Survival Of Early Life Stages Research Articles

Modeling the larval growth and survival of Pacific cod (Gadus macrocephalus) in the eastern Bering Sea

The eastern Bering Sea (EBS) is a highly productive ecosystem that supports several important commercial species such as the Pacific cod (Gadus macrocephalus). Climate variability affects the population dynamics of this stock throughout its life stages, especially early life stages, since they are particularly susceptible to environmental changes. In recent decades, warm and cold stanzas (i.e., 3–5 year periods) have been observed in the EBS, and there is evidence that they can modulate the recruitment of this stock, causing important socioeconomic impacts. Using a mechanistic individual-based model, this study investigates the spatial and temporal variability of growth and survival of Pacific cod's early life stages during 2000–2020. We examined changes by year and over space and compared our results with published literature to validate our model. We found that temperature played a key role in modulating the survival of fish larvae, observing an increase in starvation events in warmer years or locations. Periods or areas with low prey density, especially small-bodied copepods, also contributed to increased starvation. The average temperature in the fish habitat was negatively correlated with recruitment estimates from the stock assessment model. Growth was primarily temperature-driven; however, food-limited growth became more frequent when larvae were smaller during cold years. Spatially, we found that the environmental conditions in the southeastern Bering Sea may favor larval survival but reduce growth, and higher mortality may be persistent on the middle and outer shelf. Our model produces results that agree with previous field studies, and it offers a valuable tool to investigate other ecological questions on the impact of the environment on early life stages of fishes.

Anomalous ocean currents and European anchovy dispersal in the Iberian ecosystem

Unlike other upwelling areas where sardine and anchovy species dominate the pelagic ecosystems, the Western Iberian ecosystem has been consistently dominated by European sardine Engraulis encrasicolus, while anchovy had a residual presence from the start of acoustic surveys, in 1989, to 2014. Since 2015, the abundance of anchovy in the Western Iberian margins has sharply increased and continues to show an increasing trend as of 2023. It is unclear if this increase is a result of dispersal from nearby recruitment areas, higher survival rates of early life stages due to favorable environmental conditions, or both. We used a set of different models to simulate the dispersion and survival of anchovy early life stages in the Iberian region for the years preceding the increase in anchovy abundance. An ocean model simulation with the model CROCO provided the fields used as background for Lagrangian simulations coupled to an individual-based model of anchovy eggs and larvae. We simulated the years 2013-2015, and the results show that in 2014 and 2015, anomalous upper-ocean circulation patterns with strong and persistent eastward currents transported a large number of eggs and larvae from the Bay of Biscay (BoB) eastward along the Northern Iberian margin. The maximum transport occurred in June and July 2015, when 8 and 4%, respectively, of the eggs spawned in the BoB potentially reached the Iberian west coast as larvae. This process might explain the increase in anchovy abundance in the Western Iberian ecosystem. The results of the study show that episodes of anomalous intense ocean currents, when coincident with high presence of eggs, can lead to the colonization of new areas, and connectivity between areas varies dramatically with time.

A video monitoring and computational system for estimating migratory juvenile fish abundance in river systems

AbstractDiadromous fishes migrate between marine and fresh waters for reproduction. For anadromous species, which spawn in freshwater, improved access to freshwater spawning and nursery habitats and ability of juveniles to emigrate to the ocean may support population recovery. Despite the potentially enormous influence of early life stage survival on adult population size, managers and scientists have limited capacity to assess numbers of juvenile anadromous fishes leaving freshwater ecosystems. Such data are critical for evaluating reproductive success and habitat suitability and have been identified as a top priority in anadromous fish research and management. We developed a state‐of‐the‐art underwater video and computational system to collect videos to estimate abundances and migration timing for juvenile river herring (Alosa pseudoharengus; Alosa aestivalis). We collected continuous video in the Monument River (Bourne, Massachusetts, USA) from June to November 2017. We trained three types of neural network models to detect and count fish in video frames and evaluated model performance by comparing human counts to model outputs. Our top model assessed presence and absence (F1 = 87%) and counted fish (counting error 9.4%) with an accuracy comparable to human counters (F1 = 88%). Our system's capability to collect accurate counts of emigrating juveniles will provide critical information that could be related to the numbers of spawning adults, system‐specific productivity, and spawning and nursery habitat suitability. Both the video collection system and computational model may be transferrable to other sites and for other species where tracking juvenile emigration may inform management efforts.

