116 research outputs found
Ocean acidification: linking science to management solutions using the Great Barrier Reef as a case study
No full textAbstract not availableRebecca Albright, Kenneth R.N. Anthony, Mark Baird, Roger Beeden, Maria Byrne, Catherine Collier, Sophie Dove, Katharina Fabricius, Ove Hoegh-Guldberg, Ryan P. Kelly, Janice Lough, Mathieu Mongin, Philip L. Munday, Rachel J. Pears, Bayden D. Russell, Bronte Tilbrook, Eva Aba
Coral suspension feeding on fine particulate matter
No full textHigh concentrations of fine suspended particulate matter (SPM) on nearshore coral reefs are generally assumed to be a stress factor for corals. However, the extent to which SPM serves as a food source for corals has not been quantified. Using ¹⁴C-labelled natural particulate matter, this study investigates the relationship between concentration and suspension feeding on fine SPM by four common species of Scleractinian coral on the Great Barrier Reef (GBR), Australia. In ingestion trials, only one species (Porites cylindrica Dana) conformed to traditional saturation-kinetic models (Michaelis–Menten, Hollings type I) with ingestion rates reaching maximum at low to moderate SPM concentrations (4–8 mg l⁻¹). For the remaining three species (Pocillopora damicornis Linnaeus, Montipora digitata Dana and Acropora millepora Ehrenberg) ingestion rates increased linearly over the full range of SPM concentrations (1–30 mg l⁻¹). All study species assimilated a major proportion of the ingested label, but assimilation efficiency was inversely related to SPM concentration. At low concentrations (1 mg l⁻¹), estimates of assimilation efficiency ranged from 89 to 95% of the ingested SPM, decreasing to 40–50% at the highest concentrations (30 mg SPM l⁻¹). The maximum rate of SPM carbon assimilation can cover less than 5% of basic metabolic costs, which is not significantly different from reported contributions of zooplankton feeding to coral energy budgets. More importantly, SPM feeding at high particle concentrations may cover up to half of the carbon and a third of the nitrogen required for tissue growth
A tank system for studying benthic aquatic organisms at predictable levels of turbidity and sedimentation: case study examining coral growth
No full textA tank system is described for long-term exposure of sessile organisms to well-defined ranges of particle loads on a background of natural flowing seawater. Using low technology and a simple mathematical model, the concentration of suspended particulate matter (SPM) and the rate of sedimentation could be predicted and sustained with high precision. The system and operational procedures were tested in an 8-week experiment investigating the effect of SPM concentrations on the growth rates of two species of symbiotic scleractinian coral (Goniastrea retiformis and Porites cylindrica). To also evaluate the effect of shading by SPM on coral growth, two light levels corre-sponding to 3-4-m depth at the low and high particle concentrations were included in the design. The growth rates of corals in control tanks were not significantly different from those of conspecifics in situ. However, the patterns of growth rates vs. SPM and shading treatments differed between species. The growth rates of G. retiformis generally increased as a function of SPM concentration (range = ~ 1-16 mg L⁻¹), whereas the growth rates of P. cylindrica were unaffected by particle load. The shading effects corresponding to 16 mg SPM L⁻¹ at 3-4-m depth resulted in significantly reduced growth rates in both species. I hypothesize that the different growth patterns displayed by the two species are the results of different abilities to utilize SPM as a food source or different susceptibilities to SPM as a mechanical stress factor. The high level of environmental control and the constancy of SPM treatment levels were reflected in the absence of tank effects on growth rates and provided sufficient statistical power to detect relatively small differences in growth rates between corals from different treatments
Enhanced energy status of corals on coastal, high-turbidity reefs
Get PDFSedimentation and high turbidity have long been considered a major threat to corals, causing world-wide concern for the health of coral reefs in coastal environments. While studies have demonstrated that sediment conditions characteristic of inshore reefs cause stress in corals, the consequences of such conditions for the physiological status of corals require testing in field situations. Here, I compare the size of energy stores (as lipid content), a proxy for physiological condition, of 2 coral species (Turbinaria mesenterina and Acropora valida) between coastal and offshore environments. Corals on coastal reefs contained 4-fold (T. mesenterina) and 2-fold (A. valida) more lipid than conspecifics offshore, despite 1 order of magnitude higher turbidity levels inshore. Results were consistent across 4 sites in each environment. Reproductive investment in A. valida (a seasonal mass spawner) did not vary between environments, suggesting that the larger lipid stores in corals on coastal reefs are mainly somatic energy reserves. These results demonstrate that the environmental conditions on inshore, high-turbidity reefs do not always impact negatively on the physiology of corals. The contrasting lipid levels of T. mesenterina between environments may explain its greater success on coastal reefs
