Coral algae cover - Fish Pond Monitoring Project FP 2023

Authors: Erick Morales Oyola, Rudy Paddock, Daniel Hirata, and Ezra Bergson-Michelson.

Introduction:
In this survey, we observed the cover of algae both inside and outside of a reconstructed fish pond in Pā’ea, Tahiti, French Polynesia. Fish ponds, as you all know, were traditionally used by the Polynesians as a form of aquaculture. The rock barriers were used to trap adult fish within the fish pond, providing a regular supply of fish when ocean fishing was not possible. Through this survey, we hoped to further understand the ecology of the fish pond, focusing on how the microhabitat created within the rock walls would affect the marine life that the fish pond was supposed to attract. In this survey, the proposed research question was whether or not there was a difference in algae cover and genus abundance inside versus outside the fish ponds.

Methods:
We began by measuring the total area of the fish pond, which was found to be 15 meters by 15 meters. Then, we divided each length into quarters, with markings at 0, 5, 10, and 15 meters. The 0 and 15 meter marks include the area of sand directly adjacent to the rock walls of the fish pond. We laid one transect along the shoreline, labeling it as our x-axis. We laid another transect perpendicular to the shore along the fish pond wall, labeling it the y-axis. Due to limited transect availability, the x-axis points were marked with rocks for reference while in the water. Then, the bottom right corner of the quadrat was laid at each point of intersection. For example, a quadrat was laid at (0,0), then (0,5), (0,10), and (0,15). In each quadrant we estimated the total percent coverage of all algae and recorded the incidence of different algal genus’. The same process was repeated for a 15x15m square that was 15m north away from the fishpond. It was in at the same position out from the shore.

Data:
Our findings were not statistically significant, given that we obtained a P-value of 0.7413. Within the fish pond, there was a 28.00% mean coverage, whereas the control site had a mean algal coverage of 25.13%. The standard deviations for algal coverage for the fish pond and control sites were 26.14 and 22.54, respectively. Our 95% confidence gave us intervals of 28.00+/-12.808 and 25.13+/-11.044 for the fish pond and control sites. Further, the observed instance rates of genus Turbinaria, encrusting algae, genus Halameda, and the ”Other” category were higher in the fish pond. On the other hand, brown turf algae, genus Padina, and genus Sargassum were more common in the control site. Additionally, on the rock walls of the fish pond, brown turf algae was the most common algae found. There were small sporadic patches of various other algae types, including genus Halameda and encrusting algae in addition to branching and encrusting coral. The Shannon diversity index using quadrat instances for algae genuses gives the fish pond site an index of 1.55. The species evenness was found to be 0.866 with a species richness of 6. The total number of individuals was 35, and the average population size was 5.83. The Shannon diversity index for the control site was also 1.55 with a species evenness of 0.863 and a species richness of 6. The total number of individuals was 31 with an average population size of 5.17.

Discussion:
As our results were not statistically significant, we found there was no significant difference between the algal coverage between the fish pond and control sites. However, there were varying trends within each site. In both sites, algal coverage increased with depth. However, in the fish pond site, the underlying substrate was a significant factor in addition to the evident trend of depth and algal coverage. In the fish pond, genus Halimeda and genus Turbinaria were only present on rocky substrates in addition to being more common at deeper depths. Outside of the fish pond at the control site, genus Turbinaria and genus Padina were prevalent at deeper depths, with encrusting algaes being much less common. Turf algae was also less common outside of the fish pond. These observations led us to believe that the fish pond is accurately simulating the natural algal cover of the coastal ecosystems in Pā’ea. However, with only one control site, randomness in choosing the location of this site may have been a factor.

There are a few potential sources of error:

A small sampling size in terms of number of sites.
Proximity of the second site to the fish pond.

Potential areas for improvement:

More sites spread out over a greater area and variety of substrate types.
More sampling sites within the fish pond.

Conclusion:
In conclusion, we found no statistical difference between the algae coverage inside and outside the fish pond. Nonetheless, more research could be conducted to understand more about the microhabitats found within fish ponds.

Posted on August 11, 2023 04:23 AM by langzi