Prey Concentrations Research Articles

Growth Rates and Specific Aminoacyl-tRNA Synthetases Activities in Clupea harengus Larvae

Gaining robust in situ estimates of the growth rate of marine fish larvae is essential for understanding processes controlling year-class success and developing sustainable management strategies to maintain good environmental status. We measured the growth rate of Atlantic herring (Clupea harengus) larvae in the laboratory and compared it to the activity of aminoacyl-tRNA synthetases (AARS). Larvae were reared under controlled conditions for 20 days at three temperatures (7, 12, and 17 °C) using different prey concentrations (0.1, 0.3, and 2 prey·mL−1) of the copepod Acartia tonsa. The relationship between specific growth rates (SGR) and specific AARS activities was best described by a linear function—SGR = −0.1031 + 0.0017 · spAARS, r2 = 0.71, p < 0.05—when only larvae fed ad libitum were considered regardless of the temperature. When larvae fed with low concentrations of food were included in the analysis, the relationship was SGR = −0.0332 + 0.0010 · spAARS, r2 = 0.42, p < 0.05. This latter slope was rather low compared to other studies performed in zooplankton. We suggest protein degradation during the early life stages of fish as the cause of this low slope. We also studied SGR under food deprivation and the effect on specific AARS activities. We found rather high specific AARS activities in small individuals of early stages of fish, also suggesting protein degradation. Further research about protein degradation and turnover rates is needed in order to use AARS activity as a proxy for growth rates in field-caught larvae.

Identifying pathways of pharmaceutical exposure in a mesoconsumer marine fish

Pharmaceutical uptake involves processes that vary across aquatic systems and biota. However, single studies examining multiple environmental compartments, microhabitats, biota, and exposure pathways in mesoconsumer fish are sparse. We investigated the pharmaceutical burden in bonefish (Albula vulpes), pathways of exposure, and estimated exposure to a human daily dose. To evaluate exposure pathways, the number and composition of pharmaceuticals across compartments and the bioconcentration in prey and bonefish were assessed. To evaluate bioaccumulation, we proposed the use of a field-derived bioaccumulation factor (fBAF), due to variability inherent to natural systems. Exposure to a human daily dose was based on bonefish daily energetic requirements and consumption rates using pharmaceutical concentrations in prey. Pharmaceutical number and concentration were highest in prey, followed by bonefish, water and sediment. Fifteen pharmaceuticals were detected in common among bonefish, prey, and water; all of which bioconcentrated in prey and bonefish, and four bioaccumulated in bonefish. The composition of detected pharmaceuticals was compartment specific, and prey were most similar to bonefish. Bonefish were exposed to a maximum of 1.2 % of a human daily dose via prey consumption. Results highlight the need for multicompartment assessments of exposure and consideration of prey along with water as a pathway of exposure.

Larval feeding activity and use of embryonic resources determine juvenile performance of the common prawn Palaemonserratus

Phenotypic links are the potential for “carryover” of effects of experience during one life history stage into performance and selection at subsequent stages. They reflect plastic responses to the environment experienced during an early phase on the phenotype of subsequent phases. We are studying these effects by following individuals of the shrimp Palaemon serratus from the embryonic (eggs carried by females) through the larval phase (pelagic) to the juvenile phase (benthic). In experiment 1, we investigated the effects of larval prey concentration (10, 4 and 2 Artemia/mL) and larval incubation temperature (16 and 22 °C) on larval performance (metamorphosis rate, developmental duration and growth) and then on juvenile performance (survival and Specific Growth Rate, SGR, at 18 and 24 °C in 14 days). In experiment 2, we investigated the effects of embryonic incubation temperature (larval biomass and lipid content of newly hatched larvae from embryos incubated at 12 and 18 °C) and larval prey concentration on larval performance and then on juvenile performance. In both experiments, the larvae plastically increased their development time in response to the reduction in temperature and prey concentration, whereas their survival decreased with temperature and prey concentration. The quantity of lipids available at hatching decreased with decreasing embryonic incubation temperature, which reduced the larval performance, particularly with a low concentration of prey. Survival at 14 days post-metamorphosis was significantly reduced when the embryos were incubated at 12 °C compared with those incubated at 18 °C, regardless of the subsequent larval incubation conditions, revealing phenotypic links between overconsumption of embryonic yolk reserves and post-metamorphic fitness. Overall, juveniles had a better SGR at 24 than at 18 °C, and even better when incubated under stressful embryo-larval conditions (temperature and prey concentration). This study highlighted phenotypic links between developmental stages and over developmental periods of several months.

