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The importance of the ancient mangroves of the Galapagos Islands

Published on June 16, 2021

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The mangroves that inhabit the Galapagos Islands are special; there is not so much mud, and the trees are smaller and set apart from each other. In the rest of the country the mangroves are dense, and the trees are much taller.

Those characteristics, precisely, caught the attention of Denisse Fierro Arcos, marine biologist and scientist at the Charles Darwin Foundation. That motivated her to lead an investigation to find out if those ecosystems provided the same type of services.

These complex root systems are known to serve as hiding places for baby fish and also to provide a food source during the critical stage of their development.

After collecting countless samples – for a month and a half – and analyzing them, it was found that indeed these mangroves also function as nurseries for a great variety of fish; they provide them with a habitat throughout their life, even during their juvenile stage.

This is where they hide from their predators. On that list are everything from snapper and cod to sharks and various species of stingrays.

Fierro Arcos, 35, who currently lives in Australia, points out that many of these fish have real local socio-economic importance. Hence the need to protect mangroves.

Currently, under the zoning of the Galapagos Marine Reserve, in force since 2001, only 5% of the mangrove areas on the islands receive full protection from extractive activities. Those, precisely, serve to comply with the different investigations. The rest is open to fishing and human activities such as tourism.

In her research, the marine biologist worked directly with a group of scientists, including her supervisor, as this study is part of her master’s thesis. They visited a total of 28 mangrove areas on six islands of the Ecuadorian archipelago.

They used a combination of two sampling methods: remote stereo cameras and underwater visual censuses to describe the diversity and abundance of fish that live among the roots of the mangroves. This is stated in the report that has already been released and published in volume 664 of the specialized journal Marine Ecology Progress Series.

A total of 35,029 fish belonging to 93 species, 67 genera and 36 families were identified. Pomacentridae, Mugilidae, Haemulidae, and Lutjanidae were the most common families. Juveniles made up 43% of the fish. At least 30 of the species are important to local artisanal fisheries, while 80% of them are associated with reef habitats.

That “suggests that mangroves in Galapagos can provide breeding habitats for economically valued species,” the report reads.

The marine biologist comments that mangroves are little studied and that also prompted her to undertake the research, which is based on previous work to expand the understanding of the importance of these habitats and contribute to the development of strategies and policies “that can protect these areas with a more effective way. Fishermen benefit that these areas are protected.”

With the study it was known, for example, that to the west of the islands of the archipelago there is a greater concentration of species. “That may be one of the areas that needs a lot more protection, while the other areas could be a bit more open.”

Another conclusion reached is that certain areas could be closed when the fish are spawning. “There are ways to manage that, so that people can continue to work, have access to food, but at the same time take care of those mangroves. ”

Protecting the place where sharks and different species of manta rays grow and develop is also necessary to promote local tourism, as many people come to the Galapagos Islands just to see them.

The results of this research have already been delivered to the Galapagos National Park. Its members are the ones who decide if they take the information and how they are going to use it or implement it.

Ancient salt-tolerant mangroves

Galapagos mangroves are particularly remarkable due to their age. These trees grow from the volcanic floor with limited nutrients and therefore grow very slowly; any developed mangrove habitat in the islands is most likely thousands of years old. In fact, thanks to their remarkable development and richness, the mangrove forests on South Isabela were RAMSAR certified in 2002.

Galapagos mangroves are salt-tolerant trees that grow where water meets land, and thus are typically found along coastlines. In order to withstand these extremely stressful conditions, mangroves have developed a series of brilliant adaptions. One of their most notable adaptations is their root system, which typically grows above the land like stilts in twisted looping formations. This is a technique that allows the trees to absorb oxygen through the pores in their roots, as the oxygen in the water or mud in which they live is either minimal or difficult to absorb. Other mangroves, such as the black mangrove, live on higher land where water levels are lower. Black mangroves instead have tentacle-like roots (pneumatophores) covered in pores that grow up from the surface to breathe oxygen from the air.

The trees also have a variety of techniques to filter the extremely high levels of salt in their environment; some species use a mixture of techniques while others just use one. Some Galapagos mangroves (i.e., red mangroves) are able to filter up to 97% of the salt from the water where they grow. Their highly impermeable roots act as the perfect filtration system, stopping the majority of salt from ever entering the tree.

Some mangroves concentrate excess salt in old leaves, which they then shed. The mangroves’ generally vertical branches also assist in this process, acting as aerating organs to filter salt so that the water that reaches the leaves is fresh. Still, other mangroves, such as the white mangrove, secrete salt directly from the plant—they have two salt glands on each leaf base.

Visitors to the Galapagos will also notice that the mangroves have very waxy or even fuzzy leaves, which are specifically developed to reduce the amount of water that evaporates from the leaves and conserve the precious freshwater they have acquired. The leaves may also have a succulent form, enabling them to store more water in their fleshy tissue.

Mangroves are not only special because of their unique roots and filtering ability, they also play a critical role in many coastal systems, adding to the biological diversity in the Galapagos.

Mangrove forests host a rich concentration of nutrients, as well as plankton, thus making them important breeding grounds for fish, birds, and other invertebrates, including turtles, penguins, flamingos, rays and even sharks. The roots also protect animals from large predators and waves, reducing the strength of the latter by up to 75%.

Mangroves are thought to have originated in the Far East, then over millions of years, the plants and seeds floated west across the ocean to the Galapagos Islands. Mangroves live within specific zones in their ecosystem. Depending on the species they occur along the shoreline, in sheltered bays, and others are found further inland in estuaries. Mangroves also vary in height depending on species and environment.

There are four types of Galapagos mangroves: the red mangrove, the black mangrove, the white mangrove, and button mangroves. The black mangrove has the highest salt-tolerant leaves of any other species in the Galapagos and even has special salt-extracting glands. This type of mangrove can be recognized by its short aerial roots, as well as the small tentacle roots that grow vertically up from the soil and surround the tree. Red mangroves are more common in the Galapagos and can be more easily recognized thanks to the reddish wood that covers them. They are common around the low tide zone. This species is used all over the world as a source of charcoal. White mangroves have delicate white flowers, as well as stilted roots and pneumatophores. The last species, the buttonwood mangrove, is not a true mangrove, but it is frequently found around mangroves that grow at higher elevations (such as the black mangrove) and also has an aboveground root system.

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