The littoral zone along the seashore extends from the highest part of the shore washed by waves to the deepest waters just offshore where marine plants can assimilate using natural light. Many different kinds of littoral environments can be found around the shores of the Baltic: from rocky shores through sandy beaches to silt-bottomed bays with extensive reed beds; and from windswept open shores to sheltered flada lagoons almost cut off from open water. Littoral zones provide habitat for many shore species, and fish often come into these zones from more open waters to spawn.
The flora and fauna of the sea bed in the littoral zone vary according to factors including the nature of the sea bed and exposure to currents. Filamentous algae thrive along shorelines with rocky sea beds, especially in nutrient-rich waters. The most common species is the bright green blanket weed (Cladophora glomerata). Bladder wrack (Fucus vesiculosus), a key species in the Baltic Sea, can also thrive on rocky bottoms kept clear of sand by sea currents. Bladder wrack requires fairly high salinity levels, but can still grow along the Finnish coast as far north as Vaasa. Soft-bottomed shores are often colonized by common reeds (Phragmites australis), providing shelter and feeding areas for invertebrates, fish and birds. Potamogeton water weeds grow just outside the reed beds. Clean, sandy bottoms provide suitable habitat for eelgrass (Zostera marina) and marine muskgrass algae (Chara).
Growths of filamentous algae provide shelter for many small gastropods and the immature stages of gammarid shrimps and the Baltic isopod Idotea balthica. Growths of bladder wrack host an even wider diversity of marine species, including sessile species such bay barnacles and the bryozoan Electra crustulenta, as well as free-swimming gammarid shrimps, isopods, the common prawn Palaemon adspersus and mysid shrimps. Many fish also feed and shelter among bladder wrack, including three-spined and nine-spined sticklebacks, and perch.
