Spilled Oil and infaunal activity—modification of burrowing behavior and redistribution of oil

A series of experiments in Willapa Bay, Washington, indicates the degree to which the presence of spilled oil modifies the burrowing behavior of infauna and the extent to which the animals redistribute oil into interridal sediment. Small amounts of North Slope crude oil introduced at low tide directly into burrow openings (mostly made by the crustacean Callianassa) resulted in a limited and temporary reduction in the number of burrow openings. In contrast, a layerof oil-saturated sand 1 cm thick buried about 5 cm below the sediment surface sharply reduced the number of burrow openings. After a year, the few new burrows penetrated only the margins of the experimental plot, and bioturbation below the buried oil saturated sand layer declined dramatically.The experiments suggest that small amounts of oil temporarily stranded by tides in themselves have no long-range effect on burrowing behavior. The fauna, however, are capable of introducing measurable amounts of oil into the subsurface, where it is retained long after the rest of the stranded oil has washed away. A buried layer of oil-saturated sand greatly reduces infaunal activity; the oil presents an effective barrier that can persist for years.The oil incorporated into the sediment from burrow openings showed evidence of degradation after 7 months. In contrast, the layer of buried oil remained essentially undegraded after a period of two years, even though oil in lower concentrations above the layer was degraded after a period of one year. This variation in degree of dgradation of the buried oil, as well as the heterogeneity of oil distribution wherever the oil has been incorporated from the surface, emphasises the importance of careful sampling in any attempt to locate or monitor the presence of spilled oil in the substrate.     

GLORIA survey of the oceanic-continental transition of the Havre-Taupo back-arc basin

A GLORIA (Geological Long-Range Inclined Asdic) side-scan sonar survey, covering 23,000 km², provides the first complete imagery of an active and contiguous, oceanic to continental back-arc system, namely, the Havre Trough to Taupo Volcanic Zone (TVZ) New Zealand. Havre Trough tectonism and volcanism relates to a series of laterally discontinuous, mutiple spreading rifts which terminate southward at the 3-km-deep Ngatoro Basin. A 45-km sinistral offset attributed toen echelon synthetic shearing separates the basin from the actively spreading TVZ. Sonographs reveal a youthful and complex volcanic seascape with 20 newly discovered seamounts, whereas flanking regions are mantled with a largely featureless mud blanket.     

Esterification of vertebrate-like steroids in the eastern oyster (Crassostrea virginica)

The esterification of two model vertebrate steroid hormones - estradiol (E2) and dehidroepiandrosterone (DHEA) - was studied in the oyster Crassostrea virginica. The activity of acyl-CoA:steroid acyltransferase was characterized in microsomal fractions isolated from oyster digestive glands. The apparent Km and Vmax values changed with the fatty acid acyl-CoA used (C20:4, C18:2, C18:1, C16:1, C18:0 or C16:0), and were in the range of 9-17 microM, and 35-74 pmol/min/mg protein for E2, and in the range of 45-120 microM, and 30-182 pmol/min/mg protein for DHEA. Kinetic parameters were also assessed in gonadal tissue. The enzyme saturated at similar concentrations, although conjugation rates were lower than in digestive gland. Preliminary data shows that tributyltin (TBT) in the low microM range (1-50) strongly inhibits E2 and DHEA esterification, the esterification of E2 being more sensitive to inhibition than that of DHEA. Overall, results indicate that apolar conjugation occurs in oysters, in both digestive gland and gonads, at a very similar rate to mammals, suggesting that this is a well conserved conjugation pathway during evolution. Esterification, together with other mechanisms, can modulate endogenous steroid levels in C. virginica, and might be a target for endocrine disrupters, such as TBT.     

Ocean bottom seismometer detection of earthquakes on the Gorda Rise near 41.5° north

The spatial and temporal distribution of microearthquake activity associated with the southern section of the Gorda Rise was monitored during a three week period using an array of four ocean bottom seismometers (OBS's) located at 41.5° N, 127.5° W on the rise axis. Sixty-two events were detected, of which roughly half occurred during a seismic swarm following an event of magnitude 4.9 that was well-recorded on land. A total of eighteen earthquakes could be located, seventeen of which originated from the valley floor, walls, and crestal mountains while the remaining event was located to the east of the rise in the Gorda plate. Well-constrained focal depths for four earthquakes ranged from roughly 4 to 12 km. Depths in excess of 10 km for two of the events provide strong evidence for the absence of a shallow steady-state magma chamber beneath the slow-spreading portion of the Gorda rise. Most of the events are believed to be the result of uplift of the crustal blocks comprising the valley walls. Four events located at an offset of the rise near 41.5° N may be related to strike-slip movement on a developing transform fault. Two of the events that occurred during the survey were large enough to be detected and located by land-based instruments. Comparison of these locations with the OBS locations indicates that well-recorded events having magnitudes of at least 4.5 are routinely mislocated 40–50 km to the east of their actual locations in this area while lower magnitude, poorly recorded earthquakes may have significantly larger location errors.     

Exposure of grass shrimp to sediments receiving highway runoff: Effects on reproduction and DNA

A grass shrimp bioassay was carried out on sediments from three estuarine stations which were different distances from a highway storm drain. Total polycyclic aromatic hydrocarbon (PAH) concentrations were 29, 1.5 and 0.1 μg/g sediment at stations A (next to drain), B (100 m from drain) and C (500 m from drain), respectively. Lower embryo production and embryo hatching rates and a higher level of DNA strand breaks (comet assay) were observed in grass shrimp exposed to stations A and B sediments. There appeared to be an association between reproduction abnormalities and increased DNA strand breaks as a result of grass shrimp exposure to estuarine sediments receiving highway runoff.