LAUSR

Vertebrata lanosa is a small red epiphytic alga growing almost exclusively on Ascophyllum nodosum. It has recently gained attention as a food alga in the North Atlantic. We examined distribution of V. lanosa in relation to environmental factors, by measuring cover of A. nodosum and V. lanosa in sample quadrats at 27 stations in an area in southwestern Norway. The probability of finding high cover (hotspots) of V. lanosa (defined as scores of V. lanosa belonging to the upper 25 % of data) was analysed in relation to height above Chart Datum, wave exposure, cardinal direction, inclination and substratum type. The relationship between amount (cover or volume) of the host alga ( A. nodosum ) and cover of V. lanosa was also examined. A significant and positive relationship between high cover of V. lanosa and increasing wave exposure was found, which may be attributed to the fact that wave action can cause scrapes and wounds on A. nodosum branches, where spores of V. lanosa have higher chances of successful settlement and survival. The results also showed a significant negative impact of high cover or large volume of A. nodosum on V. lanosa . Finally, the probability of finding high cover of V. lanosa was highest in the middle part of the Ascophyllum zone. The results suggest that the epiphyte and its main host do not have completely overlapping habitat requirements, and that sheltered areas with high biomass of A. nodosum are likely to contain relatively little V. lanosa for harvesting.