Environmental constraints upon locomotion and predator-prey interactions in aquatic organisms: an introduction

Abstract

Environmental constraints in aquatic habitats have become topics of concern to both the scientific community and the public at large. In particular, coastal and freshwater habitats are subject to dramatic variability in various environmental factors, as a result of both natural and anthropogenic processes. The protection and sustainable management of all aquatic habitats requires greater understanding of how environmental constraints influence aquatic organisms. Locomotion and predator-prey interactions are intimately linked and fundamental to the survival of mobile aquatic organisms. This paper summarizes the main points from the review and research articles which comprise the theme issue 'Environmental constraints upon locomotion and predator-prey interactions in aquatic organisms'. The articles explore how natural and anthropogenic factors can constrain these two fundamental activities in a diverse range of organisms from phytoplankton to marine mammals. Some major environmental constraints derive from the intrinsic properties of the fluid and are mechanical in nature, such as viscosity and flow regime. Other constraints derive from direct effects of factors, such as temperature, oxygen content of the water or turbidity, upon the mechanisms underlying the performance of locomotion and predator-prey interactions. The effect of these factors on performance at the tissue and organ level is reflected in constraints upon performance of the whole organism. All these constraints can influence behaviour. Ultimately, they can have an impact on ecological performance. One issue that requires particular attention is how factors such as temperature and oxygen can exert different constraints on the physiology and behaviour of different taxa and the ecological implications of this. Given the multiplicity of constraints, the complexity of their interactions, and the variety of biological levels at which they can act, there is a clear need for integration between the fields of physiology, biomechanics, behaviour, ecology, biological modelling and evolution in both laboratory and field studies. For studies on animals in their natural environment, further technological advances are required to allow investigation of how the prevailing physico-chemical conditions influence basic physiological processes and behaviour.

Figure 1

(a) The generalized effect of a given environmental factor on whole animal performance, behaviour and ecology in aquatic organisms. A given factor can directly affect the organism's behaviour and its tissue and organ functions, and consequently whole animal performance. This can have effects at the behavioural level as well. Ultimately, altered behaviour and whole animal performance will have ecological effects. (b) The effect of temperature on the locomotion and predator–prey relationships of ectotherms. Temperature has direct effects on digestion and standard dynamic action (SDA) as well as on muscle and heart function. Effects on digestion can cause direct effects on predator–prey relationships. Effects on muscle and heart function have direct effects on swimming performance and, therefore, indirectly upon those predator–prey relationships which are dependent on locomotion. Temperature can also have direct and indirect effects on behaviour, through changes in habitat selection (a direct effect) and activity patterns (an indirect effect through change in locomotor performance). Behavioural changes will ultimately affect predator–prey relationships at the ecological level.