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To test the efficacy of seaweed taxonomic relatedness and morphological/functionalgroup membership as predictors of host-use by invertebrate epifauna, I sampled invertebrate assemblages associated with 1652 individual thalli across 32 species of seaweed. Additionally, I tested whether seaweeds within the same functional group had the potential, in the context of species loss, to functionally replace each other as habitat. In total, I found 54 776 individuals across 98 taxa of invertebrates. Similarity of invertebrate assemblages did not decrease as taxonomic distances between seaweed hosts increased; invertebrate assemblages were as different on sibling algal species as on hosts classified in different kingdoms. The utility of seaweeds as hosts for mobile invertebrates varied across components of invertebrate diversity. Invertebrate assemblage composition was different across most algal functional groups, whereas invertebrate taxon richness was different for ca. 25% of functional groups, and no differences in invertebrate abundance across algal functional groups were observed. There was substantial variation in host-use within seaweed functional groups, suggesting that overall functional group performance indicates little about the performance of the constituent species. Specifically, composition, richness and abundance of invertebrate assemblages were different across most hosts within each algal functional group. Therefore, in the event of seaweed species loss, replacements by members of the same functional group generally appear unlikely. These observations bring into question the use of general frameworks for predicting performance of seaweeds as hosts for associated invertebrates; it appears that invertebrate selection of seaweed hosts is largely dependent upon the identity of the host species.KEY WORDS: Seaweed · Invertebrate · Habitat · Taxonomic relatedness · Functional groups Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 387: [125][126][127][128][129][130][131][132][133][134][135][136] 2009 Criteria for epifauna host choice include factors internal to seaweeds: material properties such as cell structure and cell wall components, energetic storage products, and defensive biochemistry (Hay et al. 1987, Graham & Wilcox 2000, Padilla & Allen 2000, Van Alstyne & Houser 2003. These properties vary across seaweeds, resulting in differences in nutritive value and palatability (Paine & Vadas 1969, Hawkins & Hartnoll 1983. In addition to negatively acting to directly deter epifauna (Hay et al. 1987), algal defensive biochemistry can act positively to promote epifauna by conferring associational defenses: e.g. unpalatable algae are avoided by omnivorous fishes, and epifauna therefore escape predation (Hay et al. 1990). Along with these internal seaweed features, epifauna also select seaweed hosts based on external features. Architectural complexity of overall seaweed form has widely been linked to abundance and richness of invertebrates (Dean & Connel...

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Anthropogenic changes in many components of the Bay of Fundy biota have recently been reported, however a detailed assessment of benthic seaweed biodiversity has not been performed since the late 1970s. Here, we summarize 7 years (2000–2006) of temporal and spatial variation in species richness, composition, and percent cover of intertidal seaweeds in the outer Bay of Fundy, New Brunswick, Canada. In doing so, we provide up-to-date baseline records using repeatable and well-documented protocols. We document the presence of 72 species of seaweeds across four sites, and demonstrate that the biota at one of our sites is indicative of a degraded assemblage: large patches of unutilized substrate, low algal richness and abundance, with assemblages composed of hardy algal species and grazing and filter feeding invertebrates. Additionally, we compare these contemporary data with historical presence–absence records compiled from herbarium collections (1954–1978) and site surveys from 1963 to 1964 and 1978. Comparisons reveal 16 species not relocated in contemporary surveys. However, conclusions of anthropogenic changes in seaweed biodiversity are difficult to assess in the absence of high quality baseline information, and seaweeds historically found but not relocated in current sampling are easily misidentified, subtidal, or rare. We discuss the nature and value of baseline data, and make suggestions for future research.