Benthic Species and Habitats

The term benthos, coined by the German naturalist Ernst Heinrich Philipp August Haeckel in 1891 [1], comes from the Greek βένθος, which means “depth (of the sea)”. It includes the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, from shallow rivers or tidal pools down to the unseen depths of the ocean. The benthic zone hosts a striking variety of species and habitats, many of which are barely known or still undescribed. In spite of the critical role played by benthic life, the species distribution and their main features are often unknown. Moreover, in many cases we have not comprehensive understood the patterns and processes shaping the presence of benthic life. Thanks to the use of cutting-edge technologies (e.g., technical diving, underwater vehicles, and autonomous devices) and sophisticated molecular techniques, scientific research is advancing remarkably, unveiling the secrets of the benthos from the poles to the tropics, from the coastal zones down to the most inaccessible deep habitats. This Special Issue presents relevant scientific work from large-scale patterns to detailed aspects and case studies about benthic habitats and species. In detail, it includes contributions that benefit from imaging techniques, such as non-invasive approaches based on visual census and video analyses to describe habitat features and their conservation status [2,3]. Some of the studies in this Special Issue also show how imaging techniques are useful for developing 3D approaches for animal descriptions [4] and size-structured models for the study of vulnerable species [5]. In addition to the visual approach, sampling can support the study of the population structure of endangered or particularly important species to deepen our knowledge, especially regarding their biology [6] or conservation status [5,7]. Since ad hoc sampling is sometimes inevitable, powerful approaches are benefiting from fishery bycatch and other forms of sample collection [8]. Certain benthic species are also habitat formers, as they can form the physical place where a number of species live, feed, or breed, such as, for instance, seagrass meadows, coral reefs, marine animal forests, and rhodolith beds [2,9,10,11]. The work by Shmuel et al. [12], for instance, reports some observations about the different habitat uses of crabs in the genus Trapezia living in a marine animal forest. In addition, some of the contributions to this Special Issue provide new information about species distribution coupled with environmental drivers and human activities, as in the cases of the Moulay Bousselham Lagoon (Morocco, Atlantic Ocean) [13], the Siboglinidae annelid Nereilinum murmanicum in the Barents Sea [14], and the Korean Top Shell Turbo sazae expanding its habitat northward in the Korean Peninsula [15]. Benthic species can be also involved in restoration initiatives, such as for the mangrove Kandelia obovata used to replace the invasive Spartina alterniflora in an intertidal macrobenthos community at Maoyan Island (Zhejiang, China) [16], as well as oyster restoration mats on dock pilings to help restore water quality and benthic habitats in the Indian River Lagoon [17]. Finally, this Special Issue proudly includes the description of a new species, the sponge Spongilla manconiae, from Cahong Lake in Northeast Vietnam [18].