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Title: Gaping at environmental variability : how do bivalves react to changing circumstance?
Author: Robson, Anthony Albert
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2008
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Documentation of behaviour involving movement with survival value is common in vertebrates, but reports are notably lacking in sessile bivalve molluscs, primarily because of the difficulty in quantifying behaviours that occur in these generally small animals, whose behaviour is characterized by minimal movement. Such movement may, however, be critical in survival and its quantification may provide insights into strategies and environmental conditions of consequence for this important animal group. Archival tag techniques based on Hall sensors and magnets working with infrasecond resolution were used to record valve movements in shellfish {Mytilus edulis, Mytilus trossulus, Pecten maximus, Cerastoderma edule and Margaritifera margaritifera) and recommendations made with regard to correct protocol for assessing valve movement behaviours exhibited by this group. The same technology was used to examine valve movements and exhalant pumping of the blue mussel Mytilus edulis in the laboratory, and valve movements of blue mussels in the wild according to circumstance. Circumstances examined in the laboratory were food concentration, addition of suspended sediment and the presence of predators (as evidenced by addition of mussel homogenate to the water). Mussel activity was studied in the wild according to height of individuals in the inter-tidal, season, light, instantaneous water depth, temperature and the action and extent of waves. Bivalve gape angle varied over the diel cycle, being greater at night than during the day for both laboratory and wild animals and varied with season in the in situ mussels, decreasing from summer through autumn to be lowest in winter (both during the day and at night). Although all mussels in the inter-tidal closed their valves during emersion, lower-shore mussels initiated gaping later than upper-shore individuals in relation to the incoming tide. There was considerable inter-individual variance in gaping behaviour. Gape angle in the laboratory mussels correlated with extent of pumping and was, therefore, generally assumed to be a proxy for feeding behaviour. However, M. edulis pumping activity is complicated because exhalant pumping can occur from the top of the inhalant siphon in addition to the exhalant siphon and pumping may be a response to oxygen requirements rather than feeding. Valve adduction (reduction in shell valve gape angle) and subsequent abduction (increase in shell valve gape angle) events constituted a normal part of bivalve behaviour, occurring in the laboratory and the inter-tidal mussels although the reasons for this behaviour are complex and not fully understood. Valve adduction events further complicate the relationship between valve gape angle and exhalant pumping because maximum recorded exhalant pumping was not produced by pumping (cilia beat) but by valve adduction. The significance of the findings are discussed with respect to mussel strategies for acquiring nutrients and minimizing the likelihood of predation and highlight the need for future research.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available