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The effect of submarine carbon dioxide (CO 2 ) vents on seawater carbonate chemistry have been determined using hydrographical and marine carbonate data obtained from two submarine hydrothermal vent fields, as well as a reference station, all near the Jan Mayen Island in the Norwegian-Greenland Sea. We have shown that one can successfully determine the excess carbon that enters the seawater from the vents by applying a modified version of a back-calculation technique, which is traditionally used to study the invasion of excess atmospheric CO 2 in the surface ocean. As a result of this excess carbon, total dissolved inorganic carbon (C T ) in the seawater surrounding the vents was on average 12 lmol kg 21 (1-30 lmol kg 21 ) higher compared to samples obtained from a reference station outside the venting areas. The observed excess C T was most significant between 100 m and 200 m but was noticeable in all depths with the exception of the upper 10-20 m. The absence of a venting CO 2 signal in the surface water and the realism of the results are discussed. We believe the present method is promising for monitoring (detection and quantification) of CO 2 leakage into the water column due to its high sensitivity and readiness for automation.

We have investigated ihe effect of a salmon farm on the local benthos and the benthic environment. The bottom fauna was examined before establishment During this time 2417 tonnesof salmon were produced. The samples were collected from two stations within 250m of the farm site. The sediment contained mainly clay and silt, the organic content varied from 9-1 to 17-37o and there was no increase in the organic content during the sampling period.The bottom fauna in 1988 was rich and relatively similar at both stations. The species numberclose to the farm declined from 65 in 1988 to only 11 in 1989. A year after the fish farm was moved, the number of species had risen to 29.The fish farm clearly influenced the bottom fauna in thcimmediatevicinity of thesitebut no effect was found at 250m distance. The environmental conditions had improved in 1991 after abandonment of the site, but the fauna had not returned to the status measured before operations began in 1988.Correspondence: Per J. Johannessen,

A major vector for unintentional species introductions is international shipping. A wide range of organisms have been transported over long distances in ships' ballast tanks and as hull fouling. Although many desk studies and ship sampling programmes have been carried out, little information is available on changing numbers of individuals in ballast water during voyages. Detailed information could assist in evaluating the dimension of species import and future risks of unintentional species introductions by ballast water. The first European study, organised as a concerted action team and financed by the European Union, carried out several long‐term and short‐term workshops on board ships undertaking international voyages. The preliminary results from sampling the ballast water of the first four oceangoing workshops of this Concerted Action showed a decrease in numbers of specimens and taxa over time.

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