Effects of heterotrophy on the physiological responses of the scleractinian coral Goniopora lobata in Hong Kong.

• Other Authors: Chow, Ming Him.
• Format: Others
• Language: English; Chinese
• Published: 2012
• Subjects: Scleractinia; Scleractinia > China > Hong Kong; Corals > Ecology; Corals > Ecology > China > Hong Kong
• Online Access: http://library.cuhk.edu.hk/record=b5549087; http://repository.lib.cuhk.edu.hk/en/item/cuhk-328577

石珊瑚是具有自營及異營功能的生物，近年來，異營功能被認為是石珊瑚很重要的營養來源，可令牠們從珊瑚白化中復原。香港每年的海水溫度可由冬天的攝氏十三度升到夏天的三十度，這季節性的溫度變異令香港成為石珊瑚生存的邊緣地方，石珊瑚只能組成群落但不能成礁。雖然環境因素對於石珊瑚的生長並不理想，但大型的珊瑚白化仍沒有發生，這意味著香港的珊瑚比較能夠適應香港的嚴峻困難環境，珊瑚具有的異營功能或許能夠提供牠們額外的能量，作為日常新陳代謝之用。所以，這研究的目標是找出異營功能對香港石珊瑚的重要性，這研究以豐年蝦的無節幼體(Artemia salina nauplii)及團塊角孔珊瑚(Goniopora lobata)作為實驗對象，以找出石珊瑚怎樣應用異營功能來加快生長、提高生理反應及增加能量儲備。此外，這研究還成立了一種量化珊瑚白化的方法，以提供一種簡單、快捷、客觀及不破壞珊瑚為前提的方法來監測珊瑚的健康。 === 本研究紀錄了七種香港常見但具有不同珊瑚蟲大小的石珊瑚的攝食速率，結果發現團塊角孔珊瑚的攝食速率最高，每小時每公升每平方厘米珊瑚表面積的攝食率在白天和晚上分別為203±90隻及145±79隻豐年蝦的無節幼體。攝食速率跟珊瑚蟲面積大小及豐年蝦的密度有著正面的相互關係。團塊角孔珊瑚與其它石珊瑚在外觀上有所不同，牠們無論白天或是晚上也會伸出自己的觸手，這特色令牠們可以攝取更多食物，所以牠們被選為這次研究的實驗珊瑚品種。 === 在異營的情況下，團塊角孔珊瑚的蟲黃藻密度及葉綠素a的濃度在一個月後倍增，由每平方厘米珊瑚表面積的2.75±0.50 x 10⁶蟲黃藻及每平方厘米珊瑚表面積每毫升的23.82±5.42微克葉綠素a到6.00±1.57 x 10⁶蟲黃藻及每平方厘米珊瑚表面積每毫升的53.56±17.66微克葉綠素a，但沒有異營的珊瑚則沒有任何轉變。`此外，從實驗的第二個星期起，應用異營功能的情況下珊瑚的鈣化速率會較快，平均達到每平方厘米珊瑚表面積每小時每公升100微克的生長。無論有異營與否，珊瑚的最大光合作用量子效率也保持在0.6左右。 === 本研究在數碼照片及電腦圖像分析軟件的幫助下，成立了量化珊瑚白化一種簡單、客觀、無破壞性及便宜的方法。這方法使用一塊貼上黑色及白色膠紙的金屬架作為黑白色的參考，再以數碼照片去量度白化的百分比，這方法測出白化了的濱珊瑚屬個體可以達到100%的白化百分比，此外，白化百分比與光合作用效率及蟲黃藻的密度有反向的關係。這方法能有效地在水底定期監測珊瑚的顏色變化，實驗的結果顯示團塊角孔珊瑚的顏色在一年間能有顯著的變化，在春天及秋天牠們只有少於20%的白化百分比，但在夏天及冬天則有超過30%的白化百分比，這跟光合作用效率有反向的關係。 === 在季節性溫度模擬實驗中反映出異營功能可以幫助珊瑚保持光合作用效率及帶來一個較和緩的珊瑚顏色轉變，此外，從團塊角孔珊瑚珊瑚蟲/觸手的長度得知，異營功能能夠令牠們的珊瑚蟲/觸手伸得更長，反映出利用異營功能的珊瑚個體比較健康及能主動地攝取食物。 === 在一天攝氏一度的溫度轉變的另一個實驗下，團塊角孔珊瑚的白化百分比隨著溫度轉變而增加，由20%增至60%，此外，長期的高溫壓力對於牠們較有破壞性，實驗結果顯示團塊角孔珊瑚在攝氏三十四度的高溫下會把其珊瑚蟲及觸手縮回在骨骼裏，而其白化百分比在實驗後的兩個月仍沒有下降的現象；珊瑚在攝氏十二度的低溫壓力下，並慢慢地回復到牠們合適的水溫後，牠們的顏色則漸變正常，珊瑚蟲/觸手也慢慢伸出來。但在更低的低溫壓力下(攝氏十度)，珊瑚蟲則從骨骼裏脫離，不能再回復。珊瑚蟲/觸手的長度或許能夠顯示珊瑚的健康及攝食狀態，實驗結果顯示珊瑚蟲/觸手的長度與水溫一起上升，但在低溫及攝氏三十度下，珊瑚蟲/觸手會慢慢縮回。利用異營功能與否對牠們的熱適應沒有任何分別，在攝氏十二度的低溫情況下，異營更帶來負面的影響，致珊瑚有較短的半致死時間。所以，在極端低溫及高溫的情況下，石珊瑚可能使用了很多的能量去抵抗轉變，但確不能從異營中取得額外的營養。本研究最後一個實驗正正反映出這個實況，展示出團塊角孔珊瑚最佳的攝食溫度為攝氏二十三度，每小時每公升每珊瑚蟲可進食28.11±4.59隻豐年蝦，但在攝氏十四跟三十二度下，牠們每小時每公升每珊瑚蟲只吃了約6隻豐年蝦。異營功能在合適的溫度下能夠提高珊瑚的能量儲備及蟲黃藻的密度，但在極端的溫度下，能量儲備則減少，甚至比自營的珊瑚個體還要低。總括而言，異營及自營功能對石珊瑚都是非常重要，但異營功能並不是絶對可以幫助珊瑚去抵抗嚴峻的環境壓力。 === 這次研究幫助認識了異營功能對香港珊瑚群落的作用，從而知道它能夠提供營養，提高蟲黃藻密度及能量儲備，香港石珊瑚可能依靠異營功能來適應香港特殊的環境。 === Scleractinian corals form coral communities in Hong Kong, a marginal area for their growth because of its fluctuating seawater surface temperature (SST) that ranged from 13 to 30ºC throughout a year. In spite of this, mass coral bleaching has not occurred in Hong Kong. It may be possible that Hong Kong corals are tougher, well adapted to the Hong Kong stressful environment. Heterotrophy may contribute significantly to their daily metabolic demand. This research therefore aimed at finding out the roles of heterotrophy in Hong Kong corals using Artemia salina nauplii as their food. === Goniopora lobata exhibited the highest feeding rate among all species tested. It is unique in having its polyps and tentacles