Posts Tagged 'fish'

Predation in high CO2 waters: prey fish from high-risk environments are less susceptible to ocean acidification

Most studies investigating the effects of anthropogenic environmental stressors do so in conditions that are often optimal for their test subjects, ignoring natural stressors such as competition or predation. As such, the quantitative results from such studies may often underestimate the lethality of certain toxic compounds. A well-known example of this concept is illustrated by the marked increase in the lethality of pesticides when larval amphibians are concurrently exposed to the odor of potential predators. Here, we investigated the interaction between background levels of environmental predation risk (high vs. low) and ocean acidification (ambient vs. elevated CO2) in 2 × 2 design. Wild-caught juvenile damselfish, Pomacentrus amboinensis, were exposed in the laboratory to the different risk and CO2 conditions for 4 days and released onto coral reef patches. Using a well-established field assay, we monitored the in situ behavior and mortality of the damselfish for 2 days. We predicted that juvenile fish exposed to elevated CO2 and high-risk conditions would display more severe behavioral impairments and increased mortality compared to fish exposed to elevated CO2 maintained under low-risk conditions. As expected, elevated CO2 exposure led to impaired antipredator responses and increased mortality in low-risk fish compared to ambient CO2 controls. However, we failed to find an effect of elevated CO2 on the behavior and survival of the high-risk fish. We hypothesized that the results may stem from either a behavioral compensation or a physiological response to high risk. Our results provide insights into the interactive nature of environmental and natural stressors and advance our understanding of the predicted effect of ocean acidification on aquatic ecosystems.

Continue reading ‘Predation in high CO2 waters: prey fish from high-risk environments are less susceptible to ocean acidification’

Long-term exposure to elevated carbon dioxide does not alter activity levels of a coral reef fish in response to predator chemical cues

Levels of dissolved carbon dioxide (CO2) projected to occur in the world’s oceans in the near future have been reported to increase swimming activity and impair predator recognition in coral reef fishes. These behavioral alterations would be expected to have dramatic effects on survival and community dynamics in marine ecosystems in the future. To investigate the universality and replicability of these observations, we used juvenile spiny chromis damselfish (Acanthochromis polyacanthus) to examine the effects of long-term CO2 exposure on routine activity and the behavioral response to the chemical cues of a predator (Cephalopholis urodeta). Commencing at ~3–20 days post-hatch, juvenile damselfish were exposed to present-day CO2 levels (~420 μatm) or to levels forecasted for the year 2100 (~1000 μatm) for 3 months of their development. Thereafter, we assessed routine activity before and after injections of seawater (sham injection, control) or seawater-containing predator chemical cues. There was no effect of CO2 treatment on routine activity levels before or after the injections. All fish decreased their swimming activity following the predator cue injection but not following the sham injection, regardless of CO2 treatment. Our results corroborate findings from a growing number of studies reporting limited or no behavioral responses of fishes to elevated CO2.

Continue reading ‘Long-term exposure to elevated carbon dioxide does not alter activity levels of a coral reef fish in response to predator chemical cues’

Effects of hypoxia and ocean acidification on the upper thermal niche boundaries of coral reef fishes

Rising ocean temperatures are predicted to cause a poleward shift in the distribution of marine fishes occupying the extent of latitudes tolerable within their thermal range boundaries. A prevailing theory suggests that the upper thermal limits of fishes are constrained by hypoxia and ocean acidification. However, some eurythermal fish species do not conform to this theory, and maintain their upper thermal limits in hypoxia. Here we determine if the same is true for stenothermal species. In three coral reef fish species we tested the effect of hypoxia on upper thermal limits, measured as critical thermal maximum (CTmax). In one of these species we also quantified the effect of hypoxia on oxygen supply capacity, measured as aerobic scope (AS). In this species we also tested the effect of elevated CO2 (simulated ocean acidification) on the hypoxia sensitivity of CTmax. We found that CTmax was unaffected by progressive hypoxia down to approximately 35 mmHg, despite a substantial hypoxia-induced reduction in AS. Below approximately 35 mmHg, CTmax declined sharply with water oxygen tension (PwO2). Furthermore, the hypoxia sensitivity of CTmax was unaffected by elevated CO2. Our findings show that moderate hypoxia and ocean acidification do not constrain the upper thermal limits of these tropical, stenothermal fishes.

Continue reading ‘Effects of hypoxia and ocean acidification on the upper thermal niche boundaries of coral reef fishes’

Species interactions drive fish biodiversity loss in a high-CO2 world


  • Elevated CO2 did not alter competitive hierarchies of fish at volcanic vents
  • Enhanced food and reduced predation boosted density of behaviorally dominant fish
  • Population increases of dominant fish suppressed subordinate species
  • Ocean acidification can reduce local fish diversity and homogenize fish communities


Accelerating climate change is eroding the functioning and stability of ecosystems by weakening the interactions among species that stabilize biological communities against change [1]. A key challenge to forecasting the future of ecosystems centers on how to extrapolate results from short-term, single-species studies to community-level responses that are mediated by key mechanisms such as competition, resource availability (bottom-up control), and predation (top-down control) [2]. We used CO2 vents as potential analogs of ocean acidification combined with in situ experiments to test current predictions of fish biodiversity loss and community change due to elevated CO2 [3] and to elucidate the potential mechanisms that drive such change. We show that high risk-taking behavior and competitive strength, combined with resource enrichment and collapse of predator populations, fostered already common species, enabling them to double their populations under acidified conditions. However, the release of these competitive dominants from predator control led to suppression of less common and subordinate competitors that did not benefit from resource enrichment and reduced predation. As a result, local biodiversity was lost and novel fish community compositions were created under elevated CO2. Our study identifies the species interactions most affected by ocean acidification, revealing potential sources of natural selection. We also reveal how diminished predator abundances can have cascading effects on local species diversity, mediated by complex species interactions. Reduced overfishing of predators could therefore act as a key action to stall diversity loss and ecosystem change in a high-CO2 world.

