Davidson Seamount: 2006 Expedition to Ancient Coral Gardens
- Andrew DeVogelaere
Monterey Bay National Marine Sanctuary
- Jim Barry
Monterey Bay Aquarium Research Institute
- Allan Andrews
Moss Landing Marine Laboratories, California State University
- Office of Ocean Exploration
- British Broadcasting Corporation
- Monterey Bay Aquarium Research Institute
- Save The Earth
End Date: February 04, 2006
Building off the successes of an Office of Ocean Exploration (OE) expedition to Davidson Seamount in 2002, this project focused on deep-water corals. The week-long expedition in 2002 was the initial effort to characterize the biology and geology of the Davidson Seamount, 1,250 – 3,700 meters deep off Central California. Many results and products from this cruise are relevant to OE, including ocean science issues, education, outreach, and resource management. The focus of the 2006 cruise was to expand on the exploratory results of our last seamount expedition to investigate processes that generate coral distribution patterns. We used a simple model derived from results of the last cruise to test our understanding of coral distribution, and used this model to guide exploration in other regions of the Seamount (still over 99.98% unexplored). Specific regions of the seamount were targeted based on a topographic index, substratum type, and coral species depth records. Complementary studies of the biodiversity and population dynamics of seamount fauna included collections of corals for taxonomic studies, and age and growth studies of corals using innovative radiometric techniques. Addressing the public interest in seamounts, corals, and exploration, the British Broadcasting Corporation (BBC) recorded imagery from Davidson Seamount to feature in a 2006 television series, co-produced with the Discovery Channel, for broadcast in the United States and internationally. The Sanctuary West Coast Visitor Center and Monterey Bay Aquarium have plans to feature seamounts and corals in future exhibits, and high definition video imagery, as well as research findings will be pivotal in the exhibit development.
Summary to DateWhen we set out to Davidson Seamount on January 26, we had the following goals: to understand why deep-sea corals live where they do, to determine age and growth patterns of these corals, to improve species identifications from Davidson Seamount, and to share the exploration cruise with the general public. While we have yet to complete full analyses, the at-sea portion of the cruise was clearly successful.
During this 10 day research cruise, we made 70 hours of observations on the Davidson Seamount and collected 102 deep sea animal and rock specimens (some species likely new to science). The BBC was able to obtain spectacular high definition video of seamount life that they were not able to find during two previous expeditions. The two cruise web sites were updated regularly with contributions from the entire science crew. While more analyses are necessary for our science findings, we have increased knowledge on the patchiness and role of sediments and currents on deep-sea corals.
With science, it is usually a process where you develop more questions every time you learn something. We left some markers on Davidson Seamount to help us make photographic measurements over future years and determine growth rates of the giant corals. We also have a series of new hypotheses on how far corals can disperse from their parents; how coral environment chemistry changes with depth; how other species interact with corals; and the role of microtopography. Later in 2006, MBARI scientists will return to Davidson Seamount, using autonomous underwater vehicles (http://www.mbari.org/auv/), for high-resolution seafloor mapping and midwater current studies.
In terms of resource protection, we all left in awe of the spectacular nature and fragility of deep-sea corals. Upon return, we will map the location of all deep-sea corals found in and around the Monterey Bay National Marine Sanctuary, and use our new knowledge to develop a map of potential coral habitats where we have not visited yet. Managers will be able to use this information to focus activities such as cable laying in areas where corals are not expected. Marine reserves, including no-take areas, are currently being selected in central California, and these coral maps will also help inform where critical protection areas are. Now we look forward to a sharing video highlights; public presentations; complete scientific analyses; publications in science and education journals; incorporation of data into resource management documents; and the BBC series Planet Earth. This project was funded by NOAA’s Office of Ocean Exploration, the British Broadcasting Corporation, and the Monterey Bay Aquarium Research Institute.
- Age & Growth
- Habitat association
- Geological characterization
Study MethodsDavidson Seamount is located 120 kilometers to the southwest of Monterey, due west of San Simeon (35° 43’ 23”N, 122° 43’ 23”W), and is one of the largest known seamounts along the Western United States. It is 42 kilometers long and 13.5 kilometers wide. From base to crest, Davidson Seamount is 2,400 meters tall; yet, it is still 1,250 meters below the sea surface. Davidson Seamount has an atypical seamount shape, having northeast-trending ridges created by a type of volcanism only recently described (Davis et al. 2002); it last erupted about 9.5 million years ago (unpublished age data from R.A. Duncan, 2003). This large geographic feature was the first to be characterized as a “seamount” (Davidson Seamount 1990).
