During a faunal survey of the intertidal mud flat of Shinhama Lagoon on the northern coast of Tokyo Bay, parasitic bopyrid isopods, Ione cornuta Spence Bate, were found attached to the inner walls of the branchial chambers of ghost shrimps, Nihonotrypaea japonica (Ortmann). In this isopod, the females are parasites of N. japonica whereas dwarf males attach to conspecific females. To investigate the prevalence of the parasite I. cornuta, sampling of ghost shrimps was conducted every 2 to 4 weeks at the Shinhama Lagoon during the periods from August, 1994, to October, 1995, and January, 1998, to May, 1999. A total of 328 individuals (253 females, 62 males, and 13 of unknown sex) of N. japonica was collected, and 22 individuals among them (6.7%) were infected with I. cornuta. Among the infected shrimps, females accounted for 21 individuals, and only one male was infected. This skewed sex ratio is considered to simply reflect the female-biased sex ratio of this species in the field. In most cases, one individual of the parasite I. cornuta was attached within the left or the right branchial chamber of each host shrimp. No significant relationship was detected between the handedness of the major cheliped of the host shrimps and the attachment position of I. cornuta. A significant positive correlation was found between the size of the host shrimps and the size of mature females (i.e., those with brood chambers) of the parasite; however, the size of immature parasites was not correlated with the size of their host shrimp. In spite of the long sampling periods during this study, no ovigerous shrimp infected by I. cornuta was collected. This strongly suggests that infection by I. cornuta negatively affects the reproduction of the host female shrimps.

View full abstract

Occurrences of rare species of fiddler crab, Uca arcuata (De Haan, 1833) and U. lactea (Dc Haan, 1835), are newly recorded from a tidal flat at the mouth of the Aono River, Izu Peninsula, Shizuoka Prefecture, Japan. Numbers of crabs and their sexes were recorded by viewing from a distance, and several of the crabs were collected for measuring their size. Observations and sampling were conducted 12 times from September, 1999, to August, 2002, at low spring tide. During this period, three individuals of U. arcuata were recorded, all males. Numerous individuals of UU lactea were found during the same period, and the maximum number recorded was 36 in September, 2000. Ages of the crabs were estimated from carapace size, based on earlier published population studies. The largest male U. arcuata on the Aono River flat was estimated to be two years old, and the other two males were one year old. Collected males of U. lactea ranged from 15.8 to 18.5mm in carapace width, and females from 13.3 to 15.8mm; the ages of these crabs were estimated as two years or more.

View full abstract

Morphological and genetic traits of Lingula adamsi were compared among individuals from South Korea (Yellow Sea) and Japan (Ariake Sea). The Japanese population is usually identified as L. shantungensis, although this nominal species has been placed in synonymy with L. adamsi. Some studies have suggested that the Japanese population is a different species or subspecies from L. adamsi based on morphological comparisons. In this study, morphological characters of the shell of ten individuals of L. adamsi collected from southwestern South Korea, such as shape, color, and surface ornamentation, were compared with those of the Japanese population. Although the width/length ratio of the dorsal shell is significantly different between the South Korean and Japanese samples, this and all other morphological differences can be considered as intraspecific variation. The nucleotide sequences of the mitochondrial coxl gene region indicate a very low level of variation between the ten South Korean individuals and an individual from the Ariake Sea, Japan, not greater than that observed within local populations of Lingula anatina. The forms from South Korea and Japan, therefore, are best interpreted as conspecific from the viewpoint of both morphological and genetic variation.