Grazing impact of the calanoid copepods Acartia spp. on the toxic dinoflagellate Alexandrium pseudogonyaulax in the western coastal waters of Korea.

Marine dinoflagellate species in the genus Alexandrium are well known to produce paralytic shellfish poison as well as common coastal species with cosmopolitan distribution. However, few studies on the feeding of copepods on Alexandrium species have been conducted. The toxic dinoflagellate Alexandrium pseudogonyaulax contains goniodomin A and causes red tides in many countries. To investigate the relationship between the toxic dinoflagellate A. pseudogonyaulax and the calanoid copepods Acartia spp., we quantified the ingestion rates of Acartia spp. feeding on A. pseudogonyaulax as a function of prey concentration. Additionally, we estimated grazing coefficients by integrating data from field observations of Acartia spp. and coexisting A. pseudogonyaulax with laboratory measurements of ingestion rates obtained during this investigation. Furthermore, we compared the ingestion rates of Acartia spp. and other predators feeding on Alexandrium species as previously reported. The ingestion rates of Acartia spp. on A. pseudogonyaulax increased continuously with increasing mean prey concentration. The highest values among the ingestion rate of Acartia spp. feeding on A. pseudogonyaulax was 3,407 cells predator-1 d-1 (4,872 ng C predator-1 d-1) at the given prey concentration. The calculated grazing coefficients for Acartia spp. on A. pseudogonyaulax in Shiwha Bay, Korea, were up to 0.073 d-1. The results of this study suggest that A. pseudogonyaulax may decrease or maintain the population of Acartia spp. in marine food webs.

Effects of temperature and live prey concentration on Colossoma macropomum larviculture

Objective. The study evaluated the performance and survival of Colossoma macropomum larvae at different temperatures and concentrations of prey. Materials and methods. Two temperatures (28 and 32ºC) (T) and two initial daily concentrations (500 and 1,000 Artemia nauplii per larva) (CP) of prey were used. These concentrations were increased every 5 days during the first 15 days of cultivation. From the 16th to the 30th day, the larvae received exclusively a commercial diet. Results. In the first 7 days, weight (P), total length (TL) and daily specific growth rate (SGR) were higher for T32 treatments (p<0.05). After 15 days, P, TL and SGR were higher for CP1000 (p<0.05). After 22 days, P and TL suffered the effect of the initial concentration of prey and water temperature with higher values for CP1000 and T32 (p<0.05). At the end of 30 days of cultivation, P was affected only by water temperature with higher values for T32 (p<0.05). The TL showed an effect of temperature and initial concentration of prey with higher values for CP1000 and T32 (p<0.05). During feeding with a commercial diet (days 16-30 of cultivation), survival was higher for T32 (94.38±6.12%) (p<0.05), with no difference for initial prey concentration. Conclusions. It is concluded that the larviculture of C. macropomum must be carried out with a temperature of 32° C and that the food management must be differentiated during the first 15 days, positively influenced in the period of feeding with ration.

Does the Southern Green Anaconda, Eunectes murinus, seek areas of high prey concentration in southeastern Peru?

Although behavior of E. murinus was broadly described over a century ago, observations of predation by E. murinus are rare. Some evidence suggests that it may target sites when hunting. We report details of six livestock depredation events at a single locality near Puerto Maldonado, Peru. Additionally, we compare positions of three radio-tagged snakes with known locations of mineral licks in their home ranges and describe the relationship of a single radio-tagged individual with game trails. Our observations of predation at mineral licks, and the association of radio-tagged individuals with them, suggest that E. murinus may specifically target mineral licks due to high prey concentration. We believe this is the first report of a reptile actively seeking prey at mineral licks. Our observations indicate that E. murinus actively seeks areas with higher prey concentration.

