Amphipods of the deep Mississippi Canyon, northern Gulf of Mexico: ecology and bioaccumulation of organic contaminants

In five summer cruises during the period 2000-2004, seventy-four box cores were collected from eleven locations from the Mississippi Canyon (480- 2750m, northern Gulf of Mexico), and an adjacent transect (336-2920) to understand the community structure and trophic function of amphipods and for measuring the bioaccumulation of polycyclic aromatic hydrocarbons, (PAHs). Amphipods were discovered to be an important component of the macrofauna of the Mississippi Canyon (40 % of the total faunal abundance). Seventy two species, belonging to nineteen families, were collected from the study area with 61 species from the canyon and only 38 species from the non-Canyon transect. The head of the canyon (480m) was dominated by dense mats (15,880 ind/m2) of a new amphipod (Ampelisca mississippiana). The logarithm of the amphipod abundance decreased linearly with depth. The species diversity (H`) exhibited a parabolic pattern with a maximum at 1100m. The differences in amphipod abundances and biodiversities were correlated with the variation in the amount of available organic matter. The depression in diversity in the canyon head is thought to be competitive exclusion resulting from the dominance by A.mississippiana, but the high species richness is presumed to be a function of the structural complexity of the canyon. Annual secondary production of A. mississippiana was 6.93 g dry wt m-2, based on size-frequency method and corresponding to an estimated univoltine generation from a regression model. The production/biomass ratio (P/B) was 3.11. Production of this magnitude is comparable to shallow marine ampeliscids but are high for the depauperate northern Gulf of Mexico. The effect of the organic contaminants and the bioavailability to the amphipods was determined through measuring the bioaccumulation of the PAHs. The distribution of PAHs in sediments was different from the distribution in the organisms suggesting preferential uptake/depuration or uptake from pore or bottom waters. The average bioaccumulation factor (4.36 ± 2.55) and the biota sediment accumulation factor (0.24±0.13) for the total PAHs by the ampeliscids were within the range reported for other benthic invertebrates. The average bioaccumulation factors were highest for dibenzothiophenes (up to 132) and alkylated PAHs and lowest for parent high molecular weight PAHs

Hot Spots for Poly Aromatic Hydrocarbons (PAHs) in Sediments and Benthic Organisms in the Coastal Water of Qatar

The state of Qatar has a strategic location within the heart of the Arabian Gulf, the richest oil area in the world. Its extensive coastline (700 km) is experiencing some of the most radical environmental conditions in the world's oceans including extreme temperature, high UV irradiance as well as high evaporations. These extreme conditions are pushing many marine biota to function close to their physiological limits. On the top of the extreme natural hydrographic conditions, there are tremendous stress exerted by oil exploration, production and transportation and probably any remnants from the largest oil spills in history, during the Gulf war in 1991. The present study is the first comprehensive study in the Gulf that is designed to assess the spatial and temporal variability of levels of Poly Aromatic Hydrocarbons (PAHs) in sediments of the Qatari coastal water and their bioaccumulation by dominant benthic invertebrates. Sediments and dominants benthic organisms samples were collected seasonally from thirteen locations in the coastal water of Qatar starting in the winter of 2014 and for four consequent seasons. Ten abundant benthic invertebrate species representing different trophic levels were selected to assess the spatial and temporal variability of PAHs in the Qatar costal water. These species have limited or no mobility, a major criteria for selecting benthic organisms in bio-monitoring programs. These species included gastropods, bivalves, and crustaceans with different trophic positions including carnivores, omnivores, herbivores and detritivores. Samples were analyzed for 16 parent PAHs including low molecular weight parent PAHs (LPAHS) and high molecular weight parent PAHs (HPAHs), 18 alkyl homologs and dibenzothiophenes. The results of the present study will be used for ecological risks assessment. Levels of PAHs in sediments and tissue residues are found to be significantly variable with species, locations, seasons and also with distance from shore (P < 0.05). PAHs concentrations in sediments is negatively correlated with the water temperature (r = ? 0.65) indicating the impact of temperature and probably levels of UV radiations on the fate of PAHs. Levels of PAHs in sediments indicated the presence of few moderately contaminated sites near point sources. Concentrations of PAHs in sediments showed wide spatial and temporal range (5 8.5%) presenting a range of trophic levels including carnivores and filter feeders. Significant correlations (P < 0.05) were found between PAHs tissue residues concentrations and signatures of carbon and nitrogen stable isotopes emphasizing the roles of trophic pathways on the uptake and bioaccumulation levels of individual PAHs in marine invertebrates. The present results are to be supported by more samples from two more seasons. The knowledge from this study intended to assist PAHs monitoring and identification of potential sources to guide management decisions. The outcome of the study is expected to help the regulatory agency (Qatar Ministry of Environment) as well as Gulf organizations such as ROPME to improve environmental laws and set standards based on these studies.qscienc

