AgE OF BLACk CORAL (AntipAtheS dendrochriStoS) COLONIES, wITh NOTES ON ASSOCIATEd INvERTEBRATE SPECIES

In 2005, a dead 2.1-m high colony of the Christmas tree black coral, Antipathes dendrochristos Opresko, 2005, was collected from 106 m of water off southern California. Based on growth increment counts, a radiocarbon (14C) analysis, and an indirect corroboration by lead-210 dating from a second, live colony, the colony was about 140 yrs old when it died. The dead skeleton was heavily colonized by invertebrates with 2554 individuals living on the colony. Corophioid amphipods, sea anemones, brittle stars, and crinoids dominated this assemblage. Thus, along with living colonies, it is arguable that the destruction of dead antipatharian colonies may have as yet unknown effects on a range of deep-water organisms. Antipatharians (black corals) are found in all oceans, with the greatest number of species living in the subtropics and tropics. worldwide, there are about 250 species in six families. Although a few species occur in shallow waters, most live at depths of 20 m and deeper, and the deepest record is > 8000 m. Black corals develop a variety of growth forms, including arborescent, fan-shaped, unbranched, and symmetrically branched (Opresko, 2001, 2002, 2003b, 2004; d. Opresko, Oak Ridge National Laboratory, pers. comm.; Species 2000). Most of these corals live on hard substrata, such as rock ridges and walls, boulders, and cobble (grigg, 1965; Miller, 1998; Tissot et al., 2006). As with most other groups of deep-water corals, the role that black corals play in benthic ecology, and particularly their role as habitat for other species, is poorly understood (Buhl-Mortensen and Mortensen, 2004; Boland and Parrish, 2005). The Christmas tree coral, Antipathes dendrochristos Opresko, 2005 (Fig. 1A), lives in southern California waters in depths of about 90 m to at least 360 m. This irregularly arborescent species grows to about 2.5 m tall and predominantly inhabits low-relief mixed rock areas, primarily on offshore banks (Opresko, 2005; Yoklavich and Love, 2005; Tissot et al., 2006). Little else is known of the biology of this organism. From direct observations using a small manned submersible, about 15% of live colonies have invertebrates, including galatheid crabs, brittle stars, barnacles, and polychaetes, living among the polyps. A small percentage (1%–2%) of the colonies are either entirely dead or have dead branches (Tissot et al., 2006), and large numbers of sessile animals, including crinoids, basket stars, anemones, and brittle stars, live on these dead branches and trunks (Yoklavich and Love, 2005). In 2005, we collected a large dead colony and (1) estimated how long it had lived, (2) estimated its growth rate, and (3) characterized what organisms currently were living on it. In addition, we collected a second, live, colony and estimated its growth rate and age. BULLETIN OF MARINE SCIENCE, vOL. 80, NO. 2, 2007 392 Figure 1. (A) Living Antipathes dendrochristos colony, Santa Cruz Island, southern California Bight. (B) The upper trunk and branches of the dead Antipathes dendrochristos colony with its typical invertebrate assemblage. LOvE ET AL.: AgE OF BLACk CORAL COLONIES 393 Materials and Methods A dead colony of A. dendrochristos, measuring 2.1 m tall × 0.9 m wide × 1.0 m deep with a base of 4.5 cm in diameter, was collected on 13 October 2005 in 106 m of water near the shallowest part of the “Footprint,” a rocky feature located seaward of the Santa Cruz–Anacapa Island Passage, southern California (Fig. 2). The colony (located at 33°57.906́ N, 119°29.434 ́w) was in a field of small boulders, most of which were 0.25–0.75 m in diameter. This was the only A. dendrochristos colony (living or dead) that we observed in this area, although living colonies of this species are common in deeper water on the Footprint. Using the collecting arm of the research submersible delta, the colony was pulled free of an underlying boulder at its base and carried to the surface. On the support ship’s deck, the colony was placed on a white sheet to allow for detection of those organisms that fell off as the colony warmed and began to dry. The colony was cut into pieces and frozen in plastic bags, along with all associated organisms. Near this location, a living colony was also collected that provided an opportunity to estimate age from a smaller living colony. Age Estimation.