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Effects of climate change on ocean ecosystem dynamics are widespread. Oceanographic conditions vital to biological communities have already shown changes, resulting in negative impacts on several of the world’s largest fisheries. The Northern California Current (NCC) is a highly productive system that supports many important fisheries. In addition to large-scale oceanographic forcing and seasonal up- and downwelling cycles, in the last decade, the NCC also experienced two distinct marine heatwaves (MHWs) that resulted in pervasive ecosystem alterations. The 2014–16 and 2019 MHWs had contrasting oceanic and atmospheric origins and different effects on ocean temperature, providing the opportunity to identify the mechanisms important to juvenile fish recruitment processes and how they may be differentially impacted by future warming scenarios. We utilized a five-year time series (2014, 2015, 2016, 2018, and 2019) of larval fish concentration, growth, and diet as a natural experiment to investigate the impact of MHWs as well as two neutral years on cabezon ( Scorpaenicthys marmoratus ). Findings include the first published measurement of larval cabezon daily growth rates. Mean growth rates were higher during MHWs, suggesting that elevated temperatures did not pose a major growth or survival challenge. Cabezon’s fast growth response to MHW conditions demonstrates that larval cabezon were able to sustain fast growth in warmer temperatures, and were not likely prey limited. Further, larval cabezon gut fullness did not differ significantly among years. Instead, differences in diet composition and prey quality varied with larval growth. Relative to slower-growing larvae, larval cabezon with high growth rates consumed larger prey items, including larval euphausiids and amphipods. Consistent with these patterns of larval growth, nearshore recruitment of juvenile cabezon was also high during MHW years. Our findings highlight the importance of phenological coupling, or matches in timing, between cabezon and euphausiid population dynamics in that larval cabezon exhibited fast growth when the timing of flexion was coupled with the euphausiid population transition to a larger, omnivorous larval stage. Results of this study suggest that larval cabezon’s variable growth and broad diet coupled with selection for large, nutrient dense prey may be a source of resilience for its population dynamics.

Cultured naked goby ( Gobiosoma bosc ) and striped blenny ( Chasmodes bosquianus ) larvae were used to compare life history parameters for early and late periods within a long spawning season during which temperature increased by approximately 10 °C. Hatch lengths, growth rates, larval period duration, settlement length, survivorship, and other metrics of these serial spawners were determined for larvae hatched during early and late time periods with ambient average weekly water temperatures of 20.8 (standard deviation ±2.1 °C) and 29.0 (±1.0), respectively. Cultured fishes provided parameter estimates in the absence of predation mortality and with constant prey availability. Four hypotheses were tested for each species: 1) total length at hatch is not related to temperature, 2) pelagic larval period (PLD) is negatively related to temperature, 3) growth rates and survivorship are positively related to temperature, and 4) flexion and settlement lengths are negatively related to temperature. For both gobies and blennies, hatch length decreased with increasing temperature, but was not significantly related to survivorship. Larval blennies retained the yolk-sac longer than gobies. At higher temperatures, striped blenny flexion length, settlement length, PLD, and instantaneous mortality significantly decreased while instantaneous growth in length increased. Naked goby flexion lengths, settlement lengths, PLD, and mortality rates also declined with increasing water temperatures while instantaneous growth rates increased with increasing water temperatures. Average growth in length did not change significantly with temperature for either species. Survivorship in both fishes was lowest during 0 to 6 days post hatch (dph) coincident with the yolk-sac and first feeding stages. Survivorship significantly increased with larval fish total length and age (dph) for both species and time periods. Average estimated striped blenny percentage survival increased by an order of magnitude (~3 to ~32 %) with increasing temperature while average naked goby percentage survival increased from ~3 % (early) to ~11 % (late) over the 8.3 °C temperature range examined. The observed life history parameter variation with seasonal temperature changes likely function to ensure survival to settlement for at least some cohorts within a year class as part of a bet-hedging life history strategy. Data from cultured fishes provide a baseline for future evaluation of demographics and rates from field collections.

How do biogeographically different provinces arise in response to oceanic barriers to dispersal? Here, we analyse how traits related to the pelagic dispersal and adult biology of 985 tropical reef fish species correlate with their establishing populations on both sides of two Atlantic marine barriers: the Mid-Atlantic Barrier (MAB) and the Amazon–Orinoco Plume (AOP). Generalized linear mixed-effects models indicate that predictors for successful barrier crossing are the ability to raft with flotsam for the deep-water MAB, non-reef habitat usage for the freshwater and sediment-rich AOP, and large adult-size and large latitudinal-range for both barriers. Variation in larval-development mode, often thought to be broadly related to larval-dispersal potential, is not a significant predictor in either case. Many more species of greater taxonomic diversity cross the AOP than the MAB. Rafters readily cross both barriers but represent a much smaller proportion of AOP crossers than MAB crossers. Successful establishment after crossing both barriers may be facilitated by broad environmental tolerance associated with large body size and wide latitudinal-range. These results highlight the need to look beyond larval-dispersal potential and assess adult-biology traits when assessing determinants of successful movements across marine barriers.

