Teruhisa Komatsu

Use of multi-beam sonar to map seagrass beds in Otsuchi Bay on the Sanriku Coast of Japan

Seagrass beds play an important role in coastal ecosystems as primary producers and providers of habitat and environmental structure. Therefore, mapping seagrass beds is indispensable in the management and conservation of sound littoral ecosystems, and in the development of sustainable fisheries in coastal waters. Multi-beam sonar is often used to map bottom topography. We developed a mapping method to quantify the volume of seagrass using a multi-beam sonar. Seagrass beds were scanned with the multi-beam sonar and quadrat sampled to verify the distribution of seagrasses. We used software to discriminate seagrass signals from echoes to obtain a topographic profile of the bottom without seagrass; this was then subtracted from the topography including the seagrass. We then mapped seagrass distribution, calculated seagrass volume, and estimated biomass using volume and quadrat samples. We applied these methods to map a seagrass bed of Zostera caulescensin Otsuchi Bay, on the Sanriku Coast of Japan, during the growing season of 2001. A transducer was attached to a boat (one gross ton) equipped with a differential-GPS, a motion sensor, and a gyrocompass. The vessel completed a grid survey scanning whole seagrass bed with an area of 115 m ◊ 156 m at bottom depths between 2 an d8mw ithin about 40 min when traveling at a speed of 1.5 m s ‐1 (3 knots). The multi-beam sonar was able to visualize three-dimensional seagrass distribution without interpolation and easily to estimate area and volume occupied by the seagrass using hydrography software. The results indicated that Z. caulescens was distributed at bottom depths of 6‐7 m with a surface area of 3 628 m 2 and a volume of 1 368 m 3 . The mean biomass of above- and below-ground parts of seagrass were estimated to be 28.6 gDW m ‐2 (range 26.6‐30.9) and 15.9 gDW m ‐2 (range 14.1‐17.7). Our study demonstrated that multi-beam sonar is effective for mapping and quantifying the spatial distribution of seagrass beds, and for visualizing the landscape of the seagrass canopy.

Global analysis of seagrass restoration: the importance of large-scale planting

In coastal and estuarine systems, foundation species like seagrasses, mangroves, saltmarshes or corals provide important ecosystem services. Seagrasses are globally declining and their reintroduction has been shown to restore ecosystem functions. However, seagrass restoration is often challenging, given the dynamic and stressful environment that seagrasses often grow in. From our world-wide meta-analysis of seagrass restoration trials (1786 trials), we describe general features and best practice for seagrass restoration. We confirm that removal of threats is important prior to replanting. Reduced water quality (mainly eutrophication), and construction activities led to poorer restoration success than, for instance, dredging, local direct impact and natural causes. Proximity to and recovery of donor beds were positively correlated with trial performance. Planting techniques can influence restoration success. The meta-analysis shows that both trial survival and seagrass population growth rate in trials that survived are positively affected by the number of plants or seeds initially transplanted. This relationship between restoration scale and restoration success was not related to trial characteristics of the initial restoration. The majority of the seagrass restoration trials have been very small, which may explain the low overall trial survival rate (i.e. estimated 37%). Successful regrowth of the foundation seagrass species appears to require crossing a minimum threshold of reintroduced individuals. Our study provides the first global field evidence for the requirement of a critical mass for recovery, which may also hold for other foundation species showing strong positive feedback to a dynamic environment.Synthesis and applications. For effective restoration of seagrass foundation species in its typically dynamic, stressful environment, introduction of large numbers is seen to be beneficial and probably serves two purposes. First, a large-scale planting increases trial survival - large numbers ensure the spread of risks, which is needed to overcome high natural variability. Secondly, a large-scale trial increases population growth rate by enhancing self-sustaining feedback, which is generally found in foundation species in stressful environments such as seagrass beds. Thus, by careful site selection and applying appropriate techniques, spreading of risks and enhancing self-sustaining feedback in concert increase success of seagrass restoration.

Phylogeographic heterogeneity of the brown macroalga Sargassum horneri (Fucaceae) in the northwestern Pacific in relation to late Pleistocene glaciation and tectonic configurations.

