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Beached Sargassum alters sand thermal environments: Implications for incubating sea turtle eggs
Abstract
Global environmental change has featured a rise in macroalgae blooms. These events generate immense amounts of biomass that can subsequently arrive on shorelines. Such a scenario has been playing out since 2011 in the tropical and subtropical Atlantic, where Sargassum spp. have been causing periodic ‘golden tides’ in coastal habitats. Here we describe impacts on sea turtle nesting ecology, with a focus on the below-ground thermal environment for incubating eggs. Sargassum may blanket the surface of beaches due to natural wave or wind energy and can be redistributed via anthropogenic beach cleaning. When it covers egg clutches, it may alter incubation temperatures and therefore affect both embryonic survival and primary sex ratios. To evaluate the thermal impacts of Sargassum, we measured sand temperatures with data loggers buried under Sargassum cover treatments on a beach in Antigua, West Indies. Our split-plot experiment also tested for effects from shade, season (summer versus autumn), and high rainfall events. We modeled temperatures with a mixed-effects model and, surprisingly, our most compelling finding suggested that Sargassum's effects on below-ground temperatures were contingent on season. Greater Sargassum cover was associated with a cooling effect in the summer but warming in the autumn. We assume that the model term for season integrates several climate-related factors that vary seasonally in the Eastern Caribbean and modulate Sargassum's impact, including windspeeds. Comparing estimated marginal means for the high-cover treatments versus the controls, Sargassum cover led to a 0.21 °C increase in the autumn and a 0.17 °C decrease in the summer; these thermal changes can significantly impact developmental outcomes for sea turtle embryos. Atlantic nesting beach managers should monitor this macroalgal phenomenon and can use these data to begin to infer impacts on sea turtle populations and develop potential management strategies.
Supplementary resource (1)
... Sargassum stranding occurs along the Gulf of Mexico coast, resulting in negative economic [9][10][11][12][13] and environmental [13][14][15] impacts. The development of Sargassum in this region has been attributed to increasing nitrogen inputs from various land-based sources, including the Mississippi River and its tributaries [3,16]. ...
... For pieces of Sargassum, approximately 2 g of sample dried powder was weighed in tin capsules for isotopic analysis. For POM, samples were duplicated: Only the subsamples that were not treated were analysed for δ 15 Results were reported in the δ unit notation and expressed as parts per thousand relative to the international standards atmospheric N 2 for nitrogen. Analytical precision based on replicate measurements (after every five samples) of Thermo-Acetanilide was <0.1 for δ 15 N values. ...
Since 2011, the Caribbean coasts have been subject to episodic influxes of floating Sargassum seaweed of unprecedented magnitude originating from a new area “the Great Atlantic Sargassum Belt” (GASB), leading in episodic influxes and mass strandings of floating Sargassum. For the biofilm of both holopelagic and benthic Sargassum as well as in the surrounding waters, we characterized the main functional groups involved in the microbial nitrogen cycle. The abundance of genes representing nitrogen fixation (nifH), nitrification (amoA) and denitrification (nosZ) showed the predominance of diazotrophs, particularly within the GASB and the Sargasso Sea. In both location, the biofilm associated with holopelagic Sargassum harboured a more abundant proportion of diazotrophs than the surrounding water. The mean δ15N value of the GASB seaweed was very negative (−2.04‰), and lower than previously reported, reinforcing the hypothesis that the source of nitrogen comes from the nitrogen-fixing activity of diazotrophs within this new area of proliferation. Analysis of the diversity of diazotrophic communities revealed for the first time the predominance of heterotrophic diazotrophic bacteria belonging to the phylum Proteobacteria in holopelagic Sargassum biofilms. The nifH sequences belonging to Vibrio genus (Gammaproteobacteria) and Filomicrobium sp. (Alphaproteobacteria) were the most abundant and reached respectively up to 46.0% and 33.2% of the community. We highlighted the atmospheric origin of the nitrogen used during the growth of holopelagic Sargassum within the GASB and a contribution of heterotrophic nitrogen-fixing bacteria to a part of the Sargassum proliferation.
... Second, emerging hatchlings will be unable to climb over Sargassum accumulations to reach the sea and will die of dehydration (Gavio and Santos-Martínez 2018). Less obviously, beached Sargassum can alter the thermal environment of the embryos within nests (Maurer et al. 2022), cooling in summer and warming in winter. Since the sex ratio of hatchlings is determined by their thermal history, this may have implications for population dynamics. ...
Sea turtle species have life cycles that have common features such as oviparity, nesting on sandy beaches, growing as juveniles in surface waters and moving to foraging grounds before migrating— often over long distances—to natal beaches to breed. They are therefore exposed to aquatic and terrestrial influences, both abiotic (e.g. temperature, weather) and biotic (e.g. food availability, predation). Humans have exploited sea turtles for millennia and pressure on their populations has increased dramatically during the ongoing Anthropocene as human influences have increased both in power and global reach. Fishing bycatches generated by powerful unselective gears have largely replaced direct fishing as an existential threat, but meat and egg poaching persist, while burgeoning global wildlife crime threatens sea turtles, especially hawksbills. Habitat loss caused by coastal development and exponential increases in beach-based tourism have reduced nesting success. Sustained losses of coral reef and seagrass habitats have removed foraging grounds for adult turtles and both habitat types are currently projected to disappear before 2100. Environmental degradation has taken several forms. Chemical pollution through the accumulation of organics and heavy metals have affected reproduction and facilitated the transmission of fibropapillomatosis. An emerging threat due to eutrophication also needs to be considered. Marine plastic pollution is already highly damaging to sea turtles; plastic fishing gears ‘ghost-fish’ indefinitely, capturing and killing all life-history stages except eggs, while ingestion of macro and microplastics blocks/damages guts. Rising global temperature has been identified as a potential existential threat for all species because of temperature-dependent sex determination and substantial sea level rise. However, climate change is also projected to cause an order of magnitude increase in the frequency of heat waves and extreme sea level highs, both of which can kill turtle embryos. This Praeger Review concludes with a description of sea turtle occurrences around the British Isles and the anthropogenic influences upon them.
... Second, emerging hatchlings will be unable to climb over Sargassum accumulations to reach the sea and will die of dehydration (Gavio and Santos-Martínez 2018). Less obviously, beached Sargassum can alter the thermal environment of the embryos within nests (Maurer et al. 2022), cooling in summer and warming in winter. Since the sex ratio of hatchlings is determined by their thermal history, this may have implications for population dynamics. ...
beaches, growing as juveniles in surface waters and moving to foraging grounds before migrating—
often over long distances—to natal beaches to breed. They are therefore exposed to aquatic and
terrestrial influences, both abiotic (e.g. temperature, weather) and biotic (e.g. food availability, preda
tion). Humans have exploited sea turtles for millennia and pressure on their populations has increased
dramatically during the ongoing Anthropocene as human influences have increased both in power
and global reach. Fishing bycatches generated by powerful unselective gears have largely replaced
direct fishing as an existential threat, but meat and egg poaching persist, while burgeoning global
wildlife crime threatens sea turtles, especially hawksbills. Habitat loss caused by coastal development
and exponential increases in beach-based tourism have reduced nesting success. Sustained losses of
coral reef and seagrass habitats have removed foraging grounds for adult turtles and both habitat types
are currently projected to disappear before 2100. Environmental degradation has taken several forms.
Chemical pollution through the accumulation of organics and heavy metals have affected reproduc
tion and facilitated the transmission of fibropapillomatosis. An emerging threat due to eutrophica
tion also needs to be considered. Marine plastic pollution is already highly damaging to sea turtles;
plastic fishing gears ‘ghost-fish’ indefinitely, capturing and killing all life-history stages except eggs,
while ingestion of macro and microplastics blocks/damages guts. Rising global temperature has been
identified as a potential existential threat for all species because of temperature-dependent sex deter
mination and substantial sea level rise. However, climate change is also projected to cause an order of
magnitude increase in the frequency of heat waves and extreme sea level highs, both of which can kill
turtle embryos. This Praeger Review concludes with a description of sea turtle occurrences around
the British Isles and the anthropogenic influences upon them
... But some impacts are in evidence; for example, sea level rise is expected to impact nesting site availability and quality for sea turtles, while warming temperatures can affect sex ratio of offspring. 323,324 Refugia have potential to mitigate some extinction risks for species able to take advantage of them, but the evidence base is fairly new. Further, emerging modeling studies have indicated that these areas, too, are at risk; for example, Ebersole et al. (2020) 127 found that under a 4°C (7.2°F) warming scenario, there was a >50% probability that refugia for freshwater fish species would decrease in area by 42%-77% by 2070. ...
... The large concentrations of Sargassum, for example, affect the reproductive cycle of sea turtles, making it difficult for the mothers to climb to the beaches. Additionally, they impact the emergence of hatchlings after the hatching of the nests [11][12][13][14]. These concentrations also lead to the death of marine species due to reduced light and oxygen in the seas, and they adversely affect the growth of corals. ...
The Sargassum have become a cyclical phenomenon that generates ecological, economic, and social problems in the Caribbean. The situation becomes more serious in a context of voluntary acceptance of the problem, which generates difficulties regarding the behaviors to control it. This research addresses the phenomenon from the perspective of risk perception concerning Sargassum invasions in the Dominican Republic, using a tool that includes perceptual and behavioral questions. The results show an underestimation of the risk of Sargassum blooms attributed to its interpretation as a natural and inevitable phenomenon, with an insignificant effect. This underestimation does not notably affect the health or standard of living of the population involved but has not been sufficiently addressed by scientific institutions and the Dominican government. The alert about some erroneous beliefs regarding the phenomenon, as shown by these perceptions, can contribute to designing successful policies for the control and management of massive influx of Sargassum. This transformation can turn them from an environmental problem into an opportunity for sustainable development. Based on the risk analysis, actions are suggested to guarantee the sustainable management of Sargassum blooms in the Dominican Republic.
... Careful consideration should therefore be given to the spatio-temporal patterns of turtle nesting distribution and hatchling emergence if in-water sargassum harvesting is to be implemented. On the other hand, it is worth noting that whilst in-water harvesting of sargassum can pose a risk to turtle post-hatchlings, sargassum inundations also pose a significant risk to turtle hatchling survival by preventing their off-shore migration and increasing their vulnerability to predation and additional threats and can also impede nesting adults (Maurer et al., 2021(Maurer et al., , 2022. ...
