Introduction

The world’s corals are dying at the alarming rate of 600 square miles of reefs per year (Telegraph). This loss has been attributed to human encroachment, and global climate change. In order to understand the effect these factors will have on wild corals, aquacultured colonies, corals grown in captivity, can be used. If grown successfully, these captive grown corals, have the potential to not only allow use for scientific study, but also the potential to repopulate the wild coral populations (U.S. Department of Commerce). Little scientific research has been done to understand the basic parameters required for coral health and growth in captivity. This experiment was designed to test the effect that different levels of water current have on captive grown coral colonies. Thus, this study was to better understand this vital factor in coral growth, which can lead to new discoveries of coral in captivity, and this can hopefully lead to implementing these successful corals in the wild, replacing their dying counterparts and in general, make coral aquaculture more efficient.

The Experiment

For this experiment, thirty Anthelia glauca coral colonies of relatively the same size, in terms of polyp count, were separated into two groups of fifteen. Each group was subsequently divided into smaller groups of five, and were separated based on the strength of three different relative flow rates, seen here in Figure 4. The corals were then placed on a plastic rack with a ten centimeter base. The “map” of the tank, Figure 3, was created by dropping sand at the height of ten centimeters, and thus, to be accurate with the strength of flow, the corals needed to be placed in this configuration. The health and growth was assessed based on the total number of polyps for each coral colony over a seven week period.

Mapping Water Current

A 130 gallon tank was used to house the coral specimens (Figure 1). The tank contains six Maxijet 1200 pumps ,which blow water in different directions, making it difficult to determine water flow. Water flow patterns were determined by dropping aragonite sand into the tank at 6” intervals for the entire tank and measuring the direction and distance that the sand traveled. Once completed, the data was plotted on a “map” of the tank (Figure 3), resulting in a diagram of the tank showing both direction and relative strength of current. For this experiment areas that represented high, medium, and low flow relative to the flow rates of the tank, were chosen. Although the “map” does not show actual flow rates, it does compare flow in areas of the tank relative to the rest of the tank.

Biology of Anthelia Glauca

Also known as waving hand coral, Anthelia glauca is a mat building soft coral which grows via asexually reproduction (Fenner). The stalks, known as polyps, represent individual organisms attached to the colony. Increases in the number of polyps in the colony can be a good indicator of the overall health of the coral (Pet Education). Thus, the more polyps indicate more growth. This specific coral was selected in the experiment as it is known to be especially sensitive to various flow rates (Pet Education).

Aquarium Habitat

The experiment was conducted in a 130 gallon, 183cm by 91cm by 41 cm (l, w, h), rectangular glass tank, shown in Figure 2. The tank contains six pumps, and a three return lines from the main system pump, which create the water flow in the tank. The tank was maintained at a consistent 78°F with a specific gravity of 1.023g/ml. The tank was lit with a 48” Aquamedic Startlight Fixture with 2 x 150W 14,000K metal halide lamps.

Results

Over the seven week period, both experiments showed that corals (five specimens) receiving the medium strength of water flow exhibited the best growth, exhibiting, on average, an additional 18% increase in polyp count over the next highest flow. Corals in all areas of flow saw an increase in polyp count, as shown by Figure 5. However, corals receiving medium flow saw their polyp count increase by 207.4%, while the next highest increase, the low flow, only saw a growth of 189.1%. The areas of high flow did not fair as well as the others, growing, on average, 142.7%.

Conclusion

The results of this experiment, which attempted to find the optimal flow rate conductive to growth of the soft coral Anthelia glauca, suggest that Anthelia glauca prefers areas with moderate levels of flow. The corals receiving medium flow rates exhibited the best growth, growing 205.0% and 209.8% in experiments 1 and 2, respectively. These type of coral thrive under medium flow conditions in the captivity. This experiment also shows that if the corals do not receive the optimal flow rate, then their growth and well being will be affected. Thus, current is another factor in the health of corals worldwide. If they do not receive the right amount of flow, then their health will suffer, and they will potentially perish. Thus, in the field of aquaculture, there is no point in using corals receiving high and flow rates. Their growth does not compare to that of the moderate flow rates. Instead, the corals receiving medium flow, which grow the best, can be implemented in the wild as large, lush, and serve as a way to repopulate the dying reefs of the world (U.S. Department of Commerce). Thus, the success the coral find in captivity will hopefully translate to success in the wild—this aquaculture technique one way to save the dying reefs of the world.

Future Implications

Although the optimal of Anthelia glauca coral was successfully determine, and a way to better grow the species in captivity was found, not all coral have the same properties and characteristics like that of Anthelia glauca. Thus, in order to find out if moderate flow is optimal for all species of coral, more types of animals, such as the specimens in Figure 6, need to be tested. In this way, other species of coral’s sensitivity to water flow can support the results of the Anthelia glauca. Thus, the optimal flow rate can be found for all species of coral. In the field of aquaculture, this would be extremely beneficial as if this were the case, there would be no further need for pumps blasting high flow, or just merely low flow.

Works Cited