P. N. Salkeld

Use of annular flumes to determine the influence of current velocity and bivalves on material flux at the sediment-water interface

A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalveMacoma balthica and the epifaunal bivalveMytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbatorMacoma was found to increase the sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m−2). There was a significant correlation between sediment resuspension andMacoma density (r=0.99; p<0.001), which supported previous in situ field observations indicating bioturbation byMacoma enhanced sediment erodability. Biodeposition rates (g m−2 h1) ofMytilus edulis andCerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50–100% cover or >1400 mussels m−2) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20–25 cm s−1. These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.

Reproductive effort and value in different populations of the marine mussel, Mytilus edulis L.

SummaryFecundity, reproductive effort (estimated both from production measurements and from physiological data), the energetic costs of reproduction and the reproductive value of different size classes were measured for mussels at different sites and related to age and to tissue weight. Variability between sites was considerable and differences as great as 10 x were recorded between minimum and maximum values for egg production, reproductive effort and reproductive value. However, similarities between mussels from different sites were also apparent, as regards egg size, the estimated metabolic costs of egg production (based on measurements of oxygen consumption), the relationship (isometric) between egg production and body size, the fact of an increase in reproductive effort with increase in size, and the age at which maximum residual reproductive values was expressed. These relationships are discussed in terms of the fundamental reproductive strategy of the species and the degree of environmental stress imposed on the mussels at the different sites.

Responses of the mussel Mytilus edulis to copper and phenanthrene: Interactive effects

Most investigations of the responses of marine organisms to xenobiotics have concentrated on single contaminants and little is known of possible interactive effects of different classes of xenobiotics. As these latter seldom occur in environmental isolation, it is important to understand any interactions (synergistic or antagonistic) which may occur. This problem has been approached in the mussel Mytilus edulis by exposing estuarine mussels to copper (20 μg litre−1) and phenanthrene (100 μg litre−1) both individually and in combination, and measuring cytochemical subcellular and physiological responses after 3 days exposure and 3 days and 12 days recovery period. Results showed that mussels accumulated both xenobiotics during 3 days exposure. Depuration of copper was complete in 3 days recovery period, while loss of phenanthrene ranged from 30% to 70% of the concentration reached after 3 days exposure. There were no interactive effects on depuration. Both copper and phenanthrene reduced lysosomal hydrolase latency in digestive cells, and copper appeared to have a synergistic effect in preventing recovery of latency of lysosomal N-acetyl-β-hexosaminidase during the recovery period. There was evidence, in the digestive cells, of an antagonistic effect of copper on stimulation of activity of the microsomal respiratory chain (measured as NADPH-neotetrazolium reductase) by phenanthrene. Stimulation of this system by phenanthrene persisted after 12 days recovery period. There was a synergistic interaction of copper and phenanthrene on elevation of oxygen consumption and ammonium excretion. Clearance rates and scope for growth (physiological condition) were depressed by copper but not by phenanthrene after 3 days exposure. These findings are discussed in terms of known effects of copper and phenanthrene and the interactions are considered in terms of environmental effects measurements.

Sublethal biological effects and chemical contaminant monitoring of Sullom Voe (Shetland) using mussels ( Mytilus edulis )

Mussels ( Mytilus edulis ), collected from up to nine sites, were used to monitor the degree of chemical contamination (by petroleum hydrocarbons and organotins) and the associated sublethal biological effects (scope for growth) in the vicinity of the North Sea oil terminal at Sullom Voe from 1982 to 1989. Gluss Voe represented a ‘clean reference’ site at which mussels showed a very low level of contamination and a consistently high ‘scope for growth’ (>20 J g −1 h −1 ). Spatial and temporal changes in the concentration of polyaromatic hydrocarbons in the mussel tissues reflected the major sources of oil inputs and the number and size of oil spillages around the tanker loading jetties. Hydrocarbon concentrations in mussels at the oil tanker jetties were typically 10-fold higher than mussels at Gluss Voe. The concentrations of tributyltin in the tissues were greatest in the area near the tanker jetties and showed a steady decline between 1986 and 1989 which correlated with a decline in tanker activity ( r = +0.98). The results demonstrated a significant correlation between the net quantity of oil spilled during the month prior to sampling and the accumulated aromatic hydrocarbons in the mussel tissues ( r = +0.89). In addition, there was a significant negative relationship between scope for growth and the log concentration of aromatic hydrocarbons in the mussel tissues ( r = −0.83). Toxicological interpretation of tissue residue data indicated that the decline in SFG was caused by accumulated PAHs rather than TBT. Although mussels showed a significant reduction in scope for growth in Sullom Voe they were still able to grow, reproduce and maintain their populations. When these results are placed in a wider geographical context and compared with other UK sites, it is apparent that the ‘clean reference’ site in the Shetland has the lowest recorded levels of organic contaminants, and that other sites in the vicinity of the Sullom Voe Oil Terminal are less contaminated and impacted than many estuaries on the UK mainland.

The Effect Of Geographical Location On The Cellular Composition Of The Mantle Tissue Of The Mussel Mytilus-Edulis

The cellular composition of the mantle tissue of Mytilus edulis L. was determined, using quantitative microscopy (stereology) techniques, in three populations of mussels from differing environments, and the data compared. The results indicated that mussels from an estuarine or sheltered coastal environment had a greater proportion of adipogranular tissue than animals from an exposed, open coastal environment. The difference in cellular composition was attributed to differences in nutrient availability in the water column between the various sites. A 15-month transplantation of mussels from an open coast to estuarine conditions resulted in a decrease in the proportion of vesicular connective tissue in the mantle and an increase in gamete production. This suggests that Mytilus edulis can exhibit a high degree of phenotypic plasticity by using not only the more conservative strategy of nutrient storage during periods of high food availability, but also the more opportunistic approach of maximizing gamete production when conditions are favourable.