Coral Reef Science:  Development Highlights

Habib Sekha

Voss,¹ Joshua D.,  Laurie L. Richardson¹. Nutrient enrichment enhances black band disease progression in corals. Coral reefs, Volume 25, Number 4/November, 2006.

¹Department of Biological Sciences, Florida International University, Miami, FL 33199, USA

Communicated by Biology Editor H.R. Lasker

Abstract:

Infectious diseases are recognized as significant contributors to the dramatic loss of corals observed worldwide. However, the causes of increased coral disease prevalence and severity are not well understood. One potential factor is elevated nutrient concentration related to localized anthropogenic activities such as inadequate waste water treatment or terrestrial runoff. In this study the effect of nutrient enrichment on the progression of black band disease (BBD) was investigated using both in situ and laboratory experiments. Experimental increases in localized nutrient availability using commercial time release fertilizer in situ resulted in doubling of BBD progression and coral tissue loss in the common reef framework coral Siderastrea siderea. Laboratory experiments in which artificially infected S. siderea colonies were exposed to increased nitrate concentrations (up to 3 μM) demonstrated similar increases in BBD progression. These findings provide evidence that the impacts of this disease on coral populations are exacerbated by nutrient enrichment and that management to curtail excess nutrient loading may be important for reducing coral cover loss due to BBD.

Comments:

Occurance of coral diseases has often been blamed on pollution such as the discharge of polluted water (e.g. sewers). What this paper demonstrates is that at least the coral Siderastrea siderea did show an increase in progression of black band disease in laboratory experiments when the nutrient concentration was increased.

In one series of experiments a commercial fertilizer was used, and in another series, much more interesting from an aquarist’s perspective, the nitrate was increased up to approximately 0.2 ppm. This experiment did show an increase in progression of the black band disease. Please note that the corals were infected before the onset of the nutrient enrichment experiments started. That is, they did not demonstrate the initiation of the disease due to elevated nutrients, but only that it progressed faster in the presence of increased nitrate.

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S. Reynaud, C. Ferrier-Pagès, R. Mortlock, D. Allemand, R. Fairbanks. Light and temperature effects on Sr/Ca and Mg/Ca ratios in the scleractinian coral Acropora sp. Geophysical Research Abstracts, Vol. 8, 04211, 2006. SRef-ID: 1607-7962/gra/EGU06-A-04211. ^©European Geosciences Union 2006.

Abstract:

This study was designed to investigate the effect of temperature and light on Sr/Ca and Mg/Ca ratios of the skeleton of the coral Acropora sp. For this purpose, coral nubbins were cultivated in aquaria filled with natural seawater and two experiments were conducted. In the first one, 3 light intensities (100, 200 and 400 µmol m^-2s^-1) were set-up, and the temperature was kept constant (27° C). In the second experiment, corals were cultivated at 5 temperatures (21, 23, 25, 27 and 29° C) and the light level (400 µmol photons m^-2s¹) was constant. The calcification rate of the corals was followed during the whole experiment, and the newly-formed skeleton was sampled after two months to perform trace element ratios analysis.

The rates of calcification were enhanced by 5.7 and 1.7 fold following a 8° C increase in temperature or a 4 fold increase in light respectively. These results suggested that an increase in the calcification rate induced by temperature or light was due to different mechanistic. Significant correlations were obtained between Mg/Ca or Sr/Ca and seawater temperature, whereas light only induced a change in the Mg/Ca ratios. We also obtained a good correlation between Mg/Ca or Sr/Ca and calcification rates in the temperature experiment. Thus, the Mg and Sr ions react differently during skeletogenesis suggesting a strong biological control. This provides an indication that Mg and Sr have different pathways from the seawater to the skeleton and that they play different roles in the coral calcification process.

Comments:

The well known nubbins were used to measure Mg/Ca and Sr/Ca for an Acropora sp. exposed to different light or temperature conditions. An increase in calcification rate was observed if the temperature was increased at a constant light intensity or if the light intensity was increased at a constant temperature. The differences in calcification rate for the different conditions were such that the authors concluded that the calcification rate increase was due to different mechanistics. The Mg/Ca ratio increased with a rise in temperature and light intensity whereas the Sr/Ca changed (decreased) only with an increase in temperature and did not change with light intensity. So, Mg and Sr react differently during the formation of the coral’s skeleton and the authors believe that this suggests that they are strongly biologically controlled, also having different pathways with a different role/function in the calcification process.