Posts Tagged 'performance'

Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming

Ocean acidification and warming (OA-W) result mainly from the absorption of carbon dioxide and heat by the oceans, altering its physical and chemical properties and affecting carbonate secretion by marine calcifiers such as gastropods. These processes are ongoing, and the projections of their aggravation are not encouraging. This work assesses the concomitant effect of the predicted pH decrease and temperature rise on early life stages of the neogastropod Tritia reticulata (L.), a common scavenger of high ecological importance on coastal ecosystems of the NE Atlantic. Veligers were exposed for 14 days to 12 OA-W experimental scenarios generated by a factorial design of three pH levels (targeting 8.1, 7.8 and 7.5) at four temperatures (16, 18, 20 and 22 °C). Results reveal effects of both pH and temperature (T °C) on larval development, growth, shell integrity and survival, individually or interactively at different exposure times. All endpoints were initially driven by pH, with impaired development and high mortalities being recorded in the first week, constrained by the most acidic scenarios (pHtarget 7.5). Development was also significantly driven by T °C, and its acceleration with warming was observed for the remaining exposure time. Still, by the end of this 2-weeks trial, larval performance and survival were highly affected by the interaction between pH and T °C: growth under warming was evident but only for T °C ≤ 20 °C and carbonate saturation (pHtarget ≥ 7.8). In fact, carbonate undersaturation rendered critical larval mortality (100%) at 22 °C, and the occurrence of extremely vulnerable, unshelled specimens in all other tested temperatures. As recruitment cohorts are the foundation for future populations, our results point towards the extreme vulnerability of this species in case tested scenarios become effective that, according to the IPCC, are projected for the northern hemisphere, where this species is ubiquitous, by the end of the century. Increased veliger mortality associated with reduced growth rates, shell dissolution and loss under OA-W projected scenarios will reduce larval performance, jeopardizing T. reticulata subsistence.

Continue reading ‘Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming’

Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)

Species interactions are crucial for the persistence of ecosystems. Within vegetated habitats, early life stages of plants and algae must survive factors such as grazing to recover from disturbances. However, grazing impacts on early stages, especially under the context of a rapidly changing climate, are largely unknown. Here we examine interaction strengths between juvenile giant kelp (Macrocystis pyrifera) and four common grazers under hypoxia and ocean acidification using short-term laboratory experiments and field data of grazer abundances to estimate population-level grazing impacts. We found that grazing is a significant source of mortality for juvenile kelp and, using field abundances, estimate grazers can remove on average 15.4% and a maximum of 73.9% of juveniles per m2 per day. Short-term exposure to low oxygen, not acidification, weakened interaction strengths across the four species and decreased estimated population-level impacts of grazing threefold, from 15.4% to 4.0% of juvenile kelp removed, on average, per m2 per day. This study highlights potentially high juvenile kelp mortality from grazing. We also show that the effects of hypoxia are stronger than the effects of acidification in weakening these grazing interactions over short timescales, with possible future consequences for the persistence of giant kelp and energy flow through these highly productive food webs.

Continue reading ‘Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)’

Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

Continue reading ‘Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc’

Characterization of marine teleost ionocytes in the gill, skin, and inner ear epithelia and their implications for ocean acidification

Ionocytes are specialized epithelial cells that excrete or absorb ions across an epithelium to regulate ionic, osmotic and acid-base levels in internal fluids. These ionocytes perform a wide range of functions (e.g. osmoregulation, pH regulation, and calcification) across various organs (e.g. gill, skin, inner ear). As atmospheric CO2 levels rise and oceanic pH levels fall, teleosts may increase their investment on ionocytes to survive in future ocean conditions. But generally speaking, the gill, skin, and inner ear ionocytes within marine teleost are not well characterized. This dissertation contains research spanning five southern Californian teleosts: the Blacksmith Chromis punctipinnis, the Yellowfin Tuna Thunnus albacares, the White Seabass Atractoscion nobilis, the Pacific Mackerel Scomber japonicus, and the Splitnose Rockfish Sebastes diploproa. In Chapter II, I investigated the individual and group behavioral responses of the Blacksmith, a temperate damselfish, after exposure to CO2-induced low-pH conditions. In Chapter III, I describe a novel technique used to quantify skin ionocytes in larval fishes. In Chapter IV, I applied the Chapter III’s technique to document developmental patterns in the skin and gill ionocytes of larval Yellowfin Tuna. In Chapter V, I investigated larval White Seabass response to hypercapnia by monitoring oxygen consumption rate and quantifying ionocyte abundance and relative ionocyte area across development. In Chapter VI, I characterized two types of inner ear ionocytes responsible for otolith calcification in the Pacific Mackerel. In Chapter VII, I investigated whether future CO2 /pH conditions would affect the gill and inner ear ionocytes of Splitnose Rockfish. Altogether, this work across the multiple teleosts demonstrates that ionocytes 1) have the plasticity to respond to external pH stress, 2) are sufficient to maintain internal homeostasis despite significant differences in CO2/pH levels, and 3) differ greatly in protein, morphology, and function depending on the tissue in question.

