Population growth and transport of the red tide dinoflagellate, Noctiluca scintillans, in the coastal waters off Sydney Australia, using cell diameter as a tracer

Abstract

Spatial abundance patterns of the heterotrophic dinoflagellate, Noctiluca scintillans, were investigated along the southeast coast of Australia to address the hypothesis that population growth of Noctiluca is driven by anthropogenic eutrophication. Abundance patterns were related to the immediate physical flow field and not the conditions conducive to growth. Noctiluca cells were advected southward with the East Australian Current, which was the dominant transport vector for the cells in this region. Areas of population growth of Noctiluca were identified by variations in cell-size distributions. Small cells (Ͻ525 m) were considered to be capable of population growth, in contrast to red tide cells, which are known to be large (Ͼ600 m), senescent, and the end result of a long series of biological and physical processes occurring in temporally and spatially distant water masses. Small cells were therefore considered to be located closer to the region in which growth was stimulated. The proportion of small cells in the samples was significantly correlated with relatively high concentrations of chlorophyll a. Consequently, this relationship was used to show that population growth of Noctiluca may be stimulated by an increase in chlorophyll a due to sewage discharge, although the prevailing hydrological conditions determine the likelihood of such impacts. High chlorophyll a concentrations within estuaries were also found to sustain a stable but low standing stock of Noctiluca, which may seed oceanic stocks. Thus, by examining cell size rather than abundance distributions, we identified and interpreted the variance in the spatial abundance patterns of Noctiluca within a dynamic hydrological environment.

A Modeling Study of the Climatological Current Field and the Trajectories of Upwelled Particles in the East Australian Current

“…The climatology is an average, and concurrently shows scenarios that are normally separate and distinct. However, this transport of tropical EAC waters into southern coastal regions explains the biological connectivity occasionally observed along the NSW coast southward of the EAC separation point (e.g., Delacruz et al 2003).…”

The influence of upwelling, coastal currents and water temperature on the distribution of the red tide dinoflagellate, Noctiluca scintillans, along the east coast of Australia

“…In a previous study we found that the EAC has the potential to advect Noctiluca cells away from the original area that might have stimulated population growth (Dela-Cruz et al, 2003). Here we also suggest that the southward flow of the EAC may partly explain the gradual increase in the abundance of Noctiluca from Smoky Cape to Diamond Head.…”

“…The red tides have been observed over a wide range of the coast (30-36°S), although greater than 90% were observed off Sydney, Australia's largest city (Ajani et al, 2001;Dela-Cruz et al, 2003). Previous field studies have indicated that the abundance of Noctiluca in Sydney's coastal waters is highest during the spring and summer (Murray & Suthers, 1999;Dela-Cruz et al, 2002).…”

“…Most of these upwelling regions are located north of Sydney and thus it might be expected that Noctiluca would be as abundant in these northern regions as compared to off Sydney. The many reports of red tides off Sydney could therefore be a consequence of increased public awareness (Hallegraeff, 1993) and/or southward advection (Dela-Cruz et al, 2003). Certainly, the majority of recent field studies point to the significance of concentrating mechanisms (wind or currents) in determining the abundance and distribution of Noctiluca (Yin, 2003;Kang et al, 2004;Liu & Wong, 2006;Miyaguchi et al, 2006).…”

Evaluation and correction of subresolved particles by the optical plankton counter in three Australian estuaries with pristine to highly modified catchments

“…Average total subresolved particle counts in all size classes from three replicate measurements using the OPC‐1L were between 0.3 and 6.2 L −1 for filtrate. Unfiltered water from the entrances to the estuarine systems had the highest number of particle counts of up to ∼30 L −1 , likely a result of high concentrations of the red tide forming dinoflagellate, Noctiluca scintillans , observed at these sites during this study and previous studies [ Dela‐Cruz et al , 2003]. Factor analysis was used to determine if there were groupings of particle counts from unfiltered water and filtrate.…”