Day 1: Exploring Extreme Food Webs Days 2 & 3: Community Succession in Local Environments and Cold Seeps

Day 1: Extreme Food Webs Organisms in any ecosystem can be organized into categories based on how they get the energy they need to survive, grow and reproduce. We refer to these categories as trophic levels and the flow of energy as a food web. (Source: Arctic Climate Impact Assessment, ACIA)

Trophic Levels = the positions of one or more species in a food web relative to the initial source of energy Primary producers create biomass using energy from the initial source (e.g., the sun) Primary consumers get their energy from consuming primary producers Secondary consumers get their energy from consuming primary consumers Tertiary consumers get their energy from consuming secondary consumers Many organisms can occupy more than one trophic level

What gives you energy? List some of the items that provided you with energy yesterday (e.g., hamburger, salad, fish, rice, bread, fruit, milk) What’s the source? For each item, trace the item to its original energy source (e.g., milk  cow  hay  sun)

Now, create a Hydrothermal Vent Food Web! 1. Watch the Chemosynthesis and Hydrothermal Vent Life video 1. Complete the Chemosynthesis and Hydrothermal Vent Life multimedia discovery mission:

Day 2: What is Succession? Succession refers to sequential changes in the composition of species in an ecosystem over time as a result of changes in environmental conditions and interactions between species

Part 1: Thinking locally… Scenario: A farmer has agreed to work with a local conservation group to let one of his fields adjacent to a forest go fallow (unfarmed) with the intent of creating more diverse habitat for local wildlife. Discuss and record: What changes do you predict will happen to this site if there is no human intervention during the next 50 years?

Part 2: Exploring Cold Seep Community Succession Communities in the cold seep environment rely on foundation species such as tubeworms to provide habitat. Environmental conditions at cold seeps can vary considerably over time (e.g., after several years of flow seepage declines) Tubeworms can withstand environmental changes at seep and can live years or more The community of other species associated with the tubeworms, however, undergoes succession over time. Let’s look at those changes over time.

Young Tubeworm Community The community begins when chemical- rich fluids with high levels of sulfide and methane begin to seep out of the sediment and into the surrounding water Microbes (bacteria and archaea) are the first organisms to arrive on the scene as primary producers. The microbes use the sulfide and methane in the sediment for energy to create organic compounds (e.g., sugars) through the process of chemosynthesis 0 – 20 years old

Young Tubeworm Community Deep-sea mussels and tubeworms arrive early at the seep and act as primary producers because of their reliance on the symbiotic bacteria in their tissues Most other organisms cannot tolerate the high concentration of toxic sulfide and methane at this early stage, so the mussels and tubeworms enjoy little competition (other than with each other) for space and access to the seep fluids A few primary consumers are present during the early life of a seep, including shrimp, crabs, snails and worms, but the numbers of secondary and higher-order consumers are very low 0 – 20 years old

Middle-aged Tubeworm Community The once abundant mussels have begun to disappear, along with some species of shrimp and snails present during the earlier years Tubeworms, however, continue to thrive because they have root-like structures that extend down into the sediments Even though the amount of sulfide has decreased at this stage, there is still sulfide available in the sediments which the tubeworm extracts with their root-like extensions 20 – 40 years old Over time, seep fluids (e.g., methane and hydrogen sulfide) in the habitat decreases significantly

Middle-aged Tubeworm Community During this stage of succession the number of secondary consumers increases for several reasons: 1) lower toxicity of the habitat due to declines in seepage and the uptake by tubeworms for their symbiotic bacteria 1) the presence of enough sulfide and methane right at the sediment surface makes the environment more productive than the surrounding deep sea, and 1) as tubeworms grow, they create additional habitat for organisms in and around the tubeworm colonies. 20 – 40 years old

Old Tubeworm Community These conditions support the arrival of higher-order consumers (e.g, crabs, fish, sea stars) who are not adapted to survive in the presence of higher levels of toxic chemicals It is unknown how long tubeworm “bushes” in this final stage of succession can survive at cold seep environments (although it is likely to be measured in centuries!), but their persistence indicates that they must still be able to extract sulfide from beneath the sediment surface using their root-like extensions. 40+ years Eventually, as seepage declines, methane and sulfide concentrations above the sediment surface are low and are essentially the same as the surrounding seawater.

Challenge Scenario Your group just collected a sample from a cold seep tubeworm community in the Gulf of Mexico. Is this community from an old tubeworm aggregation OR from a young tubeworm aggregation associated with an early successional stage? How can you tell??

You recall learning at a recent scientific conference that researchers studying tubeworm longevity found interesting patterns in the community of animals around young vs. older tubeworms. They found that the proportion of organisms within each trophic level changed as the tubeworms aged. Because you can’t tell how old your tubeworms are, you decide to sort your sample by trophic level and see if you can determine the age of the community by comparing your results to the data in Dr. Cordes’ scientific research paper. Comparing Trophic Proportions

What do you think??