Interactions between the calanoid copepod Acartia hongi and the bloom-forming dinoflagellates Karenia bicuneiformis and K. selliformis

Copepods are a major component of metazooplankton and important prey for fish and invertebrates such as crabs, shrimps, and flatworms. Certain bloom-forming dinoflagellates can kill copepods, but there is little research on the interactions between copepods and the bloom-forming dinoflagellates Karenia bicuneiformis and K. selliformis. In this study, the survival and ingestion rates of the calanoid copepod Acartia hongi feeding on K. bicuneiformis and K. selliformis were determined as a function of prey concentration. On day 2, the survival of A. hongi incubated with K. bicuneiformis was 90–100% at all the tested prey concentrations, while that with K. selliformis was 0–20% at ≥ 582 ng C mL−1. Compared to other harmful dinoflagellates from the literature, K. bicuneiformis caused low mortality of Acartia; however, K. selliformis caused almost the highest mortality at similar dinoflagellate concentrations. With increasing mean prey concentration, the ingestion rates of A. hongi feeding on K. bicuneiformis increased on day 1, but those on K. selliformis did not increase. Acartia hongi stopped feeding on K. bicuneiformis at mean prey concentrations of ≥ 341 ng C mL−1 and K. selliformis at all prey concentrations on day 2. At the prey concentration of 1000 ng C mL−1, the ingestion rate of A. hongi feeding on K. bicuneiformis was moderate among the rates of Acartia spp. feeding on harmful dinoflagellates; however, that on K. selliformis was the lowest. These results indicate that K. bicuneiformis and K. selliformis differentially affect the survival and ingestion rates of A. hongi.

Exploring the spatial variation of mercury in the Gulf of St. Lawrence using northern gannets as fish samplers

Mercury (Hg) is a ubiquitous and pervasive environmental contaminant with detrimental effects on wildlife, which originates from both natural and anthropogenic sources. Its distribution within ecosystems is influenced by various biogeochemical processes, making it crucial to elucidate the factors driving this variability. To explore these factors, we employed an innovative method to use northern gannets (Morus bassanus) as biological samplers of regurgitated fish in the Gulf of St. Lawrence. We assessed fish total Hg (THg) concentrations in relation to their geographical catch location as well as to pertinent biotic and anthropogenic factors. In small fish species, trophic position, calculated from compound-specific stable nitrogen isotopes in amino acids, emerged as the most influential predictor of THg concentrations. For large fish species, THg concentrations were best explained by δ13C, indicating higher concentrations in inshore habitats. No anthropogenic factors, such as pollution, shipping traffic, or coastal development, were significantly related to THg concentrations in fish. Moreover, previously published THg data in mussels sampled nearby were positively linked with THg concentrations in gannet prey, suggesting consistent mercury distribution across trophic levels in the Gulf of St. Lawrence. Our findings point to habitat-dependent variability in THg concentrations across multiple trophic levels. Our study could have many potential uses in the future, including the identification of vulnerability hotspots for fish populations and their predators, or assessing risk factors for seabirds themselves by using biologically relevant prey.

Links between the three-dimensional movements of whale sharks (Rhincodon typus) and the bio-physical environment off a coral reef

BackgroundMeasuring coastal-pelagic prey fields at scales relevant to the movements of marine predators is challenging due to the dynamic and ephemeral nature of these environments. Whale sharks (Rhincodon typus) are thought to aggregate in nearshore tropical waters due to seasonally enhanced foraging opportunities. This implies that the three-dimensional movements of these animals may be associated with bio-physical properties that enhance prey availability. To date, few studies have tested this hypothesis.MethodsHere, we conducted ship-based acoustic surveys, net tows and water column profiling (salinity, temperature, chlorophyll fluorescence) to determine the volumetric density, distribution and community composition of mesozooplankton (predominantly euphausiids and copepods) and oceanographic properties of the water column in the vicinity of whale sharks that were tracked simultaneously using satellite-linked tags at Ningaloo Reef, Western Australia. Generalised linear mixed effect models were used to explore relationships between the 3-dimensional movement behaviours of tracked sharks and surrounding prey fields at a spatial scale of ~ 1 km.ResultsWe identified prey density as a significant driver of horizontal space use, with sharks occupying areas along the reef edge where densities were highest. These areas were characterised by complex bathymetry such as reef gutters and pinnacles. Temperature and salinity profiles revealed a well-mixed water column above the height of the bathymetry (top 40 m of the water column). Regions of stronger stratification were associated with reef gutters and pinnacles that concentrated prey near the seabed, and entrained productivity at local scales (~ 1 km). We found no quantitative relationship between the depth use of sharks and vertical distributions of horizontally averaged prey density. Whale sharks repeatedly dove to depths where spatially averaged prey concentration was highest but did not extend the time spent at these depth layers.ConclusionsOur work reveals previously unrecognized complexity in interactions between whale sharks and their zooplankton prey.

