Revealing coastal upwelling impact on the muscle growth of an intertidal fish

Effects of chronic high-temperature stress on muscle tissue integrity and metabolism-related genes in Clarias fuscus

The increasing prevalence of high-temperature days due to global warming presents significant challenges for aquatic ecosystems and aquaculture practices. This study investigates the effects of chronic high-temperature stress on Clarias fuscus, a catfish species native to subtropical and tropical regions. The fish were cultured for 90 days under high-temperature conditions (HT, 34 °C) and normal temperature conditions (CT, 26 °C). Histological and transcriptomic analyses were conducted to assess the impact of continuous high-temperature stress on muscle tissue. Histological examination revealed significant damage in the HT group, characterized by irregular tissue arrangement, widened muscle fiber gaps, broken muscle filaments, and cracked nuclei. Transcriptomic analysis identified 975 differentially expressed genes (DEGs) in muscle tissue under high-temperature stress, with 512 genes up-regulated and 463 down-regulated. Notably, heat shock protein (Hsp) family genes, including Hsp40, Hsp70 and Hsp90, were significantly up-regulated under heat stress. Enrichment analysis of these DEGs revealed significant alterations in protein processing, the PPAR signaling pathway, and fatty acid oxidation and metabolism within the endoplasmic reticulum. These findings suggest that C. fuscus experiences substantial tissue damage and a reduced metabolic response under high-temperature stress. This study provides a scientific foundation for future research on the adaptability of fish to temperature fluctuations.

Upwelling effects across different levels of biological organization: Integrating biochemical constituents, physiological performance and muscle transcriptomic response in the intertidal FISH Girella laevifrons (kyphosidae)

The physical-chemical variability of coastal upwelling creates a mosaic of environmental conditions that affect different levels of biological organization. Understanding the mechanisms that organisms use to cope with this variability is critical for addressing the challenges that climate change imposes on coastal ecosystems. This study integrates information on transcriptomic traits, metabolic performance, and the quantity of organic biomolecules in the intertidal fish Girella laevifrons from four locations with varying upwelling intensities. The results show that fish from locations with stronger upwelling intensity have higher levels of glucose, lipids, and proteins in their muscle tissue, in addition to better physiological performance compared to fish from sites with weaker upwelling intensity. Transcriptomic analyses revealed that genes associated with multicellular development and oxygen metabolism are more highly expressed in sites with stronger upwelling intensity, whereas genes related to protein ubiquitination are more expressed in sites with weaker upwelling intensity. In response to the mosaic of upwelling intensities (SAM-SST), and in-situ temperature, nutrients and oxygen variation observed in field, fish showed differential responses, suggesting local adaptations process that maximize ecological success in these areas with different physical-chemical conditions. Future studies should consider the integration of molecular tools to better understand the responses of organisms to environmental variability as upwelling intensities. This will help elucidate the complex interactions between environmental factors and biological responses, providing insights into how marine organisms might adapt to changing conditions. Understanding these mechanisms is essential for predicting the impacts of climate change on coastal ecosystems and for developing effective conservation and management strategies. The integration of transcriptomic data with metabolic and physiological performance measures offers a comprehensive approach to studying the adaptive responses of marine organisms to their dynamic environments considering the future responses in face to predict global change.

Exploring the relationship between upwelling intensity and socio-ecological attributes of marine exploitation areas for benthic resources (MEABRs), along the southern Humboldt Current system

The Eastern Boundary Upwelling Systems (EBUS) sustains some of the most productive marine systems on Earth. Within each of these systems, the upwelling process exhibits spatial and temporal variation resulting in marked differences in upwelling intensity and seasonality along extensive coastlines. The study of this variation is well needed, given the magnitude of the services provided by upwelling, and the impending impacts of global warming on EBUS. The critical link between the physical variability associated with upwelling intensity and its consequences on socio-ecological variables remain severely understudied. This study aimed to address such a gap by exploring the influence of coastal upwelling intensity on socio-ecological attributes of co-management units named Marine Exploitation Areas for Benthic Resources (MEABRs), along one the most productive ecosystems of the world: The southern Humboldt Current system. We evaluated the non-linear influence of upwelling on 1) the harvest of economically important resources, 2) the number of exploited species, 3) number and gender distribution of fishers involved, and 4) fishery activities. Our data indicated that on the one hand the annual harvest of commercial species, and all the exploited resources combined, were consistently higher in MEABRs associated with intermediate to high upwelling intensities. On the other hand, the harvest of kelp, the number of species harvested, and the number of fishers per MEABR increased towards low upwelling intensities, showing signals of fishery diversification. Interestingly, representation of female fishers increased towards high upwelling intensities, suggesting that multiple factors account for the variation in this, and other socio-ecological variables examined. Our study provides first-hand information about harvest levels and the allocation of fishery activities and gender distribution when MEABRs associated with different upwelling intensities are compared. Such information will assist in the identification of ecological and social vulnerabilities in a global warming scenario.

