Abstract
This work aimed at performing a large scale assessment of Diplodus spp. (Sparidae) nurseries along the rocky shore of Marseilles (France, NW Mediterranean) by locating and quantifying nursery microhabitats and estimating the settlement pattern along this shore in 2004. Nursery grounds of Diplodus spp. represented only 9% of the 52 km-long rocky shore of Marseilles. Their location, shallow rocky habitats sheltered within coves, made them vulnerable to human-induced habitat transformations. D. vulgaris settled along this coast at the end of February 2004 and D. puntazzo settled a couple of months earlier. Maximum densities observed reached 215 and 67 ind./100 m for D. vulgaris and D. puntazzo respectively. The settlement rates were spatially variable. At a regional scale, lower settlement rates were observed within the south and centre zones, compared to those observed in the west, east, and the Marseilles Bay zones. Suitable nurseries along this shore seem insufficient for the replenishment of adult assemblages, which suggests that they depend on the migration of adults from other areas. Along the Marseilles rocky shore, coastal development projects leading to the destruction of habitats would represent a major threat to the Diplodus life cycle, which could be even greater than usual given the vulnerability and small size of the nurseries. These results show that it is necessary to protect these scarce local nursery habitats and manage other nearby nurseries to ensure the survival of fish at a critical life stage and the replenishment of adult assemblages.
Highlights
Benthic and nektobenthic fish have a bipartite life cycle (Vigliola, 1998), with a pelagic larval phase and a more sedentary and benthic adult phase
Settlement is defined as the arrival of early juvenile fish to benthic nursery areas after their pelagic larval phase
This work aimed at (i) locating and (ii) quantifying Diplodus nursery grounds, and (iii) estimating the amount of settlers that settled during the winter and spring of 2004 along this shore
Summary
Benthic and nektobenthic fish have a bipartite life cycle (Vigliola, 1998), with a pelagic larval phase and a more sedentary and benthic adult phase. Settlement is defined as the arrival of early juvenile fish (referred to as “settlers”) to benthic nursery areas after their pelagic larval phase. Recruitment corresponds to the later incorporation of these juvenile fish into adult populations after their settlement and survival in nurseries (referred to as “recruits”) (Levin, 1994; Macpherson, 1998). The settlement rate can be defined as the number of new individuals joining the benthic habitat for a given nursery area. The recruitment level can be defined as the number of settlers remaining at the end of the post-settlement period, that is, those who survived and who will join adult assemblages (Macpherson, 1998)
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