Mangrove fauna monitoring trials

This week myself, Rona, Norisha, Angela and Clarisha went out to La Gigi Mangrove on Picard to conduct a trial monitoring survey of three mangrove plots to practice implementing the new monitoring protocol before the South East Monitoring starts next weekend at DJL.

With the upcoming planned eradication of cats and rats on Aldabra, SIF is undertaking monitoring to fill gaps in our knowledge of species and species groups within the ecosystem, especially those likely to be impacted – positively or negatively – by the eradication. Mangroves, and their associated fauna, are essential to ecosystem health and a key habitat, covering 1700 ha of Aldabra. Rats on Aldabra are known to thrive in mangroves, with reports that they are reaching larger sizes, breeding all year round and showing higher survivorship in this habitat. This means they are therefore likely to be having a major impact on the mangrove ecosystem. Monitoring faunal species composition, abundance and richness will give the needed insight into the impacts of rats in mangroves and the effects of an eradication.The monitoring is completed once a year because mangrove fauna is less affected by seasons than other habitats. There are three mangrove monitoring sites:La Gigi mangroves for Picard; Dune Jean-Louis (DJL) landing stage for Grande Terre; and Middle Camp for Malabar.

The aim of this monitoring is to target species that are not covered by other protocols, which may be behaviourally cryptic but are essential for mangrove function. Those groups include bivalves, gastropods (particularly snails and limpets), other molluscs, small fish like mudskippers, chitons, and isopods. Sightings of reptiles are also recorded as the herpetofauna protocol does not cover mangroves.

20 minutes of active survey is conducted per plot by one observer. Alternatively we were trialling two observers splitting the plot in half and monitor for 10 minutes at the same time to reduce time effort but they must ensure there is clear communication and definition of plot division. This is what we were practising during our trial. When observing we thoroughly inspect each plot from the ground/water level (including root systems) up to the highest visible point of the canopy, recording all observed species and the number of individuals per species/morphospecies.

Whenever we encounter an unidentified photos are taken to aid identification back at the station. I have also created a field guide for us to use with some common species we may expect to see, as well as family groups of gastropods that may allow us to identify an individual to family level in the field and potentially to genus or species back at the station with sufficient photos taken.