COP26: Climate Change & The West Indian Ocean

The 2021 United Nations Climate Change Conference brought international parties and world leaders together to accelerate action towards the Sustainable Development Goals of the Paris Agreement and the UN Framework Convention on Climate Change. It may have been the world’s best and final chance to bring runaway climate impact under control. In the spirit of this global summit, we elaborate on the importance of thorough research and continuous data in order to find solutions to this major threat to our planet.

Climate change and our oceans are inseparably connected, as 70 percent of the Earth’s surface is covered by water. The ocean influences weather both locally and globally, and in turn, changes in climate (e.g. global warming) alter many properties of the oceans.

Via our multi-ecosystem Ocean Observatory, BCSS provides real time multidisciplinary biogeochemical and ecological time-series data of environmental and oceanic change in the West Indian Ocean region. In this article, we highlight the impact on the ocean and identify which research themes of the BCSS Ocean Observatory are linked.

1. Increasing Sea Water Temperatures

Rising greenhouse gas concentrations cause ocean warming, which results in an imbalance in the warmth radiated from the sun and the energy radiated out into space. Approximately 90% of excess heat is stored in the oceans, compared to 1% in the warming atmosphere. With the rapid increase in greenhouse gasses over the past 50 years, the ocean is storing more heat than ever before.

Besides causing the melting of ice and causing rising sea levels, the warming of the ocean also results in rapid coral bleaching and loss of coral reefs, which reduces the breeding grounds for many marine species. Coral depends on microscopic algae (zoozanthellae) that live within the coral and give the coral the vibrant colour. A rise in seawater temperature stresses the coral, which makes it expel the algae. Other reasons for coral to expel algae are unusual low tides, pollution and too much sunlight. Bright white corals can recover and regain the algae, but the survival rates are very low. Coral reefs that are bleached often die, resulting in plummeting habitats for many fish species, crustaceans and megafauna, like turtles, that rely on the coral for food, shelter and use the reefs as spawning grounds.

Theme 1 (Ecosystem Function and Monitoring) and Theme 2 (Species Identification and Habitat Mapping) of the BCSS Ocean Observatory contain data sets that help understand changes in seawater temperatures, and the subsequent impact on marine life and ecosystems.

Data from the Ocean Observatory. BCSS collects data on seawater and seabed temperatures continuously at different locations. 

2. Higher Acidity Levels

As human and economic growth escalate the concentration of carbon dioxide (CO2) in the atmosphere as a result of activities such as burning fossil fuels and changing land use, the pH of the ocean’s surface waters drops, resulting in increased levels of acidity worldwide.

Ocean acidification reduces the ability of e.g. corals, plankton and shellfish to build and maintain their skeletons and shells. Plankton form the base of the food web of marine life, though as acidification of the ocean goes up, many calcifying plankton species will not be able to build their shells and will eventually die out, which will disbalance the ecosystems below the surface significantly.

“Mozambique experiences exponential damage of coral reefs owing to rising temperatures and acidicification which in turn affects biodiversity and ecology of habitats, adding pressure on fisheries and tourism.” – Dr. Mario Lebrato, Chief Scientist and Director of BCSS

It also reduces growth and survival rates during early life stages of various species. Changes in the chemical balance of the ocean can also affect the behaviour of non-calcifying organisms, as for some fish species (e.g. clownfish) it is harder to detect predators in waters with an unusually high level of acidity. Some algae species may benefit from higher CO2 levels in the ocean as they require photosynthesis. However, too much algae can out-compete coral reefs and halt the natural growth of substrates like hard coral.

Theme 1 of the BCSS Ocean Observatory (Ecosystem Function and Monitoring) monitors various relevant units (e.g. total alkalinity, dissolved inorganic carbon, dissolved CO2 and pH levels) that help understand how acidification impacts marine ecosystems. The data is compared with Theme 2 data (Species Identification and Habitat Mapping), to understand how environmental changes impact marine animals, spatial distribution and coral reef health.

Pictured is the predicted rate of dissolution of a shell of a pteropoda (type of holoplanktonic gastropod mollusks) in 2100, owing to acidification.

3. More Stratification

Seawater is stratified vertically in layers due to differences in temperature, density and salinity. This process prevents major water mixing (except in winter, owing to storms) due to the different properties of the water masses. This maintains elevated nutrient levels in deep water masses, which come to the surface after upwelling events, triggering plankton blooms and facilitating food for the ecosystem. Naturally, the ocean mixes because of currents, winds and tides, and because heat slowly moves deeper into the ocean. Stratification has increased due to the greater difference in density between the layers, which are caused by the warming climates.

