Chapter 19, Problem 32A

Summary Introduction

To analyze : 

The contrasting characters of freshwater algae and marine algae.

Introduction :

Algae are the simplest thallus photosynthetic organisms. They are usually aquatic, either marine or freshwater.

Explanation of Solution

Marine algae are known as seaweeds and can be present in shallow as well as deep water. Marine algae exhibit an endosymbiotic relationship with some marine invertebrates and help in the building of coral reefs. Spores of the marine algae are spread by ocean currents. Marine algae present in the deep regions of oceans and seas have secondary pigments (fucoxanthin, phycobilins, carotenes, xanthophylls, etc) to carry out photosynthesis which allows them to absorb light energy at greater depths. Most of them serve as primary producers and provide the food base to marine food chains. Some of them may even form blooms and decrease the oxygen concentration of seas and oceans leading to the formation of dead zones.

Freshwater algae mostly belong to Chlorophyceae and can grow in shallow (subaerial) or deep waters. The spores of the freshwater algae found on freshwater are dispersed by running water and wind. They are more abundant in slowly flowing streams. Cyanobacteria inhabit freshwater habitats and form blooms in nutrient-rich standing waters. In the littoral zones of lakes, green algae form free-floating mats. Desmids are common in ponds and streams with moderate nutrient levels. It intermingles with filamentous algae.

Conclusion

The main contrasting feature of freshwater and marine algae is their wild habitat. Marine algae have developed tolerance to the high salt concentrations and adapted to the marine habitat. Freshwater algae can be submerged or subaerial. They may even be present in the littoral zones.