Ecological communities are rarely formed within a single habitat and tend to include multiple habitats characterized by the influx and efflux of nutrients, detritus, prey and consumers among these habitats. Understanding these between-habitat effects on the community structure and dynamics has become important because this recognition may disprove previous ecological theories based on the processes within a single habitat. This paper reviews current knowledge of between-habitat interactions and their importance for community regulation in coastal ecosystems. First, I reviewed briefly some current knowledge about between-habitat interactions in general. Second, I summarized my empirical demonstrations examining the effects of allochthonous resources from subtidal habitats on the rocky intertidal community. The food web structure of the rocky intertidal habitat revealed that allochthonous sea urchins from the subtidal habitat affected the recipient food web structure and dynamics through the recipient avian predators, although the effects were different between the avian species with different foraging responses (numerical or functional). Understanding the effects of between-habitat interactions is important for the clarification of the spatial extent of community structure and habitat connectivity in landscape level, and thus indispensable for promotion of better coastal conservation and management.
On Midori River Tidal Flat and Arao Tidal Flat, which are major sandy tidal flats in Ariake Bay, Kyushu, Japan, I examined various heavy metal contents of the surface sediment to reconfirm that, among the heavy metals, only manganese deposited on the sediment at extremely high levels. On these two tidal flats, 790 to 2,230 mg kg−1 dry sediment of total manganese was detected in the surface sediment. The manganese deposited (mainly as manganese dioxide) in the sediment tends to be reduced by bacterial activities, released as manganese ion to the interstitial water of the sediment, and weakly bound electronically in an exchangeable form with organic or inorganic matter in the sediment. I also examined the manganese ion concentration of the interstitial water and the content of the exchangeable form of manganese of the sediment. High concentrations of manganese ions, as affect the physiology of the aquatic organisms, were detected from the interstitial water of the sediment on Midori River Tidal Flat (5.8 to 9.9 mg L−1), while high contents of the exchangeable form of manganese (approximately 28 mg kg−1 dry sediment) were found from the sediment on Arao Tidal Flat. It seems probable that the manganese ions reduced from the manganese in the sediment acts as one of the major limiting factors on the occurrence of the clam on these two tidal flats.
The egg production rate (EPR) of the lobate ctenophore Bolinopsis mikado was measured in summer, fall, and winter using field-collected animals whose total lengths (TL) ranged from 17 mm to 73 mm. The TL of spawning B. mikado ranged from 22 mm to 73 mm, indicating that B. mikado matures at ca. 20 mm TL. Because the percentage of spawning individuals to the total ranged from 50% to 100%, B. mikado probably spawned intermittently or daily in Tokyo Bay. Spawning individuals were found even in December and January. Bolinopsis mikado seemed to reproduce continuously in Tokyo Bay throughout the year. A multiple regression analysis between the EPR and ctenophore body size and water temperature suggested that 21.5% of EPR can be explained by these variables. The EPR increased linearly with ctenophore size, i.e. the wet-weight specific EPR (EPR*) was independent of the body size. The relationship between the EPR* and water temperature was equivalent to a Q10 value of 4.7, and was considerably higher than that of the respiration, predation, and growth rates, which may lead to quick population growth and mass occurrence of B. mikado during summer and fall in coastal waters.
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 conditions and describes the maintenance of several clonal strains kept at high abundance (>5,000 cells mL−1) for a relatively 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 peduncle. 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 μL) 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, suggesting that D. caudata can not directly utilize T. amphioxeia as prey.
Expanding the work in our previous paper (Nagai et al. 2006), which showed the close linkage of chaetognath species to changes in water temperature and reported their occurrence characteristics, chaetognath species-specific responses to climate forcing via water temperature fluctuations were ascertained by studying inter-annual linkages among climate-ocean-ecosystem elements. Using samples collected between 1972 and 2002 in the Japan Sea, an attempt was made to understand how the three dominant chaetognaths—Sagitta minima, S. nagae and S. enflata—respond to inter-annual variations of atmospheric signals and oceanic effects in the Tsushima Warm Current around climate regime shift years. Among ocean-atmosphere parameters, the winter monsoon was the most crucial for driving the ecosystem of the Japan Sea. No significant correlation with any of the other parameters was found with the southern oscillation index, but the winter monsoon index had a correlation with water temperature. The climate regime shift during 1976/77 occurred with anomalously cold water induced by a strong winter monsoon. The next climate regime shift (1988/89) appeared with a warm water anomaly due to retention of warm water formed in winter by a weak winter monsoon and increased transport volume in the Tsushima Warm Current water. Chaetognath abundance and species numbers decreased during the colder regime and increased during the warmer regime. Responding to temperature in a species-specific manner, chaetognaths varied notably in abundance. Consequently, changes in species numbers and switching of dominant species occurred. Thus, chaetognath species could be a significant indicator of climate events that influence the ecosystem in the Japan Sea.
The genetic characteristics of three populations of the tideland snail Cerithidea djadjariensis (Martin) that were recently discovered on the Pacific coast of the eastern Japan were compared with other Japanese conspecific populations of this snail on the basis of the nucleotide sequences of mitochondrial DNA. Two populations from the Pacific coast of northeastern Honshu, the Japanese mainland, showed lower genetic diversity than and no significant differentiation from populations in western Honshu and Kyushu. The foundation of these populations might be attributed to range expansion along the coast, probably due to global warming. On the other hand, the population in Tokyo Bay, which was rediscovered in 2001 on an artificial tideland, was shown to be genetically different from all other Japanese populations whose genetic structures have been analyzed. It is suggested that this population was founded by human-mediated introduction such as transportation with short-necked clams, ballast water, or hull fouling.
Buccinum striatissimum and Buccinum tenuissimum are commercially important whelks in the Sea of Japan. B. striatissimum is very similar to B. tenuissimum and their morphological variations make the identification of these species difficult, especially in case that these species are caught together because they are subject to the same environmental factors. In order to develop an easy and objective method to delineate these species, we utilized the difference of mitochondrial 16SrDNA of these two species. As a result, we could easily distinguish these two species by PCR-RFLP method using the difference of this region and AseI restriction endonuclease. In addition, we succeeded in distinguishing sympatric samples of these species, which suggests that these two species are likely to be reproductively isolated although the possibility of hybridization can not be completely ruled out.