Trends and drivers of fauna abundance of the offshore Gulf of Mexico: Narrowing the data gap in the Gulf’s largest ecosystem component


Quantitative sampling using MOC10 nets (Point Sur R/V)This project will identify long-term trends in fishes, shrimps, cephalopods, and other fauna in the deep-pelagic Gulf of Mexico (open ocean waters, from the surface to 1500 m depth), and provide this information to resource managers responsible for the numerous species that rely on deep-pelagic fauna as prey, including marine mammals (

The primary goal of this project is to address the largest existing data gap in understanding the pelagic ecosystem of the Gulf of Mexico. The deep-pelagic habitat is by far the largest component of the Gulf ecosystem, representing 90.4% of its volume. Therefore, the deep-pelagic system is simultaneously the largest and least-known ecosystem of the Gulf of Mexico.

This project uses midwater nets and acoustics to sample the deep-pelagic region. By analyzing the data collected, the project will be able to quantify spatial and temporal trends, and develop baselines for deep-pelagic fauna in the Gulf of Mexico. My role in the project is to develop chemical indicators of oceanic ecosystem disturbance/recovery.

Related Publications:

• Woodyard et. al. 2022. A comprehensive petrochemical vulnerability index for marine fishes in the Gulf of Mexico. Science of The Total Environment, Volume 820, No. 152892.

• Sutton et. al. 2022. The Open-Ocean Gulf of Mexico After Deepwater Horizon: Synthesis of a Decade of Research. Frontiers in Marine Science, Vol 9, number 753391.


NSF RAPID: Remineralization effects of enhanced allochthonous dissolved organic matter in the West Florida Shelf impacted by Hurricane Ian

Global inputs of dissolved organic matter (DOM) to continental margins have increased, apparently due to land-use and climate changes. Severe weather events, like hurricanes, offer a unique opportunity to study the effects of enhanced DOM on coastal nutrients and carbon chemistry to better understand long-term impact of these environmental changes. In particular, previous studies have demonstrated the influence of hurricanes on the chemistry of estuarine systems by the release of large amounts of organic matter buried in terrestrial environments. However, it is unclear the role of resuspended marine sediments during hurricane events and how enhanced DOM would affect coastal environmental conditions (e.g., hypoxia, acidification, nutrients) that foster harmful algal blooms (HABs). On September 28, 2022, Hurricane Ian made landfall near Cayo Costa, Florida, with 155 mph winds. It produced an 8-15 ft storm surge of marine water, a 1,000-year flood event of freshwater (30 cm of rain in 24 hours), and a large-scale devastation of historic proportions. Days after landfall, satellite images showed large-scale dark-brown plumes on the WFS, presumably loaded with land/river and resuspension-derived DOM (Figure: Ian-derived plumes at WFS; NOAA Copernicus Sentinel-3/OLCI, Sept 30/22). This unprecedented and ephemeral input of allochthonous DOM provides an ideal opportunity to analyze the effects of DOM remineralization on coastal nutrients and carbon chemistry.

Institutions: Puspa L. Adhikari (Florida Gulf Coast University, FGCU), Felix Jose (FGCU), Isabel Romero (University of South Florida, USF), Huan Chen (National High Magnetic Field Laboratory, NHMFL)


Mass Mortality of the Keystone Herbivore Diadema antillarum Underway around the Caribbean Sea  

Healthy, living Diadema urchin (photo K.Marks)

Diadema antillarum is a keystone herbivore on coral reefs throughout the Caribbean. However, from 1983-1984, a mortality event killed on average 97% of individuals and facilitated a shift from coral to macroalgae-dominated reefs in many locations. Recovery has been slow and uneven, but some locations reached densities observed before the die-off. The event in the 80s proceeded rapidly, spreading across the Caribbean in just 13 months. There was little time for the scientific community to respond, samples were not preserved, and the cause was never identified. The current event is unfolding at a similar pace, but this time we have a response network in place and the technology to determine relationships between disease and environmental variables that are indicative of reef health.

Check the Diadema response network at: AGRRA / Atlantic and Gulf Rapid Reef Assessment (


Collaborative study: Piney Point Incident, Tampa Bay, FL

Following the break in the retaining wall of the Piney Point phosphate plant, about 35 million gallons of toxic wastewater per day was released into Tampa Bay. The 77-acre pond created to hold the plant’s waste contains a mix of seawater from an old dredging project and polluted process water. Recent observations by USF scientists and other agencies document the trajectory of the toxic water into Tampa Bay and the increase in nutrient concentrations of the water column. Therefore, a large pool of nutrients, organic matter, and presumably associated organic pollutants are available for biological consumption via zooplankton grazers, the base of the marine food web in Tampa Bay. Here, we propose to collect chemical and nutrient data in zooplankton and sediments to assess the bioaccumulation of the wastewater and the health of the coastal planktonic food web and sedimentary environment in the study area.

