Processes occurring during the early life history of fish can strongly influence the success in the recruitment and the dynamics of adult populations of coastal fish. The study of these features has become a major important issue to the management of these populations. The conditions experienced during the larval stage and during the early post- settlement phase are particularly important in species that live associated with reefs during the adult phase. In these populations, the extent of the pelagic phase and the variability of other early life history traits can affect recruitment success and connectivity between populations. Within the same species, fish from different populations living under different temperature regimes are expected to vary in their early life traits such as the extent of the pelagic phase, size at settlement and early growth. Other important biological aspects such as the onset of maturation can vary along the distributional range of a species. Symphodus melops is one of the common species in nearshore ecosystems in the North East Atlantic Ocean and in the Mediterranean. In order to investigate differences in life history features along the latitudinal range of this species and the relationship between growth and environmental variables, the otolith microstructure of young adults of this species collected in several populations, from Norway to Portugal, was analyzed. Annual otolith ring deposition was investigated and growth rates estimated considering the relationship between age and size of the fishes. Pre and post settlement growth patterns were estimated through the analysis of daily rings when possible, until the 60th day after hatching. The patterns obtained from adult S. melops from the Central coast of Portugal were compared to those from newly recruited fishes in order to calibrate the reading of daily rings and the estimation of early life traits from adult otoliths. Furthermore, the counting of all the rings in adult otoliths allowed a validation of the annual ring deposition and the interpretation of some translucent areas of the otoliths as reflecting ecological transitions rather than seasonal patterns. Fish from the Central coast of Portugal tended to have faster growth and the growth indices calculated revealed a tendency for slower growth with increasing latitude. The pelagic larval duration estimated was in agreement with published information for this species, and didn’t vary between populations. Furthermore, the microstructural analysis of otoliths also revealed that in the first sixty days the growth tendencies differed between populations. These were not significant in the pre-settlement phase, but increment width significantly increased from just prior to settlement to the first days after settlement; this tendency for increasing width after settlement was significant and was particular notorious in the Portuguese population. The results also allowed the detection of other ecological transitions, also more evident in the Portuguese population, that were expressed as changes in the daily growth rate, and seemed to be related with adaptation to a demersal mode of life. The results are discussed in face of the temperature fluctuations and the extension of reproductive seasons along the latitudinal range of this species. |
