In this paper, the authors examined the impact on coral growth and reproduction of fish farm effluent in the Gulf of Aqaba (Eilat) in the Red Sea. The commonly held belief is that high particulate and nutrient levels released by such operations are damaging the corals on the local reefs. Indeed, it is generally accepted that high nutrient levels can affect coral growth and reproductive fitness. What is less commonly known is that as the nature and concentrations of these nutrients vary, so do their impacts on corals.

Two study sites were selected, the Ardaq fish farm on the north shore of the Gulf of Eilat where gilthead seabream are cultured in sea pens and a more southern “pristine” reef off the Inter-University Institute (IUI) of Eilat. The levels of nitrite, nitrate and phosphate (micromolar) measured at the two sites are listed in the table 1.

Forty branches of Acropora eurystoma were removed from each of ten different colonies located at the IUI. The resulting 400 pieces were mounted on to PVC plates, 200 were placed at 6 m depth on the reef at the IUI, and 200 were placed at 6 m depth, 20-40 m from the fish cages within the middle of fish farm. All fragments were stained with Alizarin red so that skeletal growth could be later determined. After seven months, the fragments were collected and measured for weight, linear extension of branches and “ecological volume” (the water volume occupied between the branches of the coral) and compared.

In another experiment, 190 small pieces of Stylophora pistillata were glued onto PVC plates and placed at each location. Survival rates and lateral growth were then measured at 3, 4 and 13 month intervals.

In addition, 14 colonies of similar sized Stylophora pistillata growing at each of the two sites were sampled to assess gonadal development. Finally, the lipid content of both species of coral from both sites was examined.

The result showed that Acropora grown at the fish farm site had identical survival rates to those from the IUI site. However, those from the fish farm exhibited a significant 3-fold increase in weight and linear extension, and a significant 4-fold increase in ecological volume compared to those at the IUI site.

The fragments of Stylophora showed a similar trend with those at the fish farm site showing significantly greater sizes after 13 months. However, those at the IUI site showed greater lateral growth rates, presumably due to the higher degree of deposition and accumulation of particulate matter at the fish farm site. Whereas the average growth rate of the IUI fragments was high, those at the fish farm exhibited a gradual increase in growth rate over time and eventually (after 13 months), those colonies at the fish farm site were significantly larger than those at the IUI site.

The reproductive status of Stylophora was examined in 2001 at the beginning and peak of the reproductive season (January and May 2001) and at the beginning of the 2002 (December 2001) reproductive season. The number of polyps with female gonads was higher at the fish farm in January and May 2001, but in December, all colonies at both sites had ovaries. The size of the oocytes in colonies growing at the fish farm was larger but not significantly so. However, the average number of oocytes per polyp was significantly greater at the fish farm and there were significant differences between seasons too with December 2001 having significantly greater numbers than the previous season. The proportion of colonies with male gonads was also greater at the fish farm site.

The lipid content of naturally occurring colonies of Stylophora at the fish farm site was significantly greater than at the IUI site. However, there was no difference in the lipid content of the Acropora used in the study after 7 months.

This study tends to contradict earlier studies that showed detrimental effects of increased nutrient levels on not only coral growth but also coral reproductive state. Although various studies have shown that elevated nutrient levels are generally associated with detrimental effects on coral growth and reproduction it has been proposed that the chemical form and concentration of these nutrients may actually determine whether there is a positive or negative effect. It is well known that corals will absorb ammonium and use it to enhance growth. Nutrient types and concentrations may very well dramatically determine the type of response exhibited by reef organisms. While elevated nutrients are often cited as major contributors to the decline of reef health, it is often difficult to distinguish the effects of any one factor when dealing with multiple impacts on reef health such as anthropogenic pollution, human use (i.e. SCUBA), siltation, sand deposition etc. Of course, the short term
of this study may mask any long term detrimental effects of elevated nutrient levels on coral health as well.

For aquarists the lessons are clear, the obsession with nutrients such as ammonia, nitrate and phosphate may be slightly misplaced. While it is generally advised that these nutrients be as low as possible (0 is often quoted as the ideal for ammonia for example), they may not be detrimental at certain concentrations and it may actually be beneficial to have slightly elevated levels of certain nutrients such as nitrogen to aid coral growth. Of course, one must not loose sight of the fact that hobbyist test kits are a far cry from being able to measure the levels mentioned in this study and it is probably safe to assume that the levels for many nutrients are still several times that of oligotrophic reef waters.

At this point, I would like to mention a pet “theory” of mine. One of the widespread “fads” in reef keeping today is the addition of phytoplankton cultures and other “foods” to reef aquaria. Often these are fed to tanks containing predominantly LPS corals in the belief that these coral will feed on this food. Observations are often made that the corals look much better and colorful after several weeks of such feedings. I would like to propose the theory that the benefit may not be so much from the actual ingestion of the food but the decomposition of the food leading to the generation of nitrogenous wastes which are then absorbed by the corals resulting in better pigmentation and increased zooxanthellae populations.