Media coverage:

USF researchers release initial findings on Piney Point leak | WFLA

Piney Point, Florida leak: ‘Pulse’ of nutrient-rich water dissipated (

Contamination from Piney Point has diluted in Tampa Bay, researchers say







Resuspension, Redistribution, and Deposition of the Deepwater Horizon Recalcitrant Hydrocarbons to Offshore Depocenters – REDIRECT

Multicore deployment for collecting sediment samples at depths >1000m

The natural heterogeneity of bottom topography and circulation processes are key drivers transporting materials to deeper areas in the GoM by erosion and deposition of contaminated sediments beyond the surface extent of the once existing oil slick or the subsurface plumes(s).

The proposed research will transform our understanding of the sinks, distribution, and transport processes of sedimentary hydrocarbons by investigating the connectivity of geomorphological features (erosional channels, lee depocenters, and isolated valleys), and the sedimentological and physical oceanographic processes (resuspension, advection, and re-sedimentation) affecting oil-derived hydrocarbon distribution and deposition within the BNL in the deep sea. 

Petrocarbon content (14C) and organic geochemical analyses (aliphatics, aromatics, hopanes, and steranes) will be used to quantify the concentration and degree of weathering of hydrocarbon residues. Laboratory flume analyses will test the behavior of the surface layer to determine threshold current velocities necessary to resuspend size-specific particles and, subsequently, the behavior during transport of the resuspended material, which can be utilized in sediment transport models. This study will develop a spatial and temporal perspective of the MOS deposited on the seafloor to compare with the MOS projected to have formed in the water column.


A time-series analysis of polycyclic aromatic hydrocarbons in Gulf of Mexico mesopelagic fauna 

Argyropelecus aculeatus, Image No3, DP02-16AUG15-MOC19-B080N-026-N3, LRM
Argyropelecus  aculeatus  (Photo credit: Dante Fenolio)

The Gulf of Mexico (GoM) contains abundant sources of toxic organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Due in part to the increases in the exploration of deep-marine resources in the last decade, it is likely that major PAH contamination events will occur. An example was the Deepwater Horizon Oil Spill (DWH) which was primarily a deep-pelagic event. The deep pelagic zone is by far the largest habitat in the GoM that was affected by the DWH spill. The DWH spill highlighted the large data gap for the deep ocean in the GoM.

Results from a collaborative effort between DEEPEND and C-IMAGE II Consortia indicate that the mesopelagic fauna incorporated DWH oil resulting in diet shifts after the spill and exposure to PAHs.  A 10-fold increase in PAH concentrations during 2010-2011 relative to pre-spill values (2007) and a decline in 2015-2016 were observed. The presence and composition of elevated PAHs confirmed post-spill contamination of deep-pelagic fishes.  PAH data will be integrated with those from population dynamics and stable isotope analysis to provide evidence for the effects of oil exposure to deep-pelagic communities. Analyses were conducted at the Paleoceanographic Laboratory – University of South Florida.

Related Publication:

