Turbidity: A key factor in the estimation of fish species richness and abundance in the rocky reefs of Ecuador

Abstract The effectiveness of using standardized sampling methods for fish communities in coral and rocky reefs has been widely discussed because it largely depends on the experience and skill of the observer, availability of high-definition equipment and the stability of local environmental parameters. The rocky reefs in Ecuador have highly variable conditions of turbidity, which can generate biases in the sampling of reef fish. The present work compares the effectiveness of detection of two sampling methods: 1) observer-band transects and 2) video-transects, as tools to determine the composition of fish communities in two rocky reefs subjected to high anthropic pressure and high variability in the conditions of turbidity. To achieve this goal, 48 transects of 100 m and variable-width on the dependence of turbidity conditions were performed in three geomorphological reef zones: the crest, slope, and bottom, where a community of fish was sampled from September 2017 to April 2018 using both methods. The results showed significant differences in the fish abundance recorded depending on the sampling method, the video-transect method was more efficient for the estimation of abundance. Comparison of the survey methods in reef zones showed that video-transects are more effective in detecting significant differences in abundance on the slopes of the reefs in comparison with observer-band transects. Turbidity significantly affected the abundance of fish detected by both sampling methods. Our results suggest that the video-transect method is more efficient to record fish abundance with respect to the observer-transect method under different conditions of turbidity.