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Rhodolith growth and CaCO 3 production remain poorly quantified along the SW Atlantic Ocean, and it is difficult to relate the available measurements with biomass estimates. Suboptimal conditions may clarify how harsh environments influence nodule growth and abundance, elucidating their relationship. Off the energetic South American equatorial coast a rhodolith bed (~65 km 2 ), formed mainly by Mesophyllum sp. and Lithophyllum sp., alters the regional sedimentary pattern and sustains a diverse biota. Its nodules present fast growth rates (2.8 mm year -1 ), but small biomasses (18 nodules∙m -2 covering 26 ± 3% of the substrate), resulting in a CaCO 3 production of 163.33 g m -2 ∙year -1 . Despite the small biomass, the bed seems stable, with living and dead nodules both on and inside the substrate. And the suboptimal environment apparently affects growth and abundance independently. Therefore, fast growth rates and relevant structural roles are not necessarily associated with dense rhodolith assemblages, and ecological assessments of rhodolith beds should consider the dynamics of both individual nodules and the whole population., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In this study, the ichthyoplankton in two distinct tropical seascapes, gravelly sand with rhodolith beds (SRB) and muddy sand with seagrasses, were compared. The number of eggs was higher in the seagrass beds; however, the number of fish larvae was slightly higher in the SRB. Seagrass beds present less turbulent hydrodynamics and favor the retention of eggs and spawning. A more structured habitat provides better shelter, especially for eggs. However, as ontogeny progresses, the fish can explore areas with less shelter. This behavior was observed in this study, where the less structured SRB habitat had a high density of larvae in the later developmental stage. The dominance of earlier larval stages demonstrates a preference for more protected and less turbulent seascapes for nursery and offspring rearing. The results highlight that mapping of these seascapes (e.g., seagrass and rhodolith beds) will help to establish conservation measures to protect ecological connectivity and important tropical species., (Copyright © 2020 Elsevier Ltd. All rights reserved.)