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.

No evidence for effects of mill-grinding on δ13 C, δ15 N and δ34 S values in different marine taxa.

RATIONALE: The analysis of natural variation in light stable isotopes such as carbon (δ13 C), nitrogen (δ15 N) and sulfur (δ34 S) plays an important role in deepening our understanding of ecosystems. To avoid misinterpretation, robust results are required, where pre-treatment steps such as sample homogenization are crucial to guarantee representative samples. The grinding of samples using stainless steel balls in polypropylene tubes (e.g., laboratory bead-beater) has been identified as a potential source of bias. METHODS: We tested possible effects of mill-grinding (e.g., contamination) of samples of coastal marine taxa including primary producers, primary consumers and higher trophic level fish. We compared potential impacts of homogenization by mill-grinding with hand-grinding over an extended time on δ13 C, δ15 N and δ34 S values. RESULTS: One-way Welch's analysis of variance (ANOVA) showed that there were no statistical differences between methods for all the studied taxa. Also, repeated measures ANOVA showed no evidence of effects of grinding for extended times (from 30 to 120 seconds) for δ13 C, δ15 N and δ34 S values. CONCLUSIONS: We found no evidence that grinding samples in polypropylene tubes in a bead-beater resulted in any marked alteration of the isotopic composition on the studied samples, e.g., through contamination by plastic. As such, we consider mill-grinding as an appropriate method for the homogenization of samples from a range of different marine taxa, which under controlled conditions did not affect δ13 C, δ15 N and δ34 S analysis.

Intraspecific variation and energy channel coupling within a Chilean kelp forest.

The widespread importance of variable types of primary production, or energy channels, to consumer communities has become increasingly apparent. However, the mechanisms underlying this "multichannel" feeding remain poorly understood, especially for aquatic ecosystems that pose unique logistical constraints given the diversity of potential energy channels. Here, we use bulk tissue isotopic analysis along with carbon isotope (δ13 C) analysis of individual amino acids to characterize the relative contribution of pelagic and benthic energy sources to a kelp forest consumer community in northern Chile. We measured bulk tissue δ13 C and δ15 N for >120 samples; of these we analyzed δ13 C values of six essential amino acids (EAA) from nine primary producer groups (n = 41) and 11 representative nearshore consumer taxa (n = 56). Using EAA δ13 C data, we employed linear discriminant analysis (LDA) to assess how distinct EAA δ13 C values were between local pelagic (phytoplankton/particulate organic matter), and benthic (kelps, red algae, and green algae) endmembers. With this model, we were able to correctly classify nearly 90% of producer samples to their original groupings, a significant improvement on traditional bulk isotopic analysis. With this EAA isotopic library, we then generated probability distributions for the most important sources of production for each individual consumer and species using a bootstrap-resampling LDA approach. We found evidence for multichannel feeding within the community at the species level. Invertebrates tended to focus on either pelagic or benthic energy, deriving 13-67% of their EAA from pelagic sources. In contrast, mobile (fish) taxa at higher trophic levels used more equal proportions of each channel, ranging from 19% to 47% pelagically derived energy. Within a taxon, multichannel feeding was a result of specialization among individuals in energy channel usage, with 37 of 56 individual consumers estimated to derive >80% of their EAA from a single channel. Our study reveals how a cutting-edge isotopic technique can characterize the dynamics of energy flow in coastal food webs, a topic that has historically been difficult to address. More broadly, our work provides a mechanism as to how multichannel feeding may occur in nearshore communities, and we suggest this pattern be investigated in additional ecosystems.

Sample acidification has a predictable effect on isotopic ratios of particulate organic matter along the Chilean coast.

