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I. Aquatic Ecosystems

A) On-site research on Coastal Ecosystem at the Sagami Bay, Kanagawa

1. Mid-to-long-term observation of marine environment and biomass of phytoplankton and zooplankton
2. Research on the mechanism of mass generation of harmful algae(-2009)
3. Evaluation of bio-scientific characters of Dissolved Organic Carbon and its role (-2010)
4. Influence of typhoon on coastal ecosystem
5. Influence of pressure on Physioecology of zooplankton
6. The study of copepod nauplius, a baby copepod
7. Study on the microbial communities in the sea surface microlayer (SML)

B) Coral Reef Ecosystem

1. Temporal variation of zooplankton community’s standing stock, composition and production
2. Diel variation of zooplankton community(-2012)
3. Trophic structure of zooplankton community using stable isotopic analyses
4. Biological role of coral mucus
5. Community structure of coral reefs around Malay Peninsula
6. Restoration of coral reefs (-2007)
7. Seasonal variability in ultraviolet radiation penetration and bio-optical factors in tropical coral-reef waters

C) The Production Ecology of Euphausia superba

1. Research on the artificial rearing of E. superba: the relationship among its food, growth rate and molting frequency
2. Research on Production Ecology and pressure: the influence of pressure on embryo development and behaviors of E. superba
3. Influence of parasitic organisms on the E. superba community in the Antarctic Ocean

A) A) On-site research on Coastal Ecosystem at the Sagami Bay, Kanagawa

We are conducting research on the Production Ecology of coastal organisms placed in the lower trophic level, such as phytoplankton, zooplankton and bacteria. We are also analyzing mid-to-long-term variation of the coastal ecosystem and factors contributing to this phenomenon. Investigating an increasing number of typhoons and their effects on the coastal ecosystem is another research topic in this field.
This laboratory has been conducting joint studies on the coastal ecosystem of Sagami Bay with the laboratory of Prof. Kikuchi at Faculty of Education and Human Sciences, Yokohama National University.

Sagami Bay

Sagami Bay opens its entrance to the Pacific, receiving Kuroshio Current from the south and Oyashio Current from the north toward its center. Also, Sagami and Sakawa Rivers run into the west of the bay, forming low salinity water on the surface layer. Such a complex structure of the water mass in Sagami Bay enables diverse ocean biota to be formed.
Manazuru Peninsula is located in the west part of Sagami Bay. Around the peninsula, the inflow stream from Kuroshio Current branches off in the bay and goes up northward along Izu Peninsula while another stream hits Miura Peninsula in the east of the bay and turns its direction southward along Shounan coast. These two tides meet at Manazuru Peninsula and create a rip current. That is why Manazuru Peninsula is known as one of better fishing places in Sagami Bay.

1. Mid-to-long-term observation of marine environment and biomass of phytoplankton and zooplankton

From spring to summer at coastal regions of the Temperate zone, phytoplankton, autotrophic organisms that photosynthesize and independently gain energy, start to increase very rapidly. This growth is caused by the increase of solar radiation and water temperature as well as inflowing nutrients from rivers. As the growth of phytoplankton continues, zooplankton grows rapidly by preying on phytoplankton, and productive energy is eventually transferred to the organisms at higher trophic levels, such as fish. By investigating biomass, species compositions, and the mechanism of community succession of phytoplankton and zooplankton, we are able to analyze the production-ecological role of the plankton community as food sources for industrially important fishes. This investigation also helps us to understand mid-to-long term variations of the marine environment and their causes as well as how to evaluate anthropogenic impacts on the environment.

2. Research on the mechanism of mass generation of harmful algae (-2009)

When harmful phytoplankton increases in high density, it is called Harmful Algal Blooms (HABs). It is often pointed out that HABs are globally expanding both in terms of its frequency and magnitude. In order to alleviate and prevent damage from HABs, it is imperative to expeditiously predict its occurrence of harmful algae through precise detection, identification and quantification. An identification method using morphological characters had been adopted, but this was problematic for its poor accuracy and inefficient operation. In order to overcome these problems, different methods have been devised, such as Real-Time PCR method for its better quantification quality and FISH method for its speedy analysis. Through these advanced methods, expeditious and accurate monitoring of harmful algae can be conducted in the coastal area of Sagami bay. This development also leads to an established system for monitoring, predicting and warning HABs breakout. Consequently, the study on HABs is expected to prevent HABs from damaging fisheries, contaminating human food supplies in the case of polluted seafood, and contributing to the deterioration of the coastal environment.

3. Evaluation of bio-scientific characters of Dissolved Organic Carbon and its role (-2010)

Dissolved Organic Carbon (DOC) is generally regarded as organic carbon which passes through a filter with 0.7 um of its pore size. Majority of oceanic organic substances exist in a form of DOC, and they function as a huge carbon storage, which almost equals to the quantity of CO2 in the air. By this means, DOC plays an important role for material circulation in the ocean. In the coastal area of Sagami Bay, the bacteria-utilizing DOC was found to mainly result from the biological production process in the water column.

