This project is based on material collected during the 2004 RV G.O. Sars expedition. DNA techniques will be used to determine whether Atolla sp. and Periphylla periphylla are present in the gut of mesopelagic shrimps. The lab work is done autumn and winter 2005 at the Institute of Marine Research, Flødevigen Arendal.
The identification of species consumed by predators is necessary to understand marine food webs. Pelagic shrimps can be found in large amounts in deep water (> 500 m). Many of the species are active predators on smaller zooplankton (mesozooplankton), but can also feed on dead organic compound. Mesopelagic fish and octopus predates on pelagic shrimps. This makes pelagic shrimps an important link in the food web between mesozooplankton and larger predators. Predation on medusas has been shown before in fish and crustaceans, but the degree and importance of this is not yet known. Earlier diet studies and analysis of the gut content indicates that Notostomus robustus predates on the medusas Atolla wyvillei and Periphylla periphylla.
Periphylla periphylla and Atolla sp. are two deepwater medusas with global distribution that belongs to the class Scyphozoa, order Coronata. They were observed in large amounts on the mid-Atlantic ridge down to depths of 3000m. The biomass of medusas (wet weight) was often higher than the biomass of other pelagic organisms. The medusas eat large amounts of food and may compete with fish for food resources.
Identification of the gut content by morphological methods is difficult, particularly for gelatinous organisms, because the morphology is damaged during capture and digestion. But it is possible that the DNA from the prey is not completely degraded during digestion and still can be found in the gut to predators.
One fragment of mitochondrial Cytochrome c oxidase subunit I (COI) gene from the medusa is amplified via PCR, sequenced and submitted to GenBank. PCR products will further be used as a probe to identify the medusas in the gut of the shrimps. N. robustus is dissected and the gut content taken out. The DNA is extracted, spotted onto a nylon membrane and hybridized with the labelled probe (Dot plot). There will be a colour reaction if the jellyfish DNA is present in the gut of the shrimp. The gut content of N. robustus is also microscoped and photographed to look for parts of nematocysts from jellyfishes.
There are generally few DNA sequences from marine organisms and especially for organisms in the ecosystem on the mid-Atlantic ridge. MAR-ECO wishes to use DNA based methods to characterise gut content of predators. The DNA sequences from the medusas will also make it possible to identify these species in the diets of other predators, such as fish and octopus.