Zoöp Observations: Green algaeZoöp Observations: Green algae

Hardly anyone could have missed it: the remodeled and beautiful replanted ponds of The New Institute suffer from exactly the same ailment as the previous ones: filamentous green algae of the genus Cladophora. Fifteen species of this genus are currently known in the Netherlands. They are only distinguishable from each other through a microscope. Filamentous green algae start to feel soft and a little slimy to the touch as you move your hand through them in the water. A modest growth of Cladophora is generally harmless, but as soon as the algae start to form floating mats, problems arise. The floating mats prevent circulation that is necessary for the aeration of deeper water and, by blocking the light, they kill photosynthesising organisms growing beneath.

Filamentous green algae continually form new spores as they grow. That is why removing this algae manually – which has already been done twice this year – only helps for a short time. There are various pesticides on the market against filamentous green algae, some based on copper sulphate and/or zinc oxide (also toxic to snails and other invertebrates!), others in the form of mineral clay granules with phosphate-binding agents that make ponds less nutrient-rich. A few pond enthusiasts swear by the use of tea (1 tea bag per 100,000 liters of water) and others by floating barley straw (maximum 50 grams per square meter of surface). However, the most natural and effective control of filamentous green algae is to increase the hardness of the water. However, that would mean other aquatic plants won’t grow as quickly as they do now.

In Laos, in the Mekong river basin, filamentous algae of the genus Cladophora are eaten in the form of dried and flash fried sheets (so-called kaipen), somewhat similar to the sheets of Japanese seaweed (nori) that everyone knows from sushi.