Variation of amphipod assemblage along the Sargassum stenophyllum (Phaeophyta, Fucales) thallus

Abstract

-The spatial distribution of fauna associated to marine macroalgae has mostly been investigated considering a horizontal plane. However, the macroalgal substrates can present a three-dimensional structure. In this sense, investigating how the associated fauna varies throughout a vertical plane can contribute to understanding the distribution of these organisms. The brown macroalga Sargassum presents a vertical stratification along its thallus and harbors an amphipod fauna with a variety of feeding habits. In this work, we tested if the amphipod assemblage varies along different portions of the Sargassum thallus. We collected whole Sargassum stenophyllum thalli, as well as isolated basal and distal portions, from a rocky shore located on the north coast of São Paulo, in southeastern Brazil. The composition of amphipod families varied according to the Sargassum portion and the families Corophiidae, Caprellidae and Hyalidae accounted for most of the differences. Moreover, the basal portion of Sargassum had a higher diversity of amphipod families than the distal one, which may be related to differences regarding habitat complexity (herein, measured as algal biomass) between these portions. Detritivores (such as Corophiidae) were more associated to the basal portion and herbivores to the distal portion (Hyalidae) or along the whole Sargassum thallus (Ampithoidae). The variation of amphipod assemblage along Sargassum thallus seems to result from the interaction between the fauna natural history and the differences in conditions and physical structure along the algal thallus. In this sense, the vertical stratification of Sargassum can add another source of variation to the spatial distribution of associated fauna.(GBOM, SAD) Pós

Time-since-invasion increases native mesoherbivore feeding rates on the invasive alga, Sargassum muticum (Yendo) Fensholt

“…Although different to previous feeding trials because of the incorporation of time-since-invasion, the present study also supports the ERH. These apparently contradictory conclusions may be the result of animals moving into S. muticum stands during the day for protection against visual predators, but then returning to native alga to feed during the night (Buschmann, 1990; Machado et al ., 2015). Alternatively, grazers on S. muticum could be feeding mainly on epiphytic material and detritus in the field (Viejo, 1999; Cacabelos et al ., 2010b), and may therefore avoid S. muticum under laboratory conditions due to experimental removal of epiphytes or the selection of individuals that are relatively epiphyte free.…”

The chemical defences of the invasive alga Sargassum muticum (Yendo) Fensholt correlate to mesoherbivore diversity, but not to time-since-invasion

“…Boström & Mattila, 1999;Tait & Hovel, 2012) to avoid predators, such as Palaemon serratus which were abundant in most stands of S. muticum in this study. If many grazer species found on S. muticum are not feeding on it, but are instead using it for shelter (Machado et al, 2015) or feeding solely on its epiphytes (Viejo, 1999;Cacabelos et al, 2010b) this would explain why the 'sampling effect' applies in this instance. Due to their small size, the probability that the individuals of any one grazer species were feeding directly on S. muticum tissues is likely much lower than if these individuals were adults.…”

“…Likewise, many grazers could be feeding principally on the epiphytes of S. muticum (Viejo, 1999;Cacabelos et al, 2010b) or exploiting its fronds for shelter (e.g. Machado et al, 2015). Surprisingly few studies include diversity of local grazers when examining the impacts on invasive plants and algae (Kimbro et al, 2013), and little is known about how grazer diversity might impact a species such as S. muticum.…”

Carbon dioxide removal via macroalgae open-ocean mariculture and sinking: an Earth system modeling study

“…Our assumption that zooplankton can graze on macroalgae is based on the notion that the marine biogeochemical component of "zooplankton" in UVic ESCM represents all higher trophic levels, including known macroalgae grazers such as amphipods (Jacobucci et al, 2008), gastropods (Chikaraishi et al, 2007;Krumhansl and Scheibling, 2011), sea urchins (e.g., Yatsuya et al, 2020) and fishes (e.g., Peteiro et al, 2014). Thus, we included this food web pathway to assess the sensitivity of macroalgae to potential grazers in the ocean, assuming that with large macroalgae farms the pelagic larvae of some grazing organisms like fish or urchins would settle within the farms.…”