摘要:瞭解食階結構與其因應環境變遷而產生的各種反應,對於海洋生態系的管理至關重要,因為食階結構的變異代表著能量在生態系各部位中傳遞的動態。在東海生態系中,這樣的研究格外重要,因為預料在未來的十年間,此海域遭受到的氣候變遷、人類干擾(污染、過漁、藻華與長江三峽大壩的興建)的協同效應會日益加劇。
在本計畫中,我們提出一個有別於以往的新方法來研究海洋食階結構與其變異。過去的食階結構研究是以物種間掠食者與獵物(predator-prey)的角色關係為主,雖然理論上可行,但是鑑種工作曠日廢時,要確定物種之間的食性關係更是困難,要有效率地收集到物種層級的資料相當困難。因此,本計畫將以體型大小和食階關係來探討海洋食階結構的簡化版。之所以有這樣的構想,是因為在許多文獻中都發現有證據支持在水域系統中,多半是大型生物捕食小型生物。
我們的研究目標是調查海洋系統浮游生物食階結構與變異的三項主要特性:1.體型大小分佈(生物量體型大小頻譜)(biomass-size spectrum);2. 掠食者與獵物體型大小比例(predator-prey size ratio);3. 食階能量傳遞效率。我們將會探討這三項因子對人為干擾與氣候變遷的反應。本計畫預計以採樣瓶與浮游生物網取得的浮游生物樣本,經由流式影像儀(FlowCam)與浮游動物掃描器(ZooScan)等自動化儀器來測量體型大小。將樣本依體型大小分群,進行穩定同位素(δN15 與 δC13)分析,估算出掠食者/獵物之體型大小比例。我們還計畫採用新的方向,直接以體型大小頻譜與掠食者/獵物之體型大小比例的資料,來估計能量在食階中的傳遞。
在生態研究中,能量傳遞的效率向來就不易估計。不僅耗時,而且充滿不確定性,二級生產力的估計通常僅限於大型甲殼類。因此我們計畫以另一個角度,間接地由體型大小頻譜與體型食階關係來估計水域系統中浮游生物的食階能量傳遞效率。根據新陳代謝理論
log(N)=(log(TE)/log(PPMR)-0.75)*log(M)
N :一組特定體型大小生物量的豐度
M :該組生物量
TE:食階能量傳遞效率
PPMR:掠食者/獵物之大小比例
估算出體型大小頻譜的斜率與PPMR後,便可求得TE 。 如前述,可由大小分群的穩定同位素分析得到PPMR,而藉由流式影像儀、浮游動物掃描器與顯微鏡的測量可得到體型大小頻譜資料。如此便能估算出食階能量傳遞效率。再結合放射性同位素C14 測量所得的初級生產力資料,便能估算次級生產力。接下來便能探討各項環境因子對體型大小頻譜、PPMR與食階能量傳遞效率的影響,並評估這些估算方法的不確定因素。
本研究與LORECS計畫整合,和團隊中的其他研究員合作會有許多益處。不僅可和其他LORECS團隊成員一同進行海洋探測航次,他們也會提供物理、化學參數與初級生產力測量的協助。
Abstract: Understanding trophic structure and its variation in response to a changing environment is essential to marine ecosystem management, because the variation of trophic structure represents changes of energy transfers among components of the ecosystem. This understanding is particularly important in the East China Sea region where synergistic effects of climate change and anthropogenic disturbance (pollution, overfishing, algal bloom, and construction of Yangtze River Dam, etc.) is expected to intensify in the coming decade.
Here we propose a novel size-based approach to study marine trophic structure and its variation. Traditionally, trophic structure is investigated based on species predator-prey relationships. While the theory is sound, it is difficult to collect species-specific data with enough efficiency, because identifying species requires high expertise, and is time consuming and expensive. Moreover, examining who eat whom is difficult. We propose to investigate simplified (aggregated) marine trophic structure based on size and size-specific trophic interactions. This idea is based on well-documented evidence that, often in aquatic systems, large organisms eats small organisms.
Our research goals are to investigate trophic structure and its variation in the planktonic component of marine systems based on three main elements: 1. size-distribution (biomass-size spectrum), 2. predator-prey size ratio (estimated from size-specific trophic level), and 3. trophic transfer efficiency. We will investigate how these elements respond to anthropogenic disturbance and climate change. The size distribution data from phytoplankton to zooplankton will be obtained from combination of collecting bottle and plankton net tow samples and measurements using automatic sizing instruments: FlowCam and ZooScan. The predator-prey size ratio will be obtained using size-fractionated stable isotope (δN15 and δC13). More interestingly, we propose a novel approach to estimate trophic transfer efficiency directly from the size spectrum and predator-prey size ratio.
Estimation of transfer efficiency in ecological research is difficult in practice. It is time consuming and highly uncertain, and the estimation of secondary production is often only restricted to large crustaceans. We propose alternative indirect approach to estimate trophic transfer efficiency for the planktonic component in aquatic systems based on estimating the size-spectrum and size-specific trophic level. Based on metabolic theory, we derive this equation: log(N)=(log(TE)/log(PPMR)-0.75)*log(M), where N is abundance of a biomass class, M is biomass class, TE is trophic transfer efficiency, and PPMR is predator-prey mass ratio. TE can be estimated if the slope of size-spectrum and the PPMR is known. As aforementioned, PPMR can be obtained from size fractionated stable isotope analysis and the size spectrum can be measured from combination of FlowCAM and ZooScan as well as microscope measurements. As such, trophic transfer efficiency can be estimated. Moreover, together with primary production data from C14 radioisotope measurement, secondary production can then be estimated. We can then investigate how environmental factors affect size-spectrum, PPMR, and trophic transfer efficiency. Source of uncertainty of these estimates will be evaluated.
Integration of our research with that of other PIs in the LORECS program is beneficial. Oceanographic research cruises will be carried with other team members who will assist on physical, chemical, and other biological measurement such as primary production.