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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°, 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • We applied a novel conceptual framework to guide marine conservation planning after a natural disaster event in an oceanic island. • Quantifying static (richness, abundance, and biomass) and process-based, dynamic, metrics (productivity and turnover) revealed distinct ecosystem trajectories. • Distinct trajectories in ecological metrics were best predicted by body size and trophic composition of reef fishes. • Factoring in fish biomass and productivity served to fine-tune management decisions. Understanding temporal dynamics in ecological communities is key to develop management plans that target sustainability. Process-based metrics quantify dynamic properties of ecological communities, and thereof have been recently advocated as a promising tool to guide management strategies. To date, however, their empirical application has been limited, hindering their utility to inform conservation planning in response to a range of natural and human-driven disturbances. Here, we compare the succession of fish communities after a catastrophic natural event, a volcanic eruption and the formation of nascent reefs, through the lens of complementary static (species richness, abundance, and biomass) and process-based (productivity and turnover) metrics. We found markedly contrasting dynamics between these metrics, particularly when looking at fish biomass and productivity. During incipient stages of community development, fish productivity increased exponentially, whereas the recovery of fish biomass considerably lagged behind, underscoring high rates of biomass replacement (i.e., turnover) in the system. This buffering response (higher production per unit of biomass) was best predicted by average community body size, highlighting the role of compensatory ecological mechanisms during primary ecological succession. Traits related to resource acquisition, particularly the harnessing of planktonic energy subsidies, further enhanced predicted fish biomass and productivity at local scales. This study therefore supports the burgeoning call to inform conservation and management planning through complementary metrics that give a nuanced understanding on ecosystem functioning. [ABSTRACT FROM AUTHOR]

Amphipods are one of the dominant epifaunal groups in seagrass meadows. However, our understanding of the biogeographical patterns in the distribution of these small crustaceans is limited. In this study, we investigated such patterns and the potential drivers in twelve Cymodocea nodosa meadows within four distinctive biogeographical areas across 2000 Km and 13° of latitude in two ocean basins (Mediterranean Sea and Atlantic Ocean). We found that species abundances in the assemblage of seagrass-associated amphipods differed among areas following a pattern largely explained by seagrass leaf area and epiphyte biomass, while the variation pattern in species presence/absence was determined by seagrass density and epiphyte biomass. Seagrass leaf area was also the most important determinant of greater amphipod total density and species richness, while amphipod density also increased with algal cover. Overall, our results evidenced that biogeographical patterns of variation in amphipod assemblages are mainly influenced by components of the habitat structure, which covary with environmental conditions, finding that structurally more complex meadows harboring higher abundance and richness of amphipods associated. • We examine drivers of variation in seagrass-associated amphipods across 2000 Km in two ocean basins. • Structurally more complex meadows host greater density and richness of amphipods. • Seagrass leaf area drives higher amphipod total density and species richness, and the former also increase with algal cover. • Seagrass density and epiphyte biomass drive variation in species identity, while leaf area and epiphyte biomass explain abundances. • Attributes of habitat structural complexity selected as predictors covary with environmental factors. [ABSTRACT FROM AUTHOR]