Nekton Community Research Articles

Dwarf Seahorse (Hippocampus zosterae) Density, Distribution, and Habitat Use in Texas

Seagrass beds are composed of foundation species, providing essential nursery grounds, feeding areas, and refuge for various marine life. Several species of fish and invertebrates utilize seagrasses as essential habitat. The Dwarf Seahorse (Hippocampus zosterae) is an understudied species in Texas, and little is known about its density, distribution, and habitat associations in this area of their range. Physicochemical water parameters, nekton community data, habitat data, and Dwarf Seahorse catch data were collected at 80 sites in Texas. The highest catch per unit effort (CPUE) of the target species was in Aransas Bay (0.038/m2). There was a positive relationship between the presence and percent cover of turtle grass (Thalassia testudinum) and the presence and CPUE of Dwarf Seahorses. Dwarf Seahorses were detected more often and at a higher CPUE in locations with a higher seagrass community diversity and richness. The nekton community at sites where Dwarf Seahorses were detected was also more abundant, diverse, and species rich. This is the first comprehensive study of the distribution of the Dwarf Seahorse along the Texas coast. Dwarf Seahorses were generally found in higher abundances in association with mature, stable, and diverse seagrass beds. Recommended conservation strategy to protect Dwarf Seahorses should prioritize the protection of established and mature seagrass beds. Continued directed monitoring of this species is recommended to better understand their distribution and population status.

Estuarine nekton community shows minimal response following large-scale oyster reef habitat loss in Apalachicola Bay, Florida

Estuarine nekton community shows minimal response following large-scale oyster reef habitat loss in Apalachicola Bay, Florida

Intertidal Soundscapes of Hardened and Living Shorelines: A Case Study of Habitat Enhancement

Abstract Organisms, such as fishes and invertebrates and including their larval stages, listen to underwater soundscapes to detect information about nearby habitats. Such soundscapes may be influenced by habitat degradation or enhancement, which can lead to acoustically mediated feedback loops affecting the overall ecosystem. Despite the importance of underwater sounds on ecological functioning, there have been limited studies documenting soundscapes of intertidal ecosystems and few, if any, of living shoreline soundscapes. Living shorelines would especially benefit from acoustically mediated effects for objectives like encouraging fish and invertebrate settlement. This case study used a Before‐After‐Control‐Impact design to sample soundscapes and nekton (i.e., fishes and mobile macroinvertebrates) at a living shoreline construction and a nearby hardened shoreline in Cedar Key, FL (USA). Diel soundscape patterns and acoustic attenuation at the two sites were also described a year following the living shoreline construction. In the acoustic sampling, the high frequency bands of both shorelines were dominated by invertebrate sounds that were influenced by season, site and time of day, while the low frequency band of the living shoreline was often dominated by a loud anthropogenic sound. About a year after the living shoreline installation—despite similar measured acoustic attenuation at both sites—the living shoreline featured louder sound pressure levels compared to the hardened shoreline, which may be particularly beneficial for promoting foundational species and other organism settlement. These results demonstrate that Gulf of Mexico intertidal habitats may have soundscape differences even within close proximity and that living shorelines may enhance acoustic characteristics in ways beneficial to continued shoreline development. This represents an important step in better understanding the relationships between habitat structures, nekton communities, and their associated soundscapes as well as the application of passive acoustic monitoring to improve coastal management and conservation.

Eco-Dynamic Analysis of the Community Structure of Nekton in the Northern South China Sea

