Unknown origins and one-sided friendships

During the recent floods the Environment Agency opened the sluice on the Slipper Millpond in Emsworth to reduce the risk of flooding upstream. This turned what is normally a saline lagoon into mud with a river flowing through it and I thought I'd go and have a look at what the low water levels had revealed.

The only new species that I saw was the tubeworm Ficopomatus enigmatica. It is not a native species and Wikipedia says that it is from Australia and is a major threat to native wildlife. Unsurprisingly, this isn't correct. Whilst it is now found in areas with variable salinity in temperate waters throughout the world, it is not known where it originates from and it is considered non-native in Australia. It's requirement for variable salinity means that it does not compete with most native species and as it has beneficial effects on water quality by removing suspended solids and improving the oxygen and nutrient status of the water so it may actually benefit other benthic species. There are potential negative effects but it certainly isn't a clear-cut case of 'nightmare alien invader'.

It was noticeable that many of the colonies at Emsworth were attached to litter in the mud.

Whilst there I watched a female Red-breasted Merganser fishing in the river. The whole time she was followed around by a Little Egret - presumably hoping to pick off anything that the Merganser missed or disturbed. The merganser seemed fairly tolerant of the egrets attentions but I can't help feeling that it was a rather one-sided friendship.