Climate change

Increasing coral cover and decreasing coral species diversity with decreasing light availability at depth: a study of the future effects of sea level rise on fringing reef ecosystems

Global climate change is having widespread effects on the world’s oceans. Particularly vulnerable to changing global conditions are coral reefs, which boast high biodiversity levels though they comprise a small percentage of the oceans. Sea level rise decreases light availability to corals and their symbiotic photosynthetic zooxanthellae, which are responsible for fixing the carbon that corals use to create their carbonate skeleton. Studies have shown how changing light availability with depth can be used as an indicator of coral species diversity. Species richness and diversity of corals is greatest at intermediate depths, with decreasing diversity at greater depths. This study investigated the relationship between coral species diversity and light intensity at depths of 12, 18, and 24 m on the fringing reef ecosystem off the western coast of Bonaire, Dutch Caribbean. Light intensity data were based on theoretical values provided by Beer-Lambert’s law, and video transects were conducted to determine composition of the substrata and to calculate coral species diversity and richness. Strong correlations were found between decreasing coral species diversity with depth (p = 0.041) and percent coral cover and decreasing percent cover of macroalgae and cyanobacteria with depth (p = 0.000, F = 37.60, df = 1). This indicates that while species diversity of corals decreases with lowered light intensity, corals are better able to outcompete macroalgae in environments with decreased light availability. This information is useful in understanding how reefs will respond to environmental changes brought on by sea level rise.

This student research was retrieved from Physis: Journal of Marine Science XVI (Fall 2014)19: 48-54 from CIEE Bonaire.

Date
2014
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire

Sand temperatures for nesting sea turtles in the Caribbean: Implications for hatchling sex ratios in the face of climate change

A 200-year time series of incubation temperatures and primary sex ratios for green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and leatherback (Dermochelys coriacea) sea turtles nesting in St. Eustatius (North East Caribbean)was created by combining sand temperature measurementswith historical and current environmental data and climate projections. Rainfall and spring tides were important because they cooled the sand and lowered incubation temperatures. Mean annual sand temperatures are currently 31.0 °C (SD = 1.6) at the nesting beach but show seasonality, with lower temperatures (29.1–29.6 °C) during January–March and warmer temperatures (31.9–33.3 °C) in June–August. Results suggest that all three species have had female-biased hatchling production for the past decades with less than 15.5%, 36.0%, and 23.7% males produced every year for greens, hawksbills and leatherbacks respectively since the late nineteenth century. Global warming will exacerbate this female-skew. For example, projections indicate that only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090. On the other hand, future changes to nesting phenology have the potential to mitigate the extent of feminisation. In the absence of such phenological changes, management strategies to artificially lower incubation temperatures by shading nests or relocating nest clutches to deeper depths may be the only way to prevent the localised extinction of these turtle populations. 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Geographic location
St. Eustatius

Climate Change Predictions for St-Eustatius and its possible impacts on the island

This report was created to highlight the most important climate change predictions for St. Eustatius and to highlight possible impacts on the island.

St. Eustatius (Statia) is a Caribbean island near St. Kitts and Nevis, St. Maarten and Saba. St. Eustatius has a surface of 21 square kilometres and forms part of the Dutch Caribbean. On 10-10-10 it became a special municipality of The Netherlands, together with Saba and Bonaire (together they form the BES-islands).

St. Eustatius is important for its marine and terrestrial species, some of which are endemic and/or endangered. Some examples of this include Iguana delicatissima and the newly-described endemic, Gonolobus aloiensis. However, because of the island’s small size, it is likely that climate change will threaten these species. Climate change will have different impacts on St. Eustatius.

Since 2010, the population on St. Eustatius has increased. On 01-01-2010 there were 3583 people living on St. Eustatius, but on 01-01-2014 this number grew to 4020. That is an increase of 437 people (12% compared to 01-01-2010) in just four years. Also 36% (714 persons) of the working population on St. Eustatius is working in the trade, transport or catering industry. And 31% (609 persons) is working in the government branch.

