TPO Writing - بیست و شش

TPO Writing - Twenty Six

Contrary to what you just read, there are ways to control the zebra mussel’s spread. What’s more, it is not so clear that the mussel is a serious threat to fish populations.

True, the spread of zebra mussels couldn’t be controlled in the past, but that’s because people didn’t have enough knowledge. In fact, there are effective ways to stop ships from carrying the mussels to new locations.

Here’s an example. The way zebra mussels usually travel across the ocean is that a ship takes on some fresh “ballast water” in Europe and the n empties that water into American waterways when it arrives. Full of zebra mussels, but the ship can be required to empty out the freshwater and refill with ocean water while still out in the ocean. Salt water will kill the mussels.

Second, it’s true that zebra mussels often don’t have predators in their new habitats, but that’s only in the beginning. What’s been happening in Europe is that local aquatic birds sooner or later notice there’s a new food source around and change their habits to exploit it. They switch from whatever they were eating before to eating zebra mussels. And birds can eat a lot of mussels. So zebra mussels aren’t so likely to dominate their new habitats after all.

Finally, even in habitats where zebra mussels become dominant, is the overall fish population likely to decrease. It’s true that zebra mussels may have a negative impact on fish that eat plankton. But on other fish, they can have a positive impact. For example, the mussels generate nutrients that are eaten by fish that feed near the bottom of the lake or river. So bottom feeding fish populations may increase, even if plankton-eating fish population decrease.