beach

Abstract

Reconstruction of past conditions provides important information on how ecosystems have been impacted by climate change, but generally for microhabitats worldwide there are no long-term empirical measurements. In these cases, there has been protracted debate about how various large-scale environmental proxies can best be used to reconstruct local temperatures. Here we help resolve this debate by examining how well environmental proxies hindcast sand temperatures at nest depths for five sea turtle nesting sites across the world. We link instrumental air temperature and sea surface temperature records with empirical sand temperature observations in the Atlantic (Ascension Island and Cape Verde), the Indian Ocean (Chagos Archipelago), the Caribbean (St Eustatius) and the Pacific (French Polynesia). We found strong correlations between sea surface temperatures, air temperatures and sand temperatures at all our study sites. Furthermore, Granger causality testing shows variations in sea surface temperature and air temperature precede variations in sand temperatures. We found that different proxies (air or sea temperature or a combination of both) predicted mean monthly sand temperatures within <0.5°C of empirical observations. Reconstructions of sand temperatures over the last 170 years reveal a slight warming of temperatures (maximum 0.5°C per century). An analysis of 36 published datasets revealed that the gradient of the relationship between sand temperature and air temperature is relatively constant, suggesting long-term changes in sand temperature could be extended around the world to include nesting sites where there are no empirical measurements of sand temperature. Our approaches are likely to have utility for a range of microhabitats where there is an interest in long-term changes in temperature.

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Sargassum is a genus of brown macroalgae or seaweed that can be found in shallow waters or free floating in the ocean. Sargassum patches on the open sea drift along sea current and can aggregate into larger Sargassum rafts or long slicks. Sargassum seaweeds that accumulate in the Sargasso Sea originate from The Gulf of Mexico where it blooms in the spring. This Sargassum bloom is induced by nutrient loadings from land that are discharged via the Mississippi River into the sea. Sargassum is not directly harmful on sea, in fact diverse biotic communities and animal species such as fishes, sea turtles and invertebrate depend on the seaweed for shelter and food source. However, Sargassum can potentially damage coastal ecosystems such as mangroves and seagrass beds if it accumulates on the coast. Therefore, monitoring of pelagic Sargassum is of great importance for managing coastal ecosystems.

An unprecedented amount of pelagic Sargassum invaded the Caribbean islands in the summer of 2011. Masses of Sargassum seaweed piled up on beaches trapping sea turtles and releasing high concentration of toxic hydrogen sulphide gas when it decomposes. Beside sea turtles, local tourism was also affected by the Sargassum beaching which led to temporarily closure of hotel resorts and high-cleaning costs of beaches. Climate change and increasing nitrification of seas might indicate that the amount of Sargassum in the Caribbean Sea might increase substantially within the near future.

The main objective of this research is to use multispectral data to map and classify Sargassum patches on the east coast of Bonaire. Accurate Sargassum maps will be useful for the coastal management to assess the location and coverage of Sargassum mats that have washed up along the shores and beaches. Consequently, the extent to which these Sargassum seaweeds affect nearshore benthic habitats and mangrove ecosystems in east Bonaire can be evaluated too.

Sea Turtle Conservation Bonaire (STCB) was initiated in the early 1990s to protect the island’s marine turtle populations. Our current research and monitoring efforts, which were standardized more than a decade ago, include monitoring important nesting beaches around Bonaire, conducting intensive in-water netting and snorkel surveys (capture-markrecapture), and tracking post-breeding turtle migration using satellite telemetry. These techniques provide us with a better understanding of Bonaire sea turtles’ breeding success, abundance, health, residency duration, habitat quality, growth rates, migratory paths, distant feeding grounds, and threats.
During the 2013 season, we observed 77 nests at our index beach on Klein Bonaire. Total hawksbill (54) and loggerhead (23) nests documented there were similar to numbers observed during recent years. Across Bonaire and Klein Bonaire, we observed four species crawling 231 times, including 126 confirmed or suspected nests. Because our coverage of the island was not complete and weather conditions can quickly obscure crawls, these nation-wide figures represent the minimum number of crawls and nests that occurred on Bonaire and Klein Bonaire during 2013. As in previous years, nesting activities peaked during June through August. Thirty-four green turtle nests and a single leatherback nest were recorded in northeastern Bonaire, whereas hawksbills and loggerheads primarily nested on Klein Bonaire and beaches of southern Bonaire.
We observed green turtles and hawksbills along the west coast of Bonaire, around Klein Bonaire, and adjacent to Lac during snorkel surveys. Green turtle sightings were particularly high near Lac, and netting surveys also suggested large aggregations of green turtles in shallow, sea grass foraging sites of Lac. Green turtles documented there were larger than individuals reported elsewhere in Bonaire.
Five green turtles tagged in 2003 and 2006 were reported in Nicaragua’s sea turtle harvest, valuable data about sea turtle movements which complement our satellite tracking program. Unfortunately, incidences of fibropapillomatosis among green turtles were more widespread in 2013 than recent seasons.
In 2013, we tracked a post-nesting female hawksbill turtle using satellite telemetry from Bonaire to Honduras over a period of 85 days. The turtle passed through six national territorial waters, swimming over 5,000 km (3,000 mi) to reach a general area proven to be important foraging grounds for Bonaire breeding turtles.
We also outfitted a hawksbill with a datalogger to gather information on hawksbill habitat use and behaviors. The device, which collects GPS locations and depth information, was retrieved in July, 2013. Preliminary results are consistent with previously deployed dataloggers, indicating regular movements in and out of Lac Bay.
Sadly, we recorded 18 turtles stranded during 2013, 12 of which were found dead or had to be euthanized.
We will be undertaking several new research initiatives in the year ahead, including using our tagging data to estimate the total population of sea turtles using Bonaire’s waters (which will help to inform management policy) and to estimate the tremendous growth rates of green turtles in Lac, as well as reviewing our monitoring program to ensure that protocols are as efficient as possible.