Life for many of the world’s marine fish begins at the ocean surface. Ocean conditions dictate food availability and govern survivorship, yet little is known about the habitat preferences of larval fish during this highly vulnerable life-history stage. Here we show that surface slicks, a ubiquitous coastal ocean convergence feature, are important nurseries for larval fish from many ocean habitats at ecosystem scales. Slicks had higher densities of marine phytoplankton (1.7-fold), zooplankton (larval fish prey; 3.7-fold), and larval fish (8.1-fold) than nearby ambient waters across our study region in Hawai’i. Slicks contained larger, more well-developed individuals with competent swimming abilities compared to ambient waters, suggesting a physiological benefit to increased prey resources. Slicks also disproportionately accumulated prey-size plastics, resulting in a 60-fold higher ratio of plastics to larval fish prey than nearby waters. Dissections of hundreds of larval fish found that 8.6% of individuals in slicks had ingested plastics, a 2.3-fold higher occurrence than larval fish from ambient waters. Plastics were found in 7 of 8 families dissected, including swordfish (Xiphiidae), a commercially targeted species, and flying fish (Exocoetidae), a principal prey item for tuna and seabirds. Scaling up across an ∼1,000 km² coastal ecosystem in Hawai’i revealed slicks occupied only 8.3% of ocean surface habitat but contained 42.3% of all neustonic larval fish and 91.8% of all floating plastics. The ingestion of plastics by larval fish could reduce survivorship, compounding threats to fisheries productivity posed by overfishing, climate change, and habitat loss.

Moonlight mediates trophic interactions and shapes the evolution of life-history strategies for nocturnal organisms. Reproductive cycles and important life-history transitions for many marine organisms coincide with moon phases, but few studies consider the effects of moonlight on pelagic larvae at sea. We evaluated effects of moonlight on growth of pelagic larvae of a temperate reef fish using “master chronologies” of larval growth constructed from age-independent daily increment widths recorded in otoliths of 321 individuals. We found that daily growth rates of fish larvae were enhanced by lunar illumination after controlling for the positive influence of temperature and the negative influence of cloud cover. Collectively, these results indicate that moonlight enhances growth rates of larval fish. This pattern is likely the result of moonlight’s combined effects on foraging efficiency and suppression of diel migrations of mesopelagic predators, and has the potential to drive evolution of marine life histories.

Mature age structure has been recognized as an important determinant of fecundity in fish populations. More recently it has been demonstrated that in some species, older, larger females can produce faster-growing and more viable larvae than younger, smaller females. We investigated this effect in sea perch Helicolenus percoides and collected information on fecundity as well as notochord length and oil globule volume (OGV) of larvae on the day of parturition, time to 50% mortality, and rate of change in length and OGV of cohorts of larvae in fed and unfed treatments. Absolute fecundity increased proportionally with maternal age and total length. Older, larger females produced cohorts of larvae with larger OGVs. These cohorts also had faster positive rates of change in length in the fed treatment than did cohorts of larvae produced by younger, smaller females. The OGV was positively correlated with rates of change in length and survival in the fed treatment; however, we did not detect influences on growth or survival in the unfed treatment. Further, cohorts of larvae in the unfed treatment had negative rates of change in length and lower survival compared to cohorts in the fed treatment. The results indicated that the OGV, which was affected by maternal age and size, was an important factor influencing larval growth and viability when external energy sources were available. These data provide insight into the reproductive biology of sea perch and highlight the importance of an old-growth age structure for effective larval viability and growth.