4. Influence of typhoon on coastal ecosystem

While ecological disturbance could destroy the structure of ecosystems, it is also regarded as a necessary process for maintaining healthy ecosystems. Natural factors that cause ecological disturbance include typhoons, monsoons, El Nino and so on. Typhoons discontinuously bring about major changes to the oceanic physical environment and drastically alternate the habitats of living organisms. Observing how marine environment alters due to typhoons and how living organisms respond to such changes in the coastal area of Sagami Bay extends important knowledge to predict future oceanic conditions for fishery and to control and maintain healthy marine environment.

5. Influence of pressure on Physioecology of zooplankton

The ocean, unlike land, is a unique environment in which living organisms experience huge pressure alternation. Many marine zooplankton are especially affected by constantly changing pressure due to their vertical migration.
In this laboratory, we created pressure equipment to study the influence of pressure on various zooplankton species. We have investigated, using eggs of copepod and krill, how high-pressure influence on egg development. As a result, it was figured out that eggs of several species show different pressure tolerance under high-pressure, as some species showed high hatchability while others indicated low. This result considers that different inhabitable depths, egg production depths and phylogenetic systems are reflected on their eggs different pressure tolerances.

6.The study of copepod nauplius, a baby copepod

Copepods play important roles in marine ecosystem, including a link between primary production and fish. They have some developmental stages during their growth. Above all, first developmental larva which is called nauplius has greatly different appearance compared with the adult. It suggests that this tiny larva can feed on bacterial plankton, which is considered to be too small for the adult to eat. Moreover, nauplius is known as important food item for fish larvae. Elucidation of carbon flux throughout the nauplius is crucial for the understanding of carbon transfer in the marine food webs. In our laboratory, we examine population change, food items and ingestion rate of nauplius by various approaches such as field investigation, laboratory experiment and observation with scanning electron microscope.

7. Study on the microbial communities in the sea surface microlayer (SML)

The sea surface microlayer (SML) is operationally defined as the uppermost 1-mm layer of the ocean surface. The SML covers about 70% of the Earth’s surface and is located at the boundary interface between the atmosphere and the ocean. Therefore, the SML plays a vital role in global biogeochemical cycles and climate change due to the regulation of the air-sea transfer processes of gases and particles.

Previous studies have shown that microorganisms are significantly enriched in the SML, and the investigation of the microorganisms in the SML is essential for the better understanding of the material cycles through the air-sea interface because they are both the source and sink of the substances in the atmosphere and the ocean. Our laboratory is focusing on the seasonal variability in the abundance and diversity of the microbial communities and their roles in the SML in temperate coastal waters of Sagami Bay, Japan.

B) Coral Reef Ecosystem

1. Temporal variation of zooplankton community’s standing stock, composition and production
2. Diel variation of zooplankton community(-2012)
3. Trophic structure of zooplankton community using stable isotopic analyses
4. Biological role of coral mucus
5. Community structure of coral reefs around Malay Peninsula
6. Restoration of coral reefs (-2007)
7. Seasonal variability in ultraviolet radiation penetration and bio-optical factors in tropical coral-reef waters

Research on the ecosystem structure of coral reefs and those environment conservation are investigating in Malaysia. Coral coverages and bio-diversity were observed for 3 times at the entire Malaysia Peninsula, and the preservation state of coral reefs was investigated. In recent years, several studies were conducted in coral reef ecosystems, such as planktonic production, trophic structure, monsoon influence to optical environment, recruitments of coral larva, construction of artificial reefs, and evaluations of reef fish etc.
Collaborating institutions: Universiti Kebangsaan Malaysia (UKM), Universiti Selangor (UNISEL), Universiti Malaysia Terengganu (UMT)

1. Temporal variation of zooplankton community’s standing stock, composition and production

Zooplankton in coral reef ecosystems takes an important role to link organisms of lower trophic level to those of higher level, such as corals and fishes. Investigating zooplankton’s production rate is crucial to understand material cycle within coral reef ecosystems.
We conducted a joint study with Universiti Kebangsaan Malaysia (UKM) on seasonal changes in biomass and production of zooplankton community in the coral reefs around Tioman Island, Malaysia. We estimated zooplankton community’s daily food requirement from their production rates. The result showed the possibility that existing phytoplankton were not enough to cover the food requirement of herbivorous zooplankton, and thus abundant detritus derived from coral mucus could be one of their important food sources. That is to say, phytoplankton and coral mucus-derived detritus are the origins of pelagic ecosystem of Malaysian coral reefs and support the production of zooplankton communities.

2. Diel variation of zooplankton community(-2012)

It is observed that abundance, biomass and composition of zooplankton in coral reefs differ by day and night or within one night. Collecting zooplankton for a short interval of time and observing their daily variation pattern is instrumental to precisely estimate zooplankton production rates.
We collected zooplankton from coral reefs in Redang and Tioman Islands every 3 hours for 48 consecutive hours and investigate their diurnal pattern.

3. Trophic structure of zooplankton community using stable isotopic analyses

Food web structure of plankton in coral reefs is so complicated that not many studies have been done to date. This laboratory and UMT have worked together in Bidong Island on this topic. We have investigated the food chain of the plankton communities distributed in coral reefs by collecting them on a regular basis and individually measuring the isotopic ratio of sorted zooplankton communities.