Tropical Atlantic blooms of pelagic Sargassum species are associated with severe inundation events along the coasts of Caribbean and West African nations that cause extensive ecological and socioeconomic harm. The use of in-water harvesting as a management strategy avoids the plethora of challenges associated with shoreline in-undations. Moreover, with a growing interest in the valorisation of this raw material, in-water harvesting provides the best opportunity to collect substantial amounts of 'fresh' sargassum that can be used in a variety of applications. However, in-water harvesting of sargassum will remove organisms associated with the floating habitat, resulting in loss of biodiversity, thus creating a potential management dilemma. To address this management concern, we assessed the clinging fauna associated with sargassum rafts at various distances from shore. From a total of 119 dipnet samples of sargassum, we recorded 18 taxa, across 6 phyla (Arthropoda, Mollusca, Chordata, Platyhelminthes, Nemathelminthes, Annelida) with the phylum Arthropoda being the most speciose (n = 10). Our multivariate and model selection analyses support that distance from shore and season are the most important drivers of variability in community composition and that season is the most important driver of individual abundance and number of taxa across samples. Overall, rafts within 0-3000 m of the shoreline of Barbados harbored low biodiversity and were dominated by small invertebrates (mean size: 5.5 mm) of no commercial value. Results suggest that biodiversity trade-offs associated with in-water sargassum harvesting in coastal areas are likely to be negligible.
... Observed decreases in annual abundance of nesting turtles could be realized through changes to survival and/or nesting frequency (i.e. annual breeding probability). It is unlikely that changes to transience have played a major role (Kendall et al., 2019;Levasseur et al., 2019;, and although changes to nesting habitat have occurred (Maurer et al., 2015;Maurer, Gross & Stapleton, 2022; While an in-depth regional synthesis is merited, some initial et al., 2007). In tandem with better-described distributions for nesting habitats, this approach to exploring foraging area-derived population connectivity would be a powerful tool for conservation by giving practitioners a better sense of the necessary spatial and geopolitical scales of their efforts. ...
Outside of short, infrequent visits to reproductive habitats, sea turtle lifespans are largely spent in foraging areas. Supporting imperilled populations in an era of biodiversity declines and environmental change requires improvements in the understanding of foraging distributions, plus the migratory corridors that connect foraging and reproductive habitats.
This study evaluates the migratory strategies and foraging geography of hawksbill sea turtles ( Eretmochelys imbricata ) in the Western Atlantic. The post‐nesting migrations of 22 females were tracked via satellite telemetry from Long Island, Antigua, during 2016–2019, and a state‐space model was utilized to estimate true turtle locations from Argos satellite fixes. Model output was used to characterize migratory routes and home ranges occupied during non‐migratory inter‐nesting and foraging periods.
Hawksbill migrations ( N = 19) resulted in displacements to foraging areas ranging 7–2300 km. Foraging geography varied considerably—whereas eight turtles remained in the immediate vicinity of Antigua and Barbuda (<30 km), there were also longer‐distance migrations (>470 km) to locations such as The Bahamas and Nicaragua. Inter‐nesting core home ranges (50% utilization distributions) ranged from 7 to 72 km ² , while foraging core areas ranged from 7 to 46 km ² .
These results add to evidence suggesting that, broadly, post‐nesting hawksbills forage in neritic habitats throughout the Wider Caribbean, including several high‐use areas. Short displacements to foraging habitats relatively nearby to nesting beaches appear to be the most common migratory behaviour, but individuals in a single population may exhibit various migratory strategies, resulting in basin‐wide connectivity between nesting and foraging sites. Given that a single individual or nesting population may inhabit several management jurisdictions, an idealized scenario for regional hawksbill conservation would entail data sharing between managers at linked nesting areas, foraging habitats and migratory corridors such that policies to protect key habitats and mitigate human impacts are designed and evaluated based on best‐available science.
... The origins of the sudden and recurring increased of Sargassum abundance still remain unclear (Ardhuin et al. 2019), and different hypotheses are proposed such as an increase in (i) sea surface temperature (Sissini et al. 2017), (ii) nutrients released from Amazon and Congo rivers (Oviatt et al. 2019), and (iii) deposition of dust from African desert (Johns et al. 2020). The stranding of Sargassum spp. on the coast areas have ecological issues threatening marina fauna (Cipolloni et al. n.d.;Rodríguez-Martínez et al. 2019) including endangered species such as sea turtles (Maurer et al. 2022(Maurer et al. , 2015Ross and Casazza 2008) and can lead to the disappearance of coastal ecosystems (Gledhiir and Buck 2012;van Tussenbroek et al. 2017). Decomposition of abundant brown algae biomass accumulated in coastal environment liberates toxic hydrogen sulfide (H 2 S) (Reiffenstein et al. 1992) provoking important human health issues such as respiratory diseases, neurological problems, and cardiovascular lesions (Resiere et al. 2018). ...
Since 2011, the Caribbean Islands have experienced unprecedented stranding of a pelagic brown macroalgae Sargassum inducing damages for coastal ecosystems and economy. This study measures the kinetics of metal trace elements (MTE) in Sargassum reaching different coastal environments. In July 2021, over a period of 25 days, fixed experimental floating cages containing the three Sargassum morphotypes (S. fluitans III and S. natans I and VIII) were placed in three different coastal habitats (coral reef, seagrass, and mangrove) in Guadeloupe (French West Indies). Evolution of biomasses and their total phenolic content of Sargassum reveals that environmental conditions of caging were stressful and end up to the death of algae. Concentrations of 19 metal(loid) trace elements were analyzed and three shapes of kinetics were identified with the MTE that either concentrate, depurate, or remains stable. In the mangrove, evolution of MTE was more rapid than the two other habitats a decrease of the As between 70 and 50 μg g−1 in the mangrove. Sargassum natans I presented a different metal composition than the two other morphotypes, with higher contents of As and Zn. All Sargassum morphotype are rapidly releasing the metal(oid)s arsenic (As) when they arrive in studied coastal habitats. In order to avoid the transfer of As from Sargassum to coastal environments, Sargassum stranding should be avoided and their valorization must take into account their As contents.
... Climate change also can lead to macroalgae blooms (Sargassum spp.) that might invade nesting areas of sea turtles in tropical and subtropical regions. Sargassum cover may not only affect the access of female sea turtles to their nesting beaches, but also alter nest temperatures and induce hypoxic conditions, thereby affecting embryonic survival or offspring sex ratios [158][159][160]. Changes in temperature and moisture can have dramatic effects on rates of spread of invasive weeds, potentially shading (and thus cooling) natural nest sites for many reptiles. ...
A range of abiotic parameters within a reptile nest influence the viability and attributes (including sex, behaviour and body size) of hatchlings that emerge from that nest. As a result of that sensitivity, a reproducing female can manipulate the phenotypic attributes of her offspring by laying her eggs at times and in places that provide specific conditions. Nesting reptiles shift their behaviour in terms of timing of oviposition, nest location and depth of eggs beneath the soil surface across spatial and temporal gradients. Those maternal manipulations affect mean values and variances of both temperature and soil moisture, and may modify the vulnerability of embryos to threats such as predation and parasitism. By altering thermal and hydric conditions in reptile nests, climate change has the potential to dramatically modify the developmental trajectories and survival rates of embryos, and the phenotypes of hatchlings. Reproducing females buffer such effects by modifying the timing, location and structure of nests in ways that enhance offspring viability. Nonetheless, our understanding of nesting behaviours in response to climate change remains limited in reptiles. Priority topics for future studies include documenting climate-induced changes in the nest environment, the degree to which maternal behavioural shifts can mitigate climate-related deleterious impacts on offspring development, and ecological and evolutionary consequences of maternal nesting responses to climate change.
This article is part of the theme issue ‘The evolutionary ecology of nests: a cross-taxon approach’.
... Journal-Agrarian and Natural Resource Economics In addition, the incubation temperature between 29°C and 29.5°C, suffered an increase of 0, 21°C in autumn Maurer et al., 2021a, Maurer et al., 2021b, and a decrease of 0.17°C in summer, over which the percentage of female offspring increased from 17% at 85%, and Andrew S. et al., 2022. In 2018, the Mexican Caribbean coast received a massive influx of pelagic Sargassum SPP. that accumulated and decomposed on the beaches turning the water brown in color. ...
The invasive presence of pelagic sargassum on the coasts has increased disproportionately in the last decade, causing great damage to the ecosystems of coastal and marine flora, and fauna, as well as the tourism sector, due to the fact that the sargassum when it enters into decomposition generates fetid odors, detachments of Ammonium concentrations and Hydrogen Sulfide H2S that together with hypoxic conditions were the mass death cause of species, therefore it is necessary to clean affected areas. The aim of this research was to analyze how to reduce erosion in beach dunes, through the technological implementation for the treatment of the mixture sand - dead pelagic sargassum. The methodology had a mixed approach to propose the application of centrifugation and precipitation technologies to significantly reduce beach dunes erosion. However, the machines that do not have this process present a sand-sargassum mixture as residue that, when removed, erodes the dunes. The results obtained were the proposal for the implementation of a new complementary process to those carried out by beach cleaning machines to reduce erosion, in addition to compacting the sargassum for its transfer optimization.
... This massive accumulation of algae has had a great environmental and economic impact, especially for the tourism sector, which is of great importance for the inhabitants of the Mexican Caribbean. In addition to the economic impact on tourism, it can also have a strong impact on the ecosystem: beach erosion due to removal efforts; temperatures that can be lethal for turtle embryos; nearshore fauna, such as coral colonies and seagrasses, can be affected by the change in light condition, oxygen level, and temperature [2][3][4]. ...
