Keus, B. (1985) De predatie van de garnaal (Crangon Crangon) op het broed van het nonnetje (Macoma Balthica). Master's Thesis / Essay, Biology.
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Abstract
During the summer of 1985 some investigations were carried out on predation by the shrimp (Crangon crangon) on juveniles of the bivalve (Macoma baithica). The main problem was whether this predation contributes significantly to the huge decrease in numbers of juvenile Macoma baithica that occurs during most summers. In the laboratory, shrimps from the size class 2.5 - 3.0 cm were able to eat Macoma's up to about 2.0 mm. In stomachs of shrimps of the same size class caught at high tide on the tidti flats, Macomas up to a maximum size of 1.5 mm were found. It was concluded that on the tidal flats, where most shrimps are smaller than 3 cm, Macomas larger than 2.0 mm are not predated on by Crangon crangon. Larger shrimps were found to eat larger Macomas. Large shrimps also eat more Macomas than small ones. During high tide about 4 Macomas per m2 were present in the stomachs of shrimps on the tidal flat. Based on this result, a predation of about 500 Macomas per m2 per month was estimated. The predation by a shrimp population near the tidal channel (larger shrimps) was estimated to be also about 500 Macomas per month per m2. Experiments with shrimps in enclosures on the tidal flat yielded variable results. The average number of Macomas eaten was 3.4 per shrimp per day. With this result an average predation of about 1600 Macomas per m2 per month was calculated. Fewer Macomas were eaten when Corophium volulator was also present in the cages as an alternative food source. The estimated predation pressure is not strong enough to explain the huge decrease in the numbers of juvenile Macomas during the first months of summer. A predation pressure of more than 1000 Macomas per month may account for a significant part of the mortality of juvenile Macoma in August and September.
| Item Type: | Thesis (Master's Thesis / Essay) |
|---|---|
| Degree programme: | Biology |
| Thesis type: | Master's Thesis / Essay |
| Language: | Dutch |
| Date Deposited: | 15 Feb 2018 07:31 |
| Last Modified: | 15 Feb 2018 07:31 |
| URI: | https://fse.studenttheses.ub.rug.nl/id/eprint/9228 |
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