Development and application of a bioenergetics growth model for multiple early life stages of an ecologically important marine fish

Spatial and temporal variability in temperature and food availability are key drivers of growth of marine fishes. Growth during the early life stages (ELS's) is tightly coupled to survival, and in turn, can set year-class strength (i.e. annual recruitment) and overall stock productivity of populations and fished stocks. Ontogenetic changes in physiology, dietary preferences, and growth across ELS's can be accounted for within bioenergetics models, but existing models lack resolution within larval and early juvenile stages. We leveraged daily output from a coupled physical-biogeochemical model to force a highly resolved ontogenetic bioenergetics model parametrized for an ecologically important rockfish in the California Current System. Size-at-age predictions closely track empirical growth trajectories of the ELS's. Scenario testing revealed that growth performance is disproportionately driven by changes in temperature compared to food availability. We then expanded the model to incorporate spatial climatological differences in temperature and prey concentration and found that preflexion growth potential is maximized in areas of historical spawning, suggesting the timing and location of reproduction is an adaptive strategy that places larvae in habitat favorable for survival. Growth potential for late-stage larvae (postflexion) is greatest over a broad areal extent, implying that if a particle tracking algorithm was coupled to the bioenergetics model, a wide range of larval dispersal pathways would place postflexion larvae in habitat suitable for rapid growth. Finally, growth potential of pelagic juveniles is maximized over the continental shelf and shelf-break, aligning with high juvenile catch rates from a fisheries-independent survey. In summary, this study (i) serves as a proof of concept that a bioenergetics model with high ontogenetic resolution can reproduce life stage-specific growth trajectories even though the underlying physiology data for model parameterization is imperfect and (ii) can aid future studies aimed at understanding how ecosystem processes interact with ontogenetic growth and changes in year class strength of early life stages of marine fishes.

Different responses of plankton community to mesoscale eddies in the western equatorial Pacific Ocean

The western equatorial Pacific Ocean exhibits a complex pattern of currents and mesoscale eddies. However, the impacts of dynamic hydrological systems on plankton community remain uncertain due to the low resolution of field observation. In this study, we conducted a comparative study involving regional high-resolution field observations, satellite observations, and the numerical model. Our aim was to clarify the spatial distribution characteristics and underlying factors influencing phytoplankton communities in the western equatorial Pacific Ocean under different currents and mesoscale eddies. The combination of field observations and numerical model suggested that the Mindanao Eddy (cyclonic eddy) exhibited a significantly higher total chlorophyll a concentration than the North Equatorial Current, and the contributions of diatom increased as well. In the subtropical gyre, although the intensity of a transient cyclonic eddy was weak, it still lifted the subsurface phytoplankton up and increased their chlorophyll a concentration. In the Halmahera Eddy (anti-cyclonic eddy), however, Prochlorococcus and haptophytes were the dominant groups, with lower total chlorophyll a compared to the surrounding North Equatorial Counter Current. Generally, the distributions of these phytoplankton communities were primarily influenced by variations in temperature and nutrient concentrations. Interestingly, this study further revealed that both cyclonic and anticyclonic eddies enhanced the grazing rate of microzooplankton through the increasing of prey concentration and temperature, respectively. These factors driven by different eddies affect phytoplankton communities directly or indirectly through bottom-up and top-down controls, and demonstrate the impact of different mesoscale eddies on phytoplankton community in the western equatorial Pacific Ocean, which is a region of great significance to both the regional and global ecosystems.

Implementation and assessment of a model including mixotrophs and the carbonate cycle (Eco3M_MIX-CarbOx v1.0) in a highly dynamic Mediterranean coastal environment (Bay of Marseille, France) – Part 1: Evolution of ecosystem composition under limited light and nutrient conditions