The effect of ocean acidification on otolith morphology in larvae of a tropical, epipelagic fish species, yellowfin tuna (Thunnus albacares)

Increasing ocean acidification is a concern due to its potential effects on the growth, development, and survival of early life stages of tuna in oceanic habitats and on the spatial extent of their suitable nursery habitat. To investigate the potential effects of increasing CO2 on otolith calcification of 9-day old pre-flexion stage yellowfin tuna (Thunnus albacares), an experiment was conducted at the Inter-American Tropical Tuna Commission's Achotines Laboratory in Panama during 2011. Fertilized eggs and larvae were exposed to mean pCO2 levels that ranged from present day (355 μatm) to two levels predicted to occur in some areas of the Pacific in the near future (2013 and 3321 μatm), and to an extreme value equivalent to long-term projections for 300 years in the future (9624 μatm). The results indicated significantly larger otoliths (in area and perimeter) with significant, and increasing, fluctuating asymmetry at acidification levels similar to those projected for the near future and long-term. Otoliths increased significantly in size despite a significant decrease in somatic length with increasing pCO2. A consistent correlation between otolith and somatic growth of yellowfin tuna larvae among treatments was evident (i.e., larger otoliths were still associated with larger larvae within a treatment). The observed changes in otolith morphology with increasing ocean acidification have the potential to indirectly affect larval survival through dysfunction of the mechanosensory organs, but this remains to be verified in yellowfin tuna larvae.

Maternal Transfer and Effects of Selenium on Early Life Stage Development of Redside Shiner (Richardsonius balteatus).

Maternal transfer of selenium (Se) to developing fish eggs during vitellogenesis can cause larval deformity and mortality. Previous studies have shown wide variation among fish species in both the magnitude of maternal transfer (exposure) and the egg Se concentration causing effects (sensitivity). We studied maternal transfer and effects of Se on early life stage development, survival, and growth of redside shiner (Richardsonius balteatus), a small-bodied cyprinid that has been reported to have relatively high ovary:muscle Se concentration ratios. Gametes were collected from lentic areas in southeast British Columbia (Canada) with a range of dietary Se concentrations related to weathering of waste rock from coal mining. Eggs were fertilized and reared in the laboratory from hatch to the onset of exogenous feeding. Larvae were assessed for survival, length, weight, Se-characteristic deformities, and edema. Eggs from a total of 56 females were collected, with egg Se concentrations from 0.7 to 28 mg/kg dry weight. Maternal transfer varied among sites, with egg:muscle Se concentration ratios ranging from <1 to >4. We also found that sampling residual ovaries can overestimate Se concentrations in ripe eggs by up to a factor of 5.7. A correlation between larval weight and egg Se concentration was identified, although the relationship was weak (r2 < 0.1) and appeared to be a site effect. No other relationships were observed between larval endpoints and egg Se concentrations up to the highest concentration tested, indicating that the effects threshold for this species may be >28 mg/kg dry weight in eggs. These data indicate that redside shiner is less sensitive to maternally transferred Se than most other tested fish species. Environ Toxicol Chem 2023;42:2350-2357. © 2023 SETAC.

High sensitivity to dietary imidacloprid exposure in early life stages of Folsomia quadrioculata (Collembola) populations from contrasting climates

