The effects of ocean acidification on habitat associations of coral reef fishes

Devine, Brynn Michelle (2011) The effects of ocean acidification on habitat associations of coral reef fishes. Masters (Research) thesis, James Cook University.

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Abstract

The amount of carbon dioxide dissolved in the oceans is steadily rising due to a 40% increase in atmospheric CO₂ since the industrial revolution, leading to significant changes in water chemistry. Recent studies show that larval reef fish exposed to near future concentrations of CO₂ experience impaired ability to discriminate between olfactory cues and exhibit changes in behaviour that increase post-settlement mortality. Reef fishes at all life history stages rely on olfactory cues for critical behaviours including feeding, reproduction, predator avoidance, and the establishment and maintenance of habitat associations. However, it is unknown if olfactory impairment due to elevated CO₂ observed in larval fish will affect critical ecological processes, such as habitat selection at settlement, and if sensory disruption will also occur in adults. This thesis examines the effects that CO₂ concentrations predicted to occur in the ocean this century (550-950ppm) have on habitat associations of coral reef fishes. Fishes tested in each study were selected to assess behavioural responses to high-CO₂ conditions at both larval and adult stages and across multiple reef fish taxa, using species with varying degrees of habitat specialisation and habitat use. The chapters comprising this thesis address the following questions: 1) does olfactory impairment alter habitat selections and settlement behaviour of larval reef fishes when all sensory cues are available?; 2) does elevated CO₂ cause sensory impairment in adult fish, and if so how might olfactory-mediated processes such as homing behaviour be affected?; and 3) does elevated CO₂ affect habitat preferences of habitat specialist species?

As larvae of many reef fish species settle to benthic substrates overnight and during new moon phases, when low light aids in predator avoidance, olfaction is potentially the key sensory system employed during the settlement process. The effect of elevated CO₂ on larval behaviour and habitat preferences was tested in three species of damselfishes with different habitat preferences. Although exposure to elevated CO₂ affected the ability of larvae to discriminate between common reef microhabitat odours (hard coral, soft coral, coral rubble), this olfactory impairment had no effect on the habitats selected at settlement when all sensory cues were available. However, the settlement behaviour of larvae following CO₂ exposure was significantly altered. While control larvae exhibited typical peak settlement around the new moon, larvae exposed to 850ppm CO₂ displayed highest settlement rates around the full moon and lowest settlement around new moon phases. Such a pronounced shift in settlement timing could have significant consequences for the success of settling larvae.

Following selection of preferred habitats at settlement, some reef fishes often depend on olfactory cues for recognition of selected habitats in addition to foraging and reproductive behaviours. Cardinalfishes nocturnally forage throughout the reef, returning each morning to the same daytime home resting site with the aid of olfactory cues associated with the home site. Adult five-lined cardinalfish, Cheilodipterus quinquelineatus, exposed to elevated CO₂ exhibited impaired ability to distinguish between odours of home- versus foreign-site conspecifics in pair-wise choice experiments. In a displacement experiment, fish from all CO₂ treatments exhibited a 22-31% reduction in homing success compared with control fish when released at 200m from home resting sites. While CO₂ exposed cardinalfish released directly back onto home sites exhibited similar persistence rates to control subjects, behaviour at home sites was affected, with CO₂ exposed fish exhibiting increased activity levels and venturing further from shelter. This study demonstrates that disruption of sensory mechanisms in fishes due to elevated CO₂ extends to critical adult behaviours. Coral-dwelling gobies are some of the most habitat-specialist fish species on coral reefs, spending their entire benthic life within the branches of corals. Respiration of the coral host causes nocturnal increases in CO₂ concentrations among the coral branches, possibly enabling gobies to be more tolerant to changes in ocean chemistry than other fishes. Pair-wise olfactory tests demonstrated that exposure to elevated CO₂ impaired the ability of Paragobiodon xanthosomus to discriminate between odour cues of their sole host coral (Seriatopora hystrix) and a non-preferred coral (Pocillopora damicornis). A habitat choice experiment conducted in the field revealed alterations in habitat preferences following CO₂ exposure. All control Gobiodon histrio individuals vacated dead coral habitat and successfully located new live colonies of Acropora nasuta (preferred host coral) within 24 hrs, however gobies exposed to elevated CO₂ remained on dead coral habitats and associated with both preferred (A. nasuta) and non-preferred (A. tenuis) habitats in approximately equal frequency. These results suggest that rising CO₂ could affect the fitness and survival of habitat specialist fish species by impairing their ability to select favourable habitat.

This thesis demonstrates sensory disruptions due to elevated CO₂ are present in both larval and adult reef fishes, with potential alteration of habitat associations observed in multiple species groups. While fishes may be able to compensate for olfactory impairment through use of alternative sensory mechanisms, behavioural alterations observed throughout this project suggest possible interference of critical neural pathways necessary for accurate interpretation of environmental cues. This research indicates that rising CO₂ has the capacity to affect fitness of reef fishes through changes in habitat utilization, with potentially far-reaching consequences for population dynamics and community structure.

Item ID: 29786
Item Type: Thesis (Masters (Research))
Keywords: climate change; coral reef fishes; acclimation; metabolism; ocean acidification
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2. Devine, B.M., Munday, P.L., and Jones, G.P. (2012) Rising CO2 concentrations affect settlement behaviour of larval damselfishes. Coral Reefs, 31 (1). pp. 229-238.

Chapter 3. Devine, Brynn M., Munday, Philip L., and Jones, Geoffrey P. (2012) Homing ability of adult cardinalfish is affected by elevated carbon dioxide. Oecologia, 168 (1). pp. 269-276.

Chapter 4. Devine, Brynn M., and Munday, Philip L. (2013) Habitat preferences of coral-associated fishes are altered by short-term exposure to elevated CO₂. Marine Biology, 160 (8). pp. 1955-1962.

Date Deposited: 14 Oct 2013 05:58
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 33%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 33%
06 BIOLOGICAL SCIENCES > 0699 Other Biological Sciences > 069902 Global Change Biology @ 34%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960399 Climate and Climate Change not elsewhere classified @ 50%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 50%
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