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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.

Understanding how future ocean conditions will affect populations of marine species is integral to predicting how climate change will impact both ecosystem function and fisheries management. Fish population dynamics are driven by variable survival of the early life stages, which are highly sensitive to environmental conditions. As global warming generates extreme ocean conditions (i.e., marine heatwaves) we can gain insight into how larval fish growth and mortality will change in warmer conditions. The California Current Large Marine Ecosystem experienced anomalous ocean warming from 2014 to 2016, creating novel conditions. We examined the otolith microstructure of juveniles of the economically and ecologically important black rockfish ( Sebastes melanops ) collected from 2013 to 2019 to quantify the implications of changing ocean conditions on early growth and survival. Our results demonstrated that fish growth and development were positively related to temperature, but survival to settlement was not directly related to ocean conditions. Instead, settlement had a dome-shaped relationship with growth, suggesting an optimal growth window. Our results demonstrated that the dramatic change in water temperature caused by such extreme warm water anomalies increased black rockfish growth in the larval stage; however, without sufficient prey or with high predator abundance these extreme conditions contributed to reduced survival.

MANY MARINE SPECIES have small, pelagic rarly life stages. For those species, knowledge of population connectivity requires understanding the origin and trajectories of dispersing eggs and larvae among subpopulations. Researchers have used various terms to describe the movement of eggs and larvae in the marine environment, including larval dispersal, dispersion, drift, export, retention, and larval transport. Though these terms are intuitive and relevant for understanding the spatial dynamics of populations, some may be nonoperational (i.e., not measurable), and the variety of descriptors and approaches used makes studies difficult to compare. Furthermore, the assumptions that underlie some of these concepts are rarely identified and tested. Here, we describe two phenomenologically relevant concepts, larval transport and larval dispersal. These concepts have corresponding operational definitions, are relevant to understanding population connectivity, and have a long history in the literature, although they are sometimes confused and used interchangeably. After defining and discussing larval transport and dispersal, we consider the relative importance of planktonic processes to the overall understanding and measurement of population connectivity. The ideas considered in this contribution are applicable to most benthic and pelagic species that undergo transformations among life stages. In this review, however, we focus on coastal and nearshore benthic invertebrates and fishes.

Eddies can enhance primary as well as secondary production, creating a diverse meso- and sub-mesoscale seascape at the eddy front which can affect the aggregation of plankton and particles. Due to the coarse resolution provided by sampling with plankton nets, our knowledge of plankton distributions at these edges is limited. We used a towed, undulating underwater imaging system to investigate the physical and biological drivers of zoo- and ichthyoplankton aggregations at the edge of a decaying mesoscale eddy (ME) in the Straits of Florida. Using a sparse Convolutional Neural Network we identified 132 million images of plankton. Larval fish and Oithona spp. copepod concentrations were significantly higher in the eddy water mass, compared to the Florida Current water mass, only four days before the ME's dissipation. Larval fish and Oithona distributions were tightly coupled, indicating potential predator-prey interactions. Larval fishes are known predators of Oithona , however, Random Forests models showed that Oithona spp. and larval fish concentrations were primarily driven by variables signifying the physical footprint of the ME, such as current speed and direction. These results suggest that eddy-related advection leads to largely passive overlap between predator and prey, a positive, energy-efficient outcome for predators at the expense of prey.

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 (p CO ₂) 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 p CO ₂ 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 p CO ₂, which may alter the perception of auditory information by larval cobia in a high-CO ₂ 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.

As animals with complex life cycles metamorphose from one stage to the next, carry-over effects from earlier stages can affect future mortality. To examine the relationship between early life history traits and survival, seven monthly cohorts of newly-settled bluehead wrasse Thalassoma bifasciatum were collected immediately after settlement and over sequential 3-day periods. Otolith analysis was used to quantify mean larval and juvenile growth rates, pelagic larval duration (PLD), and settlement size and condition of different age classes to identify the traits most important for survival. Overall, survivors tended to have shorter PLDs, to settle at smaller sizes and higher condition levels, and to exhibit faster early juvenile growth. Water temperature contributed to amongcohort variability in traits as warmer water led to faster larval and juvenile growth and shorter PLDs. Trait-specific fitness functions demonstrated that temperature can influence fitness by changing the nature of selection on each trait. Estimates of selection intensity revealed that settlement condition contributed the most to variation in fitness across cohorts, followed by juvenile growth. Frequent loss of low settlement condition individuals and occasional loss of the very highest condition fish suggest that particularly high settlement condition during the warmest temperatures may be detrimental. Not only does the quality of settlers vary over time, but selective loss of individuals with particular phenotypic traits is not pervasive and can vary with environmental conditions such as temperature.

