Effects of ocean warming on the larval development of coral reef fishes
McLeod, Ian Michael (2014) Effects of ocean warming on the larval development of coral reef fishes. PhD thesis, James Cook University.
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Abstract
There is an urgent need to better understand how organisms respond to changing temperatures as evidence for rapid climate warming accumulates. Climate change models predict that tropical ocean temperatures will increase by up to 4°C this century and affect the plankton communities that are the basis of food webs in most marine ecosystems. Most coral reef fishes have a bipartite life cycle with larvae that develop in the pelagic environment. Sensitivity to elevated temperatures may be magnified during the larval stage, which is the key stage for mortality, dispersal and connectivity. Previous field and experimental studies have shown that larval coral reef fishes typically exhibit increased growth rates and shorter pelagic larval durations (PLDs) with increasing temperatures within their natural temperature range. Based on this knowledge, it has been predicted that enhanced growth associated with increasing temperatures will lead to faster metamorphosis and less time in the dangerous pelagic environment. However, previous field studies have generally excluded populations from the warmest latitudes, have infrequently tested the impacts of elevated temperatures experimentally, and have not investigated the potential climate-related interactions between temperature, food availability and digestion, which may have negative effects on larval growth rates and development.
Latitudinal and temporal gradients in ocean temperature may be useful for predicting the likely response of marine species to climate warming. The ranges of coral reef fishes extend into the warmest oceanic waters on the planet, but the comparative life-history traits across their full latitudinal range are unknown. To answer this critical knowledge gap, I examined the potential effects of a temperature gradient on some key early life-history traits of two coral reef fishes, the damselfish Pomacentrus moluccensis and the wrasse Halichoeres melanurus, among 8 sites spanning the southern tropics from northern Papua New Guinea to the southern Great Barrier Reef (Chapter 2). Recently settled juveniles were collected and their otolith microstructure was analysed to estimate PLD, average daily growth and size at settlement. Latitudinal comparisons revealed a non-linear relationship between seasurface temperature (SST), and these early life history traits. Pelagic larval durations declined with increasing temperature up to 28-29°C, above which they stabilised or increased. Larval growth increased with increasing temperature to 28-29°C before stabilising or decreasing. Size at settlement tended to be highest at mid-latitudes, but overall declined with increasing temperature above 28.5°C in both species. These results indicate that the thermal optima for growth and development is reached or surpassed at low latitudes such that populations at these latitudes may be particularly vulnerable to global warming.
Likely impacts of long-term changes are often inferred from spatial gradients in temperature or short-term temperature fluctuations. However, the effects of climate change may only be apparent on decadal time scales, and there are few studies that extend over such long periods. In Chapter 3, I examined the influence of temperature and other associated environmental variables on key early life history traits of the coral reef damselfish, Pomacentrus moluccensis based on ten cohorts of newly settled fish collected over 13 years from around Lizard Island (Great Barrier Reef, Australia). Multiple regression techniques were used to measure the strength of the association between these traits and developmental temperature, rain, wind speed and solar radiation. Pelagic larval durations generally declined and growth rates generally increased with increasing temperatures to ~28°C, above which PLD tended to increase and growth rates tended to decrease. This pattern mirrored the existing latitudinal spatial patterns in these parameters (Chapter 2). This study confirmed that ~28°C is likely to be a thermal optimum, and significant warming above this level will detrimentally impact on this species. In addition, other environmental factors associated with climate change including rainfall, wind speed and solar radiation can have significant effects on larval development and should be considered in predictions of climate change effects on larval fish.
Both temperature and food supply can influence the development, growth, and metabolism of marine fishes, particularly during larval stages. However, little is known about the relative importance and potential interacting effects of ocean warming and changes to food supply on the performance of larval fishes. In Chapter 4, I tested this by raising larvae of the coral reef anemonefish, Amphiprion percula, in an orthogonal experiment comprising three temperatures (current day, +1.5°C and +3°C) and three feeding schedules. Overall, larvae grew more slowly and took longer to settle at higher temperatures and less frequent feeding, with a highly significant interaction between these factors. Fish from the lower feeding regimes had a lower body condition and decreased survivorship to metamorphosis. Routine oxygen consumption rates (ṀO₂(routine)) were a third higher for larvae raised at +3°C than those raised at current temperatures. The elevated ṀO₂(routine), and therefore greater energy use at higher temperatures may leave less energy available for growth and development, resulting in the longer time to metamorphosis.
