Sublethal effects of contaminated sediment on Arenicola marina

Purpose

The highest concentrations of environmental contaminants are generally found in marine sediments, and there is a need for knowledge concerning how and whether they affect sediment-dwelling organisms. This study aimed to assess sublethal effects in Arenicola marina exposed to two sediments from a contaminated fjord and two reference locations with different sediment characteristics.

Materials and methods

Duplicate contaminated sediments were used to investigate the robustness of current protocols for sediment testing. The two reference sediments, with different grain sizes and total organic carbon, were collected from the outer Oslofjord and the two contaminated sediments from Frierfjord. Polychaetes were exposed in quadruplicate sediment microcosms and sampled after 1, 2, 4 and 8?weeks of exposure. Oxidative stress resistance (total oxyradical scavenging capacity, TOSC) and components comprising the energy budget (cellular energy allocation, CEA) were determined for individual polychaetes.

Results and discussion

Arenicola maintained and increased body weights over the initial 4?weeks of exposure in all groups, except in one reference sediment (Elle). There were no differences between treatments in the scavenging capacity (TOSC). The most striking difference in how polychaetes partitioned energy resources was a difference in lipid and carbohydrate allocations for Arenicola held in the contaminated sediments over the initial weeks. Cellular respiration appeared to increase in polychaetes held in the Elle sediment and decreased for polychaetes held in the two Frierfjord sediments by weeks?4 and 8. In the overall CEA, this was offset by increased energy per weight stored in the Elle group, which resulted in an overall positive CEA for polychaetes held in that sediment, whereas polychaetes in the other treatments were close to neutral. Although CEA would thus indicate that Elle polychaetes had good health status, their body weight also decreased significantly over the experimental period compared to other treatments, indicating an overall negative effect.

Conclusions

This study has shown the importance of sediment characteristics when evaluating toxicity and how resource allocation can differ dramatically over a short time span in polychaetes held in similarly contaminated sediments. There were no clear effects of sediment contamination on CEA or TOSC in the polychaete A. marina. The findings are relevant for the design of both short- and long-term sediment studies.