Spatial patterns of density at multiple life stages in protected and fished conditions: An example from a Mediterranean coastal fish

Abstract

Settlement and recruitment are well known to have critical influences on the demography of most marine fishes. Few studies have compared processes like larval supply, settlement and recruitment of fishes between protected (i.e. in marine protected areas, MPAs) and unprotected conditions and little information is available about the potential influence of early life history traits (e.g. pelagic larval duration, PLD) on these processes. In the present study, using the white sea bream Diplodus sargus sargus as a model species in the south-western Adriatic Sea, we investigated: 1) potential differences in the densities of adults, settlers, recruits and 1-YOs (one year old specimens) within an MPA and in unprotected areas, at multiple spatial scales; 2) the existence of local relationships between densities of adults (i.e. spawners), settlers, recruits and 1-YOs; and 3) the possible relationships between PLD and density of settlers. Both in 2009 and 2010 the density of settlers was higher at sites down-current to the MPA and showed a significant variability at the scale of sites (kms). Density of recruits only revealed variability among sites (both in 2009 and 2010), while density of 1-YOs was variable at the scale of sites and was higher in protected condition in 2011, but not in 2010. No significant relationships were found between the densities of adults, settlers, recruits and 1-YOs at the site scale, nor between PLD and the density of settlers. Results suggest a possible decoupling in space between the sequential life history stages of fish (from settlers to 1-YOs) due to dispersal (through sea currents or active fish movements). Further study may help better understand the actual contribution of MPAs to larval supply and recruitment in both MPAs and adjacent sites.