Responses of Germlings to Acute Environmental Stress

Tang Yongzheng,Chu Shaohua,Lu Zhicheng,Yu Yongqiang,Li Xuemeng

doi:10.2174/1874070701509010127

Abstract

The responses of Sargassum thunbergii germlings to high temperature, low salinity, desiccation, combined thermal and osmotic stress (35 ºC combined with 12 psu), anthracene, and eutrophication were examined. Probit regression analysis results showed that the median lethal time (LT50) values of high temperature decreased with the increase in temperature. The 24 h median lethal temperature was 36.9 ºC. For salinity treatment, the LT50 value of fresh water was 47.6 h. Survival rates of germlings were over 60% when germlings were exposed to salinities ranging from 27 psu to 7 psu at a time interval of 108 h post-treatment. The LT50 values of desiccation and combined thermal and osmotic stress (35 ºC combined with 12 psu) were 7.0 h and 9.8 h, respectively. Anovas showed that germlings were inhibited by high concentrations of anthracene (5 mg L-1 and 10 mg L-1) with low survival rates of below 50% and low relative growth rates of below 1% after 25 days of culture; however, low concentrations (0.01-1 mg L-1) had no significant effects. In addition, neither severe eutrophication nor disproportionality of N/P showed any significant effect on the survival and growth of germlings. Of the environmental stresses tested, possible occurrence of high temperature of 40 ºC and combined thermal and osmotic stress directly impacted the survival of germlings, suggesting that the deterioration of S. thunbergii bed may be related more to increasing extreme climatic events.

Highlights

As a member of Sargassum beds, Sargassum thunbergii is ecologically important in the maintenance of a healthy coastal ecosystem [1], such as serving as a primary producer; in spawning, nursery and feeding ground for marine organisms; and as nutrient cycling controller [2]
The median lethal time was estimated for the combined thermal and osmotic stress (35 oC combined with 12 psu) which previously resulted as extreme for germlings [13]
Of the environmental stresses tested in the present study, high temperature of 40 oC and combined thermal and osmotic stress (35 oC combined with 12 psu) may directly impact the survival of germlings

Summary

Introduction

As a member of Sargassum beds, Sargassum thunbergii is ecologically important in the maintenance of a healthy coastal ecosystem [1], such as serving as a primary producer; in spawning, nursery and feeding ground for marine organisms; and as nutrient cycling controller [2]. Increased temperature is generally thought to have negative effects on spore production, germination, sporophyte growth and recruitment of seaweeds [5]. When they experience periods of temperature change, which are sufficiently high to result in disruptive stress, such damage and any reallocation of resources for protection and repair can cause slow growth, delay development and lead to mortality [6]. Anthracene is a PAH with higher solubility than most other PAHs due to its low molecular capacity and may prove a threat to the environment if widely distributed [7] It acts as a photosensitizer causing an oxidative damage of algal cells [8].

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Conclusion