The effects of light intensity and algae-induced turbidity on feeding behaviour of larval striped trumpeter

Striped trumpeter larvae reared in algal cell-induced turbid water (greenwater) fed equally well in clearwater in a light intensity range of 1–10 mol s1 m2, when evaluated in terms of both the proportion of larvae feeding and larval feeding intensity. An ontogenetic improvement in photopic visual sensitivity of larvae was indicated by improved feeding at 0·1 mol s1 m2, from 265% of larvae feeding and 0·0270·005 rotifers consumed per feeding larva min1 on day 8, to 962% and 0·2210·007 rotifers consumed larva1 min1 on day 23 post-hatching. Algal cell-induced turbidity was shown to reduce incident irradiance with depth, indicated by increasing coefficients of attenuation (1·4–33·1) with increasing cell densities (0–2106 cells ml1), though light intensities in the feeding experiment test chambers, at the algal cell densities tested, were within the optimal range for feeding (1–10 mol s1 m2). Algae-induced turbidity had different effects on larval feeding response dependent upon the previous visual environment of the larvae. Young larvae (day 9 post-hatching) reared in clearwater showed decreased feeding capabilities with increasing turbidity, from 981% feeding and 0·1530·022 rotifers consumed larva1 min1 in clearwater to 6110% feeding and 0·0420·004 rotifers consumed larva1 min1 at 56 NTU, while older clearwater reared larvae fed well at all turbidities tested. Likewise, greenwater reared larvae had increased feeding capabilities in the highest algal cell densities tested (32 and 66 NTU) compared with those in low algal cell density (6 NTU), and clearwater (0·7 NTU) to which they were naïve