Marine Food Webs Research Articles

Spatial Heterogeneity and Seasonality of Phytoplankton Responses to Marine Heatwaves in the Northeast Pacific

Abstract Marine heatwaves (MHWs) have emerged as a recurrent phenomenon in the Northeast Pacific (NEP) since 2013, with significant ecological and economic consequences. However, our understanding of the impacts of these events on phytoplankton, the primary producers in the marine food web, remains incomplete. In this study, we elucidated the phytoplankton responses during MHWs in the NEP between 1998 and 2022 and revealed contrasting phytoplankton chlorophyll anomalies between the north and south of the Transition Zone Chlorophyll Front (TZCF). Specifically, chlorophyll shows a marked increase north of the TZCF but a decrease south of it, with the most pronounced negative anomalies centered on the TZCF. Additionally, this chlorophyll response exhibits remarkable seasonal variation in space and time, consistent with the seasonal migration of the TZCF. Weakened subpolar southward Ekman transport, which may have resulted in reduced phytoplankton nutrient supply, is likely to be the major contributor to the negative chlorophyll response in this frontal region. Our results highlight the importance of previously unrecognized spatial and temporal heterogeneity of phytoplankton responses to MHWs in the NEP, which may provide insights for future ecosystem conservation and fisheries management in the NEP under MHWs. 



Assessing the Contribution of Posidonia oceanica to Mediterranean Secondary Production Through Stable Isotope Analysis

The role of seagrasses in providing a complex habitat for marine organisms is globally documented; however, few studies have investigated the trophic incorporation of endemic Mediterranean Posidonia oceanica into marine food webs. Meadows of P. oceanica are declining due to climate change and anthropogenic pressures, emphasising the need to determine its contribution in local trophic dynamics. We investigated whether benthic marine invertebrate (BMI) and fish consumers assimilate carbon directly from P. oceanica seagrass or other sources along the seagrass meadow margins in Malta. We sampled and analysed the δ13C and δ15N isotope values of P. oceanica, particulate organic matter (POM), macroalgae, 14 invertebrate taxa, and 10 fishes at three locations marginal to P. oceanica seagrass meadows. Stable isotope ratios were significantly different between all taxa (F26 = 17.37, R2 = 0.68, p < 0.01) and locations (F2 = 34.22, R2 = 0.10, p < 0.01). The source, invertebrate, and fishes were enriched in both 13C and 15N at Baħar iċ-Ċagħaq relative to the other locations, L’Aħrax and Golden Bay, likely due to the increased effluent. Stable isotope mixing models were somewhat confounded as POM and macroalgae had similar δ13C and δ15N values at each site, hampering efforts to define the resource use of the sampled taxa. However, Posidonia oceanica made the lowest contribution for both consumer groups at all locations, consistent with the results of other Mediterranean studies, suggesting that P. oceanica does not contribute significantly to the diet of consumers at seagrass meadow margins within Maltese waters.

Modelling global mesozooplankton biomass using machine learning

Mesozooplankton are a crucial link between primary producers and higher trophic levels and play a vital role in marine food webs, biological carbon pumps, and sustaining fishery resources. However, the global distribution of mesozooplankton biomass and the relevant controlling mechanisms remain elusive. We compared four machine learning algorithms (Boosted Regression Trees, Random Forest, Artificial Neural Network, and Support Vector Machine) to model the spatiotemporal distributions of global mesozooplankton biomass. These algorithms were trained on a compiled dataset of published mesozooplankton biomass observations with corresponding environmental predictors from contemporaneous satellite observations (temperature, chlorophyll, salinity, and mixed layer depth). We found that Random Forest achieved the best predictive accuracy with R2 and RMSE (Root Mean Standard Error) of 0.57 and 0.39, respectively. Also, the global distribution of mesozooplankton biomass predicted by the Random Forest model was more consistent with the observational data than other models. We used the Random Forest model to create a global map of mesozooplankton biomass which serves as a reference for validating process-based ecosystem models. The model outputs confirm that environmental factors, especially surface Chl a, a proxy for prey availability, significantly correlate with the spatiotemporal distribution of mesozooplankton biomass. The scaling relationship between the mesozooplankton biomass and Chl a can be used as an emergent constraint for model validation and development. Moreover, our model predicts that the global mesozooplankton biomass will decrease by 3% by the end of this century under the “business-as-usual” scenarios, potentially reducing fishery production and carbon sequestration. Our study contributes to predicting global mesozooplankton biomass and provides deep insights into the underlying environmental impacts on the distribution of mesozooplankton biomass.

