The effects of turtle-introduced nutrients on beach ecosystems
- Authors: Le Gouvello Du Timat, Diane Zelica Marie
- Date: 2016
- Subjects: Sea turtles , Sea turtles -- Conservation , Green turtle
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/6959 , vital:21175
- Description: Resource subsidies are flows of nutrients from one ecosystem to another. Sandy beach ecosystems are at the interface between land and sea and thus receive nutrients from both land/seascapes. The seasonal nesting of sea turtles introduces large inputs of eggs, and so nutrients, onto sandy beach ecosystems, but little is known about the effects of these spatially and temporally variable nutrient input pulses on the dynamics of consumers in the recipient system. In this study, I examined the ecological role of sea turtles as vectors of nutrients that introduce large amounts of nutrients (in the form of eggs) from distant foraging grounds into nutrient-poor beach ecosystems. Although some of the nutrients return to the sea in the form of hatchlings, nutrients from unhatched and depredated eggs, dead and predated hatchlings, as well as chorioallantoic fluid and egg shells remain on the beach and presumably enter sandy beach food webs. I hypothesized that turtle nutrients significantly increase the availability of nutrients to sandy beach ecosystems and that those nutrients are incorporated by both terrestrial and marine food webs. These hypotheses were tested by comparing isotopic signatures of 13C and 15N of consumers on beaches with high and low turtle nest densities. The response of meiofauna to the decomposition of turtle eggs was also investigated. I predicted that meiofaunal abundance is positively affected by turtle nutrients and that higher meiofaunal abundances will be obtained in decomposing, depredated nests. I tested this hypothesis by comparing meiofaunal abundance in naturally predated nests to densities away from turtle nests (as a control). An in situ experiment that mimics conditions of naturally predated sea turtle nest, was set up to test meiofaunal community responses to turtle nutrients over time. The study indicates that sea turtle eggs represent a short pulsed resource subsidy that increases the nutrient and energy budget of sandy beach ecosystems. The results show that of the five potential nutrient pathways tested, ghost crabs appear to consume egg nutrients in measurable quantities, altering their diet and feeding behaviour according to food availability. The study also showed that there was a strong, but short-lived positive response of meiofauna to the introduction of nutrients, with increased abundance of all taxa in predated nests and experimental treatments. This response was particularly strong for nematodes which peaked in abundance after seven days. I conclude that turtle-derived nutrients represent a pulsed resource subsidy that makes significant contribution to the energy budget of sandy beach/dune ecosystems.
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- Date Issued: 2016
Sea turtles as ocean ambassadors: opportunities and challenges
- Authors: Nel, Ronel
- Subjects: Sea turtles -- South Africa , Sea turtles -- Conservation , f-sa
- Language: English
- Type: text , Lectures
- Identifier: http://hdl.handle.net/10948/55258 , vital:51136
- Description: Sea turtles are ocean migrants that nest on the same beaches where they were born but forage on reefs and oceanic waters great distances away. Movement between these locations is sometimes years or even decades apart. Because of these broad-ranging movements and the many countries, they visit throughout their lives, effective conservation can only be achieved through international cooperation. However, wherever and whenever sea turtles come ashore, they fascinate people. Watching a sea turtle nest is like looking back through a window into deep time. This appearance and disappearing act of sea turtles create an enigma that elicits a multitude of disciplinary, inter-, and intradisciplinary teaching, research and engagement opportunities ranging from archaeology to social sciences, including tourism, biology and ecology, conservation and policy. In these different spheres, I operated over the last two decades to understand sea turtles, their biology and behaviour to affect their conservation. The biggest question I have pursued in my research career is to understand why the leatherback sea turtle population (Dermochelys coriacea) nesting in the iSimangaliso Wetland Park, South Africa, has not increased despite decades of protection. Another sea turtle species, namely loggerheads (Caretta caretta) nesting in the same area, experiencing similar conditions, has responded positively to conservation. Through two decades of research evaluating the intrinsic and extrinsic population drivers, such as reproductive output, age to maturity, natality and mortality, it seems evident that the population dynamics of sea turtles is much more complicated than what a simple population model would predict. From the literature, it is clear that other species, like the Mediterranean monk seal, red knot (a sandpiper) and other coastal species, are suffering a similar fate, i.e., lack of recovery despite conservation. These trends suggest that these species have become refugees in their own habitat. Marine habitats are transformed through human activities and may now be unsuitable to support larger populations under the current climate for these complex species. Current research is aimed to disentangle past and present distributions to assess if these species have responded by using alternative habitats over time or if there are body condition parameters (such as individual size, offspring size or survivorship, or metabolomics) that will point us in the direction to grow these endangered populations. Our research suggests that sea turtles, with their very complex life history facing multiple threats, live at the edge of success and extinction. Understanding and managing their path to success is a delicate balance with many aspects that need consideration.
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