Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival

Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival

Current Opinion in Environmental Sustainability, Volume 7, April 2014, Pages 82-93
Cecilia D’Angelo, Jörg Wiedenmann

http://doi.org/10.1016/j.cosust.2013.11.029

This article is in the Creative Commons.

This is a really nice review article that touches on many areas that are important to us as reefers.  As a result, it has a GREAT collection of citations that are pretty directly applicable to us and our situation.

A few quotes to whet the appetite – then go read!

We have recently shown that increased nutrient levels might not negatively affect the physiological performance of zooxanthellae as long as all essential nutrients are available at sufficient concentrations to ensure their chemically balanced growth 28.  These results could explain why some reefs and the nutritional status and metabolism of their inhabitants do not always show negative responses to eutrophication [29• ;  30•], at least in the absence of temperature and light stress.

We’ve already been making use of this fact….when you’re done reading this article, check out our post: A Nitrate Dosing Calculator For Better Tank Health (And Better Coral Color!)

Another tidbit from the article:

Most recently, however, we could demonstrate that corals exposed to elevated nitrogen levels were more susceptible to bleaching when exposed to heat and light stress [28]. Interestingly, the detrimental effects observed in these experiments could be attributed to the relative undersupply of phosphorus that resulted from the enhanced demand of the proliferating zooxanthellae population rather than to the elevated nitrogen levels themselves (Figure 1 ;  Figure 2).

 

We’ve been promoting this information (at least here on the blog) for quite a while now.

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!

Fish foraging behavior changes plankton-nutrient relations in laboratory microcosms

Fish foraging behavior changesplankton-nutrient relations in laboratory microcosms

NOVALES-FLAMARIQUE, I., S. GRIESBACH, M. PARENT, A. CATTANEO, AND R. H. PETERS, Limnol. Oceanogr., 38(2), 1993, 290-298

Full article (PDF): http://aslo.net/lo/toc/vol_38/issue_2/0290.pdf

To demonstrate that the effects of higher trophic elements on plankton in laboratory aquaria are not simple top-down or bottom-up processes, we measured phosphorus and chlorophyll concentrations in replicated month-old aquaria undergoing one of five permutations involving three fish species, Daphnia pulex, and algae.

Seems like this could be useful in managing tanks.

Flicker Light Effects on Photosynthesis of Symbiotic Algae in the Reef- Building Coral Acropora digitifera (Cnidaria: Anthozoa: Scleractinia).

Flicker Light Effects on Photosynthesis of Symbiotic Algae in the Reef- Building Coral Acropora digitifera (Cnidaria: Anthozoa: Scleractinia).

Nakamura T, Yamasaki H. Flicker Light Effects on Photosynthesis of Symbiotic Algae in the Reef- Building Coral Acropora digitifera (Cnidaria: Anthozoa: Scleractinia). Pac Sci 62(3): 341-350.

http://hdl.handle.net/10125/22710

Complete article available.

At supersaturating light intensities, photosynthesis was less inhibited by flicker light than by constant light.

Due to the lens effect, light intensity in shallow-water environments sometimes reaches more than 9,000 mmol photons m 2 sec 1, corresponding to 300 to 500% of the surface light intensity (Schubert et al. 2001, in shallow estuary).

See also:

Results of the 1991 United States-Israel Workshop, “Nutrient Limitations in the Symbiotic Association between Zooxanthellae and Reef-building Corals”

Results of the 1991 United States-Israel Workshop, “Nutrient Limitations in the Symbiotic Association between Zooxanthellae and Reef-building Corals”

Jokiel PL, Dubinsky Z, Stambler N. 1994. Results of the 1991 United States-Israel Workshop, “Nutrient Limitations in the Symbiotic Association between Zooxanthellae and Reef-building Corals”. Pac Sci 48(3): 215-218.

http://hdl.handle.net/10125/2229

Micromorphometric technique (Berner and Izhaki 1994) as well as elemental analysis (Muller-Parker et al. 1994a) showed decreasing availability of surplus carbon, giving further evidence of an impaired symbiotic relationship in ammonium-enriched treatments.

The results of Muscatine and Kaplan (1994) remind us that corals may become “nutrient-limited” only under high light conditions that allow extremely high photosynthetic rates.

Further, different species of corals show different responses to the same alterations in nutrient regime (Stambler et al. 1994a).

…the argument is made that under normal conditions in nutrient-poor tropical seas, zooxanthellate corals are successful because they are closed systems with respect to nitrogen. Growth of zooxanthellae under these conditions is not balanced with respect to fixed carbon because of the low rate of nitrogen supply.

As a result, the excess carbon is translocated to the animal host. Increasing the nitrogen supply leads to rapid growth of the zooxanthellae, with consequent reduction of translocated carbon to the host. Eutrophic conditions allow the zooxanthellae to outgrow their hosts and the host loses control over the population of its symbiotic algae. Thus, main- tenance of a balanced coral symbiotic association appears to require low ambient nutrient concentrations.

See also: Ratio of Energy and Nutrient Fluxes Regulates Symbiosis between Zooxanthellae and Corals