Munida Gregaria Research Articles

Salmon farming, overfishing and southern sea lion: Not so opportunistic responses of a top predator to human perturbations in the Patagonian Fjords

Pinnipeds are considered generalist predators that prey opportunistically on more abundant prey. Thus, their diet could be affected by natural and anthropogenic stressors, such as declines in native prey and increases in exotic prey such as escaped salmon. Using stable isotopes, we evaluated temporal and spatial variability in the diet of southern sea lion (Otaria flavescens), and assessed its response to seasonal and stochastic variability in native prey and escaped salmon. Demersal fishes (median contribution range = 50–79 %) and escaped salmon (6–44 %) were the most important prey, in all colonies and seasons examined. The median estimated contributions of caged salmon, Munida gregaria and Sprattus fuegensis were consistently lower than 10% in all colonies and seasons. Variability in the relative availability of stocked and escaped salmon, as well as in Merluccius australis and S. fuegensis, showed limited influence on the contribution of these prey to the diet. Thus, although a noticeable response was evident after a large-scale escape of farmed Atlantic salmon that occurred during the study period, the opportunistic behaviour of southern sea lion seems questionable. A better understanding of dietary responses to induced changes in prey availability may have management implications in marine habitats affected by overfishing and farming of exotic species.

Spatial variations in ectoparasite Pseudione galacanthae prevalence in the squat lobster Grimothea gregaria in Argentine Patagonia.

The bopyrid Pseudione galacanthae is an ectoparasite of the squat lobster Grimothea gregaria (Munida gregaria). This study aimed to analyze the spatial variations in the prevalence of P. galacanthae in Argentine Patagonia and the potential drivers shaping this variability. To analyze this crustacean/crustacean parasitic relationship, bottom trawl net hauls, a CTD cast, and zooplankton samplings were performed in 10 locations between 43.6° and 47.7°S. Squat lobsters were assigned to 1 of 2 morphotypes (gregaria or subrugosa), sexed, and measured, and the branchial chambers were examined in search of bopyrids. Correlation analyses were performed to identify whether environmental variables (sea bottom salinity, SBS), sea bottom temperature, depth, and calanoid copepods abundance) or population traits (median of size distribution and density of squat lobsters) were related to P. galacanthae prevalence. The gregaria morphotype was dominant in the south of San Jorge Gulf (SJG), whereas the subrugosa morphotype was more abundant in the other locations. No significant differences were observed in P. galacanthae prevalence between sexes or morphotypes. Spatial variations in prevalence were observed, reaching 15.2% in the south of SJG. P. galacanthae prevalence was correlated only with SBS. We hypothesized that the highest prevalence of P. galacanthae could be related to the presence of a tidal frontal system in the south of SJG, which could favor parasite larval retention. The prevalence reported here is the highest for bopyrid parasites in squat lobster species and reveals that this interaction could have a detrimental impact on G. gregaria populations at local scale.

Seasonal and spatial variability of vertical particle flux along the Beagle Channel (Southern Patagonia)

The Beagle Channel is a 300-km long passage connecting the Pacific and Atlantic Oceans at ~55° S, where glaciers and river streams meet subantarctic waters. Here we present the first evaluation of downward fluxes and composition of particulate matter in the channel. Settling particle fluxes were collected by sequential sediment traps deployed in two contrasting areas: one in the western part of the channel, corresponding to an early post-glacial environment (site A) and a second, fully deglaciated, river-dominated environment (site B) in the eastern part. In early summer, fluxes at both sites are driven by organic matter produced in spring, with peak organic carbon fluxes of 289 and 413 mg C m−2 d−1 at sites A and B, respectively (C:N ratios of 7.3 and 6.3, respectively). During winter, the fluxes of fecal pellets, particulate organic carbon (POC) and particulate nitrogen (PON) were at their minimum. At site A (integrated annual POC flux of 74 g C m−2 yr−1), seasonality was weak and the flux was driven by ballast material (>95% of total particle flux) of glacial origin year-around, which also promotes the POC export. According to isotopic and taxonomic analyses performed at site A, the low seasonality in the organic component of the flux appears to be mainly related to autochthonous production of nano- and picophytoplankton during autumn and winter, later replaced by microphytoplankton fluxes during spring and summer. At site B, ballast material accounted for <60% of total mass flux and the POC flux showed a marked seasonality with a well-defined maximum after the spring phytoplankton bloom. Regarding the contribution of zooplankton, fecal pellets of appendicularians dominated at the western sector of the channel (site A) while Munida gregaria pellets dominated the flux at the eastern site (site B). This work is a contribution to ongoing efforts to unveil the physical and biogeochemical variables driving the biological carbon pump and the land-sea connections in this high-latitude ecosystem threatened by climate change.

