MEPS 569:55-75 (2017)  -  DOI: https://doi.org/10.3354/meps12102

Phytoplankton biomass in a subtropical estuary: drivers, blooms, and ecological functions assessed over space and time using structural equation modeling

C. Edward Proffitt*

Department of Life Sciences, Texas A&M University - Corpus Christi, Corpus Christi, TX 78412, USA
*Corresponding author:

ABSTRACT: The Indian River Lagoon (IRL Florida, USA) estuary may be in transition from a benthic productivity state to a phytoplankton-based state because of nutrient inputs, phytoplankton blooms, and light penetration. Variation over both spatial and temporal dimensions reflects a complex ecological topology in the IRL. Understanding features such as phytoplankton blooms and subsequent effects on light penetration, dissolved oxygen, and benthic systems is challenging because of the underlying complexity. Analysis by structural equation modeling can test multivariate hypotheses involving the web of pathways linking biotic and environmental variables. A complex structural equation model composed of linkages among chlorophyll, nutrients, salinity, light penetration, dissolved oxygen (DO), etc. explained phytoplankton biomass (chl a, R2 = 0.46) and relative abundance (chl b and c) and ecological functions (light penetration, R2 = 0.60; DO, R2 = 0.42) across the IRL and over the >20 yr of monitoring data. Results indicate that IRL experiences nitrogen and phosphorus co-limitation of phytoplankton, and that changes in plankton biomass influence ecological functions of DO and light penetration. Partitioning the IRL into regions improved the model fit to observations and showed that different regions of the IRL had different drivers for phytoplankton biomass. Comparing 3 yr groups of data for long and short water residence time regions showed that phytoplankton blooms in the 2010-2012 period (including the ‘superbloom’) were driven primarily by nitrogen and less by phosphorus and that this was associated in part by decomposing phytoplankton producing high concentrations of phosphorus during this period, leading to limitation by nitrogen.


KEY WORDS: Phytoplankton · Chlorophyll a · Structural equation modeling · Nutrient · Salinity · Temperature · Indian River Lagoon · Florida


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Cite this article as: Proffitt CE (2017) Phytoplankton biomass in a subtropical estuary: drivers, blooms, and ecological functions assessed over space and time using structural equation modeling. Mar Ecol Prog Ser 569:55-75. https://doi.org/10.3354/meps12102

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