extended all day long. This characteristic allows it to grab more food during the day than the other coral species examined and hence it was chosen to be the candidate for heterotrophy studies in this research. === With heterotrophy (Artemia salina nauplii feeding), zooxanthellae density and Chl a concentration were doubled in fed G. lobata colonies in 4 weeks. Calcification rates of fed colonies were generally higher than those of unfed colonies starting from the second week of a four week experiment. === Using digital imagery and computer image analysis, an easy, objective, non-destructive and inexpensive method was developed to quantify coral bleaching in terms of its % whiteness. This % whiteness of a coral is expressed with reference to the black and white markers around a metal frame or PVC plates. It was negatively correlated with photosynthetic efficiency and zooxanthellae density. When applied on G. lobata in situ, it was found that this coral showed seasonal fluctuation with < 20% whiteness in spring and autumn, but greater than 30% whiteness in summer and winter. === Experimental set up with seasonal temperature fluctuation pattern simulating that in the field revealed that heterotrophy can help to sustain photosynthetic yield and elicit a gentle coral colour change in G. lobata over time. Moreover, fed G. lobata extended their polyps / tentacles at a greater length than the unfed colonies, suggesting that fed colonies were more healthy and active in capturing food. === Heat stress was found to be more deleterious to G. lobata colonies such that they cannot extend their polyp / tentacles nor regain their colour two months after the thermal tolerance experiment using Chronic Lethal Methodologies (CLM) approach. In contrast, colonies of G. lobata cold-stressed at 12ºC had their colour returned to normal and their polyps / tentacles extended after a few days. The degree of extension of polyp / tentacle of G. lobata could thus be used as an indication of its health or feeding status. Under the cold stressed treatment of 12ºC, heterotrophy was even detrimental and a lower median lethal time (LT50) was found in fed colonies. Hence, it is likely that corals under extreme low and high temperatures would deplete more of their energy reserves and could not replenish them because of decline in their feeding rates. To verify this, additional experiment was carried out to evaluate the relationship between coral feeding rates, symbiont responses and energy reserves at a wide range of temperature from 14ºC to 32ºC. Results showed that feeding rate of G. lobata was optimal at 23ºC and much lowered at extremes. It also showed that heterotrophy was important in enhancing coral energy reserves and symbiont density under optimal feeding temperatures (23ºC and 27.5ºC) but less important under extreme temperatures such that energy reserves became even lower than that in the unfed colonies. This suggests that heterotrophy and autotrophy are both important to coral nutrition. Under optimal condition, heterotrophy could play a significant role in supplementing corals with additional energy reserves that