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.
Impacts of earthquakes and tsunamis on marine benthic communities: A review.
Marine communities are dynamic and spatially heterogeneous. Earthquakes and tsunamis modulate the structure of marine communities at short and long-term scales. The objective of this review was to evaluate how such disturbances impact the morphodynamics of coastal areas and the dynamics and structure of marine benthic communities from soft and hard bottoms from intertidal, subtidal and deep-sea habitats. The results reveal that earthquakes and tsunamis caused mortality of algae and bivalves by dissection after coastal uplift. Changes on the vertical distribution of nematodes and coral fragmentation were also recorded. Recovery of the marine communities to pre-disturbance state occurred by migration and recolonization of impacted habitats. The meiofaunal organisms recovered quickly, while some communities recovered after three years. Information pre-disturbance is often lacking or covers a short temporal extent. It is important to establish long-term monitoring programs in areas where the likelihood of impact of disturbance of such magnitude is high to understand how marine communities are shaped at geological scales.
Characteristics of shell microstructure and growth analysis of the Antarctic bivalve Laternula elliptica from Lützow-Holm Bay, Antarctica
Growth performance of the Antarctic bivalve Laternula elliptica was examined both by shell microstructural observation and by applying a fluorescent substance, tetracycline, as a shell growth marker. The shell was composed of two calcareous layers: the thick outer layer was homogeneous or granular in structure and the thin inner layer was nacreous. The architecture of Antarctic L. elliptica was different from that of temperate L. marilina, and the ratio of thickness between the outer and inner layers appeared to be different. The growth rate of the nacreous layer was analyzed to be very low. High correlations were found between the major axis of chondrophore and both shell length and shell dry weight, respectively. It is suggested that the chondrophore is an appropriate growth indicator, and combining the information of growth increments with the fluorescent method may be useful in estimating the bivalve growth performance in the Antarctic sea.