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Mysid shrimp, Neomysis integer, were acclimated to 4 temperatures (6, 10, 15 or 20 "C) and exposed to water-soluble fractions (WSF) of light fuel oil under 2 different regimes. The first, a chronic exposure scheme, employed ng 1-' hydrocarbon levels and lasted 2 wk. The second, acute exposure, employed yg 1-' levels and exposure occurred during determination of physiological parameters. We determined oxygen consumption, ammonium excretion rates, and computed oxygen nitrogen ( 0 : N ) ratios. Oxygen consumption was more strongly influenced by temperature than was ammonia excretion. Chronic exposure for 2 wk to aromatic petroleum hydrocarbons at the ng 1-' level did not significantly affect the parameters measured. Exposure to WSF at concentrations between ca. 200 and 1000 pg 1-l produced increases in oxygen consumption and decreases in ammonia excretion; these were strongly influenced by temperature with the greatest effect of oil exposure occurring at 21.5 "C, the highest temperature tested. Laboratory rearing conditions were shown to increase oxygen consumption and ammonia excretion rates compared to those of f~eld-collected mysids; however, the relative response to oil was not affected. On February 19, 1981, the tanker 'Sefir' sank in the Baltic Sea in 50 m of water, approximately 10 km SE of the Swedish island of Oland. The cargo consisted of approximately 800 tons of No. 0 and No. 1 fuel oil. At first, leakage from the ship on the bottom appeared to be slow but later the quantities increased. When the oil surfaced, it drifted, driven by winds and surface currents and parts of it landed on the southeast coast of eland. Extensive mortality of littoral fauna was observed where the oil came ashore (Linden et al., 1983). When the vessel was raised in late April it was found that about half of the cargo had leaked out. The present studies were initiated to address several aspects of oil pollution in the Baltic Sea. We determined the acute effect on oxygen uptake and ammonia excretion of the common Baltic mysid Neornysis integer following short-term exposure to pg 1-' levels of water-soluble fractions (WSF) of this light oil. In addition, the effects on oxygen consumption and Present address: University of California, Naval Biosciences Laboratory, Naval Supply Center, Bldg 844, Oakland, California 94625, USA O Inter-Research/Printed in F. R. Germany ammonia excretion were determined for ng 1-' exposure levels at 5-d intervals for a period of 15 d. The experimental protocol incorporated tests for both the acute and chronic tests over a temperature range between 6 and 20 'C. With the exception of lowest (winter) temperatures, these span the environmental range for the species. Thus by considering the effect of temperature, a dominant physical factor of the environment, the predictive model generated from the statistical analysis hopefully has been strengthened. MATERIALS AND METHODS Collection and maintenance of mysids: Adult Neomysis integer were collected with a dipnet at Stendorren, about 80 km south of Stockholm. Several collections were made in August and September (1981) as noted in the text. The catch consisted of late juveniles, males, non-ovigerous and ovigerous females. In the lab, mysids were fed Tetramin(R' fish food twice daily. Between 500 and 1000 mysids were kept in 70 to 80 1 of flowing Baltic Sea water taken from a depth of 40 m. 30 Mar. Ecol. Prog. Ser. 12: 29-41, 1983 Fig. 1. Schematic diagram of the water-soluble fraction maker. The stirring motor was set at low speed to avoid dispersing oil in the water. A flotation valve kept the water level constant as the WSF were withdrawn by dosing pumps. (A) Water reservoir with overflow; (B) float; (C) valve connected to float; (D) outlet for dosing pumps; (E) used oil evacuation pipe; (F) electrlc stirrer Chronic oil exposure: During chronic exposure, factorial combinations of 4 temperatures and 2 oil doses (control or exposed) were used. Two 80-1 aquaria were put into each of 4 large water baths adjusted to a temperature of 6, 10, 15 or 20 "C. These temperature regimens were generally stable throughout the course of a day but did occasionally vary k 1.5 C" during warmer or cooler periods as the weather changed. The solution of water-soluble fractions used for all tanks were made in one mixer schematically shown in Fig. 1. Four dosing pumps withdrew