Bristle worms are a common invertebrate found in marine environments and aquariums, and can range in size from under a centimeter to over a meter depending on the species. They are largely scavengers, and are often seen feeding on rotting plant matter and dead animals, hence a common misconception that they kill fish and are undesirable in a marine aquarium. They arrive undetected in aquariums on stones, sediment and other commonly used display pieces. Bristle worms are classified to the class Polychaeta, which consists of around 10 000 species globally, and has been radiating into various marine and freshwater aquatic environments from the Cambrian¹.

The materials used in this experiment include 4 10cm Petri dishes, pipettes, seawater, and dead mussels for bait.

The experiment was conducted over 3 days across 3 weeks, and a number of worms were selected each week from a large aquarium population. To test the hypothesis of aggregations of Bristle worms being more efficient at locating food then lone individuals, groups of 1, 3, 5, and 10 worms were placed in separate Petri dishes along with a piece of mussel flesh around 1.5 centimeters in diameter. Worms were dropped in by the wall of the dish and the mussel was placed in the center of the dish. One randomly selected worm was observed over a 10 minute period, and a count of feeding was noted for the individual. Other notes taken included the initial feeding of any of the worms in the dish and the total number of feeding of all individuals over the 10 minutes.

The worms available for this experiment were not full size only ranging from approximately 0.5-3 centimeters in length rather than the maximum length for this species of around 10cm. Variation in the size of worms was compensated for by randomly selecting individuals from the aquarium population sample. Variation in any aspect of the bait was addressed by only using parts of the foot of the mussel in the tests, and using pieces of the same size.

Analysis was done in excel, using a single factor ANOVA foreach of the three separate data groups in the experiment. 

After running an ANOVA for each of the three variables, no significant results were found other than the ‘total feeding’ and ‘initial feeding’ counts(p-value= 0.05 & p-value = 0.04 respectively). The analysis for these 2 variables did not take into account the fact there were 10 times more worm in the fourth dish then the first, resulting in 10 times the possibility of a worm locating the food. These variables were subsequently not used.

The results for the analysis on the focal individuals found no significance, p-value = 0.45, F=0.898, however a trend can be seen in the graph in figure 1. The ANOVA output for focal worm feeding is shown in figure 2.

The p-value (0.45) for focal worm feeding shows no statistical significance across the 4 petri dishes. There is a slight trend towards increased focal worm feeding in larger groups that can be seen in figure 1, however this cannot be attributed to the effects of larger aggregations of worms based on the results of the ANOVA. None of the worms in petri dishes by themselves found the bait, and worms were more active overall when in groups, even their movement was simply moving around the perimeter of the dish rather than locating the bait.

Other than the fact there is only a small sample size due totime constraints, there are possible explanations for this slight trend in thedata. Firstly, a 10 minute observation period may not have provided sufficient timefor worms to react to stimuli and locate the food, and if this time bracket wasdoubled, worms that were not active at all during the 10 minute observation periodmay have sufficient time. Secondly, interactions between worms may have simplycaused more movement overall within larger groups, with an increase in wormsfinding the bait being a byproduct of increased activity of the worms.

A study by Jumars et. al. found that there are differencesbetween bristle worm species in relation to the particle size they will swallow^[6].Macrophagy is the term for species that swallow larger particles whole, versusMicrophagy which is the species that can only consume fine food particles. Asit is not known specifically how Eurythoecomplanata consumes food, the bait may have been inappropriate for the sizeof the individuals tested.

Further study needs to be done on this species to better understand its habits, and various improvement could be made to this experiment, both in the experimental design and data collection. Improvements to experimental design would be the use of a starvation period prior to the experiment to increase feeding behavior, and to provide a substrate in the dish as the worms had some difficulty moving on the clean petri dish, slowing their movements.

Larger bristle worm feeding

I would like to thank the tutors and students who provided assistance with this project. In particular Bernie Degnan and Sandie Degnan for guidance with experimental design, access to the aquarium, and lab equipment,and the assistant tutors (Dylan, Tahsha, and Eunice) for further help with running the experiment. 

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Photos: http://www.roboastra.com/Worms/hpwo393.htm