Prey contribution to the diet of pink cusk-eel Genypterus blacodes (Forster, 1801) revealed by stomach content and stable isotopic analyses in the southwestern Atlantic

This paper studied the diet of the pink cusk-eel Genypterus blacodes, using a combination of stable isotope (δ13C and δ15N) and stomach content analyses, from specimens captured during eight scientific trawl surveys carried out from 37°S to 53.3°S, and from 65 to 390 m depth. A total of 1615 specimens were analyzed, from which 795 (49.22 %) that ranged from 15 to 114 cm in total length (TL), contained prey. The pink cusk-eel fed mainly on fish and crustaceans. Among fishes, the most important were the notothenioid Patagonotothen ramsayi and the Argentine hake Merluccius hubbsi. The most important crustaceans consumed were the lobster krill Munida gregaria, isopods (Cirolana spp., Serolidae), stomatopods (Pterygosquilla armata) and gammarid amphipods. Ontogenetic diet shifts were detected with the TL, with an increase consumption of fish and a decrease consumption of crustaceans. Moreover, there were changes in the diet associated with depth and region. The isotopic structure of the food chain showed the classic enrichment with trophic level increase. While the stomach contents analysis in a subregion indicated that crustaceans were the predominant prey, followed by cephalopods and fish, Bayesian mixing models showed differential assimilation to pink cusk-eel muscle, with fish as the main assimilated prey and a relatively minimal inputs of crustaceans and cephalopods. Clear distinctions between the pelagic and benthic baselines were detected, with pink cusk-eel participating in both benthic and pelagic pathways. The pink cusk-eel occupied the role of top predator in the Southwestern Atlantic ecosystem (trophic level ∼4) and the δ15N did not exhibit changes with respect to an analyzed specimen of the year 1962.

Spatial distribution of Munida gregaria (Decapoda, Munididae) larvae in the silled Beagle Channel: Insights from spring and autumn surveys

The squat lobster Munida gregaria is an ecologically relevant species in southern South American waters. Nonetheless, fundamental topics regarding its larval ecology remain poorly studied, especially at the southern limit of its distribution area. Here, we investigated the abundance, size, and spatial distribution of M. gregaria larval stages (zoeae I-V and megalopa) in the Beagle Channel, during spring and autumn, and explored their relationships with variations in bathymetry and seawater physico-chemical properties at both sides of the Mackinlay pass sill. Plankton samples were collected from the inner sector of the channel, a fresh water-influenced and semi-enclosed system, to its mouth towards the Atlantic Ocean during four oceanographic cruises (springs of 2014 and 2015 and autumns of 2016 and 2017). Zoeae occurred throughout the study area in both seasons, with lower densities in autumn, whereas megalopae were detected exclusively in spring. The highest larval abundances and all developmental stages were found in the outer sector, where juveniles and adults also occurred. These spatial patterns were consistently observed across the different sampling dates. Contrary to previous reports, the coexistence of zoeae I-V during autumn would indicate that, at least in the outer sector, larvae that hatch late in the summer are able to reach advanced developmental stages. However, it remains unknown whether they fully develop in subsequent months. Significant associations among larval distribution patterns and environmental variables were detected, especially for late stages, which occurred mainly in the westernmost and shallowest part of the outer sector, characterized by highly stratified waters with the warmest bottom temperatures. All together, these results may reflect the effects of variations in local environmental conditions along the channel, related to bottom topography and degree of freshwater/oceanic influence, on larval cohort dynamics, adult reproduction, or both. Larvae hatched in spring were larger than those hatched in summer/autumn for all zoeal stages. Possible explanations for this finding are discussed. This study contributes to our knowledge of M. gregaria larval ecology, which is essential to understand its complex population dynamics in an environmentally complex geographical area, and to better predict its responses to climate change. • Zoeal stages I-V occurred in both spring and autumn. • Larval abundance and stage structure differed west and east of the Mackinlay sill. • Higher larval abundances and all larval stages occurred in the outer sector. • Advanced stages occurred mainly in shallow and highly stratified waters. • Larvae hatched in spring were larger than those hatched in summer-autumn.

