Self-induced population crashes

Posted on March 26, 2010

The attached green alga Cladophora glomerata (L.) is extremely widespread around the world and often creates serious management problems in the form of nuisance blooms, especially where nutrient levels are high.  In temperate zones it grows rapidly in spring and early summer, with a crash in midsummer when beds of the alga are sloughed off.   While the factors affecting Cladophora growth are well understood, attempts to predict the timing and magnitude of the midsummer crash have had limited success.  Although high temperatures and  nutrient deficiency have been suggested as the main causes of  midsummer sloughing, recent studies indicate that self-shading is more important.  Cladophora beds can be very dense ( up to 1kg dry  matter / m2), and at densities above 50 g / m2, most incoming light is lost within the outer five cm of the bed.  As beds increase in size, the light reaching their base falls below the minimum level for metabolism, leading to cell deterioration, weakened filaments and a higher  risk of detachment.  This process is aggravated by other factors that reduce the amount of available light, such as changing day-length, cloud cover, turbidity and the growth of epiphytic algae on the surface of Cladophora plants.

Reference:   Higgins, S.N., Hecky, R.E. & Guildford, S.J.  2008.  The collapse of benthic macroalgal blooms in response to self-shading.   Freshwater Biology 53, 2557–2572.