Behavioral traits of anemonefish affect the anemone – anemonefish mutualism

Background/Question/Methods

The anemone-anemonefish mutualism is one of the most iconic marine mutualisms. The presence of anemonefish protects the anemone from predators while the anemone provides a safe environment for the anemonefish. Recently, it has been suggested that the number of anemonefish influences anemone fitness, but those studies did not control for the effects of anemonefish biomass or behavior. Here we investigate the association of fish number, biomass and behavior on anemone fitness using Amphiprion percula and Entacmaea quadricolor. We test three hypotheses: i) the number of fish per anemone ii) the biomass of fish per anemone, and iii) the time the anemonefish spends in the anemone, ‘shyness’, will be positively correlated with anemone fitness.

We monitored fish and anemone metrics in 60 tanks for 18 months. All variables were measured at six-month intervals. For each tank, fish number was recorded along with total fish biomass. Fish shyness was obtained by video taping each tank for 12 minutes and quantifying the amount of time the fish spent within one body length of the anemone. We measured two components of anemone fitness: i) net change in the number of anemones per tank (reproduction); ii) change in area of the anemone tentacular crown (growth).

Results/Conclusions

Data from the first six months reveal that fish shyness is significantly related to anemone growth (Linear Regression: df=16, F=8.72, P=0.0052, R²=0.38). Fish shyness is not, however, a significant predictor of anemone reproduction. Further analysis revealed that there was no significant relationship between fish number or fish biomass and anemone fitness during the first 6-month period. However, these independent variables showed positive trends, and it will be interesting to see how these trends develop over 18 months once anemones have had more time to grow and reproduce.

The relationship between fish shyness and anemone growth suggests that variation in behavior among individual fish may be an important biotic driver of variation in fitness among individual anemones. Further research will focus on investigating the mechanism by which variation in fish behavior causes variation in anemone fitness.  More generally, this study highlights the importance of behavior in mediating the strength of interspecific interactions such as mutualisms, and suggests that such effects should be accounted for when investigating the dynamics of interacting populations.