Su Sponaugle

SELECTIVE MORTALITY DURING THE LARVAL-JUVENILE TRANSITION IN TWO CORAL REEF FISHES

For organisms with complex life histories, processes occurring during transitions between stages can strongly affect population dynamics. The major life history transition for many marine species is settlement from pelagic larvae to benthic or demersal juveniles. We examined differential mortality at settlement as a function of early life history traits (size-at-age, growth rates) in three cohorts of two common Caribbean coral reef fishes, Thalassoma bifasciatum and Halichoeres bivittatus (Labridae). We deployed light traps to collect late-stage larvae of each cohort. We also collected juveniles of each cohort at regular intervals (every second day) for two weeks following their first appearance on the nearshore reefs of Barbados, West Indies, during the spring (April–May) and fall (August–October) of 1997. Comparisons of otolith-derived traits exhibited by younger recruits (initial group) to those exhibited by older juveniles (survivor group) revealed that there was a difference in otolith growth during ...

EARLY LIFE HISTORY TRAITS AND RECRUITMENT PATTERNS OF CARIBBEAN WRASSES (LABRIDAE)

Despite the fact that recruitment can significantly influence the population dynamics of benthic marine populations, relatively little is known about the biological and physical processes controlling recruitment. We selected eight closely related coral reef fishes (wrasses in the family Labridae) to examine the temporal and spatial patterns of juvenile recruitment to the Caribbean island of Barbados. We used a comparative approach to study the relationships among patterns of recruitment, early life history traits, and aspects of the physical environment. For 10 wk during each of three peak recruitment (spring) seasons (1990–1992), we used a biweekly census of recently settled juveniles (8–25 mm standard length, SL) to measure the abundance of six congeners, Halichoeres bivittatus, H. radiatus, H. poeyi, H. garnoti, H. pictus, and H. maculipinna, and two confamilial labrids, Thalassoma bifasciatum and Bodianus rufus. Analysis of the otoliths of a sample of collected specimens provided estimates of larval d...

Response to ocean acidification in larvae of a large tropical marine fish, Rachycentron canadum

Currently, ocean acidification is occurring at a faster rate than at any time in the last 300 million years, posing an ecological challenge to marine organisms globally. There is a critical need to understand the effects of acidification on the vulnerable larval stages of marine fishes, as there is potential for large ecological and economic impacts on fish populations and the human economies that rely on them. We expand upon the narrow taxonomic scope found in the literature today, which overlooks many life history characteristics of harvested species, by reporting on the larvae of Rachycentron canadum (cobia), a large, highly mobile, pelagic-spawning, widely distributed species with a life history and fishery value contrasting other species studied to date. We raised larval cobia through the first 3 weeks of ontogeny under conditions of predicted future ocean acidification to determine effects on somatic growth, development, otolith formation, swimming ability, and swimming activity. Cobia exhibited resistance to treatment effects on growth, development, swimming ability, and swimming activity at 800 and 2100 μatm pCO2 . However, these scenarios resulted in a significant increase in otolith size (up to 25% larger area) at the lowest pCO2 levels reported to date, as well as the first report of significantly wider daily otolith growth increments. When raised under more extreme scenarios of 3500 and 5400 μatm pCO2 , cobia exhibited significantly reduced size-at-age (up to 25% smaller) and a 2-3 days developmental delay. The robust nature of cobia may be due to the naturally variable environmental conditions this species currently encounters throughout ontogeny in coastal environments, which may lead to an increased acclimatization ability even during long-term exposure to stressors.

Ocean acidification alters the otoliths of a pantropical fish species with implications for sensory function

Ocean acidification affects a wide diversity of marine organisms and is of particular concern for vulnerable larval stages critical to population replenishment and connectivity. Whereas it is well known that ocean acidification will negatively affect a range of calcareous taxa, the study of fishes is more limited in both depth of understanding and diversity of study species. We used new 3D microcomputed tomography to conduct in situ analysis of the impact of ocean acidification on otolith (ear stone) size and density of larval cobia (Rachycentron canadum), a large, economically important, pantropical fish species that shares many life history traits with a diversity of high-value, tropical pelagic fishes. We show that 2,100 μatm partial pressure of carbon dioxide (pCO2) significantly increased not only otolith size (up to 49% greater volume and 58% greater relative mass) but also otolith density (6% higher). Estimated relative mass in 800 μatm pCO2 treatments was 14% greater, and there was a similar but nonsignificant trend for otolith size. Using a modeling approach, we demonstrate that these changes could affect auditory sensitivity including a ∼50% increase in hearing range at 2,100 μatm pCO2, which may alter the perception of auditory information by larval cobia in a high-CO2 ocean. Our results indicate that ocean acidification has a graded effect on cobia otoliths, with the potential to substantially influence the dispersal, survival, and recruitment of a pelagic fish species. These results have important implications for population maintenance/replenishment, connectivity, and conservation efforts for other valuable fish stocks that are already being deleteriously impacted by overfishing.

