Special places: Flads of Salmisudden

In our last week’s blog you could read about flads; how they are formed, why they are so valuable and a bit about the challenges that concern conserving these important habitats. Now we want to introduce you to a specific flad that we have discovered in our underwater nature inventories and discuss its future.

Although the title indicates that there are many flads around the headland of Salmisudden (Haparanda) at the moment there is only one flad. On top of that there are smaller gloe lakes and two bays. These bays and flad are influenced by different degrees of exposure, but they are all slightly connected to each other with small trenches. The most southern bay is open to the east and has no threshold. The one north of it is partially isolated from the sea with a threshold and is on its way to form into a flad. North of this sheltered bay is the flad, which happens to be one of the most interesting and special places we have discovered on the Swedish side of the SEAmBOTH-area.

From historical photos it is apparent that the bays and seashore line are constantly altered. Pictured is Salmisudden with adjacent islands and bays formed between them, 55 years apart. The northernmost bay has formed into a shallow flad within this time. The question is, what will this picture look like in another 55 years?

We have shown a peek of this flad in an earlier blog , as it has by far the highest abundance of Chara braunii of the sites we have visited. Not only is this flad rich on this threatened charophyte but it also has a very high number of aquatic plants. Other threatened species that the flad shelters are Persicaria foliosa, Limosella aquatica, Potamogeton friesii and Elatine orthosperma. Besides being rich on vegetation this flad is an important nursing ground for fishes and is also rich on evertebrates, like freshwater sponges. With all this said, the flad is not only beautiful, but also very valuable for its ecological qualities.

An underwater landscape from the flad at Salmisviken. In this picture you can see freshwater sponges and Braun’s stonewort (Chara braunii) (Photo by Petra Pohjola, County Administrative Board of Norrbotten)

The flad is around 500 x 250 m in size and very shallow; with an average depth of 0,35 m and maximum depth of 0,8 m. It is connected to the nearest semi-enclosed bay in the south and to the sea in the northeast. This inlet is dredged and even though this dredging would not be repeated, the flad is so shallow that it is unlikely that it will form into a gloe lake but will mostly dry out due to post-glacial rebound. With a mean depth of 0,35 m and a yearly land uplift of almost 9 mm per year, most of this flad will disappear in 40 years. Even with conservation measures we may lose this valuable habitat within a human lifetime.

Fishes now bask in the sunlight in shallow water. In 40 years this landscape will not be submerged anymore. (Photo by Petra Pohjola, County Administrative Board of Norrbotten)

This realization forces us conservationists to widen our focus area and also try to look into the future. Flads are per definition short lived and especially so in the northern Baltic Sea. Flads will evetually evolve into gloe lakes, which is a different habitat. To conserve the flads, new flads must continue to form. With all logic we must shift our focus from presently valuable flads to evolving flads and also conserve them. Human impact along the coastline, for example dredging, may change the coastal habitats and there is a risk that fewer and fewer natural flads will evolve from the current bays.

In the case of the present and future flads around Salmisudden, the current hotspot for biodiversity, as well as Chara braunii, will disappear but there is hope that new ones will form at the same time. The forming flad just south of the present one is at the moment too deep for the threatened charophyte, but Chara braunii is already present along some shores. Will this be our future Chara braunii – hotspot? We should certainly keep this possiblity in mind.

This habitat in the forming flad is now situated at around one meter depth. What will it look like in the future when land uplift has put it nearer the surface and closer to the sunshine? (Photo by Petra Pohjola, County Administrative Board of Norrbotten)

Written by Petra Pohjola, County Administrative Board of Norrbotten

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