Survival of early life stages is critical for population growth. Understanding the vulnerability of these sensitive stages can therefore improve ecological risk predictions. The globally-used neonicotinoid insecticide imidacloprid does not degrade easily in soil and occurs at concentrations potentially toxic to non-target soil organisms, such as Collembola. Here, we studied the effects of dietary exposure to imidacloprid on the survival of juveniles in an arctic and a temperate population of Folsomia quadrioculata (Collembola), a commonly-occurring litter-dwelling species in the Northern Hemisphere. The exposure lasted from <24 h to 30 days since hatching at 15 °C. We assessed whether (1) the arctic population of the test species with faster development rates could be more vulnerable than the temperate population, (2) cumulative mortality could increase substantially with exposure time, and (3) the mortality risk experienced during the juvenile stage could be greater than that experienced by the adults. We found a strong concentration-dependent decline in survival in both populations, with small but significantly different LC50s, despite large differences in multiple life-history traits. Applying a General Unified Threshold model for Survival (GUTS) showed a low threshold for effects, slow damage dynamics, a 6–11-fold decrease in LC50 from 14 to 30 days of exposure, and saturation of damage at the three highest concentrations. In addition, exposure starting soon after hatching caused much more mortality than that starting in the adult stages. Our findings suggest that toxicity tests not emphasizing the neonate stages or not lasting long enough can underestimate the implications for populations of naturally abundant non-target organisms.

Survival and development of Lycorma delicatula (Hemiptera: Fulgoridae) on common secondary host plants differ by life stage under controlled conditions.

Host range assessment for emerging invasive insects is a vital step toward fully defining the issues the insect may pose. Spotted lanternfly (SLF) is an invasive species that is rapidly expanding its presence in the United States. The primary hosts facilitating this spread are tree of heaven, a plant from SLF's native range, and the economically important winegrape. Black walnut is also implicated as an important and common host plant. This study investigated the survival and development of SLF on diets that included a variety of crop host plants in the presence or absence of tree of heaven. The following plant species, 'Honeycrisp' apple, 'Reliance' peach, silver maple, and tree of heaven were paired with winegrape or black walnut throughout the study. SLF had strong development and high survival on a diet of winegrape alone, and winegrape or black walnut paired with tree of heaven. Survival parameters were reduced with all other plant pairings. In particular, SLF in the winegrape and peach diet treatment did not develop past the third nymphal instar. A second experiment evaluated the survival of early and late instar nymphs and adult SLF life stages on three specialty crops - 'Cascade' hops, muscadine grapes, and kiwifruit over a two-week period. Nymphs survived longer than adults, with survival of first and second instar nymphs on hops not differing from the control tree of heaven treatment. The adult stage survived best on kiwi and muscadine grape. Our results show tree of heaven and winegrape were the only single plant diets evaluated that are sufficient for complete SLF development, while other host plants may require additional host or hosts of sufficient nutritional quality for SLF survival.

Carryover effects of environmental stressors influence the life performance of brown trout

AbstractCarryover effects of environmental stressors occur when experiences of the environment in earlier life stages or seasons influence the performance of individuals later in life. These can be especially critical for species that have diverse developmental transition periods in their life cycle, such as salmonid fish. Sublethal changes in metabolism, size, or growth experienced in early life stages may have a long‐lasting effect on the subsequent life performance of these species, but very few studies have formally tested these changes in relation to environmental stressors. Here, we investigated whether different types of fine sediment result in carryover effects that change the life performance of migratory brown trout. First, we manipulated the early habitat conditions of brown trout through the life stages from egg to fry by incubating them in varying substrate treatments (i.e., gravel without added sediment, gravel with added fine sand, and gravel with added organic matter). Exposure to fine sediment during early development had serious effects on the metabolism, size, escape responses, timing of emergence, and potential survival of early life stages. These carryover effects were persistent and remained present over the critical life shift from relying on parentally provided resources as immobile eggs to independent exogenous feeding as parr. Second, fish were relocated as parr to either their original or different treatment environments and their metabolism, size, and growth were reanalyzed. The effects of environmental stress were observed later in their life cycle when fry from the gravel treatment were relocated to sand or organic‐rich treatments. These were found to be significantly smaller in size and had a higher metabolic rate than fry maintained in their original treatment environment. Together, our study experimentally demonstrated that the carryover effects of environmental stressors experienced in early stages may influence the fitness outcomes of migratory fish later in life. We suggest that sublethal environmental stressors should be better considered in restoration schemes and management strategies to reverse the current trend of declining salmonid populations.