water from this tank to dose the oil-exposed group at each temperature. These pumps delivered WSF solutions at a rate of about 900 m1 h' tank-'. According to the nomograms in Sprague (1969), the half-time for water turnover in the tank would be ca. 2.5 d. In the control tanks, similar (but not identical) amounts of uncontaminated water were added. Especially at the higher temperatures, these flow rates would have been insufficient to provide oxygen to the number of mysids present. Therefore, aeration was supplied to all tanks. Aeration is no doubt a primary factor for the low aromatic hydrocarbon concentrations present in the oil exposure tanks (see below). All mysids used in the chronic tests were from a single collection (August 8, 1981) when field water temperatures were 14 to l 5 "C. In the lab, the mysids were put directly into the various exposure conditions without temperature acclimation. This treatment appeared to cause no acute temperature shock. Mysids began eating TetramidRI the day following capture. Acute oil exposure: For the acute exposure regime, WSF stock solutlon was prepared following the method of Anderson et al. (1974a) using 7 %O S water at 15 'C. Subsequently, the water phase was withdrawn and : brought to the test temperature. Dilutions to provide the exposure solutions were made just prior to use in the respirometers. Mysids used for the acute tests were collected at several different times and temperature-acclimated for periods of not less than 5 d. Those exposed to 18 and 21.5 "C were acclimated for the shortest period of time due to long-term deleterious effects of this high temperature. For a corollary experiment, field-collected mysids were tested under acute exposure conditions. These animals were collected 2 h before use in respirometry. They were not fed in the lab and all other manipulations prior to respirometry were minimized to avoid 'handling effects'. Hydrocarbon analysis: A limited number of hydrocarbon analyses were performed to characterize exposure regimes. During the chronic exposure tests, flow-through solvent extractors containing carbon tetrachloride were used during a 3-d period on several tanks. During the acute tests, 100 to 200 m1 aliquots of the 100 % WSF mixture were extracted with hexane for analysis of petroleum hydrocarbons. Several different analytical procedures were used to estimate hydrocarbon levels: infrared spectrophotometry (API, 1958), ultraviolet spectrophotometry (Neff and Anderson, 1975) or quantitative gas chromatography (Rudling, 1976). Respirometry and ammonia determinations: Oxygen partial pressures were determined using the oxygen electrode in a Lexington Instruments blood gas analyzer (Laughlin et al., 1979). Ammonia, determined by measuring NH,+ levels in the medium, was measured using the phenol-hypochlorite method (Solorzano, 1969). Flasks or large test tubes served as respirometry chambers, depending on the temperature. Use of smaller containers in the lower temperatures, where oxygen consumption was lower, insured approximately equal changes in oxygen partial pressures during respirometry. Under the protocols used here, partial pressures did not drop below half air saturation. In all tests respirometry periods were from 16 to 22 h, continuing overnight. Mysids exposed to chronic low levels initially were tested in pairs in the respirometers. However, at 20 "C mortality was common for one or both members of the Laughlin and Linden: Oil effects on Neornysls lnteger 3 1 pair. Initially, we attributed this to cannibalism and the number of mysids was subsequently reduced to 1 flask-'. This step did not alleviate mortality. We believe that this mortality was, in fact, attributable to unsuccessful attempts to molt. Ecdysis is a period of high vulnerability for crustaceans under any circumstances and we suspect that at 20 "C, a relatively high temperature, it was impossible for the mysids to accrue enough metabolic reserves to sustain themselves during the process. In general, 6 replicates per factor combination were prepared but these often were reduced owing to mortality, molting or release of larvae. Water uncontaminated by WSF was used in the respirometers. Flasks containing water but no mysids had negligible decreases in oxygen concentration or

Oil pollution and Baltic mysids: acute and chronic effects of the water soluble fractions of light fuel oil on the mysid shrimp Neomysis integer