Rozan, T.F., Taillefert, M., Trouwborst, R.E., Glazer, B.T., Ma, S.F., Herszage, J., Valdes, L.M., Price, K.S. and G.W. Luther. 2002. Iron-sulfur- phosphorous cycling in the sediments of a shallow coastal bay: Implications for sediment nutrient release and benthic macroalgal blooms. Limnology and Oceanography 47(5): 1346-1354.
This is a rather interesting paper, even though the study was conducted along the Delaware coast and the sediments may not carbonate-based. The study investigated the seasonal changes in iron (Fe), sulfur (S) and phosphorous (P) levels in the first 4 cm (~1.5 inches) of sediment in a coastal embayment with residence time of 100 days. It was found that redox conditions in the sediments greatly affected the levels of these three elements in the sediments, pore waters and overlying water. In the summer months the sediments became reducing (anoxic), resulting in release of P into the surface waters. These anoxic conditions are due to the fact that the bays are considered eutrophic due to nutrient run-off and phytoplankton increases in the summer with increased light and temperatures. This results in an increase in the decay of organic matter in the sediment and hence, lower oxygen levels. This resulted in blooms of macroalgae throughout the bay. In the fall the sediments became oxic
again with an increase in redox, and a decrease in soluble P. The reason for this release of P was linked to an increased production of iron sulfides (both FeS and FeS2) and a decrease in iron (III) oxides. In the fall and winter, iron sulfide production is decreased and iron (III) oxides increased. It was felt that perhaps iron (III) oxides acted as a barrier to diffusive P flux. Most of the reactive P came from that fraction of iron that was ascorbic acid soluble (ASC-Fe). The associated production of H2S in the summer, not only promoted the dissolution of solid iron (III) oxides but also the removal of soluble Fe (II). Both of these actions enhanced soluble phosphate cycling into the sediments and the overlying water.
It was also found that the pH of the sediments decreased to 6.5 in the summer months. This resulted in the greater production of H2S, which promoted the dissolution of solid iron (III) oxides, and the removal of soluble Fe (II), both of which enhance phosphate recycling in the sediments and overlying water.
As far as I know, only a handful of authors have even mentioned the importance of measuring redox levels in sediments when it comes to sand beds in home aquariums (e.g. Sam Gamble and Bob Goemans). Although the presence of iron sulfide and oxides of iron in carbonate-dominated sediments may not be that great (?) it nevertheless raises some tempting comparisons to home aquariums. Certainly it brings attention to the importance of avoiding anoxic conditions in sediments, with its corresponding drop in redox. Perhaps this is why some aquarists report algal blooms after several years of sand bed usage or why some report algal problems with plenum systems after a year or so? These systems may have developed greater reducing environments (anoxic), resulting in the dissolution of P rich compounds, which have previously been sequestered in the sediments. Furthermore, using iron rich supplements may contribute to a pool of iron sulfides accumulating in these anoxic areas over time, again
eventually resulting in an increase in soluble P release to pore and surface waters.
Anthony, K.R.N., Connolly, S.R. and B.L. Willis. 2002. Comparative analysis of energy allocation to tissue and skeletal growth in corals. Limnology and Oceanography 47(5): 1417-1429.
Most studies on coral growth look primarily at linear increases in the skeleton and these rates are then used to judge the effects of environmental stressors on coral growth as an indication of health. However, very little work has been done on how tissue growth reacts to changes to environmental factors, and how this might relate to an indication of coral health. In this paper the goal was to develop a mathematical growth model to estimate how much energy is allocated for coral tissue growth and how much for skeletal growth, and then compare this to experimental growth data gained from exposing hemispherical ( Goniastrea retiformis ) and branching colonies ( Porites cylindrica ) to changes in environmental factors such as light (shaded and unshaded) and physical stressors such as sedimentation (filtered and raw seawater, low and high levels of sediment). The model predicted that tissue and skeletal growth would vary slightly from each other when affected by
environmental changes; however, the results did not support their hypothesis. It was found that investment in tissue growth varied fourfold to tenfold more over a given environmental range (i.e. light level, sediment level) than did investment into skeletal growth in small colonies (2-3 cm radius) and branches, a much greater variation than was predicted by the model. This was primarily due to the fact that there was a wide range in tissue growth responses that did not behave in a linear fashion in relation to linear extension of the skeleton. Due to this variation in tissue growth, they proposed that skeletal growth rates are relatively unaffected by the physical and environmental stressors they used, with tissue either thickening or thinning depending on the remaining resources available for growth. Under stressful conditions (low light, high sedimentation) energy available for tissue growth is too limited for tissue growth to keep up with skeletal growth, and the tissue begins to
utilize its lipid reserves. Given these results they concluded that under stressful conditions, tissue growth is more likely to be affected than skeletal growth, depending on how much tissue mass there is and its quality (i.e. lipid content): light and sediment load have a much greater affect on tissue growth than on skeletal growth. In other words, tissue growth responds more strongly to resource availability and stressors than skeletal growth does.
