Joshua is a graduate of the University of Tasmania where he studied Marine Science, focusing on interactions between aquaculture facilities and local environments. Subsequent to his time in Tasmania, he spent several years in the commercial aquaculture industry as a Nursery Technician.
Joshua is employed as a Research Assistant with the CRE Lab’s Mesocosm project, which is examining potential impacts of climate change on coral reef ecosystems. Joshua rotates between the Heron Island Research Station, where he maintains the project’s mini-artificial reef systems, and the Brisbane campus, where analysis of collected samples takes place.
The effects of climate change on coral reefs are well known. We know that as the climate changes, the ocean temperature is rising, and that rising temperature is leading to coral bleaching. We also know that as the carbon dioxide concentration in the atmosphere increases, the ocean is becoming more acidic, and that is reducing coral growth (as more acidic water impairs the growth of skeleton by corals).
Does rising temperature also affect coral growth, and does ocean acidification also affect coral bleaching? Well, rising temperature (beyond a certain limit) has also been irrefutably found to reduce coral growth. But the effects of ocean acidification on coral bleaching are less clear. In some studies, ocean acidification increases coral bleaching. However, in other studies, ocean acidification does not seem to have an impact.
To try to clarify this problem, I performed an experiment at the Hawaii Institute of Marine Biology from November 2014 to January 2015. Collaborating with local researchers (Dr. Ruth Gates, Dr. Ross Cunning and Chris Wall), we exposed colonies of the lace coral, Pocillopora damicornis, to two levels of ocean acidification. One of these levels (7.95 on the pH scale) will be seen in the near future whilst the other level (7.75 on the pH scale) is what the world could see towards the end of the twenty-first century, if we don’t reduce greenhouse gas emissions enough. At first there may not seem to be much between 7.95 and 7.75, however the pH scale is logarithmic (not linear), so a decrease of 0.2 pH units actually amounts to a huge increase in the level of ocean acidification.
After two months of exposure to these two levels, we then divided the corals at each level of ocean acidification into a further two groups: one that would experience no increase in water temperature (remaining at 24°C), and one that would experience an increase of 6°C (to a final temperature of 30°C). An increase of that level is often sufficient to cause coral bleaching. What we wanted to know is, will coral bleaching be worse in the corals that experienced end-of-century ocean acidification, compared to those that experienced less ocean acidification? After one week of temperature exposure, corals were snap frozen, preserving their biology for later analysis in a laboratory.
Using an airbrush of the same type used by artists, we removed the thin layer of tissue from the surface of each coral fragment to collect the single-celled algae that live within the tissue. As photosynthetic organisms, these algae provide the organic molecules that the coral tissue uses for energy. It is the loss of these algal cells from coral tissues that is the cause of the whitening (bleaching) of the coral during high temperatures. Using a microscope, we counted the number of single-celled algae from the tissue of each coral, and then calculated the total number of algal cells per square centimetre of area of coral tissue. This provided a measure of coral bleaching that could be compared between all the corals in our experiment.
In statistical analyses now underway, we are examining whether there is in fact more coral bleaching in those corals exposed to high ocean acidification compared to those that experienced less ocean acidification. This information will help us to plan for the impacts of climate change on coral reefs, and will further help to focus attention on the plight of marine ecosystems in our changing planet.
No better reason could be found for this research than in September 2014, when a coral bleaching event occurred on reefs beside the Hawaii Institute for Marine Biology due to high water temperatures. Scientists and coral reef managers in Hawaii are now planning for a second bleaching event at the same location, anticipated to occur this coming summer in 2015.
Kristen holds a Bachelors of Science (1st class Honours) in marine biology from the University of California, Santa Cruz, where she completed two Honours research theses; one at the University of Western Australia investigating the population genetics, mating systems and hybridization of the Australian seagrass Posidonia australis and the second at Stanford University examining patterns in epibiont species richness and composition as a function of size in Macrocystis pyrifera holdfasts. Upon graduation, Kristen furthered her education as an occupational trainee under Professor Rob Capon at the University of Queensland’s Institute for Molecular Bioscience. Here, she focused on computer applications to analyze and interpret the chemistry of marine invertebrates and algae to discover new natural products for use in pharmaceuticals and agrochemicals. Kristen is a certified American Academy of Underwater Sciences (AAUS) SCUBA diver having dove all over the world with organizations such as Stanford University and the National Oceanic and Atmospheric Administration (NOAA). Kristen is now affiliated with the Global Change Institute as a ‘Catlin Oceans Scholar’ scholarship recipient and joins the Coral Reef Ecosystems Laboratory as a PhD student. Combining her knowledge of phycology and chemistry, she is investigating the abundance, diversity and physiology of algal-coral interactions presently and under future conditions.
Catherine hails from Virginia and completed her BSc in Science of Earth Systems concentrating in Oceanography at Cornell University. Following graduation, she worked for Professor Drew Harvell coordinating her National Science Foundation Research Coordination Network Grant in the Ecology of Infectious Marine Disease. She participated in seagrass wasting disease projects in the San Juan Islands, Washington and coral health and water quality surveys in Puakō, Hawai’i. In 2013, she was also a program assistant for Cornell’s Earth and Environmental Systems Sustainability Semester based in Waimea, Hawai’i Island.
Currently, Catherine is an XL Catlin Oceans Scholar PhD student in the Coral Reef Ecosystems Lab and is fortunate to have been a part of the XL Catlin Seaview Survey global coral reef survey Indo-Pacific campaign in 2014. Following the survey in Timor-Leste, Catherine is focusing her thesis work in the newly independent nation combining XL Catlin and NOAA datasets. As a former NOAA Pacific Islands Fisheries Science Center intern, she is excited to initiate a research partnership between the XL Catlin Seaview Survey and NOAA in an effort to better understand the coral reefs of Timor-Leste. She will be investigating questions on coral reef benthic composition, marine biodiversity of crabs and fishes, and coral health. Hopefully, her work will contribute to in-country marine resource management at this critical point of development in Timor-Leste.
Groner ML, Burge CA, Kim CJS, Rees E, Van Alstyne KL, Yang S, Wyllie-Echeverria S, Harvell CD (2015). Widespread variation in eelgrass wasting disease in the Salish Sea. Diseases of Aquatic Organisms.
Yoshioka RM, Kim CJS, Tracy AM, Most R, Harvell CD (2015). Linking sewage pollution and water quality to spatial patterns of Porites lobata growth anomalies in Puakō, Hawai‘i. Marine Pollution Bulletin.
Groner ML, Burge CA, Couch CS, Kim CJS, Siegmund GF, Singhal S, Smoot SC, Harvell CD, Wyllie-Echeverria S, Jarrell A & JK Gaydos (2014). Diseases of Aquatic Organisms 108: 165-175. Host demography influences the prevalence and severity of seagrass wasting disease. doi: 10.3354/dao02709
Burge CA, Kim CJS, Lyles JM, & CD Harvell (2013). Special Issue Oceans and Humans Health: The Ecology of Marine Opportunists. Microb Ecol 65(4): 869-79. doi:10.1007/s00248-013-0190-7