  • Romero Isabel C., Heather Judkins, Michael Vecchione. 2020. Temporal variability of polycyclic aromatic hydrocarbons in deep-sea cephalopods of the northern Gulf of Mexico. Front. Mar. Sci. 7:54; doi: 10.3389/fmars.2020.00054
  • Cook, A., A. M. Bernard, K.M. Boswell, H. Bracken-Grissom, M. D’Elia, S. deRada, D. English, R.I. Eytan, T. Frank, C. Hu, M.W. Johnston, H. Judkins, C. Lembke, R.J. Milligan,J. Moore, B. Penta, N.M. Pruzinsky, J.A. Quinlan, T. Richards, I.C. Romero, M.S. Shivji, M. Vecchione, M.D. Weber, R. J. D. Wells, T.T. Sutton. 2020. A Multidisciplinary Approach to Investigate Deep-Pelagic Ecosystem Dynamics in the Gulf of Mexico following Deepwater Horizon. Frontiers in Marine Science, doi: 10.3389/fmars.2020.548880
  • Beth Polidoro, Cole W. Matson, Mary Ann Ottinger, D. Abigail Renegar, Isabel C. Romero, Daniel Schlenk, John Pierce Wise, Jesús Beltrán González, Peter Bruns, Kent Carpenter, Dorka Cobián Rojas, Tracy K. Collier, Thomas F. Duda, Patricia González-Díaz, Richard Di Giulio, R. Dean Grubbs, J. Christopher Haney, John P. Incardona, Guillermo Horta-Puga, Christi Linardich, Jon A. Moore, Daniel Pech, Susana Perera Valderrama, Gina M. Ralph, Kyle Strongin, Amy H. Ringwood, Bernd Würsig. 2020. A Multi- taxonomic Framework for Assessing Relative Petrochemical Vulnerability of Marine Biodiversity in the Gulf of Mexico, Science of the Total Environment,
  • Sutton, Tracey, Tamara Frank, Heather Judkins, I.C. Romero. 2020. As Gulf Oil Extraction Goes Deeper, Who Is at Risk? Community Structure, Distribution, and Connectivity of the Deep-Pelagic Fauna. In “Scenarios and Responses to Future Deep Oil Spills”, 403-418 p,
  • Romero I.C., Tracey Sutton, Brigid Carr, Ester Quintana-Rizzo, Steve W. Ross, David J. Hollander, Joseph J. Torres.. 2018. A decadal assessment of polycyclic aromatic hydrocarbons in mesopelagic fishes from the Gulf of Mexico reveals exposure to oil-derived sources. Environmental Science & Technology. DOI: 10.1021/acs.est.8b02243
  • Quintana-Rizzo et al. 2015. Changes in δ13C and δ15N in deep-living fishes and shrimps after the Deepwater Horizon oil spill, Gulf of Mexico. Marine Pollution Bulletin, 94(1-2), 241–250,

The distribution, fate, and transport of hydrocarbons deposited in northern and southern regions of the Gulf of Mexico

Exclusion zone (Southern Gulf of Mexico)

The main objective of this study was to investigate the deposition of hydrocarbons from different sources (e.g., terrestrial, oil exploration) at a more regional scale in the Gulf of Mexico (GoM). Specifically, we focused on the spatial and temporal evolution of petroleum constituents deposited on sediments from the Deepwater Horizon spill (DWH) in 2010 and from the IXTOC-I oil spill in 1979. The IXTOC-I incident that took place over three decades ago provides an important historical analog for predicting future impacts on benthic ecosystems in the northern GoM.

Results indicate that ~19,000 metric tons of weathered DWH-derived hydrocarbons (>C9 saturated and aromatic fractions) were deposited in 56% of the studied area (194,000 km2), containing 21± 10% (up to 47%) of the total amount of oil discharged and not recovered from the DWH spill. Several impacts on the environment and its recovery have been identified, but changes in the productivity of stocks at the population level may take several to many years to recover, depending on the specific life histories of target animals. This study was supported by C-IMAGE II Consortium – Dr. Steve Murawski and Dr. Dave Hollander (PIs). 

Related Publications:

  • Rohal M, Barrera N, Escobar-Briones E, Brooks G, Hollander D, Larson R, Montagna PA, Pryor M, Romero IC, Schwing P (2020) How quickly will the offshore ecosystem recover from the 2010 Deepwater Horizon oil spill ? Lessons learned from the 1979 Ixtoc-1 oil well blowout. Ecol Indic 117:106593. doi: 10.1016/j.ecolind.2020.106593
  • Romero, Isabel C., Jeff Chanton, Brad Roseheim, Jagoš R. Radović, Patrick Schwing, Dave Hollander, S. Larter, T.B.P. Oldenburg. 2020. Long-term preservation of oil spill events in sediments: the case for the Deepwater Horizon spill in the Northern Gulf of Mexico. In “Deep Oil Spills: Facts, Fate, Effects”, 285-300 p,
  • Radović, Jagoš R., Isabel C. Romero, T.B.P. Oldenburg,  S. Larter,  and John W. Tunnell. 2020. 40 years of weathering of coastal oil residues in the Southern Gulf of Mexico. In “Deep Oil Spills: Facts, Fate, Effects”, 328-340 p,
  • Bosman SH, Schwing PT, Larson RA, Wildermann NE, Brooks GR, Romero IC, et al. 2020. The southern Gulf of Mexico: A baseline radiocarbon isoscape of surface sediments and isotopic excursions at depth. PLoS ONE 15(4): e0231678.
  • Eenennaam J.S., Melissa Rohal, Paul A. Montagna, Jagoš R. Radović, Thomas B.P. Oldenburg, Isabel C. Romero, Albertinka J. Murk, Edwin M. Foekema. 2019. Ecotoxicological benthic impacts of experimental oil-contaminated marine snow deposition. Marine Pollution Bulletin (141): 164-175,
  • Romero et al. 2017. Large-scale deposition and redistribution of hydrocarbons following a deepwater oil spill. Environmental Pollution, 228: 179-189, doi:org/10.1016/j.envpol.2017.05.019
  • Murawski et al. 2016. How Did the Deepwater Horizon Oil Spill Affect Coastal and Continental Shelf Ecosystems? Oceanography 29 (3): 161-173, doi:org/10.5670/oceanog.2016.80

