Behavioral Interaction And Suitable Aquaculture Sites Of The Sea Cucumber Apostichopus Japonicus And The Sea Urchin Strongylocentrotus Intermedius

Sea urchins and sea cucumbers are ecologically important benthic organisms in kelp ecosystems.Sea urchins,as herbivores,convert the coarse particulate organic matter of kelp into fecal particles that benefit marine scavengers,including sea cucumbers.Sea urchins in turn profit from the sediment cleaned by sea cucumbers.The purpose of this study is to investigate the intraspecific and interspecific behavioral interactions of the sea cucumber Apostichopus japonicus and the sea urchin Strongylocentrotus intermedius.In addition,suitable aquaculture sites of the two species were preliminarily studied using the Maximum Entropy model(Max Ent).1.Interactions between sea urchins affected individual and group behaviors.Interaction among sea urchins remains largely uninvestigated,although the aggregation of sea urchins is common.In the present study,1,15 and 30 sea urchins S.intermedius(1.06±0.99 mm in test diameter)were placed in a 1 m~2 circular tank,respectively.Movement behaviors were recorded for 12 minutes to investigate potential interactions among sea urchins.After the 12-minute control period,we added food cues into the tank and recorded the changes in sea urchins’behaviors.There was no significant difference in the movement speed and the displacement of sea urchins among the three density groups(1,15 and 30 ind/m~2).The interaction occurred when sea urchins randomly contacted with the conspecifics and slowed down the movement speed.The speed of sea urchins after physical contacts decreased by an average of 40%in the density of 15 ind/m~2and 17%in the density of 30 ind/m~2.This interaction resulted in significantly higher randomness in the movement direction and lower movement linearity in 15 and 30 ind/m~2 than in 1 ind/m~2.After the introduction of food cues,the movement speed,displacement and dispersal distance of sea urchin groups decreased significantly in all the three densities.The dispersal distance and expansion speed of sea urchins were significantly lower in 30 ind/m~2than those in 15 ind/m~2.The present study indicates that the interaction among sea urchins limits the movement of individual sea urchin and provides valuable information into how large groups of sea urchins are stable in places where food is plentiful.2.Macroalgae and alarm cues play an important role in regulating interspecific relationships between A.japonicus and S.intermedius.Sea cucumbers A.japonicus and sea urchins S.intermedius are important mutually beneficial organisms in kelp ecosystem.However,behavioral interactions remain poorly understood,which greatly hampers our understanding on the mutualism.The present study investigated behavioral interactions between S.intermedius and A.japonicus in laboratory conditions.We revealed that the presence of sea urchins caused significant high-speed movement of A.japonicus.Interestingly,the negative effects of S.intermedius on A.japonicus were significantly reduced in the shared macroalgal area.Interspecific response to alarm cues is an efficient method for anti-predation in mutually beneficial organisms.We thus tested the responses of S.intermedius and A.japonicus to conspecific and interspecific alarm cues.For the first time,we found the interspecific responses to alarm cues between sea cucumbers and sea urchins.Conspecific responses were significantly larger than the interspecific responses in both sea urchins and sea cucumbers.The present study shed light on the mutualisms between sea urchins and sea cucumbers in kelp ecosystem.3.Suitable aquaculture sites of A.japonicus and S.intermedius.In the present study,the Maximum Entropy model(Max Ent)based on the data of sea surface temperature(SST)and the published information were used to assess the aquaculture expansion of A.japonicus and S.intermedius in China.According to the current assessment,the coastal areas of Hebei province and Tianjin have great prospects for A.japonicus aquaculture,while are currently underutilized.In the south,more than94%of the coastal areas in Zhejiang,Fujian and Guangdong provinces are suitable for the growth of A.japonicus for six months,especially the coastal areas of Lianjiang,Changle,Fuqing and Putian in Fujian province.The water temperatures are higher than25°C in more than 94 percent of China’s coastal area in July and August,which probably results in the mortality of S.intermedius in aquaculture.The present study indicates that high water temperature is the bottleneck of S.intermedius aquaculture and well explains the limited expansion of this commercially important exotic species since the introduction in 1989.We suggest a new aquaculture model of S.intermedius that extends the seed production to November to avoid the mass mortality in longline culture in summer.In the south,64 percent of coastal areas in Zhejiang and Fujian provinces are suitable for the transplantation of S.intermedius in the south.The present study suggests the ecological niche model Max Ent with the data of SST and the published information as a new tool for the assessment of the aquaculture expansion of A.japonicus and S.intermedius in China.It should be noted that only sea surface temperature was considered in this study,and relevant models need to be further studied.