Living to the range limit: consumer isotopic variation increases with environmental stress

Multiple stable isotopes (C, N & S) provide evidence for fin whale (Balaenoptera physalus) trophic ecology and movements in the Humboldt Current System of northern Chile

Reflecting the intense coastal upwelling and high primary productivity characteristic of the Humboldt Current System (HCS), the northern coast of Chile supports a diverse and productive community of marine consumers, including worldwide important pelagic fisheries resources. Although marine mammals are relatively understudied in the region, recent studies have demonstrated that fin whale (Balaenoptera physalus) is the most frequently encountered whale species, and forages in these waters year-round. However, a current lack of information limits our understanding of whether fin whales actively feed and/or remain resident in these waters or whether whales are observed feeding as they migrate along this part of the Pacific. Here, we use stable isotope ratios of carbon, nitrogen and sulphur of fin whale skin samples collected in early summer 2020 (n = 18) and in late winter 2021 (n = 22) to examine evidence of temporal isotopic shifts that could provide information on potential migratory movements and to estimate likely consumption patterns of putative prey (i.e. zooplankton, krill, pelagic fishes and Pleuroncodes sp.). We also analysed prey items in fin whale faecal plumes (n = 8) collected during the study period. Stable isotope data showed significant differences in the isotopic values of fin whales from summer and winter. On average, summer individuals were depleted in 15N and 34S relative to those sampled during winter. Whales sampled in summer showed greater isotopic variance than winter individuals, with several showing values that were atypical for consumers from the HCS. During winter, fin whales showed far less inter-individual variation in stable isotope values, and all individuals had values indicative of prey consumption in the region. Analysis of both stable isotopes and faeces indicated that fin whales sighted off the Mejillones Peninsula fed primarily on krill (SIA median contribution = 32%; IRI = 65%) and, to a lesser extent, zooplankton (SIA zooplankton = 29%; IRI copepod = 33%). These are the first isotopic-based data regarding the trophic ecology of fin whales in the north of Chile. They provide evidence that fin whales are seasonally resident in the area, including individuals with values that likely originated outside the study area. The information presented here serves as a baseline for future work. It highlights that many aspects of the ecology of fin whales in the Humboldt Current and wider SE Pacific still need to be clarified.

Identification and Characterization of a Novel Microalgal Strain from the Antofagasta Coast Tetraselmis marina AC16-MESO (Chlorophyta) for Biotechnological Applications

The wide rocky coastline of the Antofagasta hosts an intertidal ecosystem in which the species that inhabit it are routinely exposed to a wide range of physical and chemical conditions and have therefore evolved to tolerate extremes. In the search for new species of potential biotechnological interest with adaptations to a wide range of environmental conditions, the isolation and characterization of microalgae from these ecosystems is of great interest. Here, a new microalgal strain, Tetraselmis marina AC16-MESO, is described, which was isolated from a biofilm collected on the intertidal rocks of the Antofagasta coast (23°36'57.2″ S, 70°23'33.8″ W). In addition to the morphological characterization, 18S and ITS sequence as well as ITS-2 secondary structure analysis revealed an identity of 99.76% and 100% with the species Tetraselmis marina, respectively. The analyses of the culture characteristics and biochemical content showed similarities with other strains that are frequently used in aquaculture, such as the species Tetraselmis suecica. In addition, it is tolerant of a wide range of salinities, thus allowing its culture in water of varying quality. On the other hand, added to these characteristics, the results of the improvement of the lipid content in stressful situations of salinity observed in this study, together with other antecedents such as the potential in bioremediation already published for this strain by the same research group, present a clear example of its biotechnological plasticity. It is noteworthy that this strain, due to its characteristics, allows easy collection of its biomass by decantation and, therefore, a more cost-efficient harvesting than for other microalgal strains. Therefore, this new strain of Tetraselmis marina, first report of this species in Chile, and its morphologically, molecularly and biochemically description, presents promising characteristics for its use in biotechnology and as feed for aquaculture.

