摄食信息对球形棕囊藻和布氏双尾藻竞争结果的影响

浮游动物的摄食信息能增大棕囊藻囊体体积,囊体形成被认为是棕囊藻的诱导性防御机制。利用桡足类火腿伪镖水蚤和异养甲藻海洋尖尾藻释放的摄食信息,研究了诱导性防御对球形棕囊藻和布氏双尾藻的竞争的影响。结果表明,球形棕囊藻接收了火腿伪镖水蚤和海洋尖尾藻释放的摄食信息之后形成更大的囊体。防御启动后的球形棕囊藻比未接收摄食信息的球形棕囊藻更快地形成囊体,且囊体维持的时间更长。对照组和火腿伪镖水蚤摄食信息诱导的球形棕囊藻的生物体积比布氏双尾藻更高,且球形棕囊藻在竞争中占优势;而海洋尖尾藻摄食信息诱导的球形棕囊藻生物体积低于布氏双尾藻,且球形棕囊藻相对布氏双尾藻的竞争力下降。微型浮游动物海洋尖尾藻摄食信息导致球形棕囊藻相对硅藻布氏双尾藻的竞争力的下降,有利于解释硅藻先于棕囊藻发生藻华。

The presence of grazing cues changed competitive outcomes between Phaeocystis globosa and Ditylum brightwellii

Chemical cues play crucial roles in the communication and interaction between phytoplankton and zooplankton. Colony enlargement of Phaeocystis globosa in the presence of grazing cues released by zooplankton has been considered as an induced defense. Colonial Phaeocystis blooms usually occur during or following blooms of diatoms, suggesting that competitive ability of Phaeocystis is less than diatoms in some cases. However, it remains unknown whether the induced defense can lead to decreased the competitive ability of Phaeocystis versus diatoms. In this study, the competitive outcomes between induced defensive P. globosa and diatom D. brightwellii exposed to the grazing cues released from copepods Pseudodiaptomus poplesia and heterotrophic dinoflagellates Oxyrrhis marina has been investigated. Results showed that P. globosa formed significantly larger colonies when it received grazing cues released by Pseudodiaptomus poplesia and O. marina, which suggested that the defensive response of P. globosa was induced by the grazing cues in this study. The induced defensive P. globosa showed more rapid colony development and longer colony durations than non-defensive P. globosa. However, grazing cues released from Pseudodiaptomus poplesia and O. marina did not induce the defensive response in terms of length, width and silicification in the D. brightwellii. P. globosa showed significantly higher biovolume than D. brightwellii in the control and Pseudodiaptomus poplesia-induced treatment, whereas the addition of grazing cues from O. marina led to the lower biovolume of P. globosa than D. brightwellii. Based on the relative biovolumes over time of P. globosa and D. brightwellii, P. globosa exposed to grazing cues from Pseudodiaptomus poplesia was more competitive than D. brightwellii, while D. brightwellii outcompeted P. globosa in the O. marina-induced treatment. The variations in competitive dynamics between two treatments could be attributed to growth responses of D. brightwellii to grazing cues, and D. brightwellii beat P. globosa in the O. marina-induced treatment indicating that D. brightwellii might be sensitive to the grazing of microzooplankton O. marina. While induced defense in terms of colony enlargement might be efficient against microzooplankton grazers, the compromised competitive ability in growth rate would cause P. globosa to be outgrown by diatoms induced growth responses to grazing cues. The decreased competitive ability in P. globosa versus D. brightwellii in the presence of grazing cues from microzooplankton, the major consumers of phytoplankton in the field, may contribute to the appearance of diatom growth prior to that of Phaeocystis in coastal blooms. Grazing cues can potentially drive the coexistence of competitive species and promote the biodiversity in the marine systems.