Seiichi Watanabe's research while affiliated with Tokyo University of Marine Science and Technology and other places

Effect of stocking density was studied in three abalone species Haliotis discus discus (HDD), H. gigantea (HG), and H. madaka (HM) and their hybrids [HDD × HM, HM × HG and HG × HM, mother first] by rearing individually marked abalones for 217 days at low (22 % of available surface area; LD), medium (53 %; MD), and high (126 %; HD) densities. Feeding rate (FR) and feed conversion rate were observed by measuring the amount of feed ingested at an interval of 2–3 days. Reduction of growth rate with the increment of density was found in all three species [Specific growth rate in weight (G W ) HDD, LD: 0.121, MD: 0.093, HD: 0.069; HM: 0.12, 0.082, 0.061; HG: 0.254, 0.222, and 0.131] and the hybrids HDD × HM (0.18, 0.109, 0.108). The medium density produced the highest growth rates in HM × HG and HG × HM hybrids (0.284, 0.342, 0.28). A growth spurt was observed in all three species and hybrids in the last 44 days of rearing. FR varied from 0.72 to 7.97 % body weight and decreased with the increase in density in all species and hybrids. The results indicate differences in density thresholds for the three abalone species and their hybrids suggesting requirement of different aquaculture management strategies for them.

The present study aims to examine the age class composition of wild Leptodius exaratus populations, using lipofuscin as an age marker. Stereometrical quantification of lipofuscin granules on histological sections of nervous tissue from wild crabs was conducted using a fluorescence microscope. The highest concentration of lipofuscin was observed in the olfactory lobe cell mass of the brain. Five groups could be distinguished within the normal distribution of lipo-fuscin concentration values and the mean values for the groups increased linearly. This suggests that lipofuscin accumulation rate was constant between the groups. Based on the size of the specimens in the group with lowest lipofuscin concentration values (hence group 1), it is surmised that they were born in the previous reproductive season. These results suggest that the lipofuscin groups 1-5 might correspond to the 1-5+ aged groups in wild population of L. exaratus. Examination of the lipofuscin accumulation, number of molt-ings and growth of captive-reared crabs during a period of one year supported the age class estimation of wild samples.

In this study, we developed a simple and rapid restriction fragment length polymorphism (RFLP) method to distinguish the sibling species Hemigrapsus penicillatus and H. takanoi based on interspecific base substitutions within the 16S rRNA region of mitochondrial DNA. Sequencing and alignment of partial sequences revealed two haplotypes for H. penicillatus and one for H. takanoi, and five species-specific base substitutions. Digestion of the PCR products using the restriction endonuclease Dde I produced a banding pattern that was consistent with species identification based on morphological and pigmentation patterns. The sequence for H. takanoi collected in Japan showed high homology with that reported for specimens collected in Europe. This method could be useful for identification of these two species by researchers without specific taxonomic knowledge.

Survival in larval rearing experiments is difficult to estimate due to accidental losses and periodic sampling. The number of sampled fish can be a large proportion of the stocked ones, making it difficult to calculate the overall survival rate and mortality coefficient as this is based on the initial number. Here, a new method of calculating survival is proposed using the mortality coefficient. When the initial stocking density and sampled and final numbers are known, and assuming that mortality coefficient is constant, the final number of fishes can be represented by the formula N t = e−mt (N 0 − ΣN Snemdn), where t is rearing period (days), N 0 indicates initial number, N t indicates the survival number at t days of rearing, m is the natural mortality coefficient, N Sn is the sampled number in the nth sampling, and dn is the rearing period until removal of the nth sample. The provisional mortality coefficient is calculated from initial and final stocking numbers. Then values for the natural mortality coefficient are substituted into the formula with successive approximation. The coefficient, which most closely approximates the actual survival, is determined as the best fit natural mortality coefficient. Examples of larval experiments are provided to demonstrate the method and show that survival is often underestimated using traditional methods.

