Effects of bait digging on distribution and population recovery of Arenicola marina, Hydrobia ulvae and Macoma balthica have been investigated on trial plots at Blackness. Forth estuary (Scotland). A. marina rapidly recolonised the basins created by digging, but had reduced populations on the dug mounds. Its populations were dislocated for over 3 rno after digging. H. ulvae and M. balthica showed enhanced populations on the mounds for up to 2 wk, but were otherwise unaffected by digging. Factors influencing the mode of population recovery are discussed; it is suggested that enhanced basin populations of recolonising A. marina are due substantially to above-surface migration of worms into areas with increased levels of organic matter.

Acute toxicity of nickel and zinc to 2 estuarine invertebrates (Corophium volutator, Macoma balthica) has been studied at 3 temperatures (5, 10, 15°C) and a range of salinities (5 to 35 %, in 5 "/m increments), at time intervals up to 384 h. Median survival times with nickel and zinc decreased for both species as salinity decreased. Increases in temperature also caused a decrease in median survival time for C. volutatorwith both metals, and for M. balthica with zinc but not with nickel. From analysis of variance, significant factors and thelr interactions were included in response surface models for C. volutator and M. balthica separately for each element. Results indicate that the environmental variables of temperature and salinity should be considered when evaluating toxiclty of nickel and zinc in the estuarine environment.

Acute toxicity of pentavalent arsenic to 3 estuarine invertebrates (Corophium volutator, Macoma balthica, Tubitex costatus) has been studied at 3 temperatures (5, 10, 15OC) and a range of salinities (5 to 35 %o, in 5 %O increments), at time intervals u p to 384 h. Median survival times decreased as temperature and concentrat~on of arsenic increased, but salinity changes had no significant effect. From analysis of variance, significant factors and their interactions were ~n c l u d e d in response surface models for C. volutator and M. balthica separately. Results are compared with the limited data previously published. It is emphasized that environmental temperature should be considered when evaluating toxicity of arsenic in the estuarine environment.

The utility of fishes a s biomonitors for mercury in aquatic environments is widely recognised, with skeletal muscle a s the tissue normally chosen for most monitoring programmes. The liver may also be a suitable candidate tissue for monitoring, as it concentrates many pollutants to higher levels than muscle, and is closely involved with processes of metal dynamics, storage, and detoxification. Little consideration has been given previously to the validation of the use of liver for mercury biomonitoring, with regard to quantifying natural temporal vanation. This study considered such variation in the eelpout Zoarces viviparusL., a resident estuarine fish species collected from a subtidal site near a formerly major industrial mercury discharge in the Forth Estuary, eastern Scotland Llver and skeletal muscle mercury concentrations, liver weight, and body size variables were measured for 196 individual eelpout in seven 3-month periods. Liver Somatic Index (LSI) was significantly hlgher, and liver mercury concentrations significantly lower, in the summer than In other seasons. Llver mercury burden (the mass of liver mercury per fish), in contrast, showed only llmited sign~ficant seasonal variation relative to body size, implying that the observed seasonal variation of liver mercury concentratlon (by around a factor of 3 between summer and winter) results largely from the dilution of simllar burdens by a seasonally growing and shrinking liver. Such natural seasonal variation may confound the use of the muscle/liver mercury concentration ratio, which has been proposed as evldence of fish migrat~on between waters with different levels of mercury contamination. These results also suggest that, as variation in liver mercury concentrations is closely related to seasonal vanation in LSI, liver t~s s u e may not be a reliable monitor for mercury in temperate species of marine fishes with seasonally fluctuating l~v e r size.