聚苯乙烯微塑膠對藤壺幼體死亡率、生長、發育、附著及變態之影響

Abstract

微塑膠(microplastics)為直徑小於5微米(5mm)的塑膠碎片。目前已有許多研究證實攝入微塑膠會對海洋浮游生物(zooplankton)造成許多負面影響，例如：降低濾食速率、延遲發育和降低生育力。然而，目前大多數的微塑膠研究都著重在微塑膠對真浮游生物(holoplankton)的影響，相較之下，微塑膠對階段性浮游生物(meroplankton)的影響卻很少被探討。因此，本研究利用紋藤壺幼體(Amphibalanus amphitrite)做為階段性浮游生物的模式物種，探討四種不同直徑(1.7, 6.8, 10.4, 19.0 µm)與濃度(1, 10, 100, 1000 beads mL-1)之聚苯乙烯(polystyrene)微塑膠的影響。本研究結果發現紋藤壺之第二期無節幼體(stage II nauplii)皆可攝入此四種直徑之微塑膠，並且可以在幾小時之內快速排出食入之微塑膠。此四種直徑之微塑膠，不管在任何濃度下皆不會對紋藤壺幼體之死亡率、發育、生長、附著速率和變態成功率造成影響。此外，在濃度1000 beads mL-1時，微塑膠也幾乎不會降低藤壺幼體的濾食速率。整體來說，聚苯乙烯微塑膠對紋藤壺幼體周期幾乎沒有負面影響，大多數的幼體都能成功變態成藤壺成體。接著本研究更進一步延長實驗時間，繼續餵食存活之紋藤壺成體微塑膠直到成體達性成熟，產出下一個世代的幼體。我們發現微塑膠雖然對第一代的紋藤壺沒有顯著影響，卻會跨世代的影響到下一個世代的幼體，降低幼體存活率。尤其直徑越小的微塑膠，影響越顯著。除了紋藤壺之外，本研究也比較了來自不同棲地及氣候帶之藤壺幼體死亡率及微塑膠排出體外時間的差異。結果發現八種藤壺幼體死亡率(Fistulobalanus albicostatus, Tetraclita japonica formosana, Chelonibia testudinaria, Neoacasta sp., Euacasta dofleini, Darwiniella angularis, Chthamalus dalli, Balanus glandula)都沒有受到微塑膠的影響。但是棲息於岩岸及珊瑚礁的藤壺幼體，比起棲息於泥岸的藤壺幼體需要長3-4倍的時間才能排出所有微塑膠，顯示在未來微塑膠汙染可能會嚴重地影響到岩岸及珊瑚礁的藤壺浮游幼體。

Microplastics are plastic debris smaller than 5 mm in diameter. It has been shown that microplastics would cause many adverse impacts on zooplanktons such as reduce feeding rate, delay development and decrease fecundity. However, most studies evaluate the effect of microplastics focus on holoplankton, but relatively less studies focus on meroplankton. In the present study, we used the barnacle Amphibalanus amphitrite as a model organism for meroplankton to investigate the effects of four different sizes of polystyrene microplastics (diameter 1.7, 6.8, 10.4, 19.0 µm respectively) at four concentrations (1, 10, 100, 1000 beads mL-1). We found that stage II nauplii of A. amphitrite were able to ingest all four sizes of microplastics and efficiently egested them within several hours. Larval mortality, development time, growth rate, settling rate and metamorphosis percentage of microplastic treatments were not significantly different from that of control after being exposed to four different sizes of microplastics at any concentration from nauplii to cyprids. Moreover, feeding rate of nauplii (stage II- stage VI) were barely impaired at the concentration of 1000 beads mL-1. Overall, our results suggest that polystyrene microplastics have very limited impacts on the entire larval cycle of barnacle A. amphitrite. The microplastic exposed larvae could still successfully metamorphose to juvenile stage. We further extended the microplastic exposure over barnacle generations, continuously fed barnacle adults with same size of microplastic until they reproduced next generation offspring. Our results found that microplastics did not significantly affect adults of first generation but significantly increase larval mortality of next generation offspring, suggesting that microplastics have transgenerational effects. We also compared the larval mortality and retention time of microplastics between barnacle larvae from different habitats and climatic zones (Fistulobalanus albicostatus, Tetraclita japonica formosana, Chelonibia testudinaria, Neoacasta sp., Euacasta dofleini, Darwiniella angularis, Chthamalus dalli, Balanus glandula). We found that all barnacle species did not suffer increase mortality upon exposure to microplastics, but the retention time of microplastics significantly differed between barnacles lived in different habitats. Rocky shore and coral reef associated species have about 3-4 times longer microplastic retention time than the muddy shore species, suggesting that rocky shore and coral reef associated species might be more vulnerable to microplastic pollution.