Since 2011, significant and atypical arrival of two species of surface dwelling algae, Sargassum natans and Sargassum Fluitans, have been detected in the Mexican Caribbean. This massive accumulation of algae has had a great environmental and economic impact. Most works addressing this topic use high-resolution satellite imagery which is expensive or may be time delayed. We propose to estimate the amount of Sargassum based on ground-level smartphone photographs that, unlike previous approaches, is much less expensive and can be implemented to make predictions almost in real time. Another contribution of this work is the creation of a Sargassum images dataset with more than one thousand examples collected from public forums such as Facebook or Instagram, labeled into 5 categories of Sargassum level (none, low, mild, plenty, and excessive), a relevant difference with respect to previous works, which only detect the presence or not of Sargassum in a image. Several state-of-the-art convolutional networks: AlexNet, GoogleNet, VGG, and ResNet, were tested using this dataset. The VGG network trained under fine-tuning showed the best performance. The results of the carried out experiments show that convolutional neuronal networks are adequate for providing an estimate of the Sargassum level only from smartphone cameras images.
... Whether males exhibit similar migratory patterns merits further study. Hawksbills are highly imperiled in this region (Mortimer and Donnelly 2008) and face threats from human activities and global environmental change (Hamann et al. 2013;Maurer et al. 2015Maurer et al. , 2021aMaurer et al. , 2021bMaurer et al. , 2022. Because the recovery of the Caribbean population will depend in part upon survival of adults, especially considering their high reproductive value (Crouse et al. 1987), identifying and protecting adult migratory and foraging habitats should be among our top priorities for conserving this species. ...
Adult female sea turtles are highly migratory, moving between foraging and nesting areas that can be thousands of kilometers apart. Conserving sea turtles and their habitats therefore depends on knowledge of space use across these migration-linked environments. Here, we describe migratory behavior of hawksbill sea turtles (Eretmochelys imbricata), a globally imperiled species. We used satellite telemetry to characterize the movements of females from nesting areas in Jamaica (n = 4) and Antigua (n = 4), West Indies, over 1998–2001. We mapped migrations and summarized space use during inter-nesting and foraging periods with kernel utilization distributions (UDs) and minimum convex polygons. Seven of eight turtles made post-nesting migrations, with paths ranging 56–1324 km in length, representing straight-line displacements of 68–1206 km. Two turtles sampled in southern Jamaica made short-range migrations within southern Jamaican waters, whereas two from northern Jamaica migrated further to foraging areas in the waters of Belize and Honduras. Three migrants sampled at Long Island, Antigua migrated to St. Eustatius, St. Kitts, and Redonda, respectively, with a fourth individual remaining resident in northeastern Antigua. Inter-nesting movements observed for three turtles produced 50% UDs ranging 12–44 km2, with centroid depths between 4–13 m. Foraging UDs for seven turtles spanned 8–111 km2 and 2–161 m in depth. Our results reveal variable migratory strategies, demonstrate international connectivity between hawksbill foraging and nesting habitats, and provide important information for Caribbean conservation efforts such as the design of protected areas or fisheries policies.
... The origins of the sudden and recurring increased of Sargassum abundance still remain unclear (Ardhuin et al. 2019), and different hypotheses are proposed such as an increase in (i) sea surface temperature (Sissini et al. 2017), (ii) nutrients released from Amazon and Congo rivers (Oviatt et al. 2019), and (iii) deposition of dust from African desert (Johns et al. 2020). The stranding of Sargassum spp. on the coast areas have ecological issues threatening marina fauna (Cipolloni et al. n.d.;Rodríguez-Martínez et al. 2019) including endangered species such as sea turtles (Maurer et al. 2022(Maurer et al. , 2015Ross and Casazza 2008) and can lead to the disappearance of coastal ecosystems (Gledhiir and Buck 2012;van Tussenbroek et al. 2017). Decomposition of abundant brown algae biomass accumulated in coastal environment liberates toxic hydrogen sulfide (H 2 S) (Reiffenstein et al. 1992) provoking important human health issues such as respiratory diseases, neurological problems, and cardiovascular lesions (Resiere et al. 2018). ...
Since 2011, the Caribbean Islands have witnessed unprecedented massive stranding of a pelagic brown algal Sargassum spp. inducing damages for coastal ecosystems and economy. By accumulating heavy metals, Sargassum can play a role in contaminant transportation from offshore to the coast. In 2019, three genotypes of Sargassum (S. fluitans III, S. natans I, and VIII) were sampled in seven stations along a 3400 km transect in the Atlantic Ocean. Concentrations of 15 heavy metal(loid)s elements were analyzed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). Mean metal concentrations were ranked following descending order: As >Fe > Al > Mn > Cd > Zn > Ni > V > Cu > Cr > Hg. The metalloid As was the most abundant contaminant with a maximum value of 115 ppm, previously observed in the Caribbean area (80–150 ppm). At Atlantic Ocean Basin-scale, metallic element concentrations do not present spatial longitudinal gradients. Genotypes S. fluitans III and S. natans (I and VIII), present differents metal(loid)s contamination distinct patterns.
There have been beaching events of the marine alga pelagic sargassum in coastal regions of the Caribbean Sea, West African countries, and the north-northeast region of Brazil since 2011. Its presence has caused environmental and socioeconomic impacts while several studies were conducted in order to understand the causes of this phenomenon, as well as alternatives to mitigate its impacts. The objective of this research was to evaluate pelagic sargassum biomass from beaching as a raw material for the manufacture of medium-density multilayer particleboards, aiming for an application that can reduce the impacts generated by the disposal of this seaweed on beaches and landfills. These are composed of 30% sargassum particles in their inner layer and 70% sugarcane bagasse particles on their outer layers, which are bonded with castor-oil-based polyurethane resin. A physical and chemical characterization was carried out in order to evaluate sargassum particles while physical and mechanical tests were carried out in order to evaluate the panels. Results were subsequently compared with indications from different particleboard standards. A life cycle assessment was carried out to complement the feasibility study of these panels and to compare their different manufacturing processes. The multilayer panels met the minimum requirements for physical and mechanical properties established by regulations, indicating that the Sargassum spp. biomass can be used as filling. The life cycle assessment study indicates that sargassum panels produced in the Belém, PA, Brazil, region present lower environmental impacts in four of seven evaluated categories when compared to conventional panels. Given the results obtained, the use of sargassum from beaching events as raw material for panels can be presented as an alternative for reducing social, economic, and environmental impacts in the regions affected by these events.
Citation: Lyra, G.P.; Colombo, A.L.; Duran, A.J.F.P.; Parente, I.M.S.; Bueno, C.; Rossignolo, J.A. The Use of Sargassum spp. Ashes Like a Raw Material for Mortar Production: Composite Performance and Environmental Outlook. Materials 2024, 17, 1785. https://doi. Abstract: The accumulation of brown algae from the genus Sargassum has been increasing over the years in coastal regions of the Caribbean, Africa, Brazil, and Mexico. This causes harmful effects to the ecosystem, human health, the economy, and the climate due to gas emissions from its decomposition process. There is the possibility of this biomass being reused in civil construction, and some studies have been carried out on its application to common Portland cement mortar. As such, the objective of this study is to evaluate the potential of sargassum ash as a mineral addition to partially replace fine aggregates in Portland cement mortar. Characterization of the raw materials was carried out through X-ray fluorescence spectroscopy, loss on ignition, particle size distribution, Brunauer-Emmett-Teller (BET) analysis, real density, X-ray diffraction, scanning electron microscopy, and dispersion spectroscopy of electrons. The mortars were prepared by partially replacing the fine aggregate (sand) with sargassum ash at 0%, 5%, 10%, and 20%. Mortar performance was evaluated through water absorption, apparent porosity, apparent specific mass, and compressive strength 7, 28, and 63 days after curing. Lastly, a life cycle assessment was conducted in accordance with ISO standards 14040:2006 and 14044:2006. The results showed that replacing sand with sargassum ash increases water absorption and apparent porosity, and decreases the apparent specific mass and compressive strength as replacement increases. Nevertheless, the compressive strength results after 63 days for 5 and 10% replacement did not differ statistically from reference values. The life cycle assessment indicated that mortars with partial replacement of sand by sargassum ash show positive environmental impacts when compared to reference values for most categories, regardless of the scenario analyzed, especially for mortar with 10% replacement. As such, the use of sargassum ash at 10% does not alter the mortar's compressive strength values after 63 days, but does reduce its environmental impact. The application of this biomass in civil construction materials provides a destination for this algae, and that can be a solution to mitigate the social, environmental, and economic problems it has been causing.
Tropical Atlantic blooms of pelagic Sargassum spp. present major socioeconomic and ecological challenges for Caribbean and West African nations. Valorisation of sargassum provides an opportunity to ameliorate some of the damage to national economies; however, the active uptake of arsenic by pelagic sargassum creates significant barriers to its use. When defining valorisation pathways, it is important to understand arsenic speciation in pelagic sargassum, given the different levels of toxicity associated with different arsenic species. In this study, we assess the temporal variability of total arsenic and inorganic arsenic in pelagic sargassum arriving in Barbados; and test whether arsenic concentrations are linked to oceanic sub-origins. Results indicate that inorganic arsenic, the most toxic form, represents a consistent and substantial percentage of the total arsenic present in pelagic sargassum, and that variability in arsenic concentration does not appear to be driven by sample months, years or oceanic sub-origins/transport pathways.
One characteristic of global change is an increase in the frequency and magnitude of algae blooms. Although a large body of work has documented severe ecological impacts, such as mortality due to toxins or hypoxia, less research has described sublethal effects that may still affect population dynamics. Here, we focus on blooming Sargassum macroalgae in the North Atlantic and describe effects on nesting sea turtles. Since 2011, large masses of the algae have been inundating Atlantic nesting habitats. We documented the accumulation of Sargassum at Long Island, Antigua, and quantified effects on a rookery of hawksbill sea turtles (Eretmochelys imbricata). Using monitoring data from 2010–2019, we analyzed population- and individual-level patterns in nesting. Our results suggest that sea turtles respond to Sargassum at nesting beaches by shifting space use away from heavily impacted areas. We also tested for an effect on nesting success, but found no change in the years and areas most impacted by Sargassum. The algae may not increase the energetic costs of nesting after a turtle has emerged onto the beach, but we speculate that costs are imposed in algae-filled waters as turtles initially seek to emerge. As the Sargassum “invasion” continues, sea turtles at impacted sites will need to exhibit plasticity when choosing nesting sites, and nest densities may increase in areas with less Sargassum present. Individuals may also be required to expend more energy per nesting season. More broadly, this work demonstrates that algae blooms can have sublethal effects on fauna that affect population dynamics.