Global change: The Arabian Gulf ecosystem- An introduction

The Arabian Gulf is a main source of wealth and food for the people of the Gulf countries. For hundreds of years, the Gulf used to be the main source for some of the finest pearls in the world. It harbors highly diverse and productive habitats including coral reefs, mangroves, intertidal marshes, and seagrass. Another feature of the Arabian Gulf is that it hosts the second largest population of dugongs in the world's oceans. The Gulf is a shallow basin (avg. depth = 35 m) that has some of the most radical environmental conditions in the world's oceans including extreme temperature, high UV irradiance, high evaporations and limited fresh water influx, resulting in salinities that ranges from 40 up to 70 psu in some bays. On the top of the aforementioned extreme natural hydrographic conditions, there are tremendous environmental stresses exerted by the unprecedented industrialization, fossil hydrocarbon exploration and production, shipping tankers introducing non-indigenous species, power and desalination plants, and coastal development activities as well as any remnants from the largest oil spills in history, during the Gulf war in 1991. Qatar University Life Science Symposium (QULSS) is an annual event where local and world leader academics address the research priorities for the state of Qatar and the Gulf region. As headlines worldwide emphasize climatic changes, ocean acidification, eutrophication, loss of habitats, marine pollution, and toxic algal blooms as the top environmental issues threatening the health of the world's oceans and the Gulf, the QULSS of 2015 is tackling the effects of the local and global changes on the Arabian Gulf ecosystem. In QULSS-2015, marine scientists in Qatar University, along with collaborators from local, regional and international leading institutes, communicate and exchange their most recent research findings on impacts of different stressors including extreme natural conditions on the structures and functions of different species and habitats in the Gulf, to the fellow scientists, public, and policymakers. Objectives of the symposium are to increase the awareness on the ecological value of the Arabian Gulf, to initiate activities that foster marine science education, to promote interests in marine and environmental sciences among young people, to encourage young generations to pursue a career in marine environmental science/research, and to provide opportunities for networking and collaboration among scientists at the national, regional and international level as well as to strengthen scientific and research collaboration between academia, industry, and decision makers.Qscienc

Ampelisca mississippiana Soliman & Wicksten, 2007, sp. nov.

