Diet of the manatees (Trichechus manatus manatus) in Chetumal Bay, Mexico

Abstract

Manatees, as well as other sirenians, are aquatic, opportunistic herbivores. Knowledge of their diet is important to determine habitat requirements. This is the first study of manatee diet in México. Our main objective was to identify the plant species eaten by manatees in Chetumal Bay, and to establish if diet composition varied by climatic season, sex or age class. We compared plant epidermal fragments found in feces with histological descriptions and permanent collections of suspected plants and algae. Thirty-six fecal samples and nine tract digestive content samples (mouth, stomach, and cecum) were examined. We found eight distinct plant items, including seagrasses, freshwater grasses, algae and vascular plants. Halodule wrightii and Thalassia testudinum were found in 41 samples (92%), and Ruppia sp. was present in 57.8%. Another common item was red mangrove (Rhizophora mangle), found in 66.7% of samples. Additionally, we report Chara sp. and Najas sp. as part of the West Indian manatees diet outside of Florida. A multivariate analysis based on a presence/absence triangular matrix and a similarity analysis were used to test differences among samples. Season, sex or age class did not influence diet composition. All species identified are present in Chetumal Bay, suggesting that manatees do not move long distances at sea in search of food. We postulate that consumption of red mangrove by Chetumal Bay manatees may occur as compensation for the scarcity of submersed aquatic plants, which has not been reported for other habitats for this species.