The main aim is to work out the total dry biomass of each species at each tropic level. This can be presented in a pyramid of numbers or biomass and energy efficiency caluclations. Sampling at the rocky shore can be difficult because of the organisms present. It is not appropriate just to measure the abundance of different organisms as you would in a freshwater environment.


  • A sampling tray
  • D frame net
  • Identification guides, such as the freshwater invertebrate fold-out chart
  • Hand lens, plastic spoon and/or pipette
  • Equipment for measuring abiotic factors (e.g. velocity, depth, water temperature, water pH, oxygen, nitrate content, light)


Care should be taken when working in marine environments. Tides and weather conditions can change quickly. Always check tide times when planning fieldwork at the coast. Wear waterproof trousers and wellington boots. Do not work by yourself.

Summary of procedure

  • Brown seaweeds – select up to 10 algae ‘clumps’ from each quadrat (do not remove from substrate) Each ‘clump’ is a separate alga, so look for the holdfast to be sure it is separate. For each clump measure the longest frond and identify number of fronds
  • Green and red seaweeds – these can be recorded as percentage cover
  • Non-sessile organisms – organisms that can be picked up and collected into a pot. For each species separately: collect into a pot and weigh using the pan balance. Make sure you weigh the pot before and subtract the weight of the pot. Fish can be weighed with water in the pot and subtract the weight of the water. Or estimate length.
  • Sessile organisms – organisms that cannot be removed from the rock, such as limpets, anemomes and barnacles.
    Limpets: measure the size and number of the limpets; Anemones: measure basal diameter of up to 10 individuals and also note number; Barnacles: estimate abundance using SACFOR.

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