Cybium, Revue Internationale d’Ichtyologie
Copyright © 2003 Société Française d’Ichtyologie

(1) École pratique des hautes Études, UMR CNRS 8046, Université de Perpignan, 52 avenue de Villeneuve, 66860 Perpignan, FRANCE.
(2) Centre de Recherches insulaires et Observatoire de l’Environnement, B.P. 1013, Papetoai, Moorea, POLYNÉSIE FRANCAISE.

Résumé. - Le terme recrutement est sûrement le plus utilisé par les écologistes marins car il permet de rassembler sur un même problème, les océanographes biologistes, chimistes et physiciens. Différentes définitions lui sont données selon le domaine d’étude : halieutique, physiologique ou écologique. Dans cette synthèse, le recrutement est défini comme l’intégration des juvéniles dans la population d’adultes (définition écologique). Aujourd’hui, il est largement accepté que la taille des populations adultes des organismes marins benthiques à phase larvaire planctonique est déterminée en majorité par l’intensité du recrutement. Sa variabilité spatio-temporelle est pour partie responsable de celle de la structure des populations d’adultes. Cependant, peu d’études ont étudié les mécanismes responsables de cette variabilité afin de savoir si ces fluctuations dépendent principalement de processus pélagiques ou benthiques, stochastiques ou déterministes, biotiques ou abiotiques. Cette synthèse a pour but d’apporter des éléments de réponse à ce déterminisme du recrutement, en étudiant l’influence de ces processus à l’échelle d’une île corallienne et sous l’hypothèse d’une origine autochtone des larves. Ainsi, nous essayons de répondre aux questions suivantes : quelle est la relation (i) temporelle, (ii) spatiale et (iii) en intensité entre (a) le type de ponte et celui de colonisation (phase pélagique), et entre (b) le type de colonisation et celui du recrutement (phase benthique) ? L’influence relative des différents processus étudiés tels les courants océaniques (dispersifs ou tourbillonnaires), la croissance larvaire, la prédation benthique (densité-dépendante ou indépendante), sur la dynamique des poissons est spécifique de chaque question étudiée. Mais tous ces processus agissent à un degré plus ou moins important sur une étape du cycle biologique des poissons (phase pélagique ou benthique, phase de la reproduction, de la colonisation ou de l’installation) pour finalement se répercuter sur la dynamique des populations d’adultes, étape ultime du cycle biologique.

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.

Key words. - Coral reef fish - Recruitment - Autochthonous origin - Egg-larvae-juvenile relationship - Pelagic and benthic processes.