Carp Angler
The answer to the first part of your post (If this stuff can grow in depths upto 25 feet, then if it colonises any of our natural lakes, which are generally shallower than that, then can I assume that it will block out all sunlight and slowly kill the lake of all bottom dwelling invertabrae life?),
is a qualified yes! In theory it could conceivably colonise a whole natural lake such as the Meres if it takes hold.
The qualification comes from the fact that it’s a rooting plant and large waters are prone to strong wave driven currents caused by gales. Such actions can rip the anchorage out and keep the more exposed areas free of it. The areas that are most likely to blanketing on such waters, are the sheltered bays and corners. Without doubt the most likely type of waters that could be totally blanketed out are small club pools and well-sheltered lakes.
As to it killing all of the invertebrate life, the answer is no in the sort-term. The invertebrate trophic structure is such that some feed on decaying matter on and in the bed of the lake. It would however, kill over a far shorter time, all the animals that are dependent on alga for food due to blanketing. As alga growth and production is totally dependent on sunlight.
In sort, there is most likely to be a marked decrease in the bioproduction of an infected water as it is totally blanketed out. The result of this would be less food availability to fish and other animals that depend on the water for food.
On the worst affected waters (small club pools and well-sheltered lakes) the long-term situation could be that they suffer from accelerated succession. Succession is a natural process of shallowing through a build up of sediments through dead organic matter. The eventual outcome of this process is that the pool disappears and dries out. I know several ponds local to me that I fished as a kid 40 years ago that are no longer there due to this process.
What I should have pointed out in the above post when I said it was frost resistant, was that frost doesn’t kill the plant, it only subdues its growth and it dies back in the winter as do many other aquatic plants. That said, some native and non-native aquatic plants can be eradicated by prolonged freezing.
You asked are there any pros to this? There may be some short-term gains such as providing refuge for fish from predation from cormorants as the plant starts to colonise a water. On the lager more exposed waters there may be a temporary increase for a short time of some invertebrates that graze on plant. But it must be remembered that it is not a native plant, therefore its likely that few species have evolved to utilise its resource. In general terms most non-native plants both aquatic and terrestrial have few animals that feed on them.
To the best of my knowledge no one has looked at the invertebrate fauna that utilise this plant.
I hope these answers assist you in your understanding of this obnoxious plant.
It does however illustrate the ecological damage we can do by innocently bring in Allen plants species, I think!
