Competitive dominance among sessile marine organisms in a high Arctic boulder community

Abstract

In most hard substrate environments, space is a limiting resource for sessile organisms. Competition for space is often high and is a structuring force within the community. In the Beaufort Sea's Boulder Patch, crustose coralline red algae are major space occupiers. This research determined if coralline algae were com- petitively dominant over other sessile organisms. To test this hypothesis, overgrowth was documented in terms of ''winners'' and ''losers'' on the contact borders between different species. Crustose corallines occurred in over 80% of the observed interactions but were only winners in approximately half of them. Most frequently, bry- ozoans, tunicates, and sponges were superior competi- tors over crustose corallines, while at the same time these invertebrate groups were among the least abundant space occupiers.