The purpose and aims of the research were; to quantify using field sampling and laboratory experiment, the feeding rates and the natural diet of ctenophores Mnemiopsis leidyi of different sizes and classes on bivalve veliger’s and other zooplanktons and to utilize the information in the determination of the mortality rates of the above mentioned taxa. While the hypothesis to be tested was that mortality on larval stages of bivalves was due to predation by lobate and ctenophore M. leidyi (Marianne E. McNamara, Darcy J. Lonsdale, and Robert M. Cerrato 1).
Ctenophores and mesoplankton data was collected weekly from four sites: two in Great South Bay and two in Peconic Bay Estuary, from June to august 2006. Samples were collected with a mesh, preserved using formalin, classified to the lowest possible taxonomic level and counted using a dissecting scope. About 30 live ctenophores were used to analyze gut passage time. Digestion time was an average of gut clearance time (Marianne et al. 2).
Two techniques were used to analyze the relationship between zoo plankton density and ambient temperature: forward-selection and stepwise regression. There was difficulty in calculation of species specific ingestion rates leading to removal of the data from the study (Marianne et al. 2).
Mesozooplanktons abundance was 11.3-70.1 individuals at Great South Bay, and 14.7-1541.4 individuals at Peconian Bay. The zooplankton taxa were grouped into five groups: copepods, bivalve veligers, other meroplankton, fish eggs, rotifers and tintinnids, with only the copepods and meroplankton differing significantly between Great South Bay and Peconian Bay (Marianne et al. 3)..
There was no significant correlations between M.leidyi density and total mesozooplanktons abundance, which was difficult to ascertain due to limited number of sampling dates made. However for M. leidyi there was a marked difference between the two sites. The mean for M. leidyi was lowest in Peconic Bay and highest in Great South Bay (Marianne et al. 3)..
For gut content analysis of ctenophores, 3.5% of all the ctenophores didn’t have any identifiable prey. Predictors such as: seas surface temperature, numbers of veligers, and meroplankton, were not significant in digestion time analysis (Marianne et al. 3).
It was also observed that, an increase of M. leidyi lead to a decrease of Bivalve Larvae. The population of M. leidyi seemed to be the most important factor in the digestion rates of bivalve larvae (Marianne et al. 3)
Discussions and conclusions
The results of the experiment lead the following conclusions: higher amounts of Ctenophores in Great South Bay and higher abundance of M. leidyi in Peconic Bay, the ingestion rates of bivalve larvae by M. leidyi were higher than expected for Great South Bay (Quaglietta 50). In Northern U.S, similar trends of increasing ctenophores have been observed (Turner et al. 81). It was also established that bivalve veligers co-existed with M. leidyi in both study sites.
The authors were able to test their hypothesis using correlation analysis where they got a p value less than 0.01.The methodological section of the paper was too detailed and difficult to understand. I found the introduction and the results section more helpful than the methodological part. In the results section there were enough tables to present the data which was very helpful, especially the bar graphs which depicted the temporal variation of the various species.
The authors argued that the sudden increase in ctenophores might alter the food chain and have negative effect on commercially important fish. This might have negative effects on the fishing industry. Therefore further research can be done to analyze the effect of ctenophores on the fishing industry.
The article by Colin, Costello, Hansson, Titelman and Dabiri, relates to the above summarized paper in the sense that both deal with the study of ctenophores mnemiopsis leidyi; especially in relation to the feeding habits (3). The first article deals mainly with the fact that ctenophores is the main predator of bivalve larvae an idea deeply echoed in the second article. Both studies employ the same methods to study ctenophores mnemiopsis leidyi; they were picked and placed in glass jars filled with filtered sea water. However for Colin, Costello, Hansson, Titelman and Dabiri, laser sheets were used to illuminate ctenophores (4), a method which was not employed by for McNamara, Lons...