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.

IntroductionGlobally, anchovy and sardine typically display asynchronous population fluctuations with anchovy dominating during cool periods and sardine dominating during warm periods. However, this anchovy-sardine cold-warm paradigm has recently broken down in the California Current, suggesting that recruitment may not be a simple product of large-scale physical drivers. Instead, consideration of larval fish trophodynamics together with local oceanography is likely necessary to mechanistically relate survival and recruitment to the physical environment.MethodsWe examined otolith-derived metrics of northern anchovy (Engraulis mordax) growth in the context of local oceanography and anchovy in situ prey and zooplankton predators in the northern California Current (NCC).ResultsAnchovy growth was spatially variable and the regions that conferred heighted growth differed with regard to the cross-shelf extent of upwelled waters. When upwelling was restricted to the nearshore environment, anchovy larvae grew significantly faster inshore than offshore. Conversely, when the upwelling front moved farther offshore following sustained upwelling, offshore anchovy larvae grew significantly faster than inshore larvae. Modelling individual anchovy growth revealed that growth was affected by ambient copepod prey availability and gelatinous zooplankton predation pressure, with growth peaking at intermediate prey availability and the highest abundance of predators. Fast growth under high predation pressure may be indicative of the selective loss of slow growing larvae. Notably, larval anchovy abundances were high offshore but diminished immediately inshore of the upwelling front regardless of its cross-shelf position. This suggests that the upwelling front may act as a shoreward boundary for anchovy larvae, affecting their access to the highly nutritious prey base typical of the Oregon continental shelf waters in summer.DiscussionVariation in larval anchovy growth with local oceanographic conditions and fine-scale distributions of prey and predators provides a mechanistic hypothesis of food-web dynamics which will enhance our ability to predict the response of forage fishes to ecosystem variability.

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.

Measuring the spatial distribution of microparticles which include synthetic, semi-synthetic, and anthropogenic particles is critical to understanding their potential negative impacts on species. This is particularly important in the context of microplastics, which are a form of microparticle that are prevalent in the marine environment. To facilitate a better understanding of microparticle occurrence, including microplastics, we sampled subadult and young juvenile Black Rockfish ( Sebastes melanops ) at multiple Oregon coast sites, and their gastrointestinal tracts were analyzed to identify ingested microparticles. Of the subadult rockfish, one or more microparticles were found in the GI tract of 93.1% of the fish and were present in fish from Newport, and near four of five marine reserves. In the juveniles, 92% of the fish had ingested one or more microparticles from the area of Cape Foulweather, a comparison area, and Otter Rock, a marine reserve. The subadults had an average of 7.31 (average background = 5) microparticles detected, while the juveniles had 4.21 (average background = 1.8). In both the subadult and juvenile fish, approximately 12% of the microparticles were identified as synthetic using micro-Fourier Infrared Spectroscopy (micro-FTIR). Fibers were the most prevalent morphology identified, and verified microparticle contamination was a complex mixture of synthetic (∼12% for subadults and juveniles), anthropogenic (∼87% for subadults and 85.5% for juveniles), and natural ( e.g. , fur) materials (∼0.7% for subadults and ∼2.4% for juveniles). Similarities in exposure types (particle morphology, particle number) across life stages, coupled with statistical differences in exposure levels at several locations for subadult fish, suggest the potential influence of nearshore oceanographic patterns on microparticle distribution. A deeper understanding of the impact microplastics have on an important fishery such as those for S. melanops , will contribute to our ability to accurately assess risk to both wildlife and humans.