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Census of Marine Life, Census of Coral Reefs Expedition to French Frigate Shoals (October 2006)

Rubble Extraction

Lead Scientist: Gustav Paulay
Target Habitats: All proposed habitats including Forereef, Reef Crest, Backreef, Intertidal Shores, Lagoonal Sands, Lagoonal Patch Reef, La Perouse, Arc shell reefs, Acropora areas
Target Organisms: Motile, cryptic invertebrates

Description:
Most reef animals are motile, cryptic invertebrates, which dwell within the fabric of the reef in rock, algae, and sediment. Relatively few emerge nocturnally and are visible during night dives. The majority of the fauna remains hidden from view. Furthermore, species living meters deep in reef framework are virtually inaccessible, short of dismantling reef structures. Therefore, the extraction of invertebrates from rubble is indispensable as a proxy for the destruction of hard substrate that would otherwise be necessary to sample hard bottom biodiversity. Rubble extraction is a standard means used to survey coral reef biodiversity, and can be applied in a qualitative or a quantitative fashion. Pieces of rubble gathered underwater from a small area are placed in a plastic-lined mesh bag to prevent the escape of small organisms. The bagged sample is recovered by a diver using a lift bag, or from a boat using a line and float tethered to the bag. On the surface, pieces of rubble are maintained in running seawater, cracked to remove boring fauna, held under mildly anoxic conditions, and then treated with reagents such as fresh water or dilute formalin to expel resident invertebrates. After each step of the treatment the rubble is washed and the seawater is decanted and sieved in order to collect the additional animals. The cleaned rubble will be returned to the reef.

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