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Title: Effects of dissolved oxygen concentration on marine gastropod nassarius festivus
Other Titles: Han yang liang dui xiu li zhi wen luo de ying xiang
Authors: Chan, Ho Yan (陳可欣)
Department: Dept. of Biology and Chemistry
Degree: Master of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Nassariidae -- Effect of oxygen on
Water -- Dissolved oxygen -- Physiological effect
Notes: CityU Call Number: QL430.5.N3 C45 2006
Includes bibliographical references (leaves 181-212)
Thesis (M.Phil.)--City University of Hong Kong, 2006
xxvi, 212 leaves : ill. (some col.) ; 30 cm.
Type: Thesis
Abstract: As one of the major outcomes of eutrophication, ecological effects of hypoxia have received an increasing concern in the past few years. Information on effects of hypoxia on individual species, however, is scarce. The present study investigated adult physiology and behaviour, embryonic development, larval development and swimming behaviour of marine scavenging gastropods Nassarius festivus at reduced dissolved oxygen levels. N. festivus (shell length: 8 + 1 mm) were exposed to reduced oxygen levels (3.0 and 1.5 mg O2/l) and normoxia (6.0 mg O2/l) for 7 weeks. Food consumption, percentage of feeding individual, oxygen consumption rate, ammonia excretion rate, egg production, dimensions of egg capsules and embryos produced, mortality and shell growth were measured weekly. Scope for growth (SFG) was also calculated. Results showed that food consumption, percentage of individuals feeding, oxygen consumption rate, ammonia excretion rate, egg capsules production and SFG were significantly lowered at reduced dissolved oxygen levels. The size of egg capsules was similar at reduced dissolved oxygen levels. The mean number of eggs produced per capsule was 13.28, 12.46 and 12.88 for 6.0 mg O2/l, 3.0 mg O2/l and 1.5 mg O2/l, respectively. N. festivus exposed to 6.0 mg O2/l, 3.0 mg O2/l and 1.5 mg O2/l have mean shell growth rate 12%, 6% and 5%, respectively. No mortality was observed for adult N. festivus at 6.0 mg O2/l. Cumulative mortality at 3.0 mg O2/l and 1.5 mg O2/l was 7% and 15%, respectively. Stage 1 embryos were exposed to four dissolved oxygen levels (0.5, 1.5, 3.0 and 6.0 mg O2/l) and development was observed at 12-hour interval until the veliger larvae hatched. Once the veliger larvae hatched, their shell length, shell width and length of velum were measured. Significant delay in embryonic development was observed when dissolved oxygen concentration decreased. Embryos required 132, 156 and 252 hours to complete the whole embryonic development at 6.0 mg O2/l, 3.0 mg O2/l and 1.5 mg O2/l, respectively. No embryos hatched at 0.5 mg O2/l throughout the whole experiment (252 hours). Larvae hatched from egg capsules exposed to reduced dissolved oxygen concentrations (3.0 mg O2/l and 1.5 mg O2/l) had a smaller mean shell width and velum size when compared with those hatched at 6.0 mg O2/l. Mortality and swimming behaviour of larvae was recorded after exposure to six dissolved oxygen concentrations (0.5, 1.0, 2.0, 3.0, 4.0 and 6.0 mg O2/l) for 48 hours. Larvae of N. festivus exhibited median 48-h LC50 values at 1.65 mg O2/l. Under 0.5 mg O2/l, all larvae died during the first 24 hours. Swimming speed of larvae reduced significantly upon exposure to reduced dissolved oxygen levels. Larvae were reared in three different dissolved oxygen levels (3.5, 4.5 and 6.0 mg O2/l). Size of velar lobes, shell length and width of 30 larvae were measured at 4-day interval. Ingestion rates of 60 larvae were also measured. Larvae reared at 4.5 mg O2/l and 3.5 mg O2/l had significantly smaller shell length, shell width and velum in comparison with larvae reared at 6.0 mg O2/l. Ingestion rates of N. festivus larvae were similar during the first 8 days at 6.0 mg O2/l and 4.5 mg O2/l, whereas ingestion rates of larvae were significantly reduced at 3.5 mg O2/l. On day 12, larvae reared at 6.0 mg O2/l had higher ingestion rate than those at 4.5 mg O2/l. The percentage of larvae undergo spontaneous metamorphosis was reduced and metamorphosis was delayed under reduced dissolved oxygen level. At 6.0 mg O2/l, larvae of N. festivus started to metamorphose on day 8 with 100% success. At 4.5 mg O2/l, metamorphose started on day 11 with 49% of larvae competent to metamorphosis. At 3.5 mg O2/l, all larvae died before they underwent metamorphosis. Larvae reared at 4.5 mg O2/l tended to form juveniles with smaller shell length and width in comparison with those reared at 6.0 mg O2/l. Larvae reared under reduced dissolved oxygen concentration had significantly higher mortality. No mortality was observed for larvae reared at 6.0 mg O2/l. To summarize, adult N. festivus showed retardation in growth and reduction in food consumption under reduced dissolved oxygen levels. The larvae, on the other hand, showed high mortality, and reduction in swimming activities and growth under reduced dissolved oxygen levels. Since adult N. festivus play an important role in nutrient recycling on sandy shores whereas their planktonic larvae play an important trophic link between phytoplankton and higher trophic levels, hypoxic stress on this animal may lead to disruption of trophodynamics and nutrient recycling in marine coastal systems.
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