ALBERT

Description: Methane seeps in shallow waters in the northern Kattegat off the Danish coast form spectacular submarine landscapes - the 'bubbling reefs' - due to carbonate-cemented sandstone structures which are colonized by brightly coloured animals and plants. These structures may be 100 m2 in area and consist of pavements, complex formations of overlying slab-type layers, and pillars up to 4 m high. The carbonate cement (high-magnesium calcite, dolomite or aragonite) is 13C-depleted, indicating that it originated as a result of microbial methane oxidation. It is believed that the cementation occurred in the subsurface and that the rocks were exposed by subsequent erosion of the surrounding unconsolidated sediment. The formations are interspersed with gas vents that intermittently release gas, primarily methane, at up to 25 1 h-' The methane most likely originated from the microbial decomposition of plant material eposited during the Eemian and early Weichselian periods, i.e. l00 000 to 125 000 years B.P. Aerobic methane oxidation in the sediment was restricted Lo the upper 4 cm in muddy sand and to the upper 13 cm In coarse sand. Maximum aerobic methane oxidation rates ranged from 4.8 to 45.6 pm01 dm-3 d". The rock surfaces and epifauna around the seeps were also sites of methane-oxidizing activity. Integrated sulphate reduction rates for the upper 10 cm of muddy sand gave 4.2 to 26.6 mm01 m-2 d-' These rates are higher than those previously reported from similar water depths in the Kattegat but did not relate to the sediment methane content. Since gas venting occurs over several km2 of the sea floor in the Kattegat it is likely to make a significant local contribution to the cycling of elements in the sediment and the water column. The rocks support a diverse ecosystem ranging from bacteria to macroalgae and anthozoans. Many animals live within the rocks in holes bored by sponges, polychaetes and bivalves. Stable carbon isotope composition (6'") of tissues of invertebrates from the rocks were in the range -17 to -24 'A, indicating that methane-derived carbon makes little direct contribution to their nutrition. Within the sediments surrounding the seeps there is a poor metazoan fauna, in terms of abundance, diversity and biomass. This may be a result of toxicity due to hydrogen sulphide input from the gas.

Description: Occurrence of stomach wall granulomas in European smelt was studled at 6 locations along the German North Sea coast. Identification of larval nematodes inhabiting these granulomas is provided for the first time. Three species, isolated by pepsin-HC1 digestion, are involved: Hysterothylacium cf. cornutum, Cosmocephalus obvelatus and Paracuaria tridentata. 72% of all stomachs examined were affected. The ratio of number of granulomas to number of the 3 larval species free in the mesentery was 1:1.3. Differences in prevalences and intensities were significant among all locations. Granuloma abundance was highest in samples from the Elbe estuary decreasing in the other locations relative to their distance from the Elbe. There was no relationship between the number of larvae encapsulated on the stomach wall and the number of larval P decipjens in the musculature (r = 0.3). Host condition factor could not be related to number of granulomas. Smelt appaears to be an important transmitter of spiruroid nematode larvae to marine birds in this region.

Description: Stomach contents of 17 sperm whales Physeter macrocephalus stranded in Scotland and Denmark during 1990-96 were analysed. All were sub-adult or adult males and stranded between November and March. They had presumably entered the North Sea during their southward migration from feeding grounds in Arctic waters. Other studies indicate that the majority of the whales were apparently healthy. The diet of these whales was found to consist almost entirely of cephalopods, principally squid of the genus Gonatus (hereafter 'Gonatus', but probably G. fabricii, an oceanic species characteristic of Arctic waters). The other prey species identified were also mostly oceanic cephalopods: the squids Histioteuthis bonnellii, Teuthowenia megalops and Todarodes sagittatus and the octopus Haliphron atlanticus. Although these results are consistent with other recent studies in the area based on single stranded whales, they differ from results of work on whales caught during commercial whaling operations in Icelandic waters (1960s to 1980s) in that little evidence of predation on fish was found in the present study. Remains of single individuals of the veined squid Loligo forbesi, the northern octopus Eledone cirrhosa and the saithe Pollachius virens provided the only possible evidence of feeding in the North Sea. We infer that sperm whales do not enter the North Sea to feed. The timing, and large and uniform sizes of the Gonatus species eaten (most had mantle lengths in the range 195 to 245 mm), as estimated from measurements of the lower beaks, and the seasonality of the strandings is consistent with the whales having fed on mature squid, possibly spawning concentrations--as has recently been reported for bottlenose whales. Assuming that the diet recorded in this study was representative of sperm whales during the feeding season, as much as 500000 t of Gonatus could be removed by sperm whales in Norwegian waters each year and up to 3 times that figure from the eastern North Atlantic as a whole. Evidence from other studies indicates that Gonatus is an important food resource for a wide range of marine predators in Arctic waters.

Description: We describe an integrated database on European macrobenthic fauna, developed within the framework of the European Network of Excellence MarBEF, and the data and data integration exercise that provided its content. A total of 44 datasets including 465354 distribution records from soft-bottom macrobenthic species were uploaded into the relational MacroBen database, corresponding to 22897 sampled stations from all European seas, and 7203 valid taxa. All taxonomic names were linked to the European Register of Marine Species, which was used as the taxonomic reference to standardise spelling and harmonise synonymy. An interface was created, allowing the user to explore, subselect, export and analyse the data by calculating different indices. Although the sampling techniques and intended use of the datasets varied tremendously, the integrated database proved to be robust, and an important tool for studying and understanding large-scale long-term distributions and abundances of marine benthic life. Crucial in the process was the willingness and the positive data-sharing attitude of the different data contributors. Development of a data policy that is highly aware of sensitivities and ownership issues of data providers was essential in the creation of this goodwill.

