两种蟹对不同规格杂色角孔海胆苗种的捕食

Predation by two species of crabs on different sizes of juvenile sea urchin Salmacis sphaeroides

杂色角孔海胆是我国南海一种具有较高生态价值和经济价值的海胆,蟹类的捕食是影响其资源量的重要因素,但目前关于蟹类对海胆苗种的捕食效应及影响因素仍不明确。本研究在实验室条件下模拟研究了日本蟳和钝齿短桨蟹对两种规格[大规格壳径(36.50±4.11) mm,小规格壳径(22.33±1.97) mm]杂色角孔海胆苗种的捕食效应;通过在海区现场开展蟹类的诱捕实验,来进一步验证室内实验结果。结果显示,海胆的规格和捕食时长是影响蟹类捕食强度的重要因素,同时蟹的种类也会影响实验结果,日本蟳在0~24 h和24~48 h内对小规格海胆的捕食强度基本保持稳定,分别为(3.75±1.09)和(3.75±1.30)只/d,高于其对大规格海胆的捕食强度;该蟹对大规格海胆的捕食强度则随时间延长而降低,在0~24 h和24~48 h分别为(0.50±0.86)和(0.25±0.50)只/d。钝齿短桨蟹在0~24 h内对小规格海胆的捕食强度[(4.25±3.27)只/d]高于其对大规格海胆的捕食强度,且捕食强度随着时间延长而下降,在24~48 h内降低为(2.00±1.58)只/d。现场诱捕实验结果显示,以杂色角孔海胆苗种为诱饵的诱捕笼对日本蟳的平均捕获率可达(2.40±0.89)只/(笼·d),表明杂色角孔海胆对日本蟳具有较强的吸引力。综上,蟹类是杂色角孔海胆的主要威胁因素,在开展增殖放流时应采用大规格的海胆苗种,并在放流之前对海区的蟹类等敌害予以清除,以提高放流的效果。

The sea urchin species Salmacis sphaeroides holds significant ecological and economic value in the South China Sea.However,natural populations are increasingly at risk due to environmental pollution,overfishing,climate change and other factors.Stock enhancement through breeding and release could mitigate this decline,but crab predation poses a significant threat to released individuals.The predation effects on juvenile S.sphaeroides and the factors influencing these effects are not well understood.This study investigated the predation of two sizes classes of juvenile S.sphaeroides[test diameters:large,(36.50±4.11)mm;small,(22.33±1.97)mm]by Charybdis japonica and Thalamita crenata,both of which are prevalent in the South China Sea,using both indoor and filed trapping experiments.Results indicated that S.sphaeroides size and predation duration were key factors influencing predation rates,with species-specific differences between the two crab species.C.japonica exhibited high predation rates on small juveniles at both 0-24 and 24-48 h,with rates of(3.75±1.09)ind/d and(3.75±1.30)ind/d,respectively,while predation on large juveniles was significantly lower at(0.50±0.86)ind/d and(0.25±0.50)ind/d,respectively.In 0-24 h,T.crenata showed a high initial predation rate on small juveniles of(4.25±3.27)ind/d at 0-24 h,which decreased to(2.00±1.58)ind/d during 24-48 h,and exerted minimal pressure on large juveniles.Field trapping experiments revealed a strong attraction of juvenile S.sphaeroides to C.japonica,with an average capture rate of(2.40±0.89)ind/(cage·d).This study concludes that crabs are the primary predators of S.sphaeroides,and to enhance restocking efficiency,it is recommended to release large-sized sea urchin seedlings and to control potential predators such as crabs in advance.