Atlantic salmon Salmo salar and sea trout S. trutta have experienced significant declines. To mitigate the negative impacts of salmon farming, Norway has designated 29 marine protected areas, known as national salmon fjords, to safeguard key S. salar populations. We investigated the behavior of S. salar and S. trutta post-smolts relative to the spatial boundaries of one such protected area. Species-specific differences were observed, with important implications for conservation efficacy. S. trutta remained primarily within the inner fjord, hence within the protected area during their marine residency, while S. salar passed close to open-net fish farms beyond the protected zone on the way to offshore feeding grounds, highlighting the critical need to maintain low lice levels at aquaculture facilities. S. salar post-smolts migrated faster in the outer fjord than the inner fjord, indicating an acceleration of movement with increasing distance from the river mouth, potentially reducing exposure time in unprotected areas associated with elevated pathogen and parasite risk. Although 2 potential migration pathways existed from the river to the ocean, 93% of S. salar selected the same route across both study years. In conclusion, our findings indicate that the national salmon fjord provides effective spatial protection for S. trutta post-smolts but only partially fulfills its objective of safeguarding S. salar, which must transit aquaculture-intensive areas during a critical early marine life stage. These findings underscore broader concerns for other national salmon fjords, many of which share similar geographic constraints and adjacency to aquaculture operations situated along key migratory corridors.
Atlantic salmon Salmo salar is an anadromous species that exhibits a wide range of life history strategies. One of the least understood and documented strategies involves adult salmon ascending rivers in the autumn or early winter and remaining there without feeding for a full year before spawning. This study provides the first scientific documentation of year-early migratory salmon in Norway. About 5% of Atlantic salmon captured during tagging studies in the river Alta arrived a year prior to spawning. Tracking of 8 tagged fish in the river Alta showed that they entered the river a year prior to spawning and overwintered in the river after spawning. The longest recorded stay in freshwater was 21 mo (640 d). Scale analysis revealed that year-early migrants had smaller sizes at age during their ocean years but entered rivers with higher relative energy reserves. Genetic analysis showed that the year-early migrating fish belong to the river Alta and were not strayers from Russian populations. The factors shaping this strategy are still unclear but may involve balancing the loss of ocean growth and the costs of extended river residency against the advantage of escaping high ocean mortality rates.
Species interactions are mediated by animal behaviour, and are fundamental drivers of global diversity. Mutualistic interactions, whereby multiple parties benefit from an interaction, are highly context-dependent and can scale up to affect populations and communities at higher ecological levels. A well-studied example is the marine cleaning mutualism on coral reefs whereby 'cleaner' fish feed on ectoparasites that reside on 'client' species. Nonetheless, links between mutualistic behaviours, ecological variables, and potential community-level consequences remain unclear. Using Caribbean cleaner gobies Elacatinus lobeli and in situ observations of 25 cleaning stations, we quantify how mutualism-associated behaviours of cleaners and clients can be correlated with multiple local ecological variables (client diversity, cleaner behavioural phenotypes, territorial damselfish aggression, microhabitat structural complexity). Cleaner responsiveness (flight initiation distance) was associated with cleaning behaviours and therefore cleaning strategy. Cleaners showed higher selectivity towards transient over resident clients, with selectivity likely driven by resource partitioning, client identity and service quality. Cleaning behaviours and client diversity were strongly associated, and cleaner selectivity, cleaning station structural complexity (measured as rugosity), and territorial damselfish aggression were associated with cleaner and client behaviours via direct and indirect pathways. We therefore provide a valuable insight into the importance of considering multiple simultaneous, interacting context dependencies in understanding the proximate drivers underlying the functioning of species interactions.