The importance of upwelling conditions as drivers of feeding behavior and thermal tolerance in a prominent intertidal fish

Upwelling, as a large oceanographic phenomenon, increases coastal productivity and influences all levels of biological complexity. Despite decades of research on it, much remains to be understood about the impact of upwelling on the feeding behavior and thermal tolerance of important groups such as fish. Hence, our aim was to investigate how upwelling conditions modify the feeding behavior and thermal tolerance of a prominent intertidal fish, Girella laevifrons. We collected purple mussels (Perumytilus purpuratus) from upwelling (U) and downwelling sites (DU) in central Chile, and used them as prey in feeding trials and measuring the concentration of organic matter and proteins in their tissues. We assessed fish consumption rates and growth in fish collected from the same U and DU sites, feeding on either U or DU mussels. Lastly, we assessed the thermal tolerance of U and DU fish fed with the aforementioned U vs DU mussels. We found that U mussels held higher concentrations of organic matter and proteins compared to their DU counterparts. U mussels were also selected and consumed in larger amounts than DU mussels, although the origin of the fish also influenced consumption rates. Thermal tolerance assays revealed that U fish exhibited higher maximum performance (Max.pf) and critical thermal maxima (Ctmax) and lower sensitivity to temperature changes (as measured by Q10), compared to DU fish. Altogether, these results point to a strong influence of upwelling on the quality of organisms' tissues, indirectly altering key aspects of fish feeding behavior and thermal tolerance. These findings also contribute to understanding the physiological adjustments organisms make in productive upwelling systems, and how they may change in the future with ongoing climate events.

Cross-examining the influence of upwelling and seaweed quality on herbivores' feeding behavior and growth

At the regional scale, upwelling conditions are known to influence ecosystems and communities and their primary and secondary productivity. However, the influence of upwelling on local herbivore-algae interactions is less well understood. We address this question by cross-examining herbivores and seaweeds from sites associated with upwelling and downwelling conditions along the Humboldt Current System. Specifically, we quantified the feeding and benefits attained by the black sea urchin (Tetrapygus niger) and the black sea snail (Tegula atra) while consuming a widespread kelp species (Lessonia spicata). We hypothesized that food quality drives herbivores' preference, consumption, and growth rates, regardless of the origin or "prior" conditions of the consumers. Laboratory trials measured algal consumption rates with (preference) and without a choice, and consumer's growth rates, to assess the influence of food quality (algae from upwelling vs downwelling sites) and the site of origin of the consumers. Our results showed that algal quality was a prevailing factor for both herbivores: they chose, consumed more, and grew faster on high quality (upwelling) algae. By comparison, the origin of the consumer was only significant for sea snails: those coming from an upwelling site, consumed significantly more and grew faster than those from downwelling. The bulk of our results provided strong support to our hypothesis and suggest that the high nutritional quality of algae associated with upwelling centers has a strong influence on consumers' preferences, consumption, and performance (growth). The fact that origin was found to be relevant for one of the herbivores suggests that the conditions in which species grow may dictate some of their efficiency as consumers.

Artificial Light at Night (ALAN) causes size-dependent effects on intertidal fish decision-making

Artificial Light at Night (ALAN) alters cycles of day and night, potentially modifying species' behavior. We assessed whether exposure to ALAN influences decision-making (directional swimming) in an intertidal rockfish (Girella laevisifrons) from the Southeastern Pacific. Using a Y-maze, we examined if exposure to ALAN or natural day/night conditions for one week affected the number of visits and time spent in three Y-maze compartments: dark and lit arms ("safe" and "risky" conditions, respectively) and a neutral "non-decision" area. The results showed that fish maintained in natural day/night conditions visited and spent more time in the dark arm, regardless of size. Instead, fish exposed to ALAN visited and spent more time in the non-decision area and their response was size-dependent. Hence, prior ALAN exposure seemed to disorient or reduce the ability of rock fish to choose dark conditions, deemed the safest for small fish facing predators or other potential threats.

The influence of upwelling on key bivalves from the Humboldt and Iberian current systems

Eastern Boundary Upwelling Systems (EBUS) deliver cold, nutrient-rich waters, influencing coastal biota from the molecular to the ecosystem level. Although local upwelling (U) and downwelling (DU) conditions are often known, their influence on body attributes of relevant species has not been systematically compared within and between EBUS (i.e., below and above regional scales). Hence, we compared the physical-chemical characteristics of U and DU sites in the Humboldt Current system (Chile) and the Iberian Current system (Portugal). We then assessed the influence of U and DU upon eight body attributes in purple mussels (Perumytilus purpuratus) and Mediterranean mussels (Mytilus galloprovincialis), from the Humboldt and Iberian systems, respectively. We hypothesized that bivalves from U sites display better fitness, as measured by body attributes, regardless of their origin (EBUS). As expected, waters from U sites in both systems showed lower temperatures and pH, and higher nitrite concentrations. We also found that mussels from U sites showed better fitness than those in DU sites in 12 out of 16 direct U vs DU comparisons. Shell length, shell volume, organic content of soft-tissues, and mechanical properties of the shell averaged consistently higher in mussels from U sites in both Current systems. In addition, total weight, soft-tissue weight, shell weight and shell thickness were all higher in the U site at the Humboldt system but had less consistent differences at the Iberian system. Altogether, most results supported our working hypothesis and indicate that U conditions support better fitted mussels. The few attributes that did not exhibit the expected U vs DU differences in the Iberian system suggest that local and species-specific differences also play a role on the attributes of these species. These results may also serve as a reference point for further studies addressing the influence of upwelling in these productive, critically important systems.