Study on the Recovery of the Intertidal communities on Seawall from the Environmental Disturbances caused by Unusual Hot weather

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We have studied to aim recovery of the Intertidal communities on seawall from the environmental disturbances caused by unusual hot weather in 1998, especially focusing on intertidal barnacle, Semibalanus carious and its ecological role. Field studies have been conducted at Sakihama seawall in Okkirai Bay, Iwate Prefecture. during 2004-2006. PVC test plates have been set on the wall with different distances from wall to prevent predators such as sea-urchin and snails. We also investigated the effect of surface roughness for recruitment of sessile organisms by using concrete panels with different convexo-concavities. Effect of pedation by S. intermedius was investigated for barnacles and mussels in laboratory conditions.As a result of field experiments, first we found that recovery of the intertidal communities will be possible if predators such as sea-urchin Strongyrocentrotus intermedius and snails could be controlled. Laboratory experiments proved that S. intermedius preys on barnacles and mussels if the preys are small. Second, intertidal barnacle Semibalanus cariosus which is a dominant species in northern Pacific coast is essential to build up intertidal communities on the seawalls as a subsuate for secondary sessile organisms such as mussel Mytilus galloprovincialis brown alga Undaria pinnatifida, and red alga Analypus japonicus. Third, convexo-concavities are effective to facilitate recruitment of sessile organisms, but concavities tends to be filled by small sedentary animals such as bryozoans and serpulids. It seems important to set or put concavities on seawalls at an appropriate season to form long-lasting intertidal communities.For future study, it is important to invent a way to eliminate sea-urchin S. intermedius with easy to manage to form and preserve intertidal communities. This concept will be applicable for subtidal communities and may give a hint to recover from rocky-shore denudation.