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March 2012

What could possibly live in beach sand?

While on holiday at the coast, we came across a group of university students collecting sand samples on the beach.  We inquired about their activities and they said they were collecting animals from the sand for environmental monitoring.  As they looked very busy we left them to their work, but what type of animals could possibly be living in the beach sand?  We couldn’t see anything after running the sand through our fingers?


Bristle worms or Polychaeta
Photo: Shona Marks
Sea fleas or Amphipoda
Photo: Shona Marks
Pillbugs or Isopoda
Photo: Shona Marks
A mixture of snails (Gastropoda) and clams (Bivalvia)
Photo: Shona Marks

It may not seem like there are any animals living in beach sand, but the sand is alive
with very tiny invertebrates. These animals are sometimes so small we need a microscope to see them. We can’t list all the types of animals but I can describe a few of the larger, more common groups. The photographs of these animals are all taken under high magnification.

Bristle worms (Polychaeta) are more common in wet soil at the waters edge. Polychaetes are the largest group of true worms; they are closely related to earthworms and leeches. They can be scavengers, predators, grazers or filter feeders and play an important role in sediment bioturbation.

Sea fleas (Amphipoda) are a very large group of Crustacean, having about 8000 named species. The males usually have very large claws (gnathopods) to hold onto females when mating. They are mostly found in marine habitats feeding on algae. Some species live on land these are called land hoppers.

Pillbugs (Isopoda) are also a type of Crustacean. They are similar to amphipods but their bodies are flattened from top to bottom. They are most commonly found in marine habitats feeding on decaying material. Some species live on land these are called slaters.

Clams and snails (Gastropoda and Bivalvia) are the largest group of Mollusca. There are about 70,000 gastropods species currently named and about 10,000 bivalves named. Gastropods have a variety of feeding behaviours, some are predators and others are grazers feeding on algae. Bivalves are mostly filter feeders taking food particles from the water column. They are both found in marine and fresh water and on land.

Scientist and ecologists collect these and other animals from the sediment of aquatic environments in monitoring and research projects. If there is a change in the number of animals or the species present then this indicates to the researchers that there maybe a change in the environment or habitat and we need to look more closely at what is going on. The change could be natural or man made.

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