Small Life in the Sand of Rapa Nui

In just a handful of sand from the sea can be hundreds of thousands of small meiofauna animals.

This worm with many appendages is a nerillid, a member of polychaetes, which include meiofaunal as well as many larger forms.

Everyone knows the animals you can find on the beach or by snorkeling: mussels, snails, corals, sea stars, sea cucumbers and others. What few people know is that within the sediment, there are animals so small that they can hardly be seen with the bare eye. You need a microscope to see them. These animals live in the small spaces between sand grains. Typically, their size is around 100 micrometer, that is a tenth of a millimeter.

The community of animals between sand grains, generally called meiofauna, can be very rich, both in numbers and in diversity. Thousands of meiofauna species from almost all main animal groups (often called phyla) have been described from around the world. Some phyla are exclusively known from the meiofauna, others have only some representatives in the meiofauna. Often the meiofauna representatives look somewhat different from the larger relatives of the phylum, because they are adapted to the life between sand grains. To be able to move in the spaces between sand grains, a slender body form and a lack of long appendages are common features.  There are, for example, snails in the meiofauna that, at first sight, look like a worm.  They have no shell and are long and slender.

 

Flatworms sometimes have eyes. This one has a drop-shaped body form, other flatworms are longer and thinner.

Besides being rich in diversity, meiofauna animals can also be very abundant. Just a handful of sediment can have hundreds, even thousands, of meiofauna animals inside, but the numbers greatly differs much with the type of sediment.  Meiofauna animals feed on bacteria, small algae, detritus (that are smallest pieces of organic substances) or other meiofaunal animals. Meiofaunal animals are found wherever you look into marine sediments, but there are many places in the world where nobody has looked before. One such place is Rapa Nui. Very few people have observed meiofauna and nobody has ever published anything about it.  In November 2019, I undertook a small project to take a closer look at the Rapa Nui meiofauna. The project is a cooperation with ESMOI (Ecology and Sustainable Management of Oceanic Islands). To my delight, I found a wonderful diversity of exciting animals.

Roundworms or nematodes are also very abundant, although the figured roundworm, an epsolonematid with its characteristic body form, is not as often seen as other nematodes.

The sandy beaches of Anakena and Ovahe would seem to be the first place to look for meiofauna, but these sands are made up of small fragments of corals and shells.  They contain very little organic substance on which meiofauna could feed and the sand is exposed to strong wave power. Therefore, the meiofauna is actually quite poor there. A rich meiofauna was found in several samples of smaller accumulations of sediment between rocks. Many different species were found in the sand from the public swimming pool right in front of the Tongariki Cultural Center. These species include nematodes (roundworms), flatworms and small crustaceans called harpacticoids, which are present in the meiofauna all over the world. But the sediments also include beautiful worms, for which there are no common names, such as polychaetes and gastrotrichs.  In some sediments, marine mites and small marine isopods (crustaceans related to woodlice) were found. The full determination to which species the animals belong and whether they are new species or species known from other parts of the world requires a careful comparison with existing species descriptions and in some cases the collaboration with other experts.  For these reasons, the animals were documented with a camera attached to a microscope, so that all their characteristics can be checked later.

Los ostracods son animales asombrosos. Son crustáceos y tienen una cáscara como un mejillón. Ostracods fueron encontrados a menudo en los sedimentos de Rapa Nui.  

The presence of a rich and diverse meiofauna on Rapa Nui opens up the question as to how the animals got here.  Many larger marine animals, such as large worms, echinoderms, snails and mussels have small larvae that live in the plankton of the open water for a while before they settle to the ground. In this way, they can be transported by currents over long distances.  In contrast, the small meiofauna animals do not distribute larvae among the plankton, but their younger stages remain in the sediment. This means that they cannot spread over long distances. Nevertheless, they reached Rapa Nui after the island was born as a marine volcano. They could have come either on or in ships, or some of them could have reached the island on floating seaweeds, wood, volcanic pumice or, nowadays, on floating plastic litter.  It is an interesting research question to find out how meiofauna animals came to Rapa Nui.

Harpacticoids are small crustaceans that are very abundant and can be found in almost every sample of sediment.

