From the estuary of the Amazon in Brazil as far as the Cayenne peninsular in French Guiana there are a large number of wetlands lying behind the mangrove forests in dips formed in the alluvial sea deposits from the Amazon.

They make up a series of aquatic (marsh) ecosystems* characterised by very different species populations. These differences result from the history of the biological colonisation of these environments and from the capacity of the animal and plant species to spread.

The presence of man is virtually unfelt in these marshes and they are of very great bio-ecological value thanks to their originality, ecological riches, and patchwork of habitats they provide across the region. They have been colonised by specific plants suited to growing in peaty soils that are regularly waterlogged, and are home to many rare animals of significant heritage value* who live there either all year round or on a seasonal basis.

Their biological riches are unanimously recognised be it locally, nationally, or internationally. Nevertheless, these marshes and their biodiversity* are relatively little-known, both in French Guiana and Brazil, due to their inaccessibility and the low level of funding the scientific community has to study, preserve, and enhance them.

The Kaw marshes, a unique site of international importance

The Kaw marshes constitute a set of ecologically remarkable habitats amongst the stagnant and semi-stagnant aquatic ecosystems along the coast of French Guiana. It lies far away from the estuary of the Amazon (a hotspot for biodiversity* and potentially a source for the dispersal of species), is totally isolated, big (137,000 ha), and has animal and plant communities that are of outstanding biological richness.

This combination of factors has lately been recognised in both national schemes (it has been a National Nature Reserve since 1998, and is a class 1 ZNIEFF*) and international ones too (a Ramsar* site since 1993, and an IBA* zone since 2008). Most of the marshes have been wholly untouched by man as they are inaccessible by road or river. The process of colonisation is thus wholly subordinate to ecological constraints, laws, and opportunities.

The Agami Ponds: a coastal sanctuary for biodiversity

The very few zones of open water (ponds) forming permanent gashes in this immense marsh covered with floating herbaceous vegetation make up a mosaic of ecosystems which, though highly dispersed, are linked hydrologically by the waters flowing through the marshes. Whilst most of these ponds are surrounded by vast rafts of floating peat colonised by plants that like acid conditions, the Agami Ponds are highly unusual in having a relatively large number of shrub species. This structural particularity results in the Kaw marshes being a unique habitat in French Guiana. It owes its existence to a wide, ancient strip of dunes which has enabled a dense marshy forest to build up.

A floating research platform only accessible by helicopter was set up in the Agami Ponds in 2001, with funding from the French Guiana Region, to complement the research carried out as part of the National Humid Zone Research Programme (PNRZH, Programme National de Recherches sur les Zones Humides ). This station for scientific experiments provides various research teams with a unique opportunity to observe life in situ on the ponds without any significant disturbance.

Since it was set up, the studies carried out here have radically altered the perception of the marsh’s ecological value, especially of the Agami Ponds, confirming how important the place is both nationally and internationally.

Thanks to this platform it has been discovered that these ponds are colonised by a large population of black caimans (Melanosuchus niger) and that it is by far the most important breeding site in French Guiana for several species of rare birds: rufous-sided crakes (Laterallus melanophaius) (a species that is new to French Guiana), hoatzins (Opisthocomus hoazin), cocoi herons (Ardea cocoi), black-crowned night herons (Nycticorax nycticorax), great egrets (Ardea alba), anhingas (Anhinga anhinga), neotropic cormorants (Phalacrocorax brasilianus) and boat-billed herons (Cochlearius cochlearius).

It has also resulted in the discovery of the largest colony in the world of a little-known heron of which nearly 2000 pairs have been counted – the Agami heron (Agamia agami).

The Black Caiman

There is a large population of black caimans in the Agami Ponds which are protected from hunting by the fact that the site is extremely isolated. Preliminary investigations have yielded counts of 100 individuals in the dry season with a full demographic range from the youngest to the oldest, some of the animals measuring over 5 metres in length. During the rainy season, when the herons’ breeding season occurs, this number drops to a few dozen, mainly large individuals grouped near the herons’ breeding areas and feeding on chicks that have fallen out of their nests. In return the presence of the caimans protects the birds’ nesting sites against land animals feeding on eggs and young birds. In the dry season, when the bird colony is not there, it would seem that the caimans feed on fish, large numbers of which are present in the ponds at this period.

The agami heron

Until the recent discovery of a colony of nearly 2000 pairs on the Agami Ponds it was thought that this extremely shy species lived alone or in small arboreal colonies (between 3 and 15 pairs). It is currently thought that this is home to over 90% of the breeding numbers of the species.

The Agami heron is found on the coasts of Central America down to the north of South America (and especially in the Amazon and Orinoco basins) and is one of the last surviving members of an ancient line of Ciconiiformes*. It is one of the least-known herons on the American continent. It is a solitary bird and its colonies tend to be small and inaccessible, meaning that it is rarely observed and hard to study. There has been no detailed study of the Agami heron and little is known about its breeding biology, its ecology, its diet, its behaviour, its movements, and its numbers worldwide.

