Response of the benthic biomass-size structure to a high-energy submarine canyon

Abstract

IntroductionBody size regulates all biological processes, including growth, reproduction, metabolism, trophic interactions, etc., and is the master trait across organisms, populations, and communities. Despite a rich literature on the impacts of human and natural disturbances on body size, a clear knowledge gap is the effect of the submarine canyons on the benthic size structures in the deep sea, hindering our understanding of the ecological processes of these dominant ecosystems on the continental margin.MethodsTherefore, we conducted repeated sediment sampling to compare meiofauna and macrofauna biomass body-size spectrum, growth, metabolism, and size composition from a high-energy submarine canyon, Gaoping Submarine Canyon (GPSC), and the adjacent continental slope off SW Taiwan. The GPSC is a dynamic ecosystem connected to a high sediment-yield small mountain river subjected to strong internal-tide energy, swift bottom currents, frequent mass wasting events, and high terrestrial sediment inputs.ResultsWe found that the meiofauna and macrofauna were characterized by relatively larger individuals dominating on the slope to smaller ones dominating in the canyon. As a result, the community biomass, secondary production, and respiration were depressed with distinctive biomass-size composition in the canyon compared to the non-canyon slope. The environmental factors related to internal tide disturbance (i.e., bottom current velocity, duration of sediment erosion, or low light transmission) substantially influence the body size composition of the canyon benthos, while food supplies (i.e., TOC and C/N ratio) and sediment characters (i.e., grain size and porosity) correlated closely with the slope communities.DiscussionWe concluded that the disturbed condition in the GPSC may have wiped out or depressed the local benthic assemblages, and only the smaller, more resilient species could persist. Our results also highlight that the alterations of the canyon benthic community could be a reference to deep-sea ecosystems under anthropogenic disturbances or global climate change.

Contrasting carbon cycling in the benthic food webs between river-fed, high-energy canyon and upper continental slope

“…Consequently, the upper GPSC (about 200-400 m water depth) seafloor features a benthic nepheloid layer (BNL) with a thickness exceeding 100 m and a suspended sediment concentration surpassing 30 mg l -1 , sustained by current-induced resuspension related to internal tides (Liu et al, 2002;2010;Liu and Lin, 2004). The impacts of the physical disturbance on the sedimentary OC and benthos in the canyon include (i) the removal of fine particles containing 90 higher total organic carbon (TOC) content, resulting in diminished food supplies and subsequently lower meiofaunal and macrofaunal abundance, biomass, and diversity in the canyon compared to the adjacent slope (Liao et al, 2017;2020;Tung et al, 2023), and (ii) a significant negative impact on the nematode functional and trophic diversity, as well as community maturity (Liao et al, 2020), affecting various aspects of the benthic ecosystem functions, such as size structure, community growth, and respiration (Tung et a., 2023). 95…”

“…where V was the volume, L was the length, W was the width, and C was the taxon-specific conversion factor (Warwick and Gee, 1984). For the taxa without conversion factors, the biovolume was calculated from length and width using the nearest geometric shapes (e.g., cone shape: scaphopods; cylinder shape: aplacophorans, sipunculans, and nemerteans; ellipsoid shape: ophiuroids and asteroids) (Tung et al, 2023). The biovolume was first converted into wet weight by assuming a 155 specific gravity of 1.13 (Warwick and Gee, 1984).…”

“…The stock of non-living components was approximately four orders of magnitude higher than that of living components. The meiofauna and macrofauna biomass were remarkably depressed in the canyon due to physical disturbances (Liao et al, 2017;2020;Tung et al, 2023). Macrofauna had greater biomass than meiofauna on both the slope and canyon.…”

“…In contrast, the adjacent slope receives approximately an equal amount of OC flux into its biological system, despite a significantly lower influx of POC. The strong physical disturbances in GC1 have negatively impacted the benthic community structure 520 (Tung et al, 2023), resulting in meager meiofauna and macrofauna biomass and interaction flows. Nevertheless, the higher bacteria stocks and bacteria-related carbon flows could compensate for these deficiencies.…”

“…For submarine canyons on active margins, our previous work showed that strong physical disturbance in the shore-70 connected GPSC had significant negative impacts on benthic community structure and function, resulting in lower abundance, diversity, biomass, growth, respiration, and distinctly different composition compared to the nearby slope ecosystem (Liao et al, 2017(Liao et al, , 2020Tung et al, 2023). However, the carbon flows within the canyon's benthic food web in https://doi.org/10.5194/bg-2023-161 Preprint.…”