Ampelisca mississippiana, sp. nov. (Figures 1–5) Material examined. Holotype: Adult female; TL 5.6 mm. Northern Gulf of Mexico, head of the Mississippi Canyon (28 32 ' 30.7 " N, 89 49 ' 43.9 " W), 480 m, muddy bottom (approximately 73 % clay, 25.5 % silt and 1.5 % sand), 17 June 2000, R.V. Gyre. DGoMB station MT 1, USNM. Paratypes: 10 females. Mississippi Canyon (28 32 ' 6.6 " N, 89 49 ' 32.2 " W), 498 m, 2 June 2001, R.V. Gyre. DGoMB sta. MT 1, USNM. 15 females. Mississippi Canyon, 28 33 ' 12.1 " N, 89 49 ' 18.5 " W, 13 August 2002, 476 m, R.V. Gyre, USNM. 16 females. Same location, date and depth as holotype. TCWC cat. No. 2­ 9119. Other material: Approximately 300 individuals, including 3 males, same collecting locations, under study at Texas A&M University. Etymology. The name of the species refers to the Mississippi Canyon, where the specimens are found in abundance. Description. Female TL 5.6 mm. Body smooth and rather colorless. Head broad, longer than deep, subequal in length to first 3 body segments, projecting anterodorsally above antenna 1. Distal margin concave. Lower front edge oblique, convexly curved posteriorly. Anteroventral margin with short setae. Corneal lenses absent, ganglia of eyes easily visible under cuticle. Antenna 1 very short and slender, shorter than antenna 2 peduncle, article 1 robust. Peduncular article 2 long, about 1.5 x length of article 1. Article 2 slimmer than article 1. Flagellum with 7­9 articles. Antenna 2 as long as body or longer depending on age of specimen. Peduncle long and slender. Peduncle article 4 about same length as article 5. Flagellum with up to 19 articles. Flagellum setae long. Mandible with spine row with 8 spines. Palp tri­articulate, article 2 longer than either article 1 or 3, slen­ der and setose. Maxilla 1 with inner lobe conical, ending apically with 1 long seta. Outer plate with 9 spines. Palp biarticulate, second article with 4 distal sharp cusps, 4 spines and 6 setae. Maxilla 2 normal. Maxilliped with inner plate reaching to the end of palp article 1 and with several plumose setae; outer plate reaching to end of palp article 2, inner margin of outer plate lined with 8 chisel teeth, round apex with 5 setal spines, outermost two plumose. Palp with four articles, article 4 with nail as long as rest of article. Coxae 1­4 longer than broad. Coxal plate 1 expanded and rounded distally. Coxae 1 and 2 lower posterior angle with slit and bearing plumose setae on lower margin with row of setae overlying them. Gnathopod 1 simple and linear, shorter than gnathopod 2; basis long, ischium and merus short, carpus slightly longer than propodus; dactylus shorter than propodus, arched, and bearing several setules along inferior margin and one seta on outer margin; palmar portion weakly developed; armed with sets of comb spines and setal spines. Gnathopod 2 very slender, longer than gnathopod 1, carpus more than 1.5 times as long as propodus, with heavy sets of setae on distal margin; propodus heavily covered with spinose setae; dactylus about two­thirds of propodus, slightly curved with simple setae on flexor margin. Pereopod 3 and pereopod 4 almost similar. Pereopod 3 merus longer than carpus and propodus combined. Both merus and carpus bearing few long spinose setae at distal anterior margin; carpus with 1 seta on extensor surface; propodus with few simple setae on the extensor surface; dactylus very long and slender, almost straight and significantly longer than both propodus and carpus combined. Pereopod 4 coxa rectangular with rounded distal corner. Pereopod 4 similar to pereopod 3 but with much longer merus and with setae on both sides; distal anterior edge of the merus not produced. Pereopod 5 with basis having anterior margin fringed with plumose setae, posterior margin with rounded lobe. Carpus slightly longer and broader than propodus and endowed with set of 4­5 comb spines and two short spines, posterior margin with 2 sets of short spines. Propodus with very long setae on the distal end; dactylus very short. Pereopod 6 with basis roughly rectangular, anterior margin with 3 plumose setae and several spines, posterior margin rounded without any ornamentation. Carpus slightly longer than propodus, anterior margin with several spines, and 2 sets of spines on lateral surface, distal margin with long set of 4­5 comb spines and two short spines. Propodus less broad than carpus, with several spines on anterior margin. Dactylus very short. Pereopod 7 with basis straight, anterior margin with few short spines and rounded posteriorly, inferior margin of posterior lobe of basis expanded distally, passing distal end of ischium, distal margin fringed with plumose setae. Ischium longer than merus. Merus with large posterior setose lobe produced along entire margin of carpus, fringed by long plumose setae, anterior lobe slightly produced along anterior margin of carpus with 1 spine at blunt apex. Carpus with anterior edge slightly produced and notched. Propodus attached to posterior proximal portion of carpus, with notched distal anterior margin. Carpus and dactylus shorter than propodus. Dactylus broad at base and tapering distally, not curving forward. Epimeral plate 1 rounded with spine at distal margin and plumose setae at posterior margin. Epimeral plate 2 with inferior margin rounded. Epimeral plate 3 posteroventral corner with acute spine. Pleon segment 3 with posterior margin slightly convex, lower posterior margin produced into large acute tooth. Dorsal surface of segment with 2 setules. Pleon segment 4 dorsal surface with prominent wedge­shaped dorsal carina ending acutely above segment 5 and bearing 2 setae at top. Pleon segment 6 with shallow lateral crests. Pleon segments from 1 to 6 with pair of setules. Uropod 1 reaching as far as mid­rami of uropod 2, rami as long as peduncle, outer and inner rami equal. Inner ramus with 3­4 spines while outer ramus with 1 spine. Uropod 2 with inner ramus slightly longer than outer ramus. Inner margin of inner ramus and outer margin of outer ramus spinulate. Outer rami with very long subterminal robust toothed seta. Uropod 3 with peduncle strong, with 3 spines; rami equal in length, long, slender, lanceolate; outer ramus more slender than inner, broadest at proximal end, apical outer margin of inner