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Background, Aim and Scope:
Our study determined if and when an avoidance or attraction behavioural response would be displayed by Ilyanassa obsoleta when presented with a choice between harbour and reference sediments. Our goal was to develop a non-lethal approach that could be used in future assessments of the environmental quality of field sediments.
Materials and Methods:
Twenty snails were exposed in 7 L tanks to different amounts of Halifax Harbour sediments mixed with reference sediment placed in one half of a tank and reference sediments in the other. Sediments were covered with seawater, while the top half of the tank was exposed to air. One level of exposure was placed in triplicate tanks where the positioning of the snails was of 20:0, 0:20 and 10:10, in half:half of a tank. Details regarding the investigation of the set up conditions and results of exposures to specific chemicals or sediment extracts are outlined in Part 1.
Results:
The distinct avoidance of contaminated sediments and the preference for reference sediments were observed between 24 and 72 hrs of exposure, which was more pronounced with increasing percentage of harbour sediments mixed in reference sediments.
Discussion:
A decrease in avoidance was associated with a slight increase in temperature and longer exposure time and is interpreted as potential conditions favouring the degradation of contaminants and an increase in food. Part 1 of our study demonstrated the important role associated with the availability of food in reference sediments and a general lack of attraction to three biologically derived compounds known to be present in sewage discharges, i.e. a fatty acid methyl ester, cholesterol and coprostanol. The repelling properties of solvent extracts of a harbour sediment demonstrated that non polar chemicals were implicated in the avoidance response and would likely be reflecting the role of lipophilic contaminants in the avoidance response.
Conclusions:
It is proposed that the behaviour towards harbour sediments represents a balance between the avoidance of contaminants and the attraction of food. The present study provides a robust green assessment tool that is easy to set up to assess the quality of sediments.
Recommendations and
Perspectives:
The interpretation of field observations regarding the abundance of animals during environmental assessments must consider both nutritional and toxicological causes. Additional laboratory exposures are needed to determine the cause of the movement of snails away from harbour sediments, i.e. which specific chemicals play a role in the behavioural response and at which level of exposure. The degradation of contaminants should also be pursued to better understand the fate of organic compounds in this habitat.
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