The occurrence of the pod weed, Halidrys siliquosa, is recorded for thefirst time on the Portuguese coast. Several specimens of this brown algae were observedattached to the rocky surface in tide pools at 41º44′10″N8º52′34″W, extending southward its previously knowngeographical distribution. The observed shift is inconsistent with general predictions ofspecies migrations under warming climate conditions, which anticipate poleward shiftsrather than southern expansions. Although more data will be required to undoubtedlyuncover its cause, the recently observed range expansion raises important questions aboutthe generalization of the previously stated biogeographic rules.
