Updates From Sea | Cruise 2007
January 17th
By Eric Simms, Education Outreach Coordinator
The Race for Space - Succession
Space is a very valuable resource in nature, so open space typically doesn't stay that way for very long. When it is available, organisms compete to move in as quickly as they can, depending upon the conditions. The earliest organisms to arrive are typically ones that have adapted to live in the harsh conditions found in new open spaces. The recent eruptions at the East Pacific Rise have opened up a lot of new space.
Photo © 2007 D. Fornari / TowCam
You've seen this in your own environment. Consider, for example, what happens when a farmer harvests his/her crop and then leaves the field alone for a few years. At first, the soil is directly exposed to the wind, sun, rain, and snow, which are tough conditions for many plants to grow. But some plants such as grasses and weeds grow well under these conditions, and they grow quickly in the available space. These plants attract microbes and animals such as insects, mice, snakes and birds that feed on the plants or each other. Next, once the grasses are tall enough to shade the soil, keeping it from getting too hot or dry, shrubs and small trees that prefer these less extreme conditions can begin to grow. As the years pass and the trees grow, the field eventually turns into a forest. The shade and other factors cause the grasses and weeds to disappear, and a new set of animals adapted to live among the trees settle in. This process of change over time in an environment is known as succession.
Succession happens in the deep sea as well, particularly where hydrothermal vents are found. Occasionally, volcanic eruptions on the seafloor cover large areas with new lava, killing the existing worms, shrimp, crabs, mussels and bacteria found there and creating new open space. This is exactly what happened at the beginning of 2006 here at the East Pacific Rise study site in the Pacific Ocean. Scientists on this and other cruises are now studying how the chemistry and biology of this new open space on the seafloor will change over time.
Photo © 2007 D. Fornari / TowCam
Not much is known yet about the succession that occurs after a volcanic eruption on the seafloor. This is because understanding succession requires time - time to observe, measure and study what happens over the years. Since the 1991 eruption, scientists have documented some of the changes but still have many questions to answer. This recent eruption offers a new opportunity to see the changes in a community from the start. So far, scientists are finding that after an eruption, there can be high concentrations of certain chemicals in the hydrothermal vent fluids, including types of sulfide and iron. Although these chemicals are toxic to most animals, bacteria can use these chemicals for energy and are believed to be the first organisms to colonize the new lava. Not long afterwards, very small Tevnia (a type of small tubeworm) begin to attach and grow on the rock near the vents, and crabs and shrimp gradually arrive to scavenge on dead bacteria and worms.
Photo © 2007 T. Shank
Over time, the types and concentrations of chemicals in the fluids will change, creating conditions that encourage other organisms to arrive at the vents. Riftia (a large tubeworm) seem to arrive at the vents after the Tevnia and gradually replace them, followed by deep-sea mussels that form large beds near the vents. Many of these animals get their energy from chemicals in the vent fluids with the help of bacteria - so if a vent stops providing enough chemicals, the bacteria and animals will eventually die. The cycle of succession at hydrothermal vents can take months and years to unfold, starting over again with each new vent or new eruption.
In the next few logs, I'll report on how scientists are studying the changes here at the East Pacific Rise since this recent eruption. Stay tuned to find out what they are seeing so far on this cruise....
Click here for more pictures from the deep!
By the way, there is an activity in the SEAS curriculum, in the Teacher Section of this site, on this very succession story. Check it out at SEAS Activity 4: Change Over Time.
