Jonathan N. Flores, Nicolás Flaibani, M. Gabriela Palomo, Martín I. Brogger

Ecological role of the sea urchin Austrocidaris canaliculata (Cidaroida: Cidaridae) as a basibiont: Epibiont assemblages in the Marine Protected Area Namuncurá – Burdwood Bank and adjacent deep areas

Introduction

Ecological role of the sea urchin austrocidaris canaliculata (cidaroida: cidaridae) as a basibiont: epibiont assemblages in the marine protected area namuncurá – burdwood bank and adjacent deep areas. Study the sea urchin Austrocidaris canaliculata's ecological role as a basibiont. Analyze epibiont assemblages in MPA Namuncurá – Burdwood Bank and deep-sea, crucial for benthic communities.

Abstract

Organisms that provide settlement sites for sessile fauna play a key role in shaping the structure of benthic communities. Sea urchins of the order Cidaroida can offer these sites for settlement on their primary spines, which lack antifouling protection. In this study, the ecological role of Austrocidaris canaliculata (Cidaroida: Cidaridae) as a basibiont at the MPA Namuncurá – Burdwood Bank (MPA NBB) and adjacent deep-sea areas was evaluated. For this, we described the composition and the diversity of the epibiont assemblages within the MPA NBB and external deep-sea sites. Additionally, we analyzed the relationship between the size of A. canaliculata and the epibionts richness in these zones using generalized additive models. From the 120 specimens of A. canaliculata studied, epibiosis was recorded in 96.67%. A total of 39 epibiont taxa were identified, representing two kingdoms, 10 phyla, 13 classes, and 27 families, including new records of species in the study area. The highest epibiont species diversity observed was Bryozoa, followed by Cnidaria. The epibiont assemblages showed no significant differences in the estimated diversity within each zone, and the estimated epibiont richness was slightly higher in deep-sea areas. Finally, our modelling suggests that the epibiont richness is correlated with the horizontal diameter of the test, showing an opposite variation between shallow and deep-sea zones. This study provides detailed faunistic information on the epibionts associated with A. canaliculata from the MPA NBB and adjacent deep-sea areas, reinforcing the ecological role of cidaroids as basibionts in benthic ecosystems.

Review

This study meticulously investigates the ecological role of the sea urchin *Austrocidaris canaliculata* as a basibiont, focusing on the diversity and composition of epibiont assemblages within the Namuncurá – Burdwood Bank Marine Protected Area (MPA NBB) and adjacent deep-sea environments. The research successfully documents a remarkably high incidence of epibiosis (96.67%) on the primary spines of *A. canaliculata*, identifying a rich community of 39 epibiont taxa spanning multiple kingdoms and phyla, including several new species records for the study area. This detailed faunistic inventory significantly enhances our understanding of deep-sea biodiversity and the complex trophic and structural relationships in these often-understudied benthic ecosystems, reinforcing the critical ecological function of cidaroid urchins as key substrates. The methodology employed, including the description of epibiont composition and diversity, and the application of generalized additive models (GAMs) to explore relationships between host size and epibiont richness, is robust and appropriate for the study's objectives. Key findings reveal that while overall epibiont diversity did not significantly differ between zones, deep-sea areas exhibited slightly higher richness. Particularly intriguing is the discovery that the correlation between host horizontal test diameter and epibiont richness shows an opposite variation between shallow and deep-sea zones. This suggests complex, depth-dependent ecological mechanisms influencing epibiont settlement and survival, offering a compelling direction for future research into environmental drivers or host-epibiont dynamics across different bathymetric gradients. Overall, this paper provides valuable baseline data that is essential for the conservation and management of the MPA NBB and for understanding the broader ecological dynamics of deep-sea benthic communities. By thoroughly detailing the epibiont assemblages associated with *A. canaliculata*, the study not only expands the faunistic knowledge of a poorly known region but also strengthens the established ecological paradigm of cidaroids acting as important basibionts. The findings contribute significantly to marine biology, particularly in the fields of community ecology and biodiversity, by elucidating specific biotic interactions that shape deep-sea benthic landscapes.

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