Plankton and Benthos Research 

About: Plankton and Benthos Research is an academic journal published by The Plankton Society of Japan (The Japanese Association of Benthology). The journal publishes majorly in the area(s): Bay & Biology. It has an ISSN identifier of 1880-8247. It is also open access. Over the lifetime, 472 publications have been published receiving 4183 citations. The journal is also known as: Plankton and benthos research & a joint journal of the Plankton Society of Japan & the Japanese Association of Benthology.

Eutrophication and occurrences of harmful algal blooms in the Seto Inland Sea, Japan

Abstract: The Seto Inland Sea is the largest enclosed coastal sea in Japan and is also a major fishing ground includ- ing aquacultures of fish, bivalves and seaweeds. The incidents of red tides dramatically increased in frequency and scale in the Seto Inland Sea along with serious eutrophication in the 1960s and 1970s. The maximum incident of 299 was recorded in 1976, but the incident has since shown a clear decreasing trend, reaching about 100 per year in the late 1980s by virtue of regulation by law, and this level has been maintained thereafter with the level of nutrients supporting red tide occurrences. The "Law Concerning Special Measures for Conservation of the Environment of the Seto Inland Sea" was legislated in 1973 and industrial loading was decreased to half the level of 1972. The important red tide or- ganisms causing huge fishery damages by fish-kill are Chattonella antiqua, C. marina, C. ovata and Heterosigma akashiwo (Raphidophyceae), and Karenia mikimotoi and Cochlodinium polykrikoides (Dinophyceae). The maximum fishery damage (death of 14.2 million yellowtails) was 7.1 billion yen (about US $60 million) caused by C. antiqua in Harima-Nada in 1972. In 1988, a novel red-tide dinoflagellate species Heterocapsa circularisquama appeared for the first time, and has repeatedly killed both natural and aquacultured bivalves, with the highest damage of 3.9 billion yen to cultured oysters in Hiroshima Bay in 1998. Among the important red-tide organisms, C. antiqua, H. circularisquama and C. polykrikoides are rated as extremely harmful species that can easily reach the warning level of fishery damage by consuming only small amounts of nutrients. In toxic blooms, the dinoflagellate Alexandrium tamarense has become dominant in the Seto Inland Sea in the spring season, causing toxicity in short-necked clams and cultured oysters al- most every year. Many countermeasures have been applied for harmful algal blooms in Japan. Laws for the regulation of water quality have been most effective in decreasing red-tide occurrences. No physical and chemical controls have been successful except for clay treatments. Clay spraying has been investigated and implemented in Kyushu and Korea for the removal of C. polykrikoides red tides. As environment-friendly mitigation strategies for red tides, biological con- trols using algicidal bacteria and viruses are proposed. A new finding of the abundant existence of algicidal bacteria on the surface of seaweeds suggests that co-culturing fish and seaweed is a prevention strategy for harmful algal blooms by virtue of the continuous release of many algicidal bacteria to the surrounding seawater. The artificial development of seaweed beds would also be effective as a prevention strategy for red tides.

Blooms of the giant jellyfish Nemopilema nomurai: a threat to the fisheries sustainability of the East Asian Marginal Seas

Abstract: The rhizostome jellyfish Nemopilema nomurai, which is endemic to the East Asian Marginal Seas (i.e. the Bohai, Yellow, East China and Japan Seas), is unique both by its enormous body size (ca. 2 m maximum bell diameter and 200 kg wet weight) and propensity for occasional population explosionss. Massive blooms of this species have his- torically been reported only once per ca. 40 years (i.e. in 1920, 1958 and 1995), but have become increasingly frequent recently (i.e. in 2002, 2003, 2005 and 2006). Both accumulated knowledge on the spatiotemporal distributions and physical modeling of the water circulation show that the medusae are released from benthic polyps during April-June in the Yellow Sea and East China Sea, and transported by the Tsushima Current to the Japan Sea. The bloom in 2005 might be the largest ever in history; as many as 3-5� 10 8 medusae passed through the Tsushima Strait daily during the summer and there were more than 100,000 complaints from commercial fishermen. The recent blooms of N. nomurai may have been caused by environmental changes, such as increased water temperature, eutrophication, coastal modifi- cation, and over-fishing in Chinese coastal waters. Frequent jellyfish blooms can apparently be a threat to the fisheries sustainability of the East Asian Marginal Seas, one of the world's most productive fisheries grounds.

