Morphological insights into the 3-Dimensional Complexity of Rhodolith Beds

Abstract

Abstract The ecological importance of rhodolith beds lies in the fact that they are a structurally complex three-dimensional habitat formed by free-living red calcareous algae. The habitat complexity increases the ecological niches for cryptofauna and provide refuge for a high number of organisms, which is why they are considered biodiversity hotspots. Their structural importance is due to their great variety of complex and branching morphologies that create interstitial spaces between the nodules and increase their surface area. In this work, we study a rhodolith bed located in the Menorca Channel, formed by several species of red calcareous algae, that exhibit a great variety of morphologies that form an extensive and heterogeneous habitat. This study further explores the morphological diversity of this rhodolith bed, comparing the ‘core habitat’ (the best -preserved area) with the boundaries or ‘adjacent area’ where rhodolith density is lower. Our results suggest that all growth forms of rhodoliths (branched, pralines and boxwork) in the core habitat have higher interstitial space and are larger than the ones from adjacent zones. Moreover, we explore three-dimensional techniques to study morphological metrics that have historically been studied in two dimensions. The results of this study reinforce the use of three-dimensional measurements to provide more realistic data of their forms and the use of the interstitial space (IS) of branched rhodoliths as a proxy for habitat complexity. This study contributes to the knowledge of morphological diversity in deep well preserved rhodoliths beds from the North-Western Mediterranean Sea.