Sediment biota and toxic Polycyclic Aromatic Hydrocarbons interactions

Retrieved sediment core (Northern Gulf of Mexico)


Several collaborative studies in different biological fields showed the potential influence of polycyclic aromatic hydrocarbons (PAHs) on the abundance and diversity of ciliates, foraminifera, and bacteria under natural and experimental conditions. The results obtained in these studies explain the complexity of interactions between toxic compounds and biology, with some species having the potential to enhance the toxicity of crude oil, while others are affected by it, or not affected at all. Indicator studies of complex microbial/benthic communities are encouraged for specific biological groups avoiding generalizations on impact responses among taxa. Chemical analysis of PAHs was conducted at the Paleoceanographic Laboratory – University of South Florida.

Related Publications:

  • Pulster Erin L., Adolfo Gracia, Susan M. Snyder, Isabel C. Romero, Brigid Carr, Gerardo Toro-Farmer, Steven A. Murawski. 2020.. Polycyclic Aromatic Hydrocarbon Baselines in Gulf of Mexico Fishes. In “Scenarios and Responses to Future Deep Oil Spills”, 253-271 p,
  • Foekema, E.M., J.S. van Eenennaam, D. Hollander, A. Langenhoff, T.B.P Oldenburg, J. Radovic, M. Rohal, I.C. Romero, P. Schwing, A.J. Murk. 2020. Testing the effect of MOSSFA events in Benthic Multispecies Systems. In “Scenarios and Responses to Future Deep Oil Spills”, 288-299 p,
  • Schwing et al. 2017. Characterizing the variability of benthic foraminifera in the northeastern Gulf of Mexico following the Deepwater Horizon event (2010-2012). Environ. Sci. Pollut. Res, doi:org/10.1007/s11356-016-7996-z
  • Moss et al. 2016. Molecular characterization of benthic foraminifera communities from the Northeastern Gulf of Mexico shelf and slope following the Deepwater Horizon event. Deep-Sea Research Part I 115: 1-9., doi:org/10.1016/j.dsr.2016.04.010
  • Moss et al. 2016. Ciliate protists from the sediment-water interface in the Northeastern Gulf of Mexico. Deep-Sea Research Part I 106: 85-96., doi:org/10.1016/j.dsr.2015.10.001
  • Overholta et al. 2016. Hydrocarbon Degrading Bacteria Exhibit a Species Specific Response to Dispersed Oil while Moderating Ecotoxicity. Applied and Environmental Microbiology, DOI:10.1128/AEM.02379-15.

Sedimentary biogeochemical indicators of ecosystem change in the Northern Gulf of Mexico after 2010

Sediment sampling (multicore retrieving, R/V Weatherbird II)


The primary objective of this study was to investigate the impacts of the Deepwater Horizon (DWH) oil spill on the seafloor as recorded in sediments of the DeSoto Canyon region in the northeastern Gulf of Mexico. Sediment cores were analyzed at high-resolution (at 2 mm and 5 mm intervals) to evaluate the concentration, composition, and input of hydrocarbons to the seafloor through a coupling of sedimentological, geochemical, and biological approaches.

Results showed that the upper ~1 cm depth sedimentary interval (corresponding to 2010-2011) is distinct with higher hydrocarbon concentrations and signatures than in previous years.  This study demonstrates, for the first time, the sink to the seafloor of oil-derived hydrocarbons from a submerged oil spill. Our findings underline the complexity of the depositional event observed in the aftermath of the DWH event regarding multiple sources, variable concentrations, and spatial (depth-related) variability. Also, we were able to test our sampling and geochemical approaches after a marine gas well blowout (Hercules 265), indicating the importance of ocean observing systems to coordinate rapid-response efforts to effectively assess environmental impacts resulting from accidental releases of oil contaminants. Analyses were conducted in Dr. Dave Hollander and Dr. Gregg Brook’s labs (PI’s), under C-IMAGE I and DEEP-C Consortia. 

