Low prevalence of microplastic contamination in planktivorous fish species from the southeast Pacific Ocean

The gut contents of 292 planktivorous fish, from four families (Atherinopsidae, Clupeidae, Engraulidae and Scombridae) and seven species, captured along the coast of the southeast Pacific, were examined for microplastic contamination. Only a small fraction of all studied fish (2.1%; 6 individuals) contained microplastic particles in their digestive tract. Microplastics found were degraded hard fragments and threads, ranging from 1.1 to 4.9 (3.8±SD 2.4) mm in length, and of various colours, which suggests that the planktivorous fish species examined herein did not capture microplastics on the basis of their colour. The low prevalence of microplastic contamination in planktivorous fishes found in this study suggests that the risk of accidental ingestion by these species might be limited in the coastal upwelled waters of the southeast Pacific, perhaps due to small human population and highly dynamic oceanographic processes.

Predictive modelling of habitat selection by marine predators with respect to the abundance and depth distribution of pelagic prey

Understanding the ecological processes that underpin species distribution patterns is a fundamental goal in spatial ecology. However, developing predictive models of habitat use is challenging for species that forage in marine environments, as both predators and prey are often highly mobile and difficult to monitor. Consequently, few studies have developed resource selection functions for marine predators based directly on the abundance and distribution of their prey. We analysed contemporaneous data on the diving locations of two seabird species, the shallow-diving Peruvian Booby (Sula variegata) and deeper diving Guanay Cormorant (Phalacrocorax bougainvilliorum), and the abundance and depth distribution of their main prey, Peruvian anchoveta (Engraulis ringens). Based on this unique data set, we developed resource selection functions to test the hypothesis that the probability of seabird diving behaviour at a given location is a function of the relative abundance of prey in the upper water column. For both species, we show that the probability of diving behaviour is mostly explained by the distribution of prey at shallow depths. While the probability of diving behaviour increases sharply with prey abundance at relatively low levels of abundance, support for including abundance in addition to the depth distribution of prey is weak, suggesting that prey abundance was not a major factor determining the location of diving behaviour during the study period. The study thus highlights the importance of the depth distribution of prey for two species of seabird with different diving capabilities. The results complement previous research that points towards the importance of oceanographic processes that enhance the accessibility of prey to seabirds. The implications are that locations where prey is predictably found at accessible depths may be more important for surface foragers, such as seabirds, than locations where prey is predictably abundant. Analysis of the relative importance of abundance and accessibility is essential for the design and evaluation of effective management responses to reduced prey availability for seabirds and other top predators in marine systems.

Upwelling intensity modulates the fitness and physiological performance of coastal species: Implications for the aquaculture of the scallop Argopecten purpuratus in the Humboldt Current System

Understanding how marine species cope with the natural environmental variability of their native habitats will provide significant information about their sensitivity to the potential environmental changes driven by climate change. In particular, marine species inhabiting upwelling ecosystems are experiencing low seawater temperatures, as well as, acidic and low oxygen conditions as a consequence of the nature of the deep upwelled waters. Our study is focused on one of the most important socio-economical resources of the Humboldt Current System (HCS): the scallop Argopecten purpuratus which has been historically subjected to intensive aquaculture in areas influenced by upwelling processes. Here, a long-term field experiment was performed to understand how tolerant and well-locally-adapted is A. purpuratus to upwelling conditions by studying a set of fitness, physiological, and biomineralogical traits. Stronger upwelling generated a minor water column stratification, with lower temperatures, pH, and oxygen conditions. On the contrary, as upwelling weakened, temperature, pH, and oxygen availability increased. Finally, upwelling intensity also determined the number, duration, and intensity of the cooling and de-oxygenation events occurring in A. purpuratus habitat, as well as, the food availability (chlorophyll-a concentration, Chl-a). Physiologically, A. purpuratus was able to cope with stressful environmental conditions imposed by higher upwelling intensities by enhancing its metabolic and calcification rates, as well, producing higher concentrations of the shell organic matter. These physiological changes impacted the total energy budget, which was highly dependent on Chl-a concentration, and revealed important traits trade-offs with significant fitness costs (higher mortalities emerged when longer and more intense upwelling events succeed). Our study increases the knowledge about the physiological performance and tolerance of this important resource to the ocean acidification and ocean-deoxygenation imposed by variable upwelling intensities, as well as, its potential vulnerability under future changing conditions driven by a potential upwelling intensification.

