Macroalgal physical structure predicts variation in some attributes of temperate fish assemblages better than macroalgal species composition

Abstract

The importance of vegetative habitat in influencing distribution patterns, species interactions, and biodiversity is well documented in marine ecosystems, yet most previous studies on macroalgal–fish relationships have focused on influences of density and identity of macroalgae, often ignoring how the unique physical structure provided by each alga contributes to patterns. We tested whether the distribution, abundance, and biomass of rocky reef fishes could be predicted as well or better by measures of physical structure of macroalgae than by species identity and abundance. Divers visually sampled fishes and macroalgae at seven sites spread over several km at Santa Catalina Island, California, over a 1-year period, to examine how the distribution patterns of fishes related to spatiotemporal differences in the macroalgal assemblage. We found that variation in the composition, density, and diversity of the fish assemblage was equally or better explained by macroalgal structure (total surface area and height) than by macroalgal species density. In contrast, biomass and vertical distribution of fishes were better predicted by macroalgal species identity and density than by macroalgal physical structure. Of the macroalgal attributes, surface area was the best predictor of fish abundance and multivariate assemblage structure (species and their densities). However, much of the spatiotemporal variation in the fish assemblage was not explained by macroalgae, indicating that even in habitats visually dominated by macroalgae, macrophytes are only one of many factors that drive spatiotemporal variation in community structure. Our results suggest that quantifying the physical structure provided by marine macroalgae can be more useful than macroalgal species identity in predicting some aspects of fish assemblage structure.

Intertidal habitat complexity influences the density of the non-native crabHemigrapsus sanguineus

“…The spatial arrangement of structural elements in the marine environment can influence the quality of a habitat as a refuge from predators ( Eggleston et al, 1990 ; Grabowski, 2004 ; Humphries, La Peyre & Decossas, 2011 ; Hesterberg et al, 2017 ; Longmire et al, 2021 ). For example, macroalgal species with complex structure support greater densities of epifauna ( Parker, Duffy & Orth, 2001 ) and fishes ( Srednick & Steele, 2022 ). In the rocky intertidal zone, the quality of the habitat as a refuge may vary depending on how the structural elements (rocks) are arranged and the amount of crevice space available between rocks.…”

Unlocking the richness of microalgae biodiversity for potential applications

“…They are categorized based on their size, with macroalgae being visible to the naked eye and microalgae being microscopic. Macroalgae, also known as seaweed, height can vary from a few cm and can reach up to 53 m in height if present in ideal conditions [1], such as the Ochrophyta genus Sargassum and Macrocystis [2,3]. Microscopic algae can range from 0.2-200 μm and are further classified into picoalgae (algae size between 2 and 5 μm), and microalgae [4,5].…”