Pleistocene glacial oscillations and associated tectonic processes are believed to have influenced the historical abundances and distribution of organisms in the Asia Northwest Pacific (ANP). Accumulating evidence indicates that factors shaping tempospatial population dynamics and distribution patterns of marine taxa vary with biogeographical latitude, pelagic behaviour and oceanographic regimes. To detect what kinds of historical and contemporary factors affected genetic connectivity, phylogeographic profiles of littoral macroalga Sargassum horneri in the ANP were analysed based on mitochondrial (Cox3) and chloroplast (rbcL) data sets. Five distinct clades were recovered. A strong signature of biogeographical structure was revealed (ΦCT = 0.487, P < 0.0001) derived from remarkable differentiation in clade distribution, as clade I is restricted to Chinese marginal seas (Yellow–Bohai Sea, East China Sea and South China Sea), whereas clades II–V are discontinuously scattered around the main Islands of Japan. Furthermore, two secondary contact regions were identified along the south Japan‐Pacific coastline. This significant differentiation between the two basins may reflect historical glacial isolation in the northwestern Pacific, which is congruent with the estimates of clade divergence and demographic expansion during the late Quaternary low sea levels. Analysis of molecular variance and the population‐pair statistic FST also revealed significant genetic structural differences between Chinese marginal seas and the Japanese basin. This exceptional phylogeographic architecture in S. horneri, initially shaped by historical geographic isolation during the late Pleistocene ice age and physical biogeographical barriers, can be complicated by oceanographic regimes (ocean surface currents) and relocating behaviour such as oceanic drifting.

Measurements of time-averaged intensity of water motion with plaster balls

Water motion is a very important environment surrounding marine organisms. It is, however, difficult to measure currents with a propeller type of current meters in seagrass or seaweed beds in shallow waters. Therefore, we elaborate the measuring method of time-averaged intensity of water motion with plaster balls invented by Muus (1968) to set them at several depths at short vertical intervals in shallow waters. Theoretical examination is also made on the relation between speed of steady flow and dissolution rate of plaster balls by experiments in a circuit tank. These experiments revealed that the temporal rate of decrease in the 1/2 power of wet weight of plaster balls excluding a rod supporting the plaster ball was proportional to the speed of steady flow in the tank. On the basis of this relation, we propose the method for estimating the time-averaged intensity of water motion by converting the loss of wet weight of plaster ball to the speed of steady flow bringing equivalent loss. Since this method is simple and convenient, it can be applied to obtaining environmental indices of water motion not only in seagrass or seaweed forests, but also in fishing grounds culturingporphyra, yellow tail (Seriola quinqueradiata) or oysters.

Using bottom surface reflectance to map coastal marine areas: a new application method for Lyzenga's model

Remote sensing is widely used in coastal management. Lyzengas model has been traditionally used to explain the relationship between bottom surface reflectance and the radiance level measured by satellite. Due to its central assumption, this model lacks accuracy compared with the other radiative transfer models. Nonetheless, it enables, with a single and simple equation, representation of the multiple optical processes taking place in coastal areas. Mapping processes associated with this model may include radiometric correction, a technique previously pointed out as a major driver of mapping accuracy. Radiometric correction is generally based on a depth-invariant index, efficient for clear waters (Jerlov water type I to II) but largely unsuitable when transparency decreases (Jerlov water type II to III). In order to overcome this problem, we developed a new index for radiometric correction, which combines bathymetry data with attenuation coefficients. The improved efficiency of our model with regard to the traditional depth invariant index was demonstrated through two case studies: Funakoshi Bay (Japan; Jerlov water type II) and the Gabes Gulf part located off Mahares (Tunisia; Jerlov water type II to III).

Impacts by heavy-oil spill from the Russian tanker Nakhodka on intertidal ecosystems: recovery of animal community.

The impact of a heavy-oil spill from the Nakhodka on an intertidal animal community, and the recovery process of animals from the damage were surveyed from the autumn of 1997 to the spring of 2001. The field study was carried out in the rocky coast of Imago-Ura Cove, located along the Sea of Japan, where clean-up operations for oil pollution had been conducted less intensely than in other polluted areas. We have examined individual number of each animal taxon by continuously placing a quadrat of 5 m width along the entire intertidal zone of the cove. A total of 76 invertebrate taxa including 57 species of mollusks, 10 species of crustaceans were observed during the survey. The number of taxa increased from 1998 to 1999 in areas where the initial oil pollution was intense. Total individual number of benthic animals continued to increase from 1998 to 2000 in the polluted areas. The impact of oil on benthic animals was different from species to species. Some species such as Cellana toreuma and Monodonta labio confusa increased rapidly after the oil spill, whereas other species such as Patelloida saccharina lanx and Septifer virgatus did not show any apparent temporal tendencies. Population size structure of P. saccharina lanx varied greatly among years, however that of M. labio confusa did not. For P. saccharina lanx, recruitment was unsuccessful in 1997, possibly due to the effect of oil pollution. These differences in responses to oil pollution among benthic animals are considered to be caused by the differences in habitat use, susceptibility to heavy-oil, life history and migration ability. The findings suggest that it took at least 2-3 years for the intertidal animal community to recover to its original level after the oil spill.

Unusual distribution of floating seaweeds in the East China Sea in the early spring of 2012.