Accounting for environmental stress in restoration of intertidal foundation species

Abstract Restoration of foundation species in historical habitat may be difficult if adult facilitation is obligatory for survival of early life stages. On intertidal Mediterranean coasts, large‐scale loss of the dominant forest‐forming macroalga Ericaria amentacea have prompted restoration efforts using recruits. Yet, early life stages may be more susceptible to the abiotic stress that characterizes their habitat. We tested strategies to enhance resilience of lab‐cultured juveniles of E. amentacea to environmental stress in historical habitat lacking conspecifics. Juveniles were exposed in culture to fluctuations of the dominant physical stressors, irradiance and temperature, and then outplanted in upper and lower zones of their native intertidal range. Without adult canopy, juvenile outplant survival was limited to the lower tidal range, with nearly complete mortality in the upper zone. Survival was also strongly determined by spatial clumping of recruits within the outplant substrate. Longer‐term growth in the lower zone was enhanced by fluctuating mild stress in culture, with variable irradiance and concurrent heat pulses increasing post‐outplant cover by 40%–60% after 4 months. Clumping also promoted growth across experimental treatments. Synthesis and applications. Reliance on self‐facilitation feedbacks is a common barrier to foundation species restoration in high‐stress habitats. Our results suggest that without adult habitat amelioration, environmental stress limits recruit survival in intertidal algal forest. Yet, exposure to transient, low environmental stress in culture and outplanting of clumped individuals may confer resilience and allow successful establishment of early life stages in zones of reduced abiotic stress, providing a source for gradual colonization of more high‐stress areas.

An annual profile of the impacts of simulated oil spills on the Northeast Arctic cod and haddock fisheries.

We simulate the combined natural and pollutant-induced survival of early life stages of NEA cod and haddock, and the impact on the adult populations in response to the time of a major oil spill in a single year. Our simulations reveal how dynamic ocean processes, controlling both oil transport and fate and the frequency of interactions of oil with drifting fish eggs and larvae, mediate the magnitude of population losses due to an oil spill. The largest impacts on fish early life stages occurred for spills initiated in Feb-Mar, concomitant with the initial rise in marine productivity and the earliest phase of the spawning season. The reproductive health of the adult fish populations was maintained in all scenarios. The study demonstrates the application of a simulation system that provides managers with information for the planning of development activities and for the protection of fisheries resources from potential impacts.

Disentangling seasonal from maternal effects on egg characteristics in western Baltic spring-spawning herring Clupea harengus.

In marine fishes, the timing of spawning determines the environment offspring will face and, therefore, the chances of early life stage survival. Different waves of Atlantic herring Clupea harengus spawn throughout spring in the western Baltic Sea, and the survival of offspring from early in the season has been low in the most recent decade. The authors assessed changes in egg traits from early, middle and late phases of the spawning season to examine whether seasonal and/or maternal effects influenced embryo survival. At each phase, fertilized eggs of six to eight females were incubated at two temperatures (7 and 13°C), and egg size, fertilization success, mortality and time to hatch were recorded. A compilation of data from 2017 to 2020 spawning seasons indicated that mean total length of females decreased with progression of the season and increasing in situ water temperature. For the sub-set of females used in the laboratory study, early spawners were 7.6% larger and produced 14.2% larger eggs than late-spring spawners. Fertilization success was consistently high (>90%), and mortality to hatch was low (<3%). Neither the former nor latter were influenced by season, but both were influenced by maternity. This significant female effect was, however, not related to any maternal trait measured here (total length, Fulton's condition factor or age). There was no maternal effect on development rate at 7 or 13°C. The results suggest that intrinsic differences among females or among spawning waves are unlikely to markedly contribute to the poor survival observed for progeny from early in the season in this population and point towards other extrinsic factors or processes acting on eggs or early larval stages (e.g., seasonal match-mismatch dynamics with prey) as more likely causes of mortality.

