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瞭解浮游動物與它們的捕食者之間的相互作用對指導我們瞭解浮游生物群體結構形成的過程以及整個生態系統的食物網結構有著重要的作用。浮游動物的捕食者對它們的進化產生影響，同時還塑造了它們複雜的行為，其中之一便是引起它們的反攝食防禦行為。改變形態結構，生活史各參數和行為運動方式是浮游動物採取的三類最主要的可誘導防禦策略。在情況多變、動態的海洋環境中，魚類通常是主要的捕食者，反攝食行為方式對浮游動物來說特別重要，因為其他兩類防禦模式主要對口裂寬度有限制的無脊椎捕食者較為有效。 / 海洋枝角類是一組廣泛分佈的小型甲殼類動物，它們時常成為浮游動物群體中重要的一部分，在海洋食物網中扮演重要的角色。本論文對香港吐露港海域海洋枝角類的反攝食防禦行為進行了全面的研究，包括晝夜垂直遷移，水準遷移，晝夜生殖和攝食節律。這些反攝食行為應隨著物種的不同及環境的不同而發生變化。考慮到鳥喙尖嘴溞、肥胖三角溞和多形圓囊溞三種物種不同生理的結構和攝食機制，將它們的反攝食防禦行為進行比較能夠檢驗一些關於外在和內在因素對反攝食行為形成影響的假設。此項研究第一個要檢驗的假設是仙達蚤科（鳥喙尖嘴溞）和圓囊溞科(肥胖三角溞和多形圓囊溞)身體結構上的不同會造成它們的反攝食行為多樣化。另一個假設是每個物種的反攝食行為的表現會受到環境條件的影響。 / 在吐露港對海洋枝角類的晝夜垂直和水準遷移行為的研究表明：鳥喙尖嘴溞並不進行晝夜垂直遷移。在2009年8月的研究中，大部分個體全天都避開水面而處在4－8米深的位置。在2010年4月大部分群體有反向遷移的跡象，夜間分佈在較深的水中。與之相反，肥胖三角溞和多形圓囊溞都有顯著的反向晝夜遷移行為。晝夜水準遷移在2010年4月三個物種中都存在，但是在2009年8月研究中的鳥喙尖嘴溞和肥胖三角溞中卻沒有任何晝夜水準遷移的跡象。 / 以晝夜腸道的飽和度為指示，我們對吐露港海洋枝角類的晝夜攝食節律進行了研究。無論是2009年8月還是2010年4月，鳥喙尖嘴溞腸道的飽和程度都有明顯的晝夜差別，它們的腸道總是在夜裡有最高的飽和度。肥胖三角溞和多形圓囊溞的腸道飽和度的晝夜節律非常相似，並且在不同的環境條件下一天的變化規律也幾乎相同，最明顯的特徵是與光線的強度緊密相關。 / 我們同時對吐露港海洋枝角類的晝夜生殖節律，尤其是無性胚胎的發育和幼體釋放出母體的時間進行了研究。在2009年8月和2010年4月的研究中鳥喙尖嘴溞和肥胖三角溞種群都只發現了無性生殖母體。鳥喙尖嘴溞的無性胚胎全天都可能成熟，並沒有一個清晰的發育規律。例如在2009年8月，攜帶發育成熟胚胎的鳥喙尖嘴溞在夜裡時占種群的比例最高，而且幼體釋放的時間大部分都在半夜至日出之間。然而在2010年4月研究中，攜帶發育成熟胚胎的鳥喙尖嘴溞占種群的比例最高的時間大約在日落時，大部分幼體也在日落到半夜之間發生。攜帶成熟胚胎的鳥喙尖嘴溞白天要比無胚胎或者攜帶為發育成熟胚胎的鳥喙尖嘴溞處在水中的深度更深，但是夜晚在2009年9月研究中集聚在水面處，可是在2010年4月中卻沒有觀察到這種現象。 / 肥胖三角溞無性胚胎的成熟和幼體的釋放卻有著非常嚴格的晝夜節律。無性母體只在黑夜的時候才攜帶眼睛具有黑色素、發育成熟的胚胎。釋放這些幼體在天亮前全部完成。在2010年4月，雌性多形圓囊溞分為無性繁殖多形圓囊溞和有性多形圓囊溞。攜帶有休眠卵的有性多形圓囊溞全天可見，在正午時占種群的比例最低，日出時最高。攜帶有休眠卵的有性多形圓囊溞在水中的位置比整個種群的位置無論是白天還是夜晚都更加深。 無性繁殖的比例仍然高於有性繁殖多形圓囊溞的比例。多形圓囊溞無性胚胎的成熟和幼體的釋放晝夜節律沒有肥胖三角溞那麼嚴格，因為除了深夜，在日落和日出也能見到零星的攜帶成熟胚胎的多形圓囊溞。但是絶大部分攜帶成熟無性胚胎的多形圓囊溞仍然出現在黑夜。 / 此項研究提供了很好的例子，明進一步瞭解海洋生態系統中躲避捕食者的機制。例如，濾食動物鳥喙尖嘴溞不依賴光照獲得食物，它的垂直分佈模式主要受環境的影響。它不具有嚴格的胚胎成熟與後代釋放的節律因為它們不會大大增加其可見性。但是它們通常白天的腸道飽和度低於夜晚，是一種降低可見行和捕食危險的行為。相反，肥胖三角溞和多形圓囊溞需要光線來攝食，因此白天必須留在水面上，腸道更為飽和，然而它們利用近乎透明的身體和嚴格的生殖節律來降低被依賴視覺的捕食者例如魚類捕食的危險。 / Understanding interactions between zooplankton and their predators is essential in guiding our understanding of the processes responsible for structuring plankton communities and marine food web. Predators exert evolutionary force on prey and also shape the complex behavior of zooplankton species, which includes anti-predator defenses. Morphology alteration, life history shifts and behavioral changes, are three major inducible defenses adopted by zooplankton spe-cies. In highly dynamic marine environment where fish are usually the donimant predators, be-havioral anti-predator defenses are particularly important, since the others are mainly effective against gape-limited invertebrate predators. / Marine cladocerans are a group of widely distributed small crustaceans, which at times consti-tute a significant proportion of the zooplankton community and play an important role in marine food web. This thesis presents a detailed study of the anti-predator behaviors of thre marine cladoceran species in Tolo Harbour, Hong Kong, including diel vertical migration (DVM), diel horizontal migration (DHM), diel reproductive rhythm and diel feeding rhythm (DFR). The anti-predator behaviors are supposed