Risk taking in Semibalanus balanoides

Abstract

This thesis examined factors influencing the success of the larval cyprid phase, and the distribution of adult Semibalanus balanoides in the Clyde Sea. Experiments were conducted in the Clyde Sea area (2004 – 2007) because it is effectively both a closed system in its whole extent for release of nauplii and cypris settlement, and at a larger scale it is an open system for the actual settlement on individual rock types. The effect of geology, exposure and position on the shore is examined in relation to barnacle fecundity (number of eggs produced) with metamorphic rock, exposed shores and mid shore settlement of Semibalanus balanoides having higher barnacle fecundity than igneous and sedimentary rock types, sheltered shores and upper or lower shore height areas. Frustum volume was found to be a reliable non-destructive way to estimate fecundity, and egg size did not alter significantly from year to year. Supply was most reliably measured using pumps or adhesive panels, and artificial rock panels as an alternative to natural rock; the majority of cypris left after four seconds investigating artificial panels. Cannibalism takes place in the Clyde Sea with 44 % of adults investigated on the shore showing signs of this, frustum size and height didn’t affect propensity to cannibalise. Video recording demonstrated a mean of nine cypris and / or nauplii consumed per adult per hour. Settlement occurred on all major rock types in the Clyde Sea. Cypris preferentially settled on metamorphic and igneous rock types. There was no significant effect of north or south orientation on vertical panels for settlement intensification. Settlement levels were higher on natural rock substratum than artificial panels, but were not significantly different; and showed larger per area settlement on smaller areas as 1 cm2 had a mean settlement of 49.40 cypris, 5 cm² 18.40, 10 cm² 22.42, 50 cm² 13.92, 100 cm² 9.34 and 500 cm2 5.65. On natural rock around the Clyde Sea (as opposed to areas cleared for experiments), areas of < 1 cm² and 1 cm² are more common as potential settlement sites, comprising of 51.99 % and 23.98 %, respectively of available settlement area. The mean number of barnacles in the Clyde Sea area was calculated to be 9.454 x 10¹¹, which could produce a mean number of 1.444 x 10¹⁵ eggs.