Marine Ecology Progress Series

The distribution of marine predators is influenced by a variety of natural and, in some cases, anthropogenic environmental factors. In particular, the optimal foraging theory predicts that micro-habitat selection should be the result of a trade-off between prey availability, energy expenditure, and predation risk. In addition, the risk-disturbance hypothesis suggests that anthropogenic disturbance may be perceived by animals in the same way as predation risk. Habitat selection may also be locally influenced by individual behavior and physiological state (defining functional habitats): variation in their needs should affect their optimal trade-off. We tested these hypotheses in a population of bottlenose dolphins living in a tropical lagoon using a habitat modeling approach. Bottlenose dolphins were predominantly distributed within the lagoon, with a preference for the vicinity of fringing and inner reefs (with lower predation risk than the outer reef), and were located in areas of high fish productivity, consistent with optimal habitat selection. We also observed an interaction between habitat and dolphin behavior, suggesting the existence of functional habitats: foraging was more common in nearshore habitats with probable higher prey density while resting and socializing were more common further from shore. Similarly, females with calves were preferentially found in shallower waters compared to other social groups. We did not observe any effects of anthro-pogenic disturbance variables and therefore cannot conclude on the risk-disturbance hypothesis for this population.

Cetacean conservation requires ecosystem-scale management with special focus on food webs. Rorquals and sperm whales are top predators of complex open ocean food webs and, although mesopelagic fish and cephalopods are predated by these cetaceans, their contribution to their diets is not fully understood. Here, we aimed to better describe the consumption of mesopelagic fish and cephalopods by identifying preferred species consumed by rorquals and sperm whales at mid-latitudes. To do so, we combined the fish and cephalopod community composition inferred from whale faecal and marine environmental DNA samples. We analysed the prey availability and predator preferences by comparing the vertical distribution and abundance of fish and cephalopod species in the water column with the prey items found in faecal samples of rorquals and sperm whales. We found that rorqual consumed mesopelagic fish that perform diel vertical migrations (DVM) such as myctophids. These species were found in depths that matched the deep foraging behaviours during daytime and shallow foraging behaviours during night, confirming that rorquals rely on the DVM to feed at these latitudes. Also, although a high diversity of cephalopods was found across the water column, the faecal content of sperm whales was mainly composed by Histioteuthis bonellii, which was abundant between 600 and 1200 meters and matches the diving patterns described for this species in the area. In this study, we present the first comprehensive genetic analysis of the diets of rorquals and sperm whales, expanding our understanding of open ocean trophic ecology to promote effective cetacean conservation.

Climate change and anthropogenic pressures are reshaping marine food webs, altering prey availability and affecting top predators. The European Shag (Gulosus aristotelis), a coastal demersal seabird, provides a valuable model for examining environmentally mediated dietary variation, given its trophic plasticity and capacity to adjust prey use according to local availability, while also allowing assessment of potential demographic consequences. This study investigated spatial and temporal variation in diet at two Portuguese colonies (Berlengas and Arrabida) between 2016 and 2024 and assessed long-term reproductive productivity at Berlengas. A total of 468 regurgitated pellets were analysed, and diet composition was quantified using the Index of Relative Importance (IRI). Generalised additive models were applied to assess environmental, spatial, and period-specific effects on diet composition, while reproductive productivity was modelled in relation to prey biomass. Diet variation was primarily explained by environmental predictors, including sea surface temperature, chlorophyll-a concentration, and zooplankton, whereas year per se had no significant effect, indicating environmentally mediated bottom-up effects. Spatial differences between colonies reflected contrasting prey field structures, and period-specific patterns suggested increased specialisation during breeding. Higher biomass of sandeels (Ammodytidae) was positively associated with reproductive output, whereas shifts toward lower-energy prey were associated with reduced productivity. These findings demonstrate that environmentally driven dietary change has measurable demographic consequences, underscoring the importance of bottom-up processes in shaping seabird population dynamics and informing conservation strategies under ongoing climate change.

