one of the problems with understanding the ecological impacts of any Invader is the first sign we have that an Invader is coming in and causing changes is the Invader comes in and causes changes and so at that point it's too late to ask what condition the ecosystem was in before the Invader arrived so we knew we had an interesting opportunity because we had several years of data of pre-invasion conditions in the river and so if we could just keep watching the Hudson until the zebra muscle arrived and then saw how it changed then we would have a very firm basis for understanding what this Invader does to ecosystems Zebra muscles are small striped by valves like clams and oyers and it's very easy for humans to move Zebra muscles around Zebra muscles have these microscopic larv in the water column so you can imagine you might have a little water in a Bait Bucket or in an aquarium or in a live well in a boat anything like that can move zebra muscle larv around we knew it was in the Great Lakes and the Great Lakes are connected by waterways to the Hudson so it was fairly certain that they would get here slowly but steadily no matter what we had been studying the Hudson for a few years before the zebra muscle became imminent you ready David well good to go we're headed up to our long-term monitoring station we call Kingston we're going to measure a bunch of physical parameters like uh temperature dissolved oxygen light penetration we'll also take a whole host of water samples that we'll take back to the lab in process later and uh this is what we do every two [Music] weeks okay we're anchored I'll get the pump out we want to know what are the physical characteristics that these animals have to deal with so the temperature is 9.7 de C the oxygen is 104.7 % so this is a ski disc and that tells us how much sunlight is penetrating the water because it's very turbid today it doesn't have to go very deep before you can see it now right about there I can see it and then I'll look at the Rope to see where it's marked and the depth was only 20 cm the phol Plankton which are one of the members at the base of the food web need sunlight to grow so when we measure the amount of sunlight that can pass through the water we can estimate how well the algae can grow and then we want to also look at all of the other parts of the food web the bacteria protozoans the algae the Z Plankton I don't think there were many animals in there right now that there's not much in there nearly everything that we measure in the Hudson River changed when zebra muscles arrived Zebra muscles came into the river they were first seen in 1991 by 1992 there were about 500 Bon Zebra muscles in the Hudson Zebra muscles are filter feeders and they can only eat certain size class of things so they mostly eat the small algae the phytoplankton and some of the very small animals what we call Z planting they came in and they started eating and because the Z muscles could eat eat so much that it was a radical change and you could see it quite quickly we saw about an 80% loss of phytoplankton populations and the smaller Z Plankton the little tiny guys fell by about 90% and overall the amount of Z plankt in the river fell by half that's interesting because that's fish food right so we reckon that about half of the fish food in the river disappeared when zebra muscles came in so in fact the bulk of the Hudson fish Community suffered as a result of the zebra muscle infation people are going to be a little upset that they're not finding their fish something all of a sudden disappears you should kind of worry about what's going on with your ecosystem and is your water still healthy in the 1990s we understood documented described the short-term acute impacts The Invasion the rapid outbreak of the zebra muscle population the loss of phytoplankton the ensuing impacts on the other parts of the food web and on water chemistry and all that would have been true and right but it would have only been part of the story keeps bringing them fully loaded here's a rock and you can see that there are some older Zebra muscles on it these larger guys which are a few years old and then you can see all of these small ones that are attached on here these all settled out last August so now what we're seeing is each year there appears to be more and more smaller ones and that the larger ones somehow are not making it from year to year the lifespan of the muscles has gotten much shorter so it used to be that the muscles would live 6 or S years and now it appears that most of them are dying after 1 or 2 years The Logical follow-on question is why have these changes occurred um and I think it's fair to say we really don't know uh at this point there are a bunch of things that could be killing Zebra muscles in the river causing them to die younger than they used to there could be diseases in the river there could be other uh Predators other than crabs uh it could be that the muscles are themselves in just such poor condition because they've eaten themselves out of house and home we we don't know but we do know that what a zebra muscle eats depends on how big it is so only the biggest zebra muscles can eat Z Plankton and so the Z Plankton populations are starting to come back the river is always changing some of those changes are natural and they're what we would call normal progressions and some are not so again the more information you have the more you can pinpoint what's causing the changes that you see in the river we don't know if this recovery is the long-term fate of the rivit or whether this is just a a short phase itself certainly what's happening now in the Hudson is very different from what was happening in the 1990s and so that's a new problem for us to try to study and understand