Combined effects of food supply and temperature on asexual reproduction and somatic growth of polyps of the common jellyfish Aurelia aurita s.l.

Abstract: The polyp stage is an important part of the Aurelia aurita s.l. life cycle, because polyp clones are able to increase their population size by budding, providing the opportunity to increase the medusa population by the produc- tion of many ephyrae through strobilation. We investigated asexual reproduction of A. aurita polyps on an individual basis at 4 different temperatures (i.e. 18, 22, 26 and 28 o C) and at 5 different food levels (i.e. 1.7, 3.3, 6.6, 10 and 13.3 mg C polyp �1 d �1 ) in the laboratory. Three types of asexual reproduction were observed: polyps directly budded from the parent stalk (DBP), polyps budded from the parent pedal stolon (SBP), and podocysts (PC). DBP was the major repro- ductive method (94% of the total) and SBP and PC accounted for only 5 and 1%, respectively. PC were produced by the polyps kept under low food supply (�3.3 mg C polyp �1 d �1 ) and high temperature (�26°C). Production of new polyps by DBP and SBP significantly increased with increasing food and temperature. The somatic growth of parent polyps significantly increased with more food and cooler temperatures. We conclude that both increases in water temperature through global warming and increases in abundances of zooplankton prey because of eutrophication may be responsible for the prominent blooms of A. aurita medusae in East Asian coastal waters in recent times.

Successful cultivation of the toxic dinoflagellate Dinophysis caudata (Dinophyceae)

Abstract: Recently, Park et al. (2006) succeeded in cultivating the toxic dinoflagellate Dinophysis acuminata and maintaining them by feeding the ciliate Myrionecta rubra grown with a cryptophyte Teleaulax sp. After this report, the present study is the second report of propagation of a Dinophysis species (Dinophysis caudata) under laboratory condi- tions and describes the maintenance of several clonal strains kept at high abundance (� 5,000 cells mL � 1 ) for a rela- tively long period (� 4 months) when fed on M. rubra with the addition of Teleaulax amphioxeia. We confirmed that D. caudata swam actively around its ciliate prey and inserted its peduncle (feeding tube) into the ciliate. Thereafter, the prey became immobile and rounded. Dinophysis caudata actively ingested the cytoplasm of the prey through the pedun- cle. Dinophysis caudata grew at a growth rate of 1.03 divisions day � 1 when supplied with M. rubra as prey, reaching a maximum concentration of ca. 5,000 cell well � 1 (810 mL) during a 9 day growth experiment. In contrast, a culture of D. caudata was not able to be established in the absence of the ciliate or when provided with T. amphioxeia only, suggest- ing that D. caudata can not directly utilize T. amphioxeia as prey.

Effects of low dissolved oxygen on planula settlement, polyp growth and asexual reproduction of Aurelia aurita

Abstract: Tokyo Bay is one of the most eutrophicated bays in Japan, and mass occurrences of scyphozoan jellyfish Aurelia aurita have often been observed with progress of eutrophication In the coastal environment, the abundance of substrates suitable for A aurita polyps are obviously increasing by reclamation However, most suitable substrates for settling, except in the bottom-layer in the innermost part of Tokyo Bay, are occupied by other sessile organisms such as mussels, barnacles or ascidians The bottom layer is characterized by low DO concentrations (≦20 ml O2 L−1) that turn to hypoxia during summer, resulting in low recruitment and low growth of other sessile organisms To elucidate the mechanism by which mass occurrence of jellyfish occurs, adaptative behavior to hypoxia in planula larvae and the polyp stage was experimentally studied In the present study, planula settlement was promoted by a decrease in DO concentrations, and apparent growth of polyps and production of daughter polyps by asexual budding were also observed, even in the polyps cultured in hypoxic waters Moreover A aurita polyps cultured under hypoxic conditions began strobilation and ephyrae were liberated after the DO concentration levels were restored It is suggested that the occurrence of hypoxic waters is rather favorable for the survival, growth and asexual reproduction of A aurita polyps, and it can directly contribute to the consequent production of A aurita ephyrae in the next spring within Tokyo Bay