Patrones ecologicos

Coral Reefs (2007) 26:345–357 DOI 10.1007/s00338-007-0204-3

REPORT

Benthic diatom community composition in three regions of the Great Barrier Reef, Australia
S. Gottschalk Æ S. Uthicke Æ K. Heimann

Received: 21 April 2006 / Accepted: 4 February 2007 / Published online: 2 March 2007 Ó Springer-Verlag 2007

Abstract Despite their ecological importance, very little is known about thetaxonomy and ecology of benthic diatoms in coral-reef ecosystems. Diatom densities and community compositions were investigated in three distinct regions of the Great Barrier Reef (GBR): (a) Wet Tropics (WT), (b) Princess Charlotte Bay (PCB), and (c) the Outer Shelf (OS). About 209 taxa were observed in the GBR sediments studied, with an average abundance of 2.55 · 106 cells ml–1 in the upper 1 cm ofsediment. Total diatom abundances were about twice as high in inshore reefs of PCB and WT compared with OS reefs. A redundancy analysis (RDA) of diatom composition clearly grouped the three regions separately but showed little influence of grain size, nitrogen and organic carbon content of the sediments. The only distinct correlates were inorganic carbon and the distance to the mainland associatedwith OS communities. Analysis of similarity (ANOSIM) of diatom community composition revealed significant differences between all three regions. Indicator values showed that most highly abundant taxa occurred in all regions. However, several taxa were clearly identified as characteristic of particular regions. It is

hypothesised that variations in nutrient and light availability are the mostlikely explanation for the observed differences in community composition. Keywords Benthic diatoms Á Microphytobenthos Á Calcareous sediments Á Coral reefs Á Water quality Á Nutrients

Introduction Coral reefs are generally regarded as oligotrophic marine ecosystems, with very low concentrations of dissolved inorganic nutrients (Underwood 2002). Despite this, they are considered to be productiveecosystems, in part because of efficient recycling of nutrients (Sorokin 1990). Benthic microalgae are an important part of coral reef ecosystems and production of microbenthos on coral-reef soft sediments accounts for 20 to 30% of the total primary production (Sorokin 1993). About 40% of the reef area in the Great Barrier Reef (GBR) is estimated to be a suitable habitat for microphytobenthos(Uthicke and Klumpp 1998), but the vast expanses of inter-reefal areas also have potential for microalgal productivity. The microphytobenthic communities in coral-reef sediments are poorly known and understood, but extensive studies of benthic microalgae have been conducted in temperate systems (e.g., Hillebrand and Sommer 1997, 2000a, b; Hillebrand et al. 2000). Several physical factors, such as lightavailability, currents, salinity, and sediment characteristics are believed to govern benthic microalgal abundance, community composition and productivity in shallow marine habitats (MacIntyre et al. 1996; Forster et al. 2006; Frankovich et al. 2006). Differences in microphytobenthos community structure have been correlated with substrate type. Cahoon

Communicated by Environment Editor R. vanWoesik. S. Gottschalk (&) Institute of Biodiversity Research, Department of Botany, University of Rostock, 18051 Rostock, Germany e-mail: steffigottschalk@arcor.de S. Uthicke Australian Institute of Marine Science, PMB No 3, Townsville, QLD 4810, Australia K. Heimann School of Marine and Tropical Biology, Townsville, QLD 4811, Australia

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et al. (1999)found that the percentage of fine sediments showed a negative correlation with benthic microalgal biomass, while Underwood and Kromkamp (1999) stated that fine cohesive sediments supported significantly higher microalgal biomass then sandy silts or sand. Community structure of the microphytobenthos may also be regulated by nutrient availability. With few exceptions, benthic microalgal communities...