Understanding habitat association of animals and how they change through ontogeny is critical to predict the likely effects of habitat change on populations. We investigated how fine scale habitat associations of three common coral reef damselfish species changed among life-stages on reefs surrounding Lizard Island, northern Great Barrier Reef. All three species showed distinct habitat selection at settlement, however the degree to which these initial associations changed through ontogeny were species specific. Pomacentrus amboinensis associated with sandy areas throughout all life-stages; Pomacentrus chrysurus settled to areas with high cover of sand and rubble, but displayed no clear habitat preferences as juveniles or adults. Pomacentrus moluccensis settled to areas with high cover of fine branching corals before shifting to areas with relatively high cover of soft corals as adults. We also compared two different approaches to estimate habitat selection; one that quantified the benthic composition within the approximate home range of individuals versus a more widely used approach of recording a single point underneath the focal individual when they were first observed. Although results were broadly similar, the benthic composition approach revealed details that was overlooked using the single point method. Decreases in the availability of any of these preferred benthic habitats may adversely affect future populations, therefore understanding habitat associations and their transitions among life stages will be crucial in predicting future reef fish communities under ongoing coral loss and habitat change. This will require to systematically study a broader range of species, integrating relevant spatial and temporal scales.

Air temperatures are warming at faster rates than ocean temperatures, and this "land-sea warming contrast" may create reprieves from thermal stress by providing cool underwater refugia during extreme heat events. Here we tested the impacts of the "land-sea warming contrast" on physiology (metabolism) and behaviour (feeding) in the juvenile life stage of a keystone intertidal predator, Pisaster ochraceus, by experimentally manipulating air ([~]20, 25, 30) and water ([~]15, 20) temperatures (at independent rates) representing early summer, late summer, and heatwave conditions in Barkley Sound (British Columbia, Canada). We further made observations of air temperatures, sea surface temperatures, and Pisaster moribundity at our study location to support interpretation of our results. We predicted metabolism and feeding would increase with early and late summer temperatures, but decrease during heatwave conditions as animals surpass their thermal optimum. We observed the greatest mortality and lowest feeding in juvenile Pisaster exposed to cool ocean temperatures ([~]15) and high aerial temperatures typical of extreme heat events ([~]30). Feeding rates increased with heat stress duration, indicating animals may be compensating for elevated metabolism. Metabolic rates did not differ between air temperatures, but oxygen consumption was higher in animals with access to mussels than for Pisaster that were fasted. The highest levels of experimental and field moribundity were observed in August, indicating Pisaster may have accumulated physiological stress damage following elevated air and ocean temperatures throughout the summer. Our research implicates shifts in community dynamics due to the loss of this keystone species as air temperatures warm. Summary StatementCooler ocean temperatures, rather than creating thermal refugia, may cause physiological stress for juvenile Pisaster ochraceus exposed to warm air during low tide.

Atlantic puffin (Fratercula arctica, hereafter "puffin") reproductive success in the Gulf of Maine (GoM) has decreased following a recent oceanographic regime shift and subsequent rapid warming. Concurrent changes in both the regional forage fish community and puffin chick diet and provisioning rates suggest that inadequate prey resources may be driving this decline. To determine what prey GoM puffins were feeding on during two years of marine heatwave conditions, we assessed puffin diet using two methods: traditional, observational methods that utilize bill-load photography and emerging methods employing fecal DNA metabarcoding. We identified a strong correlation between the composition of chick diet as estimated through traditional and emerging methods, supporting the interpretation of DNA relative read abundance as a quantitative metric of diet composition. Both methods identified the same dominant prey groups, but metabarcoding identified a greater number of species and offered higher taxonomic resolution. Puffin adults and chicks fed on many of the same prey types, although adults consumed a greater variety of taxa and consumed more low quality prey than they provisioned chicks, as predicted by optimal foraging theory. For both age classes, diet varied both between and within years, likely reflecting changes in the local forage fish community in response to environmental variability. During these two years of marine heatwave conditions, puffins exploited unusual abundances of typically-uncommon prey, yet low puffin productivity suggests the observed dietary plasticity was not able to compensate for apparent prey shortages. Continued refinement of molecular tools and the interpretation of the data they provide will enable better assessments of how seabirds of diverse ages and breeding stages are compensating for changing forage fish communities in response to global climate change.

