Studies on some responses of Carcinus maenas (L.) and other brachyurans to hypoxia and aerial exposure
Johnson, Ian Trevor
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- © 1985 Ian Trevor Johnson. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
This work comprises a series of investigations of the effects of changes in environmental oxygen levels, which occur with hypoxia or aerial exposure, on the osmo-regulatory capacity, acid-base balance and general respiratory physiology of brachyuran crabs. The principal species studied was Carcinus maenas, although Cancer pagurus and Liocarcinus puber were also included in the aerial exposure experiments.
The effects of exposure to 4hr of moderate (Pw02 = 40 torr) or severe (Pw02 = 20 torr) hypoxia at 15°C on various blood solutes, acid-base balance and general respiratory physiology were assessed for C.maenas in low salinity (10.0, 13.5 and 19.0%.S) and fully marine (30.0%.S) media. Haemolymph pH increased at all test salinities and to an extent which was salinity/Pw02 dependent. During hypoxia the heart rate (fh) was not significantly affected at any salinity but the scaphognathite rate (fsc ) increased significantly (P<0.05) at all the media tested. Scaphognathite rate changes were greater in moderate rather than severe hypoxia. In hypotonic media hypoxia produced no changes to circulating Na+ or Mg2+ levels or to the Δ°C values but circulating Cl- levels fell and Ca2+ and lactate levels increased at salinity/ Pw02 dependent rates and extents. In the 30.0% S medium, no changes to any of the above blood ions occurred during moderate hypoxia but Ca2+ and lactate levels increased at Pw02 = 20 torr. At all test salinities original levels of blood Cl-, Ca2+ and lactate were regained within 4hr of re-oxygenation Pw02 = 130 torr). The implications of these findings have been considered in relation to the distribution of regulating species of crustaceans generally.
The effects of 24hr severe (Pw02 = 20 torr) hypoxia on haemolymph protein synthesis in fed and starved C.maenas in 13.5%.S and 30.0%.S media were studied. Blood total protein levels were higher in animals acclimated to 13.5% S whereas haemocyanin levels were higher in the 30.0%.S group. A negative linear relationship between relative haemocyanin and blood total protein was observed in animals at both salinities. In fed animals small, but non-significant (P>0.05) increases in haemocyanin and total blood protein levels were recorded at both salinities (cf. normoxic animals). In starved groups at both salinities blood protein levels were maintained under hypoxia but control animals showed a fall in protein levels.
The responses of the crabs C.maenas, C.pagurus and L.puber to short (4hr) and longer (24hr) term aerial exposure were investigated. On exposure to air oxygen consumption (M02) was reduced significantly (P<0.05) in C.pagurus and L.puber (cf. aquatic respiration rates), but the M02 of C.maenas in air was comparable to that in water. No marked change in fH or f sc were recorded in C.maenas during re-immersion following aerial exposure but in L.puber tachycardia and hyperventilation were observed. In air (4hr) there were no changes to blood lactate levels in C.maenas but pronounced changes were found in C.pagurus and L.puber. Long-term aerial exposure resulted in mortalities and significant (P<O.OS) increases in blood glucose and lactate levels in C.pagurus and L.puber but no mortalities or marked changes to these metabolites in C.maenas. The findings have been considered in relation to the structure and resistance to collapse of the gill lamellae in air.
- Department of Zoology, The University of Hull
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