Coupling oceanic mesoscale events with catches of the Pacific sardine (Sardinops sagax) in the Gulf of California

Adult fish abundance depends on survival of early life stages, which are susceptible -among other factors- to environmental variability. Ocean mesoscale events (i.e. eddies, costal upwelling, thermal fronts, cold filaments) can be mechanisms of enrichment, concentration, retention and dispersal in marine environments with effects on survival of marine species early life stages. The Pacific sardine (Sardinops sagax) is an important fishery resource in the Gulf of California (GC), and it can rapidly respond to environmental fluctuations leading to dramatic changes in its abundance and fishery availability. This research analyzed the relationship of frequency and duration of different mesoscale processes with catches of S. sagax in the GC. Generalized additive models were applied to evaluate the effects of mesoscale events on the reproduction period, assuming they would reflect on catches several months later. The results show that eddies mostly affected the seasons with anomalous catches, where optimal duration of both types of eddies were responsible for the significantly high catches, while very high cyclonic and very low anticyclonic eddy duration led to significantly low catches. During the seasons with mean catches, high frequency of coastal upwelling and low persistence of Tropical surface sea water (TSW) northward intrusion were responsible for higher catches, while lower ones were associated to higher persistence of TSW intrusion and lower coastal upwelling frequency. A decreasing trend of coastal upwelling and filaments was detected, while the opposite occurred with TSW intrusion. These aspects should be considered in climate change scenarios because if sea surface temperature continues to increase, its implications in mesoscale processes could have consequences in the Gulf of California trophic dynamics.

No evidence for temporally balanced selection on larval Pacific oysters Crassostrea gigas: a comment on Durland et al. (2021).

No evidence for temporally balanced selection on larval Pacific oysters Crassostrea gigas: a comment on Durland et al. (2021).

Post-settlement demographics of reef building corals suggest prolonged recruitment bottlenecks

For many organisms, early life stages experience significantly higher rates of mortality relative to adults. However, tracking early life stage individuals through time in natural settings is difficult, limiting our understanding of the duration of these ‘mortality bottlenecks’, and the time required for survivorship to match that of adults. Here, we track a cohort of juvenile corals (1–5 cm maximum diameter) from 12 taxa at a remote atoll in the Central Pacific from 2013 to 2017 and describe patterns of annual survivorship. Of the 537 juveniles initially detected, 219 (41%) were alive 4 years later, 163 (30%) died via complete loss of live tissue from the skeleton, and the remaining 155 (29%) died via dislodgement. The differing mortality patterns suggest that habitat characteristics, as well as species-specific features, may influence early life stage survival. Across most taxa, survival fit a logistic model, reaching > 90% annual survival within 4 years. These data suggest that mortality bottlenecks characteristic of ‘recruitment’ extend up to 5 years after individuals can be visually detected. Ultimately, replenishment of adult coral populations via sexual reproduction is needed to maintain both coral cover and genetic diversity. This study provides key insights into the dynamics and time scales that characterize these critical early life stages.

Drivers of productivity on the Agulhas Bank and the importance for marine ecosystems

The Agulhas Bank, an area of broad continental shelf extending 250 km offshore of South Africa, sustains rich and productive fisheries. However, its primary production is driven by a complex mosaic of biophysical mechanisms, highly variable in time and space. The key drivers include a system of multiple costal upwellings, complex shelf currents and an interaction with the powerful Agulhas current. The patterns of spatial and temporal variability of primary production on the Agulhas Bank are critical for the spawning and survival of early life stages of many commercially important species exploited along the coastline of South Africa. In particular, the ‘chokka’ squid fishery is an important source of revenue for the Eastern Cape coastal region in South Africa, with low catch years causing socioeconomic hardship. After spawning on the Eastern Agulhas Bank, the squid paralarvae are thought to be transported west to the Central Agulhas Bank (CAB). This region is associated with a cool, productive, but rather intermittent, oceanic feature known as the ‘cold ridge’ (CR). If and when it occurs, this feature could provide a sufficient amount of concentrated (relative to the background values) food for the paralarvae to survive during its passive or near-passive stage. To date, a long-term analysis of CR variability and the mechanisms associated with this has not been conducted. Here, we used a high-resolution biogeochemical ocean model (NEMO-MEDUSA) to investigate the drivers of the productivity on the Agulhas Bank, specifically in the vicinity of the CR. Evidence of the CR is found from November to April and variability in its strength and spatial extent is comparable to that observed in remote sensing data. Interannual variability in productivity on the CAB is correlated to wind stress and zonal currents with the most productive events associated with anomalous easterly winds and enhanced westward flow on the Bank. These events coincide with the existence of an intense CR, important for overall productivity on the Bank, which may impact the recruitment of chokka squid and other fish species. From this simulation, we observe a season of low productivity in 2012 which may potentially relate to the infamous low catch in 2013 which caused economic hardship in the area.

