Fertilization can promote the growth of thread-like algae. These algae can cover large parts of the seaweed and bottom where the young plants attach and grow. Thread-like algae can also favour certain grazing animals (mostly periwinkles and crustaceans), which can cause immense damage to the seaweed. Protect themselves with poisons and mucus Bladder wrack attempts to protect itself against grazers and other attaching algae by secreting poisons (i.e. phenols) and a mucus slem. By touching the younger parts of the seaweed, it is easy to feel the slimy mucus. It is the most upper and younger parts that are of importance for photosynthesis and reproduction.     Bladder wrack is perennial and can be as old as 10 years in the deeper parts of the Baltic. Sometimes it is possible to determine a plants age by counting the shoots between it branches. The plants grow at the top of each branch, and if bladders form, they occur early in the year. Therefore, the bladders are found at the bottom of each shoot. This method of determining its age is somewhat uncertain, especially in areas where ice can wear and tear the branches. In such a situation, new branches with bladders can grow out of bladderless stumps that are several years old. Eggs and sperm at the top Eggs and sperm form on different individuals. Reproductive organs develope in recepticles that are situated at the top of fertile shoots. Sometimes these shoots are short with many branches. Such a shoot is shown on the left-hand side of the presentation page.     Bladder wrack usually starts developing recepticles during the autumn, when the daylight hours became shorter. In the recepticles are small vase shaped formations where eggs or sperm develope. During the following summer the organs are usually fully developed and the contents are released in large quantities. A female plant can release more than 1 million eggs. The contents of these organs are usually squeezed out together with a mucus secretion while the plant is drying at low tide. Fertilization then takes place either in the water or on the bottom because the eggs are heavy and sink to the bottom close to the mother plant. From the fertilized egg, a male or a female plant grows. Page 3 of 4
Close to the water surface
Endures drought and cold
Home for many
Thread-like algae take over
Protect themselves with poison and mucus
Eggs and sperm at the top
Bladder wrack without bladders

Bladder wrack     More facts     Other names

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson