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Marine Ecology Progress Series

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MEPS 443:77-93 (2011)  -  DOI:

Sources of particulate organic matter at the ecosystem scale: a stable isotope and trace element study in a tropical coral reef

Joanna Kolasinski1,3*, Karyne Rogers2, Pascale Cuet1, Bernard Barry2, Patrick Frouin1

1Laboratoire d’Ecologie Marine, Université de La Réunion, 15 avenue René Cassin, BP7151,
97715 Saint-Denis messag cedex, Réunion, France
2National Isotope Centre, GNS Science, 30 Gracefield Road, Lower Hutt, New Zealand
3Present address: Botany Department, Rhodes University, PO Box 94, 6140 Grahamstown, South Africa

ABSTRACT: Spatial and seasonal variability of sources of particulate organic matter (POM) were evaluated in a coral reef ecosystem. Reef water POM was sampled monthly along a south-north gradient. The passage of tropical cyclone Gamede, which crossed Reunion Island in February 2007, provided an ideal opportunity to examine the impact of high river discharge. Stable isotope composition (δ13C, δ15N) was determined in oceanic, riverine and reef water POM, sedimentary organic matter (SOM), benthic primary producers and detritus. Trace elements (Ti, Fe, Cr, Ni, Cu, Zn) measured in SOM were used as additional terrestrial tracers. Stable isotope analysis of reef water showed that POM was affected by anthropogenic non-point nutrient sources, water circulation patterns and residence time. During the cold and dry season, the southern end of the reef received organic matter input derived from ocean primary production, while the middle and northern reef water POM originated primarily from SOM, reflecting an important bentho-pelagic coupling process. During the hot and wet season, reef water was enriched in benthic detritus due to higher autochthonous production. We found important spatial variability in POM sources, highlighting the importance of small-scale (hundreds of meters) studies when investigating ecosystem functioning. Although coastal tidal currents transported some river discharge material to the south of the reef, riverine POM input was limited, even after cyclone passage. We hypothesized that the major effect of the cyclone was the export of SOM and benthic detritus out of the system and that persistent disturbances such as groundwater discharges can be of greater importance than a cyclone in long-term degradation of ecosystems.

KEY WORDS: Organic matter · Stable isotopes · Trace metals · Coral reef · Cyclone · Bentho-pelagic coupling · Seasonal variation

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Cite this article as: Kolasinski J, Rogers K, Cuet P, Barry B, Frouin P (2011) Sources of particulate organic matter at the ecosystem scale: a stable isotope and trace element study in a tropical coral reef. Mar Ecol Prog Ser 443:77-93.

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