Characteristics of Settling Coral Reef Fish Are Related to Recruitment Timing and Success

Many marine populations exhibit high variability in the recruitment of young into the population. While environmental cycles and oceanography explain some patterns of replenishment, the role of other growth-related processes in influencing settlement and recruitment is less clear. Examination of a 65-mo. time series of recruitment of a common coral reef fish, Stegastes partitus, to the reefs of the upper Florida Keys revealed that during peak recruitment months, settlement stage larvae arriving during dark lunar phases grew faster as larvae and were larger at settlement compared to those settling during the light lunar phases. However, the strength and direction of early trait-mediated selective mortality also varied by settlement lunar phase such that the early life history traits of 2–4 week old recruit survivors that settled across the lunar cycle converged to more similar values. Similarly, within peak settlement periods, early life history traits of settling larvae and selective mortality of recruits varied by the magnitude of the settlement event: larvae settling in larger events had longer PLDs and consequently were larger at settlement than those settling in smaller pulses. Traits also varied by recruitment habitat: recruits surviving in live coral habitat (vs rubble) or areas with higher densities of adult conspecifics were those that were larger at settlement. Reef habitats, especially those with high densities of territorial conspecifics, are more challenging habitats for young fish to occupy and small settlers (due to lower larval growth and/or shorter PLDs) to these habitats have a lower chance of survival than they do in rubble habitats. Settling reef fish are not all equal and the time and location of settlement influences the likelihood that individuals will survive to contribute to the population

Temperature Influences Selective Mortality during the Early Life Stages of a Coral Reef Fish

For organisms with complex life cycles, processes occurring at the interface between life stages can disproportionately impact survival and population dynamics. Temperature is an important factor influencing growth in poikilotherms, and growth-related processes are frequently correlated with survival. We examined the influence of water temperature on growth-related early life history traits (ELHTs) and differential mortality during the transition from larval to early juvenile stage in sixteen monthly cohorts of bicolor damselfish Stegastes partitus, sampled on reefs of the upper Florida Keys, USA over 6 years. Otolith analysis of settlers and juveniles coupled with environmental data revealed that mean near-reef water temperature explained a significant proportion of variation in pelagic larval duration (PLD), early larval growth, size-at-settlement, and growth during early juvenile life. Among all cohorts, surviving juveniles were consistently larger at settlement, but grew more slowly during the first 6 d post-settlement. For the other ELHTs, selective mortality varied seasonally: during winter and spring months, survivors exhibited faster larval growth and shorter PLDs, whereas during warmer summer months, selection on PLD reversed and selection on larval growth became non-linear. Our results demonstrate that temperature not only shapes growth-related traits, but can also influence the direction and intensity of selective mortality

Mean otolith-derived (a) larval growth, (b) pelagic larval duration (PLD), (c) size-at-settlement, and (d) early (2 d) juvenile growth of <i>Stegastes partitus</i> settlement-stage larvae, recruits (1–10 d post settlement), and juveniles (11–28 d) by lunar phase of settlement.

<p>Effect of temperature was minimized by including only 25 monthly cohorts collected from May 2003 to August 2008 with mean water temperatures of >28°C. Error bars represent SE. Different letters above the bars indicate significant relationships among age groups, within lunar phases. Different letters within the bars indicate significant relationships among lunar phases, within age groups (capital A, B denote differences within larvae, lowercase a, b denote differences within 1–10 d old recruits, lowercase x, y denote differences within 11–28 d old juveniles). Settlement-stage larvae are not included in the last panel because they had not yet settled so did not exhibit juvenile growth.</p

Results of Kruskal-Wallis tests comparing <i>Stegastes partitus</i> early life history traits among different phases of lunar settlement (1 = first quarter; F = full moon; 3 = third quarter; N = new moon); and among three age groups (L = larvae; R = recruits 1–10 d post-settlement; J = juveniles 11–28 d post-settlement).

<p>Results of Kruskal-Wallis tests comparing <i>Stegastes partitus</i> early life history traits among different phases of lunar settlement (1 =  first quarter; F  =  full moon; 3 =  third quarter; N  =  new moon); and among three age groups (L  =  larvae; R  =  recruits 1–10 d post-settlement; J  =  juveniles 11–28 d post-settlement).</p

Results of Mann-Whitney U tests comparing <i>Stegastes partitus</i> early life history traits between small and large settlement events for larvae, recruits (1–10 d post-settlement), and juveniles (1–28 d post-settlement); and among age groups (L = larvae; R = recruits; J = juveniles).

