Feeding ecology of the estuarine copepods Pseudodiaptomus annandalei (calanoid, Swell 1919) and Apocyclops royi (cyclopoid, Lindberg 1940): herbivory, predation and prey selection

• Main Authors: Raunak Dhanker, 羅娜
• Other Authors: Hwang, Jiang-Shiou
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/5xfmxz

博士 === 國立臺灣海洋大學 === 海洋生物研究所 === 102 === Copepods play a central role in transferring carbon from lower trophic level to higher trophic level such as fish in the estuarine and marine food webs. The two copepods the calanoid Pseudodiaptomus annandalei (Swell 1919) and the cyclopoid Apocyclops royi (Lindberg 1940) are dominant estuarine copepod species. Both the species were considered to be herbivorous, and being cultured as live feed for grouper and other economical fish larvae. Little attention has so far been paid on feeding ecology of these copepod species. In this thesis, the feeding ecology and predation behavior of these two copepod species on rotifer Brachionus rotundiformis and ciliate Euplotes sp. were elucidated quantitatively as well as qualitatively. Their reproductive performance, survival, postembryonic developmental rates and population dynamics have been estimated on diets of phytoplankton (mono- and plurialgal), animal and combinations theirof. Moreover, the influence of Poly Unsaturated Aldehydes (PUAs) of diatom on development and population size of each copepod species were also investigated. For predation efficiency examination, these copepods were offered ciliate and three states of B. rotundiformis (neonates, ovigerous and non-ovigerous adults) to investigate prey choice, egg predation, prey consumption rates, size selection, and satiation levels and duration. Prey consumption rates on rotifer and ciliate were also recorded in the presence and absence of algae, the smaller Isochrysis galbana and the larger Tetraselmis chui. The predation behavior of each copepod species was videotaped by Fastcam providing information about ingestion of rotifer eggs, rotifer adults and ciliates. Both males and females of each copepod species were able to ingest on eggs, neonates, adults of rotifer and ciliate. Prey consumption rates were higher in P. annandalei than in A. royi. Regardless of sex and reproductive state of the copepods, prey consumption rates were higher on rotifer neonates than on adults and ciliates except the case of male of P. annandalei. The presence of I. galbana had no effect on prey consumption; T. chui influenced the prey consumption rates in P. annandalei. However, the presence of either I. galbana or T. chui significantly reduced the prey ingestion rates in A. royi adults. The egg consumption in copepods increased with increasing numbers of egg bearing rotifers in their environment. From a combination of neonates of B. rotundiformis with either adults rotifer or cells of Euplotes sp. copepod females preferred neonates over adult rotifers and ciliate except at higher proportion of ciliate in A. royi. The prey preference of copepods exhibited switching based on relative prey proportion in the environment. Satiated copepods rejected rotifers more often than hungry individuals. Dual feeding nature of P. annandalei attested that this is more efficient predator than A. royi. Laboratory evaluation of feeding ecology allows us to quantify relative importance of particular diet; food density and food type for commercial culture of copepod species. A thorough knowledge of feeding ecology and food niche size are prerequisite for reliable and sustained production. Both the copepods were estimated as generalist feeders rather than simple herbivorous. Therefore, the reproductive performance, survival and postembryonic developmental rates and population dynamics of each copepod species in relation to food diets and densities were also studied. With monoalgal diets, I. galbana (I), T. chui (T) and Chaetoceros sp. (C) and their different combinations (I+T, I+C, T+C and I+T+C). The reproduction and postembryonic development rates of copepods were influenced differentially by different diets. Algal diets related effects were more pronounced in P. annandalei than in A. royi. Monoalgal diet was evaluated as effective as mixed algal diet in P. annandalei. I. galbana alone has been recorded best food for reproduction and development for P. annandalei. T. chui alone was estimated to be best food for survival and fastest generation time in A. royi. Whereas the mixture of I. galbana + T. chui was found to be best diet for reproduction in A. royi. With combination of algae (either I. galbana or T. chui) and animal (different density of rotifer- 10, 20, 40, 80, 160 and 320 ind.60 ml-1) diet, the higher population growth rate was noted with increasing density of rotifer. The optimal culture condition for reliable mass culture of P. annandalei was recorded 320 ind. 60ml-1 with I. galbana. Susceptibility of copepods (nauplii, copepodites and adults) was tested to three PUAs of diatom. 2-trans, 4-trans decadienal (DD) was recorded more toxic compared to other two tested PUAs [2-trans, 4-trans haptadienal (HD); and 2-trans, 4-trans octadienal (OD)] to copepods. P. annandalei was estimated more sensitive to PUAs compared to A. royi. Further, the early stages (nauplii and copepodites) were found more sensitive to PUAs in comparison to adults of copepods. The presence of DD in the medium negatively influenced the survival, post embryonic developmental rates and population growth rates of each copepod species. This thesis provides first information on predatory efficiency and behavior of P. annandalei and A. royi on microplankton, which attests their omnivory feeding habit. Further, the wider food spectrum of these copepods suggests the underlying reasons of perennial abundance of these copepods in many tropical brackish ponds and estuaries. Present results also indicate the major role played by these copepods in shaping the community structure through predation and omnivory in their natural habitat. Subsequently, this thesis provides information about optimal food culture conditions to sustain reliable mass cultivation of these copepods for fish larviculture. Therefore, this thesis has ecological significance as well as aquaculture implications in live feed culture for growing fish larvae.