Task E. Bathyal Benthic Fauna and Sedimentary Dynamics – Understand Team
Title: The Status of Bathyal Benthic Communities near the BP Macondo Prospect.
Harriet Perry, Donald Johnson, Richard Waller – Megafauna
Chet Rakocinski, Richard Heard – Macrofauna
Charlotte Brunner – Microfauna - Benthic Foraminifera
Oil pollution can devastate the sea floor by causing major disruptions to biogeochemical
processes. Oil can cause selective and even mass mortality of the benthic meio-, macro-, and
mega-fauna (Olsgard and Gray, 1995; Montagna and Harper, 1996; Yanko et al., 1999; Ernst et
al., 2009; Martínez-Colon et al., 2009), either directly by surface coating or hydrocarbon toxicity
(i.e., Gomez-Gesteira and Dauvin, 2005), indirectly by overloading the system with organic
carbon and driving enhanced microbial respiration, or by shutting down ventilation of coastal
waters, leading to the rapid development and persistence of hypoxic or anoxic conditions at and
above the sea floor. Additionally, reductions in benthic biomass will reduce physical mixing of the
sediment by suppression of the major bioturbators. Because benthic environments of the
continental margin are highly productive, it is absolutely critical that the supply, impacts and fate
of petroleum hydrocarbons on the benthos be quantified, as immediate ecological changes are
expected and are likely to result in long term, ecosystem-scale adjustments throughout the water
column.
The benthic subsystem plays a pivotal role in the regeneration, transformation, and transfer of
energy and nutrients through various benthic–pelagic coupling mechanisms involving both
biogeochemical and biotic processes in marine and estuarine ecosystems (Twilley et al., 1999).
Macrobenthic communities mediate the functioning of the benthic subsystem in ways that affect
rates, directions, and pathways of exchange of energy and nutrients between the water column
and the sediment (Hansen and Kristensen, 1997). Furthermore, disruption of benthic function
through environmental degradation causes redirection and loss of macrobenthic trophic transfer
potential to microbial pathways (Diaz and Rosenberg, 2008). Sediment contamination poses one
of the most serious forms of environmental degradation within marine and estuarine ecosystems
(Diaz and Rosenberg, 1996).
Macrobenthic communities are ideal indicators of biotic integrity for many reasons (Rakocinski et
al., 1997): (1) benthic organisms reside directly on or within sediments, where many
contaminants are ultimately partitioned; (2) because benthic organisms are relatively sedentary,
they cannot easily avoid contaminants; (3) the macrobenthos occurs on the proper spatial scale
for assessing anthropogenic impacts; and (4) the temporal scale of macrobenthic organism life
histories enables the detection of chronic or historical environmental stress through signature
effects on resident assemblages. Because individual benthic taxa vary in their sensitivities to
different contaminants, integrated responses by macrobenthic assemblages reflect the severity
and nature of environmental stressors. Anthropogenic-related changes in macrobenthic
assemblage structure also reflect concomitant shifts in ecosystem function through changes in
trophic structure, the diversity of functional traits, and process indicators, like production
potential, community turnover rates, and biomass-size spectra (Rakocinski and Zapfe, 2005).
Benthic foraminifera are dominant members of the meiofauna at bathyal/abyssal depths,
frequently exceeding other meiofauna in biomass, biovolume and biodensity (Coull et al., 1977;
Cornelius and Gooday, 2004; Bernhard et al., 2000). For this reason, foraminifera are used here
as an indicator of the condition of the meiofauna in general. Foraminifera have been shown to be
responsive indicators of pollution, including oil contamination (Yanko et al., 1999; Ernst et al.,
2009), exhibiting signs of ill-health such as declining species diversity, declining standing stock,
assemblage changes, shallowing of infaunal habitation depths, declines in biomass, and
increases in test deformities (survey article by Martínez-Colon et al., 2009). Their utility is
enhanced by baseline reports on living foraminiferal populations in the Gulf sampled before the
spill (Phleger and Parker,1951; Parker, 1954; Reynolds, 1982; Sen Gupta and Aharon, 1994; Sen
Gupta et al., 1997; and Robinson et al., 2004; Bernhard et al., 2005).
Deep-sea megafauna are defined as organisms large enough to be determined on photographs
or taken in gear with a mesh size greater than 3 cms. They comprise a major fraction of the
benthic biomass, play a key role in transfer of organic matter and are major bioturbators of bottom
sediments. Prior to the oil spill, the deep-sea red crab (Chaceon quinquedens) was the primary
inhabitant of the continental slope of the northern Gulf of Mexico (nGOM) and was perhaps the
major bioturbator of the slope ecosystem. These crabs inhabit soft bottom areas and continuously
filter fine sediment particles that are present in the bottom muds and the section of the water
column immediately adjacent to the sediment-water interface, and thus would be expected to
provide a useful diagnostic of organismal exposure to oil contamination of deep sea sediments.
The center of abundance of red crabs in the eastern and northern GOM was located ~12 miles
north of the wellhead. Following the oil spill, these organisms were much reduced or absent from
two of the sites sampled in previous years and the giant deep-sea isopod, Bathynomus
giganteus, was abundant. The GCRL has an extensive historical database defining geographic
and bathymetric distribution and abundance of these crabs and data on heavy metals present in
tissues of red crabs from the nGOM. Sites trapped in NGI Phase 1 indicate a change in
community structure at the depths sampled. Completion of analytical work on red crab tissues
collected will provide data on exposure to oil contamination. The proposed study would trap over
the known range of the species in the nGOM to determine if the crabs had moved down-slope in
response to the oil spill or suffered mortalities as a result of the spill.
