The in situ light microenvironment of corals

The in situ light microenvironment of corals

Daniel Wangpraseurt, Lubos Polerecky, Anthony W. D. Larkum, Peter J. Ralph, Daniel A. Nielsen, Mathieu Pernice and Michael Kühl
Limnol. Oceanogr., 59(3), 2014, 917-926 | DOI: 10.4319/lo.2014.59.3.0917

Full article available!

I don’t understand the choice of words “Scalar irradiance”, but themeaning in my words, is the total irradiance from every angle.  Sunlight from “up”, light from reflections off the sand, off the coral’s own skeleton, et al.

The typical light measurement you’ll see on a hobby website using a PAR or lux meter is what this paper would be called a measurement of “downwelling irradiance”.

(Measurements of light in air don’t seem to have so many complications or aspects.)

Light is strongly scattered at the water–tissue interface and within the coral tissue, where photon trapping and redistribution leads to significant enhancement in the local scalar irradiance compared with the incident downwelling irradiance (Ku ̈hl et al. 1995; Wangpraseurt et al. 2012a).

Additionally, reflective, fluorescent, or both host pigments are synthesized by many corals, which further alters the intensity and spectral quality of light due to, for example, intense scattering and red-shifted emission (Salih et al. 2000).

Finally, photons that pass through the tissue are backscattered by the aragonite skeleton, further enhancing tissue scalar irradiance and thus photon availability for zooxanthellae photosynthesis (Enriquez et al. 2005; Marcelino et al. 2013).

Spectral scalar irradiance at the upper surfaces of faviid corals (E0) differed markedly from the incident downwelling irradiance (Ed; Fig. 3). Depending on the wavelength in the PAR region, the E0 : Ed ratio varied between 0.8 and 2.4, with the most pronounced enhance- ment at wavelengths 500–640 nm and . 680 nm (Fig. 3a–c).

[Ed:  500-640 nm is green of plant and human-color-vision “fame”, and 680nm is far-red like the light emitted from chlorophyll.]

it will be useful to compare differences between coenosarc and polyp tissue because they differ in total light exposure and spectral quality (Figs. 3, 4; Wangpraseurt et al. 2012a) and can exhibit different patterns of photoacclimation (Ralph et al. 2002).

There’s much more in there too!

They don’t go into this angle, but I think either all of, or a significant portion of, this “scalar light” other than the incident downwelling is actually “waste light”from the coral “blowing off” excess photons during photo-saturation.

Makes sense as green light isn’t well-absorbed and red light is low-function in the photosynthesis cycle.

Quoting http://plantphys.info/plant_physiology/light.shtml:

“Light beyond 700nm has insufficient quantum yeild to drive photosynthesis.”

680nm may as well be 700nm as far as this goes….”mission accomplished” in modern parlance.

The photons have had their “kick” removed in the red cases, or they’ve been made ultra-reflective in the green cases.

Seemingly contradictory to the above  (and also mentioned at that link) is the Emerson effect, where chlorophyll can use 680nm + 700nm light to significantly boost photosynthesis.

Very interesting!

Spectrometer

 

This is my Project STAR spectrometer.  It was very inexpensive.

img_3218
The Project STAR spectrometer. Clockwise from the top-left, the long, curved feature is the housing for the graduated scale; next to it is the small light-intake port; at the bottom-edge is the whitish diffraction grating which is just above, or in front of, the eyepiece.

I  use it for examining the color of different lights inside and outside.  (Don’t look directly at the sun through this device – or anything else!)

It works by taking in light via the small opening at the upper-right.

The light bounces off the diffraction grating at the bottom of the photo.

It then spreads out over the graduated scale, which is inside the curved feature at the top of the photo.

I view the scale through the eyepiece that’s at the bottom of the photo.

I don’t get a histogram showing relative wavelength intensity, but it’s really easy to see what wavelengths are strong or weak, or which ones are missing.

I love having this!

 

 

 

 

spectrometer_output
View through the eyepiece of a Project STAR spectrometer. The light is from a 48″ Phillips 6,500K T12 lamp.
spectrometer_light_intakes
The Project STAR spectrometer. Clockwise from the top-left, the long, curved feature is the housing for the graduated scale; next to it is the small light-intake port; at the bottom-edge is the whitish diffraction grating which is just above, or in front of, the eyepiece.
spectrometer_intake_port
The Project STAR spectrometer. Clockwise from the top-left, the long, curved feature is the housing for the graduated scale; next to it is the small light-intake port; at the bottom-edge is the whitish diffraction grating which is just above, or in front of, the eyepiece.
spectrometer_backlight_port
The Project STAR spectrometer. Clockwise from the top-left, the long, curved feature is the housing for the graduated scale; next to it is the small light-intake port; at the bottom-edge is the whitish diffraction grating which is just above, or in front of, the eyepiece.
spectrometer_refguide
The Project STAR spectrometer. Clockwise from the top-left, the long, curved feature is the housing for the graduated scale; next to it is the small light-intake port; at the bottom-edge is the whitish diffraction grating which is just above, or in front of, the eyepiece.