Macrobenthos of the nearshore Aleutian Archipelago, with emphasis on invertebrates associated with Clathromorphum nereostratum (Rhodophyta, Corallinaceae)

In the Aleutian Islands, Alaska, crustose coralline algae can be widespread in the low intertidal and shallow subtidal regions, and cover most available hard substrates. The longevity and slow growth-rate of coralline algae make them vulnerable to major disturbances, including anthropogenic disturbances and ocean acidification. Subtidal habitats dominated by crustose coralline algae are often associated with sea urchin-barren grounds and regarded as supporting limited invertebrate communities, especially compared with the adjacent kelp forests. Clathromorphum nereostratum is one of the most abundant crustose coralline algae found in the Aleutian Islands. Although the surface of this crustose alga exhibits little structural complexity, it can develop into crusts half-a-meter thick (2-10 cm in this study) that provide microhabitats for a variety of cryptic invertebrates. Despite the omnipresence of this alga throughout the nearshore Aleutians, very little is known about its associated faunal community. In the summers of 2006 and 2007, a benthic survey was conducted at 50 sites throughout the shallow (<20 m), nearshore Aleutian Islands as part of the Alaska Monitoring and Assessment Program. The habitat encountered at each site was categorized as soft sediment, macroalgae-dominated, or crustose coralline-dominated. At each site, scuba divers sampled three 0.06-m2 quadrats. Invertebrate communities associated with thick crustose coralline algae were compared with soft-sediment and macroalgae-dominated communities based on faunal abundance and diversity. Despite the depauperate appearance of crustose habitats, this study revealed that crustose environments support faunal communities as diverse and abundant as those found in rich macroalgal habitats.