De predatie van de garnaal (Crangon crangon) op het broed van het nonnetje (Macoma balthica)
Keus, B. (1986). De predatie van de garnaal (Crangon crangon) op het broed van het nonnetje (Macoma balthica). Interne verslagen Nederlands Instituut voor Onderzoek der Zee, 1986(5). NIOZ: Texel. 43 pp.
Part of: Interne verslagen Nederlands Instituut voor Onderzoek der Zee. Nederlands Insituut voor Onderzoek der Zee: Texel.
During the summer of 1985 some investigations were carried out on predation by the shrimp (Crangon crangon) on juveniles of the bivalve (Macoma balthica). The main problem was whether this predation contributes significantly to the huge decrease in numbers of juvenile Macoma balthica that occurs during most summers. In the laboratory, shrimps from the size class 2.5 -3.0 cm were able to eat Macoma up to about 2.0 mm. In stomachs of shrimps of the same size class caught at high tide on the tidal flats, Macoma balthica 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 volutator was also present in the cages as an altemative 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.
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