Feeding ecology of juvenile green turtles in food-poor habitats of the Persian Gulf

Abstract

The Persian Gulf hosts marine mega-herbivores that forage in its coastal habitats. Some areas, mainly along its southern coast, contain abundant benthic plants; however, marine plant resources are limited throughout most of this warm sea, which presents nutritional challenges for large herbivores. We measured curved carapace length (CCL) for 102 green turtles ( Chelonia mydas ) from foraging grounds with relatively limited plant resources surrounding Qeshm Island at the eastern Persian Gulf. The mean CCL was 41.8\xa0cm (SE\u2009=\u2009\u2009±\u20091.3\xa0cm; range\u2009=\u200918.5–99), and 93 turtles (91%) had CCL\u2009<\u200965\xa0cm, indicating the area is primarily a juvenile developmental habitat. To study feeding ecology of green turtles in the area, we analyzed esophageal lavage samples from 36 individuals captured in muddy-bottom ( n \u2009=\u200923) and sandy/rocky-bottom ( n \u2009=\u200913) habitats. Diet data showed a generalist foraging population with dietary niche variation among individuals that targeted mixtures of macroalgae, seagrasses and mangrove. Green turtles showed a slight preference for green algae ( Ulva sp.) at both sites. The mean Fulton’s body condition index for juvenile turtles was 1.14 (SE\u2009=\u2009\u2009±\u20090.03; n \u2009=\u200972), which is comparable to values reported elsewhere, and indicates that these turtles were not under-nourished. This is intriguing in light of the paucity of local food resources, and perhaps due to the absence of large sub-adults and adults with higher food demand, and/or individual dietary niche variation among resident turtles, both of which reduce competition among local green turtles for the region’s available resources.