to vary among different species as well as environmental conditions. The hypothesis being tested in this study is that the physical differences between Sididae (P. avirostris) and Podonidae (P. tergestina and P. polyohemoides) make the pattern of behavioral defenses diverse. Another hypothesis is that the exhibition of behavioral defenses by each species will be regulated by environmental conditions. / The study showed that P. avirostris did not perform DVM. In August 2009, the majority of the population avided the surface and stayed at the food-rich 4-8 m throughout the day. In April 2010, P. avirostris showed the trend of reverse DVM, descending to a little deeper water at night. On the contrary, P. tergestina and P. polyphemoides showed pronounced reverse DVM in both study periods. DHM was found in all three species in April 2010, but not in August 2009. / Diel feeding rhythm was studied using diel rhythm in gut fullness as an indicator. P. avirostris showed day-night difference in the gut fullness, with fullest guts during the night in both August 2009 and April 2010. Gut fullness rhythm in P. tergestina and P. polyphemoides was quite simi-lar to each other and different from P. avirostris. Their gut fullness was closely related with light intensity. / In both August 2009 and April 2010, P. avirostris and P. tergestina populations consisted of exclusively the parthenogenetic females. Maturation of brood in P. avirostris occurred through-out the day and there was no strict cycle. In August 2009, the highest percentage of parthenoge-netic females with mature embryos was around mid-night, and the release of neonates was maximal between mid-night and dawn. However, in the study of April 2010 the percentage was highest around dawn and maximal offspring release was between dawn and mid-night. Females carrying mature embryos always stayed deeper than females of other reproductive stages during the daytime, while during the night they aggregated at the surface in August 2009 but stay deep in April 2010. On the contrary, embryo maturation and release had a strict rhythm in P. tergestina, in which parthenogenetic females only carried mature embryos with pigmented eyes in darkness of the night and release of neonates was completed and maximal before dawn. InApril 2010 both gamongenetic and parthenogenetic females of P. polyphemoides were found. Gamogenetic P. polyphemoides females carried resting eggs all the day, with lowest percentage at noon and highest at dawn. The mean depth of the females carrying resting eggs was deeper than the mean depth of the population at both day and night. The population still consisted of more parthenogenetic females than gamogenetic females. The diel rhythm in embryo maturation and release in P. polyphemoides was not as strict as in P. tergestina, as females with mature embryos could be observed in dawn and dusk besides mid-night. However, the majority was still found in total darkness of the night. / The study provides further understanding of predator-avoidance mechanisms in marine ecosys-tem. Herbivorous