OPTIMUM ENVIRONMENTS FOR DEEP-WATER CORALS
One product of our 2002 expedition to the Davidson Seamount was a topographic characterization of the Davidson Seamount using a Topographic Position Index (TPI). TPI is a quantification of how deep a given location is, relative to its surrounding area. This index compares the depth of each cell to the mean depth of neighborhood cells, with resulting negative values indicating valleys and positive values indicating crests, while flat plains and gentle slopes are indicated by values around zero. Our cell size to calculate the index was 45 x 45 m, and the neighborhood cells made up an area of the surrounding 1.26 km2 (area of the surrounding 25 x 25 cells). In our graphic representation of the seamount, we assigned a TPI range to represent valleys (- 130 to - 29), slopes and flat areas (- 30 to 49), and crests (50 to 196) (DeVogelaere et al. 2005). Based on the distribution of coral relative to the TPI categories, a simple predictive model allows for testing assumptions about coral distribution relative to habitat. Hence, hypotheses about optimal coral habitat can be addressed.
To test optimal habitat for corals on Davidson Seamount, we will use the existing TPI map and known coral depth distributions, to sample ridge versus slope areas in paired comparisons. At the paired sites, we will identify corals (see below) and quantify their abundance. In addition, we will measure currents and food availability (particulates as a proxy) in areas where we observe differing sizes and morphologies of similar coral taxa. Current in the region and directly around individual coral colonies will be measured from moorings and from ROV-based current meters. We will deploy moorings containing acoustic doppler current profilers (ADCP – RDI Sentinel), backscatter and fluorometer sensors (Hobi-Labs Hydroscat II) on small moorings at 2 – 3 locations (peak and valley) at the beginning of the cruise, and recover them 6 days later. These local scale measurements of flow will be supplemented with fine scale flow measurements using an acoustic doppler velocimeter (ADV) mounted on the robotic arm of the ROV Tiburon. This system (Nortek ADV) is capable of measuring three axes of flow within 1 cm3, and will allow measurements of flow around several individual corals at several sites during 6 ROV dives. We will position the ROV to the side of the coral under study, minimizing its effect on the flow field. Food availability will be estimated using combined backscatter / fluorometer sensors (Hobilabs Hydroscat 2). Backscatter estimates particle densities in the water column, and the fluorometer estimates the chlorophyll concentration. We will use a combination of these as a proxy for the suspended food concentration for coral feeding. Sensors will be mounted with ADCPs on the benthic moorings, and will also be used in combination with the ADV on the ROV dives.
Comparisons of the relationship of the flow field (current speeds) and food availability (particle density and flux past corals) among coral species and between locations will test the hypothesis that species distributions, and possibly their growth rates obtained from age / growth studies, are linked strongly to current speeds or rates of particle flux or both. Near bottom currents have been shown to be important determinants of benthic community structure in several marine systems (Barry and Dayton 1991), from the bathymetrically complex Antarctic continental shelf (Barry and Dayton 1988, Barry et al. 2003, to seamounts (Genin, 1986). Detailed measurements of particle fluxes and feeding rates have been used successfully for some benthic filter feeders (e.g., Holland et al. 1987).
A related project proposed by D.A. Clague to use an autonomous underwater vehicle to create higher resolution mapping may be funded by MBARI. If this mapping is complete we will use a cell size of 3 - 5 meters for the TPI, and use the increased resolution (and rock type information) to locate our study sites.
AGE AND GROWTH
This study will continue an investigation of bamboo coral age and growth on the Davidson Seamount. This project began as a preliminary study that yielded very promising results for accurately determining the age of bamboo coral (Andrews et al. 2005). By applying a more thorough sampling design to newly collected coral, based on the findings in the preliminary study and a current study on bamboo coral from New Zealand (Andrews unpublished data), the age and growth can be described with much greater certainty. The proposed approach is to collect two full colonies that are the same size, but from different locations, to determine if differences in growth rates exist for bamboo coral. The locations will be selected based on environmental differences perceived as favorable and unfavorable to feeding and growth (e.g., current strength and particulate density differences; see above). To determine age and growth characteristics of each colony, two sampling designs will be applied to investigate linear and radial growth. Comparison of these rates within each colony will address the possibility of nonlinear growth with increasing colony size or age (Roark et al. 2003). Linear samples will be taken in a series of axial core extractions along the length of the skeletons (tip to base) and radial samples will be taken from the thickest part of the skeletons, near the base of the colony, from the edge to the center. All samples will be analyzed using lead-210 dating to determine age and growth.
