Re-Discovering Cordell Bank: Dive Expedition 30 Years Later
- Dan Howard
Cordell Bank National Marine Sanctuary
- Lisa Etherington
Cordell Bank National Marine Sanctuary
For the first time since the designation of the Cordell Bank National Marine Sanctuary (CBNMS) in 1989, and thirty years after the initial exploration of Cordell Bank by SCUBA divers from the non-profit group Cordell Expeditions, technical scientific SCUBA divers revisited the shallowest parts of Cordell Bank’s reef crest (123-193ft) on October 7-9th, 2010, deploying off of the NOAA research vessel Fulmar. Cordell Bank National Marine Sanctuary staff, Office of National Marine Sanctuary (ONMS) technical divers, University of North Carolina-Wilmington, NOAA’s Cooperative Institute for Ocean Exploration, Research and Technology (CIOERT), University of California-Davis Bodega Marine Laboratory, California Academy of Sciences, and Cordell Expeditions collaborated to put SCUBA divers on Cordell Bank and test the feasibility of using technical divers for accomplishing scientific tasks. Six technical dives were completed in rigorous conditions at five sites on Cordell Bank, with the dive teams successfully accomplishing all of the project’s science and outreach objectives (Figure 1). Divers collected samples to be archived and identified by the California Academy of Sciences and photos/videos were collected to document and characterize the habitat and communities of the upper reaches of the Bank. Data collected during this mission will be used to compare the invertebrate and fish communities to historical conditions, using photos/video from 30 years ago, and will serve as a baseline upon which to measure future change.
1. Collect data of invertebrate distribution and abundance to assess spatial variability in density, species composition, and species richness and determine habitat associations.
2. Collect invertebrate specimens to: a) obtain representatives of target taxa for archival at California Academy of Sciences (CAS); b) photo-document samples in situ for potential field identification guide based on laboratory identifications; c) target tunicates for identifying a potential invasive species; c) target hydrocoral (Stylaster sp.) for identification (genetic & morphological) and reproductive analyses, target sponges for species identification.
3. Revisit sampling sites of Cordell Expeditions from the 1970s and 1980s and collect data and specimens to assess qualitative changes in community composition over time and to compare samples with historic collection archived at CAS.
4. Collect high definition video and still images for general site characterization of the habitats and species composition of the reef crest environment.
Summary to DateThe benthic community and habitat were sampled by taking digital photographs of a 0.25m x 0.25m PVC quadrat frame that was haphazardly placed on the substrate (Figure 2). Photo quadrat images were taken approximately 2-3 m apart. Between zero and eleven photo quadrats were photographed at each site. Macro photos were taken on the second dive of October 9th at South Central Plateau in lieu of quadrat photos. Photo quadrat images will be analyzed to assess presence of species/taxa and to determine invertebrate species composition.
Video footage was acquired throughout the dives and fulfilled the objectives of assessing the reef top community and habitats as well as documenting technical divers carrying out tasks on the Bank (Figure 3). In addition, divers collected one 360 degree panoramic video shot to capture the overall scene of each of the dive locations. Video footage will be used to characterize the benthic community and make qualitative comparisons with past video footage. It will also be used for general sanctuary products, including education and outreach materials. Biological specimens collected at each of the sites included a variety of invertebrates as well as algae (Figure 4). Samples are being identified and cataloged at California Academy of Sciences.
For each of the dives, divers filled out a series of debrief questions regarding their dive experience and their overall impressions of the natural history of the Bank. These responses will be compiled along with follow-up information from the divers to complete the additional project objective of testing the feasibility of using technical divers for accomplishing science missions on Cordell Bank. The general impression from the technical divers was that SCUBA is a feasible tool for accomplishing some science missions on Cordell Bank.
Overall, the most striking observation from the series of dives on the shallower sections of Cordell Bank was the overall abundance of juvenile rockfish (Figure 5). Often it was difficult for the divers to obtain a clear shot of the bottom for the photo quadrat images due to the abundance of fish in the field of view. Divers were amazed by the pristine condition and overall abundance, diversity, and color palette of life on and near the seafloor of Cordell Bank. Minimal evidence of human impact was observed on the dives to the upper reef crest. The only evidence of derelict fishing gear was one lead fishing weight. Another item of interest included a potentially human-created hole with a metal pipe in its center at the Northern East Ridges site. These holes were originally noted and described by Cordell Expeditions. The pipe was left in the hole 30 years ago by Cordell Expedition divers.
High definition video was collected both sub-surface and topside for creating a thirty minute film piece documenting the history of SCUBA exploration of Cordell Bank, the amazing Bank community, as well as the results of the current mission. A three minute film has been produced that provides a concept piece for a longer film.