could be used to overcome stresses. However, under extreme conditions, feeding stops and heterotrophy can no longer play its role and at times, could even be detrimental to the survival of the corals. === These findings from all the experiments are useful in providing the insight needed to understand the role of heterotrophy in Hong Kong corals and their effects on various physiological responses. Heterotrophy is important to provide nutrients for better growth, higher symbiont density and increased energy reserves and it may be the reasons why Hong Kong corals are tougher and can withstand a wide range of temperature fluctuation throughout a year. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Chow, Ming Him. === Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. === Includes bibliographical references (leaves 221-251). === Abstracts also in Chinese. === Acknowledgements --- p.i === Abstract --- p.ii === 摘要 --- p.vi === Contents --- p.viii === List of Tables --- p.xv === List of Figures --- p.xvi === Chapter Chapter 1 --- General Introduction === Chapter 1.1 --- Introduction --- p.1 === Chapter 1.1.1 --- Coral reef and its importance --- p.1 === Chapter 1.1.2 --- Scleractinian corals and coral-algal symbiosis --- p.3 === Chapter 1.1.3 --- Heterotrophic nutrition --- p.4 === Chapter 1.1.4 --- Autotrophy-heterotrophy dynamics --- p.6 === Chapter 1.1.5 --- Coral growth and calcification under heterotrophy --- p.7 === Chapter 1.1.6 --- Environmental stressors and coral bleaching --- p.9 === Chapter 1.1.7 --- Coral status in Hong Kong --- p.11 === Chapter 1.2 --- Significance of the project --- p.14 === Chapter 1.3 --- Study objectives --- p.15 === Chapter 1.4 --- Study site Wu Pai (Crescent Island) and Chek Chau (Port Island) --- p.16 === Chapter 1.5 --- Coral species chosen for the experiments --- p.17 === Chapter 1.6 --- Thesis outline --- p.18 === Chapter Chapter 2 --- Diurnal Heterotrophy in Corals as a Function of Their Polyp Size === Chapter 2.1 --- Introduction --- p.23 === Chapter 2.2 --- Materials and Methods --- p.26 === Chapter 2.2.1 --- Site description and sample collection --- p.26 === Chapter 2.2.2 --- Feeding experiments --- p.27 === Chapter 2.2.3 --- Artemia density count and feeding rate determination --- p.28 === Chapter 2.2.4 --- Data analysis --- p.29 === Chapter 2.3 --- Results --- p.30 === Chapter 2.3.1 --- Feeding rate of scleractinian corals between day and night --- p.30 === Chapter 2.3.2 --- Relationships between feeding rate and coral polyp area --- p.31 === Chapter 2.3.3 --- Relationship between feeding rate, Artemia concentration and feeding duration --- p.32 === Chapter 2.4 --- Discussion --- p.34 === Chapter 2.4.1 --- Feeding rate of scleractinian corals --- p.34 === Chapter 2.4.2 --- Hong Kong underwater environment --- p.38 === Chapter 2.4.3 --- Goniopora lobata as an active feeder --- p.39 === Chapter 2.4.4 --- Day and night differences --- p.40 === Chapter 2.4.5 --- Mechanisms of coral heterotrophy --- p.42 === Chapter 2.5 --- Summary --- p.43 === Chapter Chapter 3 --- Effects of Heterotrophy on the Growth and Photosynthetic Physiological