Recent Publications

Aquaculture

1. Baldwin, A.P. and R.T. Bauer. 2003. Growth, survivorship, life-span and sex change in the hermaphroditic shrimp Lysmata wurdemanni (Decaopoda: Caridea: Hippolytidae). Marine Biology 143(1):157-166.
2. Cunha, F., SaboridoRey, F. and M. Planas. 2003. Use of multivariate analysis to assess the nutritional condition of fish larvae from nucleic acids and protein content. Biological Bulletin 204(3):339-?.
3. Curtis, C.J. 2003. Culture of harpacticoid copepods: Potential as live feed for rearing marine fish. Advances in Marine Biology, vol. 44. Academic Press, 2003, 325 pp. ISBN 0-12-026144-8.
4. McCormick, M.I. 2003. Consumption of coral propagules after mass spawning enhances larval quality of damselfish through maternal effects. Oecologia 136(1):37-45.
5. Pati, A.C. and G. Belmonte. 2003. Disinfection efficacy on cyst viability of Artemia franciscana (Crustacea), Hexarthra fennica (Rotifera) and Fahrea salina (Ciliophora). Marine Biology 142(5):895-904.

Cephalopods

1. Jantzen, T.M. and J.N. Havenhead. 2003. Reproductive behavior in the squid Sepioteuthis australis from south Australia: Ethogram of reproductive body patterns. Biological Bulletin 204(3):290-304.
2. Jantzen, T.M. and J.N. Havenhead. 2003. Reproductive behavior in the squid Sepioteuthis australis from south Australia: Interactions on the spawning grounds. Biological Bulletin 204(3):305-317.
3. Steer, M.A., Moltshaniwskyj, N.A. and A.R. Jordan. 2003. Emryonic development of the southern calamari ( Sepioteuthis australis ) within the constraints of an aggregated egg mass. Marine and Freshwater Research 54(3):217-226.

Corals

1. Fine, M. and Y. Loya. 2003. Alternate coral-bryozoan competitive superiority during coral bleaching. Marine Biology 142(5):989-996.
2. Gateno, D. and B. Rinkevich. 2003. Coral polyp budding is probably promoted by a canalized ratio of two morphometric fields. Marine Biology 142(5):971-974.
3. Kelmanson, I.V. and M.V. Matz. 2003. Molecular basis and evolutionary origins in color diversity in great star coral Montastraea cavernosa (Scleractinia: Faviidae). Molecular Biology and Evolution 20(7):1125-1133.
4. Ojika, M., Islam, M.K., Shintoni, T., Zhong, Y., Okamoto, T. and Y. Sakagami.
5. Three new cytotoxic acylspermidines from the soft coral, Sinularia sp. Bioscience Biotechnology and Biochemistry 67(6): 1410-1412.
6. Ribes, M., Coma, R. and S. Rossi. 2003. Natural feeding of the temperate asymbiotic octocoral-gorgonian Leptogorgia sarmentosa (Cnidaria: Octocorallia). Marine Ecology Progressive Series 254:141-150.
7. Sanchez, J.A., McFadden, C.S., France, S.C. and H.R. Lasker. 2003. Molecular phylogenetic analyses of shallow-water Caribbean octocorals. Marine Biology 142(5):975-985.
8. Santos, S.R., Gutierez-Rodriquez, C., Lasker, H.R. and M.A. Coffroth. 2003. Symbiodinium sp. associations in the gorgonian Pseudopterogorgia elisabethae in the Bahamas: high levels of genetic variability and population structure in the symbiotic dinoflagellates. Marine Biology 143(1):11-120.
9. Villinski, J.T. 2003. Depth-dependant reproductive characteristics for the Caribbean reef-building coral Montastraea faveolata. Marine Biology 142(6):1043-1054.
10. Yacobovitch, T., Weis, V.M. and Y. Benayahu. 2003. Development and survivorship of zooxanthellate and azooanthellate primary polyps of the soft coral Heteroxenia fuscescens: laboratory and field comparisons. Marine Biology 142(6):1055-1064.

Freshwater Fish

1. Buhrnheim, C.M. and C.C. Fernandes. 2003. Structure of fish assemblages in Amazonian rain-forest streams. Copeia 2:255-262.
2. Hee, H. 2003. Mystus impluriatus: A new species of bagrid catfish (Teleostei: Bagridae) from eastern Borneo. Copeia 2:373-378.
3. Magurran, A.E. and H.L. Queiroz. 2003. Partner choice in piranha shoals. Behaviour 140(3):289-300.

