海洋底栖生物入添量估计时做了错误的假设

海洋底栖生物入添量估计时做了错误的假设 海洋底棲生物入添量估計時做了錯誤的假設 宋克義 周雅嵐 高雄國立中山大學海洋生物研究所 海洋生物浮游幼蟲要變態為底棲生活形態時需要合適的棲所做為基質,底棲生物族群的變動乃至生活史的演化是否因此受合適棲所供給的影響,例如海洋生物繁殖季是否是針對棲所出現季節的一種必要適應,又例如珊瑚群礁的發展或復育是否受限於底質棲所的量與質,使得幼蟲附苗無著,想有效回答上述問題得要能估計合適棲所的量,才能了解海洋中合適棲所是否真有時空變化。 一般估計海洋底棲生物族群的入添量(recruitment)時都假設棲所供給不會影響附苗的密度,因此天然基質或人工基質上的附苗密度就是入添量的指標,可以用來比較不同季節以及地點的入添量。這個假設在單向水流的江、河中或可成立,但是在一般淺海,其波浪、潮汐造成水流往復的成份很高,附苗的密度就可能會受到周遭棲所供給的影響。本實驗要驗証棲所供給不會影響海洋底棲生物附苗密度的假說。 根據此假說我們預測1.單板和多板組合上附苗密度不會有差別,2.同一海域礁區和沙區附苗密度不會有差別,3.沒水流海域單板和多板組合上附苗密度不 會有差別。 實驗在南台灣珊瑚礁區海域進行,我們發現藤壺是主要著苗物種,因此藤壺在塑膠著苗板數量,結果如下: 1. 單板和多板組合上附苗密度有差別,單板上附苗密度較高(不符合原始 假說的預測), 2. 在五個地點中均發現附苗密度沙區比礁區高,而且無法用相對假說(光 線、掠食者)來解釋(不符合原始假說的預測), 3. 在我們認為沒水流海域的遊艇碼頭主要著苗物種是管蟲,附苗密度並未 見到因著苗板多少而異的現象(符合原始假說的預測)。 結果1及2均不支持棲所供給不會影響海洋底棲生物附苗密度的原始假說,而用棲所限制的假說卻可以充份解釋,結果3中沒水流域的認定可能過於主觀,但此後見之明仍需另設計實驗來驗証。 本研究的結果顯示利用附苗密度來探討入添量時空變化時一般所做的假設”棲所供給不會影響海洋底棲生物附苗密度”經不起驗証,因此一般比較不同海域入添量研究的結論都有再斟酌的必要,但另一方面應用取而代之的”棲所限制的假說”卻有可能發展出估計棲所的方法,進而同時解決入添量及棲所的估計問題。 Quantification of suitable substrate in reef habitats-A preliminary test Keryea Soong and Yalan Chou Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung, 804, Taiwan, Coral reefs are a complex environment where suitable substrate is often an abstract concept and hard to assess. Nevertheless, seasonal availability of suitable substrate has been proposed to drive the timing of reproduction of spawning coral species. To test this idea, quantification of suitable substrate is necessary. Quantification of the recruitment of sessile species is routine often using settlement panels. The densities of individuals settled on the panels can be used to infer larva supply variation among sites and/or among different times. Overall settled densities, however, is a function of two components, the number of settlers and the availability of suitable substrate. These two components can interact, termed the intensification effect, such that an increase in available substrate may decrease the density of settlers on that substrate. Pineda and Caswell noted this effect in the lab, but this has never been tested in the sea. If intensification effect also applies in the sea, available substrate can be estimated. In our investigation, we developed a “broken-beaker” model to simulate natural conditions in the sea where larvae are allowed to drift in and out of a particular reef. Then we tested its predictions by comparing settle densities (1) between reef and sand environments where suitable substrate is supposed to differ quantitatively; and (2) among sites with varying levels of flux rates, where the contribution of the “intensification effect” should vary; and (3) among clusters of varying numbers of panels that generate different amount of local substrate. Results in (1) consistently indicate sand areas had higher densities of barnacles than reef areas in three independent tests involving multiple sites. Results in (2) and (3) were inconsistent. The spatial scale of the tests may be a critical factor, since the distance between treatments in (2) and (3) was 1 m.