Earthquake and typhoon trigger unprecedented transient shifts in shallow hydrothermal vents biogeochemistry

Abstract

Shallow hydrothermal vents are of pivotal relevance for ocean biogeochemical cycles, including seawater dissolved heavy metals and trace elements as well as the carbonate system balance. The Kueishan Tao (KST) stratovolcano off Taiwan is associated with numerous hydrothermal vents emitting warm sulfur-rich fluids at so-called White Vents (WV) and Yellow Vent (YV) that impact the surrounding seawater masses and habitats. The morphological and biogeochemical consequences caused by a M5.8 earthquake and a C5 typhoon (“Nepartak”) hitting KST (12th May, and 2nd–10th July, 2016) were studied within a 10-year time series (2009–2018) combining aerial drone imagery, technical diving, and hydrographic surveys. The catastrophic disturbances triggered landslides that reshaped the shoreline, burying the seabed and, as a consequence, native sulfur accretions that were abundant on the seafloor disappeared. A significant reduction in venting activity and fluid flow was observed at the high-temperature YV. Dissolved Inorganic Carbon (DIC) maxima in surrounding seawater reached 3000–5000 µmol kg−1, and Total Alkalinity (TA) drawdowns were below 1500–1000 µmol kg−1 lasting for one year. A strong decrease and, in some cases, depletion of dissolved elements (Cd, Ba, Tl, Pb, Fe, Cu, As) including Mg and Cl in seawater from shallow depths to the open ocean followed the disturbance, with a recovery of Mg and Cl to pre-disturbance concentrations in 2018. The WV and YV benthic megafauna exhibited mixed responses in their skeleton Mg:Ca and Sr:Ca ratios, not always following directions of seawater chemical changes. Over 70% of the organisms increased skeleton Mg:Ca ratio during rising DIC (higher CO2) despite decreasing seawater Mg:Ca ratios showing a high level of resilience. KST benthic organisms have historically co-existed with such events providing them ecological advantages under extreme conditions. The sudden and catastrophic changes observed at the KST site profoundly reshaped biogeochemical processes in shallow and offshore waters for one year, but they remained transient in nature, with a possible recovery of the system within two years.

Foraging strategies under extreme events: Contrasting adaptations by benthic macrofauna to drastic biogeochemical disturbance

“…The consistently high δ 13 C values in vent crabs are attributed to the carbon intake from chemoautotrophic microbes that use high δ 13 C of DIC (average -18‰), and vent POM (~17.4‰) (11,14). Although DIC concentration peaked immediately after these extreme events, DIC values recovered to the same level as in May 2018 (9). The fact that δ 13 Compared to the vent crabs, the mollusks at the WV consistently consumed more photothan chemosynthetic sources.…”

“…Indeed, a recent biogeochemical time-series in the region showed a significant decrease in the intensity of conspicuous white color produced by the dominant chemoautotrophic sulfur bacteria (e.g. epsilonproteobacteria and gammaproteobacteria) in the WV seawater after the extreme events (9). Decreased consumption of vent associated diet in mollusks is likely due to the lowered contribution of sulfur-based chemotrophic bacteria and vent POM to intermediate consumers such as zooplankton and epi-benthic crustaceans, which make up a large dietary contribution to mollusks (11).…”

“…1). The combined effect from the earthquake and typhoon decreased the toxicity and intensity of the discharging shallow vent fluids (9), the two most important factors for structuring KST's food webs (19,20). Before the extreme events, the active Yellow Vents (YV) and the semi-inactive White Vents (WV) at the KST had distinct biogeochemical properties that supported different food webs (Fig.…”

“…In contrast, WV has low degassing activity and no discharge of toxic fluids (21). After the disturbance, the rapid change in the physical environment and reduced vent discharges led to dramatic shifts in the seawater's biogeochemistry in both YV and WV (9). While dissolved inorganic carbon (DIC) and elements recovered to pre-disturbance concentrations after two year, previously abundant native yellow sulfur accretions near the active YV disappeared ( Fig.…”

Distribution and sexual dimorphism of the crab Xenograpsus testudinatus from the hydrothermal vent field of Kueishan Island, northeastern Taiwan

“…accordingly their population size and distribution range are inevitably regulated by the hydrothermal vent [38]. Recent reports indicate that the hydrothermal vent area of Kueishan Island was affected by earthquakes, heavy precipitation and typhoons, causing the collapse and were partially buried [39,40]. Such environmental changes may further reduce the population size and distribution range of X. testudinatus [34,35].…”