Ocean acidification may make fish foolhardy

Rising carbon dioxide may rob fish larvae of their ability to sense predators and survive

Baby fish become confused and reckless in water with high levels of dissolved carbon dioxide, a new study shows. This leads to higher death rates and may mean that rising atmospheric carbon dioxide, which causes ocean acidification, will reduce the number of fish in the ocean.

“It shows we should be concerned with even minor changes in aquatic ecology, because it’s going to have dramatic effects on the survival of fish,” says Grant Brown, a freshwater behavioral ecologist at Concordia University in Montreal who was not involved in the study. “There are very fine-scale, yet extreme critical effects going on.”

Atmospheric carbon dioxide levels are projected to rise over the next century from fossil fuel burning. As carbon dioxide enters the Earth’s atmosphere, some of it is absorbed into oceans. The CO2 dissolves, as it does in carbonated beverages, and lowers the water’s pH. A lower pH is known to hinder the ability of oysters and other marine life to build calcium carbonate shells, but effects on fish are less well-known.

Marine ecologist Philip Munday of James Cook University in Townsville, Australia, and his colleagues showed previously that high levels of dissolved CO2 interfere with the sense of smell of clown fish. The larvae of clown fish and other coral reef fish rely on their sense of smell to stick close to home and avoid predators.

Culture studies of the benthic foraminifera Elphidium williamsoni: Evaluating pH, ∆[CO32−] and inter-individual effects on test Mg/Ca

We cultured the benthic foraminifera, Elphidium williamsoni, in a physicochemically stable, large volume (400 l) recirculating seawater system over a range of pH (7.6, 8.1 and 8.3) for 8 weeks. During this period the foraminifera typically deposited 1–3 new chambers which were analysed by electron probe microanalysis. Intertest Mg/Ca variations are large (± 22%, 1 standard deviation, at ambient pH) and in good agreement with variance reports from other benthic foraminifera species. These variations do not reflect changes in ambient water chemistry but must reflect biological variability between individual foraminifera, e.g. dependent on genotype or phenotype. Variations in test chemistry may reflect variability in the composition of the calcifying fluid used for test construction, variability in the amount of Mg incorporated into the test calcite or variations in the relative proportions of high and low Mg calcites incorporated in each test. Within each of the pH treatments we observed no relationship between amount of calcite deposited in the culture system and test Mg/Ca. Foraminifera test Mg/Ca is a commonly used palaeothermometer. Our study shows that variations in the relative proportions of individual foraminifera of different geochemistry, that make up a sample for chemical analysis, may affect bulk determinations of test chemistry and subsequent estimates of past climate. Foraminifera cultured at low pH produced significantly thinner chamber walls but we observed no relationship between culture pH (or seawater ∆[CO₃²⁻]) and test Mg/Ca. Pore water gradients are unlikely to develop in the culture substrate and E. williamsoni is an epibenthic species so it is doubtful that this observation reflects changes in the ambient chemistry of pore waters. This suggests that a correlation between ambient water ∆[CO₃²⁻] and test Mg/Ca is not ubiquitous in all calcitic foraminifera species. E. williamsoni is an intertidal species and is adapted to living in highly variable physicochemical conditions. Further work is required to ascertain the significance of these results to other benthic foraminifera species.

Using expert judgment to estimate marine ecosystem vulnerability in the California Current

As resource management and conservation efforts move toward multi-sector, ecosystem-based approaches, we need methods for comparing the varying responses of ecosystems to the impacts of human activities in order to prioritize management efforts, allocate limited resources, and understand cumulative effects. Given the number and variety of human activities affecting ecosystems, relatively few empirical studies are adequately comprehensive to inform these decisions. Consequently, management often turns to expert judgment for information. Drawing on methods from decision science, we offer a method for eliciting expert judgment to (1) quantitatively estimate the relative vulnerability of ecosystems to stressors, (2) help prioritize the management of stressors across multiple ecosystems, (3) evaluate how experts give weight to different criteria to characterize vulnerability of ecosystems to anthropogenic stressors, and (4) identify key knowledge gaps. We applied this method to the California Current region in order to evaluate the relative vulnerability of 19 marine ecosystems to 53 stressors associated with human activities, based on surveys from 107 experts. When judging the relative vulnerability of ecosystems to stressors, we found that experts primarily considered two criteria: the ecosystem’s resistance to the stressor and the number of species or trophic levels affected. Four intertidal ecosystems (mudflat, beach, salt marsh, and rocky intertidal) were judged most vulnerable to the suite of human activities evaluated here. The highest vulnerability rankings for coastal ecosystems were invasive species, ocean acidification, sea temperature change, sea level rise, and habitat alteration from coastal engineering, while offshore ecosystems were assessed to be most vulnerable to ocean acidification, demersal destructive fishing, and shipwrecks. These results provide a quantitative, transparent, and repeatable assessment of relative vulnerability across ecosystems to any ongoing or emerging human activity. Combining these results with data on the spatial distribution and intensity of human activities provides a systematic foundation for ecosystem-based management.

