Larval supply of Taiwan intertidal barnacles, with special reference to the early life history pattern of Tetraclita kuroshioensis (Cirripedia: Thoracica: Tetraclitidae) in the NE Coast, Taiwan

Abstract

潮間帶生物之繁殖週期具有浮游性的幼體時期及固著的成體時期。供給面生態學(Supply side ecology)主要探討幼體供給、附著及附著後死亡率與成體族群動態以及分佈之關聯性。本研究主要利用一種新設計之高效能浮游生物採集器，去探討潮間帶生物幼體供給的模式；並以台灣廣泛分佈之黑潮笠藤壺為例，去探討其幼體供給、附著以及附著後死亡率，對於成體族群結構之關係。 在這次的研究中，一種新型之浮游生物採集器被設計出來，可在漲退潮時進行採集，使得採集時間比前人設計之採集器要長，並能捕獲高多樣性的浮游生物。採集器與手撈浮游生物網所收集到之浮游生物，經由多變數分析得知在組成上並無不同，也表示這個新的採集器並沒有選擇性捕捉特定浮游生物。本研究在東北角深澳坑及和平島放置採集器捕捉幼體，發現藤壺、雙殼貝以及腹足類之幼體確實具有空間上與時間上的變異存在，並與潮汐高度及風速有高度相關。 此外，在2008年十月到2009年十月的採集期中(約十二個月)，本研究在台灣東北角兩個樣點(深澳坑與和平島)探討藤壺幼體供給之多樣性，並利用形態特徵與分子標記來做藤壺腺介幼體的分種。在形態特徵上，藤壺腺界幼體背甲長度、寬度和尾部角度以及觸角上之特徵都被選做可能的分類依據，而結果顯示利用形態特徵來做分類鑑定並不可靠，相反的利用分子標記來做分種則較為可信，也較適合微小的藤壺腺介幼體分類使用。這次的研究也探討了十九種本地常見的藤壺供給在時間與空間上的變異，並發現有其它非本地種的藤壺幼體出現在採樣當中。 在這次的研究中也發現，黑潮笠藤壺的幼體供給在夏天繁殖季中會出現好幾次高峰，夏季早期所出現的少量幼體供給並沒辦法附著到岸上，而只有夏季所出現的那次大量的幼體供給能夠提供少量的幼體附著，並入添到成體族群中。這個結果也表示，台灣的笠藤壺幼體與附著密度並不高，且較香港之前的研究為低，西北太平洋上不同的洋流及氣候特徵或許是造成這些變異存在的原因之一。Life cycle of intertidal organisms often consist a planktonic larval stage and followed by a sessile adult stage. Supply side ecology highlighted the relationship between larval supply, settlement and post-settlement mortality and their subsequent effect on the distribution and abundance of adults. The present study investigated larval supply using a newly designed plankton trap, which can efficiently sample larvae and quantify their supply patterns. The present study also focused on the early life history pattern of the abundant mid-shore barnacle Tetraclita kuroshioensis, to study the subsequent events of larval supply, settlement and post-settlement mortality on the population structure of adults at the NE Coast, Taiwan. The new designed trap in the present study can collect plankton during the splash and submerged period of the tidal cycle and yielded high diversity of catches, in which the sampling time is longer than the previously designed traps. Multivariate analysis showed that catch composition collected by the traps and the catches collected from hand-held plankton trawl net was similar, suggesting this trap was not selective. Using the new trap, the present study assessed the spatial and temporal variation in the supply of barnacle, bivalve and gastropod larvae in the NE Coast, Taiwan. Supply pattern of these larvae was affected by daily tidal range and wind speed. Diversity of larval supply of Taiwan intertidal barnacles was further investigated using this trap in ~12-month period (October, 2008 – October, 2009) at two sites (Shen Ao Kang and He Ping Dao) in the NE Coast. Morphological characters and molecular markers (CO1) are combined to identify barnacle cypris larvae. In morphological methods, carapace length, width and posterior carapace angle and antennules morphology was used to identify species. The result showed that morphological method can not identify barnacle cypris larvae to species level correctly. However, using the mitochondria CO1 molecular markers, we can identify barnacle species and proved that molecular method is more reliable to identify small-size barnacle cypris larvae in larval supply studies. The present study revealed the supply pattern of 19 common local barnacles which showed both spatial and temporal variations between these two sites. We also collected larvae of non-native barnacle species. Larval supply of the intertidal barnacle T. kuroshioensis had several supply pulses during the reproductive seasons. There were several small pulses in early summer but no settlement was followed. In summer, there was a single pulse, followed by sparse settlement and most of the settler can enter the populations as recruits (> 1 month old). Results suggesting the larvae and settlement density of Tetraclita sp. were not very high in Taiwan, as compared to the previous reported pattern in Hong Kong. Such variations can be attributed by difference in oceanographic current and climates between Taiwan and Hong Kong in the NW Pacific waters