Dietary Shifts by Green Turtles (Chelonia mydas) in the Kāne‘ohe Bay Region of the Hawaiian Islands: A 28-Year Study1

The green turtle, Chelonia mydas, has modified its feeding behavior to include the increasing abundance of nonnative algae growing in the greater Kāne‘ohe Bay area of O‘ahu in the Hawaiian Islands. Changes in diet of the green turtle are correlated with an increase in abundance of seven species of nonnative algae between 1977 and 2005. Turtles were found to be eating 130 species of marine vegetation, and the three most common were the nonnative species Acanthophora spicifera, Hypnea musciformis, and Gracilaria salicornia. These three abundant and nutritious food sources are now an important part of the turtle diet in addition to native species found in and near Kāne‘ohe Bay. Chelonia mydas behavior has shifted to include these new seaweeds within 10 years of their introduction to the region. The turtles have also gradually included an additional four less-prolific slow-growing nonnative algal species (Eucheuma denticulatum, Gracilaria tikvahiae, Kappaphycus striatum, and Kappaphycus alvarezii), but the time it has taken turtles to include these species has been longer, 20–30 years, after the seaweeds were introduced. During this same 28-year time period numbers of C. mydas have increased throughout the Hawaiian Islands.