Continue reading ‘Species interactions drive fish biodiversity loss in a high-CO2 world’

CO2-induced ocean acidification does not affect individual or group behaviour in a temperate damselfish

Open ocean surface CO2 levels are projected to reach approximately 800 µatm, and ocean pH to decrease by approximately 0.3 units by the year 2100 due to anthropogenic CO2 emissions and the subsequent process of ocean acidification (OA). When exposed to these CO2/pH values, several fish species display abnormal behaviour in laboratory tests, an effect proposed to be linked to altered neuronal GABA receptor function. Juvenile blacksmith (Chromis punctipinnis) are social fish that regularly experience CO2/pH fluctuations through kelp forest diurnal primary production and upwelling events, so we hypothesized that they might be resilient to OA. Blacksmiths were exposed to control conditions (pH ∼ 7.92; pCO2 ∼ 540 µatm), constant acidification (pH ∼ 7.71; pCO2 ∼ 921 µatm) and oscillating acidification (pH ∼ 7.91, pCO2 ∼ 560 µatm (day), pH ∼ 7.70, pCO2 ∼ 955 µatm (night)), and caught and tested in two seasons of the year when the ocean temperature was different: winter (16.5 ± 0.1°C) and summer (23.1 ± 0.1°C). Neither constant nor oscillating CO2-induced acidification affected blacksmith individual light/dark preference, inter-individual distance in a shoal or the shoal’s response to a novel object, suggesting that blacksmiths are tolerant to projected future OA conditions. However, blacksmiths tested during the winter demonstrated significantly higher dark preference in the individual light/dark preference test, thus confirming season and/or water temperature as relevant factors to consider in behavioural tests.

Continue reading ‘CO2-induced ocean acidification does not affect individual or group behaviour in a temperate damselfish’

The development of contemporary European sea bass larvae (Dicentrarchus labrax) is not affected by projected ocean acidification scenarios

Ocean acidification is a recognized consequence of anthropogenic carbon dioxide (CO2) emission in the atmosphere. Despite its threat to marine ecosystems, little is presently known about the capacity for fish to respond efficiently to this acidification. In adult fish, acid–base regulatory capacities are believed to be relatively competent to respond to hypercapnic conditions. However, fish in early life stage could be particularly sensitive to environmental factors as organs and important physiological functions become progressively operational during this period. In this study, the response of European sea bass (Dicentrarchus labrax) larvae reared under three ocean acidification scenarios, i.e., control (present condition, P CO 2   PCO2  = 590 µatm, pH total = 7.9), low acidification (intermediate IPCC scenario, P CO 2   PCO2  = 980 µatm, pH total = 7.7), and high acidification (most severe IPCC scenario, P CO 2   PCO2  = 1520 µatm, pH total = 7.5) were compared across multiple levels of biological organizations. From 2 to 45 days-post-hatching, the chronic exposure to the different scenarios had limited influence on the survival and growth of the larvae (in the low acidification condition only) and had no apparent effect on the digestive developmental processes. The high acidification condition induced both faster mineralization and reduction in skeletal deformities. Global (microarray) and targeted (qPCR) analysis of transcript levels in whole larvae did not reveal any significant changes in gene expression across tested acidification conditions. Overall, this study suggests that contemporary sea bass larvae are already capable of coping with projected acidification conditions without having to mobilize specific defense mechanisms.

Continue reading ‘The development of contemporary European sea bass larvae (Dicentrarchus labrax) is not affected by projected ocean acidification scenarios’

Warming has a greater effect than elevated CO2 on predator–prey interactions in coral reef fish

Ocean acidification and warming, driven by anthropogenic CO2 emissions, are considered to be among the greatest threats facing marine organisms. While each stressor in isolation has been studied extensively, there has been less focus on their combined effects, which could impact key ecological processes. We tested the independent and combined effects of short-term exposure to elevated CO2 and temperature on the predator–prey interactions of a common pair of coral reef fishes (Pomacentrus wardi and its predator, Pseudochromis fuscus). We found that predator success increased following independent exposure to high temperature and elevated CO2. Overall, high temperature had an overwhelming effect on the escape behaviour of the prey compared with the combined exposure to elevated CO2 and high temperature or the independent effect of elevated CO2. Exposure to high temperatures led to an increase in attack and predation rates. By contrast, we observed little influence of elevated CO2 on the behaviour of the predator, suggesting that the attack behaviour of P. fuscus was robust to this environmental change. This is the first study to address how the kinematics and swimming performance at the basis of predator–prey interactions may change in response to concurrent exposure to elevated CO2 and high temperatures and represents an important step to forecasting the responses of interacting species to climate change.

Continue reading ‘Warming has a greater effect than elevated CO2 on predator–prey interactions in coral reef fish’

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Ocean acidification in the IPCC AR5 WG II

OUP book