Abstract. Many current biogeochemical models rely on an autotrophic versus heterotrophic food web representation. However, in recent years, an increasing number of studies have begun to challenge this approach. Several authors have highlighted the importance of protists capable of combining photoautotrophic and heterotrophic nutrition in a single cell. These mixotrophic protists are known to play an important role in the carbon cycle. Here, we present a new biogeochemical model that represents the food web using variable stoichiometry. It contains the classic compartments such as zooplankton, phytoplankton, and heterotrophic bacteria and a newly added compartment to represent two types of mixotrophic protists: non-constitutive mixotrophs (NCMs) and constitutive mixotrophs (CMs). We demonstrate that the model correctly reproduces the characteristics of NCMs and CMs and proceed to study the impact of light and nutrient limitation on planktonic ecosystem structure in a highly dynamic Mediterranean coastal area, namely the Bay of Marseille (BoM, France), paying special attention to the dynamics of mixotrophic protists in these limiting conditions. In addition, we investigate the carbon, nitrogen, and phosphorus fluxes associated with mixotrophic protists and showed the following: (i) the portion of the ecosystem in terms of the percentage of carbon biomass occupied by NCMs decreases when resources (nutrient and prey concentrations) decrease, although their mixotrophy allows them to maintain a carbon biomass almost as significant as the copepod one (129.8 and 148.7 mmol C m−3, respectively), as photosynthesis increases as a food source, and (ii) the portion of the ecosystem in terms of the percentage of carbon biomass occupied by CM increases when nutrient concentrations decrease due to their capability to ingest prey to supplement their N and P needs. In addition to providing new insights regarding the conditions that lead to the emergence of mixotrophs in the BoM, this work provides a new tool to perform long-term studies and predictions of mixotroph dynamics in coastal environments under different environmental forcings.

A multistate Langevin diffusion for inferring behavior-specific habitat selection and utilization distributions.

The identification of important habitat and the behavior(s) associated with it is critical to conservation and place-based management decisions. Behavior also links life-history requirements and habitat use, which are key to understanding why animals use certain habitats. Animal population studies often use tracking data to quantify space use and habitat selection, but they typically either ignore movement behavior (e.g., foraging, migrating, nesting) or adopt a two-stage approach that can induce bias and fail to propagate uncertainty. We develop a habitat-driven Langevin diffusion for animals that exhibit distinct movement behavior states, thereby providing a novel single-stage statistical method for inferring behavior-specific habitat selection and utilization distributions in continuous time. Practitioners can customize, fit, assess, and simulate our integrated model using the provided R package. Simulation experiments demonstrated that the model worked well under a range of sampling scenarios as long as observations were of sufficient temporal resolution. Our simulations also demonstrated the importance of accounting for different behaviors and the misleading inferences that can result when these are ignored. We provide case studies using plains zebra (Equus quagga) and Steller sea lion (Eumetopias jubatus) telemetry data. In the zebra example, our model identified distinct "encamped" and "exploratory" states, where the encamped state was characterized by strong selection for grassland and avoidance of other vegetation types, which may represent selection for foraging resources. In the sea lion example, our model identified distinct movement behavior modes typically associated with this marine central-place forager and, unlike previous analyses, found foraging-type movements to be associated with steeper offshore slopes characteristic of the continental shelf, submarine canyons, and seamounts that are believed to enhance prey concentrations. This is the first single-stage approach for inferring behavior-specific habitat selection and utilization distributions from tracking data that can be readily implemented with user-friendly software. As certain behaviors are often more relevant to specific conservation or management objectives, practitioners can use our model to help inform the identification and prioritization of important habitats. Moreover, by linking individual-level movement behaviors to population-level spatial processes, the multistate Langevin diffusion can advance inferences at the intersection of population, movement, and landscape ecology.

Influence of ocean dynamics on Cuvier’s beaked whale (Ziphius cavirostris): Presence and their prey

Cuvier’s beaked whales (Ziphius cavirostris; Zc) dive below 1000 m to forage predominantly on deep-sea squids. The impact of oceanographic conditions on Zc prey and the effects of anthropogenic sounds on Zc foraging remain unclear. Zc prey distribution is patchy and potentially influenced by mesoscale oceanographic features interacting with local bathymetry. Favorable environmental conditions lead to aggregations of lower trophic level species that attract squid, and potentially increase Zc presence. We collected simultaneous active and passive acoustic data in Tanner Basin, a southern California submarine canyon, intermittently between 2017 and 2022. Passive acoustic data revealed Zc were present throughout all years, with lower presence during late summer and fall. Subsurface Zc 3D track reconstructions indicated a preference for one side of the canyon, where Zc foraged within a layer of potential prey, detected from active acoustic data. Prey concentrations, quantified as volume backscatter strength below ∼1150 m depth, exhibited an increase following the passage of mesoscale features, which were measured using Finite-size Lyapunov Exponents (FSLE). These prey increases drove immediate increases in Zc presence. Understanding potential physical drivers of Zc predator-prey dynamics is a critical first step for assessing natural variability and potential impacts of sonar use on Zc foraging behavior.

