Pictures
(Click on the thumbnails to view fullsize images.)
This is a picture of the ocean floor at our 7m research
site. The organism covering the majority of the bethos is the brown
alga Dictyota.
This figure is an example of the extent to which
Dictyota can overgrow other reef organisms. Here the green calcified
alga Halimeda opuntia is highly epiphytized by this brown seaweed.
When Dictyota grows on organisms like Halimeda, it slows their growth
rate and has detrimental impacts on its metabolism.
To evaluate the physiology of Dictyota
and gain insights into what is contributing to its prolific growth,
we use underwater physiological equipment like the Diving-PAM (see
next) shown here.
The Diving-PAM is a Pulse Amplitude Modulated
Fluorometer, specifically designed for use underwater. It allows us
to monitor aspects of photosynthesis on marine primary producers where
they naturally occur. It pulses the algae with light and records a
fluorescent response given off by the algae. The fluorescent response
correlates with the condition of the algae, especially related to
photosynthesis.
For more detailed examination of Dictyota's
metabolism, we bring it into the laboratory and run more traditional
photosynthesis measures (photosynthesis versus irradiance curves).
This is a fragment of Dictyota that has
attached using colorless hairs to sand grains, thereby helping secure
this new individual to the bottom. Such mechanisms are a likely means
of Dictyota spreading over vast regions of coral reefs in the Florida
Keys.
In this photo, a laboratory-generated
fragment of Dictyota quickly attached to Halimeda tuna. Disturbance-generated
fragments of Dictyota can strongly adhere to other reef organisms
in less than a day.
One way that fragments of Dictyota are
generated is by water motion. At our research sites, we use plaster-of-Paris
spheres that dissolve more slowly or more quickly depending upon water
motion (especially current speeds), to roughly gauge the current over
the reef.
A second manner by which fragments of
Dictyota is generated is by fish. Some fish species repeatedly take
bites from this chemically-defended seaweed and then spit them out
after realizing that Dictyota tastes bad.