Jellyfish Life Stages Shape Associated Microbial Communities, While a Core Microbiome Is Maintained Across All

The key to 650 million years of evolutionary success in jellyfish is adaptability: with alternating benthic and pelagic generations, sexual and asexual reproductive modes, multitudes of body forms and a cosmopolitan distribution, jellyfish are likely to have established a plenitude of microbial associations. Here we explored bacterial assemblages in the scyphozoan jellyfish Chrysaora plocamia (Lesson 1832). Life stages involved in propagation through cyst formation, i.e., the mother polyp, its dormant cysts (podocysts), and polyps recently excysted (excysts) from podocysts – were investigated. Associated bacterial assemblages were assessed using MiSeq Illumina paired-end tag sequencing of the V1V2 region of the 16S rRNA gene. A microbial core-community was identified as present through all investigated life stages, including bacteria with closest relatives known to be key drivers of carbon, nitrogen, phosphorus, and sulfur cycling. Moreover, the fact that half of C. plocamia’s core bacteria were also present in life stages of the jellyfish Aurelia aurita, suggests that this bacterial community might represent an intrinsic characteristic of scyphozoan jellyfish, contributing to their evolutionary success.

Carbon utilization profile of the filamentous fungal species Fusarium fujikuroi, Penicillium decumbens, and Sarocladium strictum isolated from marine coastal environments

Facultative marine filamentous fungi have recently emerged as a functional component in coastal marine systems. However, little is known about their ecological role and functions in biogeochemical cycles. Penicillium decumbens, S. strictum, and F. fujikuroi were isolated from the coastal upwelling zone off south-central Chile. Their carbon profiles were characterized using Biolog FF MicroPlates. These species used a wide range of carbon sources, mainly carbohydrates, but also amino acids, suggesting the use of metabolic routes that include glycolysis/gluconeogenesis. Substrate richness revealed a great capacity for the utilization of nutritional sources, reflected by the following Shannon Indices of utilization of specific substrates: 4.02 for S. strictum, 4.01 for P. decumbes, and 3.91 for F. fujikuroi, which reveals a high physiological capacity for oxidizing different substrates. Significant differences were found between 18 substrates utilized by all three species. Results suggest that filamentous fungi should be considered an integral part of the marine microbial community and included in biogeochemical cycling models of upwelling ecosystems.

Multifarious anchovy and sardine regimes in the Humboldt Current System during the last 150 years

The Humboldt Current System (HCS) has the highest production of forage fish in the world, although it is highly variable and the future of the primary component, anchovy, is uncertain in the context of global warming. Paradigms based on late 20th century observations suggest that large-scale forcing controls decadal-scale fluctuations of anchovy and sardine across different boundary currents of the Pacific. We develop records of anchovy and sardine fluctuations since 1860 AD using fish scales from multiple sites containing laminated sediments and compare them with Pacific basin-scale and regional indices of ocean climate variability. Our records reveal two main anchovy and sardine phases with a timescale that is not consistent with previously proposed periodicities. Rather, the regime shifts in the HCS are related to 3D habitat changes driven by changes in upwelling intensity from both regional and large-scale forcing. Moreover, we show that a long-term increase in coastal upwelling translates via a bottom-up mechanism to top predators suggesting that the warming climate, at least up to the start of the 21st century, was favorable for fishery productivity in the HCS.

