The “tsunami break:” impact of the Great East Japan Earthquake and the accompanying tsunamis on the shell growth of the invasive clam-eating snail Laguncula pulchella
The Great East Japan Earthquake and accompanying tsunamis occurred on 11 March 2011, causing huge damage to marine organisms. The invasive naticid gastropod Laguncula pulchella (Euspira fortunei), which was introduced with the imported clam Ruditapes philippinarum from China and Korea, survived the earthquake. The “growth break line” observed on the shell surface in over 90% of the individuals collected in Matsushima Bay and Matsukawa-ura Lagoon after the tsunamis was examined by scanning electron microscopy. Each shell presented three layers before and three after the growth break. However, the fracture surface consisted of five layers—two prismatic and three crossed lamellar—around the growth break line. This suggests that shell formation temporarily ceased following the tsunamis and that the five-layered shell may have developed in response to the stress caused by the tsunamis. The newly formed middle layer became thinner after the “tsunami break,” which may be the result of a rapid change in the mineralization process, including rapid shell growth and/or repair. These results suggest that the damage to and forcible removal of habitats by the tsunamis was stressful for L. pulchella. A decrease in or the cessation of shell formation after a tsunami may be a common phenomenon in mollusks that inhabit tidal flats.
Effects of Ground Uplift, Construction of an Artificial Tidal Flat and Tsunami Seawalls on Marine Life and Local Residents Following the 2011 Great East Japan Earthquake
Eight years have passed since the Great East Japan Earthquake occurred. I divided the process of the earthquake into four main events—the initial earthquake including liquefaction, subsequent tsunamis, land subsidence and ground uplift—and examined the impact of each event on marine life. Under the influence of ground subsidence, the young oysters born in the summer of 2011 were attached 50 cm or more above where the parent generation was attached. However, in 2016, due to the influence of the subsequent ground uplift, oysters attached to the top of the rock began to die. Mass colonization of Manila clams occurred after the artificial tidal flat was created and the clam fishing industry was reopened. The new seawalls were constructed seaward of the previous seawalls; thus, the overall area of the tidal flat decreased. High seawalls also break the continuity of nature between land and sea. Plans are underway to separate the industrial area and the residential area bordering the seawall. From the point of view of disaster prevention, a high seawall is necessary, but it will cause great damage to tourism and residents’ lifestyles because the sea is hardly visible. In addition to population decline and aging, revitalizing the industry after construction of the seawall is a very difficult task. Finally, I briefly discuss the differences in response to disaster prevention by comparing cases in Asia and Europe with those in Japan.
Die Populationsdynamik Von Canthocampt Us Staphylinus (Jurine) (Copepoda, Harpacticoida) Im Litoral Des Bodensees
The population dynamics of Canthocamptus staphylinus in the littoral zone of Lake Constance are described (fig. 2). Adult animals aestivate as cysts. The main part of the population emerges from the cysts in autumn. During the resting stage and the first spell after emerging, mortality is very low (fig. 3). Reproduction, expressed as numbers of ovigerous females, begins in November and reaches its maximum in January. The new generation becomes adult in May/June and encysts without previous reproduction. According to Sarvala (1979) it may be possible, that in littoral populations dormancy is induced by long day periods and temperatures of over 12° C (figs. 1, 2). In the profundal zone C. staphylinus also forms cysts, however, both light and temperature are not likely to induce this stage in depths of over 60 m.