Investigation of linear growth will entail cross sectioning at six locations along the axial skeleton from the base of each colony to the tip. Sections will be investigated for growth zones that can be quantified. Adjacent to these sections, small core samples will be extracted using a micromilling machine for use in lead-210 dating. Investigation of radial growth will entail the extraction of circular channels that follow growth zone banding patterns. The circular extractions will be taken from the edge to the center with the micromilling machine and used for lead-210 dating.
In addition to the quantitative radiometric approach stated above, an assortment of colony tip segments (where linear growth occurs) with a standard length (i.e., 30 cm lengths) will be collected from different sites where bamboo coral are present. These tip segments will be taken from colonies of different sizes and in areas where environmental conditions may be favorable or unfavorable to growth (as stated above). It is hypothesized that morphological comparisons of length to diameter, in concert with the examination of cross sections for environmental check marks in the growth zone patterns, can be used to investigate growth variability with respect to colony size, within the site, and between sites.
Lead-210 dating is a radiometric technique that uses the decay of exogenous (unsupported) lead-210 over the length or across the radius of the skeletal structure to determine age. Use of this technique will determine a growth rate, as was the case with red tree coral (Primnoa resedaeformis; Andrews et al. 2002) and bamboo (Keratoisis sp.) and precious (Corallium sp.) corals from Davidson Seamount (Andrews et al. 2005). It is a technique that has been successfully applied in other studies of deep-sea corals as well (i.e. Corallium noibe (Druffel 1990), Keratoisis sp. from off Australia (Ron Thresher, CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania 7001 Australia, personal communication)). This process involves the measurement of lead-210 via alpha-spectrometry and radium-226 via thermal ionization mass spectrometry (TIMS). Extracted samples (4 x 6 = 24), covering a span of about 150 years (ideal for tracking the decay of lead-210) will be analyzed for lead-210 and radium-226 using well established protocols (Andrews et al. 1999 and 2002). In the preliminary study, few samples were used to get a rough idea of age and whether the technique would work. For this study, an accurate determination of age and growth will require six samples for each sampling series (linear and radial on each of two full colonies) resulting in a total of 24 lead-210 assays.
Approximately 30 colony tip segments (where linear growth occurs) with a standard length (i.e., 30 cm lengths) will be collected from different sites where bamboo coral are present. These tip segments will be measured in length and diameter. Segments will also be cross sectioned in at least one location (at a set distance from the tip) and examined for growth zone patterns. Patterns visible in sections will be compared among all samples for possibility of using them as a time specific marker, allowing for comparisons of growth variability with respect to colony size, within the site, and between sites.
In 2002, we observed 20 coral taxa at the Davidson Seamount. We have images for all taxa, tissue samples for 12 taxa, and identifications for four. In 2006, we will focus on collecting additional images and associated tissue samples for taxonomic identifications. To understand genetic diversity within a seamount, conspecific coral tissue samples will be compared among ridge areas. Three taxonomists and a geneticist have expressed interest to identify collected coral samples, including Peter Etnoyer (octocorals, Natural History Museum of L.A. County); Amy Baco-Taylor (octocorals, Woods Hole Oceanographic Institute); Dennis Opresko (black corals, Oak Ridge National Laboratory); and Stephen Cairns (stony corals, National Museum of Natural History, Smithsonian Institution).
Public outreach is a primary purpose for the Monterey Bay Aquarium, the Monterey Bay National Marine Sanctuary, and the British Broadcasting Corporation. Each organization has staff developing public education material of seamounts and corals. These include a television special on seamounts, exhibits for two new Sanctuary visitor centers, and a potential exhibit for the Monterey Bay Aquarium. Staff from these three organizations will be at sea to gather high definition video and research information to support their products. In addition, the Sanctuary is currently responding to public and Advisory Council requests to include the Davidson Seamount into the Monterey Bay National Marine Sanctuary. Information on species distributions and ecological processes gathered from this proposed expedition will be shared through a management plan update process that includes web sites, public presentations, and environmental impact assessment documents.
Figures and Images
Current meter near the top of Davidson Seamount to measure water movement adjacent to a large bubble gum coral (Paragorgia arborea; Credit: NOAA/MBARI).
Acoustic Doppler Current Profiler (ADCP) moored on Davidson Seamount to measure current speed at various distances above the seamount through time (Credit: NOAA/MBARI).
Current speed at different distances above Davidson Seamount through time.
- Investigations of bamboo coral age and growth from Davidson Seamount A technical report to the Monterey Bay National Marine Sanctuary. September 2007