What Happened to Nemo: Population Dynamics of the Orange Clownfish, Amphiprion percula Over an Eight-Year Time Gap on Kimbe Island, Papua New Guinea

Abstract

Long-term studies are important for understanding the intricacies of population dynamics over time. Self-recruitment and social hierarchy are valuable tools to quantify the rates at which populations change. In mutualistic symbiosis, where two species benefit from the relationship, different selective pressures and life histories can have unintended consequences on the population dynamics of both species. Anemonefish live in a sized-based hierarchy where individuals queue to be part of the breeding pair (ranks 1 and 2). They have a mutualistic association with their host anemone; the identity of the anemone can impact their growth and fecundity. However, there is limited knowledge on the anemone lifespan and its site persistence over time. Here, we investigate rank changes and self-recruitment in Amphiprion percula and persistence in a common host anemone, Stichodactyla gigantea, on the remote island of Kimbe Island in Papua New Guinea. The populations of A. percula (n = 1,530) and their local host anemones, S. gigantea (n = 290) and Heteractis magnifica (n = 174), were sampled exhaustively in 2011 and 2019. Using DNA profiling, I determined the fate of individuals between years. We found that 21% of the A. percula population survived over the eight-year time gap compared to the 69% survival of the associated S. gigantea population in a six-year time gap. Half of the surviving A. percula individuals increased in rank and exhibited faster growth rates living on S. gigantea compared to H. magnifica. Self-recruitment was high in both years, 47% in 2011 and 39% in 2019, with one individual returning to its natal anemone. Our findings provide rare insights into one of the most charismatic symbiotic relationships in the marine environment such as the first documentation of longevity in a host anemone.