Ecosystem disruptive algal blooms of the brown tide species, Aureococcus anophagefferens and Aureoumbra lagunensis

Abstract The Pelagophyceae are marine stramenopile algae that include Aureoumbra lagunensis and Aureococcus anophagefferens, two microbial species notorious for causing harmful algal blooms. Despite their ecological significance, relatively few genomic studies of pelagophytes have been carried out. To improve understanding of the biology and evolution of pelagophyte algae, we sequenced complete mitochondrial genomes for A. lagunensis (CCMP1510), Pelagomonas calceolata (CCMP1756) and five strains of A. anophagefferens (CCMP1707, CCMP1708, CCMP1850, CCMP1984 and CCMP3368) using Nanopore long-read sequencing. All pelagophyte mitochondrial genomes assembled into single, circular mapping contigs between 39,376 base-pairs (bp) (P. calceolata) and 55,968 bp (A. lagunensis) in size. Mitochondrial genomes for the five A. anophagefferens strains varied slightly in length (42,401 bp—42,621 bp) and were 99.4%-100.0% identical. Gene content and order was highly conserved between the A. anophagefferens and P. calceolata genomes, with the only major difference being a unique region in A. anophagefferens containing DNA adenine and cytosine methyltransferase (dam/dcm) genes that appear to be the product of lateral gene transfer from a prokaryotic or viral donor. While the A. lagunensis mitochondrial genome shares seven distinct syntenic blocks with the other pelagophyte genomes, it has a tandem repeat expansion comprising ∼40% of its length, and lacks identifiable rps19 and glycine tRNA genes. Laterally acquired self-splicing introns were also found in the 23S rRNA (rnl) gene of P. calceolata and the coxI gene of the five A. anophagefferens genomes. Overall, these data provide baseline knowledge about the genetic diversity of bloom-forming pelagophytes relative to non-bloom-forming species.

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

Frontiers in Marine Science ◽

10.3389/fmars.2021.714816 ◽

2021 ◽

Vol 8 ◽

Author(s):

Eve Galimany ◽

Jessica Lunt ◽

Christopher J. Freeman ◽

I. Segura-García ◽

M. Mossop ◽

...

Keyword(s):

Clearance Rate ◽

Indian River Lagoon ◽

Brown Tide ◽

Bivalve Species ◽

Clearance Rates ◽

Interspecific Differences ◽

Brown Tides ◽

Indian River ◽

Aureoumbra Lagunensis ◽

Fish And Shellfish

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.

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