Figure 4 - Mean change in optical density in each algal treatment. Dark grey bars show the feather-duster worm data, light grey bars the controls. Error bars display ±1 standard error. Asterisks show pairs with a significant difference. There was a significant difference between treatments and controls (ANOVA: F_2,40=9.74, P<0.001). The change in optical density observed in feather-duster worms provided with Nannochloropsis sp. (N3600, n=13, mean=0.328±0.049nm) was significantly different to the mean change observed in the control for that treatment (n=3, mean=0.162±0.080nm) (T-test; t₁₃=3.40, P=0.005). The change in optical density in T-Iso sp. (I1800, n=14, mean=0.285±0.060nm) was also significantly different to the control (n=3, mean=0.155±0.119nm) (T-test; t₁₄=2.17, P=0.048). There was no significant difference between the mean control and the treatment with the feather-duster worms in the Thalassiosira sp. (Tw1200, n=13,3) treatment.