The pelagic brown macroalgae Sargassum spp. have grown for centuries in oligotrophic waters of the North Atlantic Ocean supported by natural nutrient sources, such as excretions from associated fishes and invertebrates, upwelling, and N2 fixation. Using a unique historical baseline, we show that since the 1980s the tissue %N of Sargassum spp. has increased by 35%, while %P has decreased by 44%, resulting in a 111% increase in the N:P ratio (13:1 to 28:1) and increased P limitation. The highest %N and δ15N values occurred in coastal waters influenced by N-rich terrestrial runoff, while lower C:N and C:P ratios occurred in winter and spring during peak river discharges. These findings suggest that increased N availability is supporting blooms of Sargassum and turning a critical nursery habitat into harmful algal blooms with catastrophic impacts on coastal ecosystems, economies, and human health. The macroalgae Sargassum has grown for centuries in the oligotrophic North Atlantic supported by natural nutrient sources and cycling. Here the authors show that changes in tissue nutrient contents since the 1980s reflect global anthropogenic nitrogen enrichment, causing blooms in the wider Atlantic basin.
Sea turtles present a model for the potential impacts of climate change on imperiled species, with projected warming generating concern about their persistence. Various sea turtle life-history traits are affected by temperature; most strikingly, warmer egg incubation temperatures cause female-biased sex ratios and higher embryo mortality. Predictions of sea turtle resilience to climate change are often focused on how resulting male limitation or reduced offspring production may affect populations. In the present article, by reviewing research on sea turtles, we provide an overview of how temperature impacts on incubating eggs may cascade through life history to ultimately affect population viability. We explore how sex-specific patterns in survival and breeding periodicity determine the differences among offspring, adult, and operational sex ratios. We then discuss the implications of skewed sex ratios for male-limited reproduction, consider the negative correlation between sex ratio skew and genetic diversity, and examine consequences for adaptive potential. Our synthesis underscores the importance of considering the effects of climate throughout the life history of any species. Lethal effects (e.g., embryo mortality) are relatively direct impacts, but sublethal effects at immature life-history stages may not alter population growth rates until cohorts reach reproductive maturity. This leaves a lag during which some species transition through several stages subject to distinct biological circumstances and climate impacts. These perspectives will help managers conceptualize the drivers of emergent population dynamics and identify existing knowledge gaps under different scenarios of predicted environmental change.
Relative organic content in sediment is an important determinant of ecological processes, but it can be difficult to quantify in the field. Here, we present evidence that relative organic matter content of sand may be inferred from relative coloration. For 50 sand samples collected from a beach on Long Island, Antigua, West Indies, we characterized sand color intensity (brightness) using image analysis of standardized photographs and measured percent organic matter lost on ignition with dry combustion. A linear regression provided evidence for a strong negative relationship between brightness and organic content; darker-colored sand contained more organic matter. Inferring organic content from color may provide a simple way to make field-based qualitative assessments of an important parameter in beach habitats.
While most studies assessing the ecological impacts of climate change have examined impacts from warming temperatures, less attention has been given to other parameters such as increased rainfall events. At a nesting rookery in the northern Great Barrier Reef, Australia, we used data loggers to examine the impact of heavy rainfall and shade on the nest temperatures for green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles clutches, which have temperature-dependent sex determination. In the middle of the nesting season (December–March), on 21 January 2019, 125 mm of rain fell over two days, causing the temperature to initially decrease by an average of ~ 3.6 °C in hawksbill turtle nests (n = 18) and ~ 3.5 °C in green turtle nests (n = 9). For shaded clutches during the 20-day cooling period after the rainfall event, we report average nest temperatures of ~ 27.9 °C and ~ 28.2 °C for hawksbill and green turtle clutches respectively, falling well into the male-producing range for sex determination. This was profoundly cooler than the average nest temperatures of clutches without shade and prior to the heavy rainfall, which was ~ 31.3 °C for both species. Extreme rainfall events are predicted to increase around Australia due to climate change but may help counteract impacts of atmospheric warming on sea turtle offspring sex-ratios. Our results also show the potential for artificially cooling nests by applying a combination of shade and irrigation, to counter the expected increases in the feminisation of sea turtle hatchling production worldwide.
The geographic specificity of natal philopatry (how precisely breeding individuals return to their natal origins) influences breeding biology, genetic diversity and habitat range, and therefore has important implications for species resiliency and management. Also, the age at which individuals reach sexual maturity and enter the breeding population is a vital parameter for demographic analyses. Empirical research on philopatry and maturation, however, is challenging for long‐lived animals that are difficult to observe, such as marine turtles that have complex oceanic life histories. Regional natal philopatry is well established for marine turtles, but the geographic specificity of philopatry is unclear. Similarly, estimates of age at maturity vary widely, and direct evidence is lacking. Here, we targeted these information gaps by assessing kinship among 256 females from Antigua’s Jumby Bay (JB) hawksbill turtle rookery, a population with demonstrated nest‐site fidelity and neophyte assimilation. We estimated mother–daughter and full sibling relationships with a maximum‐likelihood full‐pedigree reconstruction approach, incorporating genotypic (12 microsatellites), maternal genealogy (mitochondrial DNA) and age structure (long‐term mark–recapture) data. We validated relationships with parentage assignment and pairwise relatedness estimators. Fourteen veteran nesters were the mothers of 42 younger nesters, and 94 nesters formed 35 full sibships. Time between the first nesting records of mothers and their daughters indicated maximum time to maturity as short as 14 years in Caribbean hawksbills. Thirteen of the 14 mothers showed consistently high fidelity to JB for two decades, providing compelling evidence that 41 of these daughters originated from JB nests and returned to this 1‐km‐long natal site to breed. Rookeries with strongly philopatric individuals might have limited colonization potential and be at a disadvantage in the event of habitat loss. This study demonstrates the utility of long‐term mark–recapture data in kinship analyses for answering questions relevant to endangered species conservation.
Starting in 2011, coastal areas of the Caribbean Sea and tropical Atlantic Ocean began to experience extraordinary yearly accumulations of pelagic Sargassum brown alga. Historical reports place large quantities of Sargassum only in the North Atlantic (mostly in the Gulf of Mexico and the Sargasso Sea). Accumulations of Sargassum in the tropical Atlantic have continued. We used a numerical particle-tracking system, wind and current reanalysis data, drifting buoy trajectories, and satellite imagery to determine the origin of the Sargassum that is now found persistently in the tropical Atlantic. Our analyses suggest that during the extreme negative phase of the winter 2009-2010 North Atlantic Oscillation (NAO), unusually strong and southward-shifted westerly winds explain the transport of Sargassum from the Sargasso Sea (∼20-40oN, 80-20oW) into the far eastern North Atlantic. Our hindcast Sargassum distributions agree with surface current simulations with the inclusion of “windage”. Windage is the additional, wind-induced drift of material floating at the free surface resulting from direct wind forcing on the sea surface, as well as on floating or partially-submerged objects. In our simulations, windage is included as an added vector (speed and direction) to the model-computed surface ocean currents equivalent to 1% of surface wind velocities. Lagrangian analysis of the regional circulation suggests that (1) part of the Sargassum subsequently drifted to the southwest in the North Equatorial Current (NEC) and entered the central tropical Atlantic, arriving in the Caribbean by the spring of 2011, with (2) another portion continuing southward along the coast of Africa in the Canary Current, eventually joining the seasonally-varying system of tropical Atlantic currents and thereby delivering a large Sargassum population to the tropical Atlantic. Since then, Sargassum patches aggregate from March to September in massive windrows along the Inter-Tropical Convergence Zone (ITCZ) under the action of converging winds. The windrows follow the ITCZ in its seasonal northward migration in the central tropical Atlantic. They are stretched across the central tropical Atlantic as the ITCZ crosses the latitude of the seasonal formation of the North Equatorial Counter Current (NECC). These patches and windrows are exposed to high sunlight and open-ocean upward flux of nutrients due to eddy and wind-driven mixing in the central tropical Atlantic. During the northern spring and summer, as the Sargassum drifts farther north with the ITCZ, large portions of the population are advected into the eastern Caribbean Sea. Some of these patches remain dispersed as the ITCZ migrates southward, and re-aggregate into new windrows as the ITCZ intensifies the following March-April. If wind mixing is strong and the mixed layer is deeper than about 50-60 m in the southern tropical Atlantic at this time, the Sargassum will bloom and form a massive windrow. Otherwise, the bloom will be inhibited. The extreme 2009-2010 NAO wind anomaly could be considered as triggering a biosphere “tipping point” that caused important ocean-scale ecosystem changes in the tropical Atlantic, with significant recurrent social and economic consequences. Understanding whether this new expanded geographic range of massive Sargassum blooms is temporary or whether it will revert to its pre-2009 distribution requires sustained monitoring and research.
We report for the first time great quantities of floating
Sargassum to Serranilla Bank, in the Central Caribbean. The
island is an important nesting site for sea turtles, and by
the time the Sargassum wave arrived, the baby turtles were
disclosing. Due to the thick mat of Sargassum along the beach,
the baby turtles may have troubles to reach the ocean.
Se reporta por primera vez una gran cantidad de Sargassum flotante en Cayo Serranilla, en el Caribe central. La isla es un sitio importante para anidamiento de tortugas marinas, y al momento de la llegada del Sargassum, los nidos estaban eclosionando. Debido al espeso tapete de algas en la playa, las tortuguas puede tener problemas en llegar al mar.
