The influence of small seaweed-mussel associations upon local-scale biodiversity at a Marine Protected Area in Atlantic Canada

In a time of accelerated species and habitat loss, understanding and protecting species and habitats that contribute to biodiversity is critical. A unique strain of the widespread Irish moss (Chondrus crispus), the giant Irish moss, is found exclusively in an Atlantic Canada Marine Protected Area. This strain lacks a holdfast, but its strands entangle with blue mussels (Mytilus edulis) to create small complex habitats (clumps) surrounded by extensive bare sediments, which may contribute to local invertebrate biodiversity. This study used a field survey to examine the community of macroinvertebrates that colonize giant Irish moss-mussel clumps (IMBM) and blue mussel clumps (BM) in comparison to those colonizing bare sediments. In addition, a field experiment quantified colonization rates on clumps prepared with live mussels and giant Irish moss and on artificial mimics of both types of clumps. Two hypotheses were tested: that more complex habitats support higher levels of invertebrate diversity, and that living clumps support higher diversity levels than mimics. The results supported both hypotheses. The survey showed that the most complex habitats (IMBM) are colonized by more diverse and abundant assemblages than BM clumps and bare sediments, and that the three of them differed in species composition and abundance. The results of the field experiment showed that living clumps supported greater diversity and abundance than mimics for both IMBM and BM habitats. Overall, giant Irish moss-blue mussel associations provided the best habitat for diverse and abundant local communities, so efforts to restore these near extinct patchy habitats should be further supported.