Marine and Freshwater Research最新文献

Understanding tuna diet and its drivers can provide valuable insights into the dynamics of pelagic ecosystems and their capacity to adapt to environmental and human-induced stressors.

To reconstruct tropical tuna dietary histories by using different metrics of stomach fullness and to assess their association with fisheries-related, environmental and biological covariates.

We examined stomachs from 8229 skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) captured in the western and central Pacific Ocean between 2001 and 2021, classified each on the basis of categorical and continuous fullness metrics, then built statistical models to gauge covariate effects.

Only models for the binary fullness metric (i.e. empty or non-empty) performed well. Tuna with empty stomachs were more likely to be caught on active gear (e.g. purse seine) and earlier in the day. Skipjack and bigeye tuna with empty stomachs were more likely to be associated with floating objects (e.g. fish-aggregating devices).

Our results add to the evidence that tropical tunas forage more effectively during the day and more actively when not associated with floating objects. At the individual level, tuna stomach fullness is highly variable.

Further research is needed to understand the factors governing this promising indicator of ecosystem change.

Floodplain inundation creates a diversity of aquatic habitats that diverge in their physical, chemical and biological characteristics through space and time, influencing site-scale ecological processes, with implications for local and landscape-scale ecosystem functioning.

In this study, we characterise conditions of pools on the floodplain and pools in the main channel of the Fitzroy River, north-western Australia.

We used linear models to investigate the spatial and temporal dynamics of top–down and bottom–up forces acting on phytoplankton and zooplankton.

Floodplain pools showed considerable heterogeneity compared with the main channel and were shallow and turbid with high nutrient loads, whereas main-channel pools were deep, clear and nutrient-limited. Phytoplankton and zooplankton biomass (mass per unit volume) were considerably greater and more variable in floodplain pools than in the main channel, where both were largely absent. On the floodplain, bottom–up processes drove water-column productivity (e.g. nutrients to phytoplankton to zooplankton) to a degree not observed in the main channel, providing a valuable resource pathway supporting consumer populations locally and catchment wide. We detected no top–down effects in floodplain pools and no top–down or bottom–up effects in the main channel.

Maintaining flows that inundate the floodplain and promote habitat heterogeneity in the Fitzroy River is crucial for preserving local and landscape-scale ecosystem functioning.

Water managers should take into account the important contribution of floodplain pools to the wider riverine ecosystem and ensure these habitats are not unduely affected by water resource development.

The Great Artesian Basin (GAB) feeds thousands of springs in Australia’s arid centre, supporting relictual species not found elsewhere on Earth. Springs are considerably threatened by ongoing water abstraction by industry. Robust management plans are needed to prevent further extirpations of GAB taxa, but fundamental biodiversity knowledge is lacking.

We aimed to characterise major organismal groups in South Australian GAB springs and surrounding wetlands, their conservation and taxonomic status, and potential biodiversity hotspots and connectivity of spring ecosystems.

Focusing on South Australia as a case study, we conducted a comprehensive review of GAB spring biota based on the published scientific and grey literature.

Almost 500 taxa have been recorded from GAB springs, the majority being invertebrates. Community composition is highly heterogeneous among spring clusters and the true extent of spring biodiversity is far greater than currently known.

GAB springs have intrinsic value as refugia for both endemics and cosmopolitan taxa. GAB invertebrates are poorly conserved and largely lacking in taxonomic knowledge. We highlight several potential biodiversity hotspots that have been overlooked in the literature.

Fundamental biodiversity information on the GAB is crucial for decision making in conservation management, for industry, and for Traditional Custodians.

In Western Australia, the heritage-listed Busselton Jetty is a popular tourism, fishing and diving destination renowned for its unique marine communities.

This research describes and quantifies the fish assemblages (mean number of individuals, species diversity and biomass) at the Busselton Jetty, and makes comparisons with natural habitats in Geographe Bay.

Diver-operated stereo-video systems filmed 25-m transects along the length of the jetty, and a remotely operated vehicle stereo-video filmed 25-m transects in nearby reef, seagrass and sand habitats. Fish at all habitats were counted, identified and measured.

Fish assemblages at the defined inshore, mid-shore and offshore zones of the jetty differed significantly, whereas the number of fish, species diversity and biomass increased with distance from shore. There was no measurable effect of protection within the small sanctuary zone at the end of the jetty. Fish assemblages at the jetty differed from those in all three natural habitats, and the number of fish, species diversity and biomass were highest at the natural reef, followed by the jetty, the seagrass and the sand habitats.

The Busselton Jetty supports a distinctive fish assemblage, high species diversity and a variety of benthic communities. Changes in the fish assemblages were attributed to differences in habitat type, complexity, depth and distance from shore.

The ecological and social benefits of future man-made marine structures can be optimised by incorporating design features that promote habitat diversity and complexity.

Climate change reportedly affects global fisheries, including the highly valuable swimming crabs, an important benthic species in Asian waters.

The aim of this study was to determine the effects of El Niño–Southern Oscillation (ENSO) events on catch rates and habitat suitability of Portunus pelagicus, Portunus sanguinolentus and Charybdis feriatus in the Taiwan Strait.

We combined marine remote sensing data with Taiwanese trap vessel data to develop a weighted habitat suitability index modelling and analyse the recruitment dynamics of swimming crabs in different ENSO events.

Our results suggest that Increasing salinity (>33.5 PSU) and sea temperature (>18.6°C) during La Niña events had a positive effect on stock recruitment and habitat suitability index of P. pelagicus and C. feriatus. By contrast, P. sanguinolentus were not affected by ENSO events. The low catch rates for P. sanguinolentus in normal years and for C. feriatus and P. pelagicus in normal and El Niño years were highly consistent with the significant shrinkage of the habitat suitability index.

