Shallow and wide bays are popular among humans

Shallow bays are valuable habitats and are much sought after for recreational activities. The warm, shallow waters and the shelter of such locations create a pleasant environment for summer cottage owners and pleasure boaters alike. Wide and open bays are particularly popular with swimmers and water sportsmen.

Man's intensive use of the marine environment is not always compatible with the diverse biodiversity that hides beneath the surface. However, it is the water, aquatic plants, seabed, as well as the connection to the sea that create the ecosystem services required for recreational use.

A successful and sustainable coexistence benefits the ecosystem of a bay, as well as the people enjoying its recreational features.

The EU Habitats Directive designates lagoons and open bays as protected habitats

Lagoons, also known as sheltered and often lush marine bays, tend to be multi-layered and variously shaped in terms of aquatic vegetation. Such habitats are abundant in invertebrates and insect larvae living in the muddy bottom.

The underwater threshold or sill situated at the mouth of the bay slows the rate of water exchange within the sea, and the shallow basin also warms quickly in the spring. 

Such habits are ideal places to find the fish spawn of species like roach, perch and pike. By the time the spawn has hatched into juvenile fish, the water in the bay has warmed and the aquatic vegetation has started to grow in earnest. There is shelter and food for both the fish fry and the larger fish that prey on them. Along with wading birds and waterfowl, the angler sitting at the end of a pier or on a shoreline rock, in turn, can enjoy their role as the top predator in the lagoon’s food chain. 

 Small fish swim amongst aquatic plants and algae in shallow water.
Fish thrive in coastal lagoons.

Coastal lagoons also include flads, i.e. brackish-water lagoons formed from a sea bay in the process of post-glacial rebound. Such flad lagoons are protected by the Water Act.

Although wide and open bays are just as important as lagoons, their habitats are quite different.

In aerial imagery and maps, these wide bays look like folds of the sea sunk into the mainland or large coves that collect seawater before the coastline begins. The bottom is often sandy, or a mixture of sand and mud, and the vegetation is low-growing in such sheltered bays.

On the side of the bays facing the open sea, seagrasses and other vascular plant species survive on the moving sands. As one moves into the shallows, a coarse carpet of rough stonewort, i.e. Chara aspera, binds the bottom substrates in place.

Small crustacean invertebrates, such as amphipods and shrimps, scurry in the sand and are snapped up by passing fish. In addition to invertebrates, fish species like flounder and gobies are also hidden in the sand.

Wide and shallow shorelines attract wading birds, and large shallow bays often have bird observation towers in addition to piers and cottages.

Dredging changes shallow bays – the adverse effects can be seen even years later

The underwater conditions of shallow bays are affected by both the modification of recreational beaches and small boat traffic.

Dock structures can alter water currents, while dredging removes the protective vegetation and opens boat lanes to the open sea. Currents caused by boat propellers mix the water and resuspend sediments that have settled on the bottom.

With both moderate environmental modifications and use, the impacts on marine nature will also be kept to a minimum. Although a summer cottage shore, which is entirely free of vegetation and deepened for boat traffic, seems like a good idea at first, the adverse effects of such a drastic change will still be visible for years as the waters become turbid and fish stocks are weakened.

It is therefore worthwhile to consider marine ecosystem services when planning long-term changes to the natural environment.

Species of shallow marine bays

  • Roach, bream, rudd, etc. (Cyprinidae)
  • Perches (Percidae)
  • Pike (Esox lucius)
  • Wading birds
  • Seagrass (Zostera marina)
  • Vascular plants (Tracheobionta)
  • Rough stonewort (Chara aspera)
  • Amphipod crustaceans (Amphipoda)
  • Flounder (Pleuronectiformes)
  • Gobies (Gobiidae)