The use of an ecosystem engineered habitat: Lanice conchilega builds refuges for Crangon crangon: An experimental approach
Van Cappellen, M. (2011). The use of an ecosystem engineered habitat: Lanice conchilega builds refuges for Crangon crangon: An experimental approach. MSc Thesis. Ghent University: Gent. 38 pp.
Lanice conchilega is an important ecosystem engineer, it builds reefs and the habitat formed even by low abundances is important in the soft-bottom benthic environment. They are known to increase species richness and density. Crangon crangon is an abundant opportunistic crustacean in the East Atlantic, and the use of biogenic habitats built by L. conchilega by C. crangon as shelter has been suggested in experiments. In the current study different L. conchilega densities were used (from low density bed forms to reefs), in combination with two different water velocities and two shrimp sizes. In both the previous and current study, mimics of L. conchilega beds were used to test the ecosystem engineering effect of refuge (ruling out other effects, apart from providing physical shelter). The water velocities (15cm s-1 and 20cm s-1) were created in an experimental flume of 10,5m2. In this flume an experimental zone simultaneously provided three different habitat densities. These were bare sand as a control treatment and an intermediate density of 500 ind m-2, either combined with a low density of 200 ind m-2 or with a high density of 1000 ind m-2. In the 15cm s-1 velocity all combinations were conducted with both small (<5cm) and larger (>6cm) shrimp, whilst in the 20cm s-1 velocity only the larger shrimp (>6cm) were used. Over the course of all experiments photo capturing was used to analyse diurnal behaviour. The results show a clear preference for the L. conchilega habitat. The most preferred density was 500 ind m-2, and from here there was a size related deviation: small shrimp were more attracted to the higher density of 1000 ind m-2, while big shrimp preferred the low density of 200 ind m-2. Moreover, photo analyses revealed a diurnal pattern where less shrimp were inside the experimental zone during nightfall. Overall, this study confirmed both the use of L. conchilega reefs and low-density beds by C. crangon as shelter area, and the diurnal behaviour of C. crangon, whereby a new technique (Photo capturing) was used for the latter.
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