| dc.description.abstract | Variation in settlement and recruitment of the barnacle Semibalanus balanoides (L.) was
experimentally investigated in the high, mid and low intertidal zones at 2 adjacent sites (A and B)
on a rocky shore in Nova Scotia, Canada, following a rare occurrence of ice-scouring. Manipulations
in 100 cm2 quadrats at each intertidal height involved removal of various components of the sessile
macrofauna and macroflora, removal of the total community and a control treatment. The availability
of free space on the substratum in each quadrat was measured prior to the onset of settlement to
determine whether differences in the density of barnacles among treatments were due to differences
in the availability of free space or to manipulation. Where the density of settlers was high, it was
positively related to the availability of free space suggesting that settlement was a simple
function of the availability of free space. However, the pattern of settlement varied from the onset
to the end of settlement: quadrats from which only barnacles had been removed were occupied early in
the settlement period and later-arriving larvae were restricted to less favourable sites where free
space was available. Thus, settlement preferences may be masked when the supply of larvae is
saturating or the duration of the selction experiment is too long. Where the density of settlers was
low and free space was non-limiting, there was no relationship between the density of settlers and
the availability of free space. In the high intertidal zone at Site A, the density of settlers was
greater in treatments with ephemeral algae (wetter quadrats) than in those without (drier quadrats).
In general, early post-settlement mortality in treatments where algae had been removed increased
with intertidal height, whereas in treatments where algae were present it remained relatively
constant among heights. Post-recruitment mortality did not differ significantly among treatments in
the high intertidal zone, suggesting that factors which influence selection of the substratum by
cyprid larvae and promote early post-settlement survival may be particularly important in
determining subsequent population structure of barnacles in this zone. Post-recruitment mortality,
mainly due to predation by whelks, was highest in the low intertidal zone at both sites and did not
differ significantly between treatments. In the mid intertidal zone at Site B, whelk foraging
appeared to be constrained by desiccation stress and post-recruitment mortality was highest in
treatments with Fucus spp. Where predation is intense, initial selection of the substratum by cyprid
larvae may have little effect on the subsequent population structure of barnacles. | en_US |
