Here's another article from our archives, which was first issue in February 2010 newsletter. It was written by Dave Fosset, Dave is an honorary member of the society having served on the committee for several years also was our fishery officer for Coopers Lake. He mentioned that he gave a very interesting talk at one of our general meetings together with a slide show, showing the changes made to the lake and some of the resident Carp (all named and weighed). With a bit of luck we will be able to get him to do a repeat in the near future!

 

THE INVASION OF THE ZEBRA MUSSEL

by Dave Fossett

 

Earlier this year I did a little talk & slide show on the History of Coopers Lake. I was pleasantly surprised with the interest shown in Coopers Lake, judging by the turn out of members attending the talk.

 

When trying to condense 20 yrs into about 2 hrs, it wasn’t possible to dwell too long on every aspect of the talk. I did briefly mention that coopers was inherently a very snag ridden water, with its gravel, come rocky bars, along with an unknown amount of re-enforced concrete & other debris littered on the bottom.

 

I cant remember if I mentioned the amount of zebra mussels that were also present in Coopers. They are obviously in an environment that they like, because over the past 20 years, they have maintained a very healthy population. 

 

Because they have razor edged shells, any fishing line that comes into contact with them, will be badly damaged.  It was and still is one of the main hazards you will encounter when fishing at the lake. I’m sure those of you that have fished there, will at one time or another, have had their line shredded or cut, on the zebras, resulting in the loss of a fish.

 

In a fishing situation, there are various things that one  could do, to help reduce the risk of losing fish to cut offs from the zebra mussels & snags at coopers,  but I feel that it will take much more than a couple of lines to cover that issue. When I fish there, which isn’t very often now days, to overcome the zebra mussel & snag obstacles, I personally had to adapt my approach, which ultimately reduced my fish losses to virtually nil. 

Maybe that’s cue for an article another time!!

   

Well, we can’t do much about reducing the amount of zebras present, but I thought it may be of interest to the members, to have some understanding of what a zebra mussel actually is.

What is a Zebra mussel?  The zebra mussel, scientific name Dreissina polymorpha,  is a type of mollusc. The mollusc family also includes clams, snails, oysters & the octopus.

 

Why should you care about zebra mussels?  Well, they are one of many non native, invasive species that are disrupting the natural balance of our ecosystems.  Most of the literature that I have read on zebras has been studies taken place in the United States, where the invasion is relatively new. Regardless of where I have gleaned the information, the problems it causes are the same here in Britain, as where ever it has taken hold.

 

Physical Description.

 

Zebra mussels are bivalves. This means they are composed of two shells, a left & right valve. They grow to about one to two inches in length, a beige colour with brown stripes, hence the name zebra. Extending from the shell are byssal threads. These threads that are almost hair like and number up to 100. They are very strong protein strands that allow the zebra mussel to attach itself to just about anything in its environment, including other organisms. 

The byssal threads are so strong, that any attempt to move it from its site, will result in the shell breaking, before the byssal threads. Most other mussels lose their byssal threads when adult, but the zebra retains them for life.

 

Feeding Habits

 

Zebra mussels are filter feeders. They feed on unicellular algae, bacteria & organic detritus. Water enters the zebra via a hole called the” incurrent siphon“.  The microscopic particles within the water are sorted out by tiny hair like projections called cilia.  Edible particles are passed to the mouth. Inedible particles are expelled out through a smaller hole called the” excurrent siphon“.  These unwanted particles are combined with mucus & other matter & then deposited on the lake floor as psuedofaeces.  One zebra mussel will filter up to 8.5 litres of water per day!

Reproduction

 

Zebra mussels are dioecious. This means their population consists of male & female. When the females reach 2 years old, they can release 40,000 eggs each breeding season, (May-October every year) The male sperm are released directly into the water & fertilization occurs externally. A zebra population will grow at an ever increasing rate if the resources such as food & space are plentiful.

 

Lifestyle

 

When in favourable conditions, zebras are sessile. This means they anchor themselves to something in their environment & will remain attached to that structure indefinitely. The life span of a zebra mussel is 4-5 years. They are not choosy about what they colonise. It might be on underwater debris, boats and plants, even on crayfish, native mussels or turtles. However, when their environment conditions change, they can release hold from their byssal threads & migrate to a new & more favourable habitat. 

What areas are they native to ?

 

Zebra mussels are native to freshwater lakes & rivers in Eastern Europe & Asia, the 

How did they spread ?

 

Invasion to Europe came about since the late 1700s, after construction of an extensive Black & Caspian sea. canal network. 

They were probably carried on the underside of boats, anchor chains & propeller shafts etc. Because the zebra mussel is capable of surviving out of water in moist damp conditions for periods up to 3 weeks, anchor chain lockers provide a refuge for clusters of adult mussels, that could be released when trans oceanic ships drop anchor in freshwater ports. Its believed that the mussel invasion into the Great Lakes of United States & Canada around 1988, was inadvertently carried within the ballast water of  ocean going ships traversing the St. Lawrence seaway. 

 

The history of invasion to Britain dates back to 1820s (Cambridgeshire) & 1824 (Surrey commercial docks, greater London).

Other countries invaded include the Netherlands (1824-7), Sweden (1920), France, Germany, Finland, Italy, Switzerland, former USSR, & Spain.

 

Economic Implications

 

Power & water plants, home & abroad, spend millions of pounds or dollars each year to clean zebra mussels out of their pipe work. Large concentrations of zebra mussels colonise the insides of supply pipes to an extent where the pipes are so clogged that fresh water supply is cut off & some towns in the US experience power cuts. The psuedofaeces released by the mussels worsen the problem because they increase the acidity of the water pH which causes corrosion of the pipelines.

 

Many boat accidents over recent years on the River Thames have been caused by the zebra mussels fouling up steering & propeller mechanisms.

 

Ecological Implications

 

A study of the Great Lakes has found a dramatic decrease in the native biodiversity ( the number of different species present ), since the introduction of zebra mussels. I assume then we can apply this to our own waters here in Britain.  Species of native mussels are on the verge of extinction because the zebra mussels are altering the natural food chain. Native fish are also suffering for two reasons. Firstly, their most important food sources, algae & plankton, are being consumed by the zebra mussel. Secondly, the psuedofaeces of the zebra mussel decrease the pH of water. 

 

Fish eggs are very sensitive to pH changes & are seen to be not developing properly.

The native mussels are also declining because the zebras compete with their food & space, & they actually colonise on the native mussel, restricting their ability to move, feed & breed.  As many as 10,000 zebra mussels can attach to a single native mussel! 

 

The continuous filter feeding activity of the zebra mussels will certainly improve water clarity. Because sunlight is now reaching more excessive depths, aquatic plant growth will be increased. The zebra mussels do in fact vacuum up water pollutants that have previously destroyed water quality, but, it might come at a price.  The removed pollutants are not released in the psuedofaeces but are stored in the fat cells of the zebra mussel.

 

Anything that now eats the zebra mussel, will store those pollutants in their fat cells, but at a higher concentration. This process of passing pollutants up the food chain at increasing concentration is called bio magnification. Scientists are now concerned that humans may eventually be exposed to the toxic concentrations of these pollutants when consuming fish & waterfowl that have consumed zebra mussels.

 

No more fish & duck pie for me then….thank you!!