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|Title: ||Effects of temperature, salinity and food availability on two subtidal nassariid gastropods, Nassarius siquijorensis and Nassarius conoidalis|
|Other Titles: ||Wen du, yan du he shi wu dui liang zhong chao xia dai zhi wen luo (Xi ge zhi wen luo he Fang ge zhi wen luo) de ying xiang|
|Authors: ||Zhao, Qian ( 趙倩)|
|Department: ||Department of Biology and Chemistry|
|Degree: ||Master of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Nassarius -- Effect of temperature on.|
Nassarius -- Effect of salt on.
Nassarius -- Food.
|Notes: ||CityU Call Number: QL430.5.N3 Z45 2011|
xviii, 195 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2011.
Includes bibliographical references (leaves 160-193)
|Abstract: ||Owing to degradation of seabed communities by environmental stresses and human perturbations, species which have specialized diets in the local marine benthic community are gradually replaced by opportunistic species of which a number of them are scavengers. This study investigated how three major environmental factors, temperature, salinity and food availability, affected the survival, development, behaviour and physiology of the embryos, larvae and adults of two dominant subtidal scavenging gastropods, Nassarius siquijorensis and Nassarius conoidalis.
Mortality and developmental rate of the embryos of N. siquijorensis and N. conoidalis were investigated at nine combinations of temperature (20, 25, and 30°C) and salinity (20, 25, 30‰). The median hatching time (HD50) was calculated using the standard logistic regression. Temperature, salinity, as well as the interaction between temperature and salinity had significant effects on both survival and HD50 for both N. siquijorensis and N. conoidalis with highest survival and fastest development at 30°C and 30‰.
Larval mortality at six temperatures (10, 15, 20, 25, 30 and 35°C) and seven salinities (0, 5, 10, 15, 20, 25 and 30‰) were observed after 24 hrs and 48 hrs. Both N. siquijorensis and N. conoidalis larvae showed higher mortalities at low temperatures and salinities, especially at 10°C or at 5‰, with more than half of them died after 48 hrs. The larval mortality of N. siquijorensis under low temperatures and salinities was significantly lower than that of N. conoidalis. Respiration rate, swimming velocity, and clearance rate of the larvae of N. siquijorensis and N. conoidalis were measured at nine combinations of temperature (20, 25, and 30°C) and salinity (20, 25, 30‰). Temperature, salinity and the interaction between temperature and salinity had significant effects on oxygen consumption, clearance rate and swimming behaviour of both species. Significantly lower clearance rates and oxygen consumption rates were observed at lower salinities and temperatures, and the dispersal distance VSL was significantly higher at lower salinities.
The effects of starvation on respiration, ammonia excretion, shell length, body weight, scope for growth (SFG) and body chemical composition of N. siquijorensis and N. conoidalis were studied for 32 days. During starvation, significant decreases in respiration rate and ammonia excretion rate were observed for both N. siquijorensis and N. conoidalis. Starvation, time, and the interaction between starvation and time were found to be significant in affecting SFG for both N. siquijorensis and N. conoidalis. At the end of the experiment, the unfed individuals had significantly lower percentages of protein and fat but higher percentages of carbohydrate as compared with the control for both N. siquijorensis and N. conoidalis. Significant increases in wet weight and shell length were obtained from the control for both N. siquijorensis and N. conoidalis but the differences between species were insignificant. In another experiment in which the individuals were starved for 96 days, a significantly higher mortality was obtained for N. siquijorensis as compared with N. conoidalis.
The effects of starvation and distance from carrion on chemoreception were compared between N. siquijorensis and N. conoidalis. The time to reach carrion was species specific and was significantly affected by both starvation and the distance from the carrion. Under well-fed condition, mean time to detect carrion at 15 cm and 20 cm away from carrion were significantly shorter in N. siquijorensis than N. conoidalis. For the starved group, the mean time to detect carrion at 2.5 cm and 10 cm away from carrion, however, was significantly shorter in N. conoidalis than N. siquijorensis. For N. conoidalis, starved individuals were more sensitive to carrion than well-fed ones with higher percentages of individuals able to locate the carrion at 10 cm, 15 cm and 20 cm away from the carrion.
In summary, embryos and larvae of N. siquijorensis are more tolerant than N. conoidalis to temperature and salinity changes. This may help explain why N. siquijorensis has a wider distribution in Hong Kong waters as compared with N. conoidalis which is restricted to southern waters where salinity is relatively constant throughout the year. Both N. conoidalis and N. siquijorensis are generalist feeders adaptive to unpredictable food supply by reducing energy expenditure through decreasing respiration and ammonia excretion when starved. In recent years, they are gradually replacing species which have specialized diets in Hong Kong waters where the benthic environment suffers from various human disturbances such as eutrophication, trawling and hypoxia which directly or indirectly affects food availability. Nevertheless, N. siquijorensis grow faster than N. conoidalis when food availability is high while N. conoidalis perfom better under starvation. Their differential responses to food availability may help explain the dominance of N. siquijorensis in Hong Kong waters where the benthic environment is highly disturbed.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086608|
|Appears in Collections:||BCH - Master of Philosophy |
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