Everything Is Everywhere: Physiological Responses of the Mediterranean Sea and Eastern Pacific Ocean Epiphyte Cobetia Sp. to Varying Nutrient Concentration

Bacteria are essential in the maintenance and sustainment of marine environments (e.g., benthic systems), playing a key role in marine food webs and nutrient cycling. These microorganisms can live associated as epiphytic or endophytic populations with superior organisms with valuable ecological functions, e.g., seagrasses. Here, we isolated, identified, sequenced, and exposed two strains of the same species (i.e., identified as Cobetia sp.) from two different marine environments to different nutrient regimes using batch cultures: (1) Cobetia sp. UIB 001 from the endemic Mediterranean seagrass Posidonia oceanica and (2) Cobetia sp. 4B UA from the endemic Humboldt Current System (HCS) seagrass Heterozostera chilensis. From our physiological studies, both strains behaved as bacteria capable to cope with different nutrient and pH regimes, i.e., N, P, and Fe combined with different pH levels, both in long-term (12 days (d)) and short-term studies (4 d/96 h (h)). We showed that the isolated strains were sensitive to the N source (inorganic and organic) at low and high concentrations and low pH levels. Low availability of phosphorus (P) and Fe had a negative independent effect on growth, especially in the long-term studies. The strain UIB 001 showed a better adaptation to low nutrient concentrations, being a potential N₂-fixer, reaching higher growth rates (μ) than the HCS strain. P-acquisition mechanisms were deeply investigated at the enzymatic (i.e., alkaline phosphatase activity, APA) and structural level (e.g., alkaline phosphatase D, PhoD). Finally, these results were complemented with the study of biochemical markers, i.e., reactive oxygen species (ROS). In short, we present how ecological niches (i.e., MS and HCS) might determine, select, and modify the genomic and phenotypic features of the same bacterial species (i.e., Cobetia spp.) found in different marine environments, pointing to a direct correlation between adaptability and oligotrophy of seawater.

Stable isotope and fatty acid analyses reveal significant differences in trophic niches of smooth hammerhead Sphyrna zygaena (Carcharhiniformes) among three nursery areas in northern Humboldt Current System

Fishery pressure on nursery areas of smooth hammerhead in northern Peruvian coast have become a serious threat to sustainability of this resource. Even though, some management actions focused on conservation of the smooth hammerhead populations were proposed in recent years, their scientific foundations are often limited, and biomass of smooth hammerhead in Peruvian waters continues to decrease. To inform management and conservation, this study aims to evaluate the trophic niche of smooth hammerhead juveniles from three nursery areas in the northern Peruvian coast using stable isotope and fatty acid analyses. First, we compared the environmental characteristics of each nursery area (i.e., sea surface temperature and chlorophyll-a concentration) and concluded that nursery areas differed significantly and consistently in sea surface temperature. Subsequently, we evaluated isotopic composition of carbon and nitrogen and fatty acid profiles of muscle and liver tissues collected from juvenile smooth hammerhead from each nursery area. We found that juvenile smooth hammerhead captured in San José were enriched in heavier ¹³C and ¹⁵N isotopes compared to those captured in Máncora and Salaverry. Furthermore, the broadest isotopic niches were observed in juveniles from Máncora, whereas isotopic niches of juveniles from Salaverry and San José were narrower. This difference is primarily driven by the Humboldt Current System and associated upwelling of cold and nutrient rich water that drives increased primary production in San José and, to a less extent, in Salaverry. Compared to smooth hammerhead juveniles from Máncora, those from San José and Salaverry were characterised by higher essential fatty acid concentrations related to pelagic and migratory prey. We conclude that smooth hammerhead juveniles from three nursery areas in the northern Peruvian coast differ significantly in their trophic niches. Thus, management and conservation efforts should consider each nursery area as a unique juvenile stock associated with a unique ecosystem and recognize the dependence of smooth hammerhead recruitment in San José and Salaverry on the productivity driven by the Humboldt Current System.