4. Biological role of coral mucus

Whereas coral reefs are known as oligotrophic, its high productivity of bacteria has been also reported. This is considered that organic substances derived from coral mucus contributed for the high productivity, and the role of mucus in material cycle within coral reef ecosystems has been attracting high attention in recent years.
We have investigated the production rate of coral mucus and its use by bacteria communities.

5. Community structure of coral reefs around Malay Peninsula

In 2001, 2007 and 2013, we conducted extensive research on the coverage and structure of coral communities around Peninsula Malaysia. Each year, together with UKM and UNISEL, we visited 6 islands indicated below for 20 days and investigated 13 coral reefs in total.

The result of investigation from 2001 indicated that coral structures at Peninsula Malaysia differ between the east and west coasts; while massive corals dominated the west coast, branch corals took over the east coast. Moreover, the diversity of corals tended to be higher in the east coast as well, and the effect of monsoon was considered as a contributing factor of the different coral community structures on the east and west coasts despite the same latitude (Toda et al. 2007).

6. Restoration of coral reefs (-2007)

In order to restore coral reefs, we studied functionality of coral larvae in a new community, developing artificial corals and conducting assessment of artificial fish bed in Tioman Island. For this project, we collaborated with UKM and UNISEL.

7. Seasonal variability in ultraviolet radiation penetration and bio-optical factors in tropical coral-reef waters

Tropical corals are exposed to strong ultraviolet radiation (UVR) through the year. In shallow coral-reef waters, the high UVR stress may damage DNA of symbiotic phytoplankton. Observing seasonal variability in UVR penetration and bio-optical factors that absorb light is necessary to understand the optical environment in tropical marine ecosystems.
We conduct a joint study with Universiti Malaysia Terengganu (UMT) and Univeititi Selangor (UNISEL) on seasonal changes in UVR attenuation and bio-optical factors in coral-reef waters near Bidong Island, Malaysia. We have investigated the influence of North-East (NE) monsoon, which strongly affects the East coast of Peninsula Malaysia, , and found that there is a significant difference in UVR attenuation between NE monsoon season (November - January) and non-monsoon season (February-October). For example, UVR attenuation during NE monsoon season became shallow. We clarified seasonal variability of UVR penetration in tropical coral-reef waters.

C) The Production Ecology of Euphausia superba

1. Research on the artificial rearing of E. superba: the relationship among its food, growth rate and molting frequency
2. Research on Production Ecology and pressure: the influence of pressure on embryo development and behaviors of E. superba
3. Influence of parasitic organisms on the E. superba community in the Antarctic Ocean

Euphausia superba is the most abundant biological resource on the earth. Through artificial rearing of E. superba, we are investigating the relationship among food composition of their larva, growth rate and molting intervals.

Euphausia superbaEuphausia superbais a crustacean that lives in the Antarctic Ocean. The largest body length measures beyond 60 mm and its life-span is 5-7 years. E. superba is a key species in the Antarctic ecosystem, which serves as a food source for inhabiting animals, such as birds, whales and penguins. Its biomass, which is nearly 500,000,000 tons, is considered as the largest on the earth, and thus its biology and the amount of resources contained are widely investigated all over the world. We are working on the following research themes in a joint study with the Port of Nagoya Public Aquarium and the Australian Antarctic Division.

1. Research on the artificial rearing of E. superba: the relationship among its food, growth rate and molting frequency

The Port of Nagoya Public Aquarium is the first institute in the world to have succeeded on artificial rearing of E. superba. Through joint studies with this aquarium, we have been rearing E. superba and observing their growth for physiological ecological researches. Specific topics in our researches include the relationship between the growing rate of eggs and water temperature, the relevance among food quality, molting rate and growing rate of larva, and so on. As a result, the research proved the importance of zooplankton for the growth of E. superba despite the generally-accepted idea which considers phytoplankton as its main food resource.

2. Research on Production Ecology and pressure: the influence of pressure on embryo development and behaviors of E. superba

Eggs of E. superba are laid near the surface and sink into the ocean. When they go down to the deeper layer, at around the depth of 1,000 to 2,000 m, the eggs hatch and larva move upward to the surface again. Because of this wide-ranging OVM, E. superba face the highest pressure in their lifetime during the early growth stage, such as eggs or larva. Although the development of eggs of E. superba is often studied under the atmospheric pressure, how the eggs are influenced in the actual pressure environment has not been studied much. Moreover, pressure environment is also considered as a potential trigger for the larva’s upward movement. Therefore, this laboratory is aiming to reveal how E. superba, on its initial growth stage, is influenced by pressure.

3. Influence of parasitic organisms on the E. superba community in the Antarctic Ocean

We can find the Protozoa, Cephaloidophora pacifica Avdeev, parasitizing in the gut of E. superba living in Antarctic Ocean. We researched on the influence of this organism to the growth of krill and their ecological strategies. Also, we investigated where in the body of krill the Protozoa mainly live. Furthermore, we studied the strategy of how the organisms survive in the gut of krill, though the gut also becomes molted when the krill shed its skin.