Marine Fish

1. Asoh, K. 2003. Gonadal development and infrequent sex change in a population of the humbug damselfish, Dascyllus aruanus, in continuous coral-cover habitat. Marine Biology 142(6):1207-1218.
2. Bush, A. 2003. Diet and diel feeding periodicity of juvenile scalloped hammerhead shakrs, Sphyrna lewini, in Kaneohe Bay, Oahu, Hawaii. Environmental Biology of Fishes 67(1):1-12.
3. Bell, E.M., Lockyear, J.F., McPherson, J.M., Marsden, A.D. and A.C.J. Vincent.
4. First field studies of an endangered South African seahorse, Hippocampus capensis. Environmental Biology of Fishes 67(1):35-46.
5. Cantermil, D.P., Vaudo, J.J., Lowe, C.G., Whetherbee, B.M. and K.N. Holland.
6. Diel movement patterns of the Hawaiian stingray, Dasyatis lata: implications for ecological interactions between sympatric species. Marine Biology 142(5):841-848.
7. Fangue, N.A. and W.A. Bennett. 2003. Thermal tolerance responses of laboratory-acclimated and seasonally acclimatized Atlantic stingray, Dasyatis sabina. Copeia 2:315-325.
8. Holbrook, S.J. an R.J. Schmitt. 2003. Spatial and temporal variation in mortality of newly settled damselfish: patterns, causes and co-variation with settlement. Oecologia 135(4):532-541.
9. Holzman, R. and A. Genin. 2003. Zooplanktivory by nocturnal coral-reef fish: Effects of lights, flow and prey density. Limnology and Oceanography 48(4):1367-1375.
10. Janse, M. 2003. Considerations on the diet composition and feeding rate of dermersal sharks in 15 Euopean public aquaria. Zoo Biology 22(3):203-226.
11. Sponaugle, S., Fortuna, J., Grorud, K. and T. Lee. 2003. Dynamics of larval fish assemblages over a shallow coral reef in the Florida Keys. Marine Biology 143(1):175-190.

Miscellaneous

1. Baums, I.B., Millers, M.W. and A.M. Szmant. 2003. Ecology of a corallivorous gastropod Coralliophila abbreviata, on two scleractinia hosts. I. Population structure of snails and corals. Marine Biology 142(6):1083-1092.
2. Baums, I.B., Millers, M.W. and A.M. Szmant. 2003. Ecology of a corallivorous gastropod Coralliophila abbreviata, on two scleractinia hosts. II. Feeding, respiration and growth. Marine Biology 142(6):1093-1102.
3. Chisholm, R. 2003. Primary productivity of reef-building crustose coralline algae. Limnology and Oceanography 48(4):1376-1387.
4. Connelly, J.D. 2003. The monopolization of understory habitat by subtidal encrusting coralline algae: a test of the combined efforts of canopy mediated light and sedimentation. Marine Biology 142(6):1065-1072.
5. Estes, A.M., Kempf, J.C. and R.P. Henry. 2003. Localization and quantification of carbonic anhydrase activity in the symbiotic scyphozoan Cassiopea xamachana. Biological Bulletin 204(3):278-289.
6. Griffin, S.P., Garcia, R.P. and E. Weil. 2003. Bioerosion in coral reef communities in southwest Puerto Rico by the sea urchin Echinometra viridis. Marine Biology 143(1):79-84.
7. Larkum, A.W.D., Koch, E.M.W. and M. Kuhl. 2003. Diffusive boundary layers and photosynthesis of the epilithic algal communities of coral reefs. Marine Biology 142(6):1073-1082.
8. Leichter, J., Stewart, H.L. and S.L. Miller. 2003. Episodic nutrient transport to Florida coral reefs. Limnology and Oceanography 48(4):1394-1407.
9. Masunaga, G. and H. Ota. 2003. Growth, reproduction of the sea snake, Emydocephalus ijimae, in the central Ryukus, Japan: a mark and recapture study. Zoological Science 20(4):461-470.
10. SanMartin, G. and E. Nishi. 2003. A new species of Alcyonosyllis Glasby and Watson, 2001 (Polychaete: Syllidae: Syllinae) from Shimoda, Japan, commensal with the gorgonian Melithaea flabellifera. Zoological Science 20(3):371-376.
11. Sousa, W.P., Kennedy, P.G. and B.J. Mitchell. 2003. Propagule size and predispersal damage by insects affect establishment and early growth of mangrove seedlings. Oecologia 135(4):564-575.

Water Treatment

1. Losso, J.N., Marshall, W.E., Rao, R.M. amd R.J. Portier. 2003. Adsorption of metal ions by pecan shell-based granular activated carbons. Bioresource Technology 89(2):115-120.