Changes in prey-predator interactions in an Arctic food web under climate change

Global warming affects marine ecosystems by changing environmental conditions, ecosystem structure, and ecosystem functioning. In parts of the Arctic, increased sea temperature and decreased sea ice have led to a poleward expansion of boreal species and increased their interactions with native Arctic species. To investigate and quantify the changing interactions in an Arctic marine food web under new environmental conditions, we studied the interactions between key prey fish species in the seasonally ice-covered parts of the Barents Sea: adult polar cod (Boreogadus saida) and capelin (Mallotus villosus) and one of the major predators in the system: Atlantic cod (Gadus morhua). For this, we compared the predictive performance of threshold models predicting the abundance of adult polar cod as a function of Atlantic cod. Each model was associated with a hypothesis describing prey-predator interactions in different environmental conditions defined by threshold values of summer sea-ice or capelin stock biomass. The best predictive model showed that the predation effect of Atlantic cod on polar cod was strongest in years of low summer sea ice cover and low capelin stock biomass. Our results exemplified that Arctic species such as polar cod may experience increased predation pressure under climate change from boreal species such as Atlantic cod. These effects depend, however, not only on changes in abiotic drivers of species distributions, but also on food-web interactions involving mid-trophic level species such as capelin.

Insight into the diet of early stages of mesopelagic fishes in the Indian Ocean using DNA metabarcoding

Despite playing a critical role in oligotrophic ocean food webs, relatively little is known about the diet of mesopelagic fishes in the Indian Ocean. These fishes are an abundant component of the micronekton assemblages and are a major energy- and nutrient-rich food source, linking the plankton which they feed on to marine predators at higher trophic levels. DNA metabarcoding, a molecular method to identify species from mixed assemblages, has not been commonly used in studies of mesopelagic fish diet, but using it to analyse gut contents can greatly improve the understanding of mesopelagic fish feeding ecology. In this study, we apply DNA metabarcoding (18S rRNA and COI) to gut contents from Stomiiformes and Myctophiformes species from 20 sampling stations covering 30 ˚ of latitude on the 110 ˚ E meridian in the Indian Ocean. In total, 174 fish specimens from 13 genera were examined. Differences in the gut contents among fish families, geographic areas and fish stages were identified. Specimens within the family Myctophidae had the most diverse diet, more so in the northern sampling stations than the south. Gonostomatidae had the least diverse diet. Overall, the most frequently identified prey items from the gut contents were calanoid copepods and halocyprid ostracods. The proportion of halocyprids were also identified to be significantly different among Myctophidae larvae and juvenile specimens, which is a potential ontogenic shift in diet towards a higher ostracod contribution in juveniles as mouth gape increases. In comparison with other plankton abundance data, Copepoda were the most abundant plankton in the gut contents of all fishes sampled throughout the latitudinal gradient, allowing them to be a potential food resource through the region. There are indications that other less abundant plankton, such as like Ostracoda and Malacostraca, may be preferentially targeted by some mesopelagic fish families.

Katarium polorum n. sp., n. g., a novel thecofilosean amoeba (Cercozoa, Rhizaria) from the polar oceans.

Thecate amoebae play important roles in terrestrial and aquatic ecosystems. This study introduces a novel thecofilosean amoeba from Arctic and Antarctic sea sediments. Phylogenetic analysis based on the 18S rDNA sequence places it in the family Chlamydophryidae (order Tectofilosida, class Thecofilosea). However, the novel organism exhibits a significant genetic divergence and distinct morphology from its closest relatives, prompting us to erect the novel genus Katarium with its type species Katarium polorum. K. polorum is a consumer of diatoms and prokaryotes, indicating an important role in nutrient cycling in the polar marine food webs.