Understanding population dynamics, and how it is influenced by exogenous and endogenous factors, is important to the study and conservation of species. Moreover, for migratory species, the phenology and duration of use of a given location can also influence population structure and dynamics. For many species, breeding abundance, survival, and reproductive performance, as well as phenology of nesting, are often the most accessible, and therefore, practical elements of their life history to study. For a population of hawksbill sea turtles (Eretmochelys imbricata), we modeled population change for nesters and total adult females, survival, and breeding probability, from 25 yr of intensive tagging data. We modeled breeding probability as a function of the number of years since last breeding and tested for differences between neophyte and experienced nesters. For each year, we also estimated the number of clutches deposited per female, and phenology of use, for neophytes and experienced nesters. To implement the analysis, we developed a novel generalized multistate open robust design mark–recapture modeling framework, with parameters for survival and transition probabilities, and for each primary period, state structure and arrival, persistence, and detection probabilities. Derived parameters included abundance of observable and unobservable components of the population, residence time, expected arrival and departure periods, and per‐period intensity of study area use. Abundance of nesters increased over most of the time series. Survival probability was 0.935 ± 0.01 (estimate ± SE). Virtually all hawksbills skipped at least one year of nesting. Breeding probability increased by skipping a second year, but then decreased thereafter. Subsequent breeding probability was lower for neophyte nesters than for experienced nesters, but the effect was weaker than the effect of years since breeding. Clutch frequency varied by year, with no discernable pattern of differences between neophytes and experienced nesters. Mean arrival and departure dates also varied, with a slight shift of nesting activity to earlier in the season. The multistate open robust design model developed here provides a flexible framework for modeling the dynamics of structured migratory populations and the phenology and duration of their seasonal use of study areas.
Since 2011, beach inundation of massive amounts of pelagic Sargassum algae has occurred around the Caribbean nations and islands. Previous studies have applied satellite ocean color to determine the origins of this phenomenon. These techniques, combined with complementary approaches, suggest that, rather than blooms originating in the Caribbean, they arrive from the Equatorial Atlantic. However, oceanographic context for these occurrences remains limited. Here, we present results from synthetic particle tracking experiments that characterize the interannual and seasonal dynamics of ocean currents and winds likely to influence the transport of Sargassum from the Equatorial Atlantic into the Caribbean Sea. Our findings suggest that Sargassum present in the western Equatorial Atlantic (west of longitude 50 W) has a high probability of entering the Caribbean Sea within a year's time. Transport routes include the Guiana Current, North Brazil Current Rings, and the North Equatorial Current north of the North Brazil Current Retroflection. The amount of Sargassum following each route varies seasonally. This has important implications for the amount of time it takes Sargassum to reach the Caribbean Sea. By weighting particle transport predictions with Sargassum concentrations at release sites in the western Equatorial Atlantic, our simulations explain close to 90% of the annual variation in observed Sargassum abundance entering the Caribbean Sea. Additionally, results from our numerical experiments are in good agreement with observations of variability in the timing of Sargassum movement from the Equatorial Atlantic to the Caribbean, and observations of the spatial extent of Sargassum occurrence throughout the Caribbean. However, this work also highlights some areas of uncertainty that should be examined, in particular the effect of "windage" and other surface transport processes on the movement of Sargassum. Our results provide a useful launching point to predict Sargassum beaching events along the Caribbean islands well in advance of their occurrence and, more generally, to understand the movement ecology of a floating ecosystem that is essential habitat to numerous marine species.
Here we describe the effects of beach morphological features on loggerhead (Caretta caretta) nesting behavior on the barrier islands of the north-central Gulf of Mexico. Our results show that loggerhead crawl length decreases as beach slope increases, and our data comparing nest crawls (resulting in egg laying) versus false crawls (emergence onto the beach without laying eggs) suggest that beach slope and crawl length differ between the crawl types but elevation does not. We infer that loggerheads cue in to beach slope to reach a perceived elevation with reduced risk of inundation, crawling longer distances on flatter slopes compared with shorter distances on steep slopes, but that after this elevation is reached, other environmental variables may ultimately factor into the decision to lay eggs.
Global climate change is expected to have major impacts on biodiversity. Sea turtles have temperature-dependent sex determination, and many populations produce highly femalebiased offspring sex ratios, a skew likely to increase further with global warming. We estimated the primary sex ratio at one of the world's largest green turtle Chelonia mydas rookeries in Guinea-Bissau, West Africa, and explored its resilience to climate change. In 2013 and 2014, we deployed data loggers recording nest (n = 101) and sand (n = 30) temperatures, and identified hatchling sex by histological examination of gonads. A logistic curve was fitted to the data to allow predictions of sex ratio across habitats and through the nesting season. The population-specific pivotal temperature was 29.4°C, with both sexes produced within incubation temperatures from 27.6 to 31.4°C: the transitional range of temperatures (TRT). Primary sex ratio changed from maleto female-biased across relatively small temporal and spatial scales. Overall it was marginally female-biased, but we estimated an exceptionally high male hatchling production of 47.7% (95% CI: 36.7-58.3%) and 44.5% (95% CI: 33.8-55.4%) in 2013 and 2014, respectively. Both the temporal and spatial variation in incubation conditions and the wide range of the TRT suggest resilience and potential for adaptation to climate change if the present nesting habitat remains unchanged. These findings underline the importance of assessing site-specific parameters to understand populations' responses to climate change, particularly with regard to identifying rookeries with high male hatchling production that may be key for the future conservation of sea turtles under projected global warming scenarios.
From mid-2014 until the end of 2015, the Mexican Caribbean coast experienced a massive influx of drifting Sargassum spp. that accumulated on the shores, resulting in build-up of decaying beach-cast material and near-shore murky brown waters (Sargassum-brown-tides, Sbt). The effects of Sbt on four near-shore waters included reduction in light, oxygen (hypoxia or anoxia) and pH. The monthly influx of nitrogen, and phosphorus by drifting Sargassum spp. was estimated at 6150 and 61 kg km− 1 respectively, resulting in eutrophication. Near-shore seagrass meadows dominated by Thalassia testudinum were replaced by a community dominated by calcareous rhizophytic algae and drifting algae and/or epiphytes, resulting in 61.6–99.5% loss of below-ground biomass. Near-shore corals suffered total or partial mortality. Recovery of affected seagrass meadows may take years or even decades, or changes could be permanent if massive influxes of Sargassum spp. recur.
Thermal tolerances are affected by the range of temperatures that species encounter in their habitat. Daniel Janzen hypothesized in his “Why mountain passes are higher in the tropics” that temperature gradients were effective barriers to animal movements where climatic uniformity was high. Sea turtles bury their eggs providing some thermal stability that varies with depth. We assessed the relationship between thermal uniformity and thermal tolerance in nests of three species of sea turtles. We considered that barriers were “high” when small thermal changes had comparatively large effects and “low” when the effects were small. Mean temperature was lower and fluctuated less in species that dig deeper nests. Thermal barriers were comparatively “higher” in leatherback turtle (Dermochelys coriacea) nests, which were the deepest, as embryo mortality increased at lower “high” temperatures than in olive ridley (Lepidochelys olivacea) and green turtle (Chelonia mydas) nests. Sea turtles have temperature-dependent sex determination (TSD) and embryo mortality increased as temperature approached the upper end of the transitional range of temperatures (TRT) that produces both sexes (temperature producing 100% female offspring) in leatherback and olive ridley turtles. As thermal barriers are “higher” in some species than in others, the effects of climate warming on embryo mortality is likely to vary among sea turtles. Population resilience to climate warming may also depend on the balance between temperatures that produce female offspring and those that reduce embryo survival.
One of the frequent questions by users of the mixed model function lmer of the lme4 package has been: How can I get p values for the F and t tests for objects returned by lmer? The lmerTest package extends the 'lmerMod' class of the lme4 package, by overloading the anova and summary functions by providing p values for tests for fixed effects. We have implemented the Satterthwaite's method for approximating degrees of freedom for the t and F tests. We have also implemented the construction of Type I - III ANOVA tables. Furthermore, one may also obtain the summary as well as the anova table using the Kenward-Roger approximation for denominator degrees of freedom (based on the KRmodcomp function from the pbkrtest package). Some other convenient mixed model analysis tools such as a step method, that performs backward elimination of nonsignificant effects - both random and fixed, calculation of population means and multiple comparison tests together with plot facilities are provided by the package as well.
Marine turtles deposit their eggs in underground nests where they develop unattended and without parental care. Incubation temperature varies with environmental conditions, including rainfall, sun/shade and sand type, and affects developmental rates, hatch and emergence success, and embryonic sex. We documented (1) rainfall and sand temperature relationships and (2) rainfall, nest temperatures and hatchling sex ratios at a loggerhead turtle (Caretta caretta) nesting beach in Boca Raton, Florida, USA, across the 2010 to 2013 nesting seasons. Rainfall data collected concurrently with sand temperatures at different depths showed that light rainfall affected surface sand, effects of the heaviest rainfall events tended to lower sand temperatures but the temperature fluctuations were small once upper nest depths were reached. This is important in understanding the potential impacts of rainfall as a modifier of nest temperatures, as such changes can be quite small. Nest temperature profiles were synchronized with rainfall data from weather services to identify relationships with hatchling sex ratios. The sex of each turtle was verified laparoscopically to provide empirical measures of sex ratio for the nest and nesting beach. The majority of hatchlings in the samples were female, suggesting that across the 4 seasons most nest temperatures were not sufficiently cool to produce males. However, in the early portion of the nesting season and in wet years, nest temperatures were cooler, and significantly more males hatched.
Developing sea turtle embryos only successfully hatch within a relatively narrow temperature range, rendering this immobile life stage vulnerable to the vagaries of climate change. To accurately predict the potential impact of climate change on sea turtle egg mortality, we need to fully understand the thermal tolerance of developing embryos. We reviewed the literature on this topic, and found that published studies interpret the primary literature and subsequent reviews very differently. Based on early literature reviews, the maximum thermal tolerance of sea turtle embryos is frequently cited as either 33 or 35°C. In many sea turtle populations, however, nest temperatures often exceed 35°C by up to several degrees (usually just prior to hatchling emergence) and eggs still hatch successfully. Mean incubation temperatures up to 35°C generally produce hatchlings, although leatherback and olive ridley turtle embryos may be less tolerant of high incubation temperatures than green and loggerhead turtle embryos. Sea turtle embryos are likely to be more sensitive to the duration of time spent at potentially stressful temperatures than to the temperature alone. To complicate matters, developing embryos may change their thermal tolerance as they grow. Overall, we are only beginning to understand how exposure to high temperatures experienced in the field influences embryonic development and hatchling production. This knowledge gap is hampering our ability to predict the impacts of climate change on sea turtle populations, and future work should focus on understanding how temperature and other climatic variables influence embryonic development and, thus, crucial population attributes such as hatchling production.
