Effect of breakwater restoration work following the subsidence caused by the 2011 Tohoku Earthquake on the subtidal kelp population

Abstract

SUMMARY We conducted a 5‐year monitoring survey of a population of Eisenia bicyclis kelp at a coastal area that suffered subsidence from the 2011 earthquake and the subsequent breakwater restoration work. Due to subsidence, the former intertidal area sank to the subtidal zone, therefore, the density of E. bicyclis increased because of many recruits. However, after the restoration work, the area harboring the recruits was destroyed and landfilled. In an area that sank below the pre‐subsidence border of the kelp distribution, recruits were rare. Furthermore, an indirect effect of the restoration work was also observed on recruitment in the intact offshore kelp zone. Our results showed that the breakwater restoration work following subsidence had negative effects, not only to the density but also to the age structure of the E. bicyclis population.

Heat Stress Promotes Nitrogen Accumulation in Meristems via Apical Blade Erosion in a Brown Macroalga With Intercalary Growth

“…The present study showed that nitrogen accumulation in the meristem is promoted by heat-induced blade erosion in E. bicylis juvenile sporophytes. This property may contribute to survival during summer with warm and nutrient-poor conditions for these sporophytes, which often germinate between spring and summer (Suzuki et al, 2020). However, it is uncertain whether erose sporophytes recover and survive after summer; further research is necessary to determine this.…”

Analyses of Stalked Jellyfish in Kitsunezaki, Japan: Calvadosia nagatensis, and Two Lineages of Haliclystus inabai with Early Life Stages Observed in an Aquarium in Canada

“…Breakwater restoration work commenced at Kitsunezaki in July 2014, and a subsequent study suggested that the breakwater restoration work had a negative effect on the density and age structure of Eisenia bicyclis population in the Kisunezaki survey site [44]. The ratio of young plants decreased while the whole population became dominated by older plants; inevitable senescence of the adult population could lead to a decline in the E. bicyclis population in the future [44], and consequently reduce staurozoan recruits on E. bicyclis. Studies are needed to understand linkage between the population dynamics of the macroalgae and stauromedusa presence, reproduction and early life cycle, or even seasonality, as this study did not find any obvious pattern with respect to gonad state.…”

Successful Coastal Protection by Step Concrete Revetments in Thailand

“…The direct or indirect effects of the revetments include (1) visual impacts, (2) restrictions on beach access, (3) reduction of sand supply from a previously eroding cliff or bluff, (4) placement loss or covering the beach beneath the riprap or seawall, (5) passive erosion or the loss of beach from sea-level rise where the back beach is fixed and can no longer migrate inland, and (6) active erosion or the loss of a fronting beach because of wave interaction with a structure. Suzuki et al [12] showed that the maintenance of the revetment on the coast of Kitsunezaki, Japan, negatively affected the kelp Eisenia bicyclis. As a direct impact of the revetment construction, the kelp was squashed and buried by large rocks and construction materials.…”