Approach. This study represents a collaborative effort comprised of three interrelated projects
designed to assess benthic fauna as ecological indicators of the health of the bathyal benthic
system at several levels of organization relative to the BP oil spill incident. To maintain continuity
with previous studies, sampling will be conducted during August or September 2011 using the
USM GCRL research vessel, the R/V Tommy Munro. Red crabs, sediment, and dissolved
oxygen will be sampled in Areas 1and 2 at depths of 677, 860, 1043, and 1830 meters to
determine current bathymetric distribution. Seven commercial plastic crab traps (Fathoms Plus®)
will be fished on 366m of anchored ground tackle with a buoy line at a two to one scope. Traps
will be baited with Gulf menhaden, Brevoortia patronus and fished for ~ 18 hours. Upon retrieval
of the trap line the contents of each trap will be separated. Two adult males and two adult
females from the set will be randomly selected for dissection and tissue analysis. Crabs for
analysis will be maintained alive in refrigerated seawater systems at 5C and 36‰ salinity until
they are dissected. Carapace width (CW) and carapace length (CL) will be measured (± 1 mm)
for each crab. Crabs will be weighed and dissected on a glass dissection tray using high grade
stainless steel scissors. Samples of gill, muscle, hepatopancreas, ovary and eggs (ovigerous
females) will be removed for analysis of hydrocarbons,and dispersants. Bottom sediments will be
taken with an Ocean Instruments MC800 multicorer, which simultaneously samples 8 replicate
cores 9.5 cm by ~70 cm with an intact sediment-water interface. Companion Capetown dredge
benthic samples will also be taken. Bottom-water samples will be taken using a rosette sampler in
concert with a CTD equipped with temperature, salinity, depth, and dissolved oxygen sensors.
Megafauna Task. Changes in slope community structure were apparent in the 2010 re-survey.
Sampling was limited to a single depth stratum and it is not known if the red crabs shifted their
distribution geographically or bathymetrically in response to the oil spill. The GCRL has trapped at
1000 fathoms in Area 1 and taken red crabs so it is possible that they may have traveled downslope in response to the oil spill. The proposed study would re-survey areas previously sampled
in September 2010 and would trap in deeper waters to see if red crabs have shifted their
bathymetric distribution. Analysis of levels of hydrocarbons, dispersants, and heavy metals in red
crab tissues in concert with changes in known distribution will provide information on the impact
of oil on northern Gulf populations. Additional information on macrofaunal abundances will also
provide an indication of food resource availability for red crabs. Crabs in Areas 1 and 2 would
have the greatest potential for exposure over their geographic range.
Macrofauna Task. Concomitant changes in the slope macrofaunal community in connection with
the megafauna and microfauna will provide effective indicators of possible chronic effects of the
DwH spill. In October 2010, companion Capetown dredge samples of bottom sediments were
taken and processed for macrofauna in three established bathyal areas where megafauna were
also trapped. These samples are currently being processed. Samples from the area where red
crabs were captured contain a wide assortment of polychaetes, crustaceans, and larger
foraminferans (>500 μm), which could also serve as food for red crabs. During Phase 2 of
funding, we propose to continue joint sampling of benthic macrofauna in conjunction with
megafaunal and extended microfaunal sampling along the slope where red crabs may occur.
Sampling of benthic macrofauna will be extended in two ways during Phase 2 of this project: (1)
In addition to qualitative Capetown dredge samples for characterizing the macrofaunal community
and the relative abundances of the faunal constituents, three or four quantitative 9.525 cm
diameter cores obtained by a multicorer device will be obtained for density and biomass
estimates of the numerically dominant macrofaunal taxa; and (2) Sampling intensity will be
extended to 8 sites distributed across the two megafaunal sampling areas, as described above.
Microfauna Task. Changes in the benthic foraminifer community will be examined and compared
to those in the mega- and macro-fauna to monitor signs of ecological distress. Although no
foraminiferal samples were taken from these stations during phase 1(except for specimens >500
μm), samples of live benthic foraminifera were taken in October 2010 at sites nearby and at
depths close to those discussed herein. In Phase 2, samples will be taken from the same
multicorer casts as those used for macrofauna analysis, assuring spatial and temporal
correspondence. Cores will be sliced into 1-cm slabs from the surface to 10 cm, stained with rose
Bengal to tag specimens that are living or recently living (Bernhard, 2000), and washed on a
screen of 63 μm. The sand-size residue will be buffered with sodium borate and stored wet in
alcohol until a census of stained individuals is made.
Budget Overview.
Megafauna and sediment analyses.
Macrofauna analyses.
Microfauna analyses.
Ship Time (6 d @ 7K per d)
Direct Costs (not incl Ship Time)
Indirect Costs (@ 46.5% of Direct)
Total Requested.
–
–
–
–
–
–
–
$ 47,080
$ 34,775
$ 21,400
$ 42,000
$ 103,255
$ 89,745
$ 235,000
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