Description of the benthic fauna in natural and restored mangrove ecosystems in Mozambique



WIOMSA 12th symposium, poster presentation, October 13th, 2-3pm

THEME XXIII: Mangroves ecosystems


Mangroves, Mozambique @ IRD - Stéphanie Duvail

Authors

Torres Taimo (Univ. Eduardo Mondlane)

Júlia Sitoe (Univ. Eduardo Mondlane)

Célia Macamo (Univ. Eduardo Mondlane)

Daniela C. de Abreu (Museu de História Natural)

Background

As in all the WIO region, mangrove forests in Mozambique are under antropogenic pressure and threaned by the efects of climate change, which translates into a decrease in their coverage area, with consequent effects on the faunal community.

The loss of mangroves has the potential to significantly reduce biodiversity and ecosystem functions, with subsequent negative impact on human life. Mangrove forest restoration programs are of extreme value tools not only to promote mangrove areas recovery but also for the regain of their ecological functions (Idrus et al., 2019). 

An important indicator for assessing the recovery of mangrove habitat function and its health, is the diversity and abundance of benthic macrofauna communities that can be found at various levels of the mangrove forest.

Although there are a number of studies assessing the retoration sucess of the mangrove ecossystems floristic componente, few or non have been evaluating the restoring success of the ecosystems by looking at the fauna component. Thus, the present study aims to assess the benthic epifauna in natural and restored mangrove forests along the Mozambique coast.

Methods

The survey covers the provinces of Maputo, Gaza, Inhambane (Southern Mozambique) and Nampula (northern Mozambique). 

Restored mangrove forests chosen for the fauna study were the restored forests at the mouth of the Limpopo River in Gaza province, as these constitute a reference and an example of restoration of mangrove ecosystems in Mozambique. Restored forests of different ages were considered (2012, 2016 and 2020)

Sampling was carried out during low tide during spring tides, in the two types of mangrove forests under study. In each province and for each mangrove forest area visited, 5 transects were considered perpendicular to the coastline, with a separation of 25 m from each other. In each transect, five 5 m x 5 m squares were allocated every 20 m. Within each square, all epibenthic fauna were identified and quantified over 10 minute. For the fast moving crabs, crab burrows counted, identified by size and shape, or by observing emerging species.

Shrimp fishing, Tanzania @IRD - Stéphanie Duvail

Specimens that were difficult to identify in the field were collected and preserved in 70% ethanol and taken to the Ecology laboratory of the Department of Biological Sciences at Eduardo Mondlane University for identification. Most specimens were photographed in their natural habitat.

An analysis of the diversity and abundance of epibenthic fauna was carried out in all visited areas and restoration times.


Results

A total of 58 species of epibenthic fauna, were identified, from natural mangrove forests of Maputo, Inhambane, Nampula and Gaza provinces. These species belong to two main groups: Crustaceans and Molluscs (Gastropods and Bivalves). The crustacean presented the highest number of species, from wich crabs of the Sesarmidae and Ocypodidae families were the most common. 

Among these mangroves, it was also possible to observe sponges (Tedania anhalens) and two Gobiidae fish species (Periophthalmus sp), characteristic from mangrove habitats. In terms of species richness, Nampula province in the north of the country, presented the highest numbers, confirming to Mozambique the global characteristic latitudinal gradient of epifauna diversity increase towards lower latitudes.

In the restored mangrove forests of Gaza province (mouth of the Limpopo river) it was possible to observe a total of 27 species of benthic fauna, mainly crustaceans (crabs) of the Sesarmidae and Ocypodidae families (Paraleptuca chlorophthalmus,Cranuca inversa) and gastropods.

As expected, natural unimpacted forests had greater abundance and diversity of epibenthic species than restored forests. Nevertheless, the ecossystem restoration is visible through a clear greater diversity of species in older restored forest and a greater abundance, but less diversity in the forest restored more recently. This late aspect is a major characteristic of impacted forests where only a few species flourish, but in large numbers. All restored forests clearly showed faunal colonization, particularly by crabs of the Sesarmidae family (Parasesarma guttatum, Neosarmatium meinerti) and Gastropods which, according to Perry (1998), are an important indicator to evaluate the health of the mangrove and the recovery of the ecological function of the vegetation of the mangrove.

Conclusion

Fauna communities in natural and restored forests in Mozambique are mainly composed of Crustaceans (crabs), Gastropods (bivalves) and Gastropods (molluscs).

Crabs (Sesarmidae and Ocypodidae) and Gastropods are key groups that indicate the health and quality of mangrove ecosystems.

Mozambique in the South-North gradient presents the characteristic increase in epifauna diversity towards the equator. Maputo in the south having the least diversity and Nampula in the north the greatest.

The restoration process is an effective means of minimizing impacts, however, there is a slow return of the natural benthic community.