Spatial variations in age-0+ Merluccius hubbsi (Patagonian stock; 45º-47ºS) feeding conditions through fatty acids composition

Fatty acids (FA) play critical roles in trophic interactions in aquatic food webs, transferring from phytoplankton to fish, and being modulated by oceanographic conditions and productivity. FA are a well-established approach for studying fish feeding preferences, and can indicate habitat quality and ecosystem condition. Thus, they provide valuable information in the context of fisheries management. The aim of this research was to determine the FA profiles of age-0 + hake Merluccius hubbsi and their zooplankton prey (Euphausia spp., Munida gregaria, Themisto gaudichaudii), identify FA trophic markers, infer their diet in comparison with stomachs information, and evaluate spatial changes in FA indicators with respect to the austral spring environmental variability in the Patagonian nursery ground (San Jorge Gulf, SJG; 45º-47ºS, 65º30’−67º30’W). We hypothesize that age-0 + hake and zooplankton FA composition relate to frontal structures and chlorophyll-a concentration, revealing diatoms predominance in the SJG spring food web. Major FA in hake and zooplankton were 16:0, 16:1n7, 18:1n9, 20:5n3 and 22:6n3. Age-0 + hake profiles mostly resembled euphausiids FA composition, in agreement with the stomachs analysis. Bacterial (15:0 + 17:0 + 17:1 + 18:1n7) and a mixed signal from both diatoms (16:1n7 + 20:5n3) and dinoflagellates (18:4n3 + 22:6n3) were recorded in the profiles; these suggest the existence of a classical food web in central coastal waters of the gulf and an omnivorous one towards the north and south extremes. Results are useful for a better understanding of the SJG food web and the key role age-0 + hake play in energy transfer, contributing to ongoing M. hubbsi recruitment studies in the region.

Approaching the Ecological Role of the Squat Lobster (Munida gregaria) and the Fuegian Sprat (Sprattus fuegensis) in the Francisco Coloane Marine Area (Magellan Strait, Chile) Using a Pelagic Food Web Model

The structure and functioning of the food web of the Francisco Coloane Marine Area in the Magellan Strait, Chile, was quantified, with an emphasis on identifying the ecological role of the squat lobster (Munida gregaria) and the Fuegian sprat (Sprattus fuegensis). Food web indicators, the trophic level, and centrality indices were estimated using Ecopath with Ecosim. Dynamic simulations were carried out to evaluate the ecosystem impacts of biomass changes in squat lobster and Fuegian sprat. The model calculated a total ecosystem biomass of 71.7 t km-2 and a total primary production of 2450.9 t km-2 year-1. Squat lobster and Fuegian sprat were located in specific trophic levels of 2.3 and 2.7, respectively. Squat lobster reduction produced a decrease in the biomass of red cod (42-56%) and humpback whales (25-28%) and Fuegian sprat reduction a decrease in penguins (15-37%) and seabirds (11-34%). The Francisco Coloane Area is an immature ecosystem with productivity and energy flows values within those reported for productive ecosystems; the role of the squat lobster seems to be related to the structure of the food web, and the role of the Fuegian sprat seems to be related to the functioning of the ecosystem and to the energy transfer to top predators.

