Geospatial distribution of hypoxia associated with a Karenia brevis bloom

https://doi.org/10.1016/j.ecss.2021.107446Get rights and content

Highlights

  • Hypoxia co-occurred with a red tide bloom (Karenia brevis) in shallow waters of the eastern Gulf of Mexico in 2018.

  • Vertical stratification of the water column led to the development of the hypoxic layer that was estimated to be 655 km2.

  • The toxic dinoflagellate Karenia brevis was the dominant taxon in the red tide.

  • A large die-off of fish, turtles, and other marine life during the red tide was widely reported in the region of hypoxia.

Abstract

In 2018, the presence of bottom water hypoxia along the SW Florida coast was investigated during a bloom of the toxic dinoflagellate Karenia brevis. The bloom was first detected in November 2017. Monitoring of oxygen levels and bloom densities was carried out in 2018 and 2019 using sampling grids. Vertical profiles indicated a pycnocline at 3–4 m where warmer, lower salinity water was at the surface, while the deeper hypoxic layer was colder with higher salinity. There were significantly higher abundances of K. brevis in the surface water compared to the hypoxic bottom water in September 2018. At two fixed sites, dissolved oxygen was measured continuously showing hypoxic conditions during that month. Geospatial analysis of vertical profile data yielded an estimate that the hypoxic layer covered an area of at least 655 km2. The possible influences of red tides on hypoxic conditions along the coast of the eastern Gulf of Mexico are discussed within the context of the 2018 K. brevis bloom event. Hypoxia occurring in parallel to a red tide bloom is more likely to occur with warmer ocean temperatures and increased fluxes of nutrients and fresh water to the Gulf of Mexico after hurricanes.

Introduction

The combination of global climate change and increasing cultural eutrophication will likely exacerbate the incidence and intensity of harmful algal blooms and hypoxic events (Anderson et al., 2002; Heisler et al., 2008; Paerl and Paul, 2012; Griffith and Gobler, 2020; Phlips et al., 2020). Coastal regions can be subject to hypoxic conditions due to intense harmful algal blooms (HABs) that result in high biological oxygen demand, particularly as blooms collapse and decompose (Howarth et al., 2011). Although hypoxia is widely understood to disrupt coastal ecosystems, research on the extent of hypoxic conditions remains limited and the role of hypoxia is often overlooked unless it impacts higher trophic levels (Diaz and Rosenberg, 2008). One of the more extensively studied examples of hypoxia associated with HABs is the nearshore region of the Mississippi River discharge in the northern Gulf of Mexico, often referred to as the “dead zone” (Rabalais and Turner, 1994; Rabalais et al., 2014, Zhang et al., 2010).

Along the broad continental shelf environment of the eastern Gulf of Mexico, another potential cause of hypoxia is a red tide bloom. These blooms can extend over thousands of square kilometers and impact coastal regions all along the west coast of Florida. Red tide blooms in the eastern Gulf of Mexico frequently occur during the late summer and are most often dominated by the toxic dinoflagellate Karenia brevis (Tester and Steidinger, 1997; Vargo et al., 1987; Heil et al., 2014a). Karenia brevis produces brevetoxins, which can impact marine fauna, leading to mass mortalities (Fire et al., 2007; Landsberg et al., 2009). In turn, these mortalities, bacterial decomposition of the biomass, and the presence of high K. brevis biomass interact to create opportunities for the formation of low oxygen zones, particularly during periods of vertical water column stratification. Periods of low winds and increased solar heating during the summer can cause vertical stratification which results in the formation of a thermocline, and enhanced potential for hypoxia (He and Weisberg, 2002). Two studies of nearshore benthic and reef communities in the Eastern Gulf of Mexico before and after red tide events attributed mortality not only to exposure to brevetoxins, but also the effects of oxygen depletion, hydrogen sulfide poisoning and bacterial infections (Smith, 1975). These events can disrupt climax communities and re-structure epibenthic and fish communities for 2–3 years. The expectation is that deoxygenation of the oceans will be exasperated by climate change in areas with recurring HABs (Gobler et al., 2017; Griffith and Gobler, 2020).

In this study, a widespread hypoxia event in 2018 associated with a red tide is described along the southwest coast of Florida. The impacted region is part of the shallow West Florida Shelf (WFS) which extends over 250 km from shore in the eastern Gulf of Mexico (Weisberg et al., 2009). Along the coast, red tides are concentrated in shallow water by wind and currents resulting in elevated plankton biomass levels (Vargo, 2009). The red tide was first detected in November 2017 and partially mapped with an autonomous sailing vessel (Beckler et al., 2019). Hypoxia was found in a large area in the Gulf of Mexico in August and September 2018. The primary goals of the study were to characterize physicochemical conditions, including the intensity and geospatial distribution of hypoxia in parallel with concentrations of the dominant species, K. brevis. Specific study objectives included (1) monitoring physicochemical covariates and K. brevis levels across multiple depths and locations in waters impacted by the red tide, and (2) quantifying the severity and extent of hypoxia as a function of K. brevis concentrations and physicochemical conditions. Findings from this work provide new insights into the ecological impacts associated with the interactions of harmful algal blooms and hypoxia.

