Boot camp for baby snapper
Scientists at a laboratory outside Whangarei are putting very young snapper through comprehensive physical testing, including a full medical check-up involving smell, hearing, vision, and even anxiety testing.
The programme, at Niwa’s Northland Marine Research Centre at Bream Bay, is aimed at establishing the effects of ocean acidification and warmer sea temperatures on snapper larvae.
“Most work in this area overseas is conducted on small, tropical reef fish. To be able to look at the effects of climate change on such a highly valued commercial, customary and recreational species as snapper in New Zealand is a first for us, and very exciting,” marine ecologist Dr Darren Parsons said.
The experiment is a collaboration between Niwa, Professor Phillip Munday at James Cook University in Australia, and the University of Auckland, under the auspices of the Ministry for Primary Industries’ biodiversity fund, and Coastal Acidification, Rate, Impacts and Management (CARIM), a fouryear project funded by the Ministry for Business, Innovation and Employment, aimed at establishing the scale of acidification and how it is affecting iconic New Zealand species such as paua, mussels and snapper, and coastal ecosystems.
The snapper experiment began last month, when adult broodstock were spawned at Bream Bay and the eggs placed in tanks under four different conditions. The eggs and larvae were used for the experiment because, compared to adult fish, they are the most vulnerable to environmental change.
In one set of tanks the temperature is 18C, which matches normal conditions at the time of spawning. Other tanks are 22C, closer to sea surface temperatures reached this summer.
Carbon dioxide levels are being kept at present oceanic levels in the third set of tanks, and raised in the fourth set to match those expected at the end of this century. Each tank was stocked with thousands of eggs.
During the first 35 days, after the eggs hatched into larvae but before they became juvenile fish, scientists monitored how fast they grew, photographed them, and counted how many died. They also watched for changes in behaviour as the fish regulated the pH in their systems.
“To compensate for rising CO2 levels, fish regulate the levels of bicarbonate and chloride ions in their blood. These changes are thought to influence a neurotrasmitter in their brains, and in some other species this has resulted in a range of different behaviour and sensory effects being displayed,” Dr Parsons said.
“For example, fish will normally swim away if they can smell a predator nearby. But when the water is treated with high CO2, some species have been shown to swim towards it. This could potentially end up causing high mortality in the wild.”
The larvae were tested in a flume tank for “swimmability” with increasing water flows.
“The flume tank is like a treadmill for fish. We ramp up the speed of the treadmill until the fish can’t swim forward any more, to give us an idea of their aerobic performance and how this differs for larvae from the different experimental conditions,” he added.
Vision and hearing tests were also conducted, as well as the response of the fish to a startle stimulus that measured their ability to escape from potential harm.
Dr Parsons said the research was a “first cut” at looking at the direct effects of ocean acidification and increased temperature on fish in New Zealand waters.
“While it will take a lot of evidence before these kinds of issues can be built into management advice, this is a start at figuring out the scale of the issues and how they might unfold over time,” he said.