Nutrient enrichment can increase the thermal performance of Galápagos seaweeds

Thermal sensitivity in ectothermic organisms is often contingent upon environmental factors. Nutrient availability in particular is believed to influence the physiological responses of primary producers to global warming and is thus relevant to consider when forecasting the structure and functioning of future marine ecosystems. This study measured the effect of nutrient enrichment on the thermal sensitivity of 4 genera of Galápagos seaweeds (Ulva, Caulerpa, Padina, and Ochtodes), estimated as the thermal optimum (Topt), performance maximum (Pmax), activation energy, and deactivation energy. These parameters were quantified by modeling thermal performance curves for net photosynthesis under ambient and nutrient-enriched conditions. Our findings revealed variation in Topt among genera, ranging from 27.6° to 36.0°C. Nutrient additions enhanced Topt by ~2°C for 2 (Padina and Caulerpa) of the 4 taxa and also significantly increased Pmax in Padina, suggesting the ability for warming-induced ocean stratification and associated effects (i.e. decreasing nutrient availability) to reduce the capacities of these populations to maintain and support new growth. No significant differences in Topt or Pmax were observed for either Ulva or Ochtodes with enrichment. Ambient net photosynthesis and respiration rates were also compared across genera; Pmax rates for net photosynthesis were consistently higher than those for respiration (i.e. until just beyond Topt); however, photosynthetic Topt values were lower. Thus, this study suggests that further warming could reduce overall net primary productivity, with potentially far-reaching implications for marine food webs.

Delineating early life stages of Belone belone: analysis of external morphology and postcranial skeletal development of the garfish

During fish larvae development functional, morphological, and physiological adaptations are key in larval survival strategies and can determine mortality bottlenecks. For many fish groups such as needlefish, which play crucial roles in marine food webs, studies on early life stages are almost lacking. Herein, the development, with focus on the postcranial skeleton, of the garfish Belone belone (Linnaeus, 1761) is described and a staging system is introduced. Ten larval and juvenile life stages are proposed in three main phases: yolk sac, larval, and juvenile development. During the yolk sac phase the garfish deplete their yolk reservoirs and finish the development of their unpaired fins. During the larval period the lower jaw elongates and the needlenose stage is reached. In the juvenile phase, the upper jaw elongates until both jaws are almost equally long. Since B. belone larvae develop much of their postcranial skeleton in the late embryonic and yolk sac phases they might not experience a severe bottleneck in this early stage such as many other marine fish species. Therefore, young garfish could be more resilient to environmental changes.

Seaweed-Associated Diatoms (Bacillariophyta) in Dokdo of South Korea: I. Subphyla Melosirophytina, Coscinodiscophytina, and Class Mediophyceae

Dokdo is an island located in the easternmost part of Korea, which has high levels of biodiversity of birds and fish, especially marine invertebrates. However, the biodiversity of microalgae, especially diatoms (Bacillariophyta), is relatively unknown, despite their ecological importance as primary producers of the marine food web and bioindicators of environmental conditions associated with climate change. To understand the biodiversity of seaweed-associated diatoms from Dokdo, we collected macroalgae present at a depth 5–15 m by SCUBA diving on 17 October 2017. There were a large number of diatoms (over 130 species), even though it was a one-time survey. As it includes too many taxa to cover at once, voucher flora for other taxonomic groups will be provided through the continuous serial papers. This is the first series of seaweed-associated diatoms, with 26 species belonging to the subphyla Melosirophytina and Coscinodisophytina, and the class Mediophyceae. Among these, seven species including one new taxon were reported for the first time in Korea, which, along with the geopolitical characteristics of the survey area, proved that there is no domestic interest in seaweed-related diatoms. In particular, the appearance of species that have been reported in subtropical waters, such as the order Ardissoneales, requires continuous monitoring of marine seaweed-associated diatoms to confirm whether their colonization in Dokdo waters was due to climate change or species-specific water temperature tolerance.