Responses of Goniopora lobata === Chapter 3.1 --- Introduction --- p.52 === Chapter 3.2 --- Materials and Methods --- p.55 === Chapter 3.2.1 --- Sample collection and conditioning --- p.55 === Chapter 3.2.2 --- Coral culture experiment --- p.56 === Chapter 3.2.3 --- Feeding rate determination 57 === Chapter 3.2.4 --- Measurements of zooxanthellae density and chlorophyll a concentration --- p.57 === Chapter 3.2.5 --- Measurements of calcification rate --- p.59 === Chapter 3.2.6 --- Measurements of photosynthetic efficiency of corals --- p.61 === Chapter 3.2.7 --- Data analysis --- p.61 === Chapter 3.3 --- Results --- p.62 === Chapter 3.3.1 --- Feeding rate --- p.62 === Chapter 3.3.2 --- Zooxanthellae density and chlorophyll a concentration --- p.63 === Chapter 3.3.3 --- Calcification rate --- p.63 === Chapter 3.3.4 --- Maximum quantum yield --- p.64 === Chapter 3.4 --- Discussion --- p.65 === Chapter 3.4.1 --- Coral feeding rate, zooxanthellae density and chlorophyll a concentration --- p.65 === Chapter 3.4.2 --- Calcification rate --- p.67 === Chapter 3.4.3 --- Photosynthetic responses in fed and unfed corals --- p.69 === Chapter 3.5 --- Summary --- p.70 === Chapter Chapter 4 --- Quantifying the Degree of Coral Bleaching using Photoquadrat and Computer Image Analysis === Chapter 4.1 --- Introduction --- p.76 === Chapter 4.2 --- Materials and Methods --- p.79 === Chapter 4.2.1 --- Design of photoquadrat --- p.79 === Chapter 4.2.2 --- Photo image analysis --- p.80 === Chapter 4.2.3 --- Trial run and normalization of the technique --- p.81 === Chapter 4.2.3.1 --- Intensity of normal and bleached sections of a coral Porites sp. --- p.81 === Chapter 4.2.3.2 --- Intensity of coral Goniopora lobata under different exposure settings and contrasts --- p.82 === Chapter 4.2.4 --- Field application of the technique on other coral species --- p.82 === Chapter 4.2.5 --- Evaluation of the use of % whiteness to estimate photosynthetic physiological states of the coral Goniopora lobata --- p.83 === Chapter 4.2.5.1 --- Collection and photo taking of samples --- p.83 === Chapter 4.2.5.2 --- Photosynthetic quantum yield --- p.84 === Chapter 4.2.5.3 --- Tissue extraction and sample preservation for zooxanthellae and chlorophyll a measurements --- p.84 === Chapter 4.2.5.4 --- Zooxanthellae density count and determination of chlorophyll a concentration --- p.85 === Chapter 4.2.6 --- Data analysis --- p.86 === Chapter 4.3 --- Results --- p.87 === Chapter 4.3.1 --- Percent whiteness calculation --- p.87 === Chapter 4.3.2 --- Normalization of the technique --- p.88 === Chapter 4.3.2.1 --- Effect of simulated changes in light condition (exposure compensation) on % whiteness estimation --- p.88 === Chapter 4.3.2.2 --- Effect of simulated changes in turbidity (contrasts) on % whiteness estimation --- p.88 === Chapter 4.3.3 --- Colour change in common coral species at different seasons --- p.89 === Chapter 4.3.4 --- Relationship between % whiteness and photosynthetic physiological states of corals --- p.89 === Chapter 4.3.4.1 --- Effective quantum yield vs % whiteness --- p.90 === Chapter 4.3.4.2 --- Zooxanthellae