Dr. Urzua-Osorio, Angel

Upwelling oceanographic phenomenon is associated with increased food availability, low seawater temperature and pH. These conditions could significantly affect food quality and, in consequence, the growth of marine species. One of the most important organismal traits is somatic growth, which is highly related to skeletal muscle. In fish, skeletal muscle growth is highly influenced by environmental factors (i.e. temperature and nutrient availability) that showed differences between upwelling and downwelling zones. Nevertheless, there are no available field studies regarding the impact of those conditions on fish muscle physiology. This work aimed to evaluate the muscle fibers size, protein content, gene expression of growth and atrophy-related genes in fish sampled from upwelling and downwelling zones. Seawater and fish food items (seaweeds) samples were collected from upwelling and downwelling zones to determine the habitat's physical-chemical variations and the abundance of biomolecules in seaweed tissue. In addition, white skeletal muscle samples were collected from an intertidal fish to analyze muscular histology, the growth pathways of protein kinase B and the extracellular signal-regulated kinase; and the gene expression of growth- (insulin-like growth factor 1 and myosin heavy-chain) and atrophy-related genes (F-box only protein 32 and muscle RING-finger protein-1). Upwelling zones revealed higher nutrients in seawater and higher protein content in seaweed than samples from downwelling zones. Moreover, fish from upwelling zones presented a greater size of muscle fibers and protein content compared to downwelling fish, associated with lower protein ubiquitination and gene expression of F-box only protein 32. Our data indicate an attenuated use of proteins as energy source in upwelling conditions favoring protein synthesis and muscle growth. This report shed lights of how oceanographic conditions may modulate food quality and fish muscle physiology in an integrated way, with high implications for marine conservation and sustainable fisheries management.

Due to climate change, numerous ice bodies have been lost in the West Antarctic Peninsula (WAP). As a consequence, deglaciation is expected to impact the marine environment and its biota at physiological and ecosystem levels. Nuculana inaequisculpta is a marine bivalve widely distributed around Antarctica that plays an important role for ecosystem functioning. Considering that N. inaequisculpta inhabits coastal areas under effect of glacial melt and retreat, impacts on its nutritional condition are expected due to alterations on its physiology and food availability. To test this hypothesis, biochemical composition (lipids, proteins, and fatty acids) and energy content were measured in individuals of N. inaequisculpta collected in a fjord at different distances to the retreating glacier in the WAP. Oceanographic parameters of the top and bottom-water layers (temperature, salinity, dissolved oxygen, and chlorophyll-a) were measured to investigate how the environment changes along the fjord. Results showed that surface oceanographic parameters displayed a lower temperature and dissolved oxygen, but a higher salinity and chlorophyll-a content at nearest compared to farthest sites to the glacier. In contrast, a lower temperature and chlorophyll-a, and a higher salinity and dissolved oxygen was measured in the bottom-water layer toward the glacier. N. inaequisculpta had a higher amount of lipids (17.42 ± 3.24 vs. 12.16 ± 3.46%), protein (24.34 ± 6.12 vs. 21.05 ± 2.46%) and energy content (50.57 ± 6.97 J vs. 39.14 ± 5.80 J) in the farthest compared to the nearest site to the glacier. No differences were found in total fatty acids among all sites. It seems likely that lower individual fitness related to proximity to the glacier would not be related to nutritional quality of sediment food, but rather to food quantity.

