[Advances in Marine Biology] Advances in Marine Biology Volume 19 Volume 19 || Environmental Simulation Experiments on Marine and Estuarine Animals

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<ul><li><p>Adv . Mar . Bid . , Vol . 19, 1982. pp . 133-256 </p><p>ENVl RON M ENTAL SIM U LATlON EXPERl M ENTS ON MARINE A N D ESTUARINE ANIMALS </p><p>J . DAVENPORT </p><p>N.E.R .C . Unit of Marine Invertebrate Biology, Marine Science Laboratories. University College of North Wales. U . K . </p><p>I . I1 . </p><p>I11 . IV . V . </p><p>VI . </p><p>VII . VIII . IX . X . </p><p>XI . </p><p>Introduction . . . . . . . . . . Variability of the Inshore Environment . . </p><p>at an intertidal estuarine site . . </p><p>Development of Simulation Equipment . . </p><p>A . Temperature and salinity fluctuations </p><p>B . Rock pool physico-chemical conditions </p><p>Regimes . . . . . . . . . . . Temperature Experiments . . . . . . </p><p>B . Development . . . . . . . . C . Reproduction . . . . . . . . D . Adaptation . . . . . . . . </p><p>A . Survival . . . . . . . . . </p><p>E . Interaction with other factors . . Salinity Studies . . . . . . . . </p><p>A . Survival . . . . . . . . . B Behavioural responses </p><p>D . Growth . . . . . . . . . . E . Feeding . . . . . . . . . . </p><p>G Oxygen consumption </p><p>. . . . . . C . Reproduction . . . . . . . . </p><p>F . Osmotic/ionic responses . . . . </p><p>Oxygen Tension Studies . . . . . . </p><p>Acknowledgements . . . . . . . . </p><p>. . . . . . </p><p>Pollutant Studies . . . . . . . . Conclusions . . . . . . . . . . </p><p>References . . . . . . . . . . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>I . INTRODUCTION </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>. . </p><p>133 137 </p><p>139 143 145 160 166 166 175 177 179 </p><p>184 185 190 207 2008 209 209 230 233 236 240 242 242 </p><p>in2 </p><p>While the open sea is relatively stable in its physio-chemical makeup. indeed impressively so at depth. coastal and estuarine aquatic environments exhibit substantial fluctuations in physical </p></li><li><p>134 J. DAVENPORT </p><p>and chemical characteristics such as light intensity, turbidity, temperature, salinity and oxygen tension. These changes result from terrestrial, seasonal climatic, die1 and tidal influences. In coastal and estuarine littoral zones these various fluctuations, which interact in their effects upon organisms, are further complicated by periodic tidal emersion, with the consequent possibility of exposure of the littoral fauna to aerial and freshwater influences. </p><p>Inshore waters and estuarine areas bear the brunt of mans impact on the seas; they receive most types of deliberately released pollutants (thermal, radiological, inorganic and organic) for eventual dilution and dispersion in the great bulk of the marine hydrosphere and are also affected by accidently discharged pollutants (mainly oil). Because pollutant delivery to the environment is often intermittent, and because the subsequent fate of pollutants is affected by tides, currents, variable freshwater run-off and various chemical or biological processes, it is most unlikely that marine animals will ever be exposed to sustained steady pollutant concentrations. </p><p>For a variety of reasons animals of inshore waters have attracted rather more attention from experimental workers than have animals from the open sea. Obviously their availability and economy of collection have contributed to this, but their special attributes, evolved in response to the changeable nature of their environment have been particularly attractive to experimentalists. There are likely to be more challenging difficulties in understanding the adaptations of eurythermal or euryhaline animals compared with understanding their offshore stenothermal and stenohaline relatives. Similarly, i t is more logical to test the effects of heavy metal pollutants on inshore fish, crustaceans and molluscs, than on their deep water relatives. </p><p>Despite a predominant interest in experimental material from changeable environments, the main experimental approach adopted in the study of the effects of various environmental factors on coastal and estuarine animals has been the steady state or direct transfer experiment (see Fig. 1 ) . Conventionally this approach is used to study the effects of one environmental factor in isolation. Animals are taken from their natural habitat and held in the laboratory under constant conditions which approximate to field conditions at the time of collection, insofar as knowledge of those conditions and available experimental facilities allow. With the exception of the environmental factor under consideration, all conditions are held constant throughout the experimental period. </p></li><li><p>ENVIRONMENTAL SIMULATION EXPERIMENTS 135 </p><p>Experiment a I </p><p>Accl imat ion </p><p>Level n? </p><p>Native I eve1 t t t Sampling procedures </p><p>(for mortality, physiological </p><p>changes