The mysterious flora of the small and remote island of Motu Motiro Hiva – Salas y Gómez

by

Jean-Yves Hiro Meyer – Délégation à la Recherche, Tahiti, French Polynesia

Darko D. Cotoras – Pontificia Universidad Católica de Chile & California Academy of Sciences

Pedro Lazo Hucke – CONAF Corporación Nacional Forestal, Provincial Isla de Pascua, Rapa Nui

Sebastián Yancovic Pakarati – Manu Project – Koro Nui o te Vaikava – CAMN Rapa Nui

Motu Motiro Hiva is regarded as one of the most isolated islands in the world. It is located at about 400 km east of Rapa Nui (Isla de Pascua or Easter Island), 2,500 km west north west from the Juan Fernández Archipelago and 3,400 km from the coast of northern Chile. This extremely remote and uninhabited island is considered the easternmost point in the «Polynesian Triangle», a cultural and linguistic region comprising Hawai’i on the north, Aotearoa (New Zealand) on the south-west, and Rapa Nui on the south-east. The first Europeans who noticed Motu Motiro Hiva were the Spanish navigators José Sálas Valdés in 1793 and José Manuel Gómez in 1805, explaining the name of Salas y Gómez island.

The island is the tip of a very large seamount that rose about 3,500 m from the ocean floor around a couple of million years ago. It is very small, with a land area of about 15 ha and a maximum elevation of 30 m, with a saddle-bag shape formed by two small hills of bare rock joined by a narrow isthmus and a sandy depression approximately 70 m in diameter in the center of the west largest sector.

Motu Motiro Hiva is well known by biologists for its large seabirds colonies. A total of 20 species have been recorded, of which at least 10 have been observed breeding or nesting, including the Christmas shearwater Puffinus nativitatis, the brown noddy Anous stolidus, the sooty tern or manutara Onychoprion fuscatus, the grey noddy Anous albivitta and the Polynesian storm-petrel Nesofregetta fuliginosa, whose nearest colonies are 2,400 km away in the Gambier and 3,400 km in Rapa Iti (French Polynesia).

Recent entomological field surveys conducted in Motu Motiro Hiva have also showed its richness in terrestrial arthropods. A least 15 morphospecies, including two species of Lepidoptera (moths) and two species of Isopoda (small terrestrial crustaceans), were collected. Among the arachnids, an endemic spider, Ariadna motumotirohiva, which is morphologically close to Ariadna perkinsi from Hawai’i and to Ariadna lebronneci from the Marquesas, was recently described (Giroti et al., 2020). Moreover, Hawaiioscia rapui, an isopod first described in caves on Rapa Nui and belonging to a genus only known to the Hawaiian Islands and a few localities in coastal Costa Rica, was found in 2016.

The vascular flora remained only sparsely described until the publication of a scientific paper by the authors in 2023 (Meyer at al., 2023). The first naturalists who landed on Motu Motiro Hiva attributed the poor vegetation to its small size and low elevation subjected to partial flooding and spray action during heavy seas and storms. The Swedish botanist Carl SKOTTSBERG reported in 1956 that «a halophytic Asplenium is the only living thing observed on the far-flung reef of Sala y Gomez». Based on different photographs taken during several field expeditions conducted between 2011 and 2022, we were able to identify four different plant species.

First, the small fern with coriaceous fronds Asplenium obtusatum var. obtusatum (Aspleniaceae) known from the east coast of Australia, New Zealand, some islands of Southeastern Polynesia (in the Society, Gambier and Australs in French Polynesia and in the Pitcairn Islands) as well as in Rapa Nui, the Juan Fernández Archipelago and South America (Figure 1). The second species was the succulent herb Portulaca oleracea (Portulacaceae) with a thick fleshy stem and small bright yellow flowers (Figure 2). It is a pantropical species, presumably native to the Old World (Africa, Mediterranean or Southern Asia) and a modern introduction in Western and Eastern Polynesia. It is considered as native or a doubtful indigenous species in Rapa Nui. The third plant species is the succulent herb Sesuvium portulacastrum (Aizoaceae) with red to green stems and red-pink-lavender-white flowers forming dense mats (Figure 3). It is a pantropical coastal species found in South America, Caribbean islands, South Pacific islands, including Eastern Polynesia and the Hawaiian islands. It is one of the few flowering plants able to grow in a habitat that is inundated by salt water at each high tide. We considered this species as indigenous in Motu Motiro Hiva. Finally, we found a new island record that we considered to be new to science: it is a small (< 20 cm) succulent herb with square fleshy stems, fleshy sessile to subsessile obovate leaves with a pronounced nervation and small flowers without a corolla found in axillary short inflorescences (Figure 4). This species is related, but clearly different from Parietaria debilis (Urticaceae), an annual erect herb with non-fleshy stems and leaves, native to Australia, New Zealand, Juan Fernández Archipelago, San Ambrosio (Islas Desventuradas) and the Galápagos Islands. In New Zealand, P. debilis is reported in the islands of Kermadec, Three Kings and Chatham, where it is usually found in coastal scrub and forest around petrel or shearwater burrows, sometimes growing on exposed rock or in sand dunes.

Motu Motiro Hiva harbors a surprisingly poor flora compared to its relatively diverse avifauna and arthropod fauna. Its terrestrial flora and fauna show connections with Rapa Nui, its nearest island, but also other far away Pacific island groups, such as the Marquesas or Hawai’i. The presence of an undescribed Parietaria indicates floristic relationships with islands off the coast of South America, in particular the Juan Fernández Archipelago, the Islas Desventuradas and the Galápagos. This unique island ecosystem deserves continuous efforts of protection, especially in the face of the impacts of climate change, including sea-level rise.

Giroti A.M., Cotoras D.D., Lazo P. & Brescovit A.D. 2020. First endemic arachnid from Isla Sala y Gómez (Motu Motiro Hiva), Chile: A new species of tube-dwelling spider (Araneae: Segestriidae). European Journal of Taxonomy 722: 97-105. 

Meyer  J.-Y., Cotoras D.D., Lazo Hucke P. & Yancovic Pakarati S. 2023. The peculiar flora of Motu Motiro Hiva (Salas y Gómez, Chile) and its similarities with other small remote uninhabited Eastern Pacific Islands. Atoll Research Bulletin 632.