Red tides in the Gulf of Mexico: Where, when, and why?

Abstract

Independent data from the Gulf of Mexico are used to develop and test the hypothesis that the same sequence of physical and ecological events each year allows the toxic dinoflagellate Karenia brevis to become dominant. A phosphorus‐rich nutrient supply initiates phytoplankton succession, once deposition events of Saharan iron‐rich dust allow Trichodesmium blooms to utilize ubiquitous dissolved nitrogen gas within otherwise nitrogen‐poor sea water. They and the co‐occurring K. brevis are positioned within the bottom Ekman layers, as a consequence of their similar diel vertical migration patterns on the middle shelf. Upon onshore upwelling of these near‐bottom seed populations to CDOM‐rich surface waters of coastal regions, light‐inhibition of the small red tide of ∼1 ug chl l−1 of ichthytoxic K. brevis is alleviated. Thence, dead fish serve as a supplementary nutrient source, yielding large, self‐shaded red tides of ∼10 ug chl l−1.The source of phosphorus is mainly of fossil origin off west Florida, where past nutrient additions from the eutrophied Lake Okeechobee had minimal impact. In contrast, the P‐sources are of mainly anthropogenic origin off Texas, since both the nutrient loadings of Mississippi River and the spatial extent of the downstream red tides have increased over the last 100 years. During the past century and particularly within the last decade, previously cryptic Karenia spp. have caused toxic red tides in similar coastal habitats of other western boundary currents off Japan, China, New Zealand, Australia, and South Africa, downstream of the Gobi, Simpson, Great Western, and Kalahari Deserts, in a global response to both desertification and eutrophication.

Co-occurrence of dinoflagellate and cyanobacterial harmful algal blooms in southwest Florida coastal waters: dual nutrient (N and P) input controls

“…Blooms of Karenia spp. are initiated from 18 to 64 km offshore in the southwest Gulf, and are transported into coastal embayments by currents and tides during the bloom maintenance stage (Steidinger et al 1998, Walsh et al 2006. Lyngbya spp.…”

“…Increasing amounts of anthropogenic N and P enrichment have accompanied accelerating agricultural and industrial development and urbanization in Florida's coastal watersheds, embayments and keys (Turner et al 2006, Walsh et al 2006, Heil et al 2007, Vargo et al 2008. Nutrient over-enrichment has been linked to accelerating primary production, or eutrophication, and increased algal bloom frequencies of both harmful and non-harmful phytoplankon species in many coastal regions (Paerl 1987, 1988, Nixon 1995, Boesch et al 2001, Cloern 2001, Elmgren & Larsson 2001, including those in Florida (Tomasko et al 1996, Lapointe 1997, Turner et al 2006.…”

Trichodesmium-derived dissolved organic matter is a source of nitrogen capable of supporting the growth of toxic red tide Karenia brevis

“…Although riverine nutrients may supply some of the nitrogen (N) required to support coastal blooms, it is likely only one of many sources of N supporting offshore blooms. Additionally, calculations based on nutrients provided from groundwater, riverine, upwelling and atmospheric inputs together cannot account for the total N required to sustain large blooms that reach concentrations of 1 × 10 7 cells l −1 (Walsh & Steidinger 2001, Walsh et al 2006. Since allochthonous nutrient sources fall short of the amount of N required for growth, studies have focused on autochthonous nutrient sources.…”

Temporal variation of caspase 3-like protein activity in cultures of the harmful dinoflagellates Karenia brevis and Karenia mikimotoi

“…Karenia brevis and K. mikimotoi are unarmoured marine dinoflagellates which can form Harmful Algal Blooms (HABs). Karenia brevis is a producer of brevetoxins and is responsible for the occurrence of red tides in the Gulf of Mexico where it is well known to cause fish and marine mammal mortalities (Walsh et al, 2006). Karenia mikimotoi is common in the waters around Japan and in the Northeast…”