Marine Education Society of Australasia Home Page

banner image for Life on Australian Seashores Website

Biological Factors

Food and Predation

For any organism to grow and flourish, it must consume a certain volume of nourishing food to not only sustain it, but also to increase size and produce offspring.

At the First Trophic Level in the sea, algae absorb nutrients through their fronds from the surrounding water and create energy by the fixation of carbon in the process of photosynthesis. Algae do not take in nutrients through their holdfasts, like flowering plants take in nutrients through their root systems.

At the Second Trophic Level are the algae grazers and filter feeders. Some animals eat macroalgae fronds, while others eat microalgae, scraped off moist rock surfaces, or filtered from the plankton. The filter feeders sift plankton and detritus out of the water using various netlike structures such as basket-like cirri or gills, and deposit feeders eat mud and sand to extract the organic matter.

At the Third Tropic Level are many animals that are First-Level Carnivores, capturing and eating other organisms. The predatory molluscs are an example. The Second-Level Carnivores include flesh-eating fish, mollusc-eating birds and humans.

Click here to visit the Energy Pyramid.

For animals in a marine environment there are many feeding types, including grazers, browsers, suspension feeders, deposit feeders, carnivores and omnivores.

Look up the meanings of these words in the Glossary,


Bennett, I. (1987) W. J. Dakin's classic study: Australian Seashores. Angus & Robertson, Sydney.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. New Holland, Sydney.

Underwood, A. J. & Chapman, M. G. (1993) Seashores: a beachcomber's guide. New South Wales University Press, Sydney.


Biological Factors
Oxygen & Respiration
Food and Predation

Home Page
Rocky Shores
Tidal Levels
Intertidal Zonation
Environmental Factors
Biological Factors
Feeding Relationships


photo of Keith DaveyLife on Australian Seashores
by Keith Davey (C) 2000

Learning Consultant - Media
The University of Newcastle

email at

Scientific Consultant: Phil Colman
site created 01.01.98 : updated 01.04.2000