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

Abstract

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 favor 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.

Keywords: Kelp forest; Patagonia; benthic communities; biodiversity; habitat complexity.

FIGURE 1

Kelp Lessonia flavicans in the Strait of Magellan. Scheme (a) and photograph (b) depicting the sections of the kelp (frond, stipe, and holdfast). Lessonia flavicans belt‐shaped kelp forest in Bahía Buzos at 2 m depth (c). The scale bar in panel (a) equals 10 cm. Ilustration credit: Martin Mak; Photo credits: Catalina Velasco‐Charpentier

FIGURE 2

Map of the sampling sites, Bahía Buzos and Carrera (a), located in the Strait of Magellan (b), Chile (c)

FIGURE 3

Species richness (a) and total abundance (b) of mobile organisms associated with kelp Lessonia flavicans across austral seasons (November 2018–August 2019) and two sites, Bahía Buzos and Carrera, in the Strait of Magellan. ND, no data. Points represent the mean values (N = 10 kelps), while bars represent 95% confidence intervals (CI)

FIGURE 4

Standardized coefficients of generalized linear models including PCA axis, season and site for species richness (a) and total abundance (b) of kelp‐associated communities. Points represent the model parameters, while bars represent confidence intervals (CI). Red and blue symbols represent negative and positive standardized coefficients, respectively. CIs that do not cross 1 indicate statistically significant parameters. *Pairwise contrasts between sites (Carrera and Bahía Buzos) and between each year season and spring. The outputs are back transformed from the original log link (e = number of Euler, β = coefficient in log scale)

FIGURE 5

Canonical analysis of principal coordinates for community structure across quadrants. Red is for the kelp complexity attributes, green for sites and year seasons, and blue is for the associated species. Only species with |standardized scores| > 0.05 are shown to reduce distortions in the ordination. Darker dots indicate overlapping observations