For aquarists this study has some practical implications. Many of us use skeletal growth as a benchmark for how well our corals are doing. If this study is correct, then simply using colony growth as a sign that all is well may not be valid in every case. The thickness and quality of the tissue may be of greater significance than how fast the skeleton grows. It is thought that heterotrophy on the part of the coral can be a mechanism whereby a coral can allocate enough energy to tissue growth to allow it to keep up with skeletal growth. In fact, Anthony et al. found that the corals in high ( Goniastrea ) and intermediate ( Porites ) sediment loads actually showed increases in tissue growth, presumably due to the ingestion of particles which supplied the corals with organic carbon and other essential nutrients. This then argues against keeping crystal clear tanks in my mind, and further illustrates the importance of feeding or providing the necessary
nutrients in other forms (i.e. dissolved organic and inorganic nitrogen). Simply maximizing coral growth rates either by chemical means (high calcium and alkalinity levels) or physical means (high light, high temperatures) may not be prudent unless mechanisms are also available for maximizing tissue growth rates as well.
Interesting Citations from the Periodical Literature
The following are citations for some of the articles that might also be of interest to aquarists, which were published in the summer and fall of 2002.
- Hotos, G. N. 2002. Selectivity of the rotifer Brachionus plicatilis fed mixtures of algal species with various cell volumes and densities. Aquaculture Research 33(12): 949-958.
- Domingues, P.M., Sykes, A. and J.P. Andrade. 2002. The use of Artemia sp. or mysids as food source for hatchlings of the cuttlefish ( Sepia officinalis ); effects on growth and survival throughout the life cycle. Aquaculture International 9(4): 310-332.
- Walsh, L.S., Turk, P.E., Forsythe, J.W. and P.G. Lee. 2002. Mariculture of the loliginid squid Sepiateuthis lessoniana through seven successive generations. Aquaculture 212(1-4): 245-262.
- Anta, C., Gonzalez, N., Rodriguez, J. and C. Jimenez. 2002. A secosterol form the Indonesian octocoral Pachyclavularia violocea. Journal of Natural Products 65(9): 1357-1359.
- Biseswar, R., Moodley, G.K. and A.D. Naido. 2002. Note on an inversion of intertidal zoanthid colonies by a chaetopterid polychaete at Park Rynie Beach, Kwazulu-Natal, South Africa. South African Journal of Marine Science 24:371-374.
- LaJeunessa, T.C. 2002. Diversity and community structure of the symbiotic dinoflagellates from Caribbean reefs. Marine Biology 141(2): 387-400.
- Paul, V.J., Biggs, J. and M. Slattery. 2002. Co-occurrence of chemical and structural defenses in the gorgonian corals of Guam. Marine Ecology Progressive Series 239: 105-114.
- Shi, Y.P., Rodriguez, A.D., Barnes, C.L., Sanchez, J.A., Raptis, R.G. and P. Brown. 2002. New terpenoid constituents from Eunicea pinta. Journal of Natural Products 65(9): 1232-1241.
- Verde, E.A. and L.R. McCloskey. 2002. A comparative analysis of the photobiology of zooxanthellae and zoochlorellae symbiotic with the temperate anemone Anthepleura elegantissima (Brandt) II. Effects of light intensity. Marine Biology 141(2): 225-240.
- Kayanne, H., Hairi, S., Ide, Y. and F. Akimoto. 2002. Recovery of coral populations after the 1998 bleaching on Shiraho Reef, in the southern Ryukus, NW. Pacific. Marine Ecology Progressive Series 239: 93-104.
- Kemp, M.J. and W.K. Dodds. 2002. The influence of ammonium, nitrate and dissolved oxygen concentration on uptake, nitrification and denitrification rates associated with prairie stream substrata. Limnology and Oceanography 47(5): 1380-1393.
- Rasherd, M., Badran, M.I., Richter, C. and M. Huetel. 2002. Effect of reef framework and bottom sediment on nutrient enrichment in a coral reef of the Gulf of Aqaba, Red Sea. Marine Ecology Progressive Series 239: 277-286.
- Sakai, Y., Karino, K., Nakashima, Y. and B. Kramer. 2002. Status-dependant behavioural sex change in a polygynous coral-reef fish, Halichoeres melanurus. Journal of Ethology 20(2): 101-106.
- Whiteman, E.A. and L.M. Cote. 2002. Sex differences in cleaning behaviour and diet of a Caribbean cleaning goby. Journal of Marine Biological Association of the UK 82(4): 655-664.
- Foururean, J.W. and J.C. Zieman. 2002. Nutrient content of the seagrass Thalassia testudinum reveals regional patterns of relative availability of nitrogen and phosphorus in the Florida Keys, USA. Biogeochemisty 61(3): 229-246.
- Erickson, K.L., Gustafson, K.R., Pannell, L.K., Beutler, J.A. and M.R. Boyd.
- New dimeric macrolide glycosides from the marine sponge Myriastra clavosa. Journal of Natural Products 65(9): 1303-1306.
- Liu, Y.H., Hong, J.K., Lee, C.O., Im, K.S., Kim, N.P., Choi, J.S. and J.H. Jung. 2002. Cytotoxic pyrrolo- and furano terpenoids from the sponge Sarcotragus sp. Journal of Natural Products 65(9): 1307-1314.
- Sandler, J.S., Colin, P.L., Hooper, J.N.A. and D.J. Faulkner. 2002. Cytotoxic β-carbolines and cyclic peroxides from the palauan sponge Plakortis nigra. Journal of Natural Products 65(9): 1258-1261.
- Williams, P.G., Yoshida, W.Y., Moore, R.E. and V.J. Paul. 2002. Tasiamide, a cytotoxic peptide from the marine cyanobacterium Symploca sp. Journal of Natural Products 65(9): 1136-1339.