São Tomé and Príncipe has a large maritime territory of 160,000 km2, where you can see a unique diversity of different marine ecosystems.
A marine ecosystem can be defined as the geographic area (of any size), composed of communities of organisms and their environment, where biological and energetic interactions are greater within than with adjacent ecosystems (Zhao and Costello 2020). This biological system is characterized by two factors: the biotic (e.g. plants, animals, microbes) and the abiotic (eg sunlight, oxygen, dissolved nutrients, depth, temperature). These components influence the dynamics of natural communities at different spatial scales, from global to local.
Marine ecosystems are natural systems found in the oceans and seas, which encompass a wide variety of habitats and aquatic life forms. They are composed of different interactions between marine organisms and their physical environment.
Marine ecosystems are extremely diverse and include areas such as coral reefs, estuaries, mangroves, marine grasslands, coastal zones, among others. Each of these habitats has specific characteristics, such as the salinity of the water, the presence of rocky or sandy substrates, the availability of sunlight and the presence of ocean currents.
The islands are ideally located for fish diversity: close enough to the African continent to support fish species typical of the shelf region, but also with a narrow shelf separated by seas over 1500 m deep that provide coastal habitat for several fish.
Main aquatic ecosystems present on the islands
An estuary is a coastal zone protected from extreme weather conditions, where oceans meet rivers and nutrients and salts from the ocean mix with those from the river. As a result, estuaries are among the most productive places on Earth and support many forms of life. Because they are located where rivers join the ocean, estuaries have traditionally supported many human communities and activities such as fishing, navigation and transportation.
Mangroves are unique and highly productive coastal ecosystems that occur in transition areas between land and sea in tropical and subtropical regions. They are found in tidal regions such as estuaries, protected inlets and river deltas. A total of 15 of these ecosystems have already been identified on both islands (12 on the island of São Tomé and 3 on the island of Príncipe).
They are characterized by the presence of trees adapted (Mangroves) to saline soil conditions and periodic flooding. The species that can be found on the islands of São Mangue Branco and Mangue Vermelho. These trees have aerial and respiratory roots, called pneumatophores, which allow the exchange of gases in soils with little oxygen. Mangroves are considered blue carbon ecosystems because they are more efficient at absorbing and storing large amounts of carbon than terrestrial ecosystems.
Coral reefs are highly diverse and complex marine ecosystems made up primarily of corals, which are small marine animals known as coral polyps. These polyps secrete a hard calcareous skeleton that, over time, builds up and forms the solid structure of the reefs. In São Tomé and Príncipe these habitats are composed of some essential benthic organisms, including matrices of epileptic algae, calcareous algae, coralline algae (which form small globular structures about 5 cm in diameter on mobile substrates), macroalgae, stony corals, sponges , zoanthids and gorgonians. Rocky reefs and solid coastlines occur where basalt volcanic rock is exposed. And it is also worth mentioning the occurrence of seagrass (or seagrass, it is a species of marine plant that belongs to the group of aquatic angiosperms) along the coast of the country.
Rivers and the watercourse
The hydrographic structure of the islands is radial, from the central mountains to the coast, resulting in numerous streams and small rivers (up to 27 km in length) (for example, in São Tomé: Ió Grande, Caué, Mussacavu, Quija, Rio do Ouro , Contador; on Príncipe: Rio Papagaio;) or crater lakes (for example, on São Tomé: Lagoa Amélia). The river network is well distributed across the islands, entering the sea through the creation of small estuarine habitats (12 mangroves in São Tomé and 3 in Príncipe) or small waterfalls or cascades. Several small inland lagoons are evenly distributed across the islands.