Are kelp holdfasts islands on the ocean floor? indication for temporarily closed aggregations of peracarid crustaceans

During the colonisation process of islands, newly immigrating species often arrive as single individuals. Islands that have received single colonisers may subsequently harbour large populations of a species, while other islan ds may completely lack this species. Exchange between islands is limited, t hereby strongly affecting evolutionary processes. While this concept is wid ely used in the context of oceanic islands or habitat patches on the mainla nd, it is rarely used to explain and examine the distribution patterns of m arine invertebrates. Benthic marine organisms inhabiting patches with islan d-like features may also be restricted in their movements between patches. Once established in a patch, it may be more favourable to remain then rathe r than moving to another patch. Juveniles of species with direct developmen t may recruit to the island patch of their parents. Herein, we examined the peracarid fauna in patches: that have island-like features. i.e. kelp hold fasts. The number of peracarid species within an individual holdfast increa sed with its size. Similarly, the number of individuals per holdfast increa sed with holdfast size. However, several peracarid species showed a strongl y aggregated distribution pattern, being highly abundant in some holdfasts and almost completely absent in others. Our results suggest that these aggr egations of conspecifics may be a consequence of the peracarid reproductive biology: fully developed juveniles emerge from the female's marsupium and recruit to the immediate vicinity of their mother, showing little or no ten dency to emigrate towards other patches. At present, while it is not known how long peracarid aggregations within kelp holdfasts persist, our data sug gest that some juveniles may remain with the natal holdfast and possibly re produce therein. It is concluded that, during certain time periods, reprodu ction rates of peracarids in a holdfast may exceed their migration rates be tween holdfasts.