Mutualistic associations between benthic marine invertebrates and reef taxa are common. Sponge-dwelling gobies benefit from protection within sponge tubes and greater food availability. Sponge-dwelling gobies are hypothesized to increase sponge pump rates by consuming polychaete parasites, but such increases have not yet been demonstrated. We investigated the association between sponge-dwelling gobies (Elacatinus horsti) and two species of tube sponge (Aplysina lacunosa and Aplysina archeri) in Bonaire, Caribbean Netherlands. We visually assessed goby presence in sponges and used in situ methods with fluorescein dye to estimate feeding rates via pump rates. Aplysina archeri were more likely to host a goby than A. lacunosa. For both sponge species, pump rates of tubes with gobies were higher on average than those of tubes without gobies. Our observations, therefore, suggest that E. horsti associations with Aplysina are likely mutualistic relationships in which sponges benefit from higher feeding rates when gobies are present.

Interspecific scraping behaviors among large marine vertebrates may serve as an important mechanism for ectoparasite removal. Here, we present the first documented observations of shark-manta scraping interactions, which occurred in the Revillagigedo Archipelago, a remote marine protected area in the eastern tropical Pacific. Opportunistic video footage was collected at two dive sites between December 2024 and February 2025, capturing three discrete events in which Galapagos sharks (Carcharhinus galapagensis) initiated contact with three different oceanic manta rays (Mobula birostris). Using a focal-animal sampling approach, we quantified the number and rate of scraping events and categorized responses. Sharks scraped against mainly the ventral surfaces of mantas using their heads, gill regions, and lateral areas associated with high ectoparasite loads. Manta responses ranged from passive tolerance to active evasion, with the strongest reactions observed in response to the adult Galapagos shark. Scraping rates varied by site and shark size. These interactions occurred at or near established cleaning stations, suggesting that sharks may opportunistically use mantas as alternative cleaning substrates. While this may indicate behavioral plasticity among sharks, it raises concern about potential costs to mantas, particularly if some ectoparasites or pathogens are transferred. Our findings highlight the complexity of shifting ecological interactions among marine megafauna and underscore the importance of understanding behavioral responses to cleaning disruption for endangered oceanic mantas.

Body size is a integrative trait that has declined across ecological assemblages in the last decades. Changes in body size of early life stages and small-bodied fish are driven by complex interactions between size-dependent mortality, and temperature- and food dependent growth, and can have consequences for recruitment to the adult stock and food availability to predators. While the mechanisms can be difficult to disentangle using observational data alone, simple indicators such as mean size can provide important information about ecosystem conditions as oceans rapidly change. Using 30 years of observations from the IBTS-MIK ichthyoplankton survey in Skagerrak and Kattegat in combination with sea surface temperature data, we investigated changes in the body size of early life stages and small-bodied fishes for 10 commercial and non-commercial species using geostatistical mixed models, and trends in prey density using generalized additive models. We found positive associations between chlorophyll-a concentration and length in 8 species (3 significant), and negative associations between temperature and length in 9 species (4 significant). Standardized indices of length revealed negative trends over time for all species since 2010, and all species were smaller in 2024 compared to 2000. The decline in size since 2010 varied between 30%-1%, with a mean of 14% and 9% for species predominantly found in Skagerrak and Kattegat, respectively. The trend of decreased body sizes since 2010 coincides with rapid declines in Calanus spp. -- a key prey predicted to decline in this area at the edge of their distribution area due to climate change. In Skagerrak it also coincides with a decline in the density of large copepods (> 0.25 mm). The synchronous declines in larval size across taxonomically diverse species experiencing different rates of exploitation suggest a common response to changing environmental conditions, which could have cascading effects throughout marine food webs.