The application of otolith tools to infer the movement history of fishes requires controlled experiments to validate methods and assess confidence in inferences gained for wild specimens. The delta smelt Hypomesus transpacificus is a Critically Endangered estuarine fish endemic to the San Francisco Estuary (SFE), California, United States, and serves as a key indicator species. Understanding variation in habitat use and migratory behaviors of this species is critical for developing effective conservation and management actions. Here, we conducted an experiment using known-age cultured delta smelt and mixtures of coastal seawater and freshwaters of the upper SFE to manipulate their salinity history and examine the temporal resolution and accuracy of salinity reconstructions using otolith strontium (Sr) isotope ratios (87Sr/86Sr). Results indicated that salinity reconstructions from delta smelt otolith 87Sr/86Sr provide accurate salinity estimates (bias <0.5 ppt) in waters below 6 ppt salinity when using an SFE-wide Sr isotope to salinity mixing model. Instantaneous transitions from fresh to brackish waters at 60 days post-hatch (dph) with a salinity of 3 ppt could be detected within ~1 wk (59 ± 6 dph, mean ± SD), while transitions to higher salinities of 6 ppt at 120 dph were more difficult to detect and uncertainty increased to about 3 wk (132 ± 24 dph). These results confirm the utility of otolith geochemistry for examining the movement behaviors of fishes in complex and dynamic estuarine environments where salinity gradients can vary rapidly.
The shrimp Macrobrachium amazonicum (Heller, 1862) is a widely distributed native species in South America. This study presents an updated geographic distribution of the species through a systematic review of primary and secondary data, as well as reports of new native and non-native occurrences. The distribution extends approximately 4976 km, from the Maracaibo hydrographic ecoregion (Venezuela) to Lower Paran & aacute; (Argentina), between the latitudes 10 degrees 40'37"N and 27 degrees 20'31"S, and about 5226 km, from the Tuira River (Panama) to the Northeastern Atlantic hydrographic region (Rio Grande do Norte, Brazil), between the longitudes 79 degrees 31'30"W and 35 degrees 12'7"W. Covering much of South America and 2 hydrographic ecoregions in Panama, geographic expansion was detected with new continental and coastal records, both in native and non-native areas. New occurrences were recorded in the hydrographic ecoregions of Gurupi (Maranh & atilde;o, Brazil); Lower Piranhas-A & ccedil;u (Rio Grande do Norte, Brazil); Middle S & atilde;o Francisco (Bahia, Brazil); Upper Tocantins (Goi & aacute;s, Brazil); Middle Paraguay (Mato Grosso do Sul, Brazil); Tarauac & aacute; (Amazonas, Brazil); Maracaibo, Trinidad, and Orinoco (Venezuela); Magdalena-Sinu (Colombia); Chagres (Panama); and the High Andes of the Amazon (Bolivia). The new record in Maracaibo extended the species' range by 361 km to the north, and in Chagres, Panama, in Central America, by 51 km to the west. M. amazonicum exhibited the neotropical distribution which was already known for the species. Evidence of anthropogenic introduction in Brazilian reservoirs is supported by the absence of records in connection sites with the Orinoco and Amazon basins, which are geologically separated from the La Plata basin. The wide distribution of the species highlights its high adaptability to various environments.
Polysaccharides exhibit a multitude of biological activities, including antioxidant, antitumor, immunoregulatory, hepatoprotective, and anti-inflammatory effects, but it is not known whether such effects occur in fish. Head kidney macrophages from turbot Scophthalmus maximus L. were isolated and cultured to examine the responsiveness to natural polysaccharides as potential immune stimulators. Polysaccharides used in the research included Echinacea purpurea polysaccharide (EPP), Astragalus polysaccharide (APS), lentinan (LNT), seaweed polysaccharide (SPS), and laminarin (LAM). The test compounds were added to the cultures and assessed for their effects on the growth and immunomodulatory functions of the cells. Based on the results of cell activity, reactive oxygen species, and nitic oxide assays, APS was selected as an immune stimulator. After addition of APS to the culture medium, a comprehensive proteomic analysis was conducted to identify signaling pathways responsible for the immune effects on macrophages. Specific immune pathway proteins were upregulated in cells in response to the addition of APS, including macrophage migration inhibitory factor, myosin-α, metalloproteinase inhibitor, and collagenase type III. In particular, compared with non-stimulated cells, the expression level of the TLR22 receptor was significantly increased in stimulated macrophages (p < 0.01). A KEGG pathway analysis indicated that relevant pathways were activated, including TNF, PI3K-Akt, and NF-κB signaling pathways. ELISA and qRT-PCR analysis also indicated that APS reduced IL-1β and TNF-α levels in the cells following lipopolysaccharide (LPS) stimulation. These data suggest that APS produced an immunoprotective effect on the head kidney macrophages of turbot at 800 µg ml-1, and enhanced cell proliferation. Our results provide evidence for anti-inflammatory properties of APS. As such, APS could be a candidate immunopotentiating agent for fish.