The universal laws of thermodynamics in the process of ecosystem development have long been the common research focus of ecology and biophysics. Eco-exergy from thermodynamics is a popular theory in the study of ecosystem self-organization that has been widely used in the study of wetlands and aquatic ecosystems. This study is based on the data of bottom trawl fishery resources in the Northern South China Sea in 1964–1965, 1997–1999, 2006–2007, and 2017. Based on the eco-exergy theory, the exergy contribution rate (PC) of the nekton community and the exergy contribution rate (PL) of different organismic populations were constructed. The eco-exergy (EX) and specific eco-exergy (EXsp) of the nekton in the northeastern South China Sea were analyzed. The results show that, from 1964 to 2017, the EX and EXsp of the nekton community decreased 13.28-fold and 1.42-fold, respectively. Fish populations remained the major contributors to the EX and EXsp of the nekton community; however, compared to crustaceans and cephalopods, their role in maintaining the stability and complexity of the community structure was gradually weakened, and the genetic information per unit of biomass decreased. Meanwhile, compared to fish, the proportion of the EX of crustaceans and cephalopods in the nekton community showed an upward trend. The proportion of crustaceans increased from 2.76% in 1997–1999 to 14.84% in 2017, while that of cephalopods increased from 3.55% to 16.67%. Based on the findings, we speculate that crustaceans and cephalopods play an increasing role in the stability and complexity of the fishery resource structure in the Northern South China Sea. The species replacement in the nekton was obvious, and the dominant species of the Nekton community gradually changed from k-type species to r-type species in the Northern South China Sea.

Hurricane Effects on Seagrass and Associated Nekton Communities in the Northern Gulf of Mexico

Hurricane Effects on Seagrass and Associated Nekton Communities in the Northern Gulf of Mexico

Analysis of Nekton Communities in a Regulated River-Fed Estuary: Assessing Temporal Changes Relative to River Flow Rates in the Apalachicola Bay System, Florida

Analysis of Nekton Communities in a Regulated River-Fed Estuary: Assessing Temporal Changes Relative to River Flow Rates in the Apalachicola Bay System, Florida

Young Allis Shad Alosa alosa (Clupeidae) Would Not Be Euryphagous: An Assessment of Juvenile Diet and Prey Selectivity under Riverine-Type Conditions

Allis shad Alosa alosa hatches and develops in freshwater before migrating to the sea during its first months of life. Some field research works dedicated to the diet of the species in freshwater put forward that young stages of allis shad feed mainly on zooplankton, being opportunistic and euryphagous; their diet would diversify through ontogeny in relation to growth. However, these assumptions have never been confronted to the availability of prey, and the exact age of fish was unknown. In this work, we reared young allis shad under seminatural conditions, from 6 to 10 days posthatching until nearly 3 months old, in a trophic environment representative of a natural river. The rearing structures were designed as artificial rivers, supplied continuously by natural riverine water and zooplankton prey. Additional zooplankton was produced in separate basins and added daily in the structures. One artificial river was used to rear allis shad in 2018, and the experiment was conducted on two allis shad batches in 2019 (one batch per river). We described the nekton communities of potential prey available for allis shad in the rearing structures by sampling the water every week, and we compared these data with the stomach contents of fish captured at one and two months old posthatching to describe their diet and prey selectivity. Our results suggest that young allis shad should not be considered as opportunistic in their feeding, since clear selectivity was observed at both ages. One-month-old allis shad highly selected cladocerans, probably because they are easy to catch for fish at this age, when their swimming abilities are limited. Feeding selection at two months old drifted towards other prey taxa (dipteran larvae, ostracods, and/or copepods), whereas cladocerans were no longer preferred. Our results suggest that fish density and competition may entice two-month-old allis shad to enlarge their diet to other taxa, including benthic organisms, while one-month-old fish do not seem able to shift their diet and would fast in the absence of cladocerans. Thus, this highlights that the feeding of young allis shad may be highly challenging during their first month of growth.

An estuary stress index based on nekton relationships with thematic watershed stressors

