Abstract
SUMMARY: Temporal variability in the size at settlement (SAS), age at settlement (PLD), larval growth and recruitment patterns of a temperate wrasse, Coris julis, were examined over two recruitment seasons for a single island site from the Azores archipelago in the northeastern Atlantic. Relationships between these early life-history traits and recruitment variability over time were also investigated. Average PLD and SAS varied significantly among sampling dates over the settlement season, increasing consistently over time. This pattern was persistent over two consecutive summers. Larval growth was not a good predictor for PLD or SAS, which were in turn positively correlated with each other. Differences in recruitment magnitude over time were not related to SAS, PLD or larval growth. Instead, we found that recruits whose early pelagic stage (first 30 d) overlapped part of a period of enhanced growth (above average and independent of larval age), tended to result in the largest recruitment events; these tended to occur in the mid season. Larvae from earlier and later settlement events, overlapping periods of depressed growth, were linked to more modest recruitment events. We hypothesize that short PLD, with resulting small SAS is favoured early in the season, when post-settlement density is lowest. Over the course of the settlement season, as recruits accumulate competition may increase, and larger SAS (associated with longer PLD), may provide a competitive/survival advantage.
Highlights
Understanding the mechanisms linked to highly variable survival rates and recruitment in fish populations is one of the most important quests in fish biology and management and has major biological and economic implications (Carr and Syms, 2006)
We found significant differences in larval growth measured for the entire larval stage (‘Growth’) and for the first 30 days in the plankton (‘Growth 30 d’) (Table 1)
The temporal pattern of ‘growth 30 d’ was different from that of PLD and size at settlement (SAS) and there was no indication of a consistent increase throughout the season in either year (Fig. 3)
Summary
Understanding the mechanisms linked to highly variable survival rates and recruitment in fish populations is one of the most important quests in fish biology and management and has major biological and economic implications (Carr and Syms, 2006). Recent theories highlight growth per se as a factor determining larval survival in plankton (Takasuka et al, 2003, 2004; Fuiman et al, 2005), a more parsimonious view places greater emphasis on larval size as a factor in predation vulnerability and on growth rate as a controller of cumulative size-dependent predation mortality (but see Fuiman et al, 2005). This view is based on the premise that larger individuals are less vulnerable to predation and more likely to survive than smaller individuals, which is the basis of Anderson’s (1988) general “growth-mortality” hypothesis. This idea postulates that the probability of lethal events (predation and starvation) occurring throughout the pelagic stage is cumulative and increases with stage duration, so cohorts spending less time in the plankton should produce strong recruitment events (Leggett and Deblois, 1994)
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