Abstract: Ocean acidification and warming are the main environmental pressures and ecological problems faced by marine organisms and their dependent ecosystems at present and in the future. However, the research on the early development of marine organisms mainly focused on the impact of ocean acidification. To better understand the impacts of climate change on marine organisms, it is necessary to study the responses of marine organisms under the joint effect of ocean acidification and warming. We conducted an experiment with juvenile sea cucumber (Apostichopus japonicus) to examine the impacts of seawater acidification and warming on growth, development, and body pigmentation in key stage of body pigmentation by simulating current seawater condition and that at the end of this century. Four treatments were set up: control group (seawater temperature of the Dalian coast, pCO₂ 400 mg·kg^-1), seawater warming group (control group temperature plus 2 ℃, pCO₂ 400 mg·kg^-1), seawater acidification group (control group temperature, pCO₂ 1000 mg·kg^-1), and combined seawater warming and acidification group (control group temperature plus 2 ℃,pCO₂ 1000 mg·kg^-1). The results showed that a pH decrease of 0.23 units delayed growth, slowed pigmentation, and increased variation of body weight among individuals. In contrast, a 2 ℃ temperature increase accelerated growth and pigmentation of the juveniles, potentially neutralizing the negative effects of pH decrease. Our results indicated that juvenile sea cucumbers can gradually adapt to long-term seawater acidification and warming.

Key words: water level fluctuation, invasive plant, native plant, interspecific competition, intraspecific competition.