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Sustainability was the key theme of the Earth Summit in Rio. To feed the world’s population, sustainable ecosystem use is essential. In particular in tropical coastal areas, population density is immense, and dependence on natural resources is correspondingly high. Diverse interests collide here and lead to greater ecosystem pressure than in the open oceans or on the mainland.

In a study published by the Leibniz Center for Tropical Marine Ecology a group of authors has compiled a catalogue of indicators for identifying the condition of coastal ecosystems and has described processes driving their sustainable development. Is the coastal ecosystem functioning as well as if it had been left untouched? Is it being overused? How can it be set on the right course again? By using the catalogue of indicators, such questions can be answered.

The approach is innovative: Natural and social scientists pooled their expertise based on decades of research in tropical ecosystems such as mangroves, coral reefs, seagrass beds and coastal waters. Close interdisciplinary collaboration is a hallmark of the ZMT and is indispensable for the comprehensive description of the state and dynamics of an ecosystem.

For instance mangroves: In 1995 a long-term project was launched at the ZMT to study the tidal forests in northeast Brazil. Over a period of ten years the scientists collected data on forest structure and species diversity and assessed the socio-economic importance of more than a dozen mangrove products.

Two key indicators identified were the population structure of mangrove crabs and the quantity of food they consume. These crabs are keystone species, i.e. species that are particularly characteristic of the ecosystem. They dig burrows up to two metres deep in the muddy forest floor, providing ventilation for the soil. The crabs consume 80 per cent of the mangrove tree leaf litter – an enormous quantity – and excrete the undigested organic material with their faeces in their burrows.

In this way vital nutrients are retained in the mangroves, as otherwise the leaf litter would be washed into the sea. The mangrove trees’ dense network of stilt roots holds back large amounts of this organic material. This is one of the reasons why mangroves are more efficient at storing CO2 than tropical rainforests and play a considerable role in the global carbon cycle.

At the same time, the crabs are one of the most important sources of income for people in the local communities. More than 80 per cent of the local population base their livelihoods on mangrove products and in particular on the crabs which they laboriously dig out of their mud burrows. Important indicators characterising the system are the significance of this resource for the population as well as income alternatives and the affluence levels of crab fishers, and their participation in the management of this resource.

In their study the authors demonstrate the complex and intricate interconnections between man and nature and how they interact in a given ecosystem. With this publication the authors offer a framework for identifying the linkages between key social and ecological processes.

More information:

Dr. Inga Nordhaus
Leibniz-Zentrum für Marine Tropenökologie
Tel: 0421 / 23800 – 74
Email: inga.nordhauszmt-bremen.de

Dr. Kathleen Schwerdtner Manez
Leibniz-Zentrum für Marine Tropenökologie
Tel: 0421 / 23800 – 82
Email: kathleen.schwerdtnerzmt-bremen.de

Publication

Measuring and understanding sustainability-enhancing processes in tropical coastal and marine social–ecological systems
Marion Glaser, Patrick Christie, Karen Diele, Larissa Dsikowitzky, Sebastian Ferse, Inga Nordhaus, Achim Schlüter, Kathleen Schwerdtner Manez and Christian Wild (2012) Current Opinion in Environmental Sustainability 2012, 4:1–9