RATIONALE: Stable isotopes of carbon and nitrogen have proved to be valuable tools for researchers working across the different subfields of ecology. However, the chemical pretreatment of samples prior to analytical determination of stable isotope ratios can influence the results, and therefore conclusions regarding the ecology of the taxon or system under study. Here, we determined the effect of vapor acidification with concentrated HCl on the δ13 C and δ15 N values of particulate organic matter (POM), which are commonly used as baselines for studies of trophic ecology, or to understand oceanographic patterns. METHODS: Samples of marine POM were obtained along a large-scale latitudinal gradient (ca 3000 km) along the Chilean coast, along with a range of oceanographic variables thought to potentially influence inorganic carbon at each sampling location. A random subset of 50 samples was divided into two parts: one acidified by HCl fumigation treatment, and the other acting as a control. We compared paired differences in δ13 C and δ15 N values measured by continuous flow isotope ratio mass spectrometry and used a model selection approach to examine which oceanographic factor best explained shifts in values following acid treatment. RESULTS: Acidification resulted in statistically significant reductions in both δ13 C and δ15 N values, but the effect was relatively small. The model that best explained the differences between acidified and non-acidified δ13 C values included depth, salinity and sea-surface temperature at the sampling point. A regression of acidified on non-acidified δ13 C values shows that the treatment effect was strongest on samples more depleted in 13 C. CONCLUSIONS: The differences between δ13 C and δ15 N values in acidified and non-acidified samples are linear and predictable. This implies that the nature of the POM and its possible alteration during the acid treatment are important factors that support the reliable determination of the values of δ13 C and δ15 N of POM.

Clarifying a trophic black box: stable isotope analysis reveals unexpected dietary variation in the Peruvian anchovy Engraulis ringens.

BACKGROUND: Small fishes play fundamental roles in pelagic ecosystems, channelling energy and nutrients from primary producers to higher trophic levels. They support globally important fisheries in eastern boundary current ecosystems like the Humboldt Current System (HCS) of the SE Pacific (Chile and Peru), where fish catches are the highest in the world (per unit area). This production is associated with coastal upwelling where fisheries target small pelagic fishes including the Peruvian anchovy (Engraulis ringens). The elevated biomass attained by small pelagics is thought to reflect their low trophic position in short/simple food chains. Despite their global importance, large gaps exist in our understanding of the basic ecology of these resources. For instance, there is an ongoing debate regarding the relative importance of phytoplankton versus animal prey in anchovy diet, and ecosystem models typically assign them a trophic position (TP) of ∼2, assuming they largely consume phytoplankton. Recent work based on both relative energetic content and stable isotope analysis (SIA) suggests that this value is too low, with δ 15N values indicating that anchovy TP is ca. 3.5 in the Peruvian HCS. METHODS: We characterised the trophic ecology of adult anchovies (n = 30), their putative prey and carnivorous jack mackerel (n = 20) captured from N Chile. SIA (δ 13C and δ 15N) was used to estimate the relative contribution of different putative prey resources. δ 15N was used to estimate population level trophic position. RESULTS: Anchovies showed little variability in δ 13C (-18.7 to -16.1‰) but varied greatly in δ 15N (13.8 to 22.8‰)-individuals formed two groups with low or high δ 15N values. When considered as a single group, mixing models indicated that anchovy diet was largely composed of zooplankton (median contribution: 95% credibility limits), with major contributions of crustacean larvae (0.61: 0.37-0.77) and anchovy (preflexion) larvae (0.15: 0.02-0.34), and the assimilation of phytoplankton was negligible (0.05: 0-0.22). The modal (95% credibility limits) estimate of TP for the pooled anchovy sample was 3.23 (2.93-3.58), overlapping with recent SIA-based estimates from Peru. When the two δ 15N groups were analysed separately, our results indicate that the lower δ 15N group largely assimilated materials from crustacean larvae (0.73: 0.42-0.88), with a TP of 2.91 (2.62-3.23). Mixing models suggested high δ 15N anchovies were cannibalistic, consuming anchovy preflexion larvae (0.55: 0.11-0.74). A carnivorous trophic niche was supported by high TP (3.79: 3.48-4.16), mirroring that of carnivorous juvenile jack mackerel (Trachurus murphyi; 3.80: 3.51-4.14). Our results support recent conclusions regarding high TP values of anchovy from Peru and reveal new insights into their trophic behaviour. These results also highlight the existence of cryptic trophic complexity and ecosystem function in pelagic food webs, classically considered as simple.