The head of a tiny snail without a shell, found near Ovahe beach. The two round structures are statocysts (gravity sensors) and the teeth right of it are typical for snails and most other molluscs.

El Tavake and its future

The Tavake And its future, a challenge for Rapa NuiOne of the loveliest spots on the Island is the Moai (statue) quarry at Rano Raraku. Anyone who...

Marine Reserve in the bay of hanga roa

Marine Reserve in the bay of hanga roaAccording to the experts and the international NGOs that are dedicated to marine conservation, the oceans...

Toromiro Revives on Rapa Nui

Toromiro Revives on Rapa Nui Etnobotany Recovery   The toromiro, a sacred tree planted around ceremonial centers, was declared extinct over 50...

Wetlands of Rapa Nui affected by Climate Change

Wetlands of Rapa Nui affected by Climate Changeby Tahira Edmunds (Consultora Independiente - Independent Consultant), Cristóbal Cox (GP Consultores...

Climate Changes on Rapa Nui

Climate Changes on Rapa NuiEffects on animal life in the Eastern Pacific Ocean: El aumento de las lluvias relacionado con El Niño aumenta la...

Plastic contaminates the coast of Rapa Nui

Plastic contaminates the coast of Rapa NuiEvery year millions of tons of plastic are dumped into the oceans.  The largest part of this rubbish ends...

Overfishing on Rapa Nui

Overfishing on Rapa NuiA group of scientists, sponsored by the National Geographic Society, recently arrived on Easter Island following an...

Everything is in Motion – An Island in the Middle of the Ocean

Everything is in Motion – An Island in the Middle of the Oceanby Martin Thiel, Bernhard Steinberger & Tim KiesslingDid you know that the...

Diving, Underwater Hunting and Sharks

Diving, Underwater Hunting and SharksTestimonio de Testimony of Poki Tane HaoaHundreds of divers come to Rapa Nui every year in search of some of...

Marine Reserve in the bay of hanga roa

Marine Reserve in the bay of hanga roaAccording to the experts and the international NGOs that are dedicated to marine conservation, the oceans...

Overfishing on Rapa Nui

Overfishing on Rapa NuiA group of scientists, sponsored by the National Geographic Society, recently arrived on Easter Island following an...

Marine Park on Salas y Gómez

Marine Park on “Salas y Gómez”The international conservation organization, Oceana, and the National Geographic Society scheduled an expedition to...

A HITCH-HIKERS GUIDE TO RAPA NUI

A HITCH-HIKERS GUIDE TO RAPA NUIA HITCH-HIKERS GUIDE TO RAPA NUIby Sabine Rech - ESMOIEven though Rapa Nui is one of the most remote places on...

Mana, a Seamount off of Motu Motiro Hiva

Mana a Seamount off of Motu Motiro Hivaby Javier Sellanes Núcleo Milenio de Ecología y Manejo Sustentable de islas Oceánicas (ESMOI)–Facultad de...

Ngaru’a or Neck Pillow

Ngaru’aor Neck PillowAntiguamente los isleños no buscaban mayores comodidades en sus Hare Paenga (casas bote), en los Hare Mauku (habitaciones de...

Talismans of Rapa Nui

Talismans of Rapa NuiHo’onu o Tortuga or Turtle: In the old days, turtles were very common on Easter Island. La Perousse Bay was originally called...

The Eye of the Moai

The Eye of the MoaiBy Cristian Moreno Pakarati - Historiador / HistorianNearly three hundred megalithic statues were at one time erected on...

The Cult of the Ancestors and the Moais

The Cult of the Ancestors and the MoaisScientists, especially ethnologists, have long studied how different and complex communities were formed and...

Ara o te, the moai road

Ara o te, the moai roadHalfway up the side of the Rano Raraku volcano and buried up to their chests, more than a hundred giant statues (Moai) never...

Rock Paintings from Orongo

Rock Paintings from OrongoDuring their visit to the stone houses in Orongo where the men of the Bird-Man cult used to perform their rituals,...

German Archaeological Excavation

AVA RANGA UKA A TOROKE HAUGerman Archaeological Excavation (2nd Stage)New studies are being done by the German and Swiss archaeological team,...