Although invasions may have commenced in the 1500s, our record of invasions of alien marine and estuarine species in Japan begins largely in the 1930s. We expand the previous inventory of 10 alien species to 31 alien and cryptogenic species, underscoring that this, too, may be a striking underestimate. Most of the marine crustacean invasions into Japan have occurred along the Pacific coast; a number of alien crustaceans form abundant populations in urbanized bays near international ports. The specific geographic sources of most invasions are not known; studies have clarified the origins of the barnacle Balanus glandula (from America), but hybridization or low genetic divergence has inhibited clarification of the exact source of the crab Carcinus and the barnacle Megabalanus coccopoma. The biogeographic origins of the alien crustacean fauna in Japan include the North Atlantic and North and South Pacific oceans. We cannot distinguish between ship fouling and ballast water as vectors for most species; this said, it is probable that ship fouling has been a major contributor to the arrival of alien barnacles. No species are yet known to have been introduced solely by ballast water, but this may be an artifact of the lack of collections and identification of potential ballast-only taxa (planktonic copepods, cladocerans, and mysids). Other vectors include importations from China and Korea of shellfish for stocking, crabs for farming, and of live bait; all of these may lead to the introduction of novel genetic stocks and of associated species. There are few studies that have examined the ecological and economic impact of alien crustaceans. The barnacle Amphibalanus amphitrite appears to be competitively superior to native barnacles and has a negative impact on their densities. Alien crabs inhabit communities established by alien barnacles and mussels (which serve as their prey); these “alien communities” occur, for example, in the inner areas of Tokyo Bay. The European crab Carcinus appears to be declining in some regions while the American crab Pyromaia is increasing. The economic cost to the power industry, shipping, aquaculture and fisheries for clearing the biofouling associated with alien barnacles and other alien fouling organisms is probably severely underestimated. Although the Invasive Alien Species Act was passed in Japan in 2005, it did not refer to alien marine organisms. Consequently, preventing the introduction of alien marine species into Japan, or their subsequent dispersal along its coastline, is proving difficult to enforce.

The Tokyo bitterling Tanakia tanago (Cyprinidae) was once found throughout the Kanto Plain, central Japan, but most of their habitats have been lost due to human activities such as urbanization and improvement of paddy fields. Subsequently, conservation efforts, including captive breeding and reintroduction, have been ongoing. However, the genetic relationships among populations of this species including captive and remnant wild populations have been uncertain and thus management units for this species have been unidentified. We examined the population differentiation among 12 populations, including four wild and eight captive populations, and their relative genetic diversities to assist in conservation management decisions. Phylogeographic analyses based on partial mitochondrial cytochrome b gene sequences and microsatellite polymorphisms revealed four geographically associated genetic groups in the populations. Northern Tochigi populations have diverged from other populations (0.77% of d A ), likely stemming from allopatric fragmentation following a change in the route of the Naka River, which occurred during the middle of the Pleistocene epoch. Microsatellite analysis has revealed that the genetic diversity of each population is generally low, and that most of the populations have experienced genetic bottlenecks. For future in- and ex-situ conservation programs to succeed, the population structure and genetic variability of remnant populations need to be taken into consideration.

This study examined the ability of late stage (instar XXVI) Japanese spiny lobster Panulirus japonicus phyllosoma larvae to uptake seven l-type amino acids (AAs; aspartic acid, Asp; threonine, Thr; glutamic acid, Glu; glycine, Gly; alanine, Ala; valine, Val; and methionine, Met) from the rearing medium. The time course uptake during incubation for 5h in solutions containing 1, 2, 5, 10, or 20μM of each AA was determined using high performance liquid chromatography. There was considerable individual variation in uptake rates and even occasional release of AAs, but larvae showed net uptakes of all seven AAs. Two polar acidic AAs (Glu and Asp) were readily taken up whereas neutral AAs, including three considered as essential for crustaceans (Val, Met, and Thr), had lower uptake rates. Transient releases of AAs by the larvae were common for the AAs with the lowest uptake rates at 1–2h of incubation. Uptake rates increased with increasing AA concentration but less so for those taken up in larger amounts. Larvae took up AAs to a total of 16.4μmol/g/h for incubation in the 20μM solution. The ability to uptake nutrients directly from the medium may be important for the well-being of the larvae. KeywordsPhyllosoma-Amino acids-Uptake-Japanese spiny lobster-Nutrition

The population structure and life history of the goneplacid crab Carcinoplax vestita were investigated in Tokyo Bay, Japan, from November, 2002, to October, 2003. Catch per unit effort (CPUE) was generally constant (<100) with two exceptional peaks in June (171) and August (390), and it was always highest in the central part of the inner bay than elsewhere. The overall sex ratio was significantly biased towards males, but the proportion of males gradually decreased from November and the sex ratio was significantly biased towards females in June, August, and September. The overall size-frequency distributions for males and females were not significantly different, and there is no sexual dimorphism in body size in this species. The size-frequency distributions were bi- and/or trimodal from November to April or May, but unimodal in later months. The small- and large-sized modes consisted of newly recruited individuals and senile, post-reproductive individuals, respectively. Life-span was estimated to be about one year with exceptional individuals surviving longer. The occurrence of soft-shelled small males peaked in December, April, and August, suggesting a four-month molt cycle; however, large males and both small and large females showed no clear peaks or cycles of molting. Larger females were inseminated first, starting in April. In contrast, females concurrently began to spawn and carry embryos regardless of their body size in August. The time lag between summer hypoxia and the ovigerous period has probably contributed to the establishment of a large population in Tokyo Bay.