Long-term trends and seasonal variations in environmental conditions in Sesoko Island, Okinawa, Japan

Abstract

Knowledge of environmental factors is crucial in understanding biological and ecological processes. Yet information on the environment around Sesoko Island, Okinawa, Japan, one of the main locations for coral reef research in Japan, remains scarce. Data of air and sea surface temperature (SST), wind velocity, wave height, and frequency of typhoons have been manually recorded at Sesoko Station, Tropical Biosphere Research Station, the University of the Ryukyus from September 1990 to November 2021. Here we describe the seasonal and long-term trends in these environmental variables at Sesoko Island. Some of the key findings were that the air temperature and SST fluctuated by ~9-12°C throughout the year. A rise in air temperature and SST between 1990 and 2021 was observed in the winter and autumn season, respectively. The Degree Heating Week (DHW) based on the in-situ data reflected the bleaching observations around Sesoko Station. The DHW exceeded the critical bleaching level of 8°C-week in 1998 and the significant bleaching level of 4°C-week in 2001, 2016, and 2017. Weak southerly winds were dominant in summers, while stronger northeasterly winds were dominant in winters. The frequency of winds between 3.4 to 7.9 m/s and northeastern winds have increased through time. Typhoons generally occur between May and October, and the frequency of typhoons has not increased over the past 30 years. Wave heights never exceeded 0.5 m and were highest between July and September. These findings will provide a reliable baseline of the environment at Sesoko Island for further ecological studies.

Limited acclimation of early life stages of the coral Seriatopora hystrix from mesophotic depth to shallow reefs

“…No information is available on upwelling around Okinawa during the coral reproductive season. However, at the time of larval release, typhoons could create enough vertical water movement to potentially transport S. hystrix larvae from mesophotic depths to shallow reefs, although the frequency and paths of strong storms vary across years 9 , 33 . This stochastic connectivity may explain the absence of genetic partitioning within the water column for S. hystrix in Okinawa 26 .…”

Short-term improvement of heat tolerance in naturally growing Acropora corals in Okinawa

“…Besides temperature, several environmental factors such as lower light intensity, higher wind speed, higher water flow, and typhoons can also mitigate coral bleaching severity ( Fitt & Warner, 1995 ; Nakamura & van Woesik, 2001 ; Smith, 2001 ; West & Salm, 2003 ). However, in our study, the light and precipitation regime, wind speed, wave height, number of cloudy days, and the timing and frequency of typhoons around the study site were found to be similar in the summer of 2016 and 2017 (Table S4; Supplemental Data in Singh et al, 2022 ). This indicates that the improved heat-stress tolerance was not caused by adaptation or better environmental conditions in 2017, but by the acclimatization of the coral holobionts.…”

“…For example, failure to acclimatize to a simulated consecutive bleaching event was linked to low basal energy reserves, which in turn was attributed to the peak in temperatures coinciding with end of the reproductive season ( Grottoli et al, 2014 ; Schoepf et al, 2015 ). Acropora corals at our study site generally spawn synchronously in June, a month before the temperatures begin to rise ( Baird et al, 2022 ; Singh et al, 2022 ). Although we do not know if this is enough time for Acropora corals to recover their basal energy reserves after reproduction, the reproductive period does not overlap with increased heat stress at our study site.…”

Urbanization of a subtropical island (Okinawa, Japan) alters physicochemical characteristics and disrupts microbial community dynamics in nearshore ecosystems

“…Okinawa’s south-to-north ubanization gradient sets up a unique natural laboratory to investigate the ecological outcomes from intense urbanization of a subtropical island and creates the opportunity to fill a critical knowledge gap as islands across tropical and subtropical regions are experiencing increasing tourism demand, growing populations, and accelerating urbanization (Bertolo et al 2012; Lin et al 2013). Okinawa also has a strong land-sea connection due to frequent and intense rain events associated with a spring monsoon season and a summer/fall typhoon season (Singh et al 2022). Okinawa is located in typhoon alley, the most active region for tropical cyclones on Earth (Magee et al 2021).…”