Control and regulation of sparid recruitment (Teleostei) from the Mediterranean sea: Importance of pre- and post-settlement processes.

Population is the elementary structural component of ecosystems. Population size in marine benthic organisms with a planktonic larval phase being mainly determined by recruitment intensity, a parameter known for its variability and unpredictability, a detailed study of recruitment patterns was necessary. This four year study (1993 to 1996) concerned the importance of pre- and post-settlement processes on the recruitment of three sparid species from Mediterranean rocky shores, Diplodus puntazzo (Cetti), D. sargus (L.) and D, vulgaris (Geoffroy Saint-Hilaire). Demographic parameters of these species were studied between the settlement of larvae in shallow rocky zones:from the Marseille Gulf (43 degrees 10'N, 5 degrees 20'E) and the recruitment of juveniles into adult populations. Two different techniques were used in this study : otolith analysis and visual censuses. For the three species, the use of both techniques allowed to estimate planktonic larval durations, determine settlement and recruitment periods, link settlement intensity to climatic factors involved in larval transport, estimate growth and mortality rates while developing explanatory and inovative mathematic models, and broaden our knowledge on the biology and ecology of these fishes during this critical phase of their life cycle. Finally, the recruitment variability of Diplodus species was explained, its causes isolated, and the relative influence of the different factors involved quantified. Recruitment intensity of Diplodus depended on settlement intensity, i.e., larval amount, growth and benthic mortality. Settlement intensity varied between species by a factor 3 to 100 in relation with the size of the breeding stocks. For each species, larval amount varied by a factor 4 to 6 according to wind intensity, which controlled the transport of planktonic larvae to the coast. This variability in settlement intensity modified the recruitment intensity by a factor 2 to 3, Benthic growth depended on seawater temperature and its variations modified Diplodus recruitment by a factor 2 to 5. Benthic mortality was higth, from 43 to 99% depending on species, and was explained by predation. Mortality was density-dependent, which regulated Diplodus recruitment in dividing by a factor 2 the initial variability of larval amount. Implications in population dynamics, biogeography and evolutive ecology were discussed.