The aim of this study was to understand the relationship between acoustic characteristics and body size of Korean rockfish Sebastes schlegelii in order to better estimate the body length of S. schlegelii by passive acoustic techniques. In this study, S. schlegelii, with a body length ranging from 21.7 to 24.8 cm (mean ± SD = 23.33 ± 0.93 cm) and a body weight of 144.2 to 250.3 g were selected as subjects. The aim was to explore the relationship between the acoustic characteristics of the fish and their standardized lengths through aquarium experiments. The vocalization frequency exhibited a main peak at around 150 Hz, a sub-peak at approximately 100 Hz, and the primary vocalization band extended from 100 to 350 Hz, with a pulse duration of 15.2 ± 2.4 ms. The results indicated that the peak frequency was negatively correlated with the standardized length, swim bladder length, width, and height (p <0.001). This research contributes to the understanding of the relationship between acoustic properties and body size and suggests the potential utility of passive acoustic monitoring techniques for estimating the body lengths of target species.
Photosymbioses, in which photosynthetic microorganisms reside within heterotrophic hosts, are important components of aquatic ecosystems and are under threat from environmental warming. The immediate ecological consequences of acute warming for archetypal photosymbioses, such as those between corals and zooxanthellae, are well documented. In contrast, understanding of the evolutionary responses of photosymbioses to persistent warming remains limited and direct observations of evolution in response to warming are scarce, as many associations are slow-evolving and do not enable observations on a tractable timescale. To address this knowledge gap, we exposed the widespread microbial Paramecium bursaria-Chlorella spp. photosymbiosis to 295 d of continuous growth under +5°°C of persistent warming. We subsequently quantified the thermal responses of traits associated with symbiosis persistence and ecological function (growth rate, symbiont density [the number of symbionts within hosts], and metabolic rates) compared with cultures maintained at ambient temperature and cultures exposed to -5°°C of cooling for the same time period. Strikingly, while growth rate thermal optimum increased with warming, net photosynthesis and carbon-use efficiency (the proportion of photosynthetic carbon available for growth) both strongly declined to zero. These data suggest a significant change in ecological function with persistent warming. We also detected larger autonomous symbiont populations following 295 d of warming, and symbionts from the warm-adapted symbiosis demonstrated a ‘switch’ from exclusive growth on organic to inorganic nitrogen, suggesting that symbionts could have evolved increased autonomy from hosts. Thus, warming could erode the ecological function and promote symbiont autonomy in photosymbiosis over evolutionary timescales.
Hard substrate and vertical relief are limited habitat resources for reef-associated species in many regions. On the West Florida Shelf (WFS) of the Gulf of Mexico, red grouper Epinephelus morio act as ecosystem engineers by excavating sediments to expose limestone bedrock. Excavations can exceed 25 m in diameter and 2 m in depth and are among the most abundant WFS seafloor features at depths between 40 and 110 m. As part of a survey of hard-bottom habitats and associated reef fish assemblages, 1203 excavations were identified in WFS waters along the Florida Panhandle between 2014 and 2019. These excavations often contained subsided artificial reef material within their interior and infrequently included E. morio among observed fishes. We video-identified red snapper Lutjanus campechanus excavating sediments around 2 subsided artificial reefs in 2015 and 2017 for a total of approximately 56 min of excavation activity. A total of 24 excavation events were documented around a tire pile in 2015, and 5 were documented around a pyramid-shaped reef module in 2017. These observations help to explain the subsidence of artificial reefs and apparent excavation around their bases despite the scarcity of previously known excavating species. This suggests that L. campechanus might be ecosystem engineers on the WFS.
Fipronil (FPN) is an insecticide used in agriculture. This study focused on the biotransformation process and the histopathological effects of FPN in the liver of grass carp. Fish were exposed to environmental concentrations of FPN (3, 6, and 10 ug l-1) for up to 14 d. The alterations in phase I and II biotransformation enzyme activity (ethoxyresorufin-O-deethylase [EROD] and glutathione-S-transferase [GST]), malondialdehyde (MDA) content, and histopathology in the liver were studied on the 1st, 3rd, 7th, and 14th days. Results showed that EROD (dose-dependent) and GST activity (time-dependent) increased. The MDA content increased in a time- and dose-dependent manner. The most common types of hepatological damage were steatosis, vein dilatation, pyknosis, and increased melanomacrophage centers, probably due to oxidative stress originating from biotransformation enzyme activity (R2 = 0.88 for GST and MDA). The degree of tissue change (DTC) at the highest dose indicated moderate damage to the liver (R2 = 0.82 for GST and DTC). Nevertheless, the level of EROD and GST activity and MDA content indicated complex interactions among various phase I and phase II biotransformation enzymes which should be investigated in future studies with more replications.
