The relationship between sea anemones and their anemonefish hosts have always been symbiotic, with the anemonefish warding off potential predators of the anemone and the anemone providing a home for the anemonefish that potential anemonefish predators would think twice before entering to grab a quick snack. This interaction was thought to be the gist of their mutually beneficial relationship. It apparently goes further than that. Researcher Joe Szczebak of Auburn University in Alabama wanted to know if there was more to it than just two species mutually defending each other. He reasoned that coral reef ecosystems have plenty of life-giving oxygen sloshing through the reefs during the day, but scant oxygen at night due to the lack of photosynthesis that is essential for the creation of oxygen.
Noting that other damselfish push oxygen-rich water over corals during times of darkness, Szczebak wanted to know if anemonefish may be doing the same thing with their anemone hosts. So he and his thesis advisor Nanette Chadwick set out to determine if the anemonefish fans the water around its anemone host to supplement the anemone’s oxygen supply at night. The pair conducted their initial research at the Fuad Al-Horani’s physiology lab at the Marine Science Station in Aqaba, Jordan, SCUBA diving the Red Sea everyday for three weeks to locate their test subjects. They then isolated the fish from their anemone host, measuring each animal’s individual oxygen consumption. They determined that the anemonefish and anemone used 1.4 times more oxygen together than when apart.
“I measured the oxygen levels consumed by the fish and anemones using a technique called flow-through respirometry,” Szczebak told FishChannel. “Simply, the organism(s) is placed in a sealed container of water. Water is pumped continuously through the container. Oxygen electrodes were used to measure the oxygen content of the water immediately before it entered the container and immediately after it exited the container. The difference between these two oxygen readings at any given point in time is how much oxygen is being consumed by the organism(s) within the container.”
Szczebak studied six anemonefish and sea anemone pairs in Jordan and 12 different pairs at the Auburn University. The anemonefish studied were the two-banded anemonefish (Amphiprion bicinctus), and the sea anemone studied was the bulb-tentacle sea anemone (Entacmaea quadricolor).
Back in the United States, Szczebak set out to determine why more oxygen was used when the pair were together, so he created an additional test that involved keeping the animals viewable to each other but isolated by a plastic mesh. They were also able to still smell each other. Both species still measured oxygen levels that were lower than when they were together. Szczebak believes that physical contact is what generates the larger consumption of oxygen in the pair, having watched the anemonefish dive deep into the anemone and complete 180 degree turns within the anemone’s tentacles to open it up so water can circulate through it. When Szczebak mechanically circulated water through the anemone, its oxygen level never increased to a level it did when the anemonefish was swimming through its tentacles.