Habitat coupling writ large: pelagic-derived materials fuel benthivorous macroalgal reef fishes in an upwelling zone.

Coastal marine upwelling famously supports elevated levels of pelagic biological production, but can also subsidize production in inshore habitats via pelagic-benthic coupling. Consumers inhabiting macroalgae-dominated rocky reef habitats are often considered to be members of a food web fuelled by energy derived from benthic primary production; conversely, they may also be subsidized by materials transported from pelagic habitats. Here, we used stable isotopes (δ13 C, δ15 N) to examine the relative contribution of pelagic and benthic materials to an ecologically and economically important benthivorous fish assemblage inhabiting subtidal macroalgae-dominated reefs along ~1,000 km of the northern Chilean coast where coastal upwelling is active. Fish were isotopically most similar to the pelagic pathway and Bayesian mixing models indicated that production of benthivorous fish was dominated (median 98%, range 69-99%) by pelagic-derived C and N. Although the mechanism by which these materials enter the benthic food web remains unknown, our results clearly highlight the importance of pelagic-benthic coupling in the region. The scale of this subsidy has substantial implications for our basic understanding of ecosystem functioning and the management of nearshore habitats in northern Chile and other upwelling zones worldwide.

The complete mitochondrial genome of the rocky reef fish Cheilodactylus variegatus Valenciennes, 1833 (Teleostei: Cheilodactylidae).

Cheilodactylus variegatus is a common benthivorous marine fish inhabiting in rocky subtidal habitats in the eastern south Pacific coast of Chile and Peru. However, its biology and ecology are relatively understudied and its taxonomic assignment has been debated recently. The complete mitochondrial genome was assembled de novo and mapped to a reference using 5.97 million of reads obtained through Ion Torrent next generation sequencing, resulting in a circular sequence of 16,652 bp in length. Gene composition and arrangement comprised to that reported for most fishes and contained the typical structure of 2 rRNAs, 13 protein-coding genes, 22 tRNAs and 1 non-coding region. This mitogenome provides a valuable resource for studies of fish molecular systematics, phylogeography and population genetics.

Coastal Upwelling Drives Intertidal Assemblage Structure and Trophic Ecology.

Similar environmental driving forces can produce similarity among geographically distant ecosystems. Coastal oceanic upwelling, for example, has been associated with elevated biomass and abundance patterns of certain functional groups, e.g., corticated macroalgae. In the upwelling system of Northern Chile, we examined measures of intertidal macrobenthic composition, structure and trophic ecology across eighteen shores varying in their proximity to two coastal upwelling centres, in a hierarchical sampling design (spatial scales of >1 and >10 km). The influence of coastal upwelling on intertidal communities was confirmed by the stable isotope values (δ13C and δ15N) of consumers, including a dominant suspension feeder, grazers, and their putative resources of POM, epilithic biofilm, and macroalgae. We highlight the utility of muscle δ15N from the suspension feeding mussel, Perumytilus purpuratus, as a proxy for upwelling, supported by satellite data and previous studies. Where possible, we used corrections for broader-scale trends, spatial autocorrelation, ontogenetic dietary shifts and spatial baseline isotopic variation prior to analysis. Our results showed macroalgal assemblage composition, and benthic consumer assemblage structure, varied significantly with the intertidal influence of coastal upwelling, especially contrasting bays and coastal headlands. Coastal topography also separated differences in consumer resource use. This suggested that coastal upwelling, itself driven by coastline topography, influences intertidal communities by advecting nearshore phytoplankton populations offshore and cooling coastal water temperatures. We recommend the isotopic values of benthic organisms, specifically long-lived suspension feeders, as in situ alternatives to offshore measurements of upwelling influence.

Metagenome sequencing of the microbial community of a solar saltern crystallizer pond at cáhuil lagoon, chile.

Cáhuil Lagoon in central Chile harbors distinct microbial communities in various solar salterns that are arranged as interconnected ponds with increasing salt concentrations. Here, we report the metagenome of the 3.0- to 0.2-µm fraction of the microbial community present in a crystallizer pond with 34% salinity.