Marine sources for biotechnology: Preliminary digestive enzymes assessment of seven decapod species from the southwest Atlantic

Marine natural compounds are required by industries to improve and reduce costs of many biotechnological processes. In this work, specific activity of midgut gland digestive enzymes was measured in seven species of decapods. Alkaline and acid peptidase, lipase and amylase activities were registered in Pleoticus muelleri (Pm), Artemesia longinaris (Al), Paralomis granulosa (Pg), Lithodes santolla (Ls), Munida gregaria (Mg), Neohelice granulata (Ng), and Ovalipes trimaculatus (Ot). The highest activities for all the analyzed digestive enzymes were obtained in Pg, Ls, Mg and Ot, which were used for optimum temperature and pH measurements and to test their stability at different temperatures and pH. In general, optimal enzyme temperatures were between 30 and 50 °C in the four crustaceans. Peptidases and lipases from these species showed in general alkaline optimal pH except for those from Ot which presented high activity at the whole pH range (2–12). Amylase from Ot presented its optimal at pH 6–8 and 30–50 °C. Thermal stability of peptidases was elevated at 30 °C for the four species tested (Pg; Ls; Mg and Ot), lipases were stable mainly at 30–50 °C and amylase was stable at 10 °C, 30 °C and 50 °C during the first 30 min of the assay. In general, stability of the four enzymes from Pg was greater at alkaline pH than at acid. The other species showed stability at all pH for the four enzymes. The range of temperature and pH of the tested enzymes activity are coincident with those used in various biotechnological processes and therefore indicates the potential of these enzymes to be used for industrial procedures. Further, most of the species studied are converted into fishery residues, either by processing or by-catch, so their reuse would also contribute to the sustainability of the activity.

Who let the young-of-the-year (YOY) up? The pelagic habitat as a nursery and feeding ground area for the YOY Argentine hake Merluccius hubbsi Marini, 1933.

The young-of-the-year (YOY) Argentina hake Merluccius hubbsi remained at particular distances off the seabed at pelagic habitat, in a nursery area located in the San Jorge Gulf off south-western Atlantic. Older specimens were daylight distributed near the bottom in the demersal habitat. In this paper the authors show that the pelagic habitat is favourable for YOY hake compared to the surrounding demersal habitat by decreasing the probability of encounter with larger hake protecting the YOY against conspecific predation, and providing a better food supply. From 303 stomachs of pelagic YOY Argentine hake analysed (60-250 mm), 274 (90.43%) contained prey. Pelagic Argentine YOY hake fed almost exclusively on zooplanktonic crustaceans (Euphausia spp. and Themisto gaudichaudii). From 980 demersal specimens (14-82 cm), 572 (58.36%) contained prey, mainly the lobster krill Munida gregaria, followed by other hakes by cannibalism. The intensity of feeding was higher on pelagic layers. The allometric weight-length relationship revealed that the YOY Argentine hake find sufficient food in the pelagic habitat to live and develop, by increasing their relative body thickness. The cannibalism increases from close to zero when the YOY hake are c. 20 m off the seabed, to between 15% (cold season) and 20% (warm season) when they are 10 m off the seabed. These results suggest that the pelagic habitat is a feeding ground for YOY hake, and it is a favourable one compared to the surrounding demersal habitat by protecting the YOY from cannibalism. Pelagic YOY hakes were less abundant and more distant from the bottom during the cold season (14.3 m) than during warm one (11.4 m), probably because of natural mortality and progressive recruitment to demersal habits.

Size-related, seasonal and interdecadal changes in the diet of the Patagonian longfin squid Doryteuthis gahi in the South-western Atlantic

