here, I use a database with nearly 600 published gradients (198 of which were marine) to assess whether there is a marine latitudinal diversity gradient of similar average strength and slope as that for terrestrial organisms. Using meta-analysis techniques, I also tested which characteristics of organisms or habitats affected gradient strength and slope. The overall strength and slope of the gradient for marine organisms was significantly negative and of similar magnitude compared to gradients for terrestrial organisms. Marine gradients were on average stronger as well as steeper than freshwater gradients. Latitudinal gradients were clearly a regional phenomenon, with stronger gradients and steeper slopes for diversity assessed on regional than on local scales. The gradient parameters differed also between oceans and between different habitats, with steeper gradients related to the pelagial rather than the benthos. There were on the other hand no significant differences between hemispheres and between different gradient ranges, although such differences have often been presumed. The most important organismal characteristic related to gradient structure was body mass, with significant gradients related to large organisms. A significant increase in gradient strength with increasing trophic level was observed. The meta-analysis also revealed strongest gradients for nekton and mobile epifauna, whereas the gradients were weak for sessile epifauna and for infauna. In conclusion, marine biota reveal a similar overall decline in diversity with latitude to that observed in terrestrial realms, but the strength and slope of the gradient are clearly subject to regional, habitat and organismal features.

Description: Grazing experiments were conducted with natural mesozooplankton from Kiel Bight, Germany, using radioactive labelled phytoplankton cultures and seston size fractions. The results of experiments using phytoplankton cultures indicated that bivalve veligers performed highest clearance of particles within a size range of 4.7 to 6.3 µm, whereas optimum particle size for copepods was 15 µm. The results of experiments using labelled natural seston size fractions identified bivalve veligers and appendicularians as those responsible for the removal of particles within the smallest size class (〈2 µm). Seston size fractions larger than 5 µm were mainly cleared by copepods and nauplii. As particle size increased, the contribution of copepod clearance to total zooplankton clearance within size classes increased from 57% (〈5 µm size class) to more than 81% (30 to 100 µm size class). When the nauplii clearance rates were included, the total copepod clearance accounted for 90 to 97.6% of the total volume cleared of particles bigger than 10 µm. Despite low abundances of bivalve veligers and appendicularians in Kiel Bight at the time of the experiment, we calculated that approximately 10 and 8.5%, respectively, of the carbon ingested by total mesozooplankton was due to veliger and appendicularian grazing. The importance of bivalve veligers might be seen in their grazing on seston particles that escape predation by copepods and on the amount of energy that is therefore directed from the water column to the benthos when larvae settle.

Description: Filamentous sulfur-oxidizing bacteria and geochemical parameters of sediments at the Makran accretionary wedge in the northeastern Arabian Sea off Pakistan were studied. The upper continental slope between 350 and 850 m water depth, which is in the center of the oxygen-minimum zone, is characterized by numerous sites of small-scale seeps of methane- and sulfide-charged porewater. White bacterial mats with diameters 〈1 m were discovered at the surface of these sites using a photo-TV sled. Seep sediments, as well as non-seep sediments, in the vicinity were characterized by the occurrence of the bacterium Thioploca in near-surface layers between 0 and 13 cm depth. Thioploca bundles were up to 20 mm in length and contained up to 20 filaments of varying diameters, between 3 and 75 µm. Up to 169 ind. cm-2 were counted. Maximum numbers occurred in the top 9 cm of sediment, which contained very low concentrations of soluble sulfide (〈0.2 µM) and high amounts of elemental sulfur (up to 10 µmol cm-3). Moderate sulfate reduction activity (between 20 and 190 nmol cm-3 d-1) was detected in the top 10 cm of these sediments, resulting in a gradual downcore decrease of sulfate concentrations. CO2 fixation rates had distinct maxima at the sediment surface and declined to background values below 5 cm depth. The nutritional implications of the distinct morphology of Thioploca and of the geochemical setting are discussed and compared to other sites containing Thioploca communities.

Description: Four in situ experiments were conducted to examine the potential top-down and bottom-up control of epibenthic ciliate communities. The experiments were run in the littoral of Lake Erken and at a brackish water site on the island of Väddö on the Baltic coast of Sweden, during the spring of 2000. The experimental manipulations were the presence/absence of the natural macrozoobenthos grazer community, cross-classified with the presence/absence of additional nutrients. Epibenthic ciliates responded to both manipulation of grazers and resources, but the response was group specific. Total ciliate abundance decreased when macrozoobenthos (largely chironomids, gastropods, trichopteran larvae, isopods and amphipods) were removed, thus excluding a direct predation effect of the macrozoobenthos community on ciliates. Total ciliate biomass, but not abundance, tended to increase in the presence of additional nutrients; an effect weakly dependent on season and site. The disparity between effects of nutrients on biomass and abundance was due to effects on heterotrichs, a group of large but relatively rare algivorous ciliates. The manipulations altered the ciliate community composition, and between lakes there were differences in species richness and diversity and experiments. However, neither the removal of macrozoobenthos nor the addition of nutrients changed species richness or diversity. This runs counter to work with other taxonomic groups, which shows maximal diversity at an intermediate level of resources or predation. This can only be partially explained by the lack of direct predation effects and the open nature of the experimental system.