—Age estimation was made from cross sections taken near the base of each colony (both dead and living). For the dead colony, two cross-sections (1 mm thick) of the colony’s trunk were cut about 2 cm up from the base of the colony. Cross sections were not taken at the lowermost part of the colony because the base splayed outward and downward over the rock. growth increment age estimations were made (by B.A.B.) from cross sections of black coral mounted on glass slides. These sections were polished with increasingly fine lapping film, up to a maximum of 15-μm grit, until viewing was optimal. Both transmitted and reflected light were used to examine the sections under a Leica MZ95 dissecting microscope at 50–75× magnification. Ultimately, reflected light provided the greatest resolution of the banding patterns. Age initially was estimated in two ways with the smaller living coral section from: (1) counts of very fine, subordinate growth increments, and (2) counts of much more dominant, yet less frequent, growth increments. The difference between these age estimates was the basis for applying the lead-210 (210Pb) dating technique (30 vs 300 yrs). To estimate growth rates, measurements were made along four radial paths from the center to the outside edge of the cross-section in both the dead and living specimens. Care was taken to ensure that each radial path was clear of irregularities, such as branching scars, that may distort growth estimates. growth rate was estimated using the range of measured diameter or radius vs estimated age. Figure 2. Location of the Footprint, a rocky area located just seaward of the Santa Cruz-Anacapa Island Passage, southern California, and site of the collection of a dead Antipathes dendrochristos colony. BULLETIN OF MARINE SCIENCE, vOL. 80, NO. 2, 2007 394 Age Corroboration.—we corroborated the growth increment age using 210Pb and 14C dating. Core material from the living colony was analyzed for 210Pb and 226Ra at Moss Landing Marine Laboratories (MLML). From a portion of the colony, 25 mm in length (along the axis) core material was extracted from a series of cross-sections using a New wave® micro-milling machine. The 25 mm length of coral was sectioned into 15 pieces to allow for (1) locating the center of the skeleton throughout the length of the portion, and (2) control over use of the drill bit to extract precisely the center of the skeleton. with this instrument, core samples were accurately removed with a Brasseler® 1400 μm bit. The approach using a single core sample in determining the more plausible age estimate (30 vs 300 yrs) was related to two possible scenarios for exogenous levels of 210Pb. For a sample that was extracted from the center of a 300-yr-old coral, the ratio of 210Pb to 226Ra should be in secular equilibrium for levels that are typical of the marine environment. hence, extraction of a core sample with a diameter of 1.4 mm would have removed the first 56–70 yrs of growth (calculated based on the variation of diameter and the age estimate) and would have been deeply buried in over 200 yrs of growth; secular equilibrium is achieved at about 120 yrs (within about 98% of equilibrium). For a sample extracted from the center of a 30-yr-old coral, secular equilibrium would not have been attained, given typical exogenous levels of 210Pb were present at the time of growth. hence, extraction of a core sample with a diameter of 1.4 mm would have removed the first 6–7 yrs of growth (calculated as stated above) and would have been buried in only 24 –25 yrs of growth; formation of this material would have occurred too recently to be in equilibrium. Measurement of 210Pb and 226Ra from the sample was performed using well-established techniques at MLML, the details of which are described in Andrews et al. (2002). One cross section of the dead coral was analyzed for radiocarbon (14C) at keck Carbon Cycle Accelerated Mass Spectrometry (kCCAMS) Facility at the University of California, Irvine. The surface of the cross section was scraped off with a scalpel and discarded. The cleaned surface of both the axial center and the cross section edge was drilled using a diamond dental burr to extract about 10 mg of material. An organic 14C-free sample (for background correction) and a wood standard were also processed. Carbonates were removed with a 1N hCl treatment for 30 min. Samples were rinsed twice with MilliQ water and dried on a heating block at 80 °C. Sample CO2 was produced by combustion at 900 °C in evacuated, sealed quartz tubes in the presence of CuO and silver wire, which was reduced to graphite, as described in Santos et al. (2004), in preparation for AMS analysis. Associated Organisms.—In the laboratory, each frozen piece of the colony was thawed in cold water and stripped of associated organisms. The wash water was passed through a 63-μm sieve and the trapped material collected and preserved in formalin. After about 2 wks, this material was rinsed in fresh water, transferred to 50% ethanol, examined under a dissecting microscope, and sorted into taxonomic groups.