AbstractThe Patagonian longfin squid Doryteuthis gahi has an annual life cycle with two seasonal cohorts (autumn and spring spawners). Earlier studies on the Patagonian shelf found a predominance of Euphausiacea in the D. gahi diet, but no studies to date have investigated differences between feeding spectra of the two cohorts or decadal diet shifts. The present study investigated differences in diet of D. gahi on the Patagonian shelf sampled two decades apart, and differences between seasonal cohorts. Classical stomach content analysis and generalized additive models were used to investigate and model the influence of mantle length, sampling period and spawning cohort on the diet. Results revealed an ontogenetic diet change from ~70% Frequency of Occurrence of Euphausiacea in small squid to more than 60% FO of fish and Cephalopoda at larger sizes. Cannibalism was also frequently observed. Euphausiacea were ingested more frequently and in higher amounts during the austral summer and therefore were consumed more by the autumn spawning cohort, whereas fish was more frequently fed upon during austral winter and also by the spring spawning cohort. Cannibalism was also recorded more in austral winter months but, contrary to feeding on fish, was more prevalent in the autumn spawning cohort. Increased predation of Munida gregaria was observed in 2020 compared with 2001. This study is an important step towards improving the knowledge of D. gahi's two seasonal cohorts, providing data that can be used for future ecosystem modelling.

Decapods Associated with the Southern King Crab (Lithodes santolla) Fishery in Central Patagonia (44° S, Chile)

The southern king crab, Lithodes santolla, is an important fishery resource in the inner seas of Chilean Patagonia. The fishing gear used to catch southern king crab (bait trap) and its operation at different depths over several months provide the opportunity to gather information about relative abundance. The aim of the present study was to analyze the information collected from the catches of southern king crab and its associated fauna in the Magdalena Fjord to study the biodiversity and ecology of scavenging decapod crustaceans. Specifically, the study aimed to determine the bathymetric patterns of abundance by species, to model the abundance by season (winter and spring) and to determine the structuring pattern of scavenging decapods assemblage. Samples were collected between June and November 2019 by deploying traps in four bathymetric strata: 1 = 0–50 m; 2 = 51–100 m; 3 =101–150 m; 4 = 151–200 m. We registered a total of 673 decapod specimens associated with the southern king crab fishery, representing five species: Lithodes santolla (n = 96), Libidoclaea smithii (n = 10), Metacarcinus edwardsii (n = 58), Munida gregaria (n = 507) and Peltarion spinulosum (n = 2). The abundance of decapod species varied by month and bathymetric strata. We found bathymetric patterns for L. santolla abundance, M. gregaria, M. edwardsii, and total species abundance. The most informative model to explain scavenging decapod abundance by generalized linear model (GLM) included species and season. The null model of species co-occurrence analysis revealed that all species associations during the sampled months were random. Our study is the first that provides evidence about patterns of bathymetrical and temporal variation of scavenging decapod abundance and expands the body of knowledge regarding the biodiversity of scavenger decapods in the Magdalena Sound.

Separate Feeding Between the Pelagic Stage of the Squat Lobster Munida gregaria and the Larger Sized Zooplankton Crustacean Groups in the Beagle Channel as Revealed by Stable Isotopes

In southern Patagonia, the Beagle Channel shows very low production during winter but simultaneously sustains very dense aggregations of the pelagic stage of squat lobster (Munida gregaria), a benthic decapod whose pelagic juveniles have the largest body size within the chitinous pelagic community. To assess the coexistence of the mesozooplankton community and the pelagic M. gregaria stage under the harsh feeding winter conditions, we conducted a research cruise at two locations connected to the Beagle Channel, Yendegaia Bay (land terminating-glacier) and Pia Fjord (marine-terminating glacier). Our results showed that the zooplankton communities were similar in these two fjords, that a single pelagic group dominated in terms of biomass (pelagic Munida gregaria), and that differences in vertical distribution existed between most of the principal crustacean zooplankton and pelagic M. gregaria. All groups showed consumption of terrestrially derived organic matter, as revealed by their δ13C values. However, the isotopic composition, trophic positions (TP), and isotopic niche areas of the groups separated pelagic M. gregaria, presenting some of the lowest δ15N and the highest δ13C values, and the narrowest isotopic niche width. Pelagic M. gregaria was dominated by a single body size class along the 0–100 m water column, with no diel changes in vertical distribution, remained mostly in the upper layers (0–50 m), and benefited from the slightly higher phytoplankton concentrations at shallower depths as revealed by their higher δ13C values and low trophic position. In contrast, the other groups, including zoea M. gregaria stages, developed changes in distribution between day and night or remained deeper in the water column. These groups showed higher δ15N values, higher TP, and lower δ13C values, most of which probably fed on a nanoheterotrophs and terrestrial particulate organic matter mixture at deeper layers. Thus, the different vertical distributions, different trophic level food sources, and slightly different organic carbon sources apparently reduced any potential competence for food resources and form part of the feeding strategy that may facilitate the coexistence of the different large pelagic crustaceans under harsh feeding winter conditions in this high latitude austral region.