Temperature and prey density drive growth and otolith formation of the world's most valuable fish stock

Peruvian anchovy (Engraulis ringens) represents the largest single-species fishery worldwide. Knowledge on how temperature and prey availability influences growth and age estimation during marine fish early life stages is critical for predicting bottom-up processes impacting stock productivity under changing environmental conditions. We reared Peruvian anchovy larvae at two temperatures (14.5 and 18.5 °C) and prey concentrations [high (HF), and low (LF)] from 6 to 30 days post-hatch (dph) to measure growth rate and examine daily deposition of otolith increments. Peruvian anchovy larvae grew faster at 18.5 °C compared to 14.5 °C. Larvae reared at low prey concentration (18.5-LF) and low temperature (14.5-HF) grew 61 and 35% slower, respectively, than those at high prey and warm temperature (18.5-HF). Age and growth rates of larvae were well depicted in the otolith microstructure of well-fed larvae at 18.5 °C. However, larvae reared at 18.5-LF or 14.5-HF, had only 55 and 49% of the expected number of daily otolith increments. Our results suggest caution when attempting to explore how ocean processes regulate small pelagic stocks, the productivity of which are largely driven by changes in the survival and growth of young larvae.

Omnivore diet composition alters parasite resistance and host condition.

Diet composition modulates animals' ability to resist parasites and recover from stress. Broader diet breadths enable omnivores to mount dynamic responses to parasite attack, but little is known about how plant/prey mixing might influence responses to infection. Using omnivorous deer mice (Peromyscus maniculatus) as a model, we examine how varying plant and prey concentrations in blended diets influence resistance and body condition following infestation by Rocky Mountain wood ticks (Dermacentor andersoni). In two repeated experiments, deer mice fed for 4 weeks on controlled diets that varied in proportions of seeds and insects were then challenged with 50 tick larvae in two sequential infestations. The numbers of ticks successfully feeding on mice declined by 25% and 66% after the first infestation (in the first and second experiments, respectively), reflecting a pattern of acquired resistance, and resistance was strongest when plant/prey ratios were more equally balanced in mouse diets, relative to seed-dominated diets. Diet also dramatically impacted the capacity of mice to cope with tick infestations. Mice fed insect-rich diets lost 15% of their body weight when parasitized by ticks, while mice fed seed-rich diets lost no weight at all. While mounting/maintaining an immune response may be energetically demanding, mice may compensate for parasitism with fat and carbohydrate-rich diets. Altogether, these results suggest that a diverse nutritional landscape may be key in enabling omnivores' resistance and resilience to infection and immune stressors in their environments.

Microplastics impact simple aquatic food web dynamics through reduced zooplankton feeding and potentially releasing algae from consumer control

Concentrations of microplastics in aquatic environments continue to rise due to industrial production and pollution. While there are various concerns regarding potential deleterious effects of microplastics on ecosystems, several knowledge gaps remain, including the potential for microplastics to directly and indirectly affect biotic interactions and food web dynamics. We explored the effects of environmentally relevant microplastic concentrations on two co-exposed species of herbaceous freshwater crustaceous zooplankton, filter feeding Daphnia dentifera and selective phytoplankton grazers Arctodiaptomus dorsalis. Study organisms were exposed to different concentrations of microplastics (plastic polyethylene microspheres; low = 2.38 × 10−8 mg/L, medium = 0.023 mg/L, high = 162 mg/L), phytoplankton prey, and predator cues, simulating a simple freshwater food web. Microplastic uptake was greater by D. dentifera, but both species were characterized by decreased algal consumption in the highest microplastic concentration treatment. Importantly, aqueous chlorophyll-a concentrations at the conclusion of the experiment were greater for the high microplastic treatment than all controls and other microplastic treatments. Finally, a predator effect was only apparent for D. dentifera, with greater microplastic uptake in the presence of a predator. We conclude that microplastics may adversely impact the ability of zooplankton to feed on algae and potentially release algae from consumptive control by herbivorous zooplankton. SynopsisThis research aimed to better understand the broader food web effects of environmentally relevant microplastic concentrations on aquatic communities.