Impact of multiple-factors on health and infections in marine mussels (Perumytilus purpuratus) inhabiting contaminated sites in the Humboldt Current System

Marine organisms are increasingly exposed to a combination of environmental stressors. However, most studies focus on single factors, limiting our understanding of real-world ecological challenges. This study investigates the combined effects of metal pollution, parasites, pathogens, and environmental variables on the health of Perumytilus purpuratus, a mussel species inhabiting the coast of northern Chile. The upwelling system in this area, combined with low water turnover, creates a unique environment in which to study how multiple factors interact. Mussels were sampled from several sites affected by metal discharges. Analyses revealed that individuals from central and northern sites exhibited the highest levels of parasites, pathogens, and tissue lesions. These health impacts were strongly associated with elevated pH, salinity, cadmium and copper concentrations in the water. Findings emphasise the synergistic effects of chemical and abiotic factors, underscoring the importance of incorporating multiple factors interactions into monitoring programmes. Such an approach can enhance predictions of ecological responses, inform conservation efforts, and guide policies addressing global challenges like aquatic pollution. Our study provides critical insights into how combined factors threaten aquatic ecosystems, offering a framework for more comprehensive environmental assessment.

Macrofaunal community structure in Bahía Concepción (Chile) before and after the 8.8 Mw Maule mega-earthquake and tsunami

Faunal assemblages of subtidal sedimentary environments are key components of coastal ecosystems. Benthic communities inhabiting the coastal zone near urban centers in Concepción Bay (Chile) have been described as highly disturbed (i.e. impoverished in diversity and species richness). This is due to the frequent presence of hypoxic conditions at the bottom due to the intrusion of low oxygen Equatorial Subsurface Water, high natural productivity and the high load of organic matter generated by several anthropogenic activities. A mega-earthquake (8.8 Mw) and subsequent tsunami occurred on the coast of south-central Chile on February 27, 2010 (27F), heavily impacting Concepción Bay, which is located 30 km south of the epicenter. The objectives of the present study are: (i) to evaluate the effect produced by the mega-earthquake and tsunami on the benthic community, and (ii) to assess dissimilarity in macrofauna composition and abundance in Concepción Bay at an inter-decadal time scale based on a comparison between our sampling conducted between 2010 and 2013 and information published since 1969. Our results show that the benthic macrofauna of Concepción Bay was disturbed by the 27F (i.e. high community dissimilarity in 2010). Changes in community structure were observed at an inter-annual scale (i.e. diminished community dissimilarity in 2013), suggesting a recovery post-27F. At an inter-decadal scale, community structure post-27F was dissimilar to the structure described for the 1980's and 1990's but more similar to that reported for 1969. The reducing conditions of the sediments due to the high input of organic matter that took place in the 1980's and 1990's may explain this dissimilarity.

Macroecological patterns of planktonic unicellular eukaryotes richness in the Southeast Pacific Ocean