Fatty acid biomarkers in three species inhabiting a high latitude Patagonian fjord (Yendegaia Fjord, Chile)

The study of fatty acid biomarkers in trophic structures at sub-polar latitudes is fundamental in describing energy fluxes across ecosystems characterized by complex inter-specific interactions. Due to the presence of certain essential fatty acids obtained exclusively from predator–prey interactions, fatty acid biomarkers are widely used to identify trophic interactions. This study analyzed fatty acid compositions in three species inhabiting a relatively pristine Patagonian fjord. This fjord is geographically difficult to access, so there are very little sampling opportunities, biological and oceanographic information. In the three species collected (Ctenodiscus australis (Loven in Lutken 1871) (Echinodermata, Asteroidea, Ctenodiscidae); Munida gregaria (Fabricius 1793) (Arthropoda, Malacostraca, Munididae); Eleginops maclovinus (Cuvier 1830) (Chordata, Actinopterygii, Eleginopsidae)) along this remote area were evaluated their fatty acid trophic markers as a tool to differentiate dietary components and dietary habits. The study reported significant differences in the amount of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA), with the highest concentrations of all fatty acids in M. gregaria. The last suggests that M. gregaria is considered as a good quality food source or biological component that might support the fjord trophic web in the Southern Hemisphere. The results describe diet compositions in sampled species, and differences among species for fatty acid compositions and proportions. This provides an initial basis for future modeling or projecting how benthic ecosystems of fjords and Patagonian channels respond to food intake, particularly in environments associated with glacial systems characterized by a low phytoplankton biomass and greater sensitivity to climate variability.

Bioenergetic traits of three keystone marine species in the food web of a pristine Patagonian fjord

The Patagonian fjords are high-latitude aquatic ecosystems, highly sensitive to climate change and play a key role in the exchange of organic matter and carbon flows between terrestrial and marine environments. The bioenergetic composition of species living in these ecosystems are fundamental to understanding the distribution, seasonal variations, and exchange of organic matter within benthic communities. This study reports on the bioenergetic characteristics (lipids, protein, glucose, and energy content) of three keystone species with different life-style and feeding habits: a benthic sea star (Ctenodiscus australis); squat lobster (Munida gregaria); and a Patagonian notothenioid (Eleginops maclovinus). Samples were obtained from the Yendegaia Fjord (54°40'S - 68°50′W) in Chilean Patagonia. Our results indicate that M. gregaria has higher concentrations of lipids, proteins, glucose, and total energy compared to either E. maclovinus or C. australis. The predominance of lipids in all species is possibly related to physiological characteristics and feeding strategies. Also, may be associated with the availability of food and environmental conditions typical of a fjord ecosystem and the reproductive stage in that they were collected. These results suggest that marine animals inhabiting glacially influenced environments with low temperature and low productivity, requires a convergent physiological strategy characterized by high levels of energy storage (i.e. lipids) for metabolism and key bioenergetic processes such as growth and reproduction.

