Field work around Tetiaroa

Check our fish larvae pictures on the on-line taxonomic database
set up for the project

Alis46 In order to shed some light on the distribution of coral reef fish larvae in field conditions, a scientific campaign was organised by Serge Planes for my PhD, around the Atoll of Tetiaroa (17º S, 149º33 W) in French Polynesia. A team constituted of 6 scientific staff and 12 shipmen conducted the sampling in May 2006, aboard the N.O. Alis. The objectives of this campaign were:

  1. to obtain precise data on the environmental conditions which fish larvae encounter during their pelagic larval stage (currents, food abundance, etc.)
  2. to describe the distribution of fish larvae, both horizontally and vertically around an isolated island
  3. to correlate the two in order to understand which variables or processes control the distribution of fish larvae

The sampling grid was designed to cover a large area around the atoll, to study the influence of the distance from the island and of the position with respect to the current field (e.g. windward vs. leeward sites) on the abundance of fish larvae. 36 stations were sampled in 72 hours, day and night. This sampling unit (called a “rotation”) was repeated 4 times.

Far

The islands at the bottom of the map are Moorea and Tahiti, which are more than 40 km away from Tetiaroa. The nearest island in the other directions is hundreds kilometers away. The winds come mostly from the south-east in this region and therefore the water flowing past Moorea and Tahiti does not mix much with the water flowing in our study grid.

Near In addition to these stations, we sampled 13 more stations, closer to the atoll. This sampling was repeated two times. The flow around a deep sea island or atoll such as Tetiaroa is very complex: it generates eddies in an otherwise steady regime. The initial dispersal trajectories of propagules originating from the atoll are critical to their entry in these complex features. These stations were sampled in order to enhance the resolution of our description of initial dispersal.

At each of these stations the same sampling procedure was repeated:

  • a Multiple Opening-Closing Net and Environmental Sensing System (MOCNESS, see a picture) tow, which sampled fish larvae in a depth stratified manner (during the upward part of the tow 4 nets are opened sequentially) and recorded physical parameters of the water mass (Temperature, Salinity, Density, Fluorometry). The nets in this apparatus have a 0.8 mm mesh.
  • two Bongo nets tows (see a picture). These nets have a finer mesh (0.33 mm) and were intended to sample the smaller portion of the plankton which can contain prey items from fish larvae. Two tows were carried out at different depths in order to estimate the depth stratification of this size-fraction of the plankton.
  • an ADCP record to estimate the current speed and direction at the station.

This field effort went well and yielded over 1000 biological samples and > 400Mb of physical data, some of which are still being processed currently. Many thanks to the shipmen and captain of the N.O. Alis for their great work and to the Ifremer/INSU for the allocation of such a great research vessel. The funding for this mission came in part from a collaborative research project financed by the French ministry of research: the ACI MOOREA.

The scientific staff was constituted of Laure Carassou, Romain Crech’Riou, Cedric Guigand, David Lecchini, Claire Paris, Pascal Ung and myself. We are posing below with some of the shipmen at the end of the mission, on the front deck of the NO Alis.

Alis44

Downloads

  • Hubert N, Delrieu-Trottin E, Irisson J-O, Meyer C, Planes S. Identifying coral reef fish larvae through DNA barcoding: a test case with the families Acanthuridae and Holocentridae. Molecular Phylogenetics and Evolution, 55(3):1195-203, 2010. [PDF]

  • Irisson J-O, Paris CB, Guigand C, Planes S. Ontogenetic vertical “migration” in fish larvae: description and consequences for dispersal. Limnology & Oceanography, 55(2):909-919, 2010. [PDF]

  • Irisson, Paris, Cowen, Planes, 2009. Ontogenetic vertical “migration” in coral-reef fish larvae communities and its consequences for dispersal. Presentation, ASLO Meeting, Nice [Slides]

Contact

Laboratoire d'Océanographie de Villefranche

Station Zoologique, B.P. 28, Chemin du Lazaret, 06234 Villefranche-sur-Mer Cedex

irisson (at) normalesup.org
+33 (0)4 93 76 38 04

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