The hit movie “Finding Nemo” made them a prominence among the reef inhabitants and so many snorkelers want to see the cute anemonefish up close. But how do the fish react to these visits? Researchers have now investigated this question. The results suggest that there are significant differences in susceptibility among the clownfish species. Scientists say that “brave” species may be more likely to assert themselves in reefs that are heavily visited by humans.
The ecosystems of the oceans are coming under increasing pressure from human influence. In the coral reefs, rising water temperatures, ocean acidification, pollution and overfishing are known to threaten the organisms living there. But there is also another possible burden: In areas developed by tourism, sometimes many snorkelers and divers explore the fascinating underwater world. Previous studies have already shown that some reef dwellers can be disturbed by the physical presence of humans. The researchers at the Leibniz Center for Tropical Marine Research in Bremen and the Auckland University of Technology in New Zealand have now examined how anemonefish (Amphiprion) react to visits.
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Experimental visits to “Nemo”
These fish are a group of 29 species found in the coral reefs of the tropical Indo-Pacific including the Red Sea. What is special about these representatives of damselfish is their way of life in close symbiosis with sea anemones: While the cnidarians offer the fish in their tentacles protection from attackers, the clownfish defend their home anemones from intruders and provide them with food through leftover food and excretions. However, this close bond could also make clownfish particularly susceptible to interference from humans, because they can only evade to a limited extent due to their location.
As part of the study, the researchers have now examined the behavior of two species of clownfish off the coast of the island state of Vanuatu in the South Pacific. It was the Clark’s anemonefish (Amphiprion clarkii) and the blackfin anemonefish (Amphiprion melanopus), both of which have a comparatively large distribution area. To simulate a typical human visit, the first author of the study, Lena Trnski from the Auckland University of Technology, snorkeled on the animals’ native anemones and moved one to three meters above them in the water. She filmed the reactions of the clownfish. Video recordings of the animals without the presence of the scientist served as a comparison.
Species-dependent sensitivity
The evaluations showed: During the visits, the fish showed very different behavioral patterns depending on the species. While the Clarks anemonefish were frightened by the encounter and often hid deep in the tentacles of the anemone, the blackfin anemonefish reacted much less intensely to the presence of a human. “We actually expected that the black-fin anemonefish would hide from Lena or perhaps attack her, but most of the time they wouldn’t let her bother them. The fish were often up to a meter outside the tentacles of their anemone, ”says study director Julian Lilkendey from the Auckland University of Technology.
The researchers see the possible cause of the clear difference in behavior between the two species in their various adaptations: “We suspect that black-fin anemonefish behave more boldly in the presence of humans, since it is a highly specialized clownfish that only has a few anemone species as a partner, ”explains Trnski. “In order to find a suitable host anemone, it is advantageous for the larvae of the black fin anemonefish to fearlessly search the reef – even if this behavior also makes them more susceptible to predators. But it is precisely this fearlessness that is also evident in the fact that they do not flee from people, ”said Trnski.
As for the significance of the result, the scientists explain that “brave” clownfish species such as the black-fin anemonefish could displace more fearful species in regions that are heavily influenced by tourism. “Species that retreat into their anemone under stress for protection spend a lot of energy and time on this one escape behavior and can therefore deal less with foraging or reproduction,” says Lilkendey. “Intrepid species have an advantage over them.” Trnski adds: “The resulting displacement process could ultimately lead to a loss of biodiversity”.
According to the researchers, however, there is now a need for further research: “The ecological consequences of behavior changed by humans are still largely unexplored,” says Lilkendey. “We suspect that differences in the behavior of individual animal species could have an impact on interactions, which in turn can influence community structures and the functioning of the entire ecosystem,” says the scientist.
Source: Leibniz Center for Tropical Marine Research (ZMT), specialist article: Journal of Fish Biology, doi: 10.1111 / jfb.14492