Monitoring climate change and environmental factors is essential for understanding their effects on marine ecosystems.

This research can help implement sustainable crab fisheries.

Understanding the effects of environmental filters on the beta diversity of periphytic algae is fundamental to understanding the functioning of tropical reservoirs.

To investigate how the presence and morphological complexity of macrophytes drives the increase in beta diversity of periphytic algae and whether environmental filters have direct effects on periphytic algae.

Periphytic algae were collected from macrophyte stands quarterly in the Jazigo reservoir, north-eastern Brazil. Alpha and beta diversity were measured between the different structural complexities of macrophytes.

Alpha and beta diversity, and turnover of periphytic algae were higher in macrophytes of higher complexity (Pontederia crassipes and Ludwigia helminthorrhiza) and nestedness was higher in macrophytes of lower complexity (Cyperus articulatus). Beta diversity was driven primarily by physical and chemical variables. Dissolved inorganic nitrogen, macrophyte complexity, temperature, macroinvertebrates, light and dissolved oxygen explained the beta diversity of periphytic algae.

These results suggest that environmental filters and the structural complexity of macrophytes are determinants for the increase in alpha and beta diversity of periphytic algae. Macrophytes with greater morphological complexity favour increased availability of niches and microhabitats, and greater diversity of periphytic algae.

Habitat simplification is one of the main threats to reducing biodiversity and homogenisation of aquatic communities.

Macrobrachium amazonicum is a freshwater prawn of socioeconomic importance in the Amazon region, whose growth, reproduction and fecundity vary according to the environment.

To determine which abiotic factors influence the size and fecundity of populations of M. amazonicum in estuary and river environments.

To do so, we captured a total of 255 ovigerous females, 181 from the estuary and 74 from the river, and measured temperature, total dissolved solids, turbidity, salinity, pH, dissolved oxygen and precipitation.

We found that turbidity, precipitation and dissolved oxygen explained the variation in M. amazonicum size, and that the estuarine females were larger and had more and smaller eggs than riverine females.

Precipitation, turbidity and dissolved oxygen were found to bedetermining factors for the ecological plasticity of M. amazonicum females in different environments.

Freshwater prawn species display different reproductive strategies for distinct environments, and understanding their fecundity is important to establish efficient management policies. In addition, this information should be useful to improve the cost–benefit ratio of freshwater prawn farming in the Amazon region.

For threatened marine species, data on their vertical habitat use patterns can reveal risk of interactions with fishing gear and can inform bycatch avoidance strategies. Such data are lacking for young porbeagles (Lamna nasus), which are captured as bycatch in north-western Atlantic fisheries.

We aimed to examine temporal patterns in diving and characterise vertical habitat use of young porbeagles during summer and autumn.

We used data from short-term (28-day), high-resolution (5-min interval) pop-off satellite tags attached to 14 young (young-of-the-year and 1-year-old) porbeagles to model depth use.

Occupied depths ranged from the sea surface to 679 m, with ambient water temperatures of −0.2 to 26°C. Diel period and season were factors related to depth use.

Sharks exhibited a diel activity pattern characterised by more extensive use of the water column during the day while remaining primarily at the surface at night. Depth use differed between seasons, with summer characterised by greater affinity for surface waters (0–10 m) compared to autumn.

Young porbeagles are at risk of interaction with active fisheries on the continental shelf, but interactions may be reduced by setting gear deeper at night or during summer.

Pollution by synthetic polymers is even more problematic to the environment when this material is fragmented into small portions, forming microplastics (MPs).

We analysed the influence of the Brazilian Carnival on the abundance and richness of MPs in the Paraíba do Sul River (PSR). Specific objectives included classifying MPs by shape, colour and polymer, and quantifying and comparing the abundance and richness of surface-water MPs before, during and after Carnival.

Samples were taken from the superficial layer of the water column in 2023, by using manta net.

In total, 843 MPs were identified in the surface water of PSR. Higher MP concentrations were observed after the Carnival event than in the other two periods. Blue and black fibres were the predominant MPs. Glitter and sequin occurred only during the Carnival and post-Carnival periods. Polyester, polyamide and polyethylene were the most abundant in all the periods.

Our findings strongly indicated that Carnival represents a potential short-term source of MP introduction into the PSR basin.

A significant 170% increase in MP abundance was observed 10 days after the Carnival, which is an event occurring across multiple locations in the PSR basin.

The quagga catshark (Halaelurus quagga) is a small-sized (~370-mm total length), deep-water catshark (Family: Pentanchidae), assessed as Data Deficient on the IUCN Red List.

We aimed to bridge critical knowledge gaps on aspects of the life history and exploitation of H. quagga to make a meaningful Red List assessment, and develop management plans.

Specimens landed as bycatch in three harbours along the Laccadive Sea coast of south-western India were examined to gather the first information on exploited length classes and aspects of reproductive biology.

Halaelurus quagga had a female-dominated sex ratio, a positively allometric growth in females, and isometric growth in males. Mature H. quagga males ranged between 294 and 336 mm, and females between 315 and 370 mm, with pregnant females carrying two, three or four egg cases with embryos in each uterus.

This study provides the first information on the biology and exploitation of H. quagga, showing that the species is landed (and discarded) as bycatch in trawl fisheries, with the catches comprising a significant amount of reproductively active individuals.

The intense deep-sea bottom-trawling off south-western India is a major threat to H. quagga, and, if left unmanaged, could likely trigger a threatened category on the IUCN Red List.