Shifting roles of heterotrophy and autotrophy in coral energetics under varying turbidity
No full textSuspended particulate matter (SPM) strongly alters the trophic environment of photosymbiotic aquatic organisms. At high particles loads, phototrophic energy gains can be diminished due to light absorption by suspended particles, and stress from particle abrasion or deposition on tissues. However, energy gains are enhanced if organisms are able to use SPM as a food source. For photosymbiotic benthic suspension feeders, increases in SPM concentrations may require both phototrophic and heterotrophic acclimation to sustain a positive energy balance. This study provides an experimental analysis of the effects of contrasting light and SPM regimes on the energy budget (scope for growth) of two zooxanthellate corals (Goniastrea retiformis and Porites cylindrica). Using a factorial design in a flow-through tank system, corals were exposed for 2 months to shaded and unshaded conditions (equivalent to 3–4 m depth at 4 and 16 mg dry weight SPM l−1, respectively) and a range of controlled SPM loads with a natural organic content (∼3% w/w). In G. retiformis, rates of particle ingestion were a linear function of SPM concentration within a broad range (1–30 mg dry weight l−1). After 2 months of shading, photosynthetic acclimation was significant in G. retiformis, but did not compensate for the reduced light level, as daily respiration exceeded daily photosynthesis. However, in response to the prolonged shading, G. retiformis more than doubled its rate of particle feeding. At high SPM treatments (16 mg dw l−1), sediment feeding by this species compensated fully for the 35–47% lower phototrophy in the shaded treatment. Due to both photo- and heterotrophic plasticity, G. retiformis gained tissue and skeletal mass at all experimental levels of light and SPM. In contrast, rates of particle intake by P. cylindrica contributed <10% to the energy budget in shaded and <3% in unshaded conditions. Feeding rates of P. cylindrica were half-saturated at ∼3 mg dry weight l−1, and four- to eight-fold lower than those of G. retiformis. Skeletal growth was sustained, but tissue mass and lipid contents declined in shaded and high-SPM treatments, and carbon loss due to shading by SPM was not compensated for by particle feeding. Thus, due to a lack of photo- and heterotrophic plasticity, periods of high turbidity resulted in energy deficiency in P. cylindrica, and high turbidity conditions appeared physiologically unsustainable for this species. This study is the first to show heterotrophic plasticity in a symbiotic coral, and to show that such plasticity can offset stress from high particle loads. It demonstrates that changes in the trophic mode of some coral species are a mechanism for sustaining a positive energy balance in turbid environments, thereby broadening their physiological niche
High-sediment tolerance in the reef coral Turbinaria mesenterina from the inner Great Barrier Reef lagoon (Australia)
No full textSedimentation is an important stressor on coral reefs subjected to run-off, dredging and resuspension events. Reefs with a history of high-sediment loads tend to be dominated by a few tolerant coral species. A key question is whether such species live close to their tolerance thresholds or near their niche optima. Here, we analyse experimentally the sediment tolerance of a spatially dominant coral, Turbinaria mesenterina (Dendrophylliidae), at nearshore reefs in the central Great Barrier Reef lagoon. Testing was conducted in a 5-week tank experiment under manipulated sediment loading and flow conditions. Physiological stress was assessed based on the behaviour of three key response variables: skeletal growth rate, energy reserves (lipid content) and photosynthetic performance. Because sediment effects are likely to vary between flow regimes, sediment and flow responses were tested using a full factorial design. Sediment loads greater than 110 mg cm−2 had no effect on any of the physiological variables, regardless of flow (0.7–24 cm s−1). Turbinaria mesenterina is thus tolerant to sediment loads an order of magnitude higher than most severe sediment conditions in situ. Likely mechanisms for such tolerance are that: (1) colonies covered in sediment (60–120 μm) in low-flow were able to clear themselves rapidly (within 4–5 h); and (2) sediment provides a source of food. These results suggest that intensified sediment regimes on coastal reefs may shift coral communities towards dominance by a few well-adapted species
Designing Climate Mitigation Policy
Get PDFThis paper provides an exhaustive review of critical issues in the design of climate mitigation policy by pulling together key findings and controversies from diverse literatures on mitigation costs, damage valuation, policy instrument choice, technological innovation, and international climate policy. We begin with the broadest issue of how high assessments suggest the near and medium term price on greenhouse gases would need to be, both under cost-effective stabilization of global climate and under net benefit maximization or Pigouvian emissions pricing. The remainder of the paper focuses on the appropriate scope of regulation, issues in policy instrument choice, complementary technology policy, and international policy architectures.
