Transplants in Mugu Lagoon, California, USA of a deep—dwelling bivalve, Sanguinolaria nuttallii, into experimental enclosures containing various combinations of other filter—feeding bivalves demonstrate that linear growth in Sanguinolaria is reduced by °80% over a 2—mo period when it is confined with two other deep—dwelling species, Tresus nattallii and Saxidomus nuttalli. Sanguinolaria growth is unaffected by the presence of a shallow—dwelling species, Protothaca staminea. Results also suggest a tendency for Sanguinolaria to emigrate away from areas of high Treasus and Saxidomus density. These interactions may explain why Sanguinolaria is uncommon in natural beds of Tresus and Saxidomus, although it is abundant elsewhere within Mugu Lagoon. In contrast to Sanguinolaria, Protothaca growth is not significantly influenced by the presence of either Sanguinolaria or Tresus and Saxidomus. Thus, while no apparent interactions occur between species which occupy different living positions in the sediments, species which share a similar depth stratum interact strongly, suggesting that competition for space is the primary mechanism of interaction in this system. This assumption is partially supported by the results of another experiment in which the growth rate of Sanguinolaria is significantly depressed by the presence of unoccupied shells of dead Tresus and Saxidomus, placed in normal living position in the sediments. |