Whether a sea turtle embryo develops into a male or a female depends, as with many other reptiles, on the temperature during incubation of the eggs. With sea turtles, warm temperatures produce 100% females and, thus, increasing global temperatures have the potential to significantly alter offspring sex ratios. Nest-site selection provides a potential mechanism by which females might adjust the sex of their offspring, but necessitates a reliable cue which provides information about the thermal properties of a nest. Overstory vegetation cover was found to significantly predict temperatures in nests of the hawksbill sea turtle Eretmochelys imbricata. Nests placed under high vegetation cover are significantly cooler and remain within the male-producing range of temperatures throughout incubation. Interestingly, metabolic heating of the developing clutch is less pronounced under vegetation, further reinforcing the importance of this nesting habitat with respect to the production of males. This underscores the importance of preserving natural vegetation cover at hawksbill nesting beaches in order to maintain the thermal diversity of nesting sites and, potentially, mitigate the impacts of increasing global temperatures.
Maximum likelihood or restricted maximum likelihood (REML) estimates of the
parameters in linear mixed-effects models can be determined using the lmer
function in the lme4 package for R. As for most model-fitting functions in R,
the model is described in an lmer call by a formula, in this case including
both fixed- and random-effects terms. The formula and data together determine a
numerical representation of the model from which the profiled deviance or the
profiled REML criterion can be evaluated as a function of some of the model
parameters. The appropriate criterion is optimized, using one of the
constrained optimization functions in R, to provide the parameter estimates. We
describe the structure of the model, the steps in evaluating the profiled
deviance or REML criterion, and the structure of classes or types that
represents such a model. Sufficient detail is included to allow specialization
of these structures by users who wish to write functions to fit specialized
linear mixed models, such as models incorporating pedigrees or smoothing
splines, that are not easily expressible in the formula language used by lmer.
Air–sea coupling in the IntraAmerican seas (IAS; Caribbean Sea and Gulf of Mexico) is studied through analyses of observational data from satellite, reanalysis products, and in situ measurements. A strong coupling is found between the easterly trade wind −U and meridional SST gradient ∂T/∂y across a localized region of the southern-central Caribbean Sea from seasonal and interannual to decadal time scales. The ∂T/∂y anomaly is caused by a variation in the strength of coastal upwelling off the Venezuelan coast by the wind, which in turn strengthens (weakens) for stronger (weaker) ∂T/∂y. Wind speeds and seasonal fluctuations in IAS have increased in the past two decades with a transition near 1994 coinciding approximately with when the Atlantic multidecadal oscillation (AMO) turned from cold to warm phases. In particular, the seasonal swing from summer's strong to fall's weak trade wind has become larger. The ocean's upper-layer depth has also deepened, by as much as 50% on average in the eastern Gulf of Mexico. These conditions favor the shedding of eddies from the Loop Current, making it more likely to shed at a biannual frequency, as has been observed from altimetry data.
The frequency and intensity of harmful algal blooms (HABs) and phytoplankton community shifts toward toxic species have increased worldwide. Although most research has focused on eutrophication as the cause of this trend, many other global-and regional-scale anthropogenic influences may also play a role. Ocean acidification (high pCO(2)/low pH), greenhouse warming, shifts in nutrient availability, ratios, and speciation, changing exposure to solar irradiance, and altered salinity all have the potential to profoundly affect the growth and toxicity of these phytoplankton. Except for ocean acidification, the effects of these individual factors on harmful algae have been studied extensively. In this review, we summarize our understanding of the influence of each of these single factors on the physiological properties of important marine HAB groups. We then examine the much more limited literature on how rising CO2 together with these other concurrent environmental changes may affect these organisms, including what is possibly the most critical property of many species: toxin production. New work with several diatom and dinoflagellate species suggests that ocean acidification combined with nutrient limitation or temperature changes may dramatically increase the toxicity of some harmful groups. This observation underscores the need for more in-depth consideration of poorly understood interactions between multiple global change variables on HAB physiology and ecology. A key limitation of global change experiments is that they typically span only a few algal generations, making it difficult to predict whether they reflect likely future decadal- or century-scale trends. We conclude by calling for thoughtfully designed experiments and observations that include adequate consideration of complex multivariate interactive effects on the long-term responses of HABs to a rapidly changing future marine environment.
Effects of nest location on nest success of hawksbill turtles Eretmochelys imbricata in Barbados were investigated. Hawksbills nested more frequently on west coast than south and east coast beaches, suggesting that they prefer beaches with lower wave energy and steeper beach slopes. Sheltered beaches may be preferred because of the mechanical difficulities and energetic costs of moving onto and off high energy beaches. Hawksbills nested at specific elevations above mean sea level. Elevation was controlled by altering the distance travelled inland on beaches of different slopes. Steeper beaches may therefore be preferred because gravid females and hatchlings may have lower travel costs and lower predation risk. Nest success (number of hatchlings emerging from a nest) was highest from nests closest to mean elevation and declined at higher and lower elevations. This was because emergence success (% eggs laid that emerge as hatchlings) was highest near mean elevation. The high emergence success was due both to a high hatching success (% eggs hatching) and high escape success (% hatchlings escaping from the nest). Emergence success decreased with increasing compaction, due both to an increase in the percentage of dead embryos in nests (late pre-hatching mortality) and a decrease in escape success of hatchlings. Hawksbills preferred to nest amongst vegetation. Vegetated nest sites were less compacted than non-vegetated, and had higher escape success. Hatchling sex ratios were biased towards males on cooler south coast beaches and towards females on warmer west coast beaches. Coastal development may constrain the recovery of hawksbill populations in the Caribbean by forcing females to nest at lower elevations and by increasing compaction through heavy recreational use of beaches and clearance of beach vegetation.
Nesting by hawksbill sea turtles Eretmochelys imbricata in Barbados, West Indies, has been monitored since 1992. Data from the index beach indicate that the number of nests may have increased as much as 8-fold over this period. The estimated abundance of nesting females on Barba- dos is 1250, suggesting that this eastern Caribbean island now hosts one of the largest rookeries in the wider Caribbean, with over 230 females nesting on the index beach alone. Given its extreme east- erly position and the prevailing north-westerly current flow into the Caribbean Sea, Barbados is likely to be a significant contributor to foraging grounds throughout the region. Primary females, which are untagged and without tag scars, made up the majority of females encountered on nesting beaches in most years, suggesting that reductions in juvenile and sub-adult mortality, both nationally and regionally, are significant to the increase in number of nesting females. Females nest every 2.47 yr on average, although remigration intervals of individual females vary (range: 1 to 6 yr), sug- gesting environmental influences on nesting periodicity. The average clutch frequency estimated from the index beach was 4.1 nests per female, but that calculated from less intensively surveyed beaches was lower. Primary and Remigrant females differed in length, mass and clutch frequency; the results must be viewed with caution, however, as preliminary laparoscopic examinations re- vealed that some Primary females were not in fact nesting for their first season, and because differ- ences in nest site fidelity between the 2 groups of females could potentially cause the differences in clutch frequencies estimated.
Hawksbills have been the focus of conservation efforts over several decades and their status in the Caribbean is continuously being evaluated. Surprisingly, it appears that the island of Guadeloupe hosts one of the largest Hawksbill populations in this region, highlighting the importance of making the most recent data available for the purposes of wildlife management. Numbers of nesting females and other biometric data collected over eight nesting seasons are presented as well as a number of biological observations unique to this population. A total of 452 females were tagged, 89 of which were thought to have been previously tagged, and 58 remigrants (turtles tagged in previous seasons) were observed. Four of the remigrants were seen in three different nesting seasons, and one was seen in four. Mean minimum curved carapace length was 87.9 cm, and mean clutch size varied significantly between two study years (2002: 137 ± 26 eggs; 2004: 159 ± 29 eggs). One turtle laid a clutch of 276 eggs, the largest ever recorded for a Hawksbill. The initial estimate of the nesting population in Guadeloupe is encouraging and perhaps is a sign of increasing numbers in the wider Caribbean region. This information is important when considering the status of this endangered species, and these data need to be easily accessible to the conservation community.
We present an updated checklist of the birds of the islands of Aruba, Curaçao and Bonaire, and the islets of Klein Curaçao and Klein Bonaire, southern Caribbean, and compare this with earlier checklists (K.H. Voous, Stud. Fauna Curaçao Carib. Isl. 7: 1–260, 1957; Ardea 53: 205–234, 1965; Birds of the Netherlands Antilles, 1983). The avifaunal composition of the three main islands is relatively similar (similarity coefficients of 74–78% for residents and 65–73% for migrants) whereas the two islets are, or were in the past, inhabited mainly by sea birds. The total number of recorded resident species for these islands has increased from 115 (1957) to 168 (2006), and of migrants from 117 (1957) to 236 (2006). This increase was most prominent for the island of Aruba (residents from 34 to 56, migrants from 28 to 166), and least for Curaçao (residents from 42 to 57, migrants from 55 to 168). Historically Klein Curaçao was an important nesting site for seabirds, i.e. boobies, gulls and terns, but mining of guano in the 19th century significantly lowered the ornithological value of the islet. Klein Bonaire suffered heavily from the presence of goats but is slowly recovering following their removal and the islet's inclusion. Despite the presence of a large number of migrants, or non-breeding birds, the islands are of limited importance as a stop-over site for birds. Migrants arrive from both the north (boreal migrants from North and Middle America) and the south (austral migrants from South America). We illustrate the phenology of migration with the numbers of migrant warblers species and migrant gulls and terns, and the abundance of migrant raptors recorded on the three islands. While migrants can be observed in all months of the year, for the warblers and raptors there are clear peaks in boreal spring (Mar–Apr) and autumn (Oct–Nov), with few summering birds in the boreal summer. The gulls and terns appear to be present in more or less equal numbers during all months of the year. About two-thirds of the breeding residents are either deemed common or rather common, and this proportion is consistent for all three islands. Of the breeding residents few are common or very common on one island, and at the same time scarce or very scarce on other islands. Notable exceptions are Greater Flamingo Phoenicopterus ruber that is an abundant breeding resident on Bonaire, a regular non-breeding visitor (with several attempts of breeding) in the low hundreds on Curaçao, but is only an irregular non-breeding visitor on Aruba. Yellow Oriole Icterus nigrogularis is common as a breeding resident on Curaçao, rather common on Bonaire, but scarce on Aruba. The islands are home to six globally threatened or near-threatened species. Two species, the Caribbean Coot Fulica caribaea and the Yellow-shouldered Parrot Amazona barbadensis are represented by globally significant populations, whereas the other species (Piping Plover Charadrius melodus, Olivesided Flycatcher Contopus cooperi, Cerulean Warbler Dendroica cerulea and Golden-winged Warbler Vermivora chrysoptera) use the islands as over-wintering or stop-over site during migration. The Yellow-shouldered Parrot is found mainly on Bonaire, where there is a resident population of some 400 birds; small numbers are occasionally observed on Aruba and these may comprise migrant birds from Venezuela's Paraguaná Peninsula or may represent released birds. The Caribbean Coot is present on all three islands and its status on the islands has improved, with more breeding sites occupied and more birds present than in Voous's time. From a conservation perspective, a significant breeding population of Greater Flamingo on Bonaire and a smaller population on Curaçao are noteworthy as well as a breeding colony of Least Tern Sterna antillarum on Klein Bonaire. On the basis of the presence of these threatened and conservation-dependent species we identify fifteen Important Bird Areas, i.e. four on Aruba, five on Curaçao and six (including Klein Bonaire) on Bonaire.