density per coral surface area vs % whiteness --- p.90 === Chapter 4.3.4.2 --- Chlorophyll a concentration per cm² coral surface area vs % whiteness --- p.91 === Chapter 4.4 --- Discussion --- p.91 === Chapter 4.4.1 --- Measure of coral colour in terms of % whiteness --- p.92 === Chapter 4.4.2 --- Effects of extreme conditions in estimating coral % whiteness --- p.93 === Chapter 4.4.3 --- Changes in intensity of coral colours at different seasons --- p.95 === Chapter 4.4.4 --- Comparison with other approaches to quantify coral colour change --- p.96 === Chapter 4.4.5 --- Estimation of coral % whiteness as a tool to assess photosynthetic physiological state of corals --- p.98 === Chapter 4.4.6 --- Potential limitations of the technique --- p.100 === Chapter 4.5 --- Summary --- p.101 === Chapter Chapter 5 --- High and Low Thermal Tolerance Limits of Goniopora lobata === Chapter 5.1 --- Introduction --- p.112 === Chapter 5.2 --- Materials and Methods --- p.116 === Chapter 5.2.1 --- Sample collection and conditioning --- p.116 === Chapter 5.2.2 --- Polyp / tentacle length classification of Goniopora lobata --- p.117 === Chapter 5.2.3 --- Upper thermal limit experiment (Experiment 1) --- p.118 === Chapter 5.2.4 --- Lower thermal limit experiment (Experiments 2A and 2B) --- p.118 === Chapter 5.2.5 --- Data analysis --- p.119 === Chapter 5.3 --- Results --- p.120 === Chapter 5.3.1 --- Experiment 1 (Upper thermal tolerances of corals) --- p.120 === Chapter 5.3.1.1 --- Daily changes in the frequency of polyp / tentacle length classes of coral colonies --- p.120 === Chapter 5.3.1.2 --- Mortality and LT₅₀ --- p.121 === Chapter 5.3.1.3 --- % whiteness --- p.121 === Chapter 5.3.2 --- Experiment 2A (Lower thermal tolerances of corals, lower limit: 12ºC) --- p.122 === Chapter 5.3.2.1 --- Daily changes in the frequency of polyp / tentacle length classes of coral colonies --- p.122 === Chapter 5.3.2.2 --- Mortality and LT₅₀ --- p.123 === Chapter 5.3.2.3 --- % whiteness --- p.123 === Chapter 5.3.3 --- Experiment 2B (Lower thermal tolerances of corals, lower limit: 10ºC) --- p.124 === Chapter 5.3.3.1 --- Daily changes in the frequency of polyp / tentacle length classes of coral colonies --- p.124 === Chapter 5.3.3.2 --- Mortality and LT₅₀ --- p.125 === Chapter 5.3.3.3 --- % whiteness --- p.125 === Chapter 5.4 --- Discussion --- p.126 === Chapter 5.4.1 --- Polyp / tentacle lengths of Goniopora lobata under different temperatures --- p.126 === Chapter 5.4.2 --- The effects of heterotrophy (feeding) on G. lobata survivorship under extreme temperatures --- p.127 === Chapter 5.4.3 --- Coral colour and bleaching --- p.128 === Chapter 5.4.4 --- Upper, lower thermal tolerances and LT₅₀ of Goniopora lobata --- p.128 === Chapter 5.4.5 --- Coral recovery --- p.129 === Chapter 5.4.6 --- Corals after thermal stress --- p.130 === Chapter 5.4.7 --- Application of CLM approach and its implications --- p.131 === Chapter 5.5 --- Summary --- p.132 === Chapter Chapter 6 --- Seasonal Variations in Coral Colour and Physiological Responses of Goniopora lobata in situ and ex situ === Chapter 6.1 --- Introduction --- p.142 === Chapter 