suspension feeder P. avirostris does not rely on light to feed and its vertical distribution is subject to environmental conditions. It also does not have a strict diel rhythm in embryo maturation and release since the brood is not greatly increases their conspiciousness. However, P. avirostris always shows less full guts during the day than at night, a behavior probably reducing their risk to visual predators. On the contrary, podonid species P. tergestina and P. polyphemoides depend on light to feed, which forces them stay in well-lit water surface during the day and result in significantly higher gut fullness at the daytime, while their transpar-ent body and a strict diel rhythm in embryo maturation and release in darkness of the night help reduce the risk of predation by visual predators such as fish. / 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. / Li, Wei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 103-120). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Acknowledgements --- p.i / Table of Contents --- p.vi / List of Tables --- p.x / Chapter Chapter 1 --- Literature review --- p.1 / Chapter 2.1 --- Zooplankton anti-predator strategies --- p.1 / Chapter 2.2 --- Review on marine cladocerans --- p.10 / Chapter 2.2.1 --- Taxonomy of marine cladocerans --- p.10 / Chapter 2.2.2 --- Spatial and seasonal distribution of marine cladocerans --- p.10 / Chapter 2.2.3 --- Vertical distribution of marine cladocerans --- p.13 / Chapter 2.2.4 --- Diet behaviors --- p.13 / Chapter 2.2.5 --- Reproduction of marine cladocerans --- p.15 / Chapter 2.3 --- Objective --- p.18 / Chapter Chapter 3 --- Material and methods --- p.20 / Chapter 3.1 --- Description of study sites in Tolo Harbour --- p.20 / Chapter 3.2 --- Field sampling --- p.22 / Chapter 3.3 --- Laboratory Analysis --- p.24 / Chapter 3.4 --- Statistical Methods --- p.29 / Chapter Chapter 4 --- Results --- p.32 / Chapter 4.1 --- Physical conditions of study sites --- p.32 / Chapter 4.2 --- Anti-predator behavior of marine cladoceran species --- p.41 / Chapter 4.2.1 --- Penilia avirostris --- p.41 / Chapter 4.2.1.1 --- Diel vertical migration (DVM) and horizontal migration (DHM) --- p.41 / Chapter 4.2.1.2 --- Diel gut fullness rhythm --- p.49 / Chapter 4.2.1.3 --- Diel reproduction pattern --- p.53 / Chapter 4.2.2 --- Pseudevadne tergestina --- p.57 / Chapter 4.2.2.1 --- Diel vertical migration (DVM) and horizontal migration (DHM) --- p.57 / Chapter 4.2.2.2 --- Diel gut fullness rhythm --- p.65 / Chapter 4.2.2.3 --- Diel reproduction pattern --- p.69 / Chapter 4.2.3 --- Pleopis polyphemoides --- p.72 / Chapter 4.2.3.1 --- Diel vertical migration (DVM) and horizontal migration (DHM) --- p.72 / Chapter 4.2.3.2 --- Diel gut fullness rhythm --- p.79 / Chapter 4.2.3.3 --- Diel reproduction pattern --- p.82 / Chapter Chapter 5 --- Discussion --- p.88 / Chapter Chapter 6 --- Summary and Conclusions --- p.100 / References --- p.103

Thesis (Ph. D.)--University of Rhode Island, 2003. / Typescript. Includes bibliographical references (v. 2, leaves 331-354).

