Diving For Science 2005 Proceedings Of The American

Applications
Diving For Science 2005 Proceedings Of The American Academy Of Underwater Sciences
There are a number of possible applications of fluorescence for marine research. This is still
an emerging technology, so the applications are not mature, but interest is growing and
numerous scientists are beginning to apply fluorescence techniques to their research.
Coral recruitment
Fluorescence is showing promise as a useful tool for research on coral recruitment and
survivorship. The challenge is that newly settled corals are only about 1 millimeter in
diameter and don't look very different from their surroundings. It is almost impossible to
locate juvenile corals in the field until they are at least 5 mm in diameter, except with
painstaking search that is generally impractical. By the time corals can be found easily with
conventional techniques they are between 6 months and a year old. This misses an important
early part of their life history, and makes it difficult to estimate survivorship in natural
conditions.
Fluorescence is an effective way of detecting corals in the 1 to 5 mm diameter range.
Detecting small things is all about contrast, and fluorescence provides an excellent source of
contrast. If a coral fluoresces it will generally appear as a bright green spot against a dark
background. You do your searching at night, and since your eyes are dark-adapted the glow
is easy to spot. We have found corals less than 5 mm in diameter from more than 2 meters
away, and corals as small as 1 mm in diameter in routine sweeps of patches of reef. Figure 5
shows two photographs of the same patch of reef, one a conventional white-light photograph,
the other a fluorescence image. It is clear that this specimen could not have been found with
conventional white light, but was easy to spot with fluorescence. Not all coral recruits
fluoresce, and not everything that fluoresces is a coral, but the technique is proving to be
useful, and additional research and development are ongoing.
Benthic surface mapping
Some forms of marine life can have quite distinctive appearance in fluorescence, with the
result that they can be recognized much more easily in a fluorescence image than in a
conventional white-light image. Quantifying bottom cover by making photo or video
transects is a tried and true technique, but involves painstaking and time-consuming postprocessing,
with frame-by-frame manual interpretation. This is because there is no
automated processing technique that will subdivide the images into categories of interest.
Fluorescence may not be a complete solution, but some preliminary trials show promise. In
one exercise we wrote a set of classification rules for a fluorescence image collected over a
coral reef environment by a one-of-a-kind fluorescence laser line scan imager (Mazel et al.,
2003). In another trial, we took fluorescence photographs of settlement tiles being used in an
invertebrate settlement experiment in New England, for comparison with white-light images
of the same surfaces. It was evident that algae could be recognized and quantified much
more easily with the fluorescence images (Figure 6).
8