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Acanthurus coeruleus

Behavior

Feeding

The Blue tang 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. In this case they act to clean other fish. Blue tangs inhabit coral reefs and inshore grassy and rocky areas, where there is a high prevalence of algae. With the dying off of the sea urchin Diadema antillarum, there was a large increase in blue tang population. Blue tangs and Diadema antillarum compete for the same algae. With the death of these competitors, algae abundance increased and as such there are more resources for the blue tangs to exploit.

Juvenile blue tangs feed heavily, continuously eating. This heavy requirement of feeding is due to poor utilization of food resources. The blue tang's stomach and intestinal lining is proficient at absorbing crushed cellular content, but is not very effective at processing cellulose. This digestive system inefficiency leads to blue tangs spending more time and resources on foraging, in addition to requiring a very abundant and fast growing food source in close proximity to allow for continuous foraging.

Food Competition

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 would 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, low density territories can match the resources of those in smaller high density territories.

Cleaning Behavior

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.

Cleaner Interactions

Blue tangs act as cleaners by grazing algae as well as eating molted skin and parasites off of the client's flesh once the client comes to the cleaning station. The most common client in these interactions is the green turtle, in which the blue tang inspects the green turtle by nipping its head, limbs, tail, and carapace.

Client Interactions

When acting as clients, blue tangs normally approach cleaning stations inhabited by cleaner gobies. The blue tang's flippers are the most inspected area. Cleaners must be careful because the spine on both sides of the caudal peduncle are sharp and can inflict painful wounds.

When in the client role, blue tangs will pose as they enter the cleaning station. Posing occurs before the cleaners inspect the incoming client fish. Fish who pose while in cleaning stations have a higher chance of getting cleaned. Blue tangs almost exclusively pose through head stands.

Wound Healing

Acting as a client and getting cleaned serves a beneficial purpose after suffering an injury. Blue tangs incur many minor injuries, but infection as a result of injuries rarely leads to death. Recovery rates from both minor and major injuries are very high in blue tangs. Injured blue tangs are found to spend more time in cleaning stations compared to when further along in the healing process. This indicates that cleaning plays an important role in the wound healing process. Cleaners pick at the wound and eat the dead tissue in the peripheral area.

Social Modes

Blue tangs experience three different social modes: territorial, schooling, and wandering. Blue tangs in non-territorial mode formed schools and wandered. Territorial blue tangs do not. Territoriality reduces competition for food resources because one individual claims a territory and its resources. Schooling allows fish to better overcome food defense by other fish. Wandering allows for individual movement to feeding areas, cleaning stations, and other resources. Those in 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. Fish in schooling mode swim fast, eat at intermediate rates, and are not aggressive, even though they are often chased by damselfish. 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.

Factors Affecting Social Modes

Social behaviors are affected by outside conditions such as damselfish density, conspecific population density, and life history stage. Territorial blue tangs are found most often in the reef flat zone (sandy-bottomed flat with rocks or coral) and are rarely found in the spur zone (low coral ridges) and groove zone (sandy bottom channels). Territoriality prevalence decreases with increasing damselfish population. The time of day does not affect territoriality prevalence. Schooling was the most prevalent in areas with high damselfish densities such as the groove zone, spur zone, and crest zone (shallow reef area). Schools are most prevalent near midday. Wandering is found most often in the reef back zone (enclosed region with irregular patches of algae, rock and sand) 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, schooling and wandering increases.

Juvenile Behavior

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 were rare inside of the reef flat zone. The juveniles remained solitary on their home ranges. 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.

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