• Energy Research

Some methods of tissue preservation have significant effects on values of stable isotopes of carbon (delta(13)C) and nitrogen (delta(15)N), but studies on this topic are scattered in the literature. The goals of this study were to (1) summarize the results from studies of preservation effects in the literature and (2) test the effects of four common preservatives on delta(13)C and delta(15)N in epidermis tissue of three turtle species. Turtle tissue samples were subjected to up to five time intervals in five methods of preservation: drying at 60 degrees C for 24 h (the control), immersion in a 70% ethanol solution, immersion in a saturated NaCl aqueous solution, freezing at -10 degrees C in a frost-free freezer, and immersion in a dimethyl sulfoxide (DMSO)-ethylenediaminetetraacetic acid buffer. The delta(13)C and delta(15)N values for tissues preserved in 70% ethanol and NaCl aqueous solution were not significantly different from those of tissues dried at 60 degrees C, but samples preserved in DMSO were significantly different from dried samples. Freezing preservation had a significant effect on delta(13)C and delta(15)N at 60 d, which may have resulted from the use of a frost-free freezer. The effects of 20 different preservative methods on delta(13)C and delta(15)N in different tissues are summarized.

AbstractWhat happens in meadows after populations of natural grazers rebound following centuries of low abundance? Many seagrass ecosystems are now experiencing this phenomenon with the recovery of green turtles (Chelonia mydas), large‐bodied marine herbivores that feed on seagrasses. These seagrass ecosystems provide a rare opportunity to study ecosystem‐wide shifts that result from a recovery of herbivores. We evaluate changes in regulation of seagrass productivity in a naturally grazed tropical ecosystem by (1) comparing Thalassia testudinum productivity in grazed and ungrazed areas and (2) evaluating potential regulating mechanisms of T. testudinum productivity. We established 129 green turtle exclusion cages in grazed and ungrazed areas to quantify T. testudinum growth (linear, area, mass, productivity : biomass [P:B]). In each exclosure, we recorded temperature, irradiance, water depth, nitrogen : phosphorus ratio (N:P) of blade tissue, grazing intensity before cage placement, and T. testudinum structural and nutrient characteristics. Thalassia testudinum exhibited compensatory growth in grazed areas via stimulated blade linear growth, blade area growth, and P:B across seasonal high and low growth periods and in shallow (3–4 m) and deep (9–10 m) seagrass meadows. Irradiance, depth, and N:P ratios had significant roles in regulating mass growth and P:B of T. testudinum in ungrazed areas. Depth was a significant regulating factor of mass growth and P:B in grazed areas; rates were higher and more variable in shallow meadows than in deep meadows. Grazing intensity was also a significant regulating factor for P:B, stimulating tissue turnover with increasing grazing pressure. This study provides important insights into how recovery of a large marine herbivore can result in dramatic, sustainable changes in the regulation of seagrass productivity. We also highlight the need for a historical perspective and use of appropriate indicators, including P:B and grazing intensity, when evaluating seagrass response to green turtle grazing as meadows are returned to a natural grazed state. In an age of green turtle recovery and global seagrass decline due to anthropogenic threats, a thorough understanding of green turtle–seagrass interactions at the ecosystem level is critical to ensure the restoration of seagrass ecosystems and continued recovery of green turtle populations.

AbstractSeagrass meadows are important sites for carbon storage. Green turtles (Chelonia mydas) are marine megaherbivores that consume seagrass throughout much of their global range. With successful conservation efforts, turtle abundance will increase, leading to more meadows being returned to their natural grazed state. There is concern this may lead to a loss of carbon stored in these systems, but the effects of green turtle grazing on seagrass ecosystem carbon dynamics have not been investigated. Here we experimentally show that despite 79% lower net ecosystem production (NEP) following grazing (24.7 vs. 119.5 mmol C m−2 d−1) in a Caribbean Thalassia testudinum seagrass meadow, grazed areas maintained net positive metabolic carbon uptake. Additionally, grazing did not change the meadow production to respiration ratio, indicating it did not stimulate remineralization of sediment carbon stores. Compared to other published estimates of seagrass NEP (median: 20.6 mmol C m−2 d−1), NEP in grazed Caribbean T. testudinum meadows is similar to that in many other ungrazed systems. Our results demonstrate that while grazing does decrease potential future carbon sequestration as a result of lower NEP, it does not promote a metabolic release of current carbon stocks.

As climate-related impacts threaten marine biodiversity globally, it is important to adjust conservation efforts to mitigate the effects of climate change. Translating scientific knowledge into practical management, however, is often complicated due to resource, economic and policy constraints, generating a knowledge-action gap. To develop potential solutions for marine turtle conservation, we explored the perceptions of key actors across 18 countries in the Mediterranean. These actors evaluated their perceived relative importance of 19 adaptation and mitigation measures that could safeguard marine turtles from climate change. Of importance, despite differences in expertise, experience and focal country, the perceptions of researchers and management practitioners largely converged with respect to prioritizing adaptation and mitigation measures. Climate change was considered to have the greatest impacts on offspring sex ratios and suitable nesting sites. The most viable adaptation/mitigation measures were considered to be reducing other pressures that act in parallel to climate change. Ecological effectiveness represented a key determinant for implementing proposed measures, followed by practical applicability, financial cost, and societal cost. This convergence in opinions across actors likely reflects long-standing initiatives in the Mediterranean region towards supporting knowledge exchange in marine turtle conservation. Our results provide important guidance on how to prioritize measures that incorporate climate change in decision-making processes related to the current and future management and protection of marine turtles at the ocean-basin scale, and could be used to guide decisions in other regions globally. Importantly, this study demonstrates a successful example of how interactive processes can be used to fill the knowledge-action gap between research and management.

AbstractSomatic growth dynamics are an integrated response to environmental conditions. Hawksbill sea turtles (Eretmochelys imbricata) are long‐lived, major consumers in coral reef habitats that move over broad geographic areas (hundreds to thousands of kilometers). We evaluated spatio‐temporal effects on hawksbill growth dynamics over a 33‐yr period and 24 study sites throughout the West Atlantic and explored relationships between growth dynamics and climate indices. We compiled the largest ever data set on somatic growth rates for hawksbills – 3541 growth increments from 1980 to 2013. Using generalized additive mixed model analyses, we evaluated 10 covariates, including spatial and temporal variation, that could affect growth rates. Growth rates throughout the region responded similarly over space and time. The lack of a spatial effect or spatio‐temporal interaction and the very strong temporal effect reveal that growth rates in West Atlantic hawksbills are likely driven by region‐wide forces. Between 1997 and 2013, mean growth rates declined significantly and steadily by 18%. Regional climate indices have significant relationships with annual growth rates with 0‐ or 1‐yr lags: positive with the Multivariate El Niño Southern Oscillation Index (correlation = 0.99) and negative with Caribbean sea surface temperature (correlation = −0.85). Declines in growth rates between 1997 and 2013 throughout the West Atlantic most likely resulted from warming waters through indirect negative effects on foraging resources of hawksbills. These climatic influences are complex. With increasing temperatures, trajectories of decline of coral cover and availability in reef habitats of major prey species of hawksbills are not parallel. Knowledge of how choice of foraging habitats, prey selection, and prey abundance are affected by warming water temperatures is needed to understand how climate change will affect productivity of consumers that live in association with coral reefs.