Estuaries provide essential ecosystem functions, including serving as nurseries for fish and aquatic invertebrates (i.e., nekton). Understanding how anthropogenic stressors affect the habitat quality of estuaries is a crucial component of fisheries conservation. A meaningful composite indicator for estuary stress on the nekton community at regional scales should encapsulate major anthropogenic effects over an assemblage of important species. This study introduces a composite stressor index, using meta-analysis to synthesize trawl and seine-based sampling data on 39 nekton species from 25 monitoring programs covering 38 Pacific Coast estuaries spanning four ecoregions. Candidate stressor variables include pollution sources, urban and agricultural land use, and stream impairments, considered at different spatial scales. For each of the 39 focal species, we screened these stressors using hierarchical statistical models that account for environmental variability (e.g., salinity) across sampling events and systematic biases due to monitoring program protocols and species-specific biogeographic ranges. Based on this screening, we identified a subset of stressors most strongly related to nekton presence/absence. Then we used principal component analysis (PCA) to identify major thematic axes of variation across these stressors and the 38 estuaries. Hierarchical nekton models fit to these axes (i.e., thematic stressors) indicate that urban development is negatively related to most nekton species, while agriculture is often positively related to species presence, though with smaller estimated effects. These models were also used to create the estuary-level composite index of anthropogenic stress. Urban development is the major contributor to the index scores of most estuaries, except in the Oregon-Washington Coast ecoregion, where agriculture is dominant. The composite index indicates that estuaries in the Southern California Bight ecoregion are the most impacted, along with South San Francisco Bay.

Assessing habitat enhancement by living shoreline restoration: exploring potential caveats of nekton community metrics

Living shorelines (LS) are a nature‐based restoration technique that aims to stabilize shorelines while enhancing multiple ecosystem services. In particular, LS are frequently promoted as beneficial for enhancing essential coastal habitats for fish and mobile crustaceans (nekton). In this study, we aimed to assess the effects of LS on nekton habitat across eight LS restoration sites in coastal Alabama, U.S.A., by applying widely‐used community metrics. Nekton abundance, species richness, evenness, and diversity tended to be higher in LS and adjacent unrestored control sites than along nearby hardened shorelines. Community metrics showed no clear effect of LS compared to their adjacent controls, with substantial among‐site variation masking any restoration effect. While this may suggest an ecological equivalence between restored and control sites, there are other possible interpretations; that a lack of difference reflects sampling the same populations at nearby control and restored sites, that differences do exist but sampling effort was insufficient to detect them, or that community metrics may be too insensitive for comparing the effects of various restoration approaches on nekton habitat quality. Further exploration of individual‐based metrics such as growth and condition of key species is warranted, as these may be more sensitive for assessing restoration outcomes and guiding future project designs.

Trawl counts of nekton during seasonal migrations of pacific salmon in the North-West Pacific, Bering and Okhotsk Seas in 2022

Spatial distribution, abundance and biomass of fish species, cephalopods and jellyfishes are determined in the epipelagic layer on the data of trawl surveys conducted with RV TINRO and RV Professor Kaganovsky in the Pacific waters at Kuril and Commander Islands, western Bering Sea, and Okhotsk Sea in 2022. Modern state of the nekton communities is considered, in particular the state of pink and other species of pacific salmon in summer and autumn seasons. New data on the size-weight composition of pacific salmon are presented; materials for spatial differentiation between their regional groups of pink salmon are available.

Stagewise collapse of biotic communities and its relations to oxygen depletion along the north margin of Nanpanjiang Basin during the Permian–Triassic transition

The process of marine ecosystem collapse during the Permian–Triassic mass extinction may have varied in different paleogeographic settings and the intensity of oxygen depletion changed with different water depths. It remains largely unknown about the detailed biotic community collapse and its relation to paleo-redox condition in the deep-water basin. At the Kejiao section in the Nanpanjiang Basin of South China, the continuous sedimentation sequences and complete fossil records from the Changhsingian of Permian to the lowest Triassic provide a unique opportunity to study the progressive biotic crisis associated with oxygen deficiency in a deep-water setting. Here, we document high-resolution records of both the biodiversity dataset of different taxa and the redox data from the Kejiao section to achieve a new understanding of ecosystem deterioration associated with changes of redox conditions. The redox evolution revealed by changes in pyrite framboid size and morphology shows a change trend from lower dysoxic to oxygenated, and then to dysoxic interrupted by oxygenated and anoxic conditions in the late Changhsingian, and ending with euxinic conditions in the earliest Triassic. 60 species in 41 genera from radiolarians, bivalves, brachiopods and cephalopods were identified in the section and their occurrences show two pulses of extinction. The first pulse corresponds to the reduction in species richness of planktonic radiolarians and nektonic cephalopods, and the second pulse is documented by the wipe out of benthic brachiopods and remnant nektonic cephalopods and the decline in the species richness of benthic bivalves. This indicates the collapse of plankton and most nekton communities is ahead of the counterpart of benthos in the deepwater setting, supporting what observed in other sections in South China. The plankton and nekton communities inhabited water columns and the benthic community dwelled in the bottom water. Thus, the stagewise collapse of communities might be contributed by the expansion/migration, in particular, the downward expansion of Oxygen Minimum Zone (OMZ) documented by the information from pyrite framboids and the sedimentation.