As one of the most abundant metazoan groups on the planet, copepods are found in virtually all marine environments. They provide a key link in marine food webs between photosynthetic algae and higher trophic levels. Subsequently, copepods are preyed upon by a wide variety of organisms throughout their life history. As a result copepods have evolved a powerful escape behavior at all stages of development, in response to hydrodynamic stimuli created by an approaching predator. Typically copepods exhibit 6 naupliar stages and 5 copepodite stages before becoming adults. This work focuses on quantifying the effectiveness of the escape behavior during key periods of development. The earliest developmental stage of copepod (nauplius N1) experiences the greatest amount of viscous forces and may be at a disadvantage when exposed to larger predators at cold temperatures. The results show that the nauplius exhibits a compensatory mechanism to maximize escape performance across its thermal range. Later in development, the nauplius (N6 stage) molts into a copepodite (C1 stage) which resembles the body form of an adult copepod. Here, there is a significant morphological change with little change in mass. Escape capabilities are investigated for key stages in response to feeding strikes from natural fish predators. The results demonstrate that the improvement in escape capability of the C1 stage is effective only against certain modes of predation. Finally, successfully escaping from predation has evolutionary fitness implications and adults (post C5) are the only reproductive stage. Some species have developed unique mechanisms to avoid predation such as breaking the water surface and making aerial escapes to avoid predators while in other cases, the predator has developed unique morphology in order to reduce the amount of hydrodynamic disturbance in the water which improves capture success of copepods. By investigating copepod behavior and their ability to avoid predation at various stages of development, we can begin to understand which stages copepods are most susceptible to different types of predators and how the escape response changes as development progresses. This can help in understanding localized abundances or deficiencies of both predator and prey in the marine food web. / text

Predators can affect prey by increasing their mortality, or may reduce the fitness of prey which modify their behaviours in response to predation risks (i.e. risk effects). Non-lethal effects of predators on prey behaviours are still poorly understood, although they may have cascading effects through food webs. This thesis examined the effect of habitat structure and symbiotic associations on the interaction between predatory fish and three rhynchocinetid shrimps: Rhynchocinetes typus in temperate rocky reefs in Chile, R. brucei in tropical rocky reefs in Hong Kong and Cinetorhynchus hendersoni in coral reefs in Malaysia. Underwater observations in Chile revealed that R. typus was rarely found on substrata with simple structure where refuges were scarce or lacking, but the effect of substratum complexity on their abundance was weak, probably because low fish abundance (and hence predation risk) did not affect survival probability below a critical threshold of refuge availability. This was in accordance with the observation that shrimp and fish abundance were negatively correlated in managed areas where fishing was limited, but not in open-access areas, were fish were less abundant. In addition, shrimps tended to form large aggregations in large shelters that offered limited protection against predators. Overall, direct effects of predation on shrimp densities and population structure were weak in Chile, whereas indirect effects on shrimp distribution within reefs appear to have been mediated through behavioural responses. Shrimp and other small decapods often associate with invertebrate hosts in order to gain protection from predators. In Hong Kong, where prolonged overexploitation of large predatory fishes has resulted in dominance of small fishes, R. brucei uses two alternative hosts: an urchin (Diadema setosum) and an anemone (Entacmaea quadricolor). Underwater surveys revealed that shrimps were rarely found outside crevices and holes unless associated with anemones and urchins. Experiments in the laboratory confirmed that, when given a choice, shrimps avoided open areas and associated with anemones and urchins which protected them against fish. Shrimps also imprinted upon the host species with which they were associated when collected from the field, and selected that host when given a choice. In Malaysia, where fish were more abundant than in Chile or Hong Kong, predation risks on C. hendersoni were high during the day, and shrimps exhibited nocturnal activity seemingly to reduce predation risk. Shrimps preferred only the most complex substrata, which provided the best protection against predators, while substrata with simple structure and few refuges were avoided. Tethering experiments and field observations confirmed that diel behaviour and substratum selection were driven by predation risk. Differences in fish abundance and diversity at the three study sites resulted in varying predation risks that influenced activity patterns and habitat choice by reef shrimps. These behavioural responses of prey to predation risks and their interactions with habitat structure have important implications for predicting how human disturbances, such as overfishing or habitat degradation, may disrupt predator-prey interactions and modify food webs. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

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