Spatial and temporal patterns in barnacle settlement rate along a southern California rocky shore

Abstract

Barnacle settlement was monitored at 5 sites separated by 50 to 250 m a t Dike Rock, La Jolla, California, USA. Chthamalus spp. and Pollicipes polymerus settlement were spatially correlated at those sites. Within sites, settlement of the 2 species were correlated These results support the hypothesis of common onshore larval transport events for all sites and both species. Other spatiotemporal patterns were contrasting: 1 peak accounted for most of P polymerus settlement, while there were 5 peaks of similar magnitude for Chthamalus spp. At 2 sites, settlement plates were installed at 2 heights in the intertidal; Chthamalus spp. settlement was similar at the 2 heights, while P polyn~erus settlement was relatively different at the sites. Such spatial patterns may have resulted from a stronger behavioral component affecting settlement in P polymerus. These results suggest that, at scales of 100 m, temporal variability in settlement rate may be related to larval pool and physical transport processes, while spatial vanabllity may be associated with behavioral response and substrate availability. Chthamalus spp. settlement was hlgher at sites where rocks were surrounded by unsuitable sandy substrate, possibly because settlement on available substrate is intensified where total suitable settlement area is relatively scarce To test this, plates were installed at another site where suitable substrate was also scarce, as predicted, settlement was higher at both sites. At another study slte in Medio Camino, Mexico, settlement became more predictable anlong sites along the rocky shore after the shoreline had been partially inundated by sand, further supporting this hypothesis. The proportion of unmetamorphosed settlers of Chthamalus spp., relative to total settlement, appeared to peak on particular days of the lunar cycle and was spatially correlated at the 5 sites. The periodicity of the peaks was close to the 14.75 d spnng-to-neap cycle, suggesting that these peaks may be related to periodic shortimmersion hmes that did not allow the attached cypnds to metamorphose. Mortality of recently metamorphosed ( 5 l d ) Chthamalus spp. spat by physical damage was spatially vanable.

Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

“…Field and laboratory research 13 supports that settlement of barnacles and mussels intensifies where there is less area of suitable 14 substrate (Bertness et al, 1992;Pineda, 1994a;Osman and Whitlatch, 1995a;Hunt and 15 Scheibling, 1996;Pineda and Caswell, 1997;Berntsson et al, 2004;Rilov et al, 2008). No 16 evidence of intensification was found, however, where adult density was low and settlement 17 sparse (Jeffery, 2000).…”

“…Larvae may transport to a 13 site, but a large portion may be preyed upon before settlement (Alfaro, 2006;Porri et al, 2008a), 14 and fewer larvae may settle in sites where there are no settlement cues (Knight-Jones and 15 Stevenson, 1950;Hills et al, 1998). Similarly, consistent temporal (seasonal, Bertness et al, 16 1992;Pineda, 1994a) and spatial variability in settlement among sites separated from meters to 17 tens of kilometers (Pineda, 1994a and pers. obs.…”

“…;Rilov et al, 2008, see also Berntsson et al,18 2004) may be the result of settlement intensification due to variability in suitable area at 19 commensurate scales (Pineda and Caswell, 1997), instead of differential physical transport, 20 supply, or reproductive patterns during the season and among sites. Among nearby sites with 21 similar larval supply but differing availability or quality of substrate area for settlement (i.e., 22 sites separated 10's m, Pineda, 1994a), intensification could be predictable at some temporal and 1 spatial scales, and consistency in species interactions at those scales may also be expected. 2…”

“…In the rocky intertidal, placement choices that will differ in delivery of larval and settlement, 4 include vertical or horizontal surfaces, degree of exposure to waves, and tidal height (Porri et al, 5 2007;Porri et al, 2008b). These differences, however, are sometimes smoothed out by 6 settlement larval behavior (Pineda, 1994a). Another approach has been to place settlement 7 substrates on mooring lines (e.g., Dobrestov and Miron, 2001;Rilov et al, 2008;Dudas et al, 8 2009).…”

“…So, searching larvae must settle 11 more intensively per unit area available (Pineda, 1994a;Pineda and Caswell, 1997). 12…”