METHANE SEEPS UNDER HYPOXIA: NOVEL ECOSYSTEMS WITHIN EASTERN PACIFIC OXYGEN MINIMUM ZONES

Lisa Levin (SIO)

Link to NOAA Strategic Plan: NOAA's Mission Goal 1: Protect, Restore, and Manage the Use of Coastal and Ocean Resources through Ecosystem-based Management

RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEM

Unusual and novel ecosystems in the deep sea are often found where environmental stressors combine to create unique conditions. This project is intended to explore the benthic communities that develop where methane seepage and attendant high sulfide concentrations intersect with the natural hypoxia associated with global oxygen minimum zones (OMZs). Our initial targets were seeps in the Gulf of California and off Peru. However, the Peruvian studies could not be attempted due to logistical problems, and these have been replaced with studies of methane seep and OMZ sediments in the Pacific Northwest (CA and OR July/Oct. 2006), off Chile (Sept. 2006) and off New Zealand (Nov. 2006 / Feb. 2007). Research was conducted by utilizing US, Mexican, Chilean and New Zealand research vessels with a combination of ship-based sonar, bottom photography, multicoring, trawling, dredging and a submersible (off CA and OR). Our objectives are to (a) locate and survey novel seep ecosystems, establishing their geologic and hydrographic setting, (b) document the distribution of reducing communities in relation to geological surroundings, (c) quantify the abundance, composition, trophic structure and composition of seep assemblages and compare them to nearby oxygen minimum zone communities.

This research will advance understanding of biotic response to hyper-stressed conditions (sulfide toxicity and hypoxia), expand known biogeography of reducing ecosystems, and yield insight into evolution within ultra-extreme environments. For our group these studies will broaden our understanding of seeps as unusual environments, expand our views of marine biodiversity and contribute much needed biogeographic data for Pacific deep-sea ecosystems. Major foreign partners are Elva Escobar, Universidad Nacional Autonoma de Mexico (UNAM, Mexico), Javier Sellanes (Univ. Catolica del Norte, Chile) and Ashley Rowdan (NIWA, New Zealand). Major U.S. partners are Wiebke Ziebis (University of Southern California), Amy Baco (Marine Biological Laboratory, Craig Smith (U. Hawaii).

RESEARCH ACCOMPLISHMENTS

During this year NOAA funds from Ocean Exploration supported our participation in 3 exploration programs (1) a comparison of oxygen minimum zone (OMZ) and methane seep infauna on the Oregon and California margins: R/V Atlantis; July 2006, October 2006; (2) a comparison of oxygen minimum and methane seep faunas on the Chile margin: R/V Vidal Gormaz 30 August – 4 September 2006; (3) exploration of seep sites on the New Zealand margin: R/V Tangaroa November 2006; R/V Sonne February 2007. Sampling and analysis focused on determining benthic abundance, community composition, diversity, and food web structure. In addition faunal and sediment samples were analyzed from a previous study of the Mexico margin OMZ (R/V El Puma May 2006). All of these were collaborative efforts with numerous other scientists from multiple U.S. and international institutions. While most analyses are in progress, some of the preliminary highlights include:

• Pacific Northwest margin: Overlap between macroinfaunal species of seep sediments (Eel River – 525 m; Hydrate Ridge – 775 m) and nearby non-seep sediments at comparable depths within the E. Pacific OMZ suggests strong interactions between seep and OMZ margin ecosystems.

• Chile Margin: Concepcion seep communities revealed 108 species – nearly 5 times the number collected at nearby non-seep sites. Eight symbiont-bearing bivalve species with one commensal polychaete, and one tubeworm species were found – all new to science. Many taxa, particularly the crustaceans, appear to dwell on and off seep, providing vectors for exchange of energy between systems. Fish aggregate at seep sites and are a focus of fishing activities.

• New Zealand Margin: Discovery of 11 new seep sites with living seep fauna between 700 and 1200 m on the eastern margin of North Island reveals a New Zealand slope extensively influenced by methane seepage, but communities potentially adversely impacted by heavy trawling activities. New Zealand seep ecosystems consist of a montage of tubeworm, clam, mussel, sponge and coral aggregations intermixed with carbonate and sediment-associated communities. Many of the species collected appear to be new to science. Stable isotopic analyses of seep fauna reveal a key role for methane in the animal C pool, particularly for pogonophorans, ampharetid polychaetes and sponges and their invertebrate associates.

• Mexico margin: Single multicore drops along a transect off Mazatlan off stations from 500-1000 m reveal (a) exceptionally high organic matter content (10% Corg, 40 microgram/g Chlor a), (2) strong zonation of fauna across the oxygen minimum zone, with meiofauna (mainly nematodes) abundance maxima within the OMZ core at 500 m and macrofaunal abundance maxima at 800 m. Nematodes from 800 m depth exhibit C isotopic signatures indicative of chemosynthetic food sources.

Fig. 1 Methane seep fauna and carbonates on the Hikurangi margin, New Zealand. Photo Credits: NOAA/NIWA.