View full abstract

To investigate the invasion history and recent geographic distribution of marine organisms introduced to Japan or transferred domestically to non-native regions, a questionnaire survey on their occurrence in the field, including both published and unpublished records, was conducted in 2002-2003. A total of 105 taxa was reported by 94 respondents. According to three criteria, viz. known or unknown geographic origin, established invasion history, and presumed dispersal mechanisms associated with human activities, 42 taxa were designated as non-indigenous species introduced to Japan through human activities, 26 taxa as indigenous species that are distributed both in Japan and other countries but are introduced from abroad to Japan for fisheries or as fish bait, 20 taxa as cryptogenic species which are not demonstrably native or introduced, two taxa as non-indigenous species that have extended their range to Japan through natural dispersion, and one taxon as an indigenous species. The remaining 14 taxa were considered to have been transferred domestically to new areas. Analysis of the years of first record of 42 non-indigenous species suggests that the rate of invasion has increased over the past century, with seven or eight species being introduced per decade after 1960. Data on temporal change in geographic distribution revealed that many non-indigenous species have become widespread recently, from the Pacific coasts of central Japan to the coasts of the Sea of Japan or northward. However, the species listed in the present study are not exhaustive, and more extensive investigations covering all taxa and all presumed dispersal mechanisms are urgently needed before consideration of legislative management of introduced marine organisms.

View full abstract

There is an increasing public concern about the introduction of marine organisms, and shipping is perceived to be responsible for many unwanted introductions into Japanese waters. A total of 25 unintentionally introduced marine species has been reported in Japanese waters, comprising Annelida (two spp.), Mollusca (10 spp.), Arthropoda (nine spp.), and Chordata (two spp.) among animal taxa, and Phaeophyta (one sp.) and Chlorophyta (one sp.) among marine algae. It is estimated that 68% of these introduced species were introduced via visiting ships. Two main mechanisms, ballast water and hull fouling, are considered responsible for the dispersal of marine organisms worldwide via shipping. The relative importance of these mechanisms for the dispersal of marine organisms differs among nations and regions as a consequence of their trading patterns. Since large amounts of ballast water are discharged at ports exporting dry bulk commodities, ballast water can be considered a relatively important mechanism for introductions in such places (e.g., Australia or San Francisco Bay), whereas hull fouling might be more important in regions that import bulk commodities (e.g., Hawaii or Japan). This study estimates that hull fouling is responsible for 44% of the introduced marine species in Japan. The importance of sea chests as an alternative mechanism for transporting marine organisms around the world has only recently been recognized, and a mechanism may have been responsible for introducing the clam Mercenaria mercenaria, spider crab Pyromaia tuberculata, green crab Carcinus aestuarii, and blue crab Callinectes sapidus to Japan. To prevent the introduction of unwanted marine organisms into Japan by hull fouling, not only are advances in effective and nontoxic anti-fouling paint technology required, but also increases in the frequency of vessel dockings to inspect and clean the hulls. Furthermore, since large volumes of ballast water are exported from the Japanese coasts to many overseas regions, the Japanese government should establish regulations and develon treetment technology to minimize the unintentional export of marine organisms via ballast water.

View full abstract

The Committee for the Preservation of the Natural Environment and the Japanese Association of Benthology investigated the history and present status of marine alien benthic invertebrates and algae on the basis of lists or computer databases of catalogued specimens in the collections of museums and aquaria in Japan. Through the cooperation of 31 museums and aquaria, we recognized 24 marine alien species in 780 lots, including two gastropods, 12 bivalves, two polychaetes, five crustaceans, two ascidians, and one chlorophyte. These species include one cryptogenic species and two species introduced from other parts of Japan. A bivalve, Mytilus galloprovincialis, comprises 245 lots, followed by the striped barnacle Balanus amphitrite (100 lots), the slipper snail Crepidula onyx (75 lots), the ivory barnacle Balanus ebruneus (57 lots), and the European barnacle B. improvisus (55 lots). Most specimens of alien species were collected after 1980 in or around the Seto Inland Sea and Tokyo Bay. The results of this study are not exhaustive, and more extensive research is essential to catalogue the existence of all specimens of marine alien species in Japanese museums and aquaria.

View full abstract

Numerous alien species have been reported in Japanese waters in recent years, but identifications of these species are difficult in most cases. In the Ariake Inland Sea, two new alien gastropods were found in 2000. One of them is Nassarius (Zeuxis) sinarus (Philippi, 1851) from China. This carnivorous species has recently increased explosively in number and has become a pest, eating fish caught in traps. This problem has spread rapidly over wide regions of the Ariake Inland Sea, with goby fisheries using traps in the central and western parts of Saga Prefecture suffering most. Unfortunately, this species was initially misidentified as the endangered species Mitrella martensi (Lischke, 1871). The other alien gastropod species is Stenothyra sp. from Korea. It is an undescribed species in spite of being an alien and had never before been reported from Korea. This case shows that alien species include not only ones that are abundant in their original distribution range, but also unrecognized ones. Several other taxonomic problems posed by alien species are reviewed. Most alien species in Japan have at first been misidentified and/or confused with other species. One of the most important measures to prevent such confusion is the adequate preparation of specimens. Because alien species often appear suddenly, we can not know their origin immediately. If enough specimens are preserved, exact identification may be made through subsequent study. In this connection, alpha-taxonomy will become ever more significant from now on. Comprehensive revisional works for many taxa will be needed in order to identify the alien species.