Bob van Syoc - California Academy of Sciences
Dana Carrison - California Academy of Sciences
Greg McFall - Gray’s Reef National Marine Sanctuary
Doug Kesling - Cooperative Institute for Ocean Exploration,
Research and Technology
Dale Roberts - Cordell Bank National Marine Sanctuary
Kaitlin Graiff - Cordell Bank National Marine Sanctuary
- Non-indigenous species
- Trophic association
- Habitat association
Study MethodsSix technical dives were completed in rigorous conditions on Cordell Bank with the dive teams successfully accomplishing all of the science and outreach objectives.
Dives were completed on Cordell Bank using a team of six technical divers and four safety support divers. Each dive included two science divers and one safety diver on the bottom, as well as two mid-water science support divers who assisted in gear transfer during decompression drifts. Technical divers breathed a trimix of gases during their time on the bottom, and switched to nitrox and oxygen during decompression stages.
Dives were conducted at five sites – one site (Northern East Ridges) was surveyed on two dives conducted by two dive teams, while all other sites were only surveyed with one dive conducted by a single dive team. Three of the dive locations (Northern East Ridges, Craine’s Point, Northern West Ridge) represented historic Cordell Expedition dive locations (1980s), while two of the dive locations (Middle Ridge, South Central Plateau) represented locations where Delta submersible dives have taken place (2002-2005). Depths of the dive sites ranged from 123-193 feet. Bottom time ranged between 20 and 30 minutes, while total dive time (including decompression drift) ranged between 56 and 73 minutes. Bottom currents were estimated at 0.5 to 2 knots and visibility ranged from 30 to over 100 feet at the different dive sites.
Dive sites were located and marked using a combination of waypoints, assessment of benthic habitat layers in real-time (using GNAV software with a GPS feed of the vessel’s position), and assessment of fathometer readings. A grappling anchor with a line and surface float were deployed on the up-current and deeper side of the desired waypoint. As a result, the divers were able to follow the line down and reach the shallow targeted waypoint. Overall, the divers felt that it was fairly easy to land on the targeted location using this method. Upon reaching the bottom, divers carried out their respective tasks, which included video and still image documentation and biological specimen collection. In general, the dives included ten minutes of photo quadrat image collection, ten minutes of biological specimen collection, and ten minutes of general documentation of the habitats and communities.
The benthic community and habitat were sampled by taking digital photographs of a 0.25m x 0.25m PVC quadrat frame that was haphazardly placed on the substrate. Photo quadrat images were taken approximately 2-3 m apart. Between zero and eleven photo quadrats were photographed at each site. Macro photos were taken on the second dive of October 9th at South Central Plateau in lieu of quadrat photos. Photo quadrat images will be analyzed to assess presence of species/taxa and to determine invertebrate species composition.
Video footage was acquired throughout the dives and fulfilled the objectives of assessing the reef top community and habitats as well as documenting technical divers carrying out tasks on the Bank. In addition, divers collected one 360 degree panoramic video shot to capture the overall scene of each of the dive locations. Video footage will be used to characterize the benthic community and make qualitative comparisons with past video footage. It will also be used for general sanctuary products, including education and outreach materials.
Biological specimens collected at each of the sites included a variety of invertebrates as well as algae. Divers were instructed to collect representative invertebrates and algae that they encountered. Collection methods included hand, trowel, and knife techniques. Originally there was an attempt to photograph samples in situ alongside a numbered bag for reference. This became too cumbersome and time-intensive, and still photos of the specimens in situ were no longer taken. Instead, a video image was taken by the second diver while the first diver worked on the specimen collection. Originally, the divers were instructed to place individual specimens in separate bags, and this was carried out on October 7th dives. This method also proved to be too cumbersome and time-intensive, and the method was revised to scoop up clumps of organisms and place the whole lot in a collection bag together. Sponges were still kept in separate bags to prevent co-mingling of spicules that would make identification difficult. Photos were taken of the biological samples during the processing steps before they were preserved in the field. Samples will be identified and catalogued at California Academy of Sciences. One sediment sample was collected at the Craine’s Point site and was sent to Mary McGann (USGS) for analysis of past benthic communities.
Figures and Images
Figure 1. Map of SCUBA dive locations. All sites were sampled except for South Central Plateau.
Figure 3. Diver collecting video imagery on Cordell Bank. Photo credit: Joe Hoyt/NOAA.
Figure 4. Diver collecting invertebrate specimens on Cordell Bank. Photo credit: Joe Hoyt/NOAA.