ABSTRACT
Rhodolith beds are known worldwide to host high biodiversity to several taxa. Despite their importance, few ecological data explored the influence of rhodolith features and environmental variables on associated biodiversity, a gap that has been hampering the mapping of diversity hotspots and priority areas for conservation. In this study, we investigated large-scale spatial variations of rhodolith beds and their associated fauna, using annelid polychaetes as a biological model. We aimed to identify proxies, based on rhodolith features and environmental variables, to detect biodiversity hotspots across Southwestern Atlantic beds, laying the groundwork for mapping priority areas for conservation. With this goal, we sampled a total of 136 rhodolith nodules across seven sites with beds under distinct latitudes, depths, distances from the mainland coast of Brazil, and rhodolith densities. For each nodule sampled, we measured the volume, diameter, and mass of sediment trapped, as well as the attributes of the associated polychaetes (abundance, richness, diversity, and composition). Our results revealed a complex network of collinearities and synergisms between the rhodolith features and the majority of the polychaetes attributes (i.e., abundance, diversity, and composition). Polychaete richness, in contrast, can be explained by the combination of two proxies: (1) rhodolith nodule diameter and (2) distance of the rhodolith bed from the mainland coast. Nearshore rhodolith beds and larger nodules were associated with higher values of richness. Additionally, rhodoliths with a hollow morphology were also associated with higher values of polychaete richness. These results suggest that nearshore rhodolith beds with large and hollow nodules could be priority areas for conservation. However, further multi-taxa studies using our framework are still needed to explore other regions and scales, delineating more comprehensive proxies for predicting ecological patterns of the rhodoliths associated fauna and to identify priorities for conservation across Southwestern Atlantic beds.
Subject(s)
Biodiversity , Ecosystem , Animals , Invertebrates , BrazilABSTRACT
The phytal is characterized by the formation of seaweed beds and a great diversity of associated species, the malacofauna being one of its main components. Aiming to record the species of Gastropoda associated to the brown algae Sargassum sp. C. Agardh, 1820, this study was carried out in São Sebastião Channel, northern coast of São Paulo, and nearby areas. A total of 13945 individuals were identified, belonging to 35 families and 62 species. Cerithiidae, Phasianellidae and Columbellidae were the most abundant families, represented by 34, 33 and 17% of the total collected individuals, respectively. Bittiolum varium (Pfeiffer, 1840) (Cerithiidae) and Eulithidium affine (C. B. Adams, 1850) (Phasianellidae) are the dominant species, followed by the columbelids Mitrella dichroa (G. B. Sowerby I, 1844), Anachis fenneli Radwin, 1968 and Costoanachis sertulariarium (d'Orbigny, 1839). Among the least abundant species, some of them may be considered as of fortuitous occurrences, while others seem to be typical in those habitats, although rare. The presence of juvenile specimens was recurrent, this indicating that the algae can function as a nursery for most of these species. The expressive values found, for both abundance and number of species, illustrate the great ecological importance of the phytal habitats for the gastropod species.
O fital é caracterizado pela formação de bancos de algas marinhas e uma grande diversidade de espécies associadas, estando a malacofauna entre seus principais componentes. Com o objetivo de registrar as assembleias de gastrópodes associadas è alga parda Sargassum C. Agardh, 1820, este estudo foi realizado no Canal de São Sebastião, litoral norte do estado de São Paulo, e áreas próximas. Um total de 13945 indivíduos foram identificados, pertencentes a 35 famílias e 62 espécies. Em termos de abundância, Cerithiidae, Phasianellidae e Columbellidae foram as famílias mais representativas, com 34, 33 e 17% do total de indivíduos coletados, respectivamente. Bittiolum varium (Pfeiffer, 1840) (Cerithiidae) e Eulithidium affine (C. B. Adams, 1850) (Phasianellidae) foram as espécies dominantes, seguidas pelos columbelídeos Mitrella dichroa (G. B. Sowerby I, 1844), Anachis fenneli Radwin, 1968 e Costoanachis sertulariarium (d'Orbigny, 1839). Entre as espécies pouco abundantes, algumas podem ser consideradas como de ocorrência ocasional, enquanto outras parecem ser típicas deste ambiente, porém raras. A presença de formas juvenis mostrou-se muito recorrente para a maioria das espécies, o que parece indicar que a alga pode atuar como berçário. Os valores expressivos encontrados, tanto para a abundância de indivíduos como para o número de espécies, ilustram a grande importância ecológica apresentada por este ambiente para as espécies de gastrópodes.