Kelp forests along the southwestern and west coasts of South Africa, dominated by the species Ecklonia maxima and Laminaria pallida , are locally termed ‘the Great African Seaforest’. They form 3-dimensional biogenic habitats that provide 4 distinct microhabitats—canopy, fronds, stipe and holdfast—with the latter typically supporting the highest abundance and diversity of associated macroinvertebrates. The macrofauna inhabiting kelp holdfasts in South Africa have rarely been studied, resulting in a near complete lack of baseline data. In this study, macrobenthic assemblages from 40 E. maxima holdfasts were examined over 2 marine ecoregions and 4 locations. Macroinvertebrates were identified and counted for univariate and multivariate analyses using family-level data. A total of 120 families from 9 phyla were identified and were generally dominated by Arthropoda (48 families), Annelida (24 families) and Mollusca (23 families). Marine ecoregion had no significant effect on composition of macroinvertebrate assemblages, whereas location had a significant effect. There was no significant relationship between holdfast volume and macroinvertebrate diversity or abundance, suggesting that other environmental and physicochemical factors are important in determining community structure. This study serves as a baseline for future research aimed at understudied holdfast macroinvertebrate communities in the Great African Seaforest.
Plateau rivers are considered regional water resource depots, hydropower energy bases, cradles of aquatic dispersal, and barriers to invasive alien species. In this study, 20 major plateau rivers from Guizhou Province, China, were studied to (1) investigate the composition, functional feeding group distribution, and diversity of macroinvertebrates; and (2) assess the ecosystem health of the rivers using the macroinvertebrate Family Biotic Index. Among the macroinvertebrate species, the dammed river sections primarily contained Corbicula fluminea and C. nitens from the Lamellibranchia, the urban river sections harbored Bellamya aeruginosa and Semisulcospira cancellata from the Gastropoda, and the reference river sections contained sensitive taxa including mayfly Ecdyonurus yoshidae and caddisfly Stenopsyche tlenmushanensis . Among the major plateau rivers in Guizhou, urban river sections exhibited the highest density of macrobenthic organisms. The Shannon-Wiener index was lowest in dammed sections, followed by urban sections, while reference sections exhibited the highest diversity. As for functional feeding groups, the density of filter feeders was significantly higher than that of other groups. In contrast, the density of gatherer-collectors and the shredders was relatively low. Assessment of the aquatic ecosystem health in Guizhou Plateau rivers showed that dammed sections were primarily in an unhealthy state, urban sections mainly fell into the sub-healthy category, and reference sections had a relatively good health status. The results from this study provide baseline data that is useful for water resources management, hydropower energy utilization, and ecological and environmental protection of the plateau rivers.
Few studies have explored the relationship between benthic and planktonic assemblages in reservoirs, despite their role in food chains and maintaining ecological functions. Macroinvertebrates play a crucial role in food webs and contribute about 42% of whole-lake secondary productivity. Therefore, their status is vital for maintaining good ecological functions. In this study, we selected Nanwan Reservoir, a eutrophic thermally stratified reservoir in China, to evaluate the community of macroinvertebrates in different seasons and explore the relationships between macroinvertebrate assemblages and different planktonic groups, including phytoplankton, protozoans, rotifers, and planktonic crustaceans. Cyanophyta and Bacillariophyta dominated the phytoplankton assemblages, and their proportions varied with seasons. The bad community of macroinvertebrates in summer, autumn, and winter could be attributed to the excessive growth of Cyanophyta or other phytoplankton. Based on the results of partial least squares regression, an algorithm used for prediction, we determined that the excessive growth of algae, crustaceans, protozoans, and Cyanophyta was detrimental to the development of macroinvertebrates, and was indicative of high nutrient loads in the reservoir. However, the growth of Bacillariophyta, Chrysophyta, and Euglenophyta was advantageous to macroinvertebrate assemblages and indicated a better ecological condition of the reservoir. The results of partial least squares structural equation modeling demonstrated close associations between phytoplankton and both zooplankton and macroinvertebrates, indicating their interdependence in this reservoir system. Our study results imply that the status of macroinvertebrates can be predicted by the abundance of some planktonic assemblages, and cost savings from selecting one of the planktonic groups to monitor ecological conditions could be accomplished in future studies.