Description: Phytoplankton (〉100 µm) abundance was studied in the open waters of the Gulf of Aqaba during the summer stratification period of 1996. A succession took place among the major phytoplankton groups, with diatom numbers decreasing throughout the summer. The diazotrophic cyanobacteria Trichodesmium spp. became more prominent as the stratification period progressed; 5 Trichodesmium species were identified: T. thiebautii, T. erythraeum with tuft-shaped colonies and Trichodesmium sp. with puff-shaped colonies were common at ~102 colonies m-3 throughout the stratification period, whereas T. tenue and T. hildebrandtii were more rare. A bloom of T. thiebautii and T. erythraeum with 〉106 tuft colonies m-3 was observed in coastal waters of the Gulf during fall 1997. Tuft-shaped colonies were dominant near the surface, while puff-shaped colonies of Trichodesmium sp. were mainly found in the bottom half of the photic zone. These depth distributions were maintained for more than 2 mo, suggesting that the 2 colony types occupied distinct niches. Puff-shaped colonies were found to have higher chlorophyll a contents than tufts, but their photosynthetic activities were not significantly different. Fatty acid analysis of dominant plankton species yielded new trophic relationships for Trichodesmium spp. The Trichodesmium spp.-specific fatty acid C22:2 ω6 was found in Macrosetella gracilis (the sole copepod to graze on Trichodesmium spp.) and in chaetognaths, suggesting that these carnivorous zooplankton fed on M. gracilis. Furthermore, this fatty acid was observed in the filter-feeding Salpa maxima, which was abundantly present in the Gulf of Aqaba during June 1997.

Description: In Eckernförde Bay (western Baltic Sea) pockmark structures are induced by groundwater seeping out of the sediment. On 3 occasions in winter and spring 1993-94 we investigated the influence of groundwater on the reduction of salinity, on porewater chemistry, and on bacterial activities (methane oxidation and sulphate reduction). In 2 out of 3 sampling campaigns groundwater discharge could be detected. The concentration gradients of Cl- and SO4= are moved towards the sediment surface by the vertical advection of groundwater during seep times. Without groundwater discharge the porewater chemistry resembled the control site. Compared to the control site, the methane oxidation and sulphate reduction rates were elevated at the pockmark site, reaching maximum values of 49 and 269 µmol l-1 d-1 respectively. The groundwater venting from the pockmark had an end member composition of 80 mM Na+, 1.0 mM Ca++ and was depleted in Mg++. Due to mixing of these major cations along the groundwater/seawater interface, no CaCO3 precipitation was found around the pockmark site.

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: Latitudinal clines in species diversity in limnic and terrestrial habitats have been noted for well over a century and are consistent across many taxonomic groups. However, studies in marine systems over the past 2 to 3 decades have yielded equivocal results. We conducted initial analyses of the MarBEF (EU Network of Excellence for Marine Biodiversity and Ecosystem Function) database to test for trends in local and regional diversity over the latitudinal extent of European continental-shelf waters (36° to 81°N). Soft-sediment benthic macrofauna exhibit little evidence of a latitudinal cline in local (α-) diversity measures. Relationships with water depth were relatively strong and complex. Statistically significant latitudinal trends were small and positive, suggesting a modest increase in diversity with latitude once water-depth covariates were removed. These results are consistent regardless of whether subsets of the database were used, replicates were pooled, or component taxonomical groups were evaluated separately. Local and regional diversity measures were significantly and positively correlated. Scientific cooperation through data-sharing is a powerful tool with which to address fundamental ecological and evolutionary questions relating to large-scale patterns and processes.

Description: A model, composed of coupled particle tracking and benthic response modules, for predicting waste solids flux and benthic impacts of gilthead sea bream (Sparus aurata L.) and sea bass (Dicentrarchus labrax L.) aquaculture, was tested at six sites with different hydrodynamics, bathymetries and biomasses in the Aegean and Ionian Seas, Eastern Mediterranean with observations of sediment trap flux and benthic impact indicators. Seven sediment trap validation studies were conducted that varied in design with traps deployed either on the sea bed, attached to nets or in the water column. Model predictions of flux to traps spaced 5 m apart up to 50 m from the cages over a 13 d period were statistically significant (r2 = 0.61, n = 57, p ≤ 0.05). However, the model could not predict adequately the flux to traps spaced 2 m apart in the high-flux zone underneath cages where variability between trap observations was high. In this high-flux zone underneath cages, the averaged model flux predictions resulted in a performance of ± 49%. Statistically significant relationships were established at four sites; between modelled flux and either benthic fauna impact indicator species (S), abundance (A), A/S ratio, Shannon Wiener Index or Biomass Fractionation Index (BFI), (r2 = 0.82, 0.60, 0.57, 0.67 and 0.48, respectively; n = 24, p ≤ 0.05). Two other sites, which did not exhibit an abundance peak in enriched zones, did not fit these relationships. Using relative abundance of taxonomic groups, a modelled flux of 4.1 g m-2 d-1 was a useful boundary; on either side of this boundary, clear trends occurred in pollutant tolerant and intolerant species.