Sea Turtles as Biological Transporters of Nutrients and Energy From Marine to Terrestrial Ecosystems

Abstract

Our study quantified the nutrients and energy introduced into the nesting beach at Melbourne Beach, Florida, from distant foraging grounds by loggerhead sea turtles, Caretta caretta. The fate of eggs deposited into 97 nests was determined by monitoring nests throughout incubation. The organic matter, energy, lipid, nitrogen, and phosphorus content of fresh eggs, eggs at successive stages of development, hatchlings, and hatching remains were determined. From these analyses, we estimated the flow of energy and nutrients introduced into the 14 305 nests (∼1.6 × 106 eggs) deposited in a 21‐km stretch of Melbourne Beach in 1996. We quantified the amount of energy and nutrients incorporated into each of four pathways: ingested by nest predators; consumed by detritivores, decomposers, and plants; lost as metabolic heat or gases during embryological development and hatching; or returned to the ocean as hatchlings. Each nest introduced a mean of 688 g of organic matter, 18 724 kJ of energy, 151 g of lipids, 72 g of nitrogen, and 6.5 g of phosphorus into the beach. Twenty‐five percent of the organic matter, 27% of the energy, 34% of the lipids, 29% of the nitrogen, and 39% of the phosphorus introduced into the nests returned to the ocean as hatchlings. Quantities of energy and nutrients transported by the turtles are comparable to quantities moved by other important biological transporters. Human activities have substantially altered the quantity of energy and nutrients transported, and the distribution of those nutrients on the beach. By introducing nutrients into beach ecosystems, sea turtles may help maintain stable dune systems that are critical to their reproductive success.

The Plight of Reptiles as Ecological Actors in the Tropics

“…Tortoise and turtles are proficuous seed dispersers and the research produced to date can be summarized in a metanalysis to identify specific gaps and conservation priorities, as has been done by Sobral-Souza et al (2017) regarding reintroductions. Nutrient movement performed by land-nesting aquatic reptiles can be accessed by stable isotope research, replicating the results obtained in sea turtles (Bouchard and Bjorndal, 2000). e. Increasing quantitative research on large reptile population ecology, with emphasis on density, abundance, and biomass; most threatened species lack any estimates.…”

“…While biogeochemical cycles determine the limits of nutrient flows from terrestrial to aquatic ecosystems, the movements of these organisms can partially reverse this trend (Helfield and Naiman, 2001). Large reptiles can act as nutrient transporters in two main ways: (a) through reproduction, when aquatic reptiles lay eggs in terrestrial environments (Bouchard and Bjorndal, 2000), and (b) through predation, when aquatic reptiles are killed and dragged onto land by terrestrial predators (Veríssimo et al, 2012). Due to reproduction being a risky phase of aquatic reptile life history, during which predation is common, those processes are not necessarily separate.…”

“…Reproduction-based nutrient transport can be demonstrated in the worldwide phenomena of turtles nesting on sandy beaches (Bouchard and Bjorndal, 2000). These annual events result in the terrestrial transfer of enormous volumes of nutrients originally gathered by turtles on aquatic feeding grounds.…”

Better Living Through Biogeochemistry

“…Conversely, some recent experiments show an important role of plant diversity in nutrient cycling, as seen in the greater losses of nitrogen in seepage waters beneath depauperate fields in Minnesota . On the other hand, rare and endangered species, such as the loggerhead sea turtle, can play a critical role in nutrient cycling in some ecosystems (Bouchard and Bjorndal 2000). One can argue that losses of the American chestnut and the passenger pigeon, which probably once dominated some forests of the eastern United States, did not lead to the collapse of those ecosystems.…”

The Role of Taboos in the Protection and Recovery of Sea Turtles

“…They serve keystone functions that collectively maintain healthy and diverse seagrass bed, coral reef, and beach dune habitats (Meylan, 1988;Bouchard and Bjorndal, 2000;Leon and Bjorndal, 2002;Bjorndal and Jackson, 2003). Sea turtles also help maintain a balanced trophic structure that benefits commercially valuable fish species (Houghton et al, 2006;Lynam et al, 2006).…”