Continue reading ‘Characterization of marine teleost ionocytes in the gill, skin, and inner ear epithelia and their implications for ocean acidification’

Resistance of seagrass habitats to ocean acidification via altered interactions in a tri-trophic chain

Despite the wide knowledge about prevalent effects of ocean acidification on single species, the consequences on species interactions that may promote or prevent habitat shifts are still poorly understood. Using natural CO2 vents, we investigated changes in a key tri-trophic chain embedded within all its natural complexity in seagrass systems. We found that seagrass habitats remain stable at vents despite the changes in their tri-trophic components. Under high pCO2, the feeding of a key herbivore (sea urchin) on a less palatable seagrass and its associated epiphytes decreased, whereas the feeding on higher-palatable green algae increased. We also observed a doubled density of a predatory wrasse under acidified conditions. Bottom-up CO2 effects interact with top-down control by predators to maintain the abundance of sea urchin populations under ambient and acidified conditions. The weakened urchin herbivory on a seagrass that was subjected to an intense fish herbivory at vents compensates the overall herbivory pressure on the habitat-forming seagrass. Overall plasticity of the studied system components may contribute to prevent habitat loss and to stabilize the system under acidified conditions. Thus, preserving the network of species interactions in seagrass ecosystems may help to minimize the impacts of ocean acidification in near-future oceans.

Continue reading ‘Resistance of seagrass habitats to ocean acidification via altered interactions in a tri-trophic chain’

Ocean acidification: fish physiology and behavior

Increased atmospheric carbon dioxide (CO2) has led to increased levels of dissolved CO2 in the Earth’s oceans. This has generally decreased the pH of, or “acidified,” ocean water. Decreased pH, along with other chemical changes ultimately caused by an increase in dissolved CO2, could have direct effects on the physiology and behavior of fishes. (“Physiology” is the study of how an organism works; an organism’s physiology refers to the biological systems that allow it to function and respond to its environment.) Scientists have dedicated a lot of time and effort to studying the potential effects of OA on fish physiology and behavior. This publication will summarize the current state of our understanding on the topic, with special emphasis on Florida fishes. It will also address current challenges in understanding the real-world effects of a complex global process using data largely collected on isolated fish in laboratory experiments.

Continue reading ‘Ocean acidification: fish physiology and behavior’

The importance of environmental exposure history in forecasting Dungeness crab megalopae occurrence using J-SCOPE, a high-resolution model for the US Pacific Northwest

The Dungeness crab (Metacarcinus magister) fishery is one of the highest value fisheries in the US Pacific Northwest, but its catch size fluctuates widely across years. Although the underlying causes of this wide variability are not well understood, the abundance of M. magister megalopae has been linked to recruitment into the adult fishery 4 years later. These pelagic megalopae are exposed to a range of ocean conditions during their dispersal period, which may drive their occurrence patterns. Environmental exposure history has been found to be important for some pelagic organisms, so we hypothesized that inclusion of recent environmental exposure history would improve our ability to predict inter-annual variability in M. magister megalopae occurrence patterns compared to using “in situ” conditions alone. We combined 8 years of local observations of M. magister megalopae and regional simulations of ocean conditions to model megalopae occurrence using a generalized linear model (GLM) framework. The modeled ocean conditions were extracted from JISAO’s Seasonal Coastal Ocean Prediction of the Ecosystem (J-SCOPE), a high-resolution coupled physical-biogeochemical model. The analysis included variables from J-SCOPE identified in the literature as important for larval crab occurrence: temperature, salinity, dissolved oxygen concentration, nitrate concentration, phytoplankton concentration, pH, aragonite, and calcite saturation state. GLMs were developed with either in situ ocean conditions or environmental exposure histories generated using particle tracking experiments. We found that inclusion of exposure history improved the ability of the GLMs to predict megalopae occurrence 98% of the time. Of the six swimming behaviors used to simulate megalopae dispersal, five behaviors generated GLMs with superior fits to the observations, so a biological ensemble of these models was constructed. When the biological ensemble was used for forecasting, the model showed skill in predicting megalopae occurrence (AUC = 0.94). Our results highlight the importance of including exposure history in larval occurrence modeling and help provide a method for predicting pelagic megalopae occurrence. This work is a step toward developing a forecast product to support management of the fishery.

Continue reading ‘The importance of environmental exposure history in forecasting Dungeness crab megalopae occurrence using J-SCOPE, a high-resolution model for the US Pacific Northwest’


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Ocean acidification in the IPCC AR5 WG II

OUP book