Oyster reefs provide key ecosystem functions, including the provision of habitat for fish. While their importance in supporting fish assemblages is widely accepted, an assessment of intertidal oyster reefs at night remains a knowledge gap. Documenting habitat use at night could reveal new species reliant on these systems and help uncover diel fish movements among structured and unstructured habitats. We hypothesise that habitat use will interact with time and habitat, whereby differences in fish assemblages between oyster reef and unstructured habitats would be greater during the day. In this study, we used infrared-capable remote underwater video stations (RUVS) to sample paired intertidal oyster reefs and unstructured habitat during day and night. Assemblages using these habitats during the day do not match those at night, consistent with diel shifts observed in similar habitats. Consistent with our hypothesis, during the day oyster reefs had higher diversity and richness than unstructured habitat, whereas both habitats had low diversity and richness at night. The high relative abundance of piscivores in oyster reefs during the day suggests reefs create food webs that extend beyond benthic matter and sustain higher trophic levels. Nighttime abundances and diversity in oyster reefs dropped to levels similar to those of unstructured habitats during the day and night, likely a product of temporal niche partitioning and dynamic predation risks. Nighttime studies were important in documenting a wider suite of species and can thus provide a more complete understanding of fish-habitat interactions. Furthermore, this study used novel methods that enabled depth and size estimation from a single camera unit. While still in its infancy, this can serve as a force multiplier in monitoring intertidal habitats and lead towards a cost-effective method for standardising day/night abundance measurements and obtaining fish size estimates.

Floating life (obligate neuston) is a core component of the ocean surface food web. However, only one region of high neustonic abundance is known so far, the Sargasso Sea in the Subtropical North Atlantic, where floating life provides critical habitat structure and ecosystem services. Here, we hypothesize that floating life is also concentrated in other gyres with converging surface currents. To test this hypothesis, we collected samples through the eastern North Pacific Subtropical Gyre in the area of the North Pacific "garbage patch" (NPGP) known to accumulate floating anthropogenic debris. We found that densities of floating life were significantly higher inside the central part of NPGP than on its periphery, and there was a significant positive relationship between neuston abundance and plastic abundance. This work has important implications for the ecology and human impact of subtropical oceanic gyre ecosystems.

AO_SCPLOWBSTRACTC_SCPLOWNearshore regions in the Gulf of Maine are highly variable habitats acted upon by processes operating on multiple spatial scales and levels of biological organization. As such, they facilitate the reproduction, growth, and migration of many fish species, and are particularly tied to the life histories of many forage fishes. Temperatures in the Gulf of Maine have rapidly increased in recent decades, which may be driving changes in nearshore ecosystems. Here, we use 11 years of summer beach seine survey data within Casco Bay, Maine, to illustrate temperature-related changes to community structure. Further, we use Atlantic herring (Clupea harengus) and Atlantic silversides (Menidia menidia) as focal species to describe the effects of temperature on individual growth rates and relative abundance. The progression of seasonal use patterns and relative abundance in the nearshore with seasonal warming is evident; species that have cooler preferred temperatures are caught less frequently in the nearshore regions in late summer, when temperatures are highest. Increased temperatures were associated with significantly higher silverside growth rates and community compositions dominated by silverside. Temperature alone did not explain interannual variation in herring growth rates or predict herring-dominated nearshore community composition, and there is evidence that density-dependence may be more important to herring population dynamics. Monitoring nearshore ecosystems could provide critical insight into the dynamics of species that use these areas to facilitate reproduction, growth, and migration, and could therefore be used to identify potential changes to Gulf of Maine community and trophic ecology.

