The effect of body size on the feeding current and prey spectrum of the barnacle Amphibalanus improvisus

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Abstract
Barnacles capture prey with a cirral fan filter that is swept through the water. As the barnacles grow, the cirral fan experiences changing flow regimes, both at the level of the filter elements (Reynolds number ~ 0.01 to ~ 1) and of the cirral fan (~ 1 to ~ 100). Here, we examined the implications of barnacle size on feeding current and clearance rate as a function of filter characteristics and prey size in the barnacle Amphibalanus improvisus . The feeding current is near fore‐aft symmetric in newly settled individuals but becomes increasingly asymmetric with size. Thus, in large specimens, most flow arrives from the sides, uninterrupted by the beating fan, while in small individuals most incoming flow passes the beating fan, warning evasive prey. This change is consistent with reports of an ontogenetic change in the diet from passive phytoplankton to inclusion of evasive prey. The leakiness of the filter increases during development, from 52% to 83%, and it thus functions both as a paddle that moves water, and as a filter that strains prey from the water. Clearance rates increase with the size of the barnacle, from 20 to > 500 mL ind −1 h −1 , orders of magnitude higher than reported earlier for similarly sized barnacles. Clearance rates also increase with prey size, saturating at particle sizes of about 80 μ m or more. Barnacles thus occupy a different niche than most other co‐occurring benthic suspension feeders that retain prey down to a few microns in size.
Funding Information
  • Villum Fonden

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