Aquaculture is an emerging sector in meeting global food demands, with significant potential to accelerate fish production. However, a major bottleneck in this industry remains the challenge of fulfilling the complex nutritional needs of fish larvae, often limited by the high cost and scarce availability of appropriate feed sources. In this study, we explored the potential of live microalga Desmodesmus sp. and nutritionally enriched copepods, administered at different concentrations, as alternative dietary supplements to enhance the growth performance and survival rate of the mrigal, Cirrhinus cirrhosus larvae. The fish larvae were reared for a period of 30 days under six feeding regimes (treatments): T 1 (10–13 × 10 4 cells mL −1 live Desmodesmus sp.), T 2 (7.5–9.5 × 10 4 cells mL −1 live Desmodesmus sp. + 5–10 individuals mL −1 enriched live copepods), T 3 (5–6.5 × 10 4 cells mL −1 live Desmodesmus sp. + 10–20 individuals mL −1 enriched live copepods), T 4 (2.5–3.25 × 10 4 cells mL −1 live Desmodesmus sp. + 15–30 individuals mL −1 enriched live copepods), T 5 (20–40 individuals mL −1 enriched live copepods), and T 6 commercial feed (0.5–1 gL −1 ) as a control diet under laboratory environments. The T 3 diet exhibited the highest protein (17.87%) and fat (2.89%) content in the fish larvae, significantly higher than the control diet T 6 (16.63% protein, 2.28% fat). The T 3 diet significantly improved the larval growth in terms of gain in length (17.34 mm), gain in weight (118.81 mg), percent gain in length (299.69%), percent gain in weight (10,069.49%), and specific growth rate (15.83%). The highest survival rate was observed in T 3 (92.55%), followed by T 4 (90.15%), T 5 (85.48%), T 6 (84.21%), T 2 (82.44%), and T 1 (69.43%). This study highlights the potential of the combined Desmodesmus sp. and enriched copepods as diets for the rearing of mrigal larvae with an aim of sustainable aquaculture development.

Essential dietary trace elements, such as zinc (Zn) and manganese (Mn), critically influence a wide range of physiological, metabolic, and hormonal processes in fish larvae and post-larvae. Despite their importance for normal fish growth and skeletal development, trace mineral nutrition has not been extensively studied in the early stages of development of fish. Post-larvae of an emergent aquaculture species, Senegalese sole (Solea senegalensis), were the subject of this study in order to better understand the effects of diet supplementation of trace minerals upon fish larval development and performance. Sole post-larvae were fed a combination of organic Mn (45 and 90 mg kg−1 feed) and organic Zn (100 and 130 mg kg−1 feed) and survival, growth, mineral deposition rates, and vertebral bone status were assessed. Our results showed that although no significant effect was found on the growth performance of Senegalese sole post-larvae, Mn and Zn supplementation to a commercial microdiet for marine fish larvae at higher dietary levels (Mn at 90 mg kg−1 and Zn at 130 mg kg−1) improved larval survival, decreased the severity of vertebral malformations, and increased the deposition of Mn in bone.

Larval fishes suffer prodigious mortality rates, eliminating 99% of the brood within a few days after first feeding. Hjort (1914) famously attributed this “critical period” of low survival to the larvae’s inability to obtain sufficient food [Hjort (1914) Rapp P-v Réun Cons Int Explor Mer 20:1–228]. However, the cause of this poor feeding success remains to be identified. Here, we show that hydrodynamic constraints on the ubiquitous suction mechanism in first-feeding larvae limit their ability to capture prey, thereby reducing their feeding rates. Dynamic-scaling experiments revealed that larval size is the primary determinant of feeding rate, independent of other ontogenetic effects. We conclude that first-feeding larvae experience “hydrodynamic starvation,” in which low Reynolds numbers mechanistically limit their feeding performance even under high prey densities. Our results provide a hydrodynamic perspective on feeding of larval fishes that focuses on the physical properties of the larvae and prey, rather than on prey concentration and the rate of encounters.

The European flat oyster, Ostrea edulis , once formed extensive reefs along European coasts. These reef ecosystems are now functionally extinct, but support for their restoration is rapidly growing. Efforts are currently limited by a bottleneck in O. edulis supply. O. edulis is a challenging species to produce in a hatchery. Currently unknown causes of high mortality and hatchery crashes must be addressed to meet the increased demand for spat from the ecological restoration sector. Here we present the results of a collaborative effort between nine European hatcheries and marine research laboratories to share recent experiences, as well as production and protocol-related data. We found that crashes were widespread and suspected to be caused by diverse culprits, including Vibrio species, predatory zooplankton, and poor water quality. A Boruta regression analysis of production data identified eleven factors including water temperature in the larval tank, broodstock origin, and number of broodstock as being potentially important in explaining crashes during the larval growth phase. Eight factors including duration of larval growth stage and larval density at transfer to the settlement tank, were identified as potentially important in explaining crashes during the settlement phase. When applied to larval mortality data of batches that did not crash, the Boruta analysis identified 13 factors, including water temperature, broodstock and larval densities and broodstock origin in determining larval mortality during the larval growth stage and two factors, number of larvae in the initial larval release and broodstock origin, during the larval settlement phase. This research highlights the value of knowledge exchange between hatchery facilities in overcoming spat production problems, identifies factors that may contribute to increased larval mortality and the risk of larval crashes, as well as the importance of developing collaborative research programmes to provide for greater commonality in data collection for future coordination and production analysis.