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Coral mortality event in the Flower Garden Banks of the Gulf of Mexico in July 2016: Local hypoxia due to cross-shelf transport of coastal flood waters?


Description:

Title:
Coral mortality event in the Flower Garden Banks of the Gulf of Mexico in July 2016: Local hypoxia due to cross-shelf transport of coastal flood waters?
Author(s):
Le Hénaff, M.
Muller-Karger, F.E.
Kourafalou, V.H.
Otis, D.
Johnson, K.A.
McEachron, H.
Kang, H.
Dates of Publication:
2019
Abstract:
Remotely sensed and in situ data, in tandem with numerical modeling, are used to explore the causes of an episode of localized but severe mortality of corals, sponges, and other invertebrates at the Flower Garden Banks (FGB) National Marine Sanctuary in July 2016. At about 190 km off the Texas coast, at the top the seamount in the East FGB, up to 82% of coral reef organisms were affected in a 1–2 m thick layer on the local seafloor at ∼23 m depth. Analysis of available data pointed to low levels of dissolved oxygen being the most likely contributing factor in the observed mortality (Johnston et al., 2019). Observations show that upwelling-favorable winds in June and July 2016 carried brackish and turbid coastal waters across the northwestern Gulf of Mexico continental shelf to the FGB. This plume of coastal water was the result of exceptionally high precipitation and local river run-off. Field data provide clear evidence of thin, localized, subsurface near-hypoxic layers immediately below this turbid, low salinity coastal plume. These mid-water layers extended over longer distances (30–40 km), and reached further offshore (∼100 km), than previously reported in the region, associated with large quantities of organic matter carried offshore by the brackish plume. The surface brackish layer was observed to cover the East FGB in satellite ocean color imagery and in situ salinity measurements in late June and July 2016. Model results and sparse observations on the shelf suggest that this surface layer was ∼20 m thick. It is expected that organic matter carried in the surface layer accumulated on the seafloor of the East FGB, which was just below the brackish plume. In the absence of ventilation, this led to the local formation of a bottom hypoxic layer, similar to what is observed on the Gulf of Mexico inner to mid-shelf every summer. The conditions experienced at FGB in July 2016 are likely to affect other reefs exposed to brackish plumes with high organic matter loads. The processes of physical connectivity by transport of material is critical for reef colonization and survival, but can also be fatal to coral ecosystems. The monitoring of coral reefs should take the threat of hypoxia due to distant sources of organic matter into account.
Keywords:
Corals
Effect of flooding on
Hypoxia (Water)
Place Keywords:
Flower Garden Banks National Marine Sanctuary (Tex.)
Mexico, Gulf of
United States
Local Corporate Name:
CIMAS (Cooperative Institute for Marine and Atmospheric Studies)
OAR (Oceanic and Atmospheric Research)
AOML (Atlantic Oceanographic and Meteorological Laboratory)
NMFS (National Marine Fisheries Service)
SEFSC (Southeast Fisheries Science Center)
NOS (National Ocean Service)
NCCOS (National Centers for Coastal Ocean Science)
CoRIS (Coral Reef Information System)
Type of Resource:
Journal Article
Note:
Remotely sensed and in situ data, in tandem with numerical modeling, are used to explore the causes of an episode of localized but severe mortality of corals, sponges, and other invertebrates at the Flower Garden Banks (FGB) National Marine Sanctuary in July 2016. At about 190 km off the Texas coast, at the top the seamount in the East FGB, up to 82% of coral reef organisms were affected in a 1–2 m thick layer on the local seafloor at ∼23 m depth. Analysis of available data pointed to low levels of dissolved oxygen being the most likely contributing factor in the observed mortality (Johnston et al., 2019). Observations show that upwelling-favorable winds in June and July 2016 carried brackish and turbid coastal waters across the northwestern Gulf of Mexico continental shelf to the FGB. This plume of coastal water was the result of exceptionally high precipitation and local river run-off. Field data provide clear evidence of thin, localized, subsurface near-hypoxic layers immediately below this turbid, low salinity coastal plume. These mid-water layers extended over longer distances (30–40 km), and reached further offshore (∼100 km), than previously reported in the region, associated with large quantities of organic matter carried offshore by the brackish plume. The surface brackish layer was observed to cover the East FGB in satellite ocean color imagery and in situ salinity measurements in late June and July 2016. Model results and sparse observations on the shelf suggest that this surface layer was ∼20 m thick. It is expected that organic matter carried in the surface layer accumulated on the seafloor of the East FGB, which was just below the brackish plume. In the absence of ventilation, this led to the local formation of a bottom hypoxic layer, similar to what is observed on the Gulf of Mexico inner to mid-shelf every summer. The conditions experienced at FGB in July 2016 are likely to affect other reefs exposed to brackish plumes with high organic matter loads. The processes of physical connectivity by transport of material is critical for reef colonization and survival, but can also be fatal to coral ecosystems. The monitoring of coral reefs should take the threat of hypoxia due to distant sources of organic matter into account.
2019
2021-11-15T00:00:00Z
Grant no. NA15NOS4510226
Grant no. NA10OAR4320143
Hypoxia; Coral Reef; Upwelling; Shelf Processes; Coastal Flooding; Connectivity; Ecology.
CIMAS (Cooperative Institute for Marine and Atmospheric Studies)
OAR (Oceanic and Atmospheric Research)
AOML (Atlantic Oceanographic and Meteorological Laboratory)
NMFS (National Marine Fisheries Service)
SEFSC (Southeast Fisheries Science Center)
NOS (National Ocean Service)
NCCOS (National Centers for Coastal Ocean Science)
CoRIS (Coral Reef Information System)
Submitted
https://doi.org/10.1016/j.csr.2019.103988
Accepted Manuscript
1948
URL:
DOI:
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