Influence of pelagic and benthic, biotic and abiotic, stochastic and deterministic processes on the dynamics of auto-recruitment of coral reef fish: A review

Abstract

Influence of pelagic and benthic, biotic and abiotic, stochastic and deterministic processes on the dynamics of auto-recruitment of coral reef fish: A review. The term recruitment is widely used by marine ecologists because it allows to gather together biologists, chemical and physical oceanographers on a common problem. Various definitions are given for recruitment (halieutic, physiologic, ecologic definitions). In this review, recruitment is defined as the integration of juveniles into adult populations. Today, it is accepted that the size of adult populations of benthic marine organisms at oceanic larval phase is determined almost entirely by the intensity of recruitment. Its spatio-temporal variability is responsible for the variability of adult populations. However, a few studies have examined mechanisms responsible for this variability to know whether it depends on pelagic or benthic, stochastic or deterministic, biotic or abiotic processes. This review provides information about the determinism of recruitment by studying the influence of these processes at a coral island scale and under the hypothesis of an autochthonous origin of larvae. Thus, we try to answer the following questions: what is the (i) temporal, (ii) spatial and (iii) intensity relationship between (a) the patterns of reproduction and of colonisation (pelagic phase), and between (b) the patterns of colonisation and of recruitment (benthic phase) The relative influence of different processes studied such as oceanic currents, larval growth, density-dependent or independent of benthic predation on fish dynamics is specific of each studied question. But, all these processes act with a more or less important impact on one stage of life cycle of coral reef fish (pelagic or benthic phase, reproduction, colonisation or settlement phase) to finally influence the dynamic of adult populations. Nevertheless, it is difficult to propose which process influences the more the dynamic of recruitment. Indeed, studies suggested that 105 eggs give 100 larvae at colonisation and 10 juveniles at recruitment. The pelagic processes such as currents or larval growth have probably a more important impact than the benthic processes such as metamorphosis or reef predation. Nevertheless, the benthic processes are the last to act on adult stocks. A density-dependent benthic process such as competition for space could inhibit the influence of pelagic processes on the dynamic of recruitment. Finally, we suggest that the number of juveniles integrating adult populations depends mainly on three benthic processes: larval flux, density-dependent mortality and density-independent mortality. Their influence depends on the success of colonisation, itself depending on oceanic processes and on success of reproduction. Yet, the success of reproduction is influenced by environmental conditions. If a stress happens during the reproduction, then the level of cortisol (hormone) increases in eggs. A too high concentration of cortisol induces a malformation of eggs and therefore of larvae. This will induce a less recruitment rate. Overall, the success of one ontogenic stage depends on the success of the others.