Distribution, abundance and ecological requirements of the benthic phase of Munida gregaria (Anomura; Munididae) in the Puyuhuapi Fjord (Chilean Patagonia)

The squat lobster Munida gregaria is considered a key species within food webs of sub-Antarctic ecosystems of South America, and represents a fundamental link between detritus and higher-level predators. Although ecological aspects of its lengthy pelagic phase have been well described, those of the benthic stage remain poorly understood, particularly in Chilean Patagonia where information on the presence of benthic phases of M. gregaria has been scarce. The present paper aims to improve our knowledge of this important species, analysing benthic distribution, abundance and ecological requirements of the benthic phase of M. gregaria in the Puyuhuapi and Jacaf fjords in the Aysen Region of Chilean Patagonia. An extensive SCUBA diving survey, carried out between 2014 and 2019, allowed us to explore and document the soft seafloors inside these fjords. These benthic surveys conducted photographic transects between depths of 5 and 20 m to enumerate populations of M. gregaria and to measure sizes of individuals. The study revealed the presence of large aggregations of M. gregaria, with densities up to 4 times higher than previously reported maxima for South America. Munida gregaria appeared to be unable to live at the shallow depths of the brackish surface layer typical of fjords, though paradoxically, its presence on the seabed was linked to river outflow, and probably related to supply of organic matter. Chilean fjords are currently facing a number of challenges, particularly from climate change and other more direct anthropogenic impacts, and the key role of M. gregaria in these fjords should be considered in future monitoring activities. More particularly, the extremely high abundance of M. gregaria in Puyuhuapi Fjord should be considered in any rigorous protection measures planned for the fjord.

Inter-annual variation in the trophic niche of Magellanic penguins Spheniscus magellanicus during the pre-molt period in the Beagle Channel

Inter-annual variations in the diets of seabirds are often a reflection of resource availability, with population dynamics and community structure implications. We investigated the trophic niche of Magellanic penguinsSpheniscus magellanicusduring the pre-molt stage in 6 years (2009 and 2013-2017) at Martillo Island, Beagle Channel, Argentina, using carbon and nitrogen stable isotope analysis of feathers. We found higher values in 2009 compared to the other years for both isotopes and estimated different proportions of prey in the diet of Magellanic penguins throughout the years. In 2009, penguins consumed mainly a mixture of benthic and benthopelagic fish, whereas from 2013 to 2017, the proportion of the pelagic form of squat lobsterMunida gregaria, considered a key species in the Beagle Channel, increased over time and nearly dominated diets in 2017. Our results confirm that Magellanic penguins act as sentinels, reflecting shifts in the marine community of the Beagle Channel via inter-annual variation in their trophic niche and diet composition.

Trophic structure of southern marine ecosystems: a comparative isotopic analysis from the Beagle Channel to the oceanic Burdwood Bank area under a wasp-waist assumption

Understanding the structure and functioning of marine ecosystems has become a critical issue to assess the potential short- and long-term effects of natural and anthropogenic impacts and to determine the knowledge needed to conduct appropriate conservation actions. This goal can be achieved in part by acquiring more detailed food web information and evaluating the processes that shape food web structure and dynamics. Our main objective was to identify large-scale patterns in the organization of pelagic food webs that can be linked to a wasp-waist (WW) structure, proposed for the southwestern South Atlantic Ocean. We evaluated 3 sub-Antarctic marine areas in a regional context: the Beagle Channel (BC), the Atlantic coast of Tierra del Fuego (CA) and the oceanic Burdwood Bank area (BB). We used carbon and nitrogen isotopic information of all functional trophic groups, ranging from primary producers to top predators, and analyzed them through stable isotope-based Bayesian analyses. We found that BC and BB have a more pronounced WWstructure compared to CA. We identified species at mid to low trophic positions that play a key role in the trophodynamics of each marine area (e.g. Fuegian spratSprattus fuegensis, longtail southern codPatagonotothen ramsayiand squat lobsterMunida gregaria) and considered them as the most plausible WW species. The identification of the most influential species within food webs has become a crucial task for conservation purposes in local and regional contexts to maintain ecosystem integrity and the supply of ecosystem services for the southwestern South Atlantic Ocean.

