Sharks in the forest: relationships between kelp physical-complexity attributes and egg deposition sites of the red-spotted catshark

Foundational organisms, such as corals, mangroves, and kelps, form structurally complex habitats in multiple coastal ecosystems of the world. However, habitat complexity comprises several interrelated attributes, such as number, size, and spatial arrangement of complexity-forming elements. Understanding the roles of these attributes in determining how associated organisms use biogenic habitats remains an elusive task. Here, we assessed the relationships between several structural-complexity attributes of the kelp Lessonia trabeculata and the abundance and distribution of egg depositions by the red-spotted catshark Schroederichthys chilensis. Over 1 yr, we conducted seasonal SCUBA surveys (i.e. ca. every 10 wk) of egg capsule depositions across individual and patch scales. The number of eggs per kelp plant was modeled as a function of kelp maximum frond length, holdfast diameter, number of stipes, percentage cover, plant density, and plant aggregation. The analysis of zero-inflated generalized linear models and second-order Akaike’s information criterion indicated that the models incorporating maximum frond length and percentage cover consistently showed the best balance between fit and complexity. In general, these attributes were positively, but not necessarily linearly, linked to egg counts. The presence of egg capsules in advanced developmental stages at the end of the year indicated a high temporal persistence of eggs, particularly those occurring in taller, thicker kelps. These findings suggest that catsharks select for taller, physically stable, and thicker kelps to deposit egg capsules. Moreover, our results allow us to enhance the accuracy of the definition of shark nursery grounds, a central concept for shark conservation.