etc.) </p><p>t Collect ion </p><p>of animals Transfer t </p><p>Time I) </p><p>FIG. 1 . Format of the steady state or direct transfer experiment </p><p>The experimental animals are divided into groups. One, the control, remains at the acclimation level while the other groups are each transferred, usually directly, to situations where they encounter various levels of the factor being studied. </p><p>This type of experiment is simple, does not require complex apparatus, and is easy to repeat at almost any marine laboratory in the world. With portable equipment, and the acceptance of some compromises in the degree of control over factors other than the one under investigation useful studies may be carried out in remote areas. The Lsteady-state experiment is, however, open to criticism on several grounds, particularly when the results obtained are extrapolated uncritically to field conditions (for example when assessing likely limits to distribution of the animals). The experiment essentially consists of suddenly changing the environmental level of a particular factor and then sustaining the new level, often for long periods. Commonly, any changes induced by the procedure are attributed to the new factor level, and the trauma involved in transfer is ignored. Yet in nature such a sequence ,of events never occurs. An example from salinity studies serves to illustrate this point. The mussel, Mytilus edulis (L,), occurs in a variety of brackish water areas. In the Baltic Sea, populations of mussels are found at sites where the salinity is much lower than in the open sea (down to </p></li><li><p>136 J . DAVENPORT </p><p>5%,; Theede, 1965), but the salinity levels are quite stable, varying little even on a seasonal basis, so the animals are never exposed to sudden osmotic shocks. On the other hand, many estuarine populations of Mytilus are exposed to severe tidal fluctuations in salinity (Milne, 1940; Cawthorne, 1979a). They encounter sharp salinity changes, but no particular concentration is sustained for very long, and the mussels, like many other bivalves, survive exposure to low salinities for a few hours by closing the shell valves, and retaining water of high salinity within the mantle cavity (Milne, 1940; Gilles, 1972; Hoyaux et al., 1976; Shumway, 1977; Davenport, 1979a). Consequently, the conventional steady state experiment does not represent the environmental situation of either the Baltic or estuarine mussels. This example also illustrates another pitfall of steady state experiments. Many animals have mechanisms for avoiding damage caused by short term exposure to sub-optimal or deleterious, environmental conditions. Thus, as discussed above, bivalve molluscs reduce contact with the external environment to a greater or lesser extent when the external salinity is low; analogous behaviour is found in barnacles, gastropods, burrowing worms and hermit crabs (Newman, 1967; Foster, 1970; Davenport, 1976; Shumway and Davenport, 1977; Davenport et al., 1980). Wells (1949a, b) suggested that ArenicoZu marina (L.) avoided exposure to unfavourable media by ceasing to irrigate its burrow, while recent work (Davenport, 1977; Davenport and Manley, 1978; Manley and Davenport, 1979) has shown that several bivalve species are capable of detecting heightened environmental copper levels and can close their shell valves, or at least reduce the rate of irrigation of the mantle cavity to avoid damage during a few hours exposure to this pollutant. It has also been known for a long time (Turner et ul., 1948) by workers interested in antifouling techniques that mussels can detect chlorine and close their shell valves to survive intermittent exposure to chlorinated sea water. All of these behaviour patterns are devices to counteract transient unfavourable conditions and evolved only for short term, notably tidal, periods. In the extended direct transfer type of experiment, animals are often inspected at daily or even longer intervals; by this time overriding respiratory or nutritional demands may have forced animals to abandon their avoidance behaviour and resume normal activity in conditions to which they would not usually be exposed. </p><p>A refinement of the basic steady state experiment has been the multivariate approach pioneered especially by Costlow et aZ. (1960) and Alderdice (1963, 1972). In this type of investigation animals are </p></li><li><p>ENVIRONMESTAL SIMULATIOK EXPERIMENT8 137 </p><p>exposed to Combinations of factors (e.g. salinity and temperature, or salinity, temperature and oxygen tension, etc.) rather than single factor stresses. Obviously this approach is most useful for finding out how factors interact, and also for determining optimal laboratory or rearing conditions (Box, 1956) very rapidly. However, the experi- ments have also been used for the construction of multidimensional survival envelopes (e.g. McLeese, 1956) with the implication that these are valid for distribution in the field. The objections