Current understanding of the factors influencing hawksbill sea turtle (Eretmochelys imbricata) hatch success is disparate and based on relatively short-term studies or limited sample sizes. Because global populations of hawksbills are heavily depleted, evaluating the parameters that impact hatch success is important to their conservation and recovery. Here, we use data collected by the Jumby Bay Hawksbill Project (JBHP) to investigate hatch success. The JBHP implements saturation tagging protocols to study a hawksbill rookery in Antigua, West Indies. Habitat data, which reflect the varied nesting beaches, are collected at egg deposition, and nest contents are exhumed and categorized post-emergence. We analyzed hatch success using mixed-model analyses with explanatory and predictive datasets. We incorporated a random effect for turtle identity and evaluated environmental, temporal and individual-based reproductive variables. Hatch success averaged 78.6% (SD: 21.2%) during the study period. Highly supported models included multiple covariates, including distance to vegetation, deposition date, individual intra-seasonal nest number, clutch size, organic content, and sand grain size. Nests located in open sand were predicted to produce 10.4 more viable hatchlings per clutch than nests located >1.5 m into vegetation. For an individual first nesting in early July, the fourth nest of the season yielded 13.2 more viable hatchlings than the initial clutch. Generalized beach section and inter-annual variation were also supported in our explanatory dataset, suggesting that gaps remain in our understanding of hatch success. Our findings illustrate that evaluating hatch success is a complex process, involving multiple environmental and individual variables. Although distance to vegetation and hatch success were inversely related, vegetation is an important component of hawksbill nesting habitat, and a more complete assessment of the impacts of specific vegetation types on hatch success and hatchling sex ratios is needed. Future research should explore the roles of sand structure, nest moisture, and local weather conditions.
The Mexican Caribbean is a vital nesting destination for loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtles. Since 2015, massive periodical landings of pelagic Sargassum species (sargasso) have affected coastal ecosystems. Dense accumulations of sargasso on the shoreline may preclude access to sea turtles’ preferred nesting areas and compromise hatching. In this study, we assess whether the number of nests and hatches of loggerhead and green sea turtles has been affected by the massive influx of sargasso. We compare data from before (2010–2014) and after (2015–2019) the first sargasso event, obtained from the same 17 marine turtle camps, which collectively account for 72.3 km of sampling distance over a 210 km section of shoreline. No
differences in preferences on nesting beaches were recorded between periods for the two species. The mean number of nests per kilometer of coastline remained without statistically significant changes between periods in 16 camps and increased significantly in one camp for each species. Overall, the mean annual number of nests per kilometer of beach was 37% higher in the period after massive landings of sargasso began. The mean number of hatchlings increased significantly in one camp for C. mydas and in three for C. caretta. Periodical massive landings of sargasso from 2015 to 2019 do not appear to have compromised nesting and hatching of loggerhead and green sea turtles along the Mexican Caribbean coast.
The biggest bloom
Floating mats of Sargassum seaweed in the center of the North Atlantic were first reported by Christopher Columbus in the 15th century. These mats, although abundant, have until recently been limited and discontinuous. However, Wang et al. report that, since 2011, the mats have increased in density and aerial extent to generate a 8850-kilometer-long belt that extends from West Africa to the Caribbean Sea and Gulf of Mexico (see the Perspective by Gower and King). This represents the world's largest macroalgal bloom. Such recurrent blooms may become the new normal.
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Marine turtles migrate back to their natal region during reproduction, but the precision of this homing behavior and how the precision varies among populations and across biogeographic regions are unclear. We hypothesize that marine turtles nesting on insular landmasses navigate to their rookeries with greater precision than those nesting on continuous coastlines. We analyzed new mitochondrial and microsatellite marker data from hawksbill turtles Eretmochelys imbricata at nesting sites across Antigua and Barbuda, West Indies, to assess the scale of natal homing in the highly insular Leeward Islands. We then used published data from 15 western Atlantic rookeries to examine regional patterns of rookery structure. Mitochondrial control region data showed weak to no partitioning among nesting sites within Antigua and strong partitioning between Antigua and Barbuda, suggesting natal homing at a scale of 50 km. Microsatellite data showed weak to no partitioning between sites, indicating male-mediated gene flow. Regionally, we found stronger population structuring among rookeries of insular landmasses than among those of larger landmasses with continuous coastlines, despite shorter average rookery separation for the former. We also found a positive relationship between a rookery’s isolation index (a metric incorporating distances from larger landmasses) and its genetic divergence from proximate rookeries. These findings support our hypothesis, and we caution that insular rookeries that host marine turtles with extreme homing behavior have limited ability to colonize new nesting habitat. The unprecedented rates of development and increasing instability of present-day nesting habitat might therefore pose a greater and increasing threat to insular rookeries.
The sexual phenotype of the gonad is dependent on incubation temperature in many turtles, all crocodilians, and some lepidosaurians. At hatching, identification of sexual phenotype is impossible without sacrificing the neonates. For this reason, a general method to infer sexual phenotype from incubation temperatures is needed. Temperature influences sex determination during a specific period of the embryonic development, starting when the gonad begins to form. At constant incubation temperatures, this thermosensitive period for sex determination (TSP) is located at the middle third of incubation duration (MTID). When temperature fluctuates, the position of the thermosensitive period for sex determination can be shifted from the MTID because embryo growth is affected by temperature. A method is proposed to locate the thermosensitive period for sex determination based on modelling the embryo growth, allowing its precise identification from a natural regime of temperatures. Results from natural nests and simulations show that the approximation of the thermosensitive period for sex determination to the middle third of incubation duration may create a quasi-systematic bias to lower temperatures when computing the average incubation temperature during this period and thus a male-bias for sex ratio estimate.
Ghost crabs, Ocypode cordimanus, inhabit relatively hostile environments subject to thermal fluctuations, including both diurnal and seasonal cycles. For many ectotherms, including ghost crabs, a major challenge is to remain cool during hot daytime temperatures. This can be achieved by adopting a fossorial lifestyle, taking advantage of thermal refuge afforded by burrows of sufficient depth. Another consideration, often overlooked, is the potential advantage associated with ready access to a thermal energy source (a “charging station”) when surface temperatures are cooler. Being able to rapidly elevate body temperature during cool periods would enhance the crab's ability to maintain rate processes and carry out essential activities. We have measured ghost crab burrow temperature profiles at two times of the day with contrasting sun exposure (06:00 and 14:00), demonstrating how effective burrow depth (up to a maximum of 40 cm) provides thermal regulation below the surface of the sand (e.g., at dawn (06:00) and early afternoon (14:00) at a depth of 5 cm, temperatures (±SD) of 16.32 ± 0.96 °C and 25.04 ± 1.47 °C were recorded, respectively. Corresponding temperatures at a depth of 30 cm were 19.17 ± 0.59 °C and 19.78 ± 1.60 °C, respectively). This demonstrates that while temperature conditions at the surface vary dramatically from night to day, ghost crab burrows can maintain relatively constant temperatures at the burrow base throughout the diurnal cycle, at least during winter. As a consequence, the burrow heat signatures undergo a corresponding thermal gradient reversal between night and day, as revealed by infra-red photography. Complementing these field observations, we also determined heating and cooling times/constants for O. cordimanus in the laboratory (τ = 17.54 and 16.59 JK⁻¹, respectively), and analysed chemical composition of their carapace (external (with β Chitin evident) and internal (predominance of α Chitin)), which is the primary thermal interface with the environment. We find that ghost crabs both gain and lose heat relatively rapidly, which likely affects the range and duration of surface activities under different thermal conditions, and renders the thermal characteristics of their burrows vital for their persistence on beaches. Finally, we speculate that the distinctly contrasting thermal signatures of ghost crab burrows in comparison to the surrounding sand could in principle be used by crabs as spatial markers for navigation and to identify holes on return from nightly excursions, being identified either by direct thermal sensing or odours rising from the burrow base as a consequence of the thermal flux.
