ALBERT

Description: The anaerobic oxidation of methane (AOM) is one of the major sinks of this substantial greenhouse gas in marine environments. Recent investigations have shown that diverse communities of anaerobic archaea and sulfate-reducing bacteria are involved in AOM. Most of the relevant archaea are assigned to two distinct phylogenetic clusters, ANME-1 and ANME-2. A suite of specific 13C-depleted lipids demonstrating the presence of consortia mediating AOM in fossil and recent environments has been established. Here we report on substantial differences in the lipid composition of microbial consortia sampled from distinct compartments of AOM-driven carbonate reefs growing in the northwestern Black Sea. Communities in which the dominant archaea are from the ANME-1 cluster yield internally cyclized tetraether lipids typical of thermophiles. Those in which ANME-2 archaea are dominant yield sn-2-hydroxyarchaeol accompanied by crocetane and crocetenes. The bacterial lipids from these communities are also distinct even though the sulfate-reducing bacteria all belong to the Desulfosarcina/Desulfococcus group. Nonisoprenoidal glycerol diethers are predominantly associated with ANME-1-dominated communities. Communities with ANME-2 yield mainly conventional, ester-linked diglycerides. ANME-1 archaea and associated sulfate-reducing bacteria seem to be enabled to use low concentrations of methane and to grow within a broad range of temperatures. Our results offer a tool for the study of recent and especially of fossil methane environments.

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: 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: The role of transparent exopolymer particles (TEP) and dissolved organic carbon (DOC) for organic carbon partitioning under different CO2 conditions was examined during a mesocosm experiment with the coccolithophorid Emiliania huxleyi. We designed 9 outdoor enclosures (similar to11 m(3)) to simulate CO2 concentrations of estimated 'Year 2100' (similar to710 ppm CO2), 'present' (similar to410 ppm CO2) and 'glacial' (similar to190 ppm CO2) environments, and fertilized these with nitrate and phosphate to favor bloom development. Our results showed fundamentally different TEP and DOC dynamics during the bloom. In all mesocosms, TEP concentration increased after nutrient exhaustion and accumulated steadily until the end of the study. TEP concentration was closely related to the abundance of E. huxleyi and accounted for an increase in POC concentration of 35 2 % after the onset of nutrient limitation. The production of TEP normalized to the cell Abundance of E. huxleyi was highest in the Year 2100 treatment. In contrast, DOC concentration exhibited considerable short-term fluctuations throughout the study. In all mesocosms, DOC was neither related to the abundance of E. huxleyi nor to TEP concentration. A statistically significant effect of the CO2 treatment on DOC concentration was not determined. However, during the course of the bloom, DOC concentration increased in 2 of the 3 Year 2100 mesocosms and in 1 of the present mesocosms, but in none of the glacial mesocosms. It is suggested that the observed differences between TEP and DOC were determined by their different bioavailability and that a rapid response of the microbial food web may have obscured CO2 effects on DOC production by autotrophic cells.

Description: Chromophoric dissolved organic matter (CDOM) represents the optically active fraction of the bulk dissolved organic matter (DOM) pool. Recent evidence pointed towards a microbial source of CDOM in the aquatic environment and led to the proposal that phytoplankton is not a direct source of CDOM, but that heterotrophic bacteria, through reprocessing of DOM of algal origin, are an important source of CDOM. In a recent experiment designed at looking at the effects of elevated pCO2 on blooms of the coccolithophorid alga Emiliania huxleyi, we found that despite the 3 different pCO2 levels tested (190, 414 and 714 ppm), no differences were observed in accumulation of CDOM over the 20 d of incubation. Unlike previous mesocosm experiments where relationships between CDOM accumulation and bacterial abundance have been observed, none was observed here. These results provide some new insights into the apparent lack of effect of pCO2 on CDOM accumulation in surface waters, and question the previously proposed mechanisms and rates of CDOM production in natural phytoplankton blooms.