Unveiling Ecosystem Shifts in the Southern Benguela Through Otolith Biochronologies of Sardine (Sardinops sagax)

ABSTRACTSardine (Sardinops sagax) in the southern Benguela has shown substantial changes in population size over the past 70 years. Heavy fishing pressure in the 1950s to early 1970s caused the collapse of sardine stocks in South Africa. A fishery collapse happens because of significant alterations in the marine community, hindering the recovery of valuable commercial species and leading to cascading effects across multiple trophic levels in marine food webs. In this study, a robust 58‐year biochronology (1962–2019) was developed using archived sardine otoliths from the West of Cape Agulhas in South Africa. Sequential t‐test analysis of regime shifts (STARS) performed on the biochronology of fish growth indicated four regimes with three alteration points in 1986, 2006 and 2015 that correspond with periods of low, high, average and low biomass, respectively; that is, high growth rates occurred during the high biomass period and vice versa. A series of mixed effects models was developed to determine increment width response to selected environmental, prey availability and sardine biomass factors based on the assumption that otolith increment growth is a proxy for somatic growth. Predicted sardine growth positively correlated with sardine biomass, sea surface temperature and copepod abundance estimates. This observation suggests that sardine population dynamics exhibit a depensation mechanism, potentially destabilizing populations after the fishery collapse. Sea surface temperature and copepod abundance have been primary factors influencing sardine growth, partly because of depensatory population dynamics. Furthermore, the study improves understanding of how different factors have affected sardine growth following the collapse of the sardine fishery.

Conspicuous parasite modifies appearance and energetics of a marine copepod

Abstract Parasitism is an important driver of ecosystem processes. Copepods are fundamental trophic links in marine food webs and harbour many microeukaryotic parasites, but unreliable access to infected individuals limits quantitative studies of parasite infection costs. Calanus spp., (helgolandicus or finmarchicus), infected with the Yellow-Hyphal Parasite become pigmented and are found near the surface, suggesting predator-mediated dispersal. Conventional markers prevented phylogenetic inference but confirmed that the parasite is not Ichthyophonus hoferi, as previously thought. We identified the pigments, quantified the pigment content and respiration rate, and derived stable isotope signatures of infected and uninfected Calanus spp. to examine costs of infection. We found that the pigments were astaxanthin and β-carotene, associated with the host and parasite, respectively. Parasitized hosts had increased astaxanthin content, reduced respiration rate, and lower lipid content. Ultrastructure imaging revealed parasitic cells associated with lipids in the haemocoel. The changes to host phenotype have detrimental impacts on energetics and the ecology of Calanus. We discuss the role of pigments in parasite-host interactions and suggest that the parasite produces β-carotene pigment for its physiological benefits. The trade-off between physiological benefits of pigments and conspicuousness for parasites is relevant in zooplankton-host systems, as zooplankton rely heavily on transparency for survival.

Perturbations in a pelagic food web during the NE pacific large marine heatwave and persistent harmful diatom blooms

Unprecedented warm ocean conditions, driven by the Large Marine Heatwave (LMH) and the 2015–16 El Niño in the Northeast Pacific favored pervasive toxigenic Pseudo-nitzschia spp. blooms that caused widespread ecological impacts, but little is known about the magnitude to which marine food webs were altered. Here, we assessed the trophic transfer of domoic acid (DA; a neurotoxin) and changes in trophic position from multiple key species during the peak of the LMH and El Niño in 2015 in comparison with 2018, a reference non-anomalous warm year. DA and amino acid nitrogen isotopes (δ15N AAs) were quantified using liquid and gas chromatography mass spectrometry, respectively. Our integrative approach revealed extremely high levels of DA in anchovy viscera (>3000 μg/g) with contrasting baseline values (δ15N Phe) for southern California fish. These results together with data from northern CA revealed an unforeseen latitudinal isotopic variation in key DA vectors along California, possibly driven by anomalous restructuring of water masses. At the regional level, the observed cross-shore differences in baseline isotope values and DA toxicity suggest distinct pathways for DA trophic transfer for nearshore vs. offshore sites. Given the high levels of environmental disturbance during the LMH and persistence of toxigenic P. australis blooms, our resultant higher trophic position proxies in 2015 compared to 2018 were particularly unexpected. Such results highlight complex trophic interactions, where the trophic status of some species increased while others decreased in response to changes in net primary productivity, and biodiversity, and abundance of forage species. Our study demonstrates the use of δ15N AAs to identify pathways of N and DA trophic transfer and to quantify shifts in animal trophic position, a critical facet of understanding the response of food webs to climate change and DA production.

