Browsing by Author "Aldana, Marcela"

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    Cross-examining the influence of upwelling and seaweed quality on herbivores' feeding behavior and growth
    (2024) Sepulveda, Felipe; Quijon, Pedro A.; Quintanilla-Ahumada, Diego; Vargas, Juan; Aldana, Marcela; Fernandez, Melissa; Varas, Oscar; Zapata, Javier; Pulgar, Jose; Duarte, Cristian
    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.
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    Impact of wave exposure on seasonal morphological and reproductive responses of the intertidal limpet Fissurella crassa (Mollusca: Archaegastropoda)
    (2012) Pulgar, Jose; Alvarez, Marcos; Delgadillo, Alejandro; Herrera, Ines; Benitez, Samanta; Morales, Juan Pablo; Molina, Pilar; Aldana, Marcela; Pulgar, Victor Manuel
    Intertidal organisms have long been considered an ideal system to quantify how physical variations determine differential energy allocations in specimens inhabiting environmental gradients such as exposure to wave action. In habitats with differential intertidal wave exposure (sheltered, Sh; and exposed, E) seasonal gonadal and foot weight variations and their associations with exposure and food availability (algae abundance) were determined in the keyhole limpet Fissurella crassa. Gonadal weight is used as a measure of reproduction allocation whereas foot weight is an indirect indicator of energy allocation to survival. RNA:DNA ratio in limpets obtained from Sh and E habitats during the two different seasons was used as an indicator of biosynthetic capability. Our results indicate that algae abundance in E sites was higher in summer and lower in winter compared to Sh sites. In E sites the muscular foot weight of limpet was higher in summer in contrast to Sh sites where F. crassa muscular foot weight of limpet was higher in winter. Gonadal weight in Sh sites was higher in summer and remained constant in winter; whereas in E sites gonadal weight was lower in summer and higher in winter. RNA:DNA ratios indicate that regardless of intertidal wave exposure, F. crassa showed higher biosynthetic capability in summer. Energetic allocation in animals that inhabit sheltered intertidal habitats would support constant allocation towards reproduction. In contrast, animals that inhabit exposed habitats may favour seasonally reproduction allocation at expense of survival.
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    Individual variation in heat tolerance and metabolism in marine Antarctic organisms
    (2024) Varas, Oscar; Molina, Andres N.; Garcia-Huidobro, M. Roberto; Aldana, Marcela; Rezende, Enrico L.; Carter, Mauricio J.; Galban-Malagon, Cristobal; Pulgar, Jose M.
    Climate change is one of the main concerns to Antarctic biodiversity. Since temperature plays a crucial role in various biological traits, it is key to understand how warming may affect organisms specialized to live in the cold habitats. Although heat tolerance of several polar species is known, little emphasis has been given to individual variation and its relationship with other biological traits such as metabolic performance. In this study, we investigated the association between thermal sensitivity in metabolism (Q10) and heat tolerance (z) in six Antarctic marine organisms, including two fish species (Harpagifer antarcticus and Notothenia coriiceps), three crustaceans (Bovallia gigantea, Glyptonotus antarcticus, and Paraceradocus miersi), and one mollusk (Trophon nucelliformis). For this, we measured routine metabolic rates (RMR, mg O2/h) followed by heat tolerance measurements to reconstruct dose-response curves employing sublethal assays or thermal-collapse time (TCT) curves. Analyses reveal a negative relationship between the intercept and the slope of the temperature tolerance curves (CTmax and z values, respectively) against Q10, but only when T. nucelliformis was included in the generalized linear model. Therefore Q10 may be a good predictor of heat tolerance, but it is not true for chordate or arthropod species studied. Additionally, CTmax and z values exhibited a positive relationship consistent with previous studies. This study represents the first example of temperature tolerance curves quantified on an individual basis, and the analyses provide some evidence that thermal sensitivity in metabolism and heat tolerance are correlated. In future studies, it will be crucial to determine whether this relationship is robust and how it may impact the response of different lineages to accelerated warming.
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    Upper thermal limits and risk of mortality of coastal Antarctic ectotherms
    (2023) Carter, Mauricio J.; Garcia-Huidobro, M. Roberto; Aldana, Marcela; Rezende, Enrico L.; Bozinovic, Francisco; Galban-Malagon, Cristobal; Pulgar, Jose M.
    Antarctic marine animals face one of the most extreme thermal environments, characterized by a stable and narrow range of low seawater temperatures. At the same time, the Antarctic marine ecosystems are threatened by accelerated global warming. Determining the upper thermal limits (CTmax) is crucial to project the persistence and distribution areas of the Antarctic marine species. Using thermal death time curves (TDT), we estimated CTmax at different temporal scales from 1 minute to daily and seasonal, the predict vulnerability to the current thermal variation and two potential heatwave scenarios. Our results revealed that CTmax at 1 min are far from the temperature present in the marine intertidal area where our study species, showing Echinoderm species higher CTmax than the Chordata and Arthropods species. Simulations indicated that seasonal thermal variation from the intertidal zone contributed to basal mortality, which increased after considering moderate scenarios of heatwaves (+2 degrees C) in the Shetland Archipelago intertidal zone. Our finding highlighted the relevance of including exposure time explicitly on the CTmax estimates, which deliver closer and more realistic parameters according to the species that may be experiencing in the field.
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    Upwelling affects food availability, impacting the morphological and molecular conditions of the herviborous limpet Fissurella crassa (Mollusca: Archeogastropoda)
    (2013) Pulgar, Jose; Aldana, Marcela; Alvarez, Marco; Garcia-Huidobro, Roberto; Molina, Pilar; Pablo Morales, Juan; Pulgar, Victor Manuel
    Oceanographical processes, such as upwelling, induce variations in nutrient availability in marine ecosystems, and evidence indicates that nutrient input can strongly influence the physiological activities, structure, and dynamics of marine communities. Intertidal organisms have long been considered ideal study units in which to quantify the relationship of physical variations and differential energy allocations in specimens that undergo environmental variations, such as observed with nutrient availability. In habitats with differential nutrient input (upwelling versus non-upwelling), both food availability (algae abundance) and seasonal gonadal and foot weight variations were determined in the keyhole limpet Fissurella crassa. Gonadal weight is used as a measure of reproduction allocation whereas foot weight is an indirect indicator of energy allocation towards survival. RNA: DNA ratio in limpets was used as an indicator of biosynthetic capability. Our results indicate that, in general, algae abundance, muscular foot weight, and gonadal weight were higher in upwelling sites during all seasons studied. The same result was found for RNA: DNA ratios. Energetic allocation in animals that inhabit intertidal upwelling habitats supported a constant allocation towards reproduction and soft tissues. In contrast, animals that inhabit non-upwelling habitats showed important energetic restrictions associated with higher water temperature and lower food availability. Our results clearly show that in the keyhole limpet F. crassa food availability is a more important determinant of an individual's condition than a physical variation such as environment temperature.