Understanding juvenile survival is crucial for the population ecology of long-lived species, where parental guidance can significantly influence survival rates of completely naive juveniles. In southern elephant seals (Mirounga leonina), however, offspring receive no knowledge from their parents, only fat reserves. This research focuses on how dispersal direction on their maiden foraging trip and physical traits influence the survival of naive southern elephant seal pups at Macquarie Island. We tracked 44 pups with satellite tags during their post-weaning migration and compared their movements to the post-moult winter migrations of 58 adult females. We found that most pups (61.2%) travelled southeast, in line with the Antarctic Circumpolar Current. Pups travelling with the predominant east-southeast current had a 1.5 times higher survival rate for their first trip than those swimming westward against it. Those that swam with the current and were heavier were more likely to survive their first year. Adult females showed different dispersal patterns, where they travelled southwards towards Antarctic waters, implying that learning from experience influences their direction. Future investigations into the role of the primary eastward current in the sub-Antarctic on circumpolar movement patterns of top marine predators could expand our understanding of Southern Ocean ecology.

Nursery habitats confer higher food availability and reduced predation risk, thereby contributing disproportionately more individuals per unit area to the population compared with other habitats. Nursery status is inferred through evaluation of four metrics: density, growth, survival, and linkage between juveniles and adults. Moreover, organisms commonly use multiple habitats as nurseries throughout ontogeny to satisfy shifting resource requirements. To this end, we conducted manipulative and mensurative field experiments to evaluate two nursery metrics, abundance and survival, for juvenile blue crabs across multiple size classes and habitats, including structurally complex habitats -- seagrass meadows and salt marshes -- and unstructured habitat (sand flats) in the York River, Chesapeake Bay. We also considered effects of site-specific spatial orientation within the York River, seasonality, physicochemical variables, and postlarval influx. Our results showed that abundance was higher in both seagrass meadows and salt marshes relative to unstructured sand, and positively associated with turbidity and post-larval abundance. Notably, seagrass habitats harbored the highest abundances of small ([≤] 15 mm carapace width) juveniles, whereas salt marsh edge harbored the highest abundance of medium (16-30 mm carapace width) and large (31- 60 mm carapace width) juveniles. Moreover, survival was positively associated with juvenile size and structurally complex habitats relative to unvegetated controls. Seasonally, survival peaked in April, reached a seasonal minimum in August, and increased throughout fall. Finally, habitat-specific survival was dependent on spatial position: survival was elevated at upriver salt marsh and unstructured sand habitats compared to downriver counterparts. In nursery habitats of marine species, evaluation of survival, growth, abundance and ontogenetic habitat shifts has typically focused on relatively broad size ranges through the juvenile phase. Yet, ontogenetic shifts in habitat use may occur within much narrower size ranges, which has not been well studied and which is critical to the conservation and restoration of nursery habitats. We found that habitat-specific utilization rates differed by juvenile size class over a surprisingly narrow range of size, and were related to (1) the structural and biological characteristics of the nominal nursery habitats, (2) spatial gradients of environmental variables within the tributary, and (3) the likely trade-offs between growth and survival through ontogeny. Taken together, abundance and survival results indicate that seagrass meadows are key nurseries primarily for early-stage juveniles, whereas salt marshes are an intermediate nursery habitat for larger individuals to maximize growth-to-mortality ratios. Our results underscore the need to consider both habitats as critical nurseries for juvenile blue crabs throughout ontogeny.

