Competitive relationship between balanus amphitrite amphitrite and Pomatoleios kraussii with special reference to their larval settlement

Summary

• 1. This study was primarily undertaken to investigate the competitive relationship between Balanus amphitrite amphitrite Darwin and Pomatoleios kraussii (Baird) in Kuwait, Arabian Gulf. A part of the study has involved the determination of seasonal variations in larval settlement of the above two species. Information on seasonal fluctuations in certain environmental conditions of the study area is also provided.

• 2. Teakwood panels were exposed at various heights from 26 February 1971 to 31 March 1972.

• 3. During the period of the study the water temperature varied from approximately 12 to 32°C; salinity from 40 to 42‰ pH from 8.1 to 8.3; and dissolved oxygen from 3 to 5 cc/l. Tidal current velocities inshore ranged from 10 m/min on the flood to 13 m/min on the ebb tide.

• 4. Larval settlement of B. a. amphitrite is continuous throughout the year and there are two sharp rises of abundance: the first peak occurs in June and the second in November. The settlement of P. kraussii is during March to December with a maximum of abundance in August.

• 5. In B. a. amphitrite and P. kraussii nearest neighbours are about half as far apart as expected under conditions of randomness (R = ca. 0.5) when their densities attain 0.9 and 0.5 individual per square centimetre, respectively.

• 6. At the lower level of the exposure site (0 to 1 m below datum), encrusting ectoprocts, sponges, and filamentous algae are responsible for the heavy mortality among the low density populations of B. a. amphitrite and P. kraussii.

• 7. At the middle level (1 to 2 m above datum), where the heaviest set of larvae occurs, P. kraussii almost completely smothers B. a. amphitrite. Being eaten by brachyuran crabs is another cause of death in the last-mentioned species.

• 8. At the higher level (3 m above datum), interspecific competition for space between B. a. amphitrite and P. kraussii is largely eliminated by low intensity of larval attachment.

• 9. In all cases, death due to intraspecific competition for space between individuals of B. a. amphitrite is very rare. The same is true of P. kraussii.