Revealing environmental synchronicity that enhances anchovy recruitment in the Mediterranean Sea

Small pelagic fishes in the Mediterranean Sea constitute about half of the total landings, of which almost one-third is European anchovy. Anchovy abundance mainly depends on early life stage and juvenile survival and growth, which are susceptible to shifts in environmental processes. Due to the commercial importance of this species, it is necessary to elucidate the processes affecting recruitment strength for effective fishery management, using environmental indices to set more appropriate harvesting limits. Here, we constructed a simple index to capture synchronicity between enrichment and retention/concentration processes, which are known to affect anchovy abundance, during the first year of life. Three ecosystems in the Mediterranean were examined: Gulf of Lions, Adriatic Sea, and Strait of Sicily. The synchronicity index (SI) represented the synergic evolution over time of the chlorophyll-a concentration (CHL, enrichment process) and mixed layer depth (MLD, concentration/retention processes), and was related with the abundance of anchovy recruits obtained from published survey reports. Considering different ecosystems, when the SI was significantly higher, anchovy recruitment was promoted. This result indicated SI is consistent across ecosystems in explaining anchovy abundance fluctuations and thus could be used to enhance fisheries management and extended to assess the impact of projected environmental changes.

Resource partitioning may limit interspecific competition among Arctic fish species during early life

Arctic cod (Boreogadus saida) strongly dominates the ichthyoplankton assemblages of High Arctic seas, hence competition with other native species seldom has been studied. Yet, interspecific competition could negatively impact the survival of early life stages of fishes in Arctic areas where higher diversity prevails. We surveyed the ichthyoplankton community of the Greenland Sea, in August–September 2017. Gadids (mostly Arctic cod, with a low number of ice cod Arctogadus glacialis) and non-gadids (bigeye sculpin Triglops nybelini and gelatinous snailfish Liparis fabricii) co-dominated age-0 fish assemblages. Here, we document their diet, prey selectivity, horizontal and vertical distributions as well as that of their prey to assess resource partitioning and the potential for interspecific competition. All fish species occupied the top 30 m of the water column, but Arctic cod occurred in highest abundances over the continental slope, whereas other species distributed almost exclusively over the continental shelf. A particle track analysis suggests that Arctic cod larvae could have hatched in the open waters of the Northeast Water Polynya, drifted with the East Greenland Current, and benefited from the high secondary production associated with these oceanographic features. The diet of gadids did not overlap significantly with the diet of non-gadids, but strong selectivity for Pseudocalanus spp. and Calanus spp. copepodites among the larvae suggests potential competition for these key prey items, although limited by size partitioning of the prey. We thus conclude that interspecific competition among early life stages of Arctic fishes is limited for now. However, changing conditions and the northward range expansion of boreal species following climate change could increase competition and, in turn, negatively affect the recruitment of Arctic ichthyoplankton.

Modeling in an integrated ecosystem research framework to explore recruitment in Gulf of Alaska groundfish – Applications to management and lessons learned

The Gulf of Alaska Integrated Ecosystem Research Program (GOAIERP) supported multi-disciplinary analyses integrating physical and biological oceanography and modeling to examine how the environment influences survival and recruitment of early life stages of select commercially and ecologically important groundfish species. Recruitment is an important component of population variability, and understanding the processes influencing recruitment is central to fishery management and ecosystem planning. Determining the relative impact of advection and the environmental conditions experienced during transport between spawning and nursery areas is an inherently interdisciplinary problem. It requires consideration of physical and lower trophic level environments in concert with early life history dynamics. Here we discuss how Eulerian ecosystem models and Lagrangian Individual-Based Models for groundfish were integrated within the framework of an interdisciplinary observational program. Metrics (e.g. regionally-based averaged water temperature, integrated primary production, probability of juvenile settlement) were derived from model outputs as proxies for recruitment success. The recruitment indices were then correlated to estimated recruitment from stock assessments. Using the GOAIERP as a case study, we discuss the value that modeling can add to a field program and fisheries management planning, the challenges faced, and steps that can be taken to maximize program success. Coordination of model development, experimentation, and field sampling is necessary but can be challenging. Consideration of the appropriate sequence during data analyses and model development is critical. Careful consideration must be given to ensure that data collected in the field will inform, improve, or validate models. Sufficient time must be allocated within the program to incorporate field data collected during the program and mechanistic understandings into the models. Model outputs should be designed to have utility to management decisions and value to regional stakeholders. Collectively, the studies in this modeling program provide insight as to how models might be used to better understand recruitment processes and lead to recommendations to support the integration of ecosystem models into fisheries management.

