First limnological characterization of the tropical crater lake Amparihibe in the Makira Protected Area, Madagascar

Abstract

The newly established Makira Protected Area and its environs in Northeast Madagascar host roughly 50% of the entire Malagasy floral biodiversity, but very little was known about the two freshwater lakes found within the park. Lake Amparihibe was explored for the first time in November 2007. According to preliminary 40Ar/39Ar dating, the volcanic crater formed as far back as 25.3 million years ago, but no information is available about when the crater started to fill with water. The protected crater lake has a maximum depth of 28 m and was anoxic beyond a depth of 15 m. During the single sampling occasion, steep gradients in temperature, oxygen, conductivity and pH revealed a stable stratification. Several phyto- and zooplankton taxa showed distinct depth-specific abundance maxima along the steep physico-chemical gradients. The majority of plankton organisms have a cosmopolitan (tropical and temperate) distribution, however more taxonomic research is necessary before definitive conclusions can be drawn. Exposure of a multi-mesh gill net together with visual inspection by snorkeling yielded no presence of fish. Despite the full protection status of the park, illegal introduction of alien fish species seems a realistic threat to this pristine Malagasy lake. © Gabriele Drozdowski.