A new threat to local marine biodiversity: filamentous mats proliferating at mesophotic depths off Rapa Nui

Javier Sellanes; Matthias Gorny; Germán Zapata-Hernández; Gonzalo Alvarez; Praxedes Muñoz; Fadia Tala

doi:10.7717/peerj.12052

A new threat to local marine biodiversity: filamentous mats proliferating at mesophotic depths off Rapa Nui

PeerJ. 2021 Aug 24:9:e12052. doi: 10.7717/peerj.12052. eCollection 2021.

Authors

Javier Sellanes^{1

2}, Matthias Gorny³, Germán Zapata-Hernández^{1

2

4}, Gonzalo Alvarez^{5

6}, Praxedes Muñoz¹, Fadia Tala^{1

6

7}

Affiliations

¹ Departamento de Biología Marina, Facultad de Ciencias del Mar, Universidad Católica del Norte, Coquimbo, Coquimbo, Chile.
² Millennium Nucleus for Ecology and Sustainable Management of Oceanic Islands (ESMOI), Universidad Católica del Norte, Coquimbo, Coquimbo, Chile.
³ Oceana, Santiago, Chile.
⁴ Programa de Doctorado en Biología y Ecología Aplicada (BEA), Universidad Católica del Norte, Coquimbo, Coquimbo, Chile.
⁵ Departamento de Acuicultura, Universidad Católica del Norte, Coquimbo, Coquimbo, Chile.
⁶ Centro de Investigación y Desarrollo Tecnológico en Algas y otros Recursos Biológicos (CIDTA), Facultad de Ciencias del Mar, Universidad Católica del Norte, Coquimbo, Coquimbo, Chile.
⁷ Instituto Milenio en Socio-Ecología Costera (SECOS), Santiago, Chile.

Abstract

Mesophotic and deeper habitats (∼40 to 350 m in depth) around Rapa Nui (Easter Island) were investigated using a remotely operated vehicle. We observed extensive fields of filamentous cyanobacteria-like mats covering sandy substrates and mostly dead mesophotic Leptoseris spp. reefs. These mats covered up to 100% of the seafloor off Hanga Roa, the main village on the island, located on its western side. The highest mortality of corals was observed at depths between 70 and 95 m in this area. Healthy Leptoseris reefs were documented off the northern and southeastern sides of the island, which are also the least populated. A preliminary morphologic analysis of samples of the mats indicated that the assemblage is composed of at least four filamentous taxa, including two cyanobacteria (cf. Lyngbya sp. and Pseudoanabaena sp.), a brown alga (Ectocarpus sp.), and a green alga (Cladophora sp.). An ongoing eutrophication process is suggested as a potential driver of the proliferation of these filamentous mats off Hanga Roa village.

Keywords: Cyanophyceae; Easter Island; Lepstoseris; Marine conservation; Mesophotic reefs; Polynesia.

Grants and funding

This work was supported by grants FONDECYT 1180694 and 1181153, as well as funding from the ANID- Millennium Science Initiative ESMOI. Germán Zapata-Hernández was funded by CONICYT-PCHA/ Doctorado Nacional/2015-21151249 and Beca de Postdoctorado MINEDUC UCN-19101 N° 002. Oceana Chile contributed to the funding of the expeditions and provided the ROV. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.