Corals: environmental records of the past

Corals: environmental records of the past

Humans are wonderful creatures; our intellect has allowed us to thrive on this planet through impressive technological and scientific advances. However, this success has come at a cost. For example, most marine ecosystems are now under pressure from a variety of stressors mostly linked to human activities. In the case of coral reefs, these stressors include a combination of global pressures in the form of warming and ocean acidification, and local pressures which include overfishing, habitat destruction, pollution, increased sedimentation, to name just a few. This pressure has caused a worldwide loss and degradation of coral reefs; however, there are still questions about the full scale of these changes and on the ability of corals to withstand them. For example, we know that extreme heat can kill corals, but it is not fully understood how quickly corals can increase their tolerance to thermal stress, or how local and global stressors interact with each other. The latter is crucial because while fixing global warming and ocean acidification requires a global effort, but local governments and managers can implement policies to remove or reduce local stressors and give corals a better fighting chance in the face of climate change.

Massive colony of Sidereastrea siderea colony in Martinique. Photo: Jean-Philippe Maréchal (2021).

One of the reasons for current knowledge gaps is the lack of long-term temporal observations of key environmental parameters, such as temperature, salinity, or the pH of seawater. Historically, we either lacked the technology to monitor these parameters, access to such technology was expensive or there was no clear understanding of the need to monitor these parameters. Therefore, to put current changes in perspective, accounting for natural variability, it is necessary to find ways to fill knowledge gaps, and corals can help us to do so!

Reef forming corals precipitate a calcium carbonate skeleton that forms the reef foundation.  These skeletons come in all shapes and sizes, from the delicate and intricate branching corals to the massive types that are named as such due to their stable ball- or boulder-shaped skeleton. The skeletons of corals are attractive to paleoceanographers because they can tell us about the past, if you know how to read the stories recorded in their skeletons. This is because corals continuously deposit new layers on top of their older skeleton, thus growing bigger and bigger every year and creating a record of their history. Some massive corals can become real life giants as the can live for several centuries, never ceasing to grow. The oldest massive corals are believed to be nearly a thousand years old. But corals are living organisms that respond to their environment as we do, and their skeleton records these changes in a similar way to trees forming rings. In winter, when the waters are cold, corals tend to grow slower and form a denser skeleton while in summer, when it is warmer, corals usually grow faster and form a less dense skeleton. Therefore the skeleton of a massive coral records this seasonal rhythm in the form of annual bands that resemble the rings in the trunk of a tree.

X-ray image from a core of a massive coral showing the annual density bands.

If a year is unsually cold or warm this influences the average growth rate for that particularly year. Therefore, if we measure the distance between these annual bands, we can reconstruct the growth history of a coral throughout its life. The incorporation of elements present in seawater into the skeleton of the corals is also influenced by changes in the environment. For example, the incorporation in strontium into the skeleton varies with temperature; therefore the changes in strontium in the skeleton can be used to reconstruct the changes in the seawater temperature through time. Similarly the amount of barium in the skeleton of corals appears to respond to changes in the amount of terrestrial runoff reaching the reef.

As part of the MaCoBioS project we are planning to analyse the growth and chemistry of the skeleton of corals from Martinique and Bonaire the Caribbean. These analyses will be used to reconstruct temporal changes in terrestrial inputs into the reef, and to determine how this is linked to land use change and pollution over time. In addition, we will investigate how different corals control their internal chemistry to facilitate the formation of the skeleton and how this mechanism responds to ocean acidification and thermals stress. For this second goal we will compare corals from the tropical Caribbean with corals from the temperate Mediterranean. These projects aim to provide managers and policy makers with better information on how corals respond to changes in their environment over long periods of time so that they can take the right steps to manage the reef and help preserve these magnificent ecosystems.

The Freie Universität Berlin team (Dr. Georg Heiß, Dr. Juan Pablo D’Olivo Cordero and Dr. Moshira Hassan) collecting a coral core in Martinique. Photo: Dr. Diego Kersting

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How to bridge the Science-Policy-Society gaps to better protect and manage marine ecosystems?

How to bridge the Science-Policy-Society gaps to better protect and manage marine ecosystems?