Using long-term ecological monitoring to evaluate how climate and human-induced disturbances impact nekton communities in a Northern Gulf of Mexico estuary

Apalachicola Bay, a river-fed estuary in the northeast Gulf of Mexico is experiencing impacts from anthropogenic and climate-induced changes in freshwater inputs and sea level rise. These synergistic pressures have resulted in a historic oyster fishery collapse and the expansion of mangroves, which are displacing native salt marsh. Understanding how these natural and man-made-driven changes have affected the nekton community is essential for the sustainable management of this coastal region. To evaluate changes in nekton occurrence and distribution in Apalachicola Bay, we analyzed 20 years of biological monitoring data. Our results indicated that spatial variation in species’ populations was driven by differences in salinity, while seasonal changes were driven by temperature. Freshwater inflow is the primary driver of salinity, and these differences demonstrated that river flow reductions have the potential to alter nekton communities. The effects of climate-driven droughts and anthropogenic freshwater flow reductions on estuarine community structure highlight the importance of maintaining sufficient river flow for nursery areas, which provide ecosystem services for the region. Ultimately, these findings support the continued need for monitoring programs that track accelerating ecosystem change and provide a clearer understanding for how community composition will respond to global change.

The Nearshore Nekton Community in Relation to Phytoplankton Biomass, Biodiversity, and Water Quality in a Northeast Florida Lagoonal Estuary System

Estuaries are home to diverse, abundant fish communities. As increasing coastal development, habitat alteration and loss, and changes in water quality potentially impact fish biomass and biodiversity within estuaries, it is important to monitor for and understand changes in these important parameters, particularly as they relate to water quality. This study examined the relationships between fish catch per unit effort, fish biodiversity, and water-quality parameters—specifically phytoplankton biomass, phytoplankton biodiversity, and nutrient concentrations—from 2014 to 2016 within a lagoonal northeast Florida estuary. For this region, this is the first reported examination of the relationships between fish biodiversity, fish catch, and water quality that includes phytoplankton biomass and nutrients. We carried out monthly fish seine-net sampling, phytoplankton net tows, and water-quality sampling at 4 sites within the Guana–Tolomato–Matanzas estuary. Sites closer to Matanzas Inlet had lower fish biodiversity and higher fish catch per unit effort. Fish catch per unit effort and fish biodiversity showed a large degree of temporal variation and showed correlations with temperature, chlorophyll-a, and phytoplankton biodiversity. We examined differences between sites among fish communities in terms of water-residence time, phytoplankton biomass, and nutrient concentrations. The correlations of fish community biodiversity and CPUE with temperature, chlorophyll-a, and phytoplankton biodiversity, while important, likely represent only a subset of all the drivers regarding environmental conditions, habitat, prey, and predation, all of which influence fish community composition.

Assessing long-term outcomes of tidal restoration in New England salt marshes

Salt marshes are valuable coastal ecosystems, but many have been degraded by roads, railways, and other infrastructure that restrict tidal flow and impound watershed runoff. Restoration of tidal flow to tide-restricted salt marshes generally aims to restore native vegetation and habitat functions. Biological communities may take one or more decades to recover following tidal restoration, but outcomes are seldom assessed on that timescale. We assessed the long-term outcomes of eight tidal restorations in Rhode Island, USA using observed changes in plant and nekton communities from pre-restoration to present, and newly-collected data from a rapid assessment method. The time-series vegetation and nekton data suggest that while restoration actions promoted biological recovery, ambient factors such as inundation stress and eutrophication have worked to offset it. Rapid assessment results indicate that the cover of Phragmites australis is higher and the cover of meadow high marsh is lower at restoration marshes compared with a broad reference sample, suggesting incomplete recovery on average, although outcomes varied across the restoration marshes. Habitat integrity increased with the degree of adaptive management following restoration, as well as the age of restoration, but salt marsh restoration practitioners may need to shift their methods and expectations to accommodate human influences on ambient environmental conditions, particularly prevalent, increasing inundation stress associated with sea-level rise. Our study highlights the value of standardized long-term biological monitoring in assessing salt marsh restoration outcomes, and demonstrates how rapid assessment data can add valuable context to restoration findings.