Little seasonal variation of mercury concentrations and biomagnification in an Arctic pelagic food web

Despite numerous studies on mercury in Arctic biota, data from inaccessible, ice-covered regions − especially during the polar night and late winter − remain scarce. This scarcity results in poor understanding of the seasonal dynamics of mercury within the food web. From the Northern Barents Sea, we quantified total mercury and the dietary descriptors δ15N and δ13C as long-term dietary signals (weeks to months) in biota to a) investigate the seasonal pelagic food web structure, b) seasonality in total mercury concentration, c) and its biomagnification in the food web. Mercury and dietary descriptors were analyzed in copepods, macrozooplankton (krill, amphipods, arrow worms and pteropods) and the fishes, Atlantic cod (Gadus morhua), polar cod (Boreogadus saida) and capelin (Mallotus villosus) during spring, late summer, early,and late winter. Seasonal changes were observed in δ15N values in some macrozooplankton and capelin, and some seasonal variation was observed across the food web with depleted δ13C values in spring and enriched δ13C values in late summer. Mercury concentrations were lower (range: 2.49 ng/g dw in the krill Thyssanossa sp. – 70.55 ng/g dw in the pelagic pteropod Clione limacina) than reported from other parts of the Arctic. We found a positive linear relationship between mercury and relative trophic position represented by δ15N, i.e., biomagnification, during all seasons, except in early winter. As Clione limacina likely had different turnover rates for mercury and stable isotopes resulting in low δ15N, but high mercury concentrations in early winter, compared to the other species in the food web, the pteropod was omitted from the regression. By omitting Clione limacina, biomagnification was similar across all seasons (R2adj = 0.45). Thus, we saw clear mercury biomagnification with consistent and little seasonal variation in this high Arctic marine food web despite large seasonal fluctuations in abiotic and biotic conditions.

Potter Cove's Heavyweights: Estimation of Species' Interaction Strength of an Antarctic Food Web.

In the West Antarctic Peninsula, global warming has led to severe alterations in community composition, species distribution, and abundance over the last decades. Understanding the complex interplay between structure and stability of marine food webs is crucial for assessing ecosystem resilience, particularly in the context of ongoing environmental changes. In this study, we estimate the interaction strength within the Potter Cove (South Shetland Islands, Antarctica) food web to elucidate the roles of species in its structure and functioning. We use these estimates to calculate food web stability in response to perturbations, conducting sequential extinctions to quantify the importance of individual species based on changes in stability and food web fragmentation. We explore connections between interaction strength and key topological properties of the food web. Our findings reveal an asymmetric distribution of interaction strengths, with a prevalence of weak interactions and a few strong ones. Species exerting greater influence within the food web displayed higher degree and trophic similarity but occupied lower trophic levels and displayed lower omnivory levels (e.g., macroalgae and detritus). Extinction simulations revealed the key role of certain species, particularly amphipods and the black rockcod Notothenia coriiceps, as their removal led to significant changes in food web stability and network fragmentation. This study highlights the importance of considering species interaction strengths in assessing the stability of polar marine ecosystems. These insights have crucial implications for guiding monitoring and conservation strategies aimed at preserving the integrity of Antarctic marine ecosystems.

Habitat dimensionality and feeding strategies but not temperature as determinants of body size-trophic structure relationship in a marine food web.

