Sea anemones

The sea anemone Aiptasia pallida is a biological model for anthozoan research.
Like all cnidarians, A. pallida possesses nematocysts for food capture and defense.
Studies have shown that anthozoans, such as corals, can rapidly increase nematocyst
concentration when faced with competition or predation, suggesting that nematocyst
production may be an induced trait. The potential effects of two types of tissue damage,
predator induced (Lysmata wurdemanni) and artificial (forceps), on nematocyst
concentration was assessed. Nematocysts were identified by type and size to examine the
potential plasticity associated with nematocyst production. While no significant
differences were found in defensive nematocyst concentration between shrimp predation
treatments versus controls, there was a significant difference in small-sized nematocyst in
anemones damaged with forceps. The proportions of the different types of nematocysts between treatment types were also found to be different suggesting that nematocyst
production in A. pallida is a plastic trait.

Bleaching of reef corals and other cnidarians symbiotic with zooxanthellae can be attributed to the stress response of the host, algae or both. To determine if zooxanthellae are involved in the bleaching process, I infected a single strain of sea anemone, Aiptasia pallida with zooxanthellae from different hosts. I measured expulsion of the algae from the host during 24-hour incubations at 25, 32 and 34C, as well as photosynthetic rates at these temperatures. Photosynthesis and expulsion of zooxanthellae were inversely and directly proportional to elevated temperatures, respectively. Photosynthesis and expulsion of zooxanthellae isolated from Condylactis gigantea showed the greatest sensitivity to elevated temperature when compared to other zooxanthellae tested. These results suggest that zooxanthellae have a function in the bleaching process and that this function may be related to their photosynthetic response. Thus, the differential tolerance of zooxanthellae to stress could partly explain the spatial variability characteristic of coral-bleaching episodes.

Many marine organisms possess endosymbiotic dinoflagellates called zooxanthellae. Bleaching is the loss of zooxanthellae, but bleached hosts can be repopulated. Little is known about how repopulation is controlled. The sea anemone Aiptasia pallida was used to study the effects of feeding on repopulation. Two groups of aposymbiotic anemones were reinfected with algae from symbiotic clones. One group was fed and the other starved, and counts of algae within each anemone were made at 3 day intervals for 6 weeks. The experiment was repeated, and results showed that the rate of algal growth did not differ between fed and starved groups. However, starved anemones reached plateau more quickly and lost algal cells after plateau was reached, whereas fed anemones contained more algae and protein. This suggests that starved anemones can support an algal population initially, but cannot maintain it. Space and nutrients are implicated in having a limiting effect on maintenance of symbionts.

Periclimenes yucatanicus, P. pedersoni, and Thor sp. were nonrandomly distributed among three anemone species at different sites off southern Florida. Host selection tests showed that P. yucatanicus had a strong preference for one anemone, which could explain its field abundance with this same species. Host location tests showed that both Periclimenes species used chemical cues to detect their anemones--visual information seemed unimportant. Laboratory predation trials showed that shrimp survived significantly longer with an anemone than without in the presence of predatory fishes. The acclimation behavior of Periclimenes was described to analyze the protection mechanism. Legs and antennae were in frequent contact with the anemone, but the other body regions rarely contacted the tentacles. Additionally, antennae were used frequently to direct tentacles away from these other body regions. Coating of high contact areas with anemone mucus and avoidance of tentacles with other areas may be the method of protection.