Nobuyoshi Nanba

Effect of water flow velocity on growth and morphology of cultured Undaria pinnatifida sporophytes (Laminariales, Phaeophyceae) in Okirai Bay on the Sanriku coast, Northeast Japan

Undaria pinnatifida sporophytes, originating from the same strain, were cultured at the commercial cultivation site exposed to wave action and the uncultivated site protected from water action of Okirai Bay, Northeast Japan, from January to April 2007; simultaneously, water flow velocity, water temperature, salinity, NO3 + NO2, and chlorophyll a were monitored to investigate the effect of water environment on their growth and morphology. Water temperature and salinity fluctuated within the optimal range for their growth whereas water flow velocity at the cultivation site was greatly fast compared with that at the uncultivated site. Successive chlorophyll a increases synchronized with NO3 + NO2 decreases were observed only at the uncultivated site for over a month; indicating developments of phytoplankton blooms and their nutrient consumption under the low-flow condition. Meanwhile, blade growth rate of cultured sporophytes was higher at the cultivation site than at the uncultivated site. Their thallus size expressed by six morphological characters (blade length, stipe length, blade wet weight, stipe wet weight, blade width, and undivided blade width) at the cultivation site became large in comparison with that at the uncultivated site. Their three morphological correlations (correlations between blade length and thallus length; blade wet weight and thallus wet weight; and undivided blade width and blade width) differed between the sites. They produced a thick and flat blade at the cultivation site but formed a thin and wrinkled blade at the uncultivated site. These results show the significant impact of water flow velocity on their growth and morphology.

Formation and growth of filamentous thalli from isolated utricles with medullary filaments of Codium fragile spongy thalli

Abstract Formation and growth of filamentous thalli from isolated utricles with medullary filaments of Codium fragile (Suringar) Hariot was studied in the laboratory. Immediately after isolation of the utricles, their fusiform chloroplasts began to be transferred, leading to formation of the filamentous thalli after culture for 2–6 days. The utricles became attached to the substratum by elongation of those thalli developing immediately after the initiation of formation. Differences in medullary filament length extending from the isolated utricles had no effect on the formation of the filamentous thalli from the utricles, nor their ability to attach to the substratum. The filamentous thalli remained viable for 32 weeks. One primordium of spongy thallus surrounded by many filamentous thalli regenerated from the isolated utricles after 6 weeks of culture, and the primordium grew into young spongy thallus with four axes and filamentous thalli by 10 weeks. Furthermore, its separated axes grew into young spongy thalli by 6 weeks of separation. The filamentous thalli and utricles of the regenerated spongy thalli contain numerous fusiform chloroplasts. These results suggest that the protoplasm containing numerous chloroplasts plays an important role in vegetative reproduction of the isolated utricles and filamentous thalli.

Normality of Succession of an Intertidal Community After the Great East Japan Earthquake

On March 11, 2011, the Great East Japan Earthquake occurred with an epicenter off the Tohoku area in northern Honshu, Japan. By the Tohoku earthquake tsunami and following ground subsidence, coastal organisms seem to have experienced various physiological and biological effects. We have continuously examined influence of the earthquake to the intertidal organisms at Sakihama in Iwate Prefecture for 4 years since August 2011 by using video camera footage. The surveyed site between E.H.W.S. and E.L.W.S. that has about a 180 cm tidal range experienced a subsidence of 130 cm due to the earthquake. The first colonizers on the newly submerged substrate were barnacles Semibalanus cariosus. The hard uneven substrate formed by the settlement of the barnacle facilitated the recruitment of the green alga Ulva intestinalis first and then the mussel Mytilus galloprovincialis followed. This multilayered community structure increased in species richness for 2 years. However, the species richness subsequently decreased with increasing abundance of the sea urchin Strongylocentrotus nudus which was the causative species in rocky shore denudation in this area before the earthquake. This biological succession was almost the same as that of a previous experiment from 2004 to 2006 which was carried out to examine the ecological roles of S. cariosus using test plates installed at the same location. The main difference between the two biological successions during the two experimental periods was the occurrence of a new alien barnacle Perforatus (Balanus) perforatus after the earthquake. According to the monthly monitoring data of the sedentary organisms on the test plates set on the jetty wall in Sakihama, this barnacle was found for the first time in 2012 and has been settling on them every summer. Just after the earthquake, many barges and tugboats came from various localities in Japan for reconstruction activities along the Tohoku coast. One barge, registered in Niigata, a city on the Japan seacoast where P. perforatus has become common, was anchored near the research site in 2013 and had this barnacle on its hull and fenders. Since the settlement of the alien barnacle occurred after the earthquake, it was likely that these boats played a role in the dispersion of P. perforatus into this area. This possibility implies that the earthquake affected on the intertidal communities not only directly via the tsunamis and subsidence but also indirectly via anthropogenic activities.