Exposure to ultra-violet (UV) radiation is not only a problem for terrestrial organisms; it also affects marine plants and animals.
Life at Lizard is a blog series containing stories about life at the Australian Museum’s Lizard Island Research Station (LIRS).
The three main ways UV radiation damage is mitigated by living organisms are repair, protection (e.g. sunscreen) and avoidance. The latter method generally involves behaviour modification and is one of the facets of a study being undertaken at Lizard Island. The researcher involved in this work is PhD candidate Christoph Braun from the University of Queensland (UQ).
For his study, Christoph is using the Ambon Damselfish (Pomacentrus amboinensis), a species that can see UV radiation. These territorial damselfish also have markings on their face that reflect UV radiation, and their eyes and mucous layer on their skin are transparent to UV radiation, more so than in other species of fish.
During his recent visit to LIRS, Chris has been trying to answer the simple question: Are these fish able to avoid harmful UV radiation by making appropriate behavioural choices?
The first step for Chris was to set up fish tanks with a UV light on top and a divider down the middle with a joining ‘tunnel’ so fish are able to access both areas of the tank. One half of the tank is then covered with a plastic sheet that blocks UV radiation, and the other half is covered with a UV transparent sheet.
Catching suitable fish is the second step and Chris uses a spray mix of clove oil, ethanol and salt water to make this job a little easier underwater (more information about using clove oil to catch fish is in my ‘Goby garages’ blogpost). Once in the lab, fish are allowed two days to acclimate and recover from being caught before testing.
As Chris is testing for UV radiation avoidance behaviour, the fish are given the choice between the UV protected and UV exposed areas of the tank while a video recording is made of their responses. During the trial, the protected and exposed sides are swapped, to prevent a possible bias that a fish might have for a particular side of the tank.
Chris is particularly interested in how much time each fish spends in each side of the tank (exposed to UV radiation or protected) and also at what depth (the top half or the bottom half which is further from the light source).
Chris is collecting behavioural data for a total of 24 fish. At two hours of video per fish, analysing the video footage manually would be very tedious and time-consuming. Luckily, Chris has access to a computer programme which will turn 48 hours of fish tank footage into useable data in a fraction of the time.
If these data show there is a fishy preference for the quarter of the tank exposed to less UV radiation, Chris has support for his hypothesis that the Ambon Damselfish can in fact avoid harmful UV radiation.
As an additional project, Chris is spending some of his time fishing. Using hooks with no barbs, Chris and volunteers fish (under permit) for Coral Trout (Plectropomus leopardus). Once caught, tissue samples are taken from the trout and stored in liquid nitrogen until Chris can take them back to Brisbane.
In the lab at UQ, Chris will isolate the DNA in the samples and quantify how much damage has been caused to the DNA by UV radiation. Interestingly, the type of DNA damage Chris sees in fish (the UV radiation changes the structure of the DNA) is the same kind as occurs in humans.
As a part of this DNA damage project, Christoph needs a record of the UV radiation that reaches the fish. To collect this information, he uses spectrometers that record the quality and quantity of the light.
Some UV readings are taken above water, using a small hand-held light meter, while another spectrometer is used underwater in a custom-made housing, to measure how much UV radiation is present at the depth at which the fish are caught.
Chris will use this information together with the data collected from the tissue samples to find out whether certain fish are more susceptible to UV radiation levels that are present on coral reefs today.
Southern Cross University