Biodiversity and ecology of Bryozoa from Atlantic seamounts

Seamounts are submarine topographic structures that rise more than 1 km from the surrounding seafloor, and are common features in all ocean basins. In the Atlantic around 800 seamounts are known to be present. The ecosystems on these structures, which are usually of volcanic origin, have historically been viewed as unique, diverse and productive systems embedded in a more homogeneous deep-sea environment. While early studies suggested that seamounts are island habitats with highly endemic and ancient faunas, and that they act as stepping-stones in the dispersal of species across ocean basins, several recent analyses contradict the earlier hypotheses. Bryozoans are ideal model organisms to test these hypotheses. They exclusively comprise colonial, filter-feeding, benthic animals that ubiquitously occur in shallow shelf to bathyal depths. As most bryozoans produce very short-lived larvae, their dispersal abilities are limited and the species have a relatively restricted geographic distribution, i.e. a high degree of endemism. In spite of these advantages, this study is the first to use bryozoans as model organisms in major ecological and biogeographic analyses of seamount biota. During the last 40 years, several scientific expeditions took place to collect samples from seamounts of mainly two areas in the NE Atlantic: a cluster of seamounts around the island of Madeira, which are situated relatively close to the continental shelf, and an offshore, central Atlantic group of seamounts. Only a negligible fraction of these bryozoan samples were previously studied. During this project the bryozoan species from several seamounts in each cluster will be revised or newly described. Based on this faunal inventory, a number of biodiversity and ecological analyses will be conducted. The species distribution on the seamounts within each cluster as well as between the two seamount groups will be investigated in order to estimate the level of endemism and faunal connectivity between these sites. The seamount habitats will be characterised and the controlling factors for bryozoan species distributions and faunal gradients be determined to test to what degree the faunas are ecologically distinct between each seamount, between both seamount clusters, and between the seamounts and those of the continental shelf. Additionally, ecological niche modelling will be applied to the most conspicuous faunal elements to predict their occurrence in other Atlantic sites. The outcome of this project will significantly add to our understanding of the natural history of the North Atlantic seamounts, and of the degree of endemism and population connectivity between the different seamounts, which, as a result, may play an important role in the efforts to conserve these vulnerable deep sea habitats.

Seamounts are submarine topographic structures that rise more than 1 km from the surrounding seafloor. In the Atlantic around 800 seamounts are known to be present. The ecosystems on these structures have historically been viewed as unique, diverse and productive systems. Studies suggested that seamounts are island habitats with highly endemic and ancient faunas. Bryozoans are one of the common benthic organisms that can be found in the seamounts and they are ideal model organisms to test these hypotheses. Bryozoans exclusively comprise colonial, filter-feeding, benthic animals that ubiquitously occur in shallow shelf to bathyal depths. As most bryozoans produce very short-lived larvae, their dispersal abilities are limited and the species have a relatively restricted geographic distribution, i.e. a high degree of endemism. In spite of these advantages, this study is the first to use bryozoans as model organisms in major ecological and biogeographic analyses of seamount biota. During the present project, the bryozoan fauna from 9 seamounts of the Atlantic Ocean and Iberian continental slope were studies. Historical and recent samples were included in the study. Modern techniques for deep water sampling as the use of remote operate vehicle (ROV) were used to collect new samples and characterize the habitats. Taxonomical study of the samples has discovered 33 new species (14 already published and 29 in process of publication), besides, 17 species were re-described from the type material. More of the 50% of the species collected in each area were unknown, which could be indicating that these areas present high levels of endemism. In spite of the high number of new species, the number of species in this areas is much lower than the expected when is compared with the continental slope fauna at similar depth. By first time, the distribution of deep water bryozoans communities is analysed in relation of environmental variables. Contrary to what in shallow waters was found, in our study, substrate and micro-habitat differences have not strong influence in species composition; whereas temperature, depth and O2 saturation present significantly correlated with the variability in community composition. In summary, results of the project allowed to increase the knowledge of the diversity and ecology of bryozoans in particular and the deep water seamounts habitats in general, which will help to take decision about the possible protection of these deep water habitats.