COMBINED IMPACT OF CANNIBALISM AND ALLEE EFFECT ON THE DYNAMICS OF A PREY–PREDATOR MODEL

In ecological environment, Allee effect is one of the important factors which cause significant changes to the system dynamics. In this paper, using the theory of dynamical systems, we analyze a variation of a standard cannibalistic two-dimensional prey–predator model with Holling type-II functional response in the presence of both weak and strong Allee effects. We have analyzed the impact of strong and weak Allee effects on the dynamics of a cannibalistic system, knowing the dynamics of the cannibalistic model without Allee effect. We have deduced that in the presence of cannibalism, both strong and weak Allee effects generate bistability between equilibrium points. For strong Allee effect, bistability occurs between trivial equilibrium point and predator-free equilibrium point as well as between trivial and coexistence equilibrium points. But for weak Allee effect, bistability occurs only between coexistence equilibrium points. We also pointed out that the cannibalistic system without Allee effect exhibits tristability among the trivial equilibrium point, coexistence equilibrium point having low prey concentration and coexistence equilibrium point having comparatively high prey concentration. But in the presence of strong Allee effect, cannibalistic system experiences tristability among trivial and two other stable coexistence equilibrium points. By a comprehensive bifurcation analysis, we have observed that Allee effect enriches both the local and global dynamics of the system. Here, we have reported all possible codimension-one and codimension-two bifurcations extensively by choosing cannibalism, Allee effect and predator natural death rate as the bifurcation parameters. In the analysis of bifurcations, we have explored the existence of transcritical bifurcation, saddle-node bifurcation, Hopf bifurcation, Bogdanov–Takens bifurcation and Bautin bifurcation. Our analytical findings are validated through exhaustive numerical simulations. Finally, we have reported a comparative study between the impacts of strong and weak Allee effects on the dynamics of the cannibalistic system.

Poleward spawning of Atlantic mackerel (Scomber scombrus) is facilitated by ocean warming but triggered by energetic constraints

Abstract The Northeast Atlantic mackerel is an income breeder with indeterminate fecundity, spawning in multiple batches at optimal temperatures around 11°C in the upper water column during February–July along the continental shelf from 36–62°N. Based on macroscopic staging of gonads (N ∼62000) collected in 2004–2021, we detected an on-going extension of spawning activities into the Norwegian Sea feeding area (62–75°N), reaching stable levels around 2012 onwards. This poleward expansion increased as more fish entered the area, whilst the maximum proportions of spawners concurrently dropped from about 75 to 15% from May to July. Detailed histological examinations in 2018 confirmed the macroscopic results but clarified that 38% of the spawning-capable females in July terminated their spawning by atresia. We suggest that increased access to suitable spawning areas (≥10°C), following ocean warming from 2002 onwards, functions as a proximate cause behind the noticed expansion, whereas the ultimate trigger was the historic drop in body growth and condition about 10 years later. Driven by these energetic constraints, mackerel likely spawn in the direction of high prey concentrations to rebuild body resources and secure the future rather than current reproduction success. The ambient temperature that far north is considered suboptimal for egg and larval survival.

Optimizing intensive culture protocols for Atlantic cod (Gadus morhua) larvae

Larval cod require live prey as food, and prey concentration (PC) and feeding frequency (FF) often affect their growth and survival. Apart from this, water exchange rates/water flow (WER/WF) and water current (WC) also affect the prey resident time in the tank and larval/early juvenile behaviour, respectively. High water current is also known to induce stress in finfish larvae, and this stress response is believed to be dependent on larval developmental stage. Thus, we conducted a study to evaluate three larval rearing protocols varying in prey concentration, feeding frequency, and water current/exchange rate. Three protocols were used: low prey concentration (PC), low feeding frequency (FF), and low water flow (protocol 1); medium PC, medium FF, and medium WF (protocol 2); and high PC, high FF, and high WF (protocol 3) (see Table 1). Larvae were sampled periodically for growth and cortisol measurements. Cortisol extraction and radioimmunoassay (RIA) were conducted using methods previously validated for cod larvae. Larvae reared using protocols 2 and 3 were significantly bigger and heavier than larvae reared using protocol 1. Rearing protocol had a significant effect on the cortisol level in larval cod. Larvae showed a developmental stage-dependent stress response. Protocol 2 had significantly higher survival than protocols 1 and 3. Our results indicate that an intermediate PC, FF, and WF (protocol 2) is suitable during cod larval rearing.