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Theoretical and empirical research during the last decade suggests that increasing species richness often enhances ecosystem processes such as productivity, nutrient cycling, or resistance to disturbance. By analogous reasoning, it can be hypothesized that genetic diversity within species will have equivalent effects; however, this hypothesis has rarely been tested. We present experimental support for the positive effects of intraspecific diversity on a key trait: larval settlement in a marine invertebrate, the barnacle Balanus improvisus. Varying within‐species diversity levels of an animal over nine experiments, we found increasing larval settlement with increasing diversity (one, two, or three parental broods). Possible mechanisms explaining this pattern include: (1) facilitation of gregarious response through the presence of founder genotypes, and (2) ensuring genetic complementarity to increase future reproductive potential. Our results indicate that changing intraspecific genetic diversity could have hitherto unrecognized community‐scale implications for larval recruitment and space occupancy.

Dispersal of propagules may have far-reaching consequences for the local dynamics of open populations. In aquatic environments the dispersal and supply of larvae is strongly influenced by coastal-scale hydrodynamics. The role of local flow on settlement and recruitment is, however, poorly understood. In a test of the effect of local hydrodynamics on recruitment dynamics we studied the relationships between local flow speed and larval supply, contact rate, settlement, and recruitment rates for the barnacle Balanus improvisus. Planktonic cyprid larvae were sampled with pumps while suspended panels were used to measure initial contact (grease-coated panels), settlement (5-d immersion), and recruitment (30-d immersion). Larval supply varied with coastal-scale upwelling but was uncorrelated to local flow speed. Settlement rate was highly correlated to contact rate, and the proportion of settling larvae increased with established recruit density. In contrast to model predictions, contact rate was negatively correlated with local flow speed, which explained 33% of total variation. This correlation was maintained through settlement and recruitment suggesting that flow-mediated initial contact is an important link between larval supply and recruitment. No evidence from field studies indicated behavioral responses by larvae to flow although observations in a laboratory flume suggested active rejection of potential settlement sites at increasing flow speeds. It is suggested that initial adhesion is limited by flow speed through drag and lift forces acting on larvae. A conceptual model of mechanisms controlling the transfer of planktonic larvae to recruited benthic individuals is proposed.

In this study room temperature vulcanized (RTV) silicone surfaces with designed surface microstructure and well-defined surface chemistry were prepared. Their resistance to marine macrofouling by barnacles Balanus improvisus was tested in field experiments for deducing optimal surface topography dimensions together with a better understanding of macrofouling mechanisms. Polydimethylsiloxane (PDMS) surfaces were microstructured by casting the PDMS pre-polymer on microfabricated molds. The master molds were made by utilizing photolithography and anisotropic etching of monocrystalline silicon wafers. Several iterative casting steps of PDMS and epoxy were used to produce large quantities of microstructured PDMS samples for field studies. The microstructured PDMS surface consisted of arrays of pyramids or riblets creating a surface arithmetic mean roughness ranging from 5 to 17 microm for different microstructure sizes and geometries, as determined by scanning electron microscopy. Chemophysical properties of the microstructured films were investigated by electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectroscopy and dynamic contact angle measurements. Films were chemically homogeneous down to the submicron level. Hydrophobicity and contact angle hysteresis increased with increased surface roughness. Field tests on the west coast of Sweden revealed that the microstructure containing the largest riblets (profile height 69 microm) reduced the settling of barnacles by 67%, whereas the smallest pyramids had no significant influence on settling compared to smooth PDMS surfaces. The effect of dimensions and geometry of the surface microstructures on the B. improvisus larvae settling is discussed.

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