Disentangling the determinants of trophic structure is central to ecology. The capacity to capture subjugate and consume a prey (i.e. gape limitation) is a relevant limitation to acquire energy for most organisms, especially those in smaller size ranges. This generates a size hierarchy of trophic positions in which large organisms consume small ones. Body size is tightly correlated to gape limitation and explains a large fraction of variance in the body size-trophic position relationship. However, a considerable fraction of variance still remains to be explained. Consumer search space dimensionality (2D or 3D) and feeding strategies, temperature and the size structure of primary producers can alter the trophic structure, but tests based on information from natural food webs are scarce. We generated specific predictions about the body size trophic position relationship and evaluated them using information from a subtropical South Atlantic coastal marine ecosystem: benthic realm (2D, rocky shore and sandy beach) and the pelagic realm (3D). We characterized this marine coastal food web based on stable isotopes of carbon and nitrogen from 256 samples from primary producers (macroalgae and phytoplankton) to large predators (sand shark) in summer and winter. Consumer body size encompassed six orders of magnitude in weight from 10-2 to 6 × 104 g. Isotopic signal corresponded to an integration of carbon sources from basal consumers to top predators. The body size-trophic position relationship showed a linear positive association with different slopes for the benthic and pelagic environments. This implies a smaller predator prey size ratio for pelagic (3D) with respect to benthic consumers (2D) as theoretically expected. No seasonal differences were found in slopes and most of the overall variance in benthic environments was largely explained by feeding strategies of the different taxonomic groups. We provide an integrated evaluation on the role of body size, consumer search space and feeding strategy to understand the determinants of trophic position. Results demonstrate that integrating gape limitation hypothesis, the dimensionality of consumer search space and feeding strategies into a formal robust framework to understand trophic structure is feasible even in complex natural ecosystems.

Marine N2-fixer Crocosphaera waterburyi.

Marine N2-fixing cyanobacteria, including the unicellular genus Crocosphaera, are considered keystone species in marine food webs. Crocosphaera are globally distributed and provide new sources of nitrogen and carbon, which fuel oligotrophic microbial communities and upper trophic levels. Despite their ecosystem importance, only one pelagic, oligotrophic, phycoerythrin-rich species, Crocosphaera watsonii, has ever been identified and characterized as widespread. Herein, we present a new species, named Crocosphaera waterburyi, enriched from the North Pacific Ocean. C. waterburyi was found to be phenotypically and genotypically distinct from C. watsonii, active in situ, distributed globally, and preferred warmer temperatures in culture and the ocean. Additionally, C. waterburyi was detectable in 150- and 4000-meter sediment export traps, had a relatively larger biovolume than C. watsonii, and appeared to aggregate in the environment and laboratory culture. Therefore, it represents an additional, previously unknown link between atmospheric CO2 and N2 gas and deep ocean carbon and nitrogen export and sequestration.

Microplastic and ichthyoplankton in the Ukrainian waters of the Black Sea

The ability of planktonic and neustonic organisms to feed on microplastics and subsequently transfer it through the marine food web has been studied extensively. However, there are no studies on microplastic in the Northwestern Black Sea. The present study assesses the diversity and spatial distribution of microplastics and ichthyoplankton in two surface layers: 0–5 cm (neuston surface layer; NL) and 5–20 cm (hyponeuston layer; HL). The sampling was undertaken in June 2020 – October 2021 in the coastal (CW) and open (OW) waters of the Northwestern Black Sea. Microplastics was observed at all studied sites and was composed of fibres (75 %) and fragments (25 %). Black and red fibres were the most abundant type of fibre, and black particles dominated the fragments. Four types of polymers were identified by Raman spectroscopy: polyethylene, polyester, polyurethane, polypropylene. The concentration of microplastics near the coast significantly exceeded that of open waters; the average microplastics concentration in the CW reached 136±74 (±SE) and 46±30 particles.m-3 in the NL and HL, respectively, whereas it reached 18±3 and 2±0.8 particles.m-3 in the NL and HL of the OW, respectively. In the NL, ichthyoplankton was found only at 31 % of the sites, and at only 24 % of sites in the HL. In total, 6 species of fish were recorded. The most abundant species was the European anchovy, one of the main commercial species in the Black Sea. The ratio of microplastics to ichthyoplankton was 0.34 (or 1:2.87) for both layers, where ichthyoplankton was present. When considering all studied sites, the ratio of microplastics to ichthyoplankton was 1.07 (or 1:0.93). As ichthyoplankton is an ephemeral component of the neuston community, but microplastics is omnipresent, we may consider that comparable densities of microplastics:ichthyoplankton favour their interrelation, negative effect, and transport through the food web.

