Disentangling the links between habitat complexity and biodiversity in a kelp‐dominated subantarctic community

Habitat complexity is one of the most important factors modulating species
diversity. This feature comprises several interrelated attributes, such as
number, size, and spatial arrangement of complexity-forming elements.
However, the separate and joint effects of these attributes on diversity
and community structure are still not well understood. Here, we assess the
relationships between several structural-complexity attributes of the
subantarctic kelp Lessonia flavicans and species richness, total
abundance, and structure of kelp-associated macrobenthic communities. We
predicted that longer thalli and larger holdfasts favour greater species
richness and total abundance of invertebrate organisms. To test the
prediction, an observational sampling program was established in two sites
of the Strait of Magellan. Uni- and multivariate analyses revealed both
positive and negative effects of kelp structural-complexity attributes on
diversity. Holdfast diameter and maximum frond length, followed by thallus
wet weight, had the strongest positive fits to species richness and total
abundance; the number of stipes, on the other hand, was negatively
associated with both response variables. Longer fronds were associated
with greater abundances of spirorbid polychaetes. Larger holdfasts
supported larger abundances of Nereididae and Terebelidae polychaetes and
the limpet Nacella mytilina. Contrarily, kelps with longer fronds and more
stipes supported fewer amphipods. In this way, we demonstrate that
different dimensions of habitat complexity can have contrasting effects on
diversity and community structure, highlighting the fundamental role of
multiple dimensions of kelp habitat complexity for local biodiversity.