ramus and inner margin of outer ramus strongly setose. Telson longer than broad, deeply cleft for more than 70 % of length; distal margin acute, apices of lobes with 1­2 setae, strongly notched on outer ridge, and dorsal surface of each lobe with 1­2 fine setae. Male TL 5.5 mm. Male resembles female in shape of head and length of antennae, differing from female in characters usually sexually dimorphic as follows: presence of setal tufts on peduncle of antennae 1 and 2, gnathopod 1 propodus with palm strongly developed, armed with spines and spinose setae on palmar side. Spinose setae on Gn 1 and Gn 2 generally are much heavier in male. Hump on pleon segment 4 more prominent than in female. Dorsal surfaces of pleon segment 3 and pleon segment 4 cristate. Lateral surfaces of pereopod 7 basis with short plumose setae, uropod 3 with apical outer margin of inner ramus and inner margin of outer ramus strongly setose. Remarks. The new species resembles the northwestern Atlantic species A uncinata, A. gibba, A. pugetica and A. mexicana. These resemble the new species in the length of antenna 2 that is almost equal to or exceeds the length of the body, antenna 1 shorter than antenna 2, large posterior lobe of the merus of pereopod 7, shape of pleon segment 3, and shape of uropod 3. However they differ from the new species in the shape of the head, presence or absence of corneal lenses, the relative lengths of antennae 1 segments, the shape of the segments of pereopods 7 and the shape of uropod 2. The species are compared in Table 1. Of these species, A. uncinata most closely resembles A. mississippiana in lacking of corneal lenses. It differs from the new species in the shape of the head (Fig. 5), length of the carpus of pereopod 7 and absence of notched anterior edge from the same segment; shape of dactylus of pereopod 7, shape of the dorsal process of pleon segment 4, absence of subterminal robust long seta of uropod 2, and in having two setae instead of one on the apex of the inner lobe of maxilla 1. Discussion. According to Barnard and Thomas (1989), the Ampeliscidae is characterized by the extreme constancy of small morphological characters over wide geographic areas. Some of the species that are found in the Gulf of Mexico are also known from the northeastern Pacific with few morphological differences (Barnard, 1954 a; Mills, 1965). Barnard (1954 a) examined the ampeliscids from the Caribbean Sea and the Gulf of Mexico, and compared them with those from northeastern Pacific (Barnard 1954 b). He found that the differences in the ornamentation of pleon segment 4 for at least 12 species were not enough to separate them as new species. This close relationship between the morphological characters of the northeastern Pacific ampeliscids and those from the northwestern Atlantic was confirmed by Mills (1965). His work related this affinity in the morphological characters to common ancestors that had an amphi­American distribution before the rising of the Central American isthmus. One of those supposed amphi­American species, A. cristoides Barnard, 1954, was reinvestigated by Goeke and Heard (1983). They found that specimen from the Gulf of Mexico had a shorter antenna 1 of the female, stronger carina of the urosome, extra tooth on the inner plate of the maxilliped as well as well­developed lateral carinae of pleon segment 3. They described it as a new species, Ampelisca bicarinata. Barnard and Thomas (1989) separated A. burkei, from Florida, from its eastern Pacific twin A. lobata Holmes, 1908, based on differences in shape and setation of article 4 as well as a single spine on article 5 of pereopod 7. These works demonstrated the subtle differences between the species of the Ampeliscidae and the need for care in identifying them. Ampeliscids have been placed in species groups based on morphologically similar specimens (Kaïm­ Malka, 2000). Like Ampelisca mississippiana, the ampeliscid species A. pugetica, A. mexicana, A. uncinata, and A. gibba, from the northwestern Atlantic share common morphological characteristics including a large posterior lobe on the merus of pereopod 5, pleon segment 3 with a convex posterior edge bearing an acute spine; and uropod 3 having a lanceolate shape. They can be distinguished by features such as the shape of the head, presence or absence of corneal lenses, shape of the dorsal carina of pleon segment 4, shape of the merus and carpus of pereopod 5, shape of uropod 2, and ratio of article 2 to article 1 in antenna 1. Ecological notes. Ampelisca mississippiana n.sp. was collected from the head of the Mississippi Canyon at a depth of approximately 480 m. The new species was a numerical dominant at the head of the canyon with densities reaching 26,000 ind.m ­ 2. A. mississippiana represented more than 85 % of the total macrofauna at this location. The sediment at the head of the canyon is muddy, about 73 % mud and 25 % silt. Why might A. mississippiana occur at such high densities in this location? Ampeliscid amphipods are known to be tube dwellers collecting suspended and settling matter or raking sediment for feeding (Mills, 1967 a). Canyons are known to be a good conduit of sediment and organic matter from the continental shelf to the deep water. Gardner (1989) found that the canyon focuses internal tides, which lead to mixing near the bottom and resuspension of particulate matter producing a nepheloid layer. These sedimentary conditions might explain the existence of such high densities of this species at this location. It is known also that tube builders can withstand the shear of the current and stabilize the sloppy mud. The Ampelisca mat at the head of the canyon is likely to be of great ecological importance in recycling of organic carbon that might be transported from the shelf to the slope and the deep Gulf. The tubes stabilize sediments through reducing resuspension and erosion, which is a common ecological role for all the known sedentary tube burrowers that form mats at high densities (Gage and Tyler, 1991).Published as part of Soliman, Yousria & Wicksten, Mary, 2007, Ampelisca mississippiana: a new species (Crustacea: Amphipoda: Gammaridea) from the Mississippi Canyon (Northern Gulf of Mexico), pp. 45-54 in Zootaxa 1389 on pages 46-53, DOI: 10.5281/zenodo.17519

