Effect of Depth across a Latitudinal Gradient in the Structure of Rhodolith Seabeds and Associated Biota across the Eastern Atlantic Ocean

Rhodolith seabeds are 'ecosystem engineers' composed of free-living calcareous red macroalgae, which create extensive marine habitats. This study addressed how depth influenced the structure (size and morphology) of rhodoliths and the abundance of associated floral and faunal epibionts across the Eastern Atlantic Ocean. Sampling was carried out at two sites within five regions (Brittany, Galicia, Madeira, Gran Canaria, and Principe Island), from temperate to tropical, covering a latitudinal gradient of 47 degrees, in three depth strata (shallow, intermediate and deep), according to the rhodolith bathymetrical range in each region. Depth typically affected the rhodolith size at all regions; the largest nodules were found in the intermediate and deep strata, while rhodolith sphericity was larger at the shallow depth strata. Higher biomasses of attached macroalgae (epiphytes) were observed at depths where rhodoliths were larger. The abundance of epifauna was variable across regions and depth strata. In general, the occurrence, structure, and abundance of the associated biota across rhodolith habitats were affected by depth, with local variability (i.e., sites within regions) often displaying a more significant influence than the regional (large-scale) variation. Overall, this study showed that the rhodolith morphology and associated epibionts (flora and fauna) were mostly affected by depth, irrespective of latitude.

Automated summary

This study examined the impact of depth on the size and morphology of calcareous red macroalgae structures (rhodoliths) and the abundance of associated flora and fauna. The findings revealed that depth typically influenced the size and shape of rhodoliths, with larger nodules found at intermediate and deep depths. The biomass of attached macroalgae (epiphytes) also increased with depth. The study concluded that the morphology of rhodoliths and associated epibionts were primarily influenced by depth, regardless of latitude.