Combining in-situ water quality and remotely sensed data across spatial and temporal scales to measure variability in wet season chlorophyll-a: Great Barrier Reef lagoon (Queensland, Australia)

Michelle J Devlin,Caroline Petus,Eduardo Teixeira Da Silva,Jorge G Álvarez-Romero,Dieter Tracey,Amelia Wenger,Jon Brodie,Daniel Zeh

doi:10.1186/2192-1709-2-31

Michelle J Devlin, Caroline Petus + Show 6 more

Open Access

https://doi.org/10.1186/2192-1709-2-31

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Abstract

IntroductionCombining in-situ data from single-point time series with remotely sensed spatial data allowed a greater elucidation of changes in chlorophyll-a concentrations through wet season conditions in the Great Barrier Reef coastal waters.MethodsSingle-point time-series data were collected from 2006 to 2012 during high river flow conditions to assess changes in phytoplankton biomass (measured as chlorophyll-a). Additionally, three flood plume water types, derived from classified true-colour Aqua moderate resolution imaging spectroradiometer (MODIS) images, were used to group single-point time-series data for the phytoplankton biomass assessment.ResultsSurvey data illustrate the heterogeneity of chlorophyll-a distribution over seasonal and inter-annual cycles and the difficulty in describing community responses through the wet season. The spatial data demonstrate distinct regional differences throughout the Great Barrier Reef. The high chlorophyll-a concentrations measured in flood plume waters immediately adjacent to the inshore, highly turbid 'inner’ flood plume are a product of sufficient light, given most of the suspended solids have settled from the plume, and the availability of sufficient nutrients, which drive higher phytoplankton production and characterise the formation of secondary stage flood plumes. The formation and extent of these secondary flood plumes were mapped using MODIS true-colour satellite imagery. The distance and the location of the secondary plume water are reliant on flow, coastal hydrodynamics, and biological activity.ConclusionsThe combination of in-situ data and remotely sensed data provides information on the complexity of these coastal processes during the wet season and offers managers a more comprehensive understanding of the extent of nutrient enrichment in the Great Barrier Reef coastal area and the potential influence of flood plumes on coastal marine ecosystems.

Highlights

Combining in-situ data from single-point time series with remotely sensed spatial data allowed a greater elucidation of changes in chlorophyll-a concentrations through wet season conditions in the Great Barrier Reef coastal waters
Bluish-green waters: Due to this green pigment, where coloured dissolved organic matters (CDOM) is elevated with reduced total suspended sediment (TSS) concentrations chlorophyll/phytoplankton preferentially absorb the due to sedimentation
The difference in the productivity of the inshore Great Barrier Reef (GBR) driven by natural processes and productivity which has increased through nutrient enrichment, resulting in the accelerated growth of phytoplankton beyond a natural threshold, can be difficult to resolve

Summary

Introduction

Combining in-situ data from single-point time series with remotely sensed spatial data allowed a greater elucidation of changes in chlorophyll-a concentrations through wet season conditions in the Great Barrier Reef coastal waters. The nutrients introduced or released during high flow river discharge into the GBR are rapidly taken up by pelagic and benthic algae, and microbial communities (Alongi and McKinnon 2005), sometimes nourishing short-lived phytoplankton blooms and high levels of organic production (Furnas 1989; Furnas et al 2005, 2011). This organic matter is cycled through the marine food web and transformed, for example, into marine snow particles that may be deposited onto benthic communities, such as coral reefs, influencing their structure, productivity, and health (Anthony and Fabricius 2000; Fabricius and Wolanski 2000). COTS are of great importance in the GBR as a predator on coral and are recognised as one of the leading causes of mid-shelf coral mortality in the GBR (De’ath et al 2012)

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