Designing Climate Mitigation Policy
Get PDFThis paper provides an exhaustive review of critical issues in the design of climate mitigation policy by pulling together key findings and controversies from diverse literatures on mitigation costs, damage valuation, policy instrument choice, technological innovation, and international climate policy. We begin with the broadest issue of how high assessments suggest the near and medium term price on greenhouse gases would need to be, both under cost-effective stabilization of global climate and under net benefit maximization or Pigouvian emissions pricing. The remainder of the paper focuses on the appropriate scope of regulation, issues in policy instrument choice, complementary technology policy, and international policy architectures.global warming damages, mitigation cost, climate policy, instrument choice, technology policy
Position of egg within a clutch is linked to size at hatching in a demersal tropical fish
No full textSize variation among propagules is ubiquitous and small initial differences in size can be critical to survival, particularly in taxa where initial survival is variable and strongly size-dependent. Despite this, the sources of size variation among fish at hatching are, rarely investigated. This study examined spatial position within egg clutches as a source of size variation at hatching of the benthic spawning fish Amphiprion melanopus. We quantified within-clutch size variation at hatching and found that newly hatched larvae from the periphery (5 mm from edge) of 2-dimensional clutches were smaller in standard length, cranial depth, eye diameter and body area (7%, 8%, 4% and 11%, respectively) than larvae from the interior positions within clutches. To investigate the source of this variation, sizes of embryos at different locations with clutches were measured within 2 h of fertilisation (8 d before hatching). Newly laid embryos from the clutch periphery were smaller in length and volume than embryos from the clutch interior (> 2% and 4-6%, respectively). These eggs from the periphery also had a 33% lower rate of oxygen consumption than did embryos from the clutch interior, throughout development. The relationships between position within a clutch and egg size, oxygen consumption and larval size imply that size variation in larval fish at hatching is partly generated during early embryogenesis, either from maternal endowment or maternal nest design, and was amplified throughout development. (c) 2005 Elsevier B.V. All rights reserved
Energetic cost of photoinhibition in corals
Get PDFPhotoinhibition may constitute an energetic cost for photosynthetic organisms through damage to the photosynthetic apparatus, or by increased metabolism due to damage avoidance or repair. For several species of scleractinian corals, fluorescence techniques have revealed a significant reduction in photochemical efficiency of symbiotic dinoflagellates within coral tissue in response to excess light absorption. To date, it has been unclear whether or not photoinhibition has a negative impact on energy budgets in corals. We simultaneously quantified the
effect of exposure to excessive light on net rates of
photosynthesis and on fluorescence-derived photochemistry.
We acclimated colonies of the reef-building coral Turbinaria mesenterina to 3 different irradiance regimes in the laboratory. The corals were then exposed to light levels up to 10 times higher than their acclimation irradiance and assayed for rates of photosynthesis and photochemical yields. Results indicated that daily costs of photoinhibition are negligible. Reduced net rates of photosynthesis in the afternoon, compared to the morning, were predominantly due to enhanced afternoon rates of dark respiration. However, photoacclimation to high light levels
reduces daily energy acquisition in the long term, primarily due to decreased chlorophyll concentrations.
Therefore, although changes in the photosynthetic activity of symbiotic dinoflagellates over a diurnal irradiance cycle do not cause a measurable decline in net oxygen evolution for coral colonies, repeated exposure to excessive irradiance can reduce energy acquisition per unit surface area, and hence influence the upper limit of the depth distribution of scleractinian corals
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