Related Publications:

The Importance of Molybdenum Speciation to Nitrogen Fixation and Assimilation in Lakes

Matt Tiahlo
Matt Tiahlo collecting water, Tahoe 2011

This study aimed to determine major nutrient controls on N2 fixation and NO3  uptake in three western U.S. lakes with varying trophic status (oligotrophic Lake Tahoe; mesotrophic Walker Lake; and eutrophic Clear Lake). We also studied nutrient controls on bacterial growth, phytoplankton biomass, and total CO2 fixation.

While previous studies have shown the important role of Fe and P in the N cycle of lakes, the dynamics of these nutrients cannot always explain observed rates of N2 fixation. Therefore, we also investigated trace metal co-limitation, including the potentially most bioavailable form of Mo, Mo(V). The results obtained in this study provide a new perspective on nutrient co-limitation in the N cycle of lakes. Analyses were conducted in Dr. Douglas Capone and Dr. Sergio Sanudo-Wilhelmy labs, PIs. 

Related PublicationRomero I.C., Klein N.J., Sañudo-Wilhelmy S.A., Capone D.G. 2013. Potential trace metal co-limitation controls on N2 fixation and NO-3 uptake in lakes with varying trophic status. Frontiers in Aquatic Microbiology, doi:10.3389/fmicb.2013.00054

Biomarker isotopic signals of ecological responses to environmental change in a Salt Marsh Ecosystem

Carpinteria Salt Marsh Reserve (University of California Natural Reserve System)

The main goal of this study was to characterize the lipid and isotopic composition of leaf waxes in living salt marsh plants, to better understand how hydrogen isotope signatures in plants are affected by biological and environmental factors (e.g., climate change). 

This study explained the importance of directly measuring plant water isotopic composition and highlighted the role of transpiration in driving isotopic signals in subtropical ecosystems. Results from this study constrained the hydrogen isotopic composition of salt marsh organic matter, and further indicate the potential for plant leaf waxes to resolve paleoenvironmental change, including sea level change, in sediment cores from salt marshes. Analyses were conducted in Dr. Feakins’s lab (PI) and in the Laboratory of Stable Isotope Ecology of Tropical Ecosystems (L7) at the University of Miami.

Related Publication: Romero I. C. and Feakins S. J. 2011. Spatial gradients in plant leaf wax D/H cross a coastal salt marsh in Southern California. Organic Geochemistry 42: 618-629,


Biocomplexity of Mangroves under different Nutrient Conditions

Mangrove forest (Twin Cays, Belize)


Mangrove forests are among the most productive ecosystems playing a significant role in nutrient sequestration in coastal zones. The primary purpose of this study was to better understand the functional relationship among microorganisms, trees, and sediments. A combination of molecular, chemical, and statistical techniques was used to identify key biological and environmental factors directly controlling the community structure of microorganisms in mangrove sediments subjected to a long-term fertilization experiment with nitrogen and phosphorus (Twin Cays, Belize).

Results indicated significant disturbance not only in ecological patterns and processes of bacteria and microbial functional groups but also on plant-microbial interactions. This research further explored the ecology of marine microorganisms over different temporal and spatial scales, a necessary step to better understand the link between microbial communities and sediment geochemistry in coastal environments under disturbance. Analyses were conducted in Dr. Capone, Dr. Marilyn Fogel, Dr. Susan Ziegler, and Dr. Jed Fuhrman labs.

Related Publications:

  • Romero et al. 2015. Phylogenetic Diversity of Diazotrophs along an Experimental Nutrient Gradient in Mangrove Sediments. J. Mar. Sci. Eng. 2015, 3, 699-719; DOI:10.3390/jmse3030699.
  • Schaller et al. 2015. Variable nutrient stoichiometry (C:N:P) across trophic levels determines community and ecosystem properties in an oligotrophic mangrove system. Oecologia, doi:10.1007/s00442-015-3379-2.
  • Romero et al. 2011. Long-term nitrogen and phosphorus fertilization effects on N2 fixation rates and nifH gene community patterns in mangrove sediments. Marine Ecology: 1-11. doi:10.1111/j.1439-0485.2011.00465.x.
  • Fogel et al. 2008. Unusually negative nitrogen isotopic compositions (δ15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem. Biogeosciences 5: 1704-2008.