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Tuatara: Volume 17, Issue 1, May 1969

Frameworks of Marine Ecology

page 27

Frameworks of Marine Ecology

As a Non-Ecologist I am often impressed with the apparent contradiction between principle and practice in ecological research.

Approaches to ecology involve on the one hand, assertion of the involvement and complexity of animal relationships with their organic and physical environments. The literature shows on the other hand, that in marine ecology at least, actual research activity in field studies whether in the littoral or deep ocean, tends to be carried out at a relatively uncomplicated level. The complexities of association and community relationships are more often stressed in discussion and in theoretical approaches perhaps because field research as practiced is felt to be in some way inadequate.

The situation is more evident in marine ecological studies because of the difficulties of sampling in a mobile and often hidden environment which can obscure the detail of even the simplest relationships that are readily observable on land.

It may thus be that field studies in marine ecology have been less numerous and less effective than they might have been, for lack of clearly defined aims of study. The assumption by some workers that the natural situations they explored were dominated by inter-active processes may be unjustified and the failure of the community concept to act as a focus for study perhaps indicates that the concept itself, (meaning as it does, all things to all workers) has intrinsic defects. Some views of marine communities have almost implied an anthropomorphic conscious organisation among the organic components.

If ecology be the study of inter-relations among organisms and their organic and physical environments, then several kinds of investigation clearly throw light on these inter-relations and can be considered as contributions within the very broad definition of ecological study.

We can examine these studies for example with respect to the marine benthos, commencing with the organic factors. The first enquiry is of the uniqueness of a species and its existence in the area considered: then of the distribution of individual species or higher groups: and for example, of the availability of detrital and filterable food.

The parameters of the physical environment that can be examined are numerous and selection is generally made on grounds of feasibility of examination or measurement. In the fluid environment, we can for example measure distributions of water temperature and salinity and specific chemical components; daily, page 28 tidal, seasonal and other time variations of temperature and salinity; water movement in tidal and other currents; and depth and thus pressure.

The substrate can be characterised by examining amongst other variables, the grain size composition of sediments; the occurrence of exposed hard surfaces; the mobility of sediments; rate of deposition of sediments; and their chemical and petrological nature.

This sort of categorisation is typical of that explored in several current texts on ‘ecology’. The examples are of variables that can be sampled and measured directly. We thus have one essential element of ecological study — definitive ecology — that presents investigators with clear targets, the ultimate sum of which is the definition of the physical and organic environment.

Many present day approaches to ‘ecology’, seek correlations between pairs or groups of distributions of organisms or physical factors. This might be called associative ecology, following logically and readily from the availability of definitive material.

Similar distributions of organisms can be recognised and the nature and distribution of such associations examined. Correlations can usefully be sought of sediment type (defined perhaps by dominant grade component, by median diameter or by minimum percentage of one grain size) with occurrences of particular organisms. The most elementary correlations of animal with substrate, for example of various sessile animals with hard bottom, of filter feeders with strong currents and limited sediment supply are long established and well known. In most cases the correlation can be shown only in representational fashion. The properties of parameters that cause them to have the same distributional response in the total environment are mostly obscure, and generally not suggested by the associative method.

Both these segments of study are more properly ‘eco-geography’ than ‘ecology’. Both are dominantly static in concept since long or short term variations are generally not easily susceptible to study.

The third element of ecology endeavours to find events, processes mechanisms and responses that determine the correlations, and might be termed explanatory ecology. As an area of study this has suffered substantially from lack of achievable and acceptable targets for study in the marine field.

It is clear that such explanatory studies will produce results that by field methods are not demonstrably certain, but are the product of reasonable speculation and hypothesis. It is equally clear that the simple assertion of causal relationships does not constitute an advance in knowledge.

It is likely that two main sorts of determinative mechanisms can produce the animal in the place in which it is found.


Independent mechanisms (availability).


Interactive mechanisms (selection).

page 29

Among the first are for example the availability of larvae of suitable substrate, or appropriate temperatures.

Among the second are competition among species for area or volume of substrate, resistance to predation, and modification of the environment by one animal to permit the entry of another.

Orientation:— The targets of any ecological study must be arbitrarily set, for there are few natural limits. One might extend any field examination to the aquarium, and the laboratory, in search for the physiological basis for an animal's response to environmental demands. Equally individual or group behaviour may play a substantial part in determining the existence and viability of an animal in a given environment.

If the main aim is to interpret field studies then these can as a practical measure be examined as affecting a single species or a large group. The effect of the environment on the animal and that of the animal on the environment can be studied.

Alternatively one may, after recognising a particular association of species, or a group of animals with similar food demands, or a particular substrate niche, then look for the determinant factors in the environment selecting the observed fauna and the feed-back to the environment consequent on the existence of the selected animals.

Or one may proceed with the aim of recognising processes with less regard for the absolute species than for example for a mode of feeding or method of protection.

Scale of Application:— These aspects of ecological study can be applied to investigations of variability over large or small areas. The limited sampling of a large region will obviously produce broad-scale coarse results — contributions to zoo-geography and correlations of animal distribution with regional environmental differences. Such studies nevertheless lead directly to examination of fundamental questions of the nature of distributional boundaries and to consideration of the dependence of present situations on circumstances inherited from the late geological past.

Where closer observation is possible by camera and television or by acquiring undisturbed samples of large area and volume, then small areas of seafloor can be examined in fine detail and finer scale processes sought. Repeated sampling over small areas may well reveal successional or advective changes taking place in the fauna. Progress on all scales is needed.

The wide regional study has neither more nor less merit than detailed examination of a small area, the recognition and solution of taxonomic problems neither more nor less merit than determination of the sequence of events following a successful mollusc spatfall. Ideally it can be hoped that all the elements of the total study of marine ecology might advance in parallel with optimum interaction and feedback amongst them.