The foraging ecology of the threatened Hawaiian green sea turtle was investigated at Kapoho Bay on the east coast of the island of Hawaii from September 2006–December 2008. The objectives were to: (1) quantify the diversity and abundance of forage material in the habitat, (2) determine the composition of turtle diets, (3) investigate foraging behavior and determine if foraging selectivity was occurring, and (4) evaluate the nutritional content of forage items.

In this study, diet samples were analyzed for 121 individual turtles and 48 turtles were observed while foraging. Comparisons were made between the food items available in the habitat and what the turtles consumed. The habitat sampled was dominated by algae (92%), primarily in the form of algal turf (64%) and macroalgae (13.5%). Rhodophytes dominated the algal assemblage which was comprised of 25 species. Turtle diets were evaluated for short-term and long-term composition using three methods: (1) the bite count method using direct observation of foraging individuals, (2) esophageal lavage, and (3) stable isotope analysis. A total of 16 species of algae, terrestrial grass, and pieces of mangrove propagules were identified from the diet samples. Rhodophytes were most common, comprising 92% of the total pooled diet. Four primary diet items found in the habitat and selected by the turtles were, Amansia glomerata, Gracilaria salicornia, Acanthophora pacifica and Martensia fragilis, all Rhodophytes. The nutritional analysis of forage materials indicated generally that diet selection by turtles was influenced by the protein content, chemical composition and morphological characteristics of the forage material. Rhodophytes were generally higher in protein than Chlorophytes and Phaeophytes, except for a few select species. Implications for further efforts to improve our understanding of variation in diet and nutrition temporally and spatially are discussed.

Keywords: foraging ecology; green sea turtle; diet; turf algae, Kapoho, Hawaii; stable isotope