Relationships between early life history traits and recruitment among coral reef fishes

Like many marine organisms, coral reef fishes have complex life cycles — adults are associated with reefs and produce pelagic larvae, which settle back to the reef as juveniles after a period of time. As might be expected from their diversity, coral reef fishes exhibit considerable variation about this generalized complex life cycle, especially with regard to their early life history (i.e. egg, larval and juvenile stages). For example, some coral reef fishes produce pelagic eggs and larvae, and the larvae settle directly to reef habitats as juveniles (e.g. labrids). In other species, the eggs and larvae are pelagic and larvae make the morphological transition to the juvenile stage while in the pelagic zone, prior to settling on reefs (e.g. acanthurids, mullids). In still other taxa, benthic eggs give rise to pelagic larvae that settle directly onto reefs (e.g. pomacentrids, gobiids).

Environmental variability, early life-history traits, and survival of new coral reef fish recruits

For benthic marine organisms with complex life cycles, conditions experienced by pelagic larvae can influence juvenile survival. Trait-specific selective mortality has been documented in the laboratory and field, yet our knowledge of the factors contributing to the existence, strength, and consistency of natural selective mortality is limited. We compiled previously published and unpublished data on the common Caribbean coral reef fish, Thalassoma bifasciatum, recruiting to Barbados, West Indies, and the upper Florida Keys to examine how environmental variability during pelagic larval life influences the distribution of early life-history traits exhibited by new recruits. We explored how the scope of variability in otolith-derived traits such as larval growth, pelagic larval duration (PLD), size and condition at settlement, and early juvenile growth influences the degree to which mortality of juveniles is selective. At both locations, contrasting oceanographic conditions (periodic passage of large low-salinity North Brazil Current [NBC] rings near Barbados and seasonal variation in water temperature at Florida) led to significant differences in the early life-history traits of recruits. Mortality was most frequently selective for the two most variable traits, condition at settlement and early juvenile growth. Environmental variability (including variation in predation pressure and stress-inducing conditions) also likely influences juvenile mortality and consequently the degree to which selective loss of particular traits occurs. As we begin to better understand the spatial, temporal, and species-specific circumstances in which events occurring during larval life influence juvenile performance, studies must also be extended to examine how these processes are translated into adult fitness.

Growth Variation, Settlement, and Spawning of Gray Snapper across a Latitudinal Gradient

Abstract Newly recruited juvenile gray snapper Lutjanus griseus were collected each fall for two consecutive years (2000 and 2001) from sites in Florida and North Carolina. Spawning, settlement, and growth patterns were compared across sites based on otolith microstructure. Larval otolith growth trajectories were generally similar for larvae from different sites and years; however, the mean pelagic larval duration (PLD) was 1 d longer for fish from North Carolina than for fish from the more southern sites. As a result, fish were larger at settlement to North Carolina. Estimated juvenile growth rates ranged between 0.62 and 0.88 mm/d and differed across sites and years, growth being generally faster at the southern sites. Water temperature accounts for some of this variability; however, site-specific differences in other factors probably contributed to some of the observed differences in growth. Back-calculated spawning patterns showed a lunar association with the new and first-quarter moons at all sites e...

Otolith microstructure reveals ecological and oceanographic processes important to ecosystem-based management

Information obtained from fish otoliths has been a critical component of fisheries management for decades. The nature of this information has changed over time as management goals and approaches have shifted. The earliest and still most pervasively used data are those of annual age and growth used to calculate the demographic rates of populations in single-species management strategies. Over time, the absence of simple stock-recruitment relationships has focused attention on the youngest stages, where otolith microstructure resolved on a daily basis has become a valuable tool. As management has transitioned to more ecosystem-based approaches, the need to understand ecological and oceanographic processes has been advanced through the analysis of daily otolith microstructure. Recent field examples illustrate how otolith microstructure data have been used to reveal environmental influences on larval growth, traits that lead to higher survivorship, mechanisms of larval transport, dynamics of dispersal and population connectivity, determinants of recruitment magnitude, carry-over processes between life stages, habitat-specific juvenile survival, and identification of natal sources. Daily otolith-derived data collected at an individual level are increasingly combined with data from other disciplines and incorporated into individual-based models, which in turn can form the building blocks of complex models of ecosystem dynamics. A mechanistic understanding of the ecology of young stages is particularly necessary in light of a rapidly changing ocean environment, as we need to be able to predict individual and population responses to perturbations. Otolith microstructure analysis is an important tool in our management arsenal, contributing to a broader understanding of the oceanographic and ecological processes underlying ecosystem dynamics.

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.

Drag-induced deformation : a functional feeding strategy in two species of gorgonians

Abstract The Jamaican gorgonians Pseudoptorogorgia acerosa (Pallas) and P. americana (Gmelin) exhibit whole colony flexibility in regions of moderate to high water movement. Juvenile colonies were tested under laboratory conditions to delinate the functional consequences of flexibility. Comparison of the drag forces exerted on flexible and artificially stiffened colonies in different flows to the forces required to detach colonies in the field suggested that the reduction in drag afforded by flexible colony deformation is not critical to preventing dislodgement. A further consequence of colony deformation was the reduction in the range of flow velocities encountered by the polyps relative to mainstream current velocity. Colonies appeared to feed most successfully when exposed to intermediate mainstream velocities of 10–15 cm·s−1. Therefore, the reduction of flow velocities at the level of the polyp broadens the range of ambient velocities over which successful feeding can occur, and as such, may be the most important consequences of flexibility.