Herbicides are among the most detected pesticides in coastal environments. Herbicides may impact non-target organisms, but invertebrates that have a symbiotic relationship with microalgae (zooxanthellae) may be particularly susceptible. How zooxanthellae influence the response of organisms to herbicides, however, remains untested. We exposed zooxanthellate and azooxanthellate Cassiopea xamachana medusae to environmentally relevant concentrations of the herbicide atrazine (0 µg L ^− 1, 7 µg L ^− 1 and 27 µg L ^− 1) for 20 days. We hypothesised that atrazine would have adverse effects on the size, rate of bell contractions and, respiration of medusae, but that effects would be more severe in zooxanthellate than azooxanthellate medusae. We also predicted that photosynthetic efficiency, chlorophyll a (Chla) content and zooxanthellae density would decrease in zooxanthellate medusae exposed to atrazine. Both zooxanthellate and azooxanthellate medusae shrank, yet the size-specific respiration rates were not constant during the experiment. Photosynthetic efficiency of zooxanthellate medusae significantly decreased at 7 and 27 µgL⁻¹ atrazine, but atrazine did not affect the Chla content or zooxanthellae density. Our results showed that even though atrazine inhibited photosynthesis, zooxanthellae were not expelled from the host. We conclude that the presence of zooxanthellae did not increase the susceptibility of C. xamachana medusae to atrazine.

除草剂是沿海环境中检出率最高的杀虫剂之一。除草剂可能会影响非目标生物，但与微藻（虫黄藻）有共生关系的无脊椎动物可能特别容易受到影响。然而，虫黄藻如何影响生物体对除草剂的反应仍未得到证实。我们将虫黄藻和偶氮黄藻Cassiopea xamachana medusae暴露于环境相关浓度的除草剂莠去津（0 µg L  ^{−  1}、7 µg L  ^{−  1}和 27 µg L  ^{−  1}) 20 天。我们假设莠去津会对水母的大小、钟形收缩率和呼吸产生不利影响，但这种影响在虫黄藻中比在偶氮黄原藻中更为严重。我们还预测，暴露于莠去津的虫黄藻水母的光合效率、叶绿素a (Chl a ) 含量和虫黄藻密度会降低。虫黄藻和偶氮黄藻水母都缩小了，但在实验过程中，特定尺寸的呼吸速率并不是恒定的。虫黄藻美杜鹃在7和27 µgL ^-1阿特拉津时的光合效率显着降低，但阿特拉津对Chl a没有影响含量或虫黄藻密度。我们的结果表明，即使阿特拉津抑制光合作用，虫黄藻也不会从宿主中排出。我们得出的结论是，虫黄藻的存在并不会增加水产假单胞菌对阿特拉津的敏感性。