Physiological flexibility; a necessity for life in anoxic and sulphidic habitats
In: Hydrobiologia. Springer: The Hague. ISSN 0018-8158; e-ISSN 1573-5117, more Related to:Hagerman, L. (1998). Physiological flexibility; a necessity for life in anoxic and sulphidic habitats, in: Baden, S. et al. Recruitment, colonization, and physical-chemical forcing in marine biological systems: Proceedings of the 32nd European Marine Biology Symposium, held in Lysekil, Sweden, 16-22 August 1997. Developments in Hydrobiology, 132: pp. 241-254. https://dx.doi.org/10.1007/978-94-017-2864-5_20, more |  |
| Keywords | Anoxic conditions
Bioenergetics
Chemical compounds > Sulphur compounds > Sulphides
Diseases > Human diseases > Hypoxia
Properties > Physicochemical properties
Respiration > Anaerobic respiration
Marine/Coastal |
| Abstract | Shallow marine areas and brackish water are often characterized by extensive short- or long-term fluctuations in physical parameters: temperature, salinity, oxygen. Sulphide can accumulate as a consequence of oxygen deficiency.Diel fluctuations in oxygen can in non-exposed shallow waters vary from 0 to 300% saturation, at the same time temperature can increase to 30 °C while salinity can decrease or increase. These types of short-term fluctuations impose a great demand on the immediate response of the organism: the organism must be able to maintain ‘normal’ physiological processes and behaviour as long as possible to minimize, for instance, the risk of predation by more tolerant species. Apparently competing species can on a small scale be separated in space by different abilities to tolerate diel or local fluctuations in environmental conditions. Short-term adaptations are often different from those used under long-term fluctuations which often cover larger areas.Energetics are most favourable with aerobic metabolism. The maintenance of a constant aerobic metabolism over as wide an oxygen range as possible is influenced by various ex- and in-trinsic factors but must be considered a primary adaptation to decreasing oxygen tensions in active benthic animals. Active animals that often are exposed to large variations in oxygen tensions have developed the best behaviour to increase the availability of oxygen and thus to regulate their aerobic metabolic rate despite an often low tolerance of severe hypoxia or anoxia. High temperatures decrease the ability to regulate and might force an anaerobic metabolism. Besides behavioural and ventilatory/circulatory adaptations improved haemolymph pigment characteristics are important in supplying oxygen under hypoxia. These adaptations are well developed in eurythermal and euryhaline shallow water and rock-pool crustaceans but best developed in sediment-living organisms which besides hypoxia can also be influenced by hypercapnia and sulphide. The highly toxic sulphide complicates the pattern. Active epibenthic organisms can simply avoid sulphide by moving away. Endobenthic or inactive organisms must try to exclude it temporarily, or adapt to the presence of sulphide. Burrow-constructing benthic invertebrates are dependent on their ability to ventilate and thus oxygenate at least parts of their burrows to oxidize the sulphide diffusing into the burrow water. During hypoxia in the overlying water or during ventilatory pauses the oxygen in the burrows will not be sufficient and the animal will be exposed to sulphide.Animals digging and crawling into the sediment more frequently and over longer time are more continuously exposed to severe hypoxic, anoxic and sulphidic conditions and have therefore developed strategies permitting survival under long anoxic and high sulphide exposure. Long-term exposure involves adaptations to decrease metabolic expenditure during aerobic metabolism and to use anaerobic pathways with a miminum drain on energy stores, both as a protection and to prolong survival. Benthic animals from a wide range of phyla have developed different strategies resulting in survival for many weeks under adverse environmental conditions. |
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