Ask an Explorer

Questions were sent to the science party during the Davidson Seamount: Exploring Ancient Coral Gardens expedition. Selected questions and answers are offered below.


Questions from: Augustine Kelly

Answers from: Andrew DeVogelaere, Huff McGonigal, Jim Barry, Chad King, and Lisa Borok

• Q: Are there tuna on the Davidson Seamount? Are they year round inhabitants or seasonal visitors? How big are they?

• A: On this expedition, we haven't been studying the upper ocean where albacore tuna live (in the top 50 m of water). Albacore follow warmer temperatures along California in the fall and travel long distances around the Pacific seasonally. Albacore tuna are a popular recreational and commercial fishery along the West Coast, including the nearby ports of Morro Bay and Monterey Bay.

• Q: Are there swordfish on the Davidson Seamount? Year round or seasonal? How big are they?

• A: A swordfish fishery operates in all the surface and offshore waters off California, including the Davidson Seamount region. To learn about their size and seasons, we have a review of fisheries in the Monterey Bay National Marine Sanctuary that can be downloaded.You can also look up fishery information at the Pacific Fishery Management Council Web site.

• Q: Are there rockfish on the Davidson Seamount? Year round or seasonal? How big are they?

• A: We have not seen any rockfishes on the Davidson Seamount on this expedition, but we saw one thornyhead rockfish on our last NOAA/Monterey Bay Aquarium Research Institute expedition, in 2002. Our scientists could think of only two species in central California that can reach the depths of 1,500 m (4,920 ft). The shallowest peak on the Davidson Seamount is 1,290 m (4,192 ft), so rockfishes would be found only near the top — the bottom of the seamount is more than 3,300 m (10,820 ft) down.

• Q: Are there hot gas vents on the Davidson Seamount or on any nearby seamounts?

• A: There are no hot vents off the California coast. The Davidson Seamount last erupted about 10 million years ago, so it's not currently an active volcano. We have, however, seen lots of evidence of volcanic action from the past. We saw lava tubes in the "Big Valley" area, and there are lava boulders, called pillow basalts, everywhere. In Monterey Bay, there are cold-water seeps that are caused by fluids beneath the seabed leaking out at places like scarps, faults, and slides.

• Q: Is there any quantity of rare minerals on these seamounts? What are they?

• A: Davidson Seamount was formed by volcanic eruptions more than 9.8 million years ago. As a result, most of the rocks here are basalts (lava) and other igneous (volcanic) materials. The surface of the old lava is coated with thin mineral layers, such as manganese crusts, that have precipitated out of seawater.

• Q: What is the water temperature on the bottom? And what is the sea-floor depth?

Seawater temperature below 1,000 m (3,280 ft) tends to be constant and COLD! Today we took a reading of 1.6° C (about 34.8° F) at 2,480 m depth near the northeast end of the seamount. Be sure to check out our Mission Facts for more on temperature. You'll find the link at the bottom of our Welcome Page for this expedition:

http://www.oceanexplorer.noaa.gov/explorations/06davidson/welcome.html


Question from: Gabrielle Baumgartner, science teacher, School of the Madeleine; Berkeley, California

My students and I are studying food webs. We are wondering: What do deep-sea organisms eat in places where the sunlight does not reach? Last year, we learned about chemotrophic bacteria.

Answer from: Lisa Borok

Much of the deep sea appears to be fed by the "compost" from the upper sunlit portions of the sea. As plants and animals at the surface die and decay, they fall toward the sea floor, just like leaves and decaying material fall onto a forest floor.

We call this decaying material "marine snow," because it looks a little bit like white fluffy bits. In her 1951 book The Sea Around Us, the famous ecologist Rachel Carson wrote that the dust and other material from the top of the ocean might fall to the depths "flake upon flake, layer upon layer — a drift that has continued for hundreds of millions of years . . . the material of the most stupendous 'snowfalls' the Earth has ever seen." When Japanese scientists first described seeing the fluffy stuff from a submarine, they said it must be Carson's "snow," and the name stuck.

Over the past 20 years or so, scientists have measured the amount of useable material in marine snow and found that there is plenty of carbon and nitrogen to feed many of the scavengers in the deep sea.

Many animals in the dark parts of the ocean filter marine snow from the water or scavenge it from the seabed. Carnivory (the eating of flesh) is another very common lifestyle. Some animals have special lures to attract prey, or they have huge or flexible mouths to eat whatever comes along. As you've studied already, some organisms rely on bacteria for food, either by filtering it out of the water, grazing it off marine snow particles, consuming it in the sediments, or by hosting symbiotic bacteria in their tissues.


Question from: Pat Smith

I'm curious why lead-210 (instead of another element) is used to age corals.

Answer from: Allen Andrews

We use lead-210 because it is a naturally occurring radioisotope that is taken up by the coral skeleton. This isotope is specifically useful because it decays at a half-life of 22.26 years. Hence, it is useful for age determination up to about 120 years. Typically, I trace the changes in lead-210 activity from the most recent growth to the oldest growth. If you take a look at the Coral Ageing essay on this expedition Web site, there is a good description of the theory and application. So far, I've had success with this technique for several species and hope to refine the estimates we have for bamboo coral.


Question from: Karen N., age 5; San Luis Obispo, California

When did the volcano last erupt?

Answer from: Lisa Borok

The last time Davidson erupted was about 9.8 million years ago! There's nothing active about this volcano right now, but the whole seamount is made up of old lava rocks. We're sending some neat photos of them back with our daily logs — check them out!


Question from: Robin Monti, student, Rollins College; Winter Springs, Florida

Have you seen much evidence of human-caused damage to the deep-sea corals you are studying this week? If so, what type and to what extent?

Answer from: Huff McGonigal

While the Davidson Seamount is really a relatively pristine place, it is not beyond the reach of human influence. During our hours of exploration, we have found some trash on the seamount, including a coke bottle, a tin can, and a bucket. We also came across a telecommunications cable that runs along the side of the seamount. Despite these isolated signs of humans, the habitat on the seamount is healthy and vibrant. NOAA is considering including the Davidson Seamount as part of the nearby Monterey Bay National Marine Sanctuary.  If this happens, NOAA regulations will help protect the corals, sponges, and fish on the seamount from any future threats, such as bio-prospecting, deep-water trawling, and mineral extraction.  Thanks for your question!

 


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