Description: Spatial and temporal variability in environmental factors can exert major influences on survival and growth of living organisms. However, in many key areas of fisheries science (e.g. growth, survival and recruitment determination), environmental heterogeneity is usually ignored because of insufficient environmental or fisheries data or lack of evidence that such heterogeneity impacts response variables. For the eastern Baltic Sea (ICES Subdivisions 25 to 32), we evaluated spatial and temporal differences in conditions affecting the survival of cod Gadus morhua L. eggs at survival on four distinct spawning sites within the assessment area. We intercalibrated ways of quantifying the volume of water ('reproductive volume') at each site where salinity, oxygen and temperature conditions permitted successful egg development. We have developed and compared a time series (1952 to 1996) of reproductive volumes among the areas to identify spatial differences. The results of 2 independent volume-estimation methods are comparable, indicating that highly significant differences exist among the sites, and that the westernmost spawning ground, Bornholm Basin, has on average the highest reproductive volume and the lowest variability among the 4 sites. These findings may be useful in evaluating how spatial and temporal variability in environmental conditions affect egg hatching success and possibly recruitment in the Baltic stock.

Description: Natural marine bacteria populations collected from nearshore waters produce different types of siderophores depending on the degree of iron limitation. These siderophores can facilitate iron uptake in the marine diatom Phaeodactylum tricornutum. Water samples from 15 stations along the Italian coast of the northwest Adriatic Sea were collected and filter fractionated (3.0, 0.8 and 0.2 µm). Siderophore production in the fractions was determined using cross-feeding experiments with siderophore-auxotrophic bacteria. At most stations sampled, bacteria collected in the 3.0 and 0.8 µm filters produced siderophores which stimulated growth in Morganella morganii, the indicator strain for α-keto/ α-hydroxy acids. The results suggest that MGF (ŒMorganella-Growth Factor¹) production is common among filamentous and appendaged bacteria or strains associated with particles. Natural bacteria populations grown in iron-deficient media stimulated growth of all the indicator strains in the cross-feeding tests. Examples of known MGF which supply iron to M. morganii were tested for their ability to act as iron source for the marine diatom P. tricornutum. Iron uptake from 55Fe-MGFs was measured in P. tricornutum cells grown in Fe-sufficient and Fe-deficient media. Unchelated iron (55FeCl3 ) and 55FeEDTA were used as controls. The uptake of iron from the 55Fe-MGF and 55FeCl3 by Fe-deficient cells was higher (109 to 150 pgFe mg-1) than from 55FeEDTA (34 pgFe mg-1). Similarly, Fe-sufficient P. tricornutum took up iron from the 55Fe-MGF and 55FeCl3 to the same extent (~50 pgFe mg-1) while minimal uptake (8 pgFe mg-1) was measured from FeEDTA. In growth experiments where iron-deficient diatom cells were incubated in media containing different sources of iron, e.g. FeCl3, Fe-MGF and FeEDTA, a greater increase in number was observed in cells supplied with Fe-MGF. Further experiments also show that the uptake of Fe from MGF was enhanced by light and that a reduction step was involved in the uptake process. MGF also promoted the uptake of colloidal ferrihydrites. This study gives further evidence that siderophores produced by bacteria can be utilized by phytoplankton as an iron source. We therefore suggest that these substances play an important role in increasing the availability of iron to phytoplankton in coastal waters and thus are major factors defining the chemistry of iron in the marine environment.

Description: Marine angiosperms, or seagrasses, continue to be a major focus of marine biologists because of their important ecological role in many coastal ecosystems. Seagrass population biology could benefit from a population genetic perspective because genetic data enable the extraction of useful demographic information such as isolation and gene flow between demes. Moreover, population genetic processes may contribute to the growing ecological risks of local population extinction. Progress in seagrass genetics is partly driven by novel genetic markers which detect variation at the DNA level and overcome the limited polymorphism of allozymes. Key results of studies in the past decade, mostly using RAPD and microsatellites, were (1) considerable genetic and genotypic (clonal) diversity is present in several species in contrast to earlier notions of low polymorphism detected at allozyme loci, and (2) genetic differentiation among populations seems to be the rule despite earlier reports of genetic uniformity. Pronounced genetic structure was detected between populations of 4 species examined thus far (Posidonia oceanica, P. australis, Zostera marina, Thalassia testudinum). The FST estimates varied widely and ranged from 0.01 to 0.623 across studies and species. Genetic differentiation at a systematic range of scales was only studied in eelgrass Zostera marina, where it was positively correlated with geographic distance. The high polymorphism of RAPD or microsatellite markers will allow the augmention of indirect estimates of gene flow by methods detecting individual immigration events through paternity analysis or assignment tests. Important conservation related issues such as the level of inbreeding and the effective population size have also been obtained from genetic marker data, but results are too scarce at the moment to allow generalizations. In Zostera marina and Posidonia australis, several population genetic attributes such as clonal diversity, mating system and effective population size varied among populations within species, highlighting that there is no Œtypical¹ population. An important gap in our knowledge is whether the effects of natural population fragmentation and patchiness enhance the genetic isolation of populations due to anthropogenic disturbances. It is also unclear whether genetic differentiation displayed at marker loci are correlated with fitness-related plant traits, and whether genetic or genotypic diversity is important for medium- to long-term meadow persistence. An assessment of the genetic and genotypic diversity at marker loci should be combined with experiments on the ecological plasticity and reaction norms of genotypes composing the populations in question. This way, the role of genetic diversity for seagrass population maintenance and growth in the face of changing environmental conditions can be evaluated.

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