6.2 --- Materials and Methods --- p.147 === Chapter 6.2.1 --- Seasonal field study --- p.147 === Chapter 6.2.2 --- Laboratory study --- p.148 === Chapter 6.2.3 --- Data analysis --- p.150 === Chapter 6.3 --- Results --- p.152 === Chapter 6.3.1 --- Ambient seawater temperature, effective quantum yield and % whiteness of Goniopora lobata colonies in the natural environment --- p.152 === Chapter 6.3.2 --- Zooplankton abundance and biomass --- p.153 === Chapter 6.3.3 --- Responses of G. lobata under the simulated environmental conditions --- p.154 === Chapter 6.3.3.1 --- Coral mortality --- p.154 === Chapter 6.3.3.2 --- Seasonal maximum quantum yields --- p.155 === Chapter 6.3.3.3 --- Seasonal feeding rates --- p.155 === Chapter 6.3.3.4 --- Seasonal change in coral colours --- p.156 === Chapter 6.4 --- Discussion --- p.156 === Chapter 6.4.1 --- Coral colour change, effective quantum yield, seawater temperature, zooplankton abundance and coral heterotrophy in the natural environment --- p.157 === Chapter 6.4.2 --- Coral responses under simulated seasonal change conditions --- p.160 === Chapter 6.4.3 --- Comparison of coral responses to seasonal change under natural and simulated laboratory conditions --- p.163 === Chapter 6.4.4 --- Limitations of this simulation approach --- p.165 === Chapter 6.5 --- Summary --- p.167 === Chapter Chapter 7 --- Effects of Temperature and Heterotrophy on Physiological Responses and Energy Reserves of Goniopora lobata === Chapter 7.1 --- Introduction --- p.177 === Chapter 7.2 --- Materials and Methods --- p.180 === Chapter 7.2.1 --- Sample collection and acclimation --- p.180 === Chapter 7.2.2 --- Design of the experiment --- p.181 === Chapter 7.2.3 --- Artemia feeding experiments --- p.181 === Chapter 7.2.4 --- Coral tissue extraction and analysis --- p.182 === Chapter 7.2.4.1 --- Zooxanthellae and chlorophyll a measurement --- p.183 === Chapter 7.2.4.2 --- Protein content analysis --- p.184 === Chapter 7.2.4.3 --- Carbohydrate content analysis --- p.184 === Chapter 7.2.4.4 --- Total lipid content analysis --- p.185 === Chapter 7.2.5 --- Photosynthetic quantum yield measurement --- p.186 === Chapter 7.2.6 --- Coral colour quantification --- p.186 === Chapter 7.2.7 --- Data analysis --- p.187 === Chapter 7.3 --- Results --- p.188 === Chapter 7.3.1 --- Feeding rate --- p.188 === Chapter 7.3.2 --- Zooxanthellae density --- p.188 === Chapter 7.3.3 --- Chlorophyll a (Chl a) content --- p.190 === Chapter 7.3.4 --- Protein content --- p.191 === Chapter 7.3.5 --- Carbohydrate contents --- p.191 === Chapter 7.3.6 --- Total lipids --- p.192 === Chapter 7.3.7 --- Maximum quantum yield --- p.193 === Chapter 7.3.8 --- Coral colour --- p.194 === Chapter 7.4 --- Discussion --- p.195 === Chapter 7.4.1 --- Feeding responses under different temperatures --- p.196 === Chapter 7.4.2 --- Symbiont responses under different temperatures --- p.198 === Chapter 7.4.3 --- Energy reserves --- p.199 === Chapter 7.4.4 --- Autotrophy-heterotrophy dynamics --- p.201 === Chapter 7.5 --- Summary --- p.202 === Chapter Chapter 8 --- Summary and Perspectives --- p.212 === References --- p.221