View full abstract

The clam Ruditapes philippinarum is a commercially important fishery resource in Japan. Because the amount of production has been decreasing gradually in Japan, the clam has been imported from China and Korea in recent years to provide seed for aquaculture and also for recreational shellfish gathering. The object of this study is to confirm whether alien species are being introduced together with the clam and to obtain information on their distribution in Japanese waters. Three species of mollusk-eating moon snail, Euspira fortunei, Glossaulax didyma, and Glossaulax reiniana, were collected from sacks filled with R. philippinarum imported from China. Seven other gastropod species, nine species of bivalves including Meretrix pethechialis, the purse crab Phiiyra pisum, and a brachiopod, Lingula unguis, were also collected from the sacks. Almost all the unintentionally introduced animals were living and were directly released with commercially introduced clams into Mangoku-ura Inlet, Miyagi Prefecture, by a fishermen's cooperative. Although the snail Euspira fortunei is not indigenous to the eastern and northern coasts of Japan, relatively large populations of it occur in the clam production areas of Lake Hamana (Shizuoka), the estuary of the Obitsu River (Chiba), and Mangoku-ura Inlet. I believe that a population of this invasive snail has already been established at least in Mangoku-ura Inlet and is becoming a new, strong predator of the clam stocks. Prevention of further spread and estimation of the rate of predation are important to the clam culture. Among the 22 alien species recorded in this survey, seven were also found in the native communities. The effect of the alien population on the preexisting population is also important problem to be solved.

View full abstract

Recently much attention has been devoted to the introduction of foreign organisms into marine and estuarine communities. Among many marine alien invertebrates in Japanese waters, only four species of polychaete are known as introduced species. In the world, 74 species of polychaete belonging to 15 families have been revealed as introduced or cryptogenic species. Among them, Spionidae, Sabellidae, Serpulidae (including Spirorbinae), and Nereididae are the most frequently reported. These families are found on the shells of introduced oysters, scallops, and other commercially important mollusks, and also on algae. The main introduction vectors are ballast water and fouled ships. Additionally, some species imported and exported as “fishing bait worms” have possibly settled successfully at non-native localities. We summarize here the worldwide invasion of polychaetes and discuss the ongoing problems concerning them.

View full abstract

Two introduced crab species, Pyromaia tuberculata and Carcinus aestuarii, occur abundantly in organically polluted waters in Japan. Population studies of these crabs have been conducted in Tokyo Bay, in which summer hypoxia causes destruction of the benthic animal populations on the bottom of the innerhalf of the bay. In fall, a population of P. tuberculata quickly recolonizes that bottom, which has recovered from the hypoxia, by settlement of larvae. Settled crabs reach maturity by the next spring, then release larvae until the subsequent summer hypoxia. Released larvae disperse to the outerhalf of the bay, resulting in recruitment of juveniles into the local population. These recruits reach maturity before the fall under the normoxic conditions prevailing there, then release larvae for recolonization of the innerhalf of the bay. Carcinus aestuarii grows along the shores of river-mouths and in a lagoon of the inner bay, but migrates out onto the bay bottom during fall to spring, when it releases larvae. Released larvae settle along the shores during the spring. Settled crabs grow on the shores with adult crabs that had returned from the bay bottom. Thus the crabs on the shores avoid encountering the bottom hypoxia. These results suggest that the main factor that has allowed the establishment of the new introduced populations in Tokyo Bay is complementarity between the life cycle of these crabs, including adult migration or larval dispersal, and the seasonal availability of a habitat that is recovering from hypoxia.

View full abstract