INTRODUCTION

         The Minerals Management Service (MMS) advanced a 4-year plan of integrated physical/biological research to be conducted in northeastern Gulf of Mexico beginning in 2001: "Integrated Oceanographic Study of the Northeastern Gulf of Mexico (IOS-NEGOM)" (Sulak et. al., 2001). This plan, outlined in the "MMS GOM Region Planning Document" (MMS, 2000a) and its companion document "Elements of Interagency Agreement (EIA) between MMS & USGS" (Boland, 2000) define the principal questions to be addressed and the information needs for the IOS-NEGOM study. The overall IOS-NEGOM study area (Figure 1) encompasses a 52 x 1000 km² sector of the central and eastern NEGOM region (Longitude 84.34^o to 88.75^o W, 10 m to 500 m isobaths) (MMS, 2000b).  The USGS, as part of continuing long term policy to help address MMS information needs in the region, undertook research to address those topics that provide an integrated basis of understanding of structure and function of key biological communities and critical habitats in relation to physical processes. USGS scientists from the Coastal Ecology and Conservation Research Group, Florida Integrated Science Center, Gainesville, Florida have identified acquisition of fundamental knowledge on fish and megafaunal invertebrate community structure and function as a primary long-term study goal. The guiding interagency principal question is: "What are the potential [biological] impacts from oil and gas activities" (EIA) and in particular on live-bottom and hard-bottom biotopes?." The USGS study plan responds to MMS OCS information needs and will provide direct input to management decisions that impact the regulation of offshore oil and gas operations. The present cruise report summarizes the final IOS-NEGOM biological field mission undertaken by the USGS CEC Research Group.
 

Figure 1. The NEGOM study area (Polygon) with 2003 western and comparative 2002 mission sites indicated. (isobaths are in meters)
 

BACKGROUND

         The outer continental shelf of the northeastern Gulf of Mexico (NEGOM) is populated with a large number of hard-bottom topographical features (Gardner et al., 2000; Gardner et al., 2001a).  Parker et al. (1983) estimated that there was substantially more hard bottom habitat in this area compared to that in the northwestern Gulf of Mexico and along the Atlantic coast. The eastern part of the NEGOM region is separated from the western part, by the DeSoto Canyon (Figure 1), which forms a physical and hydrographic barrier separating shelf and slope faunas (Shipp and Hopkins, 1978). The region's hard-bottom habitats were first characterized by Ludwick and Walton (1957) from an intensive single-beam echo sounding survey revealing an extensive area of "pinnacles" in the western NEGOM region. Recently, the USGS used a Kongsberg Simrad EM 1002 Multibeam Mapping System to produce high resolution maps of the northwestern Florida shelf and Mississippi-Alabama shelf/slope (Gardner et al., 2002). Mapping resulted in 4 m resolution subarea maps (Gardner et al., 2000; Gardner et al., 2001b) identifying individual rock formations. Additionally, co-registered acoustic backscatter maps were generated (Gardner et al., 2001a). The work of Gardner et al. (2001a) describes many of the reef pinnacles and hardgrounds on the Mississippi-Alabama shelf. These structures consistently have a sand build-up on to the north and an eroded moat to the south caused by the Loop current. Other structures found on this part of the shelf include a prominent ridge, a salt dome, and several large landslide scars with resultant slumps (Gardner et al., 2001a).

         Our focus on reef-like topographic features is due to the sensitivity of hard bottom communities to disturbance (Rezak et al., 1990) and their significance as both trophic and spawning habitat (Coleman et al. 1996; Koenig et al., 2000). Topographical features affect water circulation along the shelf edge (Moum and Nash, 2000) and may have significant effects on ocean mixing (Lueck and Mudge, 1997).  They may also exert dominant biological influence through topographic-hydrographic interaction (Hamner et al., 1988; Witman et al., 1993). Near-reef current measurements in the western NEGOM suggest topographically induced turbulence exists (Kelly et al., 2000). Increased turbulence may enhance availability of plankton to planktivores through current compression over topographic features (Genin et al., 1986) and potentially increase production over broad areas of heterogeneous relief, such as the Pinnacles (Weaver et al., 2002). Changes in near-bottom flow may also control local small-scale epifaunal and fish distributions (Genin et al., 1986; Messing et al., 1990; MacDonald et al., 1996). These observations suggest that the biological community is tightly coupled to physical structure (topography) and resultant hydrographic processes (turbulent fields), related to the interaction of physical structure and currents. The present research seeks to further define the basis of physical-biological coupling, and aspects of community structure and function (e.g., species dominance, trophodynamics, population age structure, reproductive cycles, and recruitment), biotope affinities, and critical habitat parameters on these topographical features as many are well known fishing areas (Moe, 1963) considered essential fish habitat by NOAA Fisheries.
 

