Benthic Faunal Baselines in the Gulf of Mexico: A Precursor to Evaluate Future Impacts

This chapter provides a comparison between recently developed, post-oil spill baseline measurements throughout the Gulf of Mexico (GoM) and previous, pre-oil spill baselines for benthic foraminifera, meiofauna, and macrofauna for areas impacted by the Deepwater Horizon (2010) and Ixtoc 1 (1979–1980) oil spills. This comparison will provide two primary outcomes: (1) assessment of any lasting changes in benthic faunal assemblages caused by the Deepwater Horizon and Ixtoc 1 oil spills in the Gulf of Mexico and (2) augmentation of pre-oil spill baselines or establishment of “new normal” post-oil spill baseline measurements that can be utilized to quantitatively assess impact, response, and recovery of benthic fauna in the event of a future oil spill

Soft-walled monothalamous and Nodellum-like foraminifera and gromiids (Protista) at the Håkon-Mosby Mud Volcano (Barents Sea slope)

We describe the occurrence of basal (‘primitive’) foraminifera and gromiids (a distinct taxon related to the foraminifera) in different bathyal habitats of the Håkon Mosby Mud Volcano (HMMV, Barents Sea). The foraminifera include two distinct groupings: (1) soft-shelled monothalamous foraminifera (‘allogromiids’, ‘saccamminids’ and ‘psammosphaerids’) and (2) brown organic-walled foraminifera (genera Conicotheca, Nodellum, Placopsilinella and Resigella). Samples were analysed from (1) the ‘hot centre’ of the volcano where fluid upflow was maximal; (2) smooth and structured muds in a ‘warm’ area of the centre where fluid upflow was reduced; (3) areas covered by Beggiatoa mats; (4) an area colonised by siboglinid polychaetes (‘pogonophores’); and (5) areas of ‘normal’ seafloor outside the volcano. Together, the studied organisms represented 57.8 % (‘normal’ seafloor; n?=?418), 28.5 % (‘warm centre’; n?=?122), and 26.4 % (Beggiatoa mats; n?=?5) of all ‘live’ (stained) foraminifera in three samples (0–1 cm layer) that were sorted for all stained foraminifera. In total, the 17 samples examined yielded 21 ‘allogromiid’ (organic-walled), 25 ‘saccamminid’ (agglutinated) and 5 other morphospecies among the monothalamous foraminifera, as well as 5 ‘brown-walled’ and 5 gromiid morphospecies. Four taxa were identified to species (Conicotheca nigrans, Resigella moniliforme, R. polaris, Micrometula hyalinosphaera); another seven were assigned to the genera Bathyallogromia, Conqueria, Nodellum, Placopsilinella, Resigella, Tinogullmia and Vanhoeffenella. All others were undescibed at the genus level. Some species, notably ‘Saccamminid sp. 5’, C. nigrans and Nodellum sp., were distributed in sediment layers down to 5 cm depth, and sausage-shaped gromiids were also present in the deeper layers of some samples. The number of basal foraminiferal and gromiid morphospecies varied considerably from site to site. It was relatively high north of the volcano (42 morphospecies in 4 samples) and in the ‘warm centre’ (28 morphospecies in 2 samples), somewhat lower southwest of the volcano (at least 13 morphospecies in 2 samples) and in the siboglinid field (14 morphospecies in three samples), and substantially reduced in the bacterial mat area (5 morphospecies in 6 samples). The scarcity of these protists at the bacterial mat sites is probably a consequence of high sulfide concentrations. No stained foraminifera or gromiids were observed at the ‘hot centre’ site. In general, assemblages from within and around the HMMV resembled those reported from other bathyal sites, notably in the Porcupine Seabight. Saccamminid sp. 5, by far the most common species in our samples, belongs to a ‘lamp-like’ morphotype that is widely distributed in the oceans. The wall structure, and the presence of what appears to be an internal partition across the base of the neck, is reminiscent of some komokiaceans

Characterizing the Variability of Benthic Foraminifera in the Northeastern Gulf of Mexico following the Deepwater Horizon Event (2010-2012)

Following the Deepwater Horizon (DWH) event in 2010 subsurface hydrocarbon intrusions (1000-1300 m) and an order of magnitude increase in flocculent hydrocarbon deposition caused increased concentrations of hydrocarbons in continental slope sediments. This study sought to characterize the variability [density, Fisher\u27s alpha (S), equitability (E), Shannon (H)] of benthic foraminifera following the DWH event. A series of sediment cores were collected at two sites in the northeastern Gulf of Mexico from 2010 to 2012. At each site, three cores were utilized for benthic faunal analysis, organic geochemistry, and redox metal chemistry, respectively. The surface intervals (∼0-10 mm) of the sedimentary records collected in December 2010 at DSH08 and February 2011 at PCB06 were characterized by significant decreases in foraminiferal density, S, E, and H, relative to the down-core intervals as well as previous surveys. Non-metric multidimensional scaling (nMDS) analysis suggested that a 3-fold increase in polycyclic aromatic hydrocarbon (PAH) concentration in the surface interval, relative to the down-core interval, was the environmental driver of benthic foraminiferal variability. These records suggested that the benthic foraminiferal recovery time, following an event such as the DWH, was on the order of 1-2 years