Diversity and Zonation of Benthic Amphipod Crustaceans Affected by the Mississippi Submarine Canyon in the Northern Gulf of Mexico

Amphipod crustacean diversity and zonation are described from the large Mississippi Canyon that extends from the continental shelf across the entire continental margin. Benthic amphipods were sampled on four cruises from 2000 to 2004 from six locations in the Mississippi Canyon from depths of 480 through 2,750 m, and compared with five locations in a second transect on the open continental slope approximately 100 km west of the canyon to assess the canyon effect on the structure and composition of amphipod assemblages. Five replicates were collected from each location using 0.2 m-2 GOMEX box corer. Amphipods amounted to 40% of the total faunal abundance within the canyon compared to only 4% in the non-canyon samples. Of the seventy-two species (19 families) collected, 61 were encountered in the canyon compared to 38 on the non-canyon transect. The trough-like head of the canyon (480 m) supported high densities (4,446-26,933 ind./m2) of the filter feeding, tube dwelling ampeliscid amphipod (Ampelisca mississippiana), the highest densities sampled compared to any other single species, at any other location, either within or outside the canyon, reflecting extreme flux of organic detritus from the continental shelf. The dominance by this single species suppressed the within - habitat (alpha) diversity and evenness, compared to relatively high diversity within the 1,000-1,500 m depths interval both in and outside the canyon. The species richness and alpha diversity exhibited mid-depth maxima at ca. 1,100 m both in and out of the canyon. High species richness (61) over the entire length of the canyon is presumed to be a function of greater topographic complexity and intermittent mass wasting of sediment down the canyon axis. The absence of nestedness is attributed to the amphipod reproductive pattern that lacks dispersive larval stages and brooding comparatively small numbers of eggs in this taxon. Despite depressed diversity at the head of the canyon, the fact that the number of amphipod species in the Mississippi Canyon was 1.5 times their numbers on the adjacent slope suggests that this physiographic feature enriches geographic-scale species diversity.DGoMB study was funded by the U.S. Department of Interior, Minerals Management Service (Contract 30991), now Bureau of Ocean Energy Management (BOEM). The taxonomic and data analysis were partly supported by the Egyptian Ministry of Higher Education through a scholarship to YS.Scopu

Seasonal and body size-dependent variability in the bioaccumulation of PAHs and their alkyl homologues in pearl oysters in the central Arabian Gulf

Spatiotemporal concentration patterns for 19 parents and their alkyl homologues were measured in Pinctada radiata from 7 locations in the central Arabian Gulf around Qatar in the winter, spring and summer (2014–2015). The concentrations of PAHs ranged from 20 to 2240 (262 ± 38.0 ng·g−1 dw) with the highest occurrence in the Doha harbor (738.4 ± 197.3 ng·g−1 dw) and the lowest in the west coast of Qatar (48.3 ± 5.8 ng·g−1 dw). Residual PAHs in the oysters were about two times higher in winter than in spring and summer (P 55 % of the ΣPAHs. Statistically significant differences in PAHs profiles among oysters were due in part to differences in lipid contents and shell biometrics. Principal component analysis (PCA) and diagnostic ratios for sources identifications suggested that PAHs accumulations in oysters were due to petrogenic and fuel combustion.This work was made possible by NPRP grant 6-442-1-087 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made here are solely the responsibility of the authors.Scopu

