title: Vertical migration of Karenia brevis in the northeastern Gulf of Mexico observed from glider measurements.
abstract: The toxic marine dinoflagellate, Karenia brevis (the species responsible for most of red tides or harmful algal blooms in the Gulf of Mexico), is known to be able to swim vertically to adapt to the light and nutrient environments, nearly all such observations have been made through controlled experiments using cultures. Here, using continuous 3-dimensional measurements by an ocean glider across a K. brevis bloom in the northeastern Gulf of Mexico between 1 and 8 August 2014, we show the vertical migration behavior of K. brevis. Within the bloom where K. brevis concentration is between 100,000 and 1,000,000cellsL-1, the stratified water shows a two-layer system with the depth of pycnocline ranging between 14-20m and salinity and temperature in the surface layer being <34.8 and >28°C, respectively. The bottom layer shows the salinity of >36 and temperature of <26°C. The low salinity is apparently due to coastal runoff, as the top layer also shows high amount of colored dissolved organic matter (CDOM). Within the top layer, chlorophyll-a fluorescence shows clear diel changes in the vertical structure, an indication of K. brevis vertical migration at a mean speed of 0.5-1mh-1. The upward migration appears to start at sunrise at a depth of 8-10m, while the downward migration appears to start at sunset (or when surface light approaches 0) at a depth of ∼2m. These vertical migrations are believed to be a result of the need of K. brevis cells for light and nutrients in a stable, stratified, and CDOM-rich environment.
authors.affiliation: College of Marine Science, University of South Florida, 140 7th Avenue South, Saint Petersburg, FL 33701, United States. Electronic address: huc@usf.edu.
authors.forename: Chuanmin
authors.initials: C
authors.lastname: Hu
authors.affiliation: College of Marine Science, University of South Florida, 140 7th Avenue South, Saint Petersburg, FL 33701, United States.
authors.forename: Brian B
authors.initials: BB
authors.lastname: Barnes
authors.affiliation: College of Marine Science, University of South Florida, 140 7th Avenue South, Saint Petersburg, FL 33701, United States; School for the Environment, University of Massachusetts Boston, Boston, MA 02125, United States.
authors.forename: Lin
authors.initials: L
authors.lastname: Qi
authors.affiliation: College of Marine Science, University of South Florida, 140 7th Avenue South, Saint Petersburg, FL 33701, United States.
authors.forename: Chad
authors.initials: C
authors.lastname: Lembke
authors.affiliation: College of Marine Science, University of South Florida, 140 7th Avenue South, Saint Petersburg, FL 33701, United States.
authors.forename: David
authors.initials: D
authors.lastname: English
mesh_terms: D004141:Dinoflagellida / Q000502:physiology*; D004784:Environmental Monitoring; D060851:Gulf of America; D057097:Harmful Algal Bloom / Q000502:physiology*; D054712:Salinity; D012623:Seawater / Q000469:parasitology*; D013472:Sunlight; D013696:Temperature
keywords: Glider; Harmful algal blooms (HABs); Karenia brevis; Remote sensing