The temporal dynamics of energy reserves are associated with the physiological processes (i.e., reproduction) in marine fishes, in which storage organs play a key role for efficient energy investment. We evaluated the temporal (i.e., seasons) and intra-individual (i.e., organs) dynamics of adult female swordfish (Xiphias gladius) during its feeding period off the Chilean coast in the southeastern Pacific Ocean (SEPO). The biochemical composition (i.e., lipids, proteins, and glucose), energy content and fatty acid profile of the muscle, liver and gonad were evaluated during the austral autumn, winter, and spring. Our results showed principally an intra-individual effect in both the muscle and liver in the autumn and spring. Herein, a trend of higher amounts of lipids and total energy were found in the muscle, while the liver showed greater protein and glucose contents. Consequently, the muscle showed a higher saturated, monounsaturated, and polyunsaturated fatty acid contents than the liver. Although the gonad showed no significant temporal effect in the lipids and proteins contents, an increasing trend of each biochemical constituent, fatty acid group and gonadosomatic index were found from autumn to winter. Consistently, the glucose and total energy content as well Fulton's condition factor were significantly higher in winter. These findings reflect the spatial-temporal physiological dynamic of swordfish based on the storage of energy reserves in different organs during its feeding period. In this way, the products obtained from swordfish could have an added value depending on the season and capture zone, which could benefit the exploitation and regulation measures of this resource under an ecological approach of conservation and sustainability in the SEPO.

Parasites can alter the reproductive performance of their hosts, and to avoid or mitigate the resulting fitness loss, hosts may increase their current reproductive output to compensate for the future loss due to the parasitic infection. Fecundity compensation can be exploited by parasites for their own transmission (exploitation of host compensatory responses by parasites). However, this phenomenon has rarely been reported in second intermediate hosts of trematodes and its mechanisms and consequences largely unexplored. Along the east coast of the South Pacific, the second intermediate host, the mollusk Fissurella crassa, has been observed to display higher muscular foot, greater shell length and weight, and a higher gonadosomatic index when parasitized by metacercariaes of Proctoeces humboldti compared to non-parasitized hosts. In this study, we examined the histology, biochemistry (glucose, lipids, and proteins), and levels of sex hormones (estradiol and progesterone) in both parasitized and non-parasitized female individuals of F. crassa. Our findings revealed that the gonad of parasitized limpets had a higher density of oocytes, but these had a smaller individual area. Additionally, the gonadal tissue of parasitized limpets exhibited lower glucose content but higher lipid content. Notably, the levels of progesterone increased with parasite intensity. These results suggest that F. crassa possesses the ability to compensate for the negative effects of parasites by increasing the number of oocytes through biochemical and hormonal mechanisms. Our study contributes to the limited research on the impact of metacercariae on the reproduction of second intermediate hosts. Furthermore, we discuss how these changes in parasitized limpets could benefit parasite transmission.

Swordfish (Xiphias gladius), a highly migratory fishery resource of great importance in the Southeastern Pacific Ocean (SEPO), is a species with late sexual maturation, high longevity, and a large body size that spawns and reproduces several times throughout its adulthood. In the present study, we hypothesized that the Biochemical-Ecological Composition (BEC) of the gonad (measured as the lipid, protein, glucose, and energy contents) and its bio-stoichiometric ratios (lipid/protein: L/P; lipid/ glucose: L/G) would be influenced by both female body size (lower jaw fork length in cm, LJFL: <180, 180–260, >260) and time (trimesters: 1,2,3; years: 2017, 2019). Our results revealed that in relation to their body size, female swordfish gonads varied significantly in their BEC, but not in their L/P and L/G ratios during their quarterly development within an annual cycle. These variations in the BEC were noticeable in females of medium (180–260) and larger (>260) sizes. Particularly, as the year progressed, females stored significant amounts of energy during their trophic migration, made evident by the increase in the lipid and protein contents of the gonads, which reached maximum levels towards the end of the year, during the second and third trimesters. These high energy reserves can be used for the reproduction during the last trimester of the year (i.e. austral spring–summer), when the warm temperature and high productivity in the SEPO are optimal for the successful development of oocytes. Future studies considering an ecosystem approach should analyze the classes of lipids and types of fatty acids that are involved in the reproduction of this species, and how they are acquired through the consumption of lipid-rich prey, and subsequently metabolized to be used in reproduction and during early ontogeny.

