Ecology of a North Sea pockmark with an active methane seep

ABSTRACT: At a large North Sea pockmark, with active methane seeps, surface sediments were found to have higher insoluble sulphide concentrations than sedlments from the surrounding area. The fauna of the pockmark was characterized by 2 species which have not pi-evlously been reported from the Fladen Ground in the northern North Sea. These species were a b~valve, Thyasira sarsi (which is known to contain endosymbiotic sulphur-oxidising bacteria) and a mouthless and gutless nematode, Astomonerna sp., which also contains endosymbiotic bacteria The nematode was the dominant meiofauna species in the pockmark sediments. Both macro-lnfauna and total nematodes were in low abundance in samples taken from the base of the pockmark. Sediment samples from the pockmark contained numerous otoliths, implying that substantial winnowing of the sediment had taken place. This was supported by studies on the sulphide concentrations in the sediment which showed multiple layering of the sediments on the sides of the pockmark, suggesting displacement. The carbon isotope compositions (6I3c) of the tissues of benthic animals from in and around the pockmark were generally in the range -16 to -2O%, indicating that little methane-derived carbon was contributing to their nutrition. T sarsi had the most 13c-depleted tissues, -31.4 to -35.1 L, confirming the nutritional dependence of this species on chemoautotrophic bacteria that utilize reduced sulphur.

Aquatic Distribution And Heterotrophic Degradation Of Polycyclic Aromatic-Hydrocarbons (PAH) In The Tamar Estuary

Variations in the concentrations and microheterotrophic degradation rates of selected Polycyclic Aromatic Hydrocarbons (PAH) in the water column of the Tamar Estuary were investigated in relation to the major environmental variables. Concentrations of individual PAH varied typically between i and 50 ng l−1 Based on their observed environmental behaviour the PAH appeared divisible into two groupings: (1) low molecular weight PAH incorporating naphthalene, phenanthrene and anthracence and (a) the larger molecular weight homologues (fluoranthene, pyrene, chrysene, benz(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)-pyrene). Group 1 PAH showed a complex distribution throughout the estuary with no significant correlations with either salinity or suspended particulates. Based on their relatively low particle affinity and high water solubilities and vapour pressures, volatilization is proposed as an important process in determining their fate. Microheterotrophic turnover times of naphthalene varied between x and 30 days, and were independent of suspended solids with maximum degradation rates located in the central and urban regions of the Estuary. When compared with the flushing times for the Tamar (3–5 days), it is probable that heterotrophic activity is important in the removal of naphthalene (and possibly the other Group 1 PAH) from the estuarine environment. In contrast Group 2 PAH concentrations exhibited highly significant correlations with suspended particulates. Highest concentrations occurred at the turbidity maximum, with a secondary concentration maximum localized to the industrialized portion of the estuary and associated with anthropogenic inputs. Laboratory degradation studies of benzo(a)pyrene in water samples taken from the estuary showed turnover times for the compound of between 2000 and 9000 days. Degradation rates correlated positively with suspended solids. The high particulate affinity and microbial refractivity of Group 2 PAH indicate sediment burial as the principal tate of these PAH in the Tamar Estuary. Estuarine sediments contained typically 50–1500 ng g−1 dry weight of individual PAH which were comparable to the levels of Group 2 PAH associated with the suspended particulates. Highest concentrations occurred at the riverine end of the estuary resulting from unresolved inputs in the catchment. Subsequent dilution by less polluted marine sediments together with slow degradation results in a seaward trend of decreasing concentrations. However, there is a secondary maximum of PAH superimposed on this trend which is associated with urban Plymouth.

Some Practical Considerations In The Measurement Of Pollution Effects On Bivalve Mollusks And Some Possible Ecological Consequences

A consideration of some physiological (rates of oxygen consumption, the scope for growth) and cellular (the cytochemical latency of a lysosomal enzyme) processes in bivalve molluscs suggests that animal size and seasonal changes related to the gametogenic cycle are important sources of natural variability. Correcting for size using regression techniques, and limiting measurements to one part of the gametogenic cycle, reduces observed natural variability considerably. Differences between populations are then still apparent, but the results of laboratory experiments with hydrocarbons from crude oil suggest that it should be possible to detect sub-lethal effects due to pollution (the ‘signal’) in the presence of the remaining natural variability (the ‘noise’). Statistical considerations, taken together with results from current studies on Mytilus edulis and Scobicularia plana, indicate that sample sizes of 10–15 individuals should suffice for the detection of possible pollution effects. The physiological effects to be expected in the presence of sub-lethal levels of polluting hydrocarbons are on a scaie that can cause significant ecological damage to a population through a reduction in fecundity and the residual reproductive value of the individuals.

Effects Of Oil On Digestive Cells In Mussels - Quantitative Alterations In Cellular And Lysosomal Structure

Structural changes were observed in the digestive tubule epithelial cells of Mytilus edulis following long-term exposure to the water accommodated fraction (WAF) of North Sea crude oil (30 μg · l−1 total oil derived aromatic hydrocarbons). The changes observed involved a reduction in the height of the digestive cells beyond that demonstrated in a normal feeding cycle. In addition there was a loss of the normal synchrony of the digestive cells to a point where nearly all the tubules exhibited an appearance similar to that which is usually termed ‘reconstituting’. These alterations were quantified using an image analysis technique and the mean height of the digestive cells used as an index of digestive function or state. Long-term exposure also induced a radical alteration of the structure of secondary lysosomes within the digestive cells, resulting in the formation of large lysosomes, believed to be autolysosomes. Stereological analyses showed that these lysosomes are reduced in numbers and greatly increased in volume in comparison with controls. There is a concomitant increase in surface area of lysosomes per unit volume of digestive cell compared with control conditions. These alterations are indicative of fundamental changes in secondary lysosomal function involving an autophagic response to oil derived hydrocarbons. which would contribute to the reduction of digestive cell cytoplasm. These cellular alterations are discussed in terms of their use as indices of cell injury, in response to oil.

The Nematode-Copepod Ratio And Its Use In Pollution Ecology

The nematode/copepod ratio is critically examined with a view to adding some precision to its proposed use in pollution ecology. At two unpolluted intertidal sites, differing markedly in sediment grade, the metabolic requirements of copepods are shown to be equivalent to the requirements of that fraction of the nematode population which feeds in the same way. The partitioning of this total energy requirement among individuals depends on the distribution of individual metabolic body sizes and the relative rates of metabolism. The distribution of body sizes is constrained by the sediment granulometry, which affects nematodes and copepods differently. These considerations enable precise predictions of the nematode/copepod ratios expected in unpolluted situations, against which observed ratios can be compared.

Physiological Ecology Of 2 Populations Of Mytilus-Edulis-L

Seasonal cycles in the rates of oxygen consumption, feeding, absorption efficiency and ammonia-nitrogen excretion in two populations of Mytilus edulis were measured in the field under ambient conditions and related to body size, the gametogenic cycle, the concentration of suspended particulate matter in the water and temperature. Relationships between the various physiological variables are also considered and protein and energy budgets estimated. Both the “scope for growth” and the “relative maintenance cost” were seasonally variable, demonstrating a minimum capacity for growth in the winter and a maximum capacity in the summer. In one population subjected to abnormally high temperatures in the winter the scope for growth was negative for four or five months between January and May. These population differences are discussed and the potential for using physiological integrations in intra-specific comparisons of fitness is identified.