Effects of hypersalinity on the behaviour, physiology and survival of commercially important North Sea crustaceans
Thesis or dissertation
- © 2011 Katie Louise Smyth. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
Despite the increasing number of hypersaline discharges associated with desalination and, more recently, solute mining activities, there is little existing information relating to the effects such environmental disruptions may have on populations of commercially-important crustacean species. The present studies aim to redress this information-gap with novel investigations which have addressed some hypersalinity-induced behavioural and physiological responses of three crustacean species, the European lobster, Homarus gammarus (L), and two crab species, the brown crab, Cancer pagurus (L) and the velvet crab, Necora puber (L).
All three species feature prominently in the East Yorkshire fisheries, and are found typically in full salinity seawater environments that show little salinity variability. The development of extensive gas storage caverns underground in East Yorkshire, UK, has led to the commencement of the discharge offshore of large volumes of hypersaline brine effluent into the local, normally salinity-stable habitat of the three test species The combined volume and concentration of this discharge has the potential to raise the salinity in the local environment and these studies have focused on the possible ecological and commercial implications of such changes.
Each species was found to have a threshold value of hypersalinity above which halotaxic, preference behaviour was evoked (salinity 50 for H. gammarus and N. puber and salinity 45 for C. pagurus). The relationship between cardioventilatory activity and hypersalinity of H. gammarus and N. puber was examined under conditions when escape from the test salinity was prevented. Both showed a significantly decreased mean scaphognathite beat rate beyond a critical salinity value (salinity of 50 and 45 for H. gammarus and N. puber respectively). These salinities are consistent with the onset of the preference behaviour of these species. The heart rate of H. gammarus is also negatively related to increased salinity. These significant reductions in cardioventilation resulted in increased mortalities at salinities > 50–55. Significant changes to haemolymph pH and levels of haemolymph protein, haemocyanin, glucose and ammonia also occurred when test H. gammarus and N. puber were given sufficient time to acclimate to a test salinity. These changes made were typical of those under hypoxia in these and other decapod species and are consistent with the observed changes to the cardioventilatory behaviour.
These findings prompt the novel hypothesis that hypersaline exposure beyond limits, which vary inter-specifically, elicits a switch to anaerobic respiration, even when the animals are in a fully-oxygenated medium. Results showed that when exposed to hypersaline conditions, H. gammarus was a weak iono-regulator, with the haemolymph ionic concentration increasing directly with that of the external medium whilst remaining slightly hypo-ionic to it. Late-postmoult H. gammarus were found to be less tolerant of hypersalinity than intermoult ones and, even when the carapace was approaching full hardness, were intolerant of salinities > 40. Contrastingly, C. pagurus with 96h LC50 at a salinity of 55.5 was the most tolerant of the three species tested. The lack of significant haemolymph change in this species suggests a strong degree of osmo- and iono- regulation. Under hypersaline exposure N. puber regulated haemolymph variables within the range of salinity 35–50. Higher salinities were found to require a more protracted acclimation period.
The combined effects of haemolymph and cardioventilatory changes found for the test species demonstrate that unavoidable exposure to hypersaline conditions results in a lowered fitness and eventual death. Inevitably, this will impact negatively on commercial crustacean shellfisheries in and around the areas of brine discharge unless the discharge itself is managed and monitored appropriately.
- Department of Biological Sciences, The University of Hull
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