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?

TY - JOUR

T1 - Coral mortality event in the Flower Garden Banks of the Gulf of Mexico in July 2016

T2 - Local hypoxia due to cross-shelf transport of coastal flood waters?

AU - Le Hénaff, Matthieu

AU - Muller-Karger, Frank E.

AU - Kourafalou, Vassiliki H.

AU - Otis, Daniel

AU - Johnson, Kimberley A.

AU - McEachron, Lucas

AU - Kang, Hee Sook

PY - 2019/11/15

Y1 - 2019/11/15

N2 - 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.

AB - 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.

KW - Coastal flooding

KW - Connectivity

KW - Coral reef

KW - Ecology

KW - Hypoxia

KW - Shelf processes

KW - Upwelling

UR - http://www.scopus.com/inward/record.url?scp=85073919648&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85073919648&partnerID=8YFLogxK

U2 - 10.1016/j.csr.2019.103988

DO - 10.1016/j.csr.2019.103988

M3 - Article

AN - SCOPUS:85073919648

VL - 190

JO - Continental Shelf Research

JF - Continental Shelf Research

SN - 0278-4343

M1 - 103988

ER -