The increase in stratification accelerates global warming, as warmer water on the surface can absorb less CO2 from the atmosphere, which leaves more CO2 in the atmosphere. The higher concentration of CO2 in the atmosphere in turn warms the Earth’s surface more, including upper levels of the ocean. As stratification slows down the mixing of different parts of the oceans, ecosystems are directly impacted as some depend on colder water coming in seasonally, and nutrients and plankton are less equally spread.

By monitoring sea temperatures continuously, among other parameters that show stratification, BCSS Ocean Observatory’s Theme 1 (Ecosystem Function and Monitoring) contributes to learning more about stratification. The theme also includes zooplankton surveys that contribute to understanding if the base of the food chain is changing over time, owing to stratification, warming and ocean acidification.

4. Change in Marine Life Distribution

With currents dynamics changing as a result of sea levels rising and temperatures going up, oceanic nutrients are distributed differently. As environmental factors change, food-supply, shelter and nurseries also shift over time, forcing many marine species to move to different locations. Upwelling and downwelling are necessary to mix nutrients and plankton to different layers of the ocean. The marine species living in these different layers depend on the up- and downwelling events for food supply. When food is scarce, the marine animals are forced to seek nutrients elsewhere, pushing them out of their familiar environments.

As habitats are being damaged or changed due to climate change (different sea temperatures, erosion of coastal reefs and mangrove forests etc.), shelter is less abundant, which means many (juvenile) species seek other spaces to inhabit that are less favourable in terms of protection, food supply and other factors.

Through monitoring marine animals in time and space, BCSS collects data on the distribution, behaviour and migration of species. The data is gathered through the Ocean Observatory’s Theme 2 (Species Identification and Habitat Mapping) and Theme 3 (Migratory Fish Populations Dynamics). This helps to understand habitat exploitation and any substantial shift in behaviour or habitat use driven by environmental factors.

As coral reefs are being damaged, shelter is less abundant, which means many (juvenile) species seek other spaces to inhabit that are less favourable. © Iris Uijttewaal

5. Rising Sea Levels

The rising sea level has significant impact on the shoreline via erosion and affect both human settlements and marine life as ecosystems change at a higher rate than anticipated. The changing sea levels are mainly caused by the warming of the ocean. As polar ice sheets and glaciers melt, the water adds to the global volume of the oceans. Thermal expansion is also an important driver for rising sea levels; as ocean temperatures rise, water expands. More than half of the sea-level rise that occurred over the past 27 years is due to thermal expansion.

The effect of sea-level rise impacts both marine life and coastal communities, as it causes for foreshore-based habitats to erode, saltwater to intrude into soil and erosion of beaches. In turn, this leads to the relocation of both animals and humans, as coastal areas become uninhabitable.

6. Disturbance of Coastal Environments

Mangrove forests and coastal coral reefs are under pressure due to rising sea levels and sea water temperatures going up, threatening the physical, economic and food security of coastal communities – around 40% of the world population. As coastal reefs provide key ecological services, e.g. hosting thousands of fish species, local communities all over the world turn to the coast for their source of protein. With coral reefs diminishing as a result of e.g. rising sea temperatures and extreme weather, fish populations are declining at an equal rate. Small-scale fishing also determines the income of many populations living near the sea, and disturbance of coastal environments pushes this demographic to look for other, less secure and scarcer sources of income. 

Through the BCSS Ocean Observatory platform, we have been collecting environmental (remote sensing, seawater) and ecological (marine life) data for three years, across over 100 km of coastline. To date, we average around 200 days of monitoring at sea per year, which equals to over 20,000 km of ocean surveyed in major ecosystems, including open ocean, coral and rocky reefs, seagrass meadows, sandy beaches, mangrove forests and pinnacles. The Ocean Observatory is a permanent time-series initiative, providing open-source data to further support conservation and to assist environmental decisions at a high level. The platform also provides education and training opportunities through the volunteering and internship programs.

For questions about this article, please contact:
Iris Uijttewaal, Bazaruto Center for Scientific Studies
+44 7 882 030 249

For questions about BCSS data, please contact:
Dr. Mario Lebrato, Bazaruto Center for Scientific Studies

Host of the first permanent Ocean Observatory focused on multi-ecosystem time series research in Africa, the Bazaruto Center for Scientific Studies (BCSS) was established in 2017 as in independent, non-profit organisation with a mission to protect and support the fragile ecosystems of the Bazaruto Archipelago, Mozambique. The research station is located on Benguerra Island, off the coast of Mozambique.
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