Cross-continental shelf trends in coral ∂15N on the Great Barrier Reef:further consideration of the reef nutrient paradox

Potential sources of nitrogen for the scleractinian coral Porites lobata in a transect across the central region of the Great Barrier Reef, Australia are investigated, and the response curve of the δ 15 N was found to be curvilinear, yielding a highly significant parabolic relationship with distance from shore.

Abstract

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 180:131-138 (1999) - doi:10.3354/meps180131 Cross-continental shelf trends in coral δ15N on the Great Barrier Reef: further consideration of the reef nutrient paradox P. W. Sammarco1,*, M. J. Risk2, H. P. Schwarcz2, J. M. Heikoop2,** 1Louisiana Universities Marine Consortium (LUMCON), 8124 Hwy. 56, Chauvin, Louisiana 70344, USA 2School of Geography and Geology, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4M1, Canada *E-mail: [email protected] **Present address: EES-1, MS-D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA ABSTRACT: In this study, we investigate potential sources of nitrogen for the scleractinian coral Porites lobata in a transect across the central region of the Great Barrier Reef, Australia. The experiment followed a 1-way, Model I, nested ANOVA design. We sampled colonies of P. lobata from 12 reefs spanning the 110 km wide continental shelf at 5 m depth, and determined the δ15N signature in tissue extracts (with zooxanthellae; n = 46). The response curve of the δ15N was found to be curvilinear, yielding a highly significant parabolic relationship with distance from shore (p < 0.001, second-order least-squares polynomial regression). Highest values of δ15N were observed inshore (5.0 to 5.5o/oo), lowest values at the mid-shelf (~3.8o/oo), and high values again offshore (5.2o/oo). We suggest the following causal factors, based on environmental characteristics and phenomena known to occur in this region: (1) inshore corals may be receiving much of their nitrogen from terrigenous sources; (2) mid-shelf corals may be receiving at least some of their nitrogen from associated algal mats known to possess high rates of nitrogen-fixation in this region, which in turn could lower δ15N values; and (3) offshore corals may be receiving their nitrogen from seasonal, nutrient-rich, cold-water intrusions or upwellings, documented to occur in this area. KEY WORDS: δ15N · Corals · Upwelling · Nutrient sources · Trophic shifts Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 180. Publication date: May 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.