Ecosystem components in the Bering sea convention area: results from studies and fisheries prospective

Recent features in oceanography, forage base, and biological diversity, as well as fisheries prospective in the Bering Sea Convention area are considered. Since 1950, a sharp increase in water temperature has been observed, and thermal regime shifts occurred in 1977 and 2014. Composition and structure of zooplankton communities are virtually the same as in the western Bering Sea basin. Zooplankton community is comprised by a small number of widely distributed species, which belong to macrozooplankton and constitute a valuable food source for upper trophic levels. Nekton biomass is small, an order of magnitude lower than on the shelf. Neighboring continental slope and underwater ridges, as well as seasonal migrations of lower boreal and lower boreal-subtropical species support high species richness of nekton community. Pelagic and benthopelagic species of fish and squid, which occur on the shelf and slope, usually do not migrate into the Convention area in large quantities, except for walleye pollock, which was actively harvested in this area in 1983–1992. However, in the up-coming years, it is impossible to resume pollock fishery in the Convention area, based on the modern state of pollock resources.

Биогенная составляющая фосфоритового горизонта среднего турона в разрезе Сеноманская стенка. Статья 2. Биостратиномический анализ

The paper presents biostratinomicalcharacteristics of the Cenomanian and the Turonian fossilcomplexes found in theMiddle Turonian phosphorite horizon from the Senomanskaya Stenka section (Volgograd region, Zhirnovsk district) constituting the basis of the benthic colonies and nekton communities. Probable interpretations for the settings contributory to generation of the phosphorite inclusion clusters are provided.

Seasonal variability of nektonic community structure and phylogenetic diversity in Weizhou Island, the Beibu Gulf

The favorable natural conditions and variety of habitats in the Beibu Gulf provide a basis for harboring a high diversity of marine organisms. Sustainable coastal ecosystem management can be benefited from a comprehensive assessment of species diversity. In this study, we analyzed the seasonal changes in nektonic phylogenetic and community structures in the waters of Weizhou Island in the northern Beibu Gulf. The results showed that both the nektonic phylogenetic diversity and community structure in the northern Beibu Gulf exhibited strong seasonal differences between spring and autumn. The catch density was 291.9 kg per km2 in spring and 1081.1 kg per km2 in autumn. Phylogenetic diversity of nektonic communities obviously increased from spring to autumn, while phylogenetic patterns changed from clustering to overdispersion. The seasonal patterns of nektonic communities were mainly related to the different fishing intensities in spring and autumn. Summer fishing intensity in the Beibu Gulf was effectively controlled by a mid-summer fishing moratorium, during which nektonic diversity and fish stocks rapidly recovered from the larval pool. Our study revealed that fishing intensity had a greater impact on nektonic communities at smaller spatial scales, and even exceeded the effects of environmental factors.