Floating seaweeds play important ecological roles in offshore waters. Recently, large amounts of rafting seaweed have been observed in the East China Sea. In early spring, juveniles of commercially important fish such as yellowtail accompany these seaweed rafts. Because the spatial distributions of seaweed rafts in the spring are poorly understood, research cruises were undertaken to investigate them in 2010, 2011, and 2012. Floating seaweed samples collected from the East China Sea during the three surveys contained only Sargassum horneri. In 2010 and 2011, seaweed rafts were distributed only in the continental shelf and the Kuroshio Front because they had become trapped in the convergence zone of the Kuroshio Front. However, in 2012, seaweed was also distributed in the Kuroshio Current and its outer waters, and massive strandings of seaweed rafts were observed on the northern coast of Taiwan and on Tarama Island in the Ryukyu Archipelago. Environmental data (wind, currents, and sea surface height) were compared among the surveys of 2010, 2011, and 2012. Two factors are speculated to have caused the unusual distribution in 2012. First, a continuous strong north wind produced an Ekman drift current that transported seaweed southwestward to the continental shelf and eventually stranded seaweed rafts on the coast of Taiwan. Second, an anticyclonic eddy covering northeast Taiwan and the Kuroshio Current west of Taiwan generated a geostrophic current that crossed the Kuroshio Current and transported the rafts to the Kuroshio Current and its outer waters. Such unusual seaweed distributions may influence the distribution of fauna accompanying the rafts.

Possible change in distribution of seaweed, Sargassum horneri, in northeast Asia under A2 scenario of global warming and consequent effect on some fish

Global warming effects on seaweed beds are already perceptible. Their geographical distributions greatly depend on water temperatures. To predict future geographical distributions of brown alga, Sargassum horneri, forming large beds in the northwestern Pacific, we referred to future monthly surface water temperatures at about 1.1° of longitude and 0.6° of latitude in February and August in 2050 and 2100 simulated by 12 organizations under an A2 scenario of global warming. The southern limit of S. horneri distribution is expected to keep moving northward such that it may broadly disappear from Honshu Island, the Chinese coast, and Korean Peninsula in 2100, when tropical Sargassum species such as Sargassum tenuifolium may not completely replace S. horneri. Thus, their forests in 2100 do not substitute those of S. horneri in 2000. Fishes using the beds and seaweed rafts consisting of S. horneri in East China Sea suffer these disappearances.

But next time?: Unsuccessful Establishment of the Mediterranean Strain of the Green Seaweed Caulerpa taxifolia in the Sea of Japan

We conducted a survey of 63 public aquariums in Japan by means of a questionnaire asking if a green seaweed, Caulerpa taxifolia, was cultured or exhibited in aquariums under the network of the public aquarium association of Japan in 1997. Of 51 aquariums, 16 cultured or exhibited C. taxifolia. Most of the public aquariums possessing C. taxifolia purchased them from aquarium shops or received them from another public aquarium as a donation. Notojima aquarium reported temporal establishment of C. taxifolia in the Sea of Japan between the summer and autumn of 1992 and 1993. C. taxifolia was released into the sea from a 1 m3 cage that was submerged in an open pool. Two colonies with diameters less than 2 m were found near the mouth of a water outflow pipe in both years. Molecular analysis of the ITS rDNA gene of the aquarium strain of Notojima clarified that the seaweed is the same as the aquarium-Mediterranean and Californian invasive strain. Unsuccessful establishment of the invasive strain of C. taxifolia in the Sea of Japan is probably due to water temperatures in winter that are lethal for C. taxifolia. C. taxifolia remains present in many public and private aquariums. If C. taxifoliawere to be released in more temperate waters of Japan, there would be a high risk of establishment and, thus, impact on the marine ecosystem. This suggests that the trade, culture and exhibition of C. taxifolia should be strongly avoided to reduce the chances of accidental release of this harmful species.

Entropy and Nonlinear Nonequilibrium Thermodynamic Relation for Heat Conducting Steady States

Among various possible routes to extend entropy and thermodynamics to nonequilibrium steady states (NESS), we take the one which is guided by operational thermodynamics and the Clausius relation. In our previous study, we derived the extended Clausius relation for NESS, where the heat in the original relation is replaced by its “renormalized” counterpart called the excess heat, and the Gibbs-Shannon expression for the entropy by a new symmetrized Gibbs-Shannon-like expression. Here we concentrate on Markov processes describing heat conducting systems, and develop a new method for deriving thermodynamic relations. We first present a new simpler derivation of the extended Clausius relation, and clarify its close relation with the linear response theory. We then derive a new improved extended Clausius relation with a “nonlinear nonequilibrium” contribution which is written as a correlation between work and heat. We argue that the “nonlinear nonequilibrium” contribution is unavoidable, and is determined uniquely once we accept the (very natural) definition of the excess heat. Moreover it turns out that to operationally determine the difference in the nonequilibrium entropy to the second order in the temperature difference, one may only use the previous Clausius relation without a nonlinear term or must use the new relation, depending on the operation (i.e., the path in the parameter space). This peculiar “twist” may be a clue to a better understanding of thermodynamics and statistical mechanics of NESS.