A study on H. magnifica and A. chrysopterus

After reading about various models aimed at analyzing mutualism in general, I decided to take some time and read studies that have been performed on anemones and anemonefish so that I can further understand their relationship and more appropriately choose a modeling approach. This study, conducted by  S.J. Holbrook and R.J. Schmitt in Moorea, French Polynesia over a three-year period and initiated in August 1999, provided much evidence supporting the ways in which anemones and anemonefish benefit one another, specifically how anemonefish affect anemones' growth, reproduction, and survival. 

• Anemones that harbored anemonefish grew nearly 3x faster than those that did not.
• The average daily growth increment was similar for those anemones that hosted 1 or 2 adult anemonefish, and both these growth rates were significantly greater than for anemones that lacked fish.
• Asexual reproduction was enhanced by the presence of anemonefish: anemones occupied by 2 fish underwent fission much more often (~2x expected rate) than those containing 1 (~expected rate) or 0 fish (~ ½  expected rate)
• Anemones that harbored fish experienced a much lower-than-expected probability of dying than those lacking fish: of 14 deaths, 11 were anemones without fish, 2 were anemones with 1 fish, and just 1 was an anemone with 2 fish.

Based on the models I have come across so far in my research, this information will help greatly. I have encountered many model equations containing parameters such as a, the factor by which one mutualist benefits the other. Now, at least for the benefits received by the anemone, I know that the presence of an anemonefish not only raises d, the mortality rate, but it also increases r, some growth rate, and b, some 'birth' rate. 

The authors point out that anemones could potentially derive both direct and indirect nutritive benefits from fish: anemones might directly ingest particles dropped by the fish or absorb their wastes, which could provide sources of regenerated nitrogen, sulfur, and phosphorous in addition to small prey and plankton they capture. And for at least some species of anemone, adult anemonefish defend their host anemone from specialized tentacle-eating fish predators such as Butterflyfish.

The authors also presented ways in which anemones appear to aid their resident anemonefish:

• Sea anemones provide an enemy-free space for anemonefish from its predators.
• The anemone acts as a nest site for an anemonefish: the anemonefish lay their eggs on the hard substrate beneath the oral disc of the anemone, where they are tended by the male fish.

As of now, I believe that anemonefish are obligate mutualists of anemones and thus cannot live without a host anemone, while anemones are merely facultative mutualists with anemonefish. Since there exists facultative, obligate, and obligate-with-thresholds mutualism, it will be interesting to determine where on this spectrum the anemone-anemonefish mutualism lies.