Two Decades of Match-Mismatch in Northeast Arctic Cod – Feeding Conditions and Survival

The successful recruitment of Northeast Arctic (NEA) cod is thought to depend on sufficient and suitable prey for the newly hatched larvae, in particular the nauplii stages of the lipid-rich calanoid copepod species Calanus finmarchicus. The role of spatial and temporal variations in prey availability in combination with temperature and other factors in influencing growth and survival of cod larvae is, however, incompletely understood. By combining an individual based model for NEA cod larvae at the Norwegian coast with a high-resolution ocean model and a nutrient-phytoplankton-zooplankton-detritus model providing 18 years of daily environmental conditions and prey availability we assessed larval growth and survival until they settle in their feeding habitat in the Barents Sea in early fall. We find on average a two-week delay from the peak timing of first-feeding cod larvae to the peak in prey availability. In warm years, more larvae experience food limitation than in normal years. The positive effects of high temperature on growth, survival and ultimately recruitment are nonetheless larger than the negative effects of food limitation. Food limitation mainly affects larvae spawned in southern areas or late in the spawning season as these larvae experience the highest temperatures and have the highest energy requirements. Our findings highlight the spatial and temporal differences in mechanisms that regulate growth and survival of early life stages of NEA cod and suggest that spatially resolved data may be essential for understanding match-mismatch dynamics.

Microscopic life stages of Arctic kelp differ in their resilience and reproductive output in response to Arctic seasonality

ABSTRACT Kelp forests are important habitats in the strongly environmentally and seasonally variable Arctic. There is a critical lack of knowledge about how seasonal conditions and climate change scenarios influence survival and reproduction of kelp early life stages. To better understand the regulation of kelp life cycle processes in this harsh environment we focused on the physiological performance and reproductive success of early life stages in Alaria esculenta and Laminaria digitata from Kongsfjorden, Spitsbergen. Gametophyte growth and survival during Arctic winter and subsequent sporophyte recruitment under spring conditions were investigated. Winter conditions (2°C, complete darkness) halted gametophyte growth and prevented the onset of gametogenesis in both species. The gametophytes of L. digitata but not A. esculenta became fertile after returning to spring conditions, suggesting that sporogenesis, sexual reproduction and recruitment in A. esculenta must occur successively during summer/autumn while in L. digitata a new generation of sporophytes could develop from over-wintering gametophytes. The effects of simulated canopy shading (offering protection against extreme irradiance stress, particularly as sea ice retreats), present-day and projected Arctic summer seawater temperatures, and nutrient levels on gametophyte survival, fertility and sporophyte recruitment success were also investigated in both species. A. esculenta gametophytes had greater survival and reproductive success than L. digitata, except under very low light (simulating dense canopy). In contrast, shading was required for reproductive success in L. digitata gametophytes. Predicted summer temperatures of 9°C reduced sexual reproduction in both species. Interactions observed between these environmental drivers probably reflect species-specific seasonal patterns of survival and reproduction. These differences between kelp species in response to abiotic factors and light levels (simulated canopy shading) suggest that climate change could alter community structure in the Arctic through effects on sexual reproduction and sporophyte recruitment success. HIGHLIGHTS• Gametophytes were able to endure long periods of darkness.• Parental kelp canopy is key for gametophyte survival and recruitment.• Climate change may alter kelp recruitment patterns.