Chapter 7 – Methods for the measurement of seagrass abundance and depth distribution

This chapter introduces simple and robust methods for quantifying seagrass abundance in the presence or absence of clear environmental gradients. It also provides the suitable descriptors of seagrass abundance and describes approaches to quantify this at the appropriate scales. Seagrass biomass is best obtained seasonally for any baseline study, using different approaches, depending on the resources available. The above ground biomass of seagrass meadows may be estimated by taking or measuring, at random, a suitable number of quadrats of an adequate size. The determination of meadow biomass requires the knowledge of the cover and approximate dimensions of the seagrass meadow and the selection of two or more sites in the area where the random quadrats are measured or harvested. Whenever the area is too large to allow adequate coverage through direct biomass harvesting, or when harvesting is restricted, a relationship between biomass and a ranked estimate of biomass can be determined by developing a regression equation from a small number of destructive samples. All of the above- and belowground plant material within the quadrats must be efficiently collected, cleaned of debris and epiphytes, dried and weighed to quantify biomass. Sampling seagrass requires a specific research question before it is commenced.