This summer I have been continuing research on a series of artificial reefs we built last summer in the Sea of Abaco between Mermaid’s Reef and Eastern Shores. For this study, we mapped seagrass and then built artificial reefs in areas with different amounts of seagrass. Next, we manipulated the number of fish (focusing on white grunts) and we are comparing fish diet and condition among reefs. In ecological terms, I am asking whether seascape context affects the nature of density-dependent condition for white grunts. In layman’s terms, I am studying how the amount of seagrass around reefs and the number of other fish on reefs can affect the amount of food available and subsequently the condition/health of fish on the reef. More information on previous studies on grunts and artificial reefs can be found here and here.
For part of this experiment, I needed to know if grunts were moving among reefs. Juvenile grunts are reported to have extremely high site fidelity. Even though they may travel 100 meters or more out in to the seagrass to feed each night, grunts make it back to the same coral head on the same reef to rest every day. To determine if grunts were moving around or staying on their home reef on our artificial reef array, we tagged them with an injectable elastomer dye. This dye is fluorescent and is just like a little tattoo that will stay with the grunts for a few months. We created a unique color code for each reef and tagged grunts on their tail/caudal peduncle.
Last month we tagged over 200 grunts and all grunts that we re-sighted stayed on their home reef. We also tried to move grunts around to see if they would stay on a new reef or find their way back to their home reef. Three separate times we moved about 10-15 grunts more than a half mile (>800m) and the very next day we observed some back at their home reef! None stayed at the new reef. We found similar results from a tagging and re-location experiment in the Bight of Old Robinson a couple years ago using French grunts. This also agrees with an older study conducted in the U.S. Virgin Islands which found grunts can move up to 3 km to find their home reef (Ogden and Ehrlich 1977 Marine Biology). This amazing homing ability is just another thing that makes grunts so fascinating. In sum, in the words of Kristin Williams, “Grunts love their home!”