Description: We fertilised 12 mesocosms with NE Atlantic phytoplankton with different Si:N ratios (0:1 to 1:1). After 1 wk, we added mesozooplankton, mainly calanoid copepods at natural densities to 10 of the mesocosms; the remaining 2 mesocosms served as controls. A trend of increasing diatom dominance with increasing Si:N ratios and species-specific correlations of diatoms to Si:N ratios were not changed by the addition of mesozooplankton. Large unicellular and chain-forming diatoms, thin-walled dinoflagellates (Gymnodiniales) and ciliates were reduced by copepod grazing while armoured dinoflagellates remained unaffected. Nanoplanktonic flagellates and diatoms profited from the addition of copepods, probably through release from ciliate grazing.

Description: Herbivory can greatly modify benthic community structure by affecting the distribution of algal species. To deter herbivores, algae have developed several mechanisms, including the induction of chemical and morphological defenses, which may be influenced by nutrient availability. We tested 4 red (Chondrophycus flagellifera, Cryptonemia seminervis, Osmundaria obtusiloba, Pterocladiella capillacea), 4 brown (Dictyota menstrualis, Lobophora variegata, Sargassum vulgare, Stypopodium zonale), and 1 green (Codium decorticatum) algae for inducible defenses following exposure to direct consumption by an amphipod community dominated by Elasmopus brasiliensis. In addition, the effects of water-borne cues from nearby grazed conspecifics and non-grazing consumers on the induction of defenses were examined in C. decorticatum under natural and enhanced (200% natural) nutrient levels. Induction of defense was assessed in choice-feeding assays, using live algae or artificial food containing non-polar extracts of amphipod-exposed (treated) and non-exposed (control) algae. Palatability levels, estimated as the relative difference in wet mass due to consumption in feeding assays between grazer-exposed and control plants, declined significantly in 3 species after the acclimatization period. Tissue from the directly consumed red alga P. capillacea (live alga) was significantly less palatable than tissue from the control plants. Likewise, a significant effect was observed in the brown alga L. variegata. Similar, although not statistically significant, trends were observed in 6 other species. For the green alga C. decorticatum, nutrient enrichment did not affect induction of defenses by herbivores, yet unfertilized plants were more palatable than fertilized conspecifics.

Description: Connell¹s intermediate disturbance hypothesis (IDH) postulates that diversity peaks at an intermediate level of disturbance frequency or intensity. To test the validity of this concept for the species-poor marine hard-bottom community of the Western Baltic, we chose an in situ experimental approach. Undisturbed fouling communities of 2 different successional stages, 3 and 12 mo old, were submitted to various levels of emersion intensities, defined as time spans of continuous exposure to the air d-1. Disturbance levels ranged from 0.25 h up to 12 h of daily exposure. The study on 3 mo old communities was repeated in 2 subsequent years, 1999 and 2000. Species richness, evenness and diversity (Shannon index) were recorded to measure the effect of intensity treatments on community structure. The IDH was confirmed in the first year, when diversity was found to peak at intermediate disturbances. However, for communities of both successional stages, diversity-disturbance relationships were U-shaped or not significant in the second year. This ambiguous picture basically confirms the validity of the mechanisms proposed by the IDH, but shows that their forcing can be masked by fluctuations in environmental parameters, such as climatic conditions. An extension of the model is proposed, that considers diversity enhancement under extreme conditions due to a disturbance-induced change in community structure. Furthermore we discuss a conceptual linkage of the IDH to the multiple stable-state hypothesis. Finally, we found community stability not to be positively correlated with community age and complexity.

Description: Some marine mammals may increase their underwater locomotor efficiency by taking down little air for dives and descending passively, although at the point of maximum depth they presumably have to use energy to counteract the downthrust, to stop themselves sinking further. Birds, having considerable quantities of body-associated air, would appear not to have this option. However, measurements of locomotor activity and inspiratory behaviour of free-living, diving penguins has revealed that birds regulated the inspired air volume so that upthrust, primarily derived from depth-related changes in air volume, was minimal and constant at the preferred foraging depth. Although this results in minimized costs of travel, it means total body oxygen stores have to vary with depth, something that helps explain why dive duration is so closely correlated with depth in birds.