In recent years, studies focusing on microbial biogeography have been developed, but macroecological processes in marine microorganisms remain unclear, especially in seemingly continuous environments such as the Southeast Pacific Ocean (SPO), where information on microbial distribution patterns is limited, and they may vary depending on the habitat and lifestyle. We used unicellular planktonic eukaryotes as model organisms to determine their biogeographic patterns in the SPO, identify the underlying ecological and historical-evolutionary processes and compare with other microorganism groups. Our analyses were based on the Niche Theory to model species diversity distribution using large open-access ecological and physical-biogeochemical databases based on Bayesian approaches, an integrated nested Laplace approximation (INLA), and Generalized Additive Models (GAM). As a result, two richness hotspots were observed, which are associated with coastal and offshore regions in the central southern areas of SPO. The richness hotspots were associated mainly with nutrients (N/Si ratio) and Mixed Layer Depth (MLD), which could be explained by highly productive upwelling events in the SPO. In contrast, the negative correlation of predicted richness with low pH is strongly related to the effect of calcareous shells (tests), as lower pH levels hinder the formation and stability of calcium carbonate shells in protists like foraminifera and radiolaria, thereby affecting overall unicellular planktonic eukaryote diversity. Our results support the role of ecological processes related to productivity, energy dynamics, and ecological limits in shaping broad-scale diversity patterns of unicellular planktonic eukaryotes in the SPO. The results show colonization and extinction dynamics through species replacement (i.e. High Turnover) along the Chilean and Equatorial coasts associated mainly with the Hotspots of their biodiversity, but also a gradual species loss (i.e. High Nestedness) along the Peruvian Coast associated mainly with the Coldspots of their biodiversity; highlighting how local environmental fluctuations can shape these planktonic microorganisms' behavior, ecology and distribution. The distribution patterns of planktonic unicellular eukaryotes show little evidence of the effects of historical and evolutionary processes. This is because the high dispersal capacity of planktonic microbes probably dilutes the influence of these processes in environments lacking clear barriers to species dispersal. Additionally, the effect of historical events could be highlighted in specific taxonomic groups at the kingdom, phylum level or habitat type and addressing gaps about latitudinal richness in the SPO. This provides insight into the spatial distribution of marine microbes and contributes to conservation efforts, as these organisms are an essential foundation of the upper levels of the food web.

Influence of the El Niño-Southern Oscillation on SST Fronts Along the West Coasts of North and South America

Along the west coasts of North, Central, and South America, sea surface temperature (SST) fronts are important for circulation dynamics and promoting biological activity. Prevailing equatorward winds during summer results in offshore Ekman transport and upwelling along the coast, where fronts often form between cold, upwelled water and warmer offshore waters. The interannual variability in winds, coastal upwelling, sea level anomalies, and SST in these regions have been linked to the El Niño-Southern Oscillation (ENSO), however SST fronts have received less attention. Here, we investigate the interannual variability of SST fronts off North, Central, and South America using satellite SST data spanning 1982-2018. Anomalies of fronts within 0-300 km offshore indicate interannual variability that coincides with ENSO events in most regions. Frontal activity generally decreases during El Niño events and increases during La Niña events. The decrease in fronts off Peru and Chile during El Niño coincides with the seasonal peak in frontal activity, while off the United States the decrease occurs when frontal activity is at a seasonal minimum. We also utilized satellite measurements of wind stress and sea level anomaly to investigate how ENSO oceanic and atmospheric forcing mechanisms affect frontal activity. Decreases in frontal activity during El Niño events are largely due to oceanic forcing (i.e., coastal Kelvin waves) off Central and South America and to both oceanic forcing and atmospheric teleconnections off the United States. This study furthers our understanding of the influence of ENSO on coastal upwelling regions in the eastern Pacific Ocean.

Long-term monitoring for conservation: closing the distribution gap of Arctocephalus australis in central Chile

OBJECTIVES

Here, we present the first record of stable colonies of the South American fur seal (Arctocephalus australis), in an area where their presence has never been documented (hereafter distribution gap), as well as an update of the current distribution range of the species in central Chile.

RESULTS

A national synoptic aerial census of pinnipeds was performed during the austral summer of 2019 on the Chilean coast. An additional aerial census was conducted in the same area during the austral spring of 2019 as well as a maritime census during the austral summer of 2020. The data showed the presence of South American fur seals in central Chile within their well-known distribution gap. The total abundance was registered in three colonies where fur seals were sighted: one non-breeding colony, Punta Topocalma (summer 2019: mean = 46 ± 3; spring 2019: mean = 9 ± 1); and two breeding colonies, Punta Curaumilla (summer 2019: mean = 595 ± 7; spring 2019: mean = 45 ± 4; summer 2020: mean = 744 ± 5) and Isla Santa María (summer 2019: mean = 246 ± 6). Specifically, we suggest that it is crucial to elucidate the origin of the described settled colonies, and to determine whether there has been an augment in the distribution range from either the northern population, the southern population, or both simultaneously.