<p>Results of Mann-Whitney U tests comparing <i>Stegastes partitus</i> early life history traits between small and large settlement events for larvae, recruits (1–10 d post-settlement), and juveniles (1–28 d post-settlement); and among age groups (L =  larvae; R  =  recruits; J =  juveniles).</p

Intensity and shape (as cubic <i>b</i>-splines) of selective pressures acting on two otolith-derived traits, mean larval growth and PLD, in 13 cohorts of <i>Stegastes partitus</i> for three different seasonal periods, winter, spring, and summer.

<p>Intensity and shape (as cubic <i>b</i>-splines) of selective pressures acting on two otolith-derived traits, mean larval growth and PLD, in 13 cohorts of <i>Stegastes partitus</i> for three different seasonal periods, winter, spring, and summer.</p

Characteristics of Settling Coral Reef Fish Are Related to Recruitment Timing and Success

<div><p>Many marine populations exhibit high variability in the recruitment of young into the population. While environmental cycles and oceanography explain some patterns of replenishment, the role of other growth-related processes in influencing settlement and recruitment is less clear. Examination of a 65-mo. time series of recruitment of a common coral reef fish, <i>Stegastes partitus</i>, to the reefs of the upper Florida Keys revealed that during peak recruitment months, settlement stage larvae arriving during dark lunar phases grew faster as larvae and were larger at settlement compared to those settling during the light lunar phases. However, the strength and direction of early trait-mediated selective mortality also varied by settlement lunar phase such that the early life history traits of 2–4 week old recruit survivors that settled across the lunar cycle converged to more similar values. Similarly, within peak settlement periods, early life history traits of settling larvae and selective mortality of recruits varied by the magnitude of the settlement event: larvae settling in larger events had longer PLDs and consequently were larger at settlement than those settling in smaller pulses. Traits also varied by recruitment habitat: recruits surviving in live coral habitat (vs rubble) or areas with higher densities of adult conspecifics were those that were larger at settlement. Reef habitats, especially those with high densities of territorial conspecifics, are more challenging habitats for young fish to occupy and small settlers (due to lower larval growth and/or shorter PLDs) to these habitats have a lower chance of survival than they do in rubble habitats. Settling reef fish are not all equal and the time and location of settlement influences the likelihood that individuals will survive to contribute to the population.</p></div

Relationship between mean otolith-derived (a) larval growth and (b) size-at-settlement of <i>Stegastes partitus</i> recruits and adult conspecific density from June 2007 to August 2008.

<p>Relationship between mean otolith-derived (a) larval growth and (b) size-at-settlement of <i>Stegastes partitus</i> recruits and adult conspecific density from June 2007 to August 2008.</p

Mean otolith-derived (a) larval growth, (b) pelagic larval duration (PLD), (c) size-at-settlement, and (d) early (2 d) juvenile growth of <i>Stegastes partitus</i> settlement-stage larvae (dark gray bars), recruits (1–10 d post-settlement; light gray bars), and juveniles (11–28 d; white bars) by size of light trap pulse (larvae) and size of settlement event (recruits/juveniles).

<p>Effects of temperature and lunar phase were minimized by including only individuals from cohorts that encountered mean water temperatures of >28°C and settled during the darker half of the lunar cycle. Error bars are SE. Different letters above the bars indicate significant differences among age groups, within events of a given size. Different letters within the bars indicate significant differences between small and large events, within age groups (capital A, B denote differences within larvae, lowercase a, b denote differences within 1–10 d old recruits, lowercase x, y denote differences within 11–28 d old juveniles). Settlement-stage larvae are not included in the last panel because they had not yet settled so did not exhibit juvenile growth.</p

Rayleigh statistics for lunar and tidal amplitude synchrony in settlement and successful spawning of <i>Stegastes partitus</i> in the upper Florida Keys.

<p>Recruits were obtained from monthly surveys; settlement-stage larvae were obtained from light traps. Otolith microstructure of recruits was used to back-calculate settlement timing and recruit densities were adjusted for mortality to provide a more precise estimate of settlement magnitude. All tests were significant at p<0.001. Z is the Rayleigh test statistic; Day is the mean peak in lunar or maximum tidal amplitude calculated from mean vector angle; s is the mean angular deviation; Day 1 is the new moon.</p><p>Rayleigh statistics for lunar and tidal amplitude synchrony in settlement and successful spawning of <i>Stegastes partitus</i> in the upper Florida Keys.</p