Our study will examine the toxic effects of four contaminant metals on digestive enzymes in marine polychaetes. These worms are abundant and ubuqitous in many marine sediments and are exposed to high metal concentrations, particularly in some coastal regions near industrial and sewage treatment activities. The effects of ingested metals on digestive enzymes may have important consequences for both worms-that is, interfering with their ability to survive in certain regions-and on their possible impacts on metal mobilization out of sediments via bioturbation.

Polychaetes are invertebrates belonging to the Annelida phylum. Frequently they are the most abundant group of invertebrates found in sediment (Miller, 2004) and typically display a high tolerance for toxic chemicals (Ward and Hutchings, 1996). Different species of polycheates can have different modes of feeding. They can be carnivores, filter feeders or deposit feeders. We are specifically looking at deposit feeding polychaetes which have been found to have high protease activity in their gut fluid (Mayer et al., 1997) and ingest large amounts of potentially contaminated sediment.

Proteases are enzymes responsible for the breakdown of proteins. They are important components of the gut fluid of polychaetes and other marine invertebrates. Proteases activity results in the generation of free amino acids and other compounds small enough to be transported across the gut lining where they can be distributed to various tissues within the body through the circulatory system of the worm.

Previous studies (Mayer, 2002) have found that the presence of Cu has an inhibitory effect on proteolytic enzymes in the gut fluid of deposit feeding polychaetes. However they did not test for the effects of other metals that are also present in high concentration in most contaminated sediments. The decreased activity of proteolytic enzymes could lead to decreased digestive ability of the worms and possibly decreased assimilation of organic matter and overall nutrition. These worms are at the lower part of a larger marine food web and many organisms such as bottom-feeding fish and crustaceans depend on there abundance.

As a preliminary experiment we will test the effect of dissolved Hg, Cr, Cd, and Pb on the activity of protease by adding different concentrations of dissolved metals to a solution of commercially obtained protease. This is to ensure that we are able to detect the inhibitory effects of the metals, at least at elevated levels, on the protease activity. If the results show an effect we will proceed to experiments using the polychaete gut fluid in vitro. The activity of the protease in this experiment as well as all the following experiments will be measured using Perkin Elmer, Wallac Victor² 1420 Multilebel Counter, which measures the frequency of fluorescent light impulses released when the enzyme breaks protein down.

Replicate aliquots of gut fluid retrieved from the chosen species of polychaete worms (Nereis sp.) according to the method in Mayer et al. (1999) will be incubated with:

1. Various concentrations of dissolved metal
2. Algal cells labeled with various concentrations of metal
3. Sediment containing various concentration of metal

We will also expose live worms to the same sources of contaminations as described above. The reason for doing the experiment in vitro as well as in vivo is to test the difference between the extracted gut fluid and the live worms’ digestive system when exposed to metal.