Declines of large predatory fish due to overexploitation are restructuring food webs across the globe. It is now becoming evident that restoring these altered food webs requires addressing not only ecological processes, but evolutionary ones as well, because human-induced rapid evolution may in turn affect ecological dynamics. In the central Baltic Sea, abundances of the mesopredatory fish, the three-spined stickleback (Gasterosteus aculeatus), have increased dramatically during the past decades. Time-series data covering 22 years show that this increase coincides with a decline in the number of juvenile perch (Perca fluviatilis), the most abundant predator of stickleback along the coast. We studied the interaction between evolutionary and ecological effects of this mesopredator take-over, by surveying the armour plate morphology of stickleback and the structure of the associated food web. First, we investigated the distribution of different stickleback phenotypes depending on predator abundances and benthic production; and described the stomach content of the stickleback phenotypes using metabarcoding. Second, we explored differences in the relation between different trophic levels and benthic production, between bays where the relative abundance of fish was dominated by stickleback or not; and compared this to previous cage-experiments to support causality of detected correlations. We found two distinct lateral armour plate phenotypes of stickleback, incompletely and completely plated. The proportion of incompletely plated individuals increased with increasing benthic production and decreasing abundances of adult perch. Stomach content analyses showed that the completely plated individuals had a stronger preference for invertebrate herbivores (amphipods) than the incompletely plated ones. In addition, predator dominance interacted with ecosystem production to determine food web structure and the propagation of a trophic cascade: with increasing production, biomass accumulated on the first (macroalgae) and third (stickleback) trophic levels in stickleback-dominated bays, but on the second trophic level (invertebrate herbivores) in perch-dominated bays. Since armour plates are defence structures favoured by natural selection in the presence of fish predators, the phenotype distribution suggest that a novel low-predation regime favours sticklebacks with less armour. Our results indicate that an interaction between evolutionary and ecological effects of the stickleback take-over has the potential to affect food web dynamics.

Chorusing is widespread across the animal kingdom. Animal calling behavior is often driven by phenological and environmental factors such as seasonality, lunar period, and temperature. Now, in the Anthropocene, factors such as increased anthropogenic noise levels are also affecting calling behavior. Many fish call in choruses to attract mates, but the dynamics that drive fish calling behavior have rarely been studied in the field. We investigated how seasonality, lunar period, ambient noise, and temperature influenced the calling behavior of two species of toadfish, the plainfin midshipman (Porichthys notatus) and putatively, the Atlantic midshipman (Porichthys plectrodon). Acoustic recordings from a two-year period in twelve different locations, spanning two ocean basins showed that midshipman chorus presence was driven by seasonality and lunar period. Furthermore, chorus frequency increased with increasing temperature. Chorus levels were strongly influenced by seasonality and increased somewhat with increasing noise levels. Taken together, these results indicate that midshipman calling behavior was strongly influenced by interacting environmental conditions. Understanding the various impacts of each driver will facilitate predictions of changes in midshipman calling due to future changes in environmental conditions.

Many marine species have a pelagic larval phase that undergo dispersal among habitats. Studies on marine larval dispersal have revealed a large variation in the spatial scale of dispersal, and accumulated evidence has shown that seascape patchiness is the major determinant for variation in self-recruitment. However, few studies have investigated the influence of geographic settings on marine larval dispersal. Bays or lagoons generally enhance the retention of larvae, while larvae are more likely to be flushed by strong currents in open coasts. To examine associations between larval dispersal, geographic setting, and hydrodynamics, we compared fin-scale dispersal patterns, self-recruitment, and local retention of two anemonefishes (Amphiprion frenatus and A. perideraion) between a semi-enclosed bay and an open coast in the Philippines combining genetic parentage analysis and biophysical dispersal modelling. Contrary to our expectations, parentage analysis revealed lower estimates of self-recruitment in the semi-closed bay (0-2%) than in the open coast (14-15%). The result was consistent with dispersal simulations predicting lower local retention and self-recruitment in the former (0.4% and 19%) than in the latter (2.9% and 38%). Dispersal modelling also showed that cross-shore currents toward offshore were much stronger around the semi-closed bay and were negatively correlated with local retention and self-recruitment. These results suggest that stronger cross-shore currents around the semi-closed bay transport anemonefish larvae to the offshore and mainly contributed to the lower self-recruitment. Our results highlight difficulty in predicting self-recruitment from geographic setting alone and importance of hydrodynamics on it.