The worldwide working group on herons consequently considers it to be a priority to set up a research programme into the species. The data that most urgently needs to be gathered relates to threats to the populations, identifying ecological needs (in terms of diet and nesting habitat), and factors determining successful breeding.

Hoatzins

Its name comes from the Aztec and it is one of the rarest herbivorous birds. It is strictly folivore*, and eats nearly 50 or so different species, in particular moutouchis (Pterocarpus officinalis). Its crop is fifty times bigger than its stomach and carries out the necessary mastication and bacterial fermentation for it to be able to assimilate a large quantity of plant material every day.

Another unusual feature is that its chicks are born with two functional claws on the joint of each wing, enabling it to move about in trees and shrubs. These claws are similar to those of the Archæoptéryx (the oldest known bird fossil from the late Jurassic period, 150 million years ago) but this would appear to be a secondary adaptation related to its limited flying ability. It is able to dive and swim to escape predators.

The main threat to this species is the destruction of its habitats and their being turned into farmland (polders or rice fields). Its ability to adapt to changes brought about by man (hunting, disturbances, and the destruction of its habitats) is virtually nil because of its limited mobility and specialised diet.

The relatively high levels of accumulated sand (ancient dune strip) around the edge of the Agami Ponds mean that the Moutouchis have developed well and established a dense marshy forest. This arboreal vegetation is used throughout the year for breeding and feeding by ‘families’ of hoatzins that live in distinct colonies on the edge of the ponds. The structure of these trees is modified by the hoatzins feeding on them, resulting in the production of many dead branches. In an environment that is predominantly macrophytic* with floating herbaceous vegetation, the presence of dead sticks is invaluable to the arboreal herons who use them to make their nests.

A window onto the intimate functioning of the marsh

Given that the water tends to be naturally highly oligotrophic* here, the very few nutritional elements which are available in the ponds are rapidly and lastingly immobilised by the very abundant floating and submerged macrophytic biomass.

During the rainy season the large colony of birds is responsible for the intense fertilisation the water with their droppings. During the dry season, when the birds have left and light levels are high, this nutritional potential results in very strong eutrophication*. This situation, with abundant nutrients in the middle of a poor marsh that is in the process of drying out, is essential for the breeding and feeding of a very large number of fish species. This abundance means the ponds are a very attractive environment within the marshes as a whole, and predators – especially black caimans – concentrate here.

With the arrival of the rains and rising water levels the young and adult fish disperse throughout the flooded marshes, leading to a very pronounced drop in the numbers within the pond and consequently to the number of caimans.

In parallel to this, the heavy precipitation dilutes and impoverishes the nutritional content of the waters and thus the ponds’ productivity.

With the return of birds and their daily trips outside the marshes to feed their chicks, nutritional elements initially exported by the fish and caimans are brought back to where they started.

The waters of the ponds are also colonised by various species of submerged carnivorous plants (bladderworts) which derive the nitrogen and phosphorus they need in order to grow from their highly original diet of zooplankton*. In the very particular and transitory situation of the eutrophication of the ponds by bird droppings, this palliative strategy is relatively inappropriate. The plants’ survival therefore depends upon the oligotrophic* conditions pertaining in the marshes as a whole.

An outstanding site for scientific research

With its great biological wealth and being wholly unaffected by human disturbance, the Agami Ponds are home to animal populations of great heritage value* and are an outstanding site for carrying out research into the behaviour and conservation of rare species.

The Mediterranean Institute of Ecology and Paleoecology (IMEP, Institut Méditerranéen d’Ecologie et de Paléoécologie), the Group for the Study and Protection of Birds in French Guiana (GEPOG, Groupe d’Etudes et de Protection des Oiseaux de Guyane), and the Kaw-Roura Marshes National Nature Reserve carried out a preliminary study in 2008 into the biology, ecology, and behaviour of the Agami heron. The results are very promising and provide the basis for understanding the species’ strategies during an essential phase of its life cycle – breeding.

This mission also made it possible to establish the most suitable protocols and ways of operating to study this colony, and thus provides the grounding for more ambitious research projects.

The aim of these research programmes, developed in partnership with environmental actors in French Guiana, is to build up a body of scientific knowledge about the functioning, the biological interactions, and the structure of trophic food chains* in the Agami Ponds and, especially, about the role colonising birds and caimans play both for the ponds and the marshes as a whole.

An additional aim is to add to the currently highly fragmentary knowledge about the biology, ecology, and the status of the species, populations, and heritage* communities of the Kaw marshes. This is required to draw up strategies for the lasting conservation of the species and their habitats, and to communicate these strategies to the scientific community, decision-makers, and the general public, something for which French Guiana and France have an international responsibility.

Finally the natural wealth, ecological originality, and beauty of the landscape mean that the Agami Ponds are an ideal pedagogical tool for popularising science and educating the general public in environmental issues and helping them understand the threats to wetlands, their range of flora and fauna, and the importance of safeguarding them.

These research programmes now receive funding and strong moral, technical, and scientific support from institutions and not-for-profit organisations in French Guiana and France. Nevertheless carrying out an integral research programme into the Agami Ponds would require additional funding.