Sargassum washing ashore on the beaches of the Caribbean Islands since 2011 has caused problems for the local environments, tourism, and economies. Although preliminary results of Sargassum distributions in the nearby oceans have been obtained using measurements from the Medium Resolution Imaging Spectrometer (MERIS), MERIS stopped functioning in 2012, and detecting and quantifying Sargassum distributions still face technical challenges due to ambiguous pixels from clouds, cloud shadows, cloud adjacency effect, and large-scale image gradient. In this paper, a novel approach is developed to detect Sargassum presence and to quantify Sargassum coverage using the Moderate Resolution Imaging Spectroradiometer (MODIS) alternative floating algae index (AFAI), which examines the red-edge reflectance of floating vegetation. This approach includes three basic steps: 1) classification of Sargassum-containing pixels through correction of large-scale gradient, masking clouds and cloud shadows, and removal of ambiguous pixels; 2) linear unmixing of Sargassum-containing pixels; and, 3) statistics of Sargassum area coverage in pre-defined grids at monthly, seasonal, and annual intervals. In the absence of direct field measurements to validate the results, limited observations from the Hyperspectral Imager for the Coastal Ocean (HICO) measurements and numerous local reports support the conclusion that the elevated AFAI signals are due to the presence of Sargassum instead of other floating materials, and various sensitivity analyses are used to quantify the uncertainties in the derived Sargassum area coverage. The approach was applied to MODIS observations between 2000 and 2015 over the Central West Atlantic (CWA) region (0–22°N, 63–38°W) to derive the spatial and temporal distribution patterns as well as the total area coverage of Sargassum. Results indicate that the first widespread Sargassum distribution event occurred in 2011, consistent with previous MERIS findings. Since 2011, only 2013 showed a minimal Sargassum coverage similar to the period of 2000 to 2010; all other years showed significantly more coverage. More alarmingly, the summer months of 2015 showed mean coverage of > 2000 km2, or about 4 times of the summer 2011 coverage and 20 times of the summer 2000 to 2010 coverage. Analysis of several environmental variables provided some hints on the reasons causing the inter-annual changes after 2010, yet further multi-disciplinary research (including in situ measurements) is required to understand such changes and long-term trends in Sargassum coverage.
The increase in mass of embryonic sea turtles (Chelonia mydas, Caretta caretta) with incubation time can be described by a decaying exponential growth equation and appears sigmoidal in pattern. The coefficients required to fit the growth equation to the embryonic data vary among and within species depending on the mass and incubation times of the sea turtle population. When groups of eggs are incubated in artificial nests where gas exchange can be manipulated, rates of growth and hatching success are related to nest gas exchange. Maximal rates of growth (incubation ≅ 60 days) and hatching success occur in a respiratory environment quite similar to that measured in natural nests. As movement of respiratory gases between the nest and the atmosphere is limited, embryonic rates of growth and egg hatching success are reduced.
Sudden beaching of huge seaweed masses smother the coastline and form rotting piles on the shore. The number of reports of these events in previously unaffected areas has increased worldwide in recent years. These 'seaweed tides' can harm tourism-based economies, smother aquaculture operations or disrupt traditional artisanal fisheries. Coastal eutrophication is the obvious, ultimate explanation for the increase in seaweed biomass, but the proximate processes that are responsible for individual beaching events are complex and require dedicated study to develop effective mitigation strategies. Harvesting the macroalgae, a valuable raw material, before they beach could well be developed into an effective solution.
Eggs of hawksbill turtles, Eretmochelys imbricata, from Antigua were incubated at constant tempe ratures. The pivotal temperature (the temperature at which 50% of each sex is produced) for the sample was estimated to be 29.2 °C. Sand temperatures at the depth of turtle nests were recorded over two nesting seasons at Pasture Bay, Antigua. Although sand temperatures were sometimes higher than the pivotal temperature, more often they were lower. On this basis, it is unlikely that hatchling hawksbill turtles in this area have the highly female-biased sex ratios reported for some other reptiles.
We determined individual nest placement patterns for female leatherbacks nesting at Awa:la-Ya:lima:po, French Guiana, by measuring distance from the nest to several landscape features, such as the highest spring tide line (HSTL) and the vegetation line. Distance from the nest to the HSTL differed significantly between females, indicating the existence of individual nesting patterns. There was a significant repeatability of nest site choice relative to the HSTL, indicating that females showed within-individual consistency in their nest placement. Despite individual preferences, there was much within-individual variation and a lack of predictability in the nesting patterns; that is, the locations of subsequent nests could not be predicted based on knowledge of previous nest choices, indicating a certain degree of scatter. The significant repeatability suggests that nest choice behaviour in female leatherbacks is heritable and may show the potential for further evolution. We tested sea-finding ability of hatchlings, a potential consequence of nest site choice, in Matapica, Suriname, by using orientation arenas to quantify the strength and direction of travel after emergence. The orientation tests showed that hatchlings were unable to move seaward in vegetated arenas, providing evidence that vegetation acts as a strong selective pressure driving nest placement seaward. It appears that leatherbacks have adopted a regional rather than a local optimum for nest placement patterns, possibly resulting from their weak beach fidelity and the frequent erosion and destruction of their nesting beaches. We discuss the evolutionary and conservation implications for this species in the context of current environmental changes.
The function relating phenotypic sex ratio to incubation temperature in reptiles can vary in a number of ways in addition to simple differences in the temperatures giving 50% of each sex. This paper offers terminology and definitions for describing these relationships. These definitions accomodate interactions between genetic and environmental effects on sexual differentiation, and variability within populations. The paper also discusses the concept of a sensitive stage/period within incubation during which temperature can affect the direction of sexual differentiation. Thermosensitive period has previously been assessed in a variety of ways. A suggestion for a more general way of defining thermosensitive stage/period is made.
Whether a turtle embryo develops into a male or a female depends, as with many other reptiles, on the temperature during incubation of the eggs. With sea turtles, warm temperatures produce 100% females. Therefore, global warming has the potential to drastically alter their sex ratios. Air temperatures on Antigua have increased by 0.7°C over the last 35 years. Measurements in both the sand and the clutches laid by hawksbill turtles (Eretmochelys imbricata) at Pasture Bay, Antigua, show that for important parts of the nesting season temperatures are already above the level producing 50% of each sex (pivotal level). Comparisons are made to sand temperature measurements taken on this beach in 1989 and 1990. It is estimated that fewer males were produced in 2003 than in the previous years. Recommendations are made for close monitoring of the fertility of eggs and for research on any turtles nesting at cooler times of year.
Protracted or intense rainfall may affect the reproductive success of reptilian species on a number of levels ranging from the availability of prey, the integrity of the nesting site and the subsequent survivability of offspring. For sea turtles (a species displaying temperature sex determination) nesting throughout the tropics and subtropics, rainfall has previously been shown to influence the development environment of clutches; in its extreme resulting in high levels of egg or hatchling mortality. Yet when compared to other abiotic variables affecting clutch success, rainfall has received relatively little attention. We therefore examined how fluctuations in local rainfall at a tropical nesting site for leatherback turtles (Dermochelys coriacea) affected the nest environment. Temperature data loggers placed within clutches (n = 8) revealed that protracted rainfall had a marked cooling effect on nests, so that seasonally improbable male-producing temperatures (< 29.75 °C) were produced. We use these data to explore how rainfall may ultimately influence the sex ratios of sea turtle hatchlings both within and between nesting seasons, and discuss the importance of robust estimates of rainfall for future demographic models.
Basic reproductive data from 21 green turtle ( Chelonia mydas ), 8 leatherback (Dermochelys coriacea), 7 hawksbill ( Eretmochelys imbricata ), 7 olive ridley ( Lepidochelys olivacea ),6 loggerhead ( Caretta caretta ), 1 Kemp's ridley ( Lepidochelys kempi ), and 1 flatback ( Chelonia depressa ) populations are provided. Some intraspecific and interspecific relationships between size of nester and clutch, egg size and hatchling size are analyzed. Measurements of reproductive rates (=numbers of hatchlings per female per year) in 11 populations varied from 35 to 200 in an olive ridley and loggerhead colony, respectively. Nesting behavior of each species is described in terms of type of nesting emergence and time spent on the nesting beach (=chelonery). The relatively large number of yolkless eggs laid by many leatherbacks and by some hawksbills invites further study. Some aspects of sea turtle nesting behavior and reproduction are compared to those of other chelonians.
In species with temperature-dependent sex determination (TSD), global climate change may result in a strong sex ratio bias that could lead to extinction. The relationship between sex ratio and egg incubation at constant temperature in TSD species is characterized by two parameters: the pivotal temperature (P) and the transitional range of temperature that produces both sexes (TRT). Here, we show that the proportion of nests producing both sexes is positively correlated to the width of the TRT by a correlative approach from sex ratio data collected in the literature and by simulations of TSD using a mechanistic model. From our analyses, we predict that species with a larger TRT should be more likely to evolve in response to new thermal conditions, thus putting them at lower risk to global change.
Phenotypic sex in sea turtles is determined by nest incubation temperatures, with warmer temperatures producing females and cooler temperatures producing males. The common finding of highly skewed female-biased hatchling sex ratios in sea turtle populations could have serious repercussions for the long-term survival of these species and prompted us to examine the thermal profile of a relatively pristine hawksbill nesting beach in Guadeloupe, French West Indies. Data loggers placed at nest depth revealed that temperatures in the forested areas were significantly cooler than temperatures in the more open, deforested areas. Using these temperatures as a predictor of sex ratio, we were able to assess the relative contributions of the different beach zones to the primary sex ratio: significantly more males were likely to be produced in the forested areas. Coastal forests are therefore important male-producing areas for the hawksbill sea turtle, and this has urgent conservation implications. On Guadeloupe, as on many Caribbean islands, deforestation rates are high and show few signs of slowing, as there is continual pressure to develop beachfront areas. The destruction of coastal forest could have serious consequences both in terms of local nesting behavior and of regional demography through the effects on population sex ratios. Human alterations to nesting habitat in other reptile taxa have been shown to modify the thermal properties of nest sites in ways that can disrupt their ecology by allowing parasite transmission, increasing vulnerability to climate change, or rendering existing habitat unsuitable.
An atlas of sea turtle nesting habitat for the Wider Caribbean Region
- K L Eckert
- A E Eckert
Eckert, K.L., Eckert, A.E., 2019. An atlas of sea turtle nesting habitat for the Wider
Caribbean Region, Revised edition. In: WIDECAST Technical Report No. 19. Godfrey,
Illinois.
Influence of diminished respiratory surface area on survival of sea turtle embryos
- Phillott
Phillott, A.D., Parmenter, C.J., 2001. Influence of diminished respiratory surface area on
survival of sea turtle embryos. J. Exp. Zool. 289, 317-321. https://doi.org/10.1002/
1097-010x(20010415/30)289:5%3C317::aid-jez5%3E3.0.co;2-0.