OBJECTIVES

         Our USGS team established a study plan with five main objectives (Sulak et al. 2001). The objectives are outlined below and were developed to exploit the capabilities, expertise, and existing strategic OCS research direction of USGS.

• Map the study area using a high-resolution multibeam mapping system (HRMBS). HRMBS mapping will be used to identify areas of hard bottom and to resolve the zone of reef influence on nearby soft bottom habitat.  The total areal extent of the reef biotope is much greater than the physical reef structures themselves, due to the halo of reef-dependent, reef-influenced communities surrounding and extending well away from reefs.  This heterogeneous habitat (reef plus halo biotopes) is apparent in acoustic reflectivity surveys (Gardner et al., 2000), in the form of high reflectivity substrate surfaces (reef rubble, and current-swept and biologically reworked sediment) adjacent to hard-bottom areas. Mapping will serve both to accurately locate target study reefs, and to define overall topography including the locations of all hard-bottom features. Precise mapping of topographical features will allow more detailed and coordinated studies of processes on individual features on a scale relevant to the biotic community. High-resolution bathymetry is now available for the eastern NEGOM Pinnacles area (Gardner et al., 2000) and the western area will be mapped in 2001. From the HRMBS mapping the area of each biotope type will be calculated and resulting bathymetry, shaded relief, and backscatter products will be prepared as Arcview project files for use by other researchers (especially our collaborators and cooperators).
   
• Determine the community structure of fish and epifaunal assemblages, on hard bottom, in the eastern NEGOM area.  The composition and abundance of the fish assemblage, focusing on non-resource species that comprise the forage base, will be resolved and compared to previous work in the western NEGOM. Inner (60-80 m) and outer (100-120 m) shelf-edge features will be compared and related to other deep reef habitats in the Gulf of Mexico and Caribbean. Megafauna and encrusting epifauna assemblages will be compared between the eastern and western NEGOM.
  
           Data developed from community structure analyses will be used to test specific hypotheses regarding potentially different NEGOM communities on either side of De Soto Canyon.  Important questions to be phrased as hypotheses would include: Do eastern OCS reef fish communities serve as distributional stepping stones for the translocation of species west of De Soto Canyon? Is the winnowing of species composition a gradual latitudinal, temperature-related phenomenon, or does faunal transition take place more abruptly across large-scale physical discontinuities (e.g., De Soto Canyon), and across local-scale biotope boundaries. Also we expect to develop a model to predict hard bottom diversity from geologic and oceanographic parameters.
   
• Determine the energy sources of driving the system and define the trophic linkage among dominant fish and megafaunal invertebrate taxa.  A second major USGS research question for the IOS-NEGOM study, is what are the sources of nutrients driving the ecosystem. Addressing this question will entail definition of trophic linkages and trophodynamics of dominant fish and megafaunal invertebrate communities inhabiting critical heterogeneous biotopes — in relation to energy sources (water column and benthic) and physical processes (topography, currents). Research in this regard will extend from ongoing USGS food habit and food web studies in the NEGOM-CMEP (western IOS-NEGOM) (Sulak and Weaver, 2001) and will coordinate with data collected from proposed IOS-NEGOM oceanography sampling and existing historical energy source data.  Analyses for the current project would consist of carbon and nitrogen (and possibly sulfur) stable isotope tissue analyses to determine the sources of energy input, to define horizontal (inshore versus deep-water; off-reef versus on-reef) and vertical trophic linkages, and to specify the trophic levels occupied by microvore and megavore predators.
   
• Determine life history aspects of dominant forage base species.  There is little information on these ecologically key taxa. Productivity (turnover rate) and resilience to disturbance are functions of longevity and reproductive mode. Important life history parameters such as, age, growth rate, and sexual pattern, will be determined to assess the sensitivity to disturbance of this faunal component.
   
• Determine what fish spawn and recruit to the IOS-NEGOM area. The SEAMAP ichthyoplankton database will be synthesized with special regard to reef fish species. The regional composition of ichthyoplankton will be summarized and placed in context with knowledge of Gulf-wide patterns.

         The objective of the TM-2003-01 cruise was the completion of investigations on community structure including:

• ROV video and digital still documentation and quantification of fish and invertebrate community structure.
   
• Completion of stable isotope collection from a target number of thirty individuals from each taxonomic or ontogenetic entity.
   
• Completion of ROV video exploration and faunal inventory of NEGOM-West comparative reef and habitat types.

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