The integrated biochemical condition (IBC) of gonads is closely related to the reproductive success of highly migratory marine species. The IBC of gonads can be influenced not only by size and/or age, but also by environmental conditions. Here, female swordfish, Xiphias gladius, that migrate to temperate regions with a marked seasonality (e.g., the Southeastern Pacific Ocean, SEPO) were compared in relation to the IBCs (lipids, proteins, glucose and, fatty acid profiles) of their gonads; individuals with two body size ranges and distinct degrees of sexual maturity were evaluated, and considered as: small and/or virginal (SV: <170 cm lower jaw fork-length (LJFL), oocyte size (OS) <0.08 mm) vs large and/or maturing females (LM: >190 cm LJFL, OS >0.133 mm). This comparison was conducted in two environmentally contrasting seasons (winter vs spring). Our results showed that the gonadosomatic index (GSI) was significantly higher in LM than SV. Lipid contents varied significantly between seasons and body sizes. The highest lipid concentrations were recorded in the spring in large females. No significant differences were found when comparing the protein and glucose contents of the two evaluated seasons or body size ranges of the studied females. In turn, the fatty acid (FA) profiles of female gonads significantly varied for both seasons and body size ranges. A high content of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs) were recorded in female gonads in the spring. The SFAs C16:0 and C18:0, the MUFA C18:1n9, and the essential PUFA C22:6n3 were the main contributors to the observed differences between spring and winter. These results could be used as indicators of the nutritional condition and health status of swordfish individuals. Hence, the IBC of female swordfish gonads have great potential to aid in estimating survival rates and stock abundances of this species. The integration of this information constitutes an asset in fishery management models with an ecosystem approach.

Decapods have successfully colonized changing coastal habitats throughout the world by adapting their behavior, physiology, and biochemistry. Biochemical reserves, such as lipids and fatty acids (FAs), play fundamental roles in this adaptation process. These energy reserves are key for the development of decapods and their composition mainly depends on the type and quality of food available in their habitats. This study evaluated the lipid content and FA composition of three tissues (hepatopancreas, gills, and muscle) in two widely distributed, semi-terrestrial coastal crab species in Chile, Cyclograpsus cinereus from the upper intertidal and Hemigrapsus crenulatus from estuaries. This evaluation aimed to assess the physiological role of the bioenergetic reserves of these crabs, which tolerate fluctuating environmental conditions. Our results showed that both species had a higher lipid content in the hepatopancreas and a lower lipid content in its gills and muscle. All three of the evaluated tissues in C. cinereus showed high contents of saturated fatty acids (SFAs), and its hepatopancreas displayed the highest contents of monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs). In turn, H. crenulatus had the highest contents of MUFAs and PUFAs in its gills and muscle tissues, including an important amount of eicosapentaenoic acid (EPA). The FA content of C. cinereus may indicate an adaptive physiological response aimed at maintaining its cellular fluid balance during periods of desiccation in the upper intertidal zone. In contrast, the FAs found in H. crenulatus may be linked to the high activity of the sodium‑potassium pump in its gills, in order to maintain osmoregulation in estuaries.

This study focused on gathering available information on Pleuroncodes monodon, a widely distributed crustacean in the Humboldt Current System. Off the Chilean coast, this species presents benthic habits and constitutes the main resource of the industrial crustacean fishery; many studies have been carried out on its life cycle during the last century. In contrast, off the coast of Peru, this species exhibits mainly pelagic habits, with latent information gaps on aspects of its life history and no commercial fishery activities, such as catching, taking or harvesting from the marine environment. P. monodon is an ecologically important species, as a source of energy for its predators, which include invertebrates, birds, marine mammals and fish of commercial interest. Thus, P. monodon seems to play a key role in this ecosystem, mainly as an intermediate link between top predators and the first links in the food chain. In addition, this species presents various adaptation strategies to the changing oceanographic parameters of the areas it inhabits, even tolerating hypoxic environments and great depths in order to avoid being predated. Likewise, from an economic viewpoint, it has a high commercial value as a marine bioresource with great potential in the pharmaceutical and food industries. Considering this, more studies must be carried out to corroborate the biological, ecological, and fishing importance of this species in order to generate efficient management measures and ensure a sustainable fishery.