We live on a blue planet, where 71% of the earth’s surface is covered by oceans, lakes and rivers. There is now an increasing interest for our oceans as evidenced by various international initiatives such as the adoption of a UN Sustainable Development Goal dedicated to the ocean. However, there is a lot to be done and catch up on because the marine environment has for a long time been a stepchild in environmental policies and conservation. The impacts of human activities on marine ecosystems are not visible to most people and therefore have not entered the public awareness to the same extent as the degradation of terrestrial ecosystems or the loss of animals or plants on land. What’s more, the marine environment still has many blank spots for science, but its importance for society is undeniably huge. A large source of the protein consumed by people comes from the sea and the oceans support the livelihoods of billions of people around the world. Oceans regulate the global climate by absorbing vast quantities of carbon and they are the largest producer of oxygen.

Fishing boat and coasts in St Lucia. Photo credit: Fabiola Espinoza Cordova

In MaCoBioS, a consortium of international researchers from many different scientific disciplines seek to answer some urgent questions, regarding the impacts of human activities on marine ecosystem functions, the supply of ecosystem services from these, and the potential of solutions that combine better marine management and protection with the mitigation of environmental changes, foremost adaptation to clime change. Yet, for scientific knowledge and understanding to be taken up, policy makers and environmental managers have to be included throughout the process. Science communication must ensure that results and evidence-based recommendations reach this important target group, who use this knowledge to formulate policies and plans that in turn contribute to improve marine management and conservation.

Unfortunately, while this sounds quite straightforward, the reality is more complex and challenging. Mobilizing different kinds of knowledge (for instance local and indigenous knowledges) in order to improve the management of marine resources requires pluralistic and interdisciplinary approaches. Science needs to interrogate prevailing power asymmetries within and among existing institutions, question its own scientific assumptions, and the values and interests that are the result of the power asymmetries and assumptions.

In addition, the language of science and the language of policy are rarely compatible, finding a common denominator and being able to speak to one another is therefore of utmost importance. Here, science and scientists have an important task – learning to speak the language of policy and practitioners, that overcomes historically diverging views and interests. Moreover, although science is complex in itself, providing evidence-based recommendations must account for the messiness of the policy process. At each phase of this process different short and long term economic, social and political interests and power clash with each other. Thus, policies may either be compromises of different trade-offs or benefit specific sectorial interests first and foremost.  

Within MaCoBioS we seek to provide evidence-based guidance for marine policy formulation and innovative research pathways. We do this because we want to support policymakers in developing cost-effective strategies in order to improve marine and coastal ecosystem management and protection. Doing so is particularly important in the light of the ongoing and expected climate changes. MaCoBioS partners are combining ecological and social science research carried out in three regions (the Caribbean, the western Mediterranean and the North Sea) in order to find out how environmental change affects not just the marine and coastal ecosystems, but also people and communities depending on these.

Getting a more complete picture of the interconnectedness between society and the marine and coastal ecosystems, and understanding how dependent communities are on ecosystem services allows for the formulation of better and more equitable policies. Understanding the societal dimensions and accounting for these in policies and management plans supports their implementation and uptake, reducing potential resistance by people and communities.

Illustration of sea level rise in France. Photo credit: Rémy Simide

For instance, in Barbados we seek to better study how power dynamics and different ways policy makers understand adaptation to climate change influence policy and planning. Moreover, what does it mean for social justice and environmental integrity when actions are implemented on the ground? Understanding how the adaptation challenge is problematized and what processes shape who decides, who is vulnerable, whose values counts and what interventions to prioritize is key if we want to translate scientific knowledge into transformative change.

In Martinique, we apply a gender and intersectional lens and focus on understanding the impacts of climate change (including aspects of loss and damage) on marine and coastal ecosystems and people’s livelihoods. Here, we emphasize local knowledge, the perception of risk, as well as dependencies, needs, and aspirations of communities relying on marine and coastal ecosystem services in order to support inclusive and informed decisions made under the uncertainty posed by climate change.

Text by Torsten Krause, Alicia N’guetta and Fabiola Espinoza Córdova

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