Comparison of the cross-shelf phytoplankton distribution of two oceanographically distinct regions off Australia

Linda H. Armbrecht*, Peter A. Thompson, Simon W. Wright, Amandine Schaeffer, Moninya Roughan, Jorijntje Henderiks, Leanne K. Armand

*Corresponding author for this work

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9 Citations (Scopus)

Abstract

The coastline of Australia spans tropical to temperate latitudes and encompasses a highly diverse phytoplankton community. Yet little is known about environmental driving forces of compositional and distributional patterns in natural phytoplankton communities of Australia. We investigate the relationships of phytoplankton (pico-, nano-, microphytoplankton, determined by microscopy and CHEMTAX) with a variety of environmental variables along cross-shelf gradients. Case studies were conducted in two highly distinct oceanographic regions of Australia (2010/2012): the tropical-temperate Coffs Harbour region (~. 30°S, 153°E), where the shelf is narrow (~. 30. km), and the tropical Kimberley region (~. 16°S, 122°E), where the shelf is wide (~. 200. km). We distinguished three water masses in both study regions: relatively cold, nutrient-rich inshore waters; oligotrophic, stratified offshore waters; and cold, nutrient-rich deep waters. Most phytoplankton taxa (cyanobacteria, cryptophytes, dinoflagellates, haptophytes and prasinophytes) showed group-specific relationships with similar environmental variables in both regions. Diatoms occurred in nutrient-rich inshore waters in the Kimberley, whereas they were widely spread across the narrow continental shelf at Coffs Harbour. Off Coffs Harbour, a senescent bloom of the diatom Leptocylindrus danicus probably caused shelf-scale surface nutrient depletion. While microphytoplankton clearly increased, pico- and nanophytoplankton decreased with distance from the coast over the wide shelf in the Kimberley region. In contrast, the abundance of individual phytoplankton size-classes remained relatively constant across the narrow Coffs Harbour shelf. We conclude that general similarities exist between the relationship of phytoplankton and cross-shelf environmental variables in the two sites and assign differences primarily to the varying spatial resolution of our case studies.

Original languageEnglish
Pages (from-to)26-38
Number of pages13
JournalJournal of Marine Systems
Volume148
DOIs
Publication statusPublished - 1 Aug 2015

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Keywords

  • Continental shelf
  • Microscopy
  • CHEMTAX
  • Phytoplankton size-classes
  • Diatoms
  • Synechococcus

Cite this

Armbrecht, L. H., Thompson, P. A., Wright, S. W., Schaeffer, A., Roughan, M., Henderiks, J., & Armand, L. K. (2015). Comparison of the cross-shelf phytoplankton distribution of two oceanographically distinct regions off Australia. Journal of Marine Systems, 148, 26-38. https://doi.org/10.1016/j.jmarsys.2015.02.002