Shedding light on coral reefs
New research quantifies light availability on coral reef ecosystems

Date:
September 11, 2020
Source:
Bermuda Institute of Ocean Sciences
Summary:
New research generates the largest characterization of coral reef
spectral data to date. These data are an initial step in building
a quantitative understanding of reef water clarity. With these
data, coral reef scientists can begin to develop models to address
fundamental questions about how reefs function, such as how much
light reaches the various reef zones or how ecological zonation
on reefs might be driven by light absorption.



FULL STORY ========================================================================== Earlier this year, Bermuda Institute of Ocean Sciences (BIOS) senior
scientist and coral reef ecologist Eric Hochberg published a paper in
the journal Coral Reefs that put numbers to a widely accepted concept
in reef science: that materials in seawater (such as phytoplankton,
organic matter, or suspended sediment) can affect how much light, as
well as the wavelength of light, reaches the seafloor. This, in turn,
impacts the ecology of organisms, including corals and algae, that live
on the seafloor and rely on that light for photosynthesis.


========================================================================== "Given that reef ecosystems are driven by photosynthesis, there should
really be a greater interest in light ecology on reefs," Hochberg
said. "In order to do that, you need to have numbers, so this paper is a
start in that it generates the first reasonably large data set on water
clarity on reefs." Along with Stacy Peltier, a former research technician
at BIOS, and Ste'phane Maritorena, a researcher at the Earth Research
Institute at the University of California at Santa Barbara, Hochberg
collected and analyzed 199 water column profiles across the reefs and
deep waters of Hawaii and Bermuda using an instrument called a profiling reflectance radiometer (PRR), or "water rocket." A 2.5 foot-long (0.76
meter) metal tube with fins, the PRR simultaneously measures the spectrum (intensity for each color of the rainbow) of light in the water column
coming down from the surface, as well as the spectrum of light reflected
up from the bottom. The instrument is tethered to a laptop by a data cable
and deployed over the side of a boat, allowing scientists to monitor it
in real-time as it drifts to the bottom, collecting data profiles along
the way at a rate of 15 measurements per second.

With these numbers, Hochberg and other coral reef scientists can begin
to conduct models to address fundamental ecological questions, such as
how much light reaches the various reef zones (fore-reef, reef flat,
and lagoon) or how ecological zonation on reefs might be driven by
light absorption.

For example, while the outer reef area is generally more clear and
allows more blue light to penetrate to deeper depths, lagoon areas are
more turbid (cloudy) and allow more green light to penetrate to deeper
depths. "Different colors of water reach different depths in different
zones, which matters for the communities that live on the bottom,"
Hochberg said. "The pigments that organisms have might change depending
on light availability -- not just how much light is available, but what
color of light is available."

========================================================================== Story Source: Materials provided by
Bermuda_Institute_of_Ocean_Sciences. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Eric J. Hochberg, Stacy A. Peltier, Ste'phane Maritorena. Trends and
variability in spectral diffuse attenuation of coral reef
waters. Coral Reefs, 2020; DOI: 10.1007/s00338-020-01971-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200911110800.htm

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