Nekton use of co-occurring aquaculture and seagrass structure on tidal flats

On the extensive tidal flats of Willapa Bay (Pacific coast, USA), oyster culture, seagrass, and mudflats create a mosaic of intertidal habitats. Structured habitats are generally considered to increase abundance and diversity of associated species, but less attention has been paid to roles of different kinds of structure (seagrass meadows, reefs, farm infrastructure) or co-occurring structure in shaping nekton assemblage structure. Here, we investigated the effects of different oyster culture methods (suspended culture and bottom culture) on nekton communities and abundance across a gradient of seagrass habitats, during multiple seasons, and using both seine and video sampling methods. Of 23 major estuarine taxa, 2 were generally associated with vertical structure (eelgrass or suspended culture), 3 were seagrass specialists, and 3 primarily used habitats lacking vertical structure (mudflats and bottom culture). Where oyster culture was present, 5 taxa associated with on-bottom and 2 taxa associated with suspended culture. Assemblage structure responded to co-occurring structure as expected from responses to each structure type independently (i.e. additive effects of seagrass and oyster culture). In contrast to much empirical evidence in structured habitats, seagrass density was a poor predictor of overall fish abundance. These findings together suggest that maintaining a mosaic of available habitats is favorable for promoting diversity in Willapa Bay.

Seines and baited remote underwater video document consistent spatiotemporal patterns in nekton communities of subtropical coastal habitats

Monitoring nekton using multiple types of gear over a range of estuarine habitats is necessary for assessing changes in ecosystems, the effects of natural and anthropogenic disturbances, and management related to habitat restoration and protection. To assess the utility of 2 types of gear (seines and baited remote underwater videos [BRUVs]) used in many monitoring programs, nekton community metrics were compared across 3 adjacent, hydrologically distinct coastal basins in Florida Bay (Florida, USA) across seasons (wet vs. dry) and 3 water-years (2016-2019). In these basins, projects are underway to restore freshwater inflow. Spatiotemporal patterns in catch per unit effort and species richness were consistent among types of gear, and nekton assemblages differed significantly among basins. Although similar in size and spatial area, the 3 study basins were notably different in habitat (hydrology, water depth, substrate, submerged aquatic vegetation), and 1 basin exhibited distinct basin-specific trends in nekton community structure and lower nekton abundance and species richness across types of gear. Temporal differences in nekton assemblages reflected seasonal shifts and were strongly affected by the passage of Hurricane Irma in 2017. Although seines and BRUVs revealed similar patterns, seine surveys captured more overall species diversity and prey species, while BRUVs could be used in a greater variety of habitats and documented more predators. These results demonstrate the effectiveness of complementary types of gear in tracking variation in estuarine communities and highlight the importance of a sampling design that successfully monitors species throughout the food web and estuarine seascape.

Vulnerability of the Small-Scale Fishery to Climate Changes in the Northern-Central Adriatic Sea (Mediterranean Sea)

Climate change is altering the functioning of ecosystems and species distribution worldwide, with negative impacts on human activities, including fisheries. The Adriatic Sea is an extremely productive area for fisheries, due to the strong outflow of nutrients from rivers and the periodic mixing of nutrients from the Mediterranean. However, the Adriatic Sea is also a semi-closed basin, where species do not have the ability to move to higher latitudes to avoid warming of the waters. Climate change acts on biodiversity in a variety of ways, such as causing changes in the trophic network—favoring the intake of thermophilic alien species, often in competition with local species—and altering the biological cycles of acclimatized marine species to temperate–cold climates. These problems become critical factors for the survival of species and for fisheries relying on these resources. Within this context, to have estimates of possible modifications of the nektonic community in the near future could be quite useful for preparing adaptation plans. In this paper, using Maximum Entropy models under RCP 4.5 and 8.5 scenarios, we estimated the future habitat suitability for a set of marine nektonic species of different thermal affinity (e.g., cold, temperate and warm species) within GSA17 (Northern and Central Adriatic Sea), among the most productive—and most exploited—areas of the Mediterranean Sea. This study shows how, at the current pace, climate change could modify marine ecosystems to the extent that future habitat suitability will decrease for nearly half of the species considered, with a decrease in landings from 13.5 to 86.9%, depending on the scenario. Only for the blue crab Callinectes sapidus has an increase in habitat suitability been observed. For most of the species considered, temperature was the most important variable to explain the probability of relative presence within the GSA17. On the other hand, GSA17 climatic conditions in the near future under the tested scenarios could become a suitable environment for tropical species, which could find here a suitable habitat, at least in terms of thermal features. Results of the present study can help the management of fishery resources and local markets in the near future, providing information to predict changes in the composition of the aquatic community and draw up management plans that take into account the effects of climate change.