Northern range extension of the seagrass Halodule emarginata Hartog.

The seagrass Halodule emarginata is an endemic tropical species of Brazil, previously found from São Paulo to Bahia. The present study gives more ecological information of this species and report the extension of its northern range where it occurs in an estuarine area of Aquiraz-Ceará, semiarid coast of Brazil. In November 2014, the meadow was discovered, georeferenced and mapped. Five cores were collected for morphometrical analyses of H. emarginata and associated florofaunistic species. Two beds of H. emarginata with areas of 177.8 m2 and 5012.3 m2 were identified in the estuary of the Pacoti River, indicating an extension of its known range by 1500 km to the north. Despite the emarginate apex, morphological patterns revealed that specimens were slightly less developed than previously described in the literature, probably due to estuarine stress. However, algal biodiversity (seven species) in the studied meadows was within the range observed for other estuarine meadows in Brazil, with presence of Rhodophyta and Chlorophyta. The main groups of invertebrate megafauna were present, including 13 taxa mainly of Mollusca, Crustacea and Polychaeta. This meadow will be monitored in order to understand its dynamics and relationships with other florofaunistic species and its responses to environmental variations. [ABSTRACT FROM AUTHOR]