Increased use of non-native algae species in the diet of the Green Turtle (Chelonia mydas) in a primary pasture ecosystem in Hawaii

Abstract

The Green Turtle, Chelonia mydas, has modified its feeding behavior over the past 36 years to include the increasing abundance of non-native algae growing in the greater Kaneohe Bay area of Oahu, Hawaii. Changes in diet of the Turtles are correlated with an increase in abundance of non-native algae. Turtles are eating 135 species of marine vegetation including the following seven non-native species: Acanthophora spicifera, Hypnea musciformis, Gracilaria salicornia, Eucheuma denticulatum, Gracilaria tikvahiae, Kappaphycus striatum and Kappaphycus alvarezii. Non-native algae now represent 0.64 proportion of the Turtle diet. The present study for the additional 8 years 2005–2012, shows the utilization of non-native species for food has increased 24% since the last study that included 28 years 1976–2005. Average time for the Turtles to make the shift to non-native species is 10–12 years for the more invasive species and 20–30 years for the slower growing species. During this same time period the numbers of C. mydas, body size, and growth rates have also increased, partly due to the increased abundance of the additional non-native food items. This study verifies that the trend of Turtles eating higher amounts of non-native algae in Kaneohe Bay is now stronger than first reported in 2009.