If we look at the coastal protection of St. Eustatius, than it is clear that this s predominantly natural, except for the protection near NuStar, the harbour and in Oranjestad Bay, which are man-made. This is also one of the reasons why most of the island is vulnerable to erosion, because there is no protection.

The nature on St. Eustatius has many strengths, weaknesses, opportunities and threats (SWOT).The most important strengths are good maintenance of the national parks, high biodiversity and the presence of marine and terrestrial protected areas. There are also opportunities for nature on the island. The most important one is scientific research, on many different kinds of species. Unfortunately, however, island’s nature also faces some threats and weaknesses. The greatest threats are non-native and invasive species (cows, goats, etc.), climate change and pollution. The most important weaknesses are a lack of environmental awareness, limited area of the island and small research populations (amount of species present on the island).

Climate change will affect St. Eustatius. IPCC predictions predict that temperatures will rise by approximately a minimum of 0.7 ˚C to a maximum of 2.4 ˚C by the end of the century, according to RCP 4.5 Precipitation rates will, according to RCP 4.5, vary by a maximum of -29% to a maximum of +14%. Sea levels will rise by approximately 0.5-0.6 meters by the end of the century (IPCC, 2013). This is all compared to the mean of the period 1986-2005.

These predictions will have some impacts on St. Eustatius. Climate change will especially have an impact on six different areas. These include: erosion, extreme events, coral reefs, human health, nature and tourism. The erosion rate is likely to increase in the future because of climate change. This will have a huge impact on the island. Also extreme events, like storms/hurricanes, are likely to happen more often in the future, with more extreme strengths. This will affect the corals around the different reefs that surround St. Eustatius. Not only will storms affect corals, but also rising sea temperatures will have a negative impact. Human health will also suffer under the effects of climate change. Mosquito density is likely to increase in the future, because of a more wet climate (IPCC, 2013). These mosquitos can spread diseases like dengue fever and the West Nile Virus. Terrestrial species will also experience the negative impacts of climate change. The main impact will be a shift in ecological zones. Finally, tourism can also suffer the negative impacts of climate change.

Date
2015
Data type
Other resources
Theme
Research and monitoring
Geographic location
St. Eustatius
Author

The impacts of sea-level rise on the index nesting beach on Klein Bonaire for three species of sea turtle

Abstract:

Globally, all extant sea turtles species are endangered due to centuries of uncontrolled exploitation, furthermore they face future threats from climate change. The Caribbean is home to six of the seven extant marine turtle species. Sea turtles have various nesting and feeding grounds across the Caribbean but return to their natal beaches to breed. This study focuses on nesting sea turtles in Bonaire, a small island in the south of the Caribbean, which has three breeding species; the Green, Loggerhead and Hawksbill turtle. The index beach is “No Name” beach on the small islet of Klein Bonaire, which is 800m west of Bonaire.

Global sea-level rise projections range between 0.18-0.59m by 2100 (IPCC, 2007). However, the Caribbean region could experience 25% greater sea-level rise than the global average with suggestions up to 1.6m. Sea-level rise threatens nesting beaches and is expected to negatively impact the sea turtles. This investigation measured beach profiles along “No Name” beach to create contours of elevation. The nests were identified, monitored and plotted onto maps. Analysis of the distance from the nest to the HTM and elevations of nests indicate that Loggerheads are more at risk from sea-level rise. However for all sea-level rise scenarios there will be beach area and nests lost (using 2012 data). Where natal beaches cannot retreat, they may be lost to sea-level rise; turtles must adapt to climate changes or will face an even greater population decline. 

Date
2012
Data type
Other resources
Theme
Research and monitoring
Geographic location
Bonaire
Author

How much time can herbivore protection buy for coral reefs under realistic regimes of hurricanes and coral bleaching?

