Dispersal of Pederson cleaner shrimp among host sea anemones: Impacts of shrimp body size and social group interactions

Abstract

Pederson shrimp Ancylomenes pedersoni are the most common cleaners of reef fishes in the Caribbean Sea. They also are obligate associates of sea anemones, especially corkscrew anemones Bartholomea annulata; together these shrimp and anemones form cleaning stations that are visited by client fishes for ectoparasite removal. Pederson shrimp therefore likely impact the abundance and diversity of reef fishes by enhancing fish health through reduction of parasite loads and physiological stress levels. Shrimp dispersal patterns among host anemones affect the stability and locations of cleaning stations, but the extent to which shrimp move among anemones remains unknown. Here we quantify rates and patterns of association with and dispersal among host sea anemones by these shrimp, and how they vary with characteristics of both the shrimp (body size, social rank, social group size) and the anemone host (body size, distance to nearest neighbor). Laboratory experiments revealed that shrimp level of association with anemones increases with both shrimp body size and social rank, but not with anemone size. Field observations on patch reefs at St. Thomas, USVI, indicated that shrimp social group size, and to a lesser extent, shrimp body size, significantly impact dispersal among hosts, but that other factors have little or no effect at the time scale examined. Some shrimp move frequently among anemones in the field, changing hosts on a daily basis. We conclude that large shrimp may not be affected by the presence of small conspecifics, but small shrimp may dramatically alter their anemone association behaviors when large shrimp are present. Large female shrimp remain with each host anemone for longer durations on average than do small juvenile and male shrimp, which often depart from crowded anemones and arrive at others nearby. Frequent dispersal by Pederson shrimp among anemones likely requires client fishes to search often for new cleaning stations, with consequent impacts on patterns of fish habitat use, diversity and abundance on Caribbean coral reefs.