Dispersal and Diving Adjustments of the Green Turtle Chelonia mydas in Response to Dynamic Environmental Conditions during Post-Nesting Migration

In response to seasonality and spatial segregation of resources, sea turtles undertake long journeys between their nesting sites and foraging grounds. While satellite tracking has made it possible to outline their migration routes, we still have little knowledge of how they select their foraging grounds and adapt their migration to dynamic environmental conditions. Here, we analyzed the trajectories and diving behavior of 19 adult green turtles (Chelonia mydas) during their post-nesting migration from French Guiana and Suriname to their foraging grounds off the coast of Brazil. First Passage Time analysis was used to identify foraging areas located off Ceará state of Brazil, where the associated habitat corresponds to favorable conditions for seagrass growth, i.e. clear and shallow waters. The dispersal and diving patterns of the turtles revealed several behavioral adaptations to the strong hydrodynamic processes induced by both the North Brazil current and the Amazon River plume. All green turtles migrated south-eastward after the nesting season, confirming that they coped with the strong counter North Brazil current by using a tight corridor close to the shore. The time spent within the Amazon plume also altered the location of their feeding habitats as the longer individuals stayed within the plume, the sooner they initiated foraging. The green turtles performed deeper and shorter dives while crossing the mouth of the Amazon, a strategy which would help turtles avoid the most turbulent upper surface layers of the plume. These adjustments reveal the remarkable plasticity of this green turtle population when reducing energy costs induced by migration.

Beach nourishment impacts on bacteriological water quality and phytoplankton bloom dynamics

A beach nourishment with approximately 1/3 fine-grained sediment (fines; particle diameter <63 μm) by mass was performed at Southern California's Border Fields State Park (BFSP). The nourishment was found to briefly (<1 day) increase concentrations of surf-zone fecal indicator bacteria (FIB) above single-sample public health standards [104 most probable number (MPN)·(100 mL)(-1)] but had no effect on phytoplankton. Contamination was constrained to the nourishment site: waters 300 m north or south of the nourishment were always below single-sample and geometric mean [≤ 35 MPN · (100 mL)(-1)] standards. Nourishment fines were identified as a source of the fecal indicator Enterococcus ; correlations between fines and enterococci were significant (p < 0.01), and generalized linear model analysis identified fines as the single best predictor of enterococci. Microcosm experiments and field sampling suggest that the short surf-zone residence times observed for enterococci (e-folding time 4 h) resulted from both rapid, postplacement FIB inactivation and mixing/transport by waves and alongshore currents. Nourishment fines were phosphate-rich/nitrogen-poor and were not correlated with surf-zone phytoplankton concentrations, which may have been nitrogen-limited.