set out above for single stress steady state experiments apply equally to multivariate studies, with the additional comment that, if it is unnatural or unphysiological to expose animals to instantaneous single factor shocks, then it is surely even more artificial to impose sudden multifactor changes. </p><p>Dissatisfaction with some aspects of the steady state experi- mental approach has spurred an increasing number of workers to develop apparatus to provide experimental regimes which more closely reflect the changeable nature of the environment, at least for one factor (e.g. temperature, salinity, oxygen tension) at a time. Initial steps in this direction were taken with temperature alone (e.g. Grainger, 1956; Khan, 1965). However, following the salinity studies of Tucker (1970a), several researohing groups have developed apparatus to mimic the salinity fluctuations of estuaries or coastal lagoons. Such salinity studies have been the most common form of environmental simulation experiment performed so far, although the project at the Netherlands Institute for Sea Research, Texel has been running for several years, and some thermal, oxygen tension and pollutant studies have also been performed. </p><p>Since the literature devoted to such studies is still relatively compact, and because the recent advent of microprocessor tech- niques holds out the promise of relatively cheap and flexible apparatus to facilitate simulation studies, the time appears ripe for a review of the field. </p><p>11. VARIABILITY OF THE INSHORE ENVIRONMENT </p><p>It would normally be appropriate to replace the unphysiological aspects of steady state experiments by conditions of temperature, salinity or oxygen tension which animals are likely to encounter in nature. For realistic simulation studies therefore adequate inform- ation is required about the source and form of natural fluctuations ir! </p></li><li><p>138 ,J. DAVENPORT </p><p>levels of various environmental factors. For the sublittoral environment, whether coastal or estuarine, there is an extensive amount of information about temperature and salinities, simply because physical oceanographers interested in currents and mixing processes rely heavily upon these data in their calculations. Unfortunately much of this information is either somewhat inaccessible, or not well correlated with biological data. Also, except for a few estuarine studies (e.g. Sanders et al., 1965), little detailed information is available about short term (i.e. tidal or diel) changes in temperature or salinity. For the intertidal environment data is much sparser and often incomplete. For example, Southward (1958) showed that barnacles at Plymouth U.K. were exposed to a 16 deg C thermal change between tidal extremes in the summer; this observation was valuable, but gave no idea of the exact form of the temperature changes encountered by the animals over a 24 h period, although it seemed likely that temperature changes associated with emersion/immersion would be quite abrupt. Detailed information about the form and amplitude of changes in salinities and temperatures occurring in the intertidal zone over periods of as much as 24 h at different times of the year was virtually absent until the work of Cawthorne (1979a), itself indequate, being collected from only one particular estuarine site. An area of rather greater knowledge lies in the characteristics of the specialized rock pool environment, including fluctuations in oxygen tension and pH, which have been monitored by several workers (e.g. Stephenson et al., 1934; Pyefinch, 1943; Read, 1969; Ganning, 1971; Daniel and Boyden, 1975) and will be discussed in detail later. </p><p>Most monitoring of polluted marine or estuarine environments has been carried out over weeks, months or years with emphasis being placed upon relatively infrequent chemical and biological sampling; the possibility or consequences of tidal or diel fluctuations in pollutant concentration have largely been ignored. However, the effects of thermal pollution, in the form of power station discharges, have attracted the attention of many researchers, and the first major review of the field was published as long ago as 1965 (by Naylor). Broadly speaking, power stations have two effects upon the environment. First, and most obviously, their discharges heat up the inshore waters nearby, the temperature increment decreasing with distance from the discharge point. In terms of fluctuations in environmental temperature this effect simply means that the fluctuations occur rather higher up the temperature scale than they would have done in the absence of the station. Secondly, power </p></li><li><p>ENVIRONMENTAL SIMULATION EXPEHIMESTS 139 </p><p>stations apply sudden thermal increases (usually of the order of 10degC in about 5s) to organisms entrained in the cooling water passing through the stations condensers. This latter effect can be very damaging, especially in summer when o...</p></li></ul>