Report: Oceans’ deteriorating health nearing ‘irreversible’

A sobering new report warns that oceans face a “fundamental and irreversible ecological transformation” not seen in millions of years as greenhouse gases and climate change already have affected temperature, acidity, sea and oxygen levels, the food chain and possibly major currents that could alter global weather.

The report, in Science magazine, doesn’t break a lot of new ground, but it brings together dozens of studies that collectively paint a dismal picture of deteriorating ocean health.

“This is further evidence we are well on our way to the next great extinction event,” said Ove Hoegh-Guldberg, director of the Global Change Institute at the University of Queensland in Australia and a co-author of the report.

John Bruno, an associate professor of marine sciences at the University of North Carolina at Chapel Hill and the report’s other co-author, isn’t quite as alarmist, but he’s equally concerned.

“We are becoming increasingly certain that the world’s marine ecosystems are reaching tipping points,” Bruno said, adding, “We really have no power or model to foresee” the impact.

Media advisory: Ocean acidification findings for Puget Sound to be announced

WHAT: Learn where Puget Sound waters have particularly low pH values compared to what is normal for ocean waters and what proportion is probably the result of man-made carbon dioxide from the atmosphere. View a buoy and sleek University of Washington-built Seaglider on board the ship that is about to deploy them off the Washington coast. They will be used to monitor ocean water, destined to end up in Puget Sound, for such things as acidification.

Impact of medium-term exposure to CO2 enriched seawater on the physiological functions of the velvet swimming crab Necora puber

Ocean acidification (OA) is predicted to play a major role in shaping species biogeography and marine biodiversity over the next century. We tested the effect of medium-term exposure to OA (pH 8.00, 7.30 and 6.70 for 30 d) on acid–base balance in the decapod crab Necora puber—a species that is known to possess good extracellular buffering ability during short-term exposure to hypercapnic conditions. To determine if crabs undergo physiological trade-offs in order to buffer their haemolymph, we characterised a number of fundamental physiological functions, i.e. metabolic rate, tolerance to heat, carapace and chelae [Ca²⁺] and [Mg²⁺], haemolymph [Ca²⁺] and [Mg²⁺], and immune response in terms of lipid peroxidation. Necora puber was able to buffer changes to extracellular pH over 30 d exposure to hypercapnic water, with no evidence of net shell dissolution, thus demonstrating that HCO₃^– is actively taken up from the surrounding water. In addition, tolerance to heat, carapace mineralization, and aspects of immune response were not affected by hypercapnic conditions. In contrast, whole-animal O₂ uptake significantly decreased with hypercapnia, while significant increases in haemolymph [Ca²⁺] and [Mg²⁺] and chelae [Mg²⁺] were observed with hypercapnia. Our results confirm that most physiological functions in N. puber are resistant to low pH/hypercapnia over a longer period than previously investigated, although such resistance comes at the expenses of metabolic rates, haemolymph chemistry and chelae mineralization.

Post-doctoral research fellow in animal ecophysiology

Faculty of Science and Technology
School of Marine Science and Engineering
Ref: A1797
Salary £30747 pa – Grade 7

You will be required to work with Prof. John I. Spicer and Dr Piero Calosi in collaboration with other members of the Ocean Acidification UK Programme on a NERC-funded project. This is a multidisciplinary research programme which will involve the PDRF working between Plymouth and Aberdeen. The broad aim of the project is that to determine the ecophysiological responses of a number of marine invertebrates exposed to warming and high CO2 at set times.