Section snippets

Materials and methods

The study area encompassed approximately 1200 km2, with relatively shallow depths ranging from 5 m to 20 m (Fig. 1). Sampling was initiated in September 2018 in response to an unusual mass mortality of fish and benthic invertebrates. A network of water sampling sites was established to determine the extent and severity of hypoxia in the study region. The network included three major components:

  • 1)

    Three sampling cruises (09/26/2018, 10/29/2018, 09/17/2019) involving 21 sites (Fig. 1, solid circles)

Results

Water physical, optical, dissolved oxygen and phytoplankton species. The first detection of Karenia brevis was reported in October 2017 by the Florida Wildlife Research Institute (FWRI) through routine discrete sampling (https://myfwc.com/research/redtide/). The weekly FWRI monitoring program tracked the expansion of the bloom in low, medium and high (>106 cells L−1) concentrations throughout the event. High concentrations of Karenia brevis were detected at many locations in July 2018 and the

Discussion

Over the past two decades, much of the attention on marine hypoxia has focused on large-scale persistent or recurring phenomena, such as the 18,000 km2 “dead zone” associated with the Mississippi River discharge (Rabalais and Turner, 1994; Scavia et al., 2003; IWG-HABHRCA, 2016), coastal upwelling of deep low oxygen water, and recurring hypoxia associated with intense cyanobacteria blooms in lakes, such as Lake Erie (Scavia et al., 2014; Smith et al., 2015; IWG-HABHRCA, 2016; Watson et al., 2016

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was funded by the National Science Foundation award 1853041 to N. Nelson, E. Phlips, and E. Milbrandt. RECON operations and maintenance were supported by NOAA through a subaward from the Gulf of Mexico Coastal Ocean Observing Network (GCOOS) to E. Milbrandt. Additional support was provided by the R. Vince Family and Goldman Sachs Gives. Field and lab assistance were provided by student interns from the University of Iowa Department of Earth and Environmental Science. The

References (55)

  • D. Scavia et al.

    Assessing and addressing the re-eutrophication of Lake Erie: central basin hypoxia

    J. Great Lake. Res.

    (2014)
  • R.E. Sipler et al.

    Bacteriocidal effects of brevetoxin on natural microbial communities

    Harmful Algae

    (2014)
  • E.A. Urquhart et al.

    A method for examining temporal changes in cyanobacterial harmful algal bloom spatial extent using satellite remote sensing

    Harmful Algae

    (2017)
  • G.A. Vargo

    A brief summary of the physiology and ecology of Karenia brevis Davis (G. Hansen and Moestrup comb nov.) red tides on the West Florida Shelf and of hypotheses posed for their initiation, growth, maintenance and termination

    Harmful Algae

    (2009)
  • S.B. Watson et al.

    The re-eutrophication of Lake Erie: harmful algal blooms and hypoxia

    Harmful Algae

    (2016)
  • R.H. Weisberg et al.

    A coordinated coastal ocean observing and modeling system for the West Florida Continental Shelf

    Harmful Algae

    (2009)
  • M.L. Wells et al.

    Harmful algal blooms (HABs) and climate change: what do we know and where do we go from here?

    Harmful Algae

    (2015)
  • D.M. Anderson et al.

    Harmful algal blooms and eutrophication: nutrient sources, composision, and consequences

    Estuaries

    (2002)
  • J.S. Beckler et al.

    Harmful algae bloom monitoring via a sustainable, sail-powered mobile platform for inland and coastal monitoring

    Frontiers in Marine Science

    (2019)
  • Committee on Environment and Natural Resources. Scientific Assessment of Hypoxia in U.S. Coastal Waters

    (2010)
  • J.K. Craig et al.

    Hypoxia-induced habitat shifts and energetic consequences in atlantic croaker and brown shrimp on the Gulf of Mexico shelf

    Mar. Ecol. Prog. Ser.

    (2005)
  • R.J. Diaz et al.

    Spreading dead zones and consequences for marine ecosystems

    Science

    (2008)
  • S.E. Fire et al.

    Brevetoxin exposure in bottlenose dolphins (Tursiops truncates) associated with Karenia brevis blooms in Sarasota Bay, Florida

    Mar. Biol.

    (2007)
  • L.J. Flewelling et al.

    Brevetoxicosis: red tides and marine mammal mortalities

    Nature

    (2005)
  • FLSTSSN, Archived Sea Turtle Stranding Data

    (2018)
  • C.J. Gobler et al.

    Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific oceans

    Proc. Natl. Acad. Sci. Unit. States Am.

    (2017)
  • G.R. Hasle

    Phototactic vertical migrations in marine dinoflagellates

    Oikos

    (1950)
  • Cited by (11)

    • Nitrogen-enriched discharges from a highly managed watershed intensify red tide (Karenia brevis) blooms in southwest Florida

      2022, Science of the Total Environment
      Citation Excerpt :

      This study empirically investigates the dynamics of coastal K. brevis blooms in southwest Florida and several watershed covariates along a major flow path to the coast, to identify persistent and systematic anthropogenic drivers of blooms as targets for management and policy intervention. We focus on K. brevis blooms between Charlotte Harbor and the Caloosahatchee River (Fig. 1), a region whose wildlife, public health, and economic activity have suffered adverse impacts (Court et al., 2021; Gravinese et al., 2020; Milbrandt et al., 2021; Sonak et al., 2018). Past empirical investigations of ‘the anthropogenic hypothesis’—that anthropogenic nutrient inputs intensify K. brevis blooms along Florida's Gulf Coast—support its mechanistic plausibility.

    • Relationships between blooms of Karenia brevis and hypoxia across the West Florida Shelf

      2022, Harmful Algae
      Citation Excerpt :

      Examining 16 years of CTD data collected over the West Florida Shelf, we identified three hypoxic events in 2005, 2014, and 2018, that co-occurred with major HABs. Other studies have identified hypoxia associated with HABs on the West Florida Shelf in 2005 (Hu et al. 2006), 2014 (Driggers et al. 2016), and 2018 (Milbrandt et al. 2021); however, no study has examined this relationship across longer time scales and on a larger geographic scope in this region. We hypothesize that HAB-hypoxia events were driven by the temporal coincidence of HABs and associated climatological factors.

    View all citing articles on Scopus
    View full text