The basic principles of communication via chemical mediators

The biological interactions mentioned above rest on one fundamental biological phenomenon chemoreception. This non-visual mode of perception appears to be particularly well developed in marine organisms, indeed it compensates for the lack of visual facility commonly encountered in the turbid or dark marine environment. The importance of chemoreception is further demonstrated by the often substantial increase in activity of chemo-receptor organs in marine organisms. 

In a general sense, communication will be positive if the mediator enhances growth or leads to favourable modification of the behaviour of the receiving oiganism. Such a supply may lead to commensalism, proto-cooperation and eventually symbiosis. Interaction is said to be negative when the mediator is toxic in itself (antibiotic, antiseptic or toxic) or brings about a lethal metabolic or behavioural modification in the receiver. 

In this field, the literature shows that, in many cases, mediation processes are involved in the maintenance of intra- or inter-specific relationships in microbial, algal or animal populations. 

Although comparatively few cases have been analysed, the evidence too often being obtained de vitro rather than de situ, it can be demonstrated that such relationships do exist between marine organisms and are indeed quite likely to occur in the natural environment. 

The inter-dependency of bacterial species has been described for a number of cases. One example is the close dependency of sulphate-reducing bacteria on the presence of an associated heterotrophic microflora which supply the bacteria with additional growth factors and favour reduction of the medium (Cahet, 1965, 1966 LeGall and Postgate, 1974). Moreover, the production of hydrogen sulphide binds them to sulpho-oxidisers within the ecosystem (called sulphuretum by Baas-Becking, 1925). 

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