Populations across a species range may be locally adapted, and failure to recognize this variation can lead to inaccurate predictions of their resilience or vulnerability to climate change. Because life history traits are directly linked to fitness, life history theory can serve as a useful framework for evaluating how populations within species may respond to rapid environmental change. However, relatively few studies quantify multiple life history traits and their tradeoffs across many populations, especially in marine taxa. Here, we used a 10-month laboratory experiment to quantify a suite of reproductive traits in populations spanning the strongest latitudinal temperature gradient in the worlds coastal oceans. We examined reproductive traits in wild-captured adults exposed to simulated local conditions for 7 native Atlantic and 4 introduced Pacific populations of the marine predatory gastropod Urosalpinx cinerea. Our data reveals that reproductive season length, the number of reproductive attempts, and annual fecundity unimodally peaked at mid-latitude populations, the species range-center. Introduced populations had comparably few spawning attempts and low fecundity despite a longer reproductive period in a less seasonal environment. We then conducted a second experiment quantifying thermal tolerance of developing embryos from 3 native populations, which revealed high sensitivity to temperature at early life stages but weak population differentiation. Taken together, our data reveal stark differences in reproduction that appear to reflect "fast" and "slow" paced lifestyles, which may maximize fitness by spreading the risk of reproductive failure over a single season or lifetime. Our results indicate that warm range-edge populations are highly vulnerable to warming, as low embryonic thermal tolerance may shorten the spawning season and warming is likely to reduce fecundity. This study highlights heterogeneity in life history traits across marine populations that may underlie differential vulnerability to climate warming. Open research statementAll data and code will be publicly available via Figshare and the NSF Biological and Chemical Oceanography Data Management Office (BCO-DMO).

Introduced species can have profound impacts on communities by displacing and consuming native species. The intertidal communities in the Gulf of Maine have been radically altered through a suite of invasions including the herbivorous snail Littorina littorea and the omnivorous crab Carcinus maenas leading to morphological and spatial distribution changes in two native gastropod grazers (Littorina saxatilis and Littorina obtusata). Subsequently, another intertidal omnivorous crab Hemigrapsus sanguineus has become abundant in the intertidal, occurring in areas which were once refuges from crab predation. In order to quantify the potential impact of H. sanguineus on native snails, we conducted both in and ex situ experiments, testing the susceptibility of different sized snails to predation by introduced crabs. Additionally, we measured the distribution, abundance, and morphology of intertidal snails and crabs. Smaller snails of all species were the most susceptible to predation, although susceptibility differed among snail species. Littorina saxatilis was the most vulnerable to predation, with 73 and 64% of the population susceptible to large H. sanguineus and small C. maenas, respectively, while more than 89% of the L. littorea population was resistant to predation. Littorina saxatilis has been relegated to the high intertidal where there is high abiotic stress and poor-quality food, but until the invasion of H. sanguineus, there was little predation risk. Now, it seems that L. saxatilis is at the most risk of all three snail species, and may be at threat of local extirpation at locations with high populations of H. sanguineus.

Small juvenile and larval teleosts are typically more susceptible to starvation and predation, so the largest individuals tend to survive. However, most support for this bigger is better hypothesis is experimental and does not account for the variation in food availability, competition, and other conditions that alter how starvation and predation affect small fish. To assess how natural populations experience size-selective mortality, we reviewed the past 30 years of literature on the subject while compiling 76 effect sizes of longitudinal survival data, which evaluates selection against size classes, to test for evidence that bigger is better. Our meta-analysis shows that the effect of body size on survival is consistently weak across species, populations, times, and locations. We discuss several reasons why larger young teleosts may not have a distinct survival advantage. We argue that they: 1) may be more profitable or noticeable to predators, 2) are unable to outgrow all their predators, and 3) require more resources, increasing their predator exposure out of necessity to forage. We recommend that mortality not be treated as constant across young teleost size classes, as different ecological conditions may favour smaller, larger, or neither size class. We suggest that the relationship between metabolic scope and mortality, geographic gradients in the importance of predation and starvation, and the interactive effects of alternative sources of mortality with predation and starvation in warming oceans are underexplored and could change how we think about the relationship between young teleost size and survival. Investigating these drivers will be important as temperatures rapidly rise, altering growth in wild fish.