Finally, in Chapter 5, I examined food processing, digestion, and growth of larval A. percula at current-day and at an increased temperature (+3°C). Larvae exhibited rapid, temperature-independent growth in the 24 h following satiation feeding. ṀO₂(routine) and peak ṀO₂ during digestion were 55 ± 16% and 28 ± 11% higher at 31.5°C. Elevated temperature had no significant effect on the energy used to digest and assimilate a meal (0.53 ± 0.05 J), digestion duration (6.3 ± 0.3 h), or the percent of total meal energy used for digestion (11.7 ± 1%). These results suggest that even if fish larvae can secure the food necessary to satisfy higher routine metabolism in a warmer ocean, they may not be able to process food at the necessary speed to maintain current-day growth rates.
Overall, this thesis shows that, contrary to some optimistic suggestions, climate warming is likely to have negative impacts on larval coral reef fishes. Impacts are likely to be most severe for low latitude populations living in the naturally warmest temperatures, which appear to be already living close to their thermal optima. Since routine metabolic rate increases with increasing temperature, individuals must consume more food to maintain the same level of growth at higher temperatures. However, the planktonic communities that are food for many coral reef fish are predicted to become more variable or decline with climate change, and even if food is plentiful larvae may not be able to process it at the necessary speed to maintain current-day growth rates. Elevated temperatures and reduced food supplies are therefore likely to lead to slower larval growth and protracted development in the pelagic environment, with effects on larval survival and dispersal, and population connectivity and persistence.
| Item ID: | 39244 |
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| Item Type: | Thesis (PhD) |
| Keywords: | coral reef fishes; coral reef; fishes; GBR; global warming; Great Barrier Reef; larvae; ocean warming; ocean; Papua New Guinea; Queensland; temperature |
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| Additional Information: | Publications arising from this thesis are available from the Related URLs field. The publications are: McLeod, Ian M., Rummer, Jodie L., Clark, Timothy D., Jones, Geoffrey P., McCormick, Mark I., Wenger, Amelia S., and Munday, Philip L. (2013) Climate change and the performance of larval coral reef fishes: the interaction between temperature and food availability. Conservation Physiology, 1 (1). pp. 1-12. McLeod, I.M., McCormick, M.I., Munday, P.L., Clark, T.D., Wenger, A.S., Brooker, R.M., Takahashi, M., and Jones, G.P. (2015) Latitudinal variation in larval development of coral reef fishes: implications of a warming ocean. Marine Ecology Progress Series, 521. pp. 129-141. McLeod, I.M., Parsons, D.M., Morrison, M.A., Van Dijken, S.G., and Taylor, R.B. (2014) Mussel reefs on soft sediments: a severely reduced but important habitat for macroinvertebrates and fishes in New Zealand. New Zealand Journal of Marine and Freshwater Research, 48 (1). pp. 48-59. Wenger, Amelia S., McCormick, Mark I., Endo, Geoff G.K., McLeod, Ian M., Kroom, Frederieke J., and Jones, Geoffrey P. (2014) Suspended sediment prolongs larval development in a coral reef fish. Journal of Experimental Biology, 217. pp. 1122-1128. Brooker, R.M., Munday, P.L., Mcleod, I.M., and Jones, G.P. (2013) Habitat preferences of a corallivorous reef fish: predation risk versus food quality. Coral Reefs, 32 (3). pp. 613-622. Wenger, A.S., McCormick, M.I., McLeod, I.M., and Jones, G.P. (2013) Suspended sediment alters predator–prey interactions between two coral reef fishes. Coral Reefs, 32 (2). pp. 369-374. McLeod, Ian M., Parsons, Darren M., Morrison, Mark A., Le Port, Agnès, and Taylor, Richard B. (2012) Factors affecting the recovery of soft-sediment mussel reefs in the Firth of Thames, New Zealand. Marine and Freshwater Research, 63 (1). pp. 78-83. |
| Date Deposited: | 25 Jun 2015 02:55 |
| FoR Codes: | 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 33% 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 33% 06 BIOLOGICAL SCIENCES > 0699 Other Biological Sciences > 069902 Global Change Biology @ 34% |
| SEO Codes: | 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 33% 96 ENVIRONMENT > 9603 Climate and Climate Change > 960310 Global Effects of Climate Change and Variability (excl. Australia, New Zealand, Antarctica and the South Pacific) @ 33% 96 ENVIRONMENT > 9699 Other Environment > 969902 Marine Oceanic Processes (excl. Climate Related) @ 34% |
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