Marine trophodynamic studies have been developed mainly through the evaluation of stomach contents. However, these studies only reflect the feeding of a few days, showing a "snapshot" of the food consumed for a short time. Currently, new complementary techniques have been developed to evaluate the diet of predators using biochemical markers (fatty acids, FAs) and can, in turn, consider the rate of renewal of these biochemical constituents in body tissues. In the jumbo squid Dosidicus gigas, an important fishery resource in the Humboldt Current System, we identified and analyzed the stomach contents (prey) of D. gigas collected along the coasts of Chile in order to compare the FA profiles of its prey with those of three of its principal tissues and/or organs (digestive gland, gonad and mantle muscle). The analyses of the stomach contents indicate that D. gigas feeds on fish, crustaceans and squids, as previously have been reported. Regarding the FAs, the digestive gland presented the highest concentration and diversity of FAs, followed by the gonad and then the mantle. In turn, when comparing the FAs of the digestive gland of D. gigas with the FA profiles of its preys, the crustacean Pleuroncodes monodon and the fish Lampanyctus sp. presented the closest similarity, especially with a high contribution of essential FAs and PUFAs. Our findings indicate that during the cold season (austral winter), individuals of D. gigas may present an energy optimization strategy, characterized by the intake of prey with a high energy content rich in PUFAs, such as crustaceans and small fishes. This study not only contributes to the understanding of the squid biology and their trophodynamic, but also has important implications to improve fishery management within an ecosystem approach. This is relevant because D. gigas and its prey have suffered heavy exploitation, with a significant reduction in their biomass.

The estuarine crab Hemigrapsus crenulatus has a wide distribution range along the coast of the South Pacific Ocean (from 20 °S to 53 S°). This decapod is abundant in these coastal and estuarine habitats and plays a key ecological role as prey of the snook fish (Eleginops maclovinus) and kelp gull (Larus dominicanus). Its diet consists of detritus, dead fish, and crustaceans, and the macroalgae Ulva sp. In response to contrasting environmental conditions and anthropogenic impacts along the Chilean coast, H. crenulatus may present intraspecific variations in its reproductive traits and changes in the elemental composition of its embryos, directly affecting its biological fitness. Along the Chilean coast, female individuals were collected during late spring 2019 and early summer 2020 (from November 2019 to February 2020) in six areas of Chile (north: Tongoy (30°S); south-central: Lenga (36°S), Tubul (37°S); south austral: Calbuco (41°S), Castro (42°S), Quellón (43°S). The environmental conditions (i.e. sea surface temperature, precipitation and chlorophyll α) present during each sampling event were also recorded. We evaluated the reproductive parameters of females (fecundity, reproductive output (RO)) as well as their body size (carapace width and dry weight), volume, water content, dry weight, elemental composition (carbon, hydrogen, nitrogen: CHN), and finally the energy content of their embryos. Our results indicated that the environmental conditions of the sea water temperature, precipitation (proxy of water salinity) and chlorophyll α (proxy of food availability) have direct effects on the reproductive parameters of females and the characteristics of their embryos. We observed a low fecundity and high RO in Calbuco and Quellón, where precipitation was high (i.e. diluted salinity) and temperatures and productivity was low. For embryo traits, the highest values of volume and water content were observed in female crabs from the estuarine areas (i.e. Tongoy, Lenga, Tubul), values much higher than those found in the internal sea of Chile (i.e. Calbuco, Castro, Quellón). For the elemental composition, we observed high nitrogen levels and a low C:N proportion in embryos from female crabs from Lenga (a nitrogen enriched area). Fluctuating environmental variables among localities proved to modulate intraspecific variations in females and embryos of H. crenulatus, revealing different reproductive strategies, particularly in the quality and energy investment per embryo, which subsequently influenced successful embryogenesis and larval survival.