Sub-Saharan Africa Freshwater Fisheries under Climate Change: A Review of Impacts, Adaptation, and Mitigation Measures

Sub-Saharan Africa’s freshwater fisheries contribute significantly to the livelihoods and food security of millions of people within the region. However, freshwater fisheries are experiencing multiple anthropogenic stressors such as overfishing, illegal fishing, pollution, and climate change. There is a substantial body of literature on the effects of climate change on freshwater fisheries in Sub-Saharan Africa. This study reviews the existing literature and highlights the effects of climate change on freshwater fisheries, the adaptation strategies of fishery-dependent households in response to the effects, and fisheries’ management and mitigation efforts in the face of climate change. The general effects of climate change on freshwater environments include warming water temperatures, increased stratification, modified hydrological processes, and increased pollutants. These effects adversely affect the physiological processes of fish and the overall wellbeing of fishery-dependent people. To cope with the effects of fluctuating fishery resources due to climate change, fishery-dependent people have adopted several adaptation strategies including livelihood diversification, changing their fishing gear, increasing their fishing efforts, and targeting new species. Several management attempts have been made to enhance the sustainability of fishery resources, from local to regional levels. This study recommends the participation of the resource users in the formulation of policies aimed at promoting climate change adaptation and the resilience of freshwater fisheries for sustainable development.

Stoichiometric and stable isotope ratios of wild lizards in an urban landscape vary with reproduction, physiology, space and time

Spatial and temporal variation in stoichiometric and stable isotope ratios of animals contains ecological information that we are just beginning to understand. In both field and lab studies, stoichiometric or isotopic ratios are related to physiological mechanisms underlying nutrition or stress. Conservation and ecosystem ecology may be informed by isotopic data that can be rapidly and non-lethally collected from wild animals, especially where human activity leaves an isotopic signature (e.g. via introduction of chemical fertilizers, ornamental or other non-native plants or organic detritus). We examined spatial and temporal variation in stoichiometric and stable isotope ratios of the toes of Uta stansburiana (side-blotched lizards) living in urban and rural areas in and around St. George, Utah. We found substantial spatial and temporal variation as well as context-dependent co-variation with reproductive physiological parameters, although certain key predictions such as the relationship between δ¹⁵N and body condition were not supported. We suggest that landscape change through urbanization can have profound effects on wild animal physiology and that stoichiometric and stable isotope ratios can provide unique insights into the mechanisms underlying these processes.

Trophic niche segregation allows range-extending coral reef fishes to co-exist with temperate species under climate change

Changing climate is forcing many terrestrial and marine species to extend their ranges poleward to stay within the bounds of their thermal tolerances. However, when such species enter higher latitude ecosystems, they engage in novel interactions with local species, such as altered predator-prey dynamics and competition for food. Here, we evaluate the trophic overlap between range-extending and local fish species along the east coast of temperate Australia, a hotspot for ocean warming and species range extensions. Stable isotope ratios (δ¹⁵ N and δ¹³ C) of muscle tissue and stomach content analysis were used to quantify overlap of trophic niche space between vagrant tropical and local temperate fish communities along a 730 km (6°) latitudinal gradient. Our study shows that in recipient temperate ecosystems, sympatric tropical and temperate species do not overlap significantly in their diet-even though they forage on broadly similar prey groups-and are therefore unlikely to compete for trophic niche space. The tropical and temperate species we studied, which are commonly found in shallow-water coastal environments, exhibited moderately broad niche breadths and local-scale dietary plasticity, indicating trophic generalism. We posit that because these species are generalists, they can co-exist under current climate change, facilitating the existence of novel community structures.

Toward a mechanistic understanding of trophic structure: inferences from simulating stable isotope ratios

Stable isotope ratios (SIR) are widely used to estimate food-web trophic levels (TLs). We built systems dynamic N-biomass-based models of different levels of complexity, containing explicit descriptions of isotope fractionation and of trophic level. The values of δ15N and TLs, as independent and emergent properties, were used to test the potential for the SIR of nutrients, primary producers, consumers, and detritus to align with food-web TLs. Our analysis shows that there is no universal relationship between TL and δ15N that permits a robust prognostic tool for configuration of food webs even if all system components can be reliably analysed. The predictive capability is confounded by prior dietary preference, intra-guild predation and recycling of biomass through detritus. These matters affect the dynamics of both the TLs and SIR. While SIR data alone have poor explanatory power, they would be valuable for validating the construction and functioning of dynamic models. This requires construction of coupled system dynamic models that describe bulk elemental distribution with an explicit description of isotope discriminations within and amongst functional groups and nutrient pools, as used here. Only adequately configured models would be able to explain both the bulk elemental distributions and the SIR data. Such an approach would provide a powerful test of the whole model, integrating changing abiotic and biotic events across time and space.