Abyssal seafloor response to fresh phytodetrital input in three areas of particular environmental interest (APEIs) in the western clarion-clipperton zone (CCZ). (May 2023)

• Record Type: Journal Article
• Authors: Cecchetto, Marta M.; Moser, Annabell; Smith, Craig R.; van Oevelen, Dick; Sweetman, Andrew K.
• Is Part Of: Deep sea research. Volume 195(2023)
• Publication Date: 2023-05
• Subjects: Deep-sea mining -- Polymetallic nodules -- Clarion clipperton zone (CCZ) -- Area of particular environmental interest (APEI) -- Benthic ecosystem functioning -- Pulse-chase experiments -- Carbon cycling; Oceanography -- Periodicals; Océanographie -- Périodiques; 551.4605
• DOI: 10.1016/j.dsr.2023.103970
• Languages: English
• ISSNs: 0967-0637

Abstract

Abstract: The abyssal seafloor (3500–6000m) remains largely unexplored but with deep-sea mining imminent, anthropogenic impacts may soon reach abyssal communities. Thus, there is a growing need for baseline studies of biodiversity, ecosystem functioning, and connectivity in both potential mining and no-mining areas across the Clarion-Clipperton Zone (CCZ), a key target region for polymetallic nodule mining. In this study, in situ pulse-chase lander experiments were conducted for 1.5 days in three no-mining areas (called Areas of Particular Environmental Interest, or APEIs) in the western CCZ, a region with a seafloor particulate organic carbon (POC) flux gradient. A decreasing trend was seen in mean seafloor respiration, macrofaunal abundance, and biomass from the more eutrophic APEI 7 to the more oligotrophic APEI 1, although this trend was not statistically significant (p = 0.18) most likely due to small samples sizes and high variability. In this study, most (96%) of the 13 C-labeled processed phytodetritus was respired within 1.5 days. Experimental uptake of phytodetritus by macrofauna and bacteria was detected but was lower than in the previously studied and more eutrophic eastern CCZ over similar time scales (1.5 d). Bacteria dominated the short-term (∼1.5 d) uptake of organic carbon at the seafloor, yet macrofauna processed more organic carbon per unit biomass than previously found in the eastern CCZ (0.003 mg C m −2 d −1 and 0.5 × 10 −5 mg C m −2 d −1 for the western and eastern CCZ, respectively). Our study provides important information on C-uptake and respiration rates in areas set aside from mining in the western CCZ and suggests high variability may occur in the rates of benthic Corg -cycling across the CCZ. We recommend that benthic ecosystem functions be explored across gradients of POC flux which may be a major environmental factor driving ecosystem dynamics in the CCZ. Highlights: Abyssal seafloor response to fresh phytodetrital input in three Areas of Particular Environmental Interests (APEIs) in the Clarion-Clipperton Zone (CCZ). Bacteria dominated the short-term uptake of organic carbon at the seafloor. Although not statistically significant, our data show a decreasing trend following a decreasing POC flux to the benthos. Most carbon was respired within the first 1.5 days. Clear need for baseline studies assessing benthic ecosystem functioning within the APEI network in the CCZ.