Abstract:

Coral reefs have been more severely impacted by recent climate instability than any other ecosystem on Earth. Corals tolerate a narrow range of physical environmental stress, and increases in sea temperature of just 1 1C over several weeks can result in mass coral mortality, often exceeding 95% of individuals over hundreds of square kilometres. Even conservative climate models predict that mass coral bleaching events could occur annually by 2050. Unfortunately, managers of coral-reef resources have few options available to meet this challenge. Here, we investigate the role that fisheries conservation tools, including the designation of marine reserves, can play in altering future trajectories of Caribbean coral reefs. We use an individual-based model of the ecological dynamics to test the influence of spatially realistic regimes of disturbance on coral populations. Two major sources of disturbance, hurricanes and coral bleaching, are simulated in contrasting regions of the Caribbean: Belize, Bonaire, and the Bahamas. Simulations are extended to 2099 using the HadGEM1 climate model. We find that coral populations can maintain themselves under all levels of hurricane disturbance providing that grazing levels are high. Regional differences in hurricane frequency are found to cause strikingly different spatial patterns of reef health with greater patchiness occurring in Belize, which has less frequent disturbance, than the Bahamas. The addition of coral bleaching led to a much more homogenous reef state over the seascape. Moreover, in the presence of bleaching, all reefs exhibited a decline in health over time, though with substantial variation among regions. Although the protection of herbivores does not prevent reef degradation it does delay rates of coral loss even under the most severe thermal and hurricane regimes. Thus, we can estimate the degree to which local conservation can help buy time for reefs with values ranging between 18 years in the Bahamas and over 50 years in Bonaire, compared with heavily fished systems. Ultimately, we demonstrate that local conservation measures can benefit reef ecosystem services but that their impact will vary spatially and temporally. Recognizing where such management interventions will either help or fail is an important step towards both achieving sustainable use of coral-reef resources and maximizing resource management investments. 

Date
2011
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire

Can a thermally tolerant symbiont improve the future of Caribbean coral reefs?

The detrimental effect of climate change induced bleaching on Caribbean coral reefs has been widely documented in recent decades. Several studies have suggested that increases in the abundance of thermally tolerant endosymbionts may ameliorate the effect of climate change on reefs. Symbionts that confer tolerance to temperature also reduce the growth rate of their coral host. Here, we show, using a spatial ecosystem model, that an increment in the abundance of a thermally tolerant endosymbiont (D1a) is unlikely to ensure the persistence of Caribbean reefs, or to reduce their rate of decline, due to the concomitant reduction in growth rate under current thermal stress predictive scenarios. Furthermore, our results suggest that given the documented vital rates of D1a-dominated corals, increasing dominance of D1a in coral hosts may have a detrimental effect by reducing the resilience of Caribbean reefs, and preventing their long-term recovery. This is because Caribbean ecosystems appear to be highly sensitive to changes in the somatic growth rate of corals. Alternative outcomes might be expected in systems with different community-level dynamics such as reefs in the Indo-Pacific, where the ecological costs of reduced growth rate might be far smaller.

Date
2013
Data type
Scientific article
Theme
Research and monitoring

Estimating sex ratios in Caribbean hawksbill turtles: testosterone levels and climate effects

Evolutionary theory predicts that male and female offspring should be produced at a 1:1 ratio, but this may rarely be the case for species in which sex is determined during incubation by temperature, such as marine turtles. Estimates of primary sex ratio suggest that marine turtle sex ratios are highly skewed, with up to 9 females per male. We captured juvenile hawksbill turtles Eretmochelys imbricata in waters around Anegada, British Virgin Islands, a regionally important foraging aggregation, and analysed concentrations of plasma testosterone and oestradiol-17β from 62 turtles to estimate sex ratio. There were 2.4 to 7.7 times more females than males. Testosterone concentrations correlated with sampling date and sea surface temperature (SST), with higher concentrations in the late summer when SST was highest, suggesting that assigning sex through threshold values of sex hormones must be carried out cautiously. The sex ratio in the juvenile foraging aggregation around Anegada is more male biased than at other locations, suggesting that turtles at Anegada have resilience against feminising effects of climate change. Future work should (1) integrate the relative contributions of different genetic stocks to foraging aggregations and (2) investigate the annual and seasonal cycles of sex hormones, and differences among individuals and life history stages. 

Date
2013
Data type
Scientific article
Theme
Research and monitoring
Journal