MBARI - Davidson Expedition 2006

Exploring Ancient Coral Gardens

Davidson Expedition January 26-February 4, 2006

This expedition has been made possible by grants from NOAA Office of Exploration, the BBC, and MBARI.

The news release for this expedition is available on: http://www.mbari.org/news/news_releases/2006/davidson.html.

(Skip to history and background information)

Davidson Expedition

Jim Barry

Western Flyer

Tiburon

Purpose:

Why study deep-sea corals?

Recent advances in technology enable us to explore deep in the ocean and study corals. There are relatively few studies on deep-sea corals, but initial findings indicate that a diverse group of these corals exist, and that some are hundreds of years old. The corals also seem to provide essential habitat for other groups of smaller species that live among them. Increasing the sense of urgency in studying deep-sea corals is their fragility, and the extensive human impacts to them from fisheries where nets are trawled along the seafloor. These nets effectively catch bottom fishes, but also bring up 'non-target' or 'bycatch' species such as corals. The taxonomy of deep-sea corals, essentially their names and how they are related, is still challenging because of the relatively few scientific collections and high quality images. While we are beginning to see patterns of where they are found in the deep sea, such as on rocky ridges, we are not yet sure why they grow best in these locations. So, with deep-sea corals, we have a situation where lots of basic, exciting science questions have yet to be answered to help address conservation needs of these spectacular organisms.

Plan:

Cruise History and Background:

Biology -

Diversity of Animal Life on Seamounts (from NOAA OE Davidson 2002 expedition)

Edward W. Seidel
Director, Marine Resources Aquarium Booth Bay, Maine
After observing deep-sea areas on and around seamounts for even a short time, one notices a stark pattern of where to find animals. Flat areas are a virtual desert with very little animal life, but as soon as there is some vertical relief, an oasis of animals explodes into view. Even something as small as a volleyball-sized rock is enough to become a haven for animal life.

This phenomena occurs for two basic reasons: Seamounts provide structure for animals to live on, and the structure creates oceanographic effects that promote the production of food. Many of these deep-sea animals, such as gorgonians, mushroom corals, and sponges, spend their entire lives permanently attached to rocks, and therefore depend on ocean currents to bring their food to them. A seamount, rising up out of the sea floor, has strong currents that frequently run over it, providing the animals living along its flanks with a constant supply of planktonic food.

Even small rocks become a haven for animal life. (Image courtesy MBARI)

These same currents also produce localized upwelling of water around the seamount. Nutrients like nitrates and phosphates, which are critical to the growth of phytoplankton, are lifted from the deep to the sunlit surface waters. These nutrients fuel an explosion of planktonic plant and animal growth, and attract larger animals such as whales, sharks, tunas, and seabirds to a veritable feast.

Seamounts are "hot spots" of biodiversity. Think of a seamount as an underwater island. Ocean currents carry larvae, like shipwrecked mariners, from various geographically distant areas. Seamounts provide a place for these lost larvae to settle and grow, so you find animals living side by side that normally are not found together.

This graph shows that nutrients increase in deeper waters. Currents around the seamount create upwellings that lift nutrients to the surface. (Image courtesy MBARI)

Davidson Seamount is geologically young but has remarkable biological communities, including large, dense patches of sponges and apparently extremely old coral forests, with individuals commonly reaching more than 3 m in height. Rare species, such as the black-footed albatross and the federally listed endangered sperm whales, have been sighted at the seamount. Two commercial fisheries currently operate in the waters above Davidson Seamount—drift gill netting for swordfish and sharks and trolling for albacore tuna. It is not known how or if these fisheries impact other species at the seamount. Its proximity to numerous fishing ports and the developing technologies in deep-water fishing make Davidson extremely vulnerable to increased fishing pressure.

Geology -

Geology of Davidson Seamount
David Clague, Senior Scientist
Monterey Bay Aquarium Research Institute

Davidson Seamount is one of a group of submarine volcanoes off the continental margin offshore central California between Lat 37.5° to Lat 34.0°. Davidson, along with Guide, Pioneer, Gumdrop, and Rodriguez, are morphologically unlike typical ocean island volcanoes.

All of the seamounts in the group are complex NE-SW trending structures, consisting of parallel ridges separated by sediment-filled troughs. The ridges are constructed parallel to the fossil spreading centers abandoned when the San Andreas fault system formed. On each of these seamounts, a series of knobs are aligned along the ridges; however, craters like those commonly topping oceanic volcanoes are lacking. The lack of collapse craters suggests that the lavas that built the seamounts were never stored in chambers within the volcanoes, as is so common at other oceanic volcanoes.

The surfaces of the seamounts are built mainly of blocky lava flows, although some pillow lava has been seen on the their deeper flanks. Near the summit, layered deposits of volcanic ash and pyroclastic materials are found. These volcaniclastic rocks indicate mildly explosive eruptions of gas-rich lava near the summit of the volcano.

Ar-Ar laser fusion ages of mineral separates indicate that Davidson formed about 9 to 15 million years ago, so it formed 5 to 12 million years after the underlying ocean crust.

The volcanic rocks found on Davidson Seamount are predominantly differentiated alkalic basalt, hawaiite, mugearite, and trachyte. These evolved lavas are highly viscous (thick and pasty) and form short, thick flows and steep-sided knobby structures at the vents. The high viscosity of these lavas also likely inhibited the loss of gas bubbles, thereby making the eruptions more explosive. The lavas traveled to the surface carrying up rare xenoliths (foreign rocks) of mantle materials as well as a range of coarsely crystallized fragments of lava slowly solidified at depth.

Reference

http://www.mbari.org/volcanism/Seamounts/Seam-ContlMarg.htm