Proximate Composition and Nutritional Quality of the Meat of the Squat Lobster Munida gregaria (Fabricius 1973)

ABSTRACT The squat lobster Munida gregaria has been recognized as a potential resource in several countries. However, data about its composition and nutritional value are scarce. This study provides information about the nutrients and nutritional quality of M. gregaria meat. Meat yield, proximate composition, cholesterol content, and fatty acid (FA) and amino acid (AAs) profiles were analyzed, and nutritional quality indexes were estimated. The average meat yield was 9.93%. The yearly average of the proximate composition of the M. gregaria meat (g/100 g meat) was moisture = 77.6, protein = 13.7, lipids = 3.84, and ash = 2.19. The average annual cholesterol content was 6.60 mg/100 g. The predominant FA (%) was C20:5ω3 (23.6), followed by C18:1ω9c (20.9), C22:6ω3 (18.5), and C16:0 (16.3); the unsaturated fatty acids were 72.8% of the total FA. The main AAs (g/100 g protein) were glutamic acid (15.1), leucine (9.47), and aspartic acid (8.51). Regarding the nutritional quality, the polyunsaturated FA/saturated FA ratio (1.99), ω3/ω6 ratio (8.62), atherogenic index (0.26), thrombotic index (0.56), hypocholesterolemic/hypercholesterolemic ratio (4.07), and polyene index (2.58) showed that M. gregaria meat provides lipids that are beneficial to the human diet. Moreover, M. gregaria meat provides high-quality proteins, which are well balanced in their essential AAs composition.

Are hakes truly opportunistic feeders? A case of prey selection by the Argentine hake Merluccius hubbsi off southwestern Atlantic

Prey selection and feeding strategy of the Argentine hake Merluccius hubbsi were investigated by analyzing the diet and prey availability in the main nursery area of the Patagonian stock (42.4°–46.4 °S, 70–102 m depth). Stomach contents from fish captured using a bottom trawl net, and zooplankton samples collected with a Bongo net, were analyzed. Acoustic data were examined to identify pelagic aggregations and quantify relative prey abundance. The Argentine hake M. hubbsi fed mainly on crustaceans (92.7%IRI), followed by fish (7.1%IRI) and cephalopods (0.2%IRI). Among crustaceans, the diet was dominated by euphausiids (Euphausia spp.), the lobster krill Munida gregaria, and the hyperiid amphipod Themisto gaudichaudii. The most consumed fish was other hake by cannibalism. Prey availability was also numerically dominated by the euphausiids (Euphausia spp.), followed by the hyperiid amphipod T. gaudichaudii and the lobster krill M. gregaria. Ontogenetic dietary changes were detected: consumption of euphausiids and amphipods decreased with predator´s total length, and the consumption of the lobster krill M. gregaria was higher in adult specimens. The Argentine hake M. hubbsi showed positive prey selection for lobster krill M. gregaria. The consumption of Euphausiids decreased with the increasing acoustic abundance of the lobster krill M. gregaria. The cannibalism was denso-independent. The Argentine hake appeared to be opportunistic when the proportion of prey eaten to the proportion present in the environment was compared, but deeper analyses confirmed that zooplankter with increased abundances and higher energy density was the preferred prey.

The opportunistic sense: The diet of Argentine hake Merluccius hubbsi reflects changes in prey availability

Changes in the abundance of some species in the San Matías Gulf (north Patagonia, Argentina) have been observed in recent years; in particular increases in crustaceans populations that could be influencing the trophic relationships and food web structure. The Argentine hake Merluccius hubbsi has been the main demersal resource that supports a fishery since 1971. Given that M. hubbsi is a generalist and opportunistic predator, its diet from the perspective of specific composition and feeding strategy was evaluated. Fourteen species were identified belonging to four zoological groups (3 fishes, 4 molluscs, 6 crustaceans and 1 bryozoan). The most commonly consumed prey was the lobster krill Munida gregaria (index of relative importance -%IRI- 72.19%) followed by the white shrimp Peisos petrunkevitchi (%IRI 19.04%) and M. hubbsi (%IRI 7.95%). Most prey were infrequently consumed and at low abundances, which it is common for a generalist-opportunistic predator. Substantial changes in the diet composition were detected when compared to a previous study, showing a large increase in crustacean occurrence in concordance with the abundance changes observed in the environment. The results from this study highlighted the importance to consider information about population trends and trophic relationships to better understand the dynamics of marine communities under exploitation.