Bivalve Feeding on the Brown Tide Aureoumbra lagunensis in a Shallow Coastal Environment

Abstract

Brown tides formed by Aureoumbra lagunensis decrease light penetration in the water column and are often followed by hypoxic events that result in the loss of fish and shellfish. To understand the ability of bivalve filter feeders to control and prevent A. lagunensis blooms, we exposed eastern oysters (Crassostrea virginica), hooked mussels (Ischadium recurvum), and hard clams (Mercenaria mercenaria) to a naturally co-occurring brown tide in the Indian River Lagoon (IRL), Florida, United States. Bivalves were exposed in the laboratory to multiple concentrations (104 to 106 cells mL–1) of isotopically labeled (13C and 15N) A. lagunensis cells. The standard clearance rate (herein clearance rate) of each bivalve species was calculated using flow cytometry to quantify A. lagunensis cell removal. The highest clearance rates were at 104 cells mL–1, but values varied across bivalve species (2.16 ± 0.30, 3.03 ± 0.58, and 0.41 ± 0.12 L h–1 for C. virginica, I. recurvum, and M. mercenaria, respectively). Although clearance rates decreased with increasing bloom concentrations, bivalves were still consuming algal cells at all concentrations and were retaining and assimilating more cells at the highest concentrations, as revealed by δ13C and δ15N values. We highlight interspecific differences among bivalve species in the removal of A. lagunensis, supporting the importance of healthy and diverse filter feeding communities in estuaries, especially as threats of brown tides and other HABs are increasing in the Anthropocene.

Filtration Rate of the Solitary, Pleated Tunicate Styela plicata on the Brown Tide-Forming Pelagophytes Aureoumbra lagunensis and Aureococcus anophagefferens

“…In a follow-on study, eastern oysters, hooked mussels, and hard clams were exposed to isotopically labeled ( 13 C and 15 N) A. lagunensis at cell densities of 10 4 and 10 6 cells mL -1 . Clearance rates declined with increasing algal density, but bivalves assimilated the greatest number of cells at bloom concentrations (10 6 cells mL -1 ) (Galimany et al, 2021). Interspecific variation in filtration rate indicates the importance of a biodiverse suspension feeding community in the IRL.…”

“…A conservative estimate of filtration capacity at lagoon-scale using their laboratory-based measures of filtration rate of the Eastern oyster and hard clam (the most common species targeted for restoration efforts) estimate filtration of 0.002% the volume of the IRL at brown tide concentrations of 10 4 cells mL -1 . An additional 1% is estimated based on restored oyster reefs found in Mosquito Lagoon only but doesn't consider the suite of filter feeding organisms throughout the ecosystem (Galimany et al, 2021). The authors caution that laboratory-based estimates are merely a proxy for conditions in the field, but still provide evidence for these nature-based solutions of improving water quality.…”

“…In response to eutrophication and loss of filter-feeders worldwide, numerous studies have investigated the ability of oysters, tunicates, and other grazers to attenuate nutrients (e.g., Cerco and Noel, 2007;Buzzelli et al, 2013;Kellogg et al, 2013;Bricker et al, 2018), bacteria (e.g., Draughon et al, 2008) and affect top-down control on bloom-forming phytoplankton (including brown tide, e.g., Galimany et al, 2017;Galimany et al, 2020;Galimany et al, 2021). While considered non-toxic, brown tides formed by Aureoumbra lagunensis, and another pelagophyte Aureococcus anophagefferens Hargraves et Sieburth (DeYoe et al, 1997), affect bivalve and zooplankton feeding due to their cellular structure (e.g., mucilaginous secretions), accumulated biomass, or a combination of these factors (Anderson et al, 2002).…”

Oyster Reefs Are Reservoirs for Potential Pathogens in a Highly Disturbed Subtropical Estuary

“…The eastern oyster, Crassostrea virginica, is an important suspension feeder in the IRL and other estuaries [23][24][25], wherein it filters a wide variety of organic and inorganic particles [26][27][28], including bacteria [25,29], from large volumes of water. Some particles are rejected prior to digestion in the form of pseudofeces, while others are ingested and either assimilated into biomass or excreted as feces [30][31][32].…”

First record of the alien hooked mussel Ischadium recurvum (Rafinesque, 1820) (Bivalvia: Mytilidae) in Belgium

“…Ischadium recurvum is an important prey item for crustaceans [10] and waterfowl [11]. The species is a filter feeder, feeding mainly upon suspended phytoplankton [12][13], including brown tide (Aureoumbra lagunensis) [14]. Ischadium recurvum has separate sexes [15], reaches maturity at a shell length of about 25 mm [2] and has a single annual spawning cycle [16].…”