Shallow-water habitats are being restored in the Sacramento-San Joaquin River Delta with the goal of enhancing phytoplankton production and food availability for higher trophic levels. However, elevated grazing pressure from the non-native freshwater clam Corbicula fluminea and localized depletions of dissolved inorganic nitrogen may limit phytoplankton biomass accumulation in restored habitats. To evaluate interactions between nutrients and grazing on phytoplankton productivity and biomass accumulation, Sacramento River water high or low in phytoplankton biomass was amended with wastewater effluent, presence of C. fluminea, or both, in 48 h in situ incubations. We measured changes in chl a concentration, phytoplankton community composition, and photosynthetic efficiency as well as carbon and nitrogen uptake rates as indicators of phytoplankton responses. Diatoms dominated phytoplankton communities before and after incubation. Chl a concentrations increased 0.7 and 7.4 times in the high and low phytoplankton biomass controls, respectively, and 4.5 and 14 times in the high and low phytoplankton biomass effluent-added treatments, respectively. In the clam treatments, chl a accumulation was suppressed to near zero regardless of effluent additions or initial phytoplankton biomass. In treatments with clams and effluent combined, phytoplankton photosynthetic efficiency was nearly 50% lower than in the effluent-only treatments, suggesting phytoplankton were stressed in the presence of clams. This experiment demonstrated that the presence of clams can prevent the accumulation of phytoplankton biomass, both directly by clam filtering and indirectly by depressing phytoplankton photosynthetic efficiency and rate of growth. We recommend that future wetland restoration projects promoting increased phytoplankton biomass assess clam settlement likelihood as well as nutrient availability.
Microplastic (plastic particles <5 mm in size) contamination is ubiquitous in nature and known to interact with organisms ranging from microbes to mammals. Notably, recent studies have shown that microplastics may interfere with photosymbiosis, an ecologically important association that has suffered pronounced recent declines in the face of contemporary climate change. However, limited findings thus far have largely focussed on select marine associations. Whether freshwater photosymbioses may also be affected remains poorly understood. Here, I aimed to help bridge this gap by asking whether microplastic contamination impacts several traits (growth rate, symbiont density, metabolic rate and feeding rate) in a common, widespread freshwater photosymbiosis, the Paramecium bursaria-Chlorella spp. association. To address how productivity, an important ecosystem service provided by photosymbiosis globally, could be affected, I also measured changes in photosymbiotic net productivity (net photosynthesis rate). To do so, I exposed the symbiosis to microplastics (microbeads extracted from commercial face wash) under laboratory conditions. My key result was that, compared with non-contaminated control cultures, the contaminated symbiosis demonstrated lower net productivity. This response raises concern for primary production rates in freshwater ecosystems contaminated with microplastics, adding to an established story of widespread degradation associated with microplastic pollution globally.
The main aim of this study was to investigate high-frequency depth changes in wild adult Atlantic cod Gadus morhua. The analysis was based on depth measurements collected with implanted data storage tags. The study was part of a ranching project carried out in an Icelandic fjord. In the project, net bags with frozen fish were regularly provided during the daytime at 4 stations where some cod formed distinct ‘herds’ (‘herd cod’) that did not mingle much with the rest of the unconditioned cod in the fjord (‘wild cod’). After tagging, some of the cod resumed life in the herds, whereas other cod left the herds immediately. On 20 subsequent Mondays, the electronic tags were programmed to measure at the highest frequency (every 30 s), and these results were used to study high-frequency depth changes in 4 wild cod and 4 herd cod, the latter as a control group. Several times, rapid cyclical depth changes were observed in both groups. This behaviour, which sometimes lasted for hours, was highest during dawn and dusk in wild cod but peaked during daytime in herd cod after deployment of the feed bags. The occurrence and properties of these vertical undulations varied greatly between fish, dates, and time of day. Most commonly, the periods of the cycles varied between 1 and 4 min and the heights between 2 and 4 m, but there were examples of much larger undulations. The results indicate that wild adult cod swim along vertically undulating paths when searching for prey, most likely to optimize foraging.
