Cyclical Patterns and a Regime Shift in the Character of Phytoplankton Blooms in a Restricted Sub-Tropical Lagoon, Indian River Lagoon, Florida, United States

Edward J Phlips,Susan Badylak,Lauren M Hall,Natalie G Nelson,Margaret A Lasi,Janice D Miller,Jean C Lockwood,Charles A Jacoby

doi:10.3389/fmars.2021.730934

Abstract

This paper examines the character of phytoplankton blooms in a restricted sub-tropical lagoon along the Atlantic coast of central Florida. The results of the 23-year study (1997–2020) provide evidence for multiple types of variability in bloom activity, including cyclical patterns, stochastic events, and most prominently a regime shift in composition and intensity. Cyclical patterns (e.g., El Niño/La Niña periods) and stochastic events (e.g., tropical storms) influenced rainfall levels, which in turn impacted nutrient concentrations in the water column and the timing and intensity of blooms. In 2011, a major change occurred in the character of blooms, with a dramatic increase in peak biomass levels of blooms and the appearance of new dominant taxa, including the brown tide speciesAureoumbra lagunensisand other nanoplanktonic species. Results of quantitative analyses reveal system behavior indicative of a regime shift. The shift coincided with widespread losses of seagrass community and reduced drift algae biomass. A combination of exceptionally low water temperatures in the winters of 2009/2010 and 2010/2011, hypersaline conditions associated with drought conditions, and high light attenuation caused by blooms appear to have contributed to the widespread and protracted decline in seagrass and drift macroalgal communities in the lagoon, leading to shifts in distribution of internal and external nutrient sources toward phytoplankton.

Highlights

One of the challenges in defining changes in phytoplankton bloom intensity and composition is accounting for different forms of variability, including cyclical patterns, linear trends, and regime shifts
Temporal patterns in bloom dynamics can be linked to recurring changes in key environmental conditions at multiyear intervals, such as El Niño/La Niña cycles that affect rainfall levels and in turn alter external nutrient loads, water residence times and a range of other water quality conditions, including plankton dynamics (Lipp et al, 2001; Zhu et al, 2017; Zhao et al, 2018; Jiménez-Quiroz et al, 2019)
This paper examines the character of phytoplankton blooms in a restricted sub-tropical ecosystem along the east coast of Florida, the northern Indian River Lagoon (NIRL), which is comprised of three inter-connected sub-regions; the NIRL proper, Mosquito Lagoon, and Banana River Lagoon (Phlips et al, 2011, 2015)

Summary

Introduction

One of the challenges in defining changes in phytoplankton bloom intensity and composition is accounting for different forms of variability, including cyclical patterns, linear trends, and regime shifts. Perhaps the most widely studied is seasonality, such as spring blooms in temperate latitudes, which can in Regime Shift of HABs part be related to increases in temperature and incident irradiance (Siegel et al, 2002; Winder and Cloern, 2010; Chiswell et al, 2015). Sub-tropical and tropical regions experience less seasonal variation in irradiance and temperature, increasing the focus on other drivers of temporal patterns of phytoplankton biomass and composition, such as wet versus dry periods, or tropical storm activity (Bienfang et al, 1984; Phlips et al, 2015, 2020). Peaks in the abundance of the globally distributed toxic dinoflagellate Pyrodinium bahamense have been correlated to high rainfall associated with El Niño periods in Florida and the Indo-Pacific (Phlips et al, 2006, 2020; Usup et al, 2012)

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