Physical drivers of chlorophyll and nutrients variability in the Southern-Central Arabian Gulf

The southern-central Arabian Gulf demonstrates a poor understanding of nutrients and chlorophyll dynamics in physical-biogeochemical settings. Here, using data of chlorophyll, nutrients and hydrographic parameters collected in two cruises in summer 2019 and winter 2020, we examined variability in nutrients and chlorophyll concentrations, and the driving mechanisms. Summer thermal stratification enhanced by intrusion of fresher surface water plume from the Arabian Sea developed a hypoxic zone (DO  0.05). Photo-protective carotenoids content in summer (0.59 mg/m3) was about 2.7 times their winter concentration. Winter cooling resulted in downwelling of dense water on the shallow coastal banks, which enhanced near bottom oxygen concentrations and swept away nutrient-rich water resulting in lower winter chlorophyll. This research features aspects of the physical and biogeochemical drivers underpinning the dynamics of nutrients and chlorophyll in the central Gulf.This work was funded by QU Grant [QUST-2-CAS-2019-44]

Macrobenthos in the central Arabian Gulf: a reflection of climate extremes and variability

The arid subtropical ecosystem of the central Arabian Gulf was used to explore the combined effects of low primary productivity, high salinities, and variable temperatures on the composition and structure of benthic macrofauna at 13 sites encircling the Qatar Peninsula in winter and summer (or late spring) of 2010 and 2011. The low abundance, biomass, and remarkably high species turnover may be a reflection of the oligotrophic, thermally variable, hypersaline coastal environment. The number of species and within-habitat diversity was lowest in the highest salinities but increased with finer-grained sediments and lower salinity. A remarkable temporal variation in species composition observed may reflect insufficient primary production to sustain new populations recruited from the seasonal exchange of water from the adjacent Sea of Oman. Low abundances accompanied by continued replacement of species may be a "new model" for extremely arid conditions associated with global warming. 2015, Springer International Publishing Switzerland.We would like to thank the Qatar National Research Fund (QNRF) for field work support (NPRP 08-497-1-086), as well as Canadian Healthy Oceans Network (CHONe) and Taiwan's Ministry of Science and Technology for supporting data analysis and manuscript preparation (MOST 103-2119-M-002-029-MY2). We also thank captain and crew of the R/V "Mukhtabar Al Bihar" and the Qatar University Environmental Studies Center laboratory staff and technicians for their work at sea and conducting chemical and biological analyses.Scopu

Bathymetric zonation of deep-sea macrofauna in relation to export of surface phytoplankton production

Author Posting. © Inter-Research, 2010. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 399 (2010): 1-14, doi:10.3354/meps08388.Macrobenthos of the deep, northern Gulf of Mexico (GoM) was sampled with box cores (0.2 m2) along multiple cross-depth transects extending from depths of 200 m to the maximum depth of the basin at 3700 m. Bathymetric (depth) zonation of the macrofaunal community was documented for 6 major taxa (a total of 957 species) on the basis of shared species among geographic locations; 4 major depth zones were identified, with the 2 intermediate-depth zones being divided into east and west subzones. Change of faunal composition with depth reflects an underlying continuum of species replacements without distinct boundaries. The zonal patterns correlated with depth and detrital particulate organic carbon (POC) export flux estimated from remotely-sensed phytoplankton pigment concentrations in the surface water. The Mississippi River and its associated mesoscale eddies, submarine canyon, and deep sediment fan appear to influence the horizontal zonation pattern through export of organic carbon from the ocean surface and the adjacent continental margin. On the local scale, near-bottom currents may shape the zonation pattern by altering sediment grain size, food availability, and larval dispersal. This study suggests a macroecological relationship between depth, export POC flux, and zonation; parsimonious zonal thresholds need to be tested independently for other continental margin ecosystems.This research was funded by the U.S. Department of Interior, Minerals Management Service, Contract No. 1435-01-99-CT-30991