The area of the northern Gulf of Mexico continental shelf influenced by the Mississippi and Atchafalaya rivers is subject to perennial and severe oxygen deficiency most summers. The strongest correlate of the area of low oxygen (called hypoxia, or dissolved oxygen less than 2 milligrams per liter) in mid-summer is the load of NO2+3 in May of the preceding spring. The relationship is strong, but variability can occur from year to year due to weather conditions, including tropical storm activity, local weather systems, shifts in direction of winds from the predominantly southeastern direction to from the north and west. Weather conditions in mid-summer 2018 pushed a hypoxic area that often extends well into Texas towards the central Louisiana shelf so that the seabed footprint was much less than expected, but was thicker in volume. The hypoxic bottom-water area was calculated at 7,040 square kilometers, the fourth smallest since 1985, but the prediction was for 17,000 square kilometers. High river discharge and high nutrient concentrations in May 2017 led to a prediction of 26,131 square kilometers. The calculated area was 22,720, which was less than the prediction. There was insufficient time to finish off the western end of the bottom-area map. A multivariate analysis of 27 years of ancillary data and size of bottom-water hypoxic area identifies the greatest positive parameters of influence to be May NOx load, May orthophosphate load, May NH4 load, and June-July river discharge. Negative influences on summer area of hypoxia were high wind velocity, maximum wind gust, and wind direction two weeks prior to the cruise (i.e., from the north and west). The latter are weather conditions and are not predictive in the form of a forecast several months out from the time of the mapping cruise, nor helpful with nutrient mitigation efforts in the watershed.

Shallow continental shelves support productive pelagic and benthic communities. In this study, we characterize water column and benthic production in the northeastern Gulf of Mexico focusing on the effect of light availability. Measurements were made between November 2015 and September 2016 on the shelf at water depths between 12 and 17 m. We measured benthic primary production and respiration as change in oxygen over time in chambers. Phytoplankton production was measured using 14C-bicarbonate incubations in a photosynthetron. Substantial benthic productivity ranging from 0.07 to 0.94 g C m-2 d-1 occurred in this region with highest productivity in the summer. Phytoplankton productivity ranged between 0.5 and 4.6 g C m-2 d-1, with maximum rates occurring in the spring. Given that light on the bottom in this region is usually between 0.2 and 3.1% surface irradiance, benthic microalgae make a significant contribution to a total primary production in the shallow waters of the northeastern Gulf of Mexico.

In the northern Gulf of Mexico (NGOM), spatiotemporal patterns in zooplankton are observed due to the complex nature of the Loop Current (LC) and associated eddies, which create zones of enhanced primary production, especially in the dynamic region where the northern extent of the LC and Mississippi River plume interact. We studied the abundance, distribution, and diversity of zooplankton in relation to environmental conditions in May 2015, July 2015, and June and July of 2016 in the northern and western Gulf. Zooplankton in the NGOM consisted of primarily copepods, chaetognaths, polychaete larvae, larvaceans, ostracods, cnidarians, decapod larvae, and echinoderm larvae. Copepods were the most dominant group, representing ~60% of the zooplankton abundance. Chaetognaths were the second most dominant group, with highest abundances in regions closest to the Mississippi River plume. Zooplankton abundance was lowest closest to the LC frontal zone, and species specific relationships emerged based on distance to the LC, as well as freshwater inflow from the Mississippi River plume. This study aims to provide new information to understand the spatial and temporal patterns of biological-physical interactions between zooplankton and the environment in the NGOM.

Gelatinous zooplankton (jellyfish) consist of numerous highly varied taxa and play a key role in shaping marine ecosystems. Jellyfish – mainly medusae, ctenophores often exhibit seasonal population blooms in response to environmental triggers, and rapidly produce enormous biomass that impacts the marine food web and fisheries. In the Gulf of Mexico, three species in particular have been associated with massive blooms: Aurelia aurita, Chrysaora quinquecirrha, and Phyllorhiza punctata. Aurelia is one of the well-studied Scyphozoa species, and research has been conducted on factors that cause it to bloom. A quantitative description of phase-structured abundance of jellyfish allows understanding impacts of environmental changes on jellyfish dynamic and potential triggers of blooms. A full life history of the scyphomedusae has been modeled including benthic and pelagic phases (ephyrae, juvenile medusa, and mature adult medusa). In this study we report the development of an individual-based model for Aurelia sp. and simulation experiments to examine the population dynamics of the species and predictions of the population trends under a changing environment.

Oil spill accidents have been a consistent issue along the Gulf Coast and in the adjacent estuaries as a result of offshore oil drilling and tanker ship collisions. To minimize the ecological damage and optimize the emergency response, oil spill operational systems have been developed to provide advanced predictions for the fate and transport of oil. These systems require practical-resolution numerical models for computational efficiency and yet neglect small-scale flow features, such as tidal eddies that are commonly observed at the entrance of Texas/Louisiana lagoon-type estuaries. This research investigate the tidal eddies and their influence on the transport of passive tracers at the inlet of Galveston Bay, Texas. A grid sensitivity study on the numerical model (SUNTANS) are conducted. The result implies the practical resolution of ~400 m that simply captures the net transport through the entrance does not guarantee the correct prediction of the tidal eddies nor their effects on particle transport, which typically converge at the resolution of ~140 m. We proposed a subgrid-scale eddy model as a prototype to represent the tidal eddies at the operational scale. This research is aimed at developing and testing innovative methods for the improvement of oil spill predictions in the next-generation oil spill models operated by the Texas General Land Office and the Texas Water Development Board.

Exposure to oil has been shown to be lethal to most phytoplankton species, however some are able to survive and grow at a normal or reduced growth rates. This ability to tolerate oil exposure appears to be independent of the class and phylum of the phytoplankton and their ability to consume components of oil heterotrophically. We therefore conducted an experiment on oil resistant chlorophyte; Dunaliella tertiolecta in control and water accommodated fraction of oil with and without metabolic inhibitors targeting biochemical pathways (photosynthetic electron transport, cyclic electron transport of PSI, Kreb’s cycle, mitochondrial electron transport, pentose-phosphate pathway and photo-respiration). We found inhibiting pathways such as photosynthetic electron transport and pentose-phosphate pathway were lethal, however inhibition of pathways such as mitochondrial electron transport chain and cyclic electron transport around PSI caused growth arrest in cells. Pathways such as photorespiration and Kreb’s cycle appear to play a critical role in oil tolerating ability of Dunaliella tertiolecta. Analysis of photo-physiology revealed alteration in the photosynthetic apparatus under inhibition of photo-respiration and not Kreb’s cycle. Further studies on how these photo-respiration and Kreb’s cycle help the survival of Dunaliella tertiolecta is under way. Furthermore, the importance of these two pathways in other oil tolerant phytoplankton will also be tested.