Rapid assessment of tissue nitrogen in cultivated Gracilaria gracilis (Rhodophyta) and Ulva lactuca (Chlorophyta)

Abstract

Tissue nitrogen content and thallus colour were quantified using a rapid assessment method based on the Pantone^®matt uncoated formula guide for raft-cultivated Gracilaria gracilis Steentoft, Irvine et Farnham at Saldanha Bay and tank-cultivated Ulva lactuca Linnaeus at Jacobsbaai in 2001–2002. For Gracilaria a relationship between thallus colour and tissue nitrogen, as well as a transition between green-yellows and yellow-browns that occurs between 0.8 and 1.3 mg N per g tissue (Pantone^® colours 460U–455U), was found, with the green-yellow colours indicating nitrogen-starved material and the yellow-browns indicating nitrogen-replete material. For Ulva a transition between green-yellow and green  occurred at a tissue nitrogen content of between 1.5 and 1.7 mg N per g tissue (Pantone^®colours 585U–583U). This  elationship can be used by seaweed farmers for cultivation management as a quick guide to determine nutritional status of the seaweeds, and as an indication of protein content when the seaweeds are used as feeds.

Keywords: cultivated seaweeds, Pantone^®; thallus colour; tissue nitrogen

African Journal of Aquatic Science 2009, 34(2): 169–172