Blue Tang

Appearance

Although the body of the reef fish can vary in shade from light to dark blue, the dorsal, anal and caudal fins are golden blue. As juveniles, the edges on their dorsal and anal fins and the rings around their eyes are purple-blue, blue or blue-green. Their colors change during growth from a yellow juvenile, yellow tailed blue subadult and the blue adult phase.

Distribution

''Acanthurus coeruleus'' is common off the coast of Florida, The Bahamas, and other places in the Caribbean Sea, including Bonaire. Blue Tangs are very common in Belize and especially Ambergris Caye. They are also common in the Gulf of Mexico. They are also found south to Brazil and north to New York.

Behavior

Atlantic blue tangs engage in cleaning behaviors with other fish as both cleaners and clients. In these interactions, cleaners removes parasites and other materials from the surface of the client. Clients benefit by having ectoparasites and damaged tissue removed from the outside of their body. Removal of unwanted organisms and tissue can lead to improved health maintenance.Blue tangs experience three different social modes: territorial, schooling, and wandering. Blue tangs in non-territorial modes form schools and wander, while territorial blue tangs do not. Territoriality reduces competition for food resources because one individual claims both a territory and its resources. Additionally, schooling allows fish to better overcome food defense by others, and wandering allows for individual movement to feeding areas, cleaning stations, and other resources. Social behaviors are affected by outside conditions such as damselfish density, conspecific population density, and life history stage.

Those in the territorial mode are aggressive and actively chase intruding blue tangs. They swim slower and feed more frequently than non-territorial blue tangs. Schooling fish form compact groups with other blue tangs in addition to other species. Territorial blue tangs are found most often in the reef flat zone and are rarely found in the spur zone or groove zone . Territoriality prevalence decreases with increasing damselfish population, and the time of day also does not affect territoriality prevalence.

Fish in schooling mode swim fast, eat at intermediate rates, and are not aggressive, even though they are often chased by damselfish. Schooling is the most prevalent in areas with high damselfish densities such as the groove zone, spur zone, and crest zone , while schools are most prevalent near midday.

Blue tangs in the wandering mode keep to themselves and are not aggressive. They swim quickly and are often chased by other fish. Wandering blue tangs also visit cleaning stations more often than those in the other modes. Wandering is found most often in the reef back zone and during the morning. With an increase in conspecific population density, blue tang individuals become more territorial. Small, juvenile blue tangs are territorial, but the incidence of territoriality in the larger classes decreases. However, in these fish, schooling and wandering increases.Juvenile blue tangs exhibit different behavior than both conspecific and congeneric adults. Juveniles are prevalent in the reef crest zone, spur zone, and on the fringe of the reef flat zone, but are rare inside of the reef flat zone. Juveniles remain solitary on their home ranges, and home range territory size increases with body size. These territories overlap with those of [''Stegastes''] damselfish. Juvenile blue tangs are aggressive in territory defense. They try to avoid ''stegastes'', and are rarely chased by these damselfish.

Food

Atlantic blue tangs inhabit coral reefs and inshore grassy and rocky areas, where there is a high prevalence of algae. They are herbivorous, and their diet consists only of algae. They eat the algae from the reefs in which they reside, as well as off the bodies of surrounding fish. By eating the algae off of other fish, the blue tang serve as cleaners for them. With the decline in the ''Diadema antillarum'' population, the blue tang population increased since the algal resources that the two animals usually competed for were more abundant.

Juvenile blue tangs eat continuously and feed heavily. This heavy feeding requirement is due to their poor utilization of food resources. The blue tang's stomach and intestinal lining are proficient at absorbing crushed cellular content, but are not very effective at processing cellulose. This digestive system inefficiency leads blue tangs to spend more time and resources on foraging on a very abundant and fast-growing food source in close proximity. This close proximity to an abundant food source allows for continuous foraging.Food distribution, density, and accessibility can determine population density and territory size in blue tangs. Territories with low biogenic structure are larger than those of higher biogenic structure. Since the algal food resources are less dense in low-biogenic structured areas, these territories would have to be larger in order to include the necessary amount of food. This is in accordance with the Ideal free distribution model. This model states that competitors should adjust their distribution in accordance with habitat quality such that each individual will gain the same amount of resources.

According to this model, there should be a lower density of blue tangs on low-biogenic structured territories compared to higher-biogenic structured territories where there is a higher abundance of food. In both territories, each individual will receive similar amounts of resources due to competition. There is no significant difference in feeding rates of blue tangs on each type of territory, meaning that those in larger, uncolonized, and low density territories can match the resources of those in smaller high density territories.