One of the consequences of the increase of CO2 in the atmosphere is the acidification of oceans, which has already increased since the industrial revolution, and is projected to continue in the future. Considerable research effort has been placed on understanding the effects of ocean acidification (OA) on marine fauna. Some of the detrimental effects of a decrease in ocean pH are related to the damage of the protective shells of many invertebrates, and to the loss of predator recognition in reef fishes. However, the effects of OA on the susceptibility of predation of marine larval organisms remain uninvestigated. Given the high vulnerability of larval developmental stages in marine food webs, more research must be performed on the predation susceptibility of marine larvae under projected oceanic acidification conditions to better apprehend the upcoming effects of climate change. I propose exploring the predation rates upon two economically and ecologically important animal groups: bivalve larvae (i.e. mangrove oysters, Crassostrea gasar) and tuna larvae (i.e. blackfin tuna, Thunnus atlanticus) under predicted levels of ocean acidification. First, I will obtain adult mangrove oysters and will hold them in sea water. I will induce spawning and will artificially fertilize the eggs. 11 h after fertilization, larvae will be placed at equal densities in 1 of 3 pH treatments for one day: 8.069 (ocean pH), 7.949 (2050 pH projections), 7.824 (2100 pH projections), similar to previous work. One day is enough to notice significant differences in survival between acidic conditions, beyond which mortality is high in all treatments. I will also obtain small box jellyfish (i.e. Cubozoa) that will serve as predators of oyster larvae. They will be held under the same 3 separate pH treatments as oysters. During the conditioning day, jellyfish will be fed twice a day an even mix of acidic- and controlled-treatment oyster larvae to avoid habituation bias during the experimental trials. After one day, survival rates of oyster larvae will be measured and they will be placed in a test cup with a given number of jellyfish for 1 h. After the experiment, the survival rates of oyster larvae will be measured again. The experimental treatments will follow a factorial design: 3 oyster larvae conditioning treatments x 3 jellyfish conditioning treatments x 3 test tank pH levels, for a total of 27 treatments with a minimum of 10 replicates each. This experiment will be completed in one month at the Smithsonian Tropical Research Institute (STRI) by Dr. Rachel Collin and myself. STRI owns 16 30-gallon tanks specifically equipped for ocean acidification experiments. A similar experiment will be performed with blackfin tuna larvae caught at sea the next year for a month. As most studies on the effect of OA on marine fishes have been performed on reef fishes, using a pelagic fish species will provide insight into the effects of climate change in open ocean ecosystems. Larvae will be held in the laboratory under the 3 same pH treatments as the oyster larvae for 5 days. This conditioning time is common in studies of the effect of OA on fishes, beyond which no further behavioural change is observed. The number of individuals consumed by cannibalism, common in tuna species, will be recorded. Any significant change in the predation susceptibility of larvae could have drastic effects on marine food web recruitments; effects that could cascade down to humans through an unsustainable fishing industry, since bivalves and tunas sustain a variety of economically important species. Depending on the outcome of this first experiment and external funding, other related studies could be performed. Other predator or bivalve and tuna species could be used. Finally, I could also start experiments on rearing bivalves and tunas under OA projections through successive developmental stages. By doing so, I could perform similar behavioural experiments exploring the impact of development under more acidic conditions (i.e. misshaped, more porous shells in bivalves or otoliths in tunas) on juvenile and/or adult behaviour. For instance, I could perform experiments on the mating behaviour of bivalves and tunas that have been raised under OA projections as mating behaviour is also one of my fields of expertise.
Chuard, Pierre J.C., Grant E. Brown, James W.A. Grant
2016 Behavioural Processes
2- Local predation risk shapes spatial and foraging neophobia patterns in Trinidadian guppies
Elvidge, Chris K., Pierre J.C. Chuard, Grant E. Brown
2016 Current Zoology