Amphipods

More Than Mud

Summary
Examine the effects of pollution on amphipods using data from the Chesapeake Ecotox Research Program.

Introduction
Where is the benthos? In a deep, mysterious part of the ocean? Yes, but it can also be in areas right near shore. The benthos is simply the assemblage of organisms that live on, in or near the bottom of a body of water. Benthos can be divided into several types based on where the organisms live on the bottom:

• infauna - organisms living in the sediment (worms, clams)
• epifauna - organisms living on or attached to the sediment or substrate (oysters, barnacles, seagrass)
• demersal - organisms that live close to the sediment or substrate and feed on infauna or epifauna (flounder, crabs)

or their size:

• macrobenthos: > 1mm in size
• meiobenthos: >0.1mm and < 1mm in size
• microbenthos: < 0.1mm in size

When thinking of benthic habitats, sand, mud and a few worms probably come to mind. But there are many different types of benthic habitats and organisms, from a complex of tunnels in the mud housing worms and clams to oyster reefs with invertebrates and fish hiding in the nooks and crannies. Benthic communities are vital to the ecosystem at large. They supply food and habitat to primary and secondary producers, and are veritable restaurants for pelagic fish. Their resident filter feeders such as oysters, tubeworms and sponges help improve water quality. But benthic communities are also one of the aquatic areas most vulnerable to human-induced problems, especially eutrophication and contamination.

Because most benthic organisms can move only limited distances if at all, they cannot escape as industrial contaminants accumulate in the sediment, or when eutrophication causes their habitat to become anoxic (devoid of oxygen). Instead, many organisms die or suffer impaired growth, reproduction or foraging and escape abilities. As a result of their sensitivity, benthic organisms often make good biological indicators of poor environmental conditions. Scientists can assess the quality of an aquatic habitat by monitoring the abundance of an indicator species.

Water bodies all over the world, including the Chesapeake Bay, the nation's largest estuary, are suffering from poor water quality. One indicator species being used to study the environmental condition of the Chesapeake Bay is the amphipod Leptocheirus plumulosus. An amphipod is a small crustacean found in all types of aquatic environments and even on land. L. plumulosus burrows in the sediment to avoid predation. It is highly sensitive to various pollutants, yet is easy to grow in the lab making it a good species for pollution experiments. This month's data activity will focus on a Chesapeake Ecotox Research Program experiment of the burrowing response of L. plumulosus to polluted sediments.

Data Activity
Access the Chesapeake Ecotox Research Program data. The data in the columns are the reburrowing times (in seconds) for individual amphipods that have been transferred from one sediment type to another. Determine the average time for each of the treatments (columns) and create a bar graph comparing averages for all four treatments.

Discussion Questions

• Which set of amphipods had the fastest average reburrowing time? Which had the slowest? Why?
• Did the type of sediment the amphipod originated from have an effect on reburrowing times (e.g., compare times for "clean to clean" and "clean to Baltimore")? Why do you think that is?
• Do you think Leptocheirus plumulosus is a good biological indicator for contamination in the Baltimore Harbor?
• If you lived in a watershed that had Leptocheirus plumulosus living in it, how would you set up an experiment using L. plumulosus as the biological indicator?