In the wavy open sea, plants with submerged leaves grow
Typical sea plants are adapted to grow in salt water and withstand strong waves. However, in the shady bays of the Baltic Sea, where the rivers flow, you can also see a variety of freshwater plants. In the coastal waters of shallow bays, reeds often thrive, forming large reed beds. However, reeds do not tolerate salty water and large waves. Plants with floating leaves also cannot grow on the coast open to the waves, because storms simply tear them apart. Only submerged aquatic plants survive here. Seagrass with long narrow leaves can be seen on the seabed. The sea is mainly dominated by various types of algae there.
- Plants that tolerate saline water
- Plants that tolerate waves
- Plants with large floating leaves
- Different types of algae
Think!
- Which conditions do plants growing in the sea have to cope with?
Different types of algae grow at different depths
There are different colours and shapes of large algae visible to the naked eye. Green algae need the most light to grow, browns need less, and reds can survive in darker places than others. Therefore, zones of different coloured algae can be seen in the sea as the depth increases.
The rocks near the shore are often covered with bright green plant formations that move in the water like hair. These are various species of green algae. One of the most common species is Cladofora - "coarse seaweed".
Brown algae can be found deeper than the green algae zone. The best known of these is the bladderwrack. While growing in the sea, it is greenish-brown in colour, and when thrown ashore, it soon turns dark brown.
At a depth of about five meters, the zone of red algae begins because it is already too dark for brown algae. The best known red algae in the Baltic Sea is clawed fork weed. Red algae produce a gelatin-like gelling agent called agar, which is used, for example, to make marmalade.
- Green algae
- Red algae
- Brown algae
Bonus: Piles of bladderwrack on the beach
The smell of the decaying bladderwrack on the beach drifts from far away as you approach the coast. The bladderwrack thrown onto the coast is of interest to both people and other coastal inhabitants. People have always fertilised their coastal fields with it. Warm decaying piles of bladderwrack attract many insects and spiders, which in turn attract shorebirds. These piles are also liked by the grass snakes, who lay their eggs there.
Unicellular algae are the most important producers in the sea
As in lakes and rivers, floating unicellular algae called phytoplankton grows in the near-surface waters of the sea. Multicellular algae can only grow in the narrow areas of the coastal sea, but phytoplankton can grow everywhere in the sea. However, there are somewhat more of them in the warm coastal waters.
Small algae are the most important producers in the sea. Algae in all the world's seas provide most of the oxygen in the atmosphere. Phytoplankton is eaten by small floating animals - zooplankton, which in turn are food for larger animals.
There are thousands of species of small algae in the Baltic Sea. They come in all sorts of interesting shapes. The two most numerous groups among them are flagellates and diatoms, and they are most numerous in early spring and autumn.
A separate group is formed by cyanobacteria, formerly also known as "blue-green algae". Currently, scientists have placed them among the bacteria. Cyanobacteria can release toxic substances into the water.
Bonus: Excessive growth of cyanobacteria
When seawater is the warmest, usually in July and August, cyanobacteria can start to multiply en masse. But it can also happen at other times. Clusters of cyanobacteria in seawater usually form green lumps. People who bathe in such water may develop a rash, swelling, and headache. Cattle or pets that drink water containing the bacteria from near-shore puddles may even die.
I now know that…
In the sea, the most numerous plants are various types of algae. Different groups of algae grow in zones at different depths. Green algae needs the most light, brown needs less, and red can do quite well in the darker water. The most important producers in the sea are unicellular algae called phytoplankton.