Consequences of terrestrial top predator control by Patagonian sheep farmers for coastal marine food webs

Most seabird species avoid predation by locating their breeding colonies in predator-free islands, inaccessible cliffs, capes, or on the mainland in Antarctica, the only continent without terrestrial predators. Departing from this general rule, a significant number of large Magellanic penguin (Spheniscus magellanicus) colonies exist nowadays in South American Atlantic mainland shores spanning a wide latitudinal range. Based on published radiocarbon dating of colonies, along with historical and archaeological records, we postulate that the current distribution of these colonies may be a response to predator eradication by sheep farmers. This would have made breeding habitats near marine food resources accessible and may have also reduced competition with neighboring colonies. We employed stable isotope analysis to estimate the penguin contribution to the diet of four pumas responsible for killing thousands of penguins in a breeding colony located within a coastal national park. Furthermore, we used a bioenergetic model to quantify the consumption of forage fish under different population distribution and abundance scenarios. We briefly discuss the implications of our results in the context of conservation policies aimed at establishing ecosystem baselines along the Patagonian shores.

Urban estuary serves as a critical nexus for the land-sea transfer of the terrestrial pathogen Toxoplasma gondii

Terrestrial runoff is a key pathway for the transmission of the terrestrial pathogen Toxoplasma gondii from land to sea, posing a significant threat to marine ecosystems. Understanding the mechanisms by which T. gondii is transported from terrestrial to marine environment is crucial for developing effective prevention and control strategies for toxoplasmosis in marine organisms. This study investigates the transport of T. gondii through terrestrial runoff in the Sow River, a representative watershed in Weihai, China. Surface water, bottom water and sediment samples were collected and analyzed for T. gondii DNA using PCR methods. Out of 5328 samples, the prevalence of T. gondii was found to be 8.61 % in surface water, 9.80 % in bottom water and 16.61 % in sediment, with sediment identified as a significant reservoir. Additionally, estuarine zones showed a higher prevalence of T. gondii (16.80 %) compared to riverine areas (9.00 %). The study further revealed that seasonal climate variations, such as temperature and precipitation, had no significant impact on the distribution of T. gondii. However, there was significant spatial variability, with estuarine conditions facilitating increased pathogen transmission. These findings highlight the importance of estuaries and sediments as key conduits for T. gondii entry in marine food webs. The results provide a theoretical basis for designing infection prevention and control strategies aimed at protecting marine ecosystems.

Seasonal Distribution of Key Small-Sized Fish in the South Inshore of Zhejiang, China

Small-sized fish are a vital food source for large predatory commercial fish and play a key role in marine food webs, bridging lower and higher trophic levels. They are indispensable in maintaining the energy flow and material cycling within aquatic ecosystems. This study utilized bottom-trawl survey data from 2017 to 2020 along the south inshore of Zhejiang, China, complemented by concurrent environmental data, to examine the influence of environmental factors on the resource density and seasonal distribution patterns of four dominant small-sized fish species. The research findings indicated that SSH (sea surface height) and Chl (chlorophyll-a concentration) emerged as the key environmental factors influencing resource densities, with all four species exhibiting similar preferences toward these variables. However, significant disparities were observed in their preferences for SST (sea surface temperature), SSS (sea surface salinity), and DO (dissolved oxygen). The various species’ resource density and distribution patterns underwent significant seasonal variations. Additionally, the seasons and regions with the highest resource densities consistently aligned, occurring predominantly in autumn within the northern waters of the study area. This research further elucidated the environmental predilections and seasonal spatial distribution traits of small-sized fish in the south inshore of Zhejiang, an important feeding ground for economic fish species in the East China Sea. This provides scientific backing for forecasting alterations in coastal fishery resources under environmental and climate change scenarios and supports ecosystem-based fisheries management strategies.