Anthropogenic impacts on marine ecosystems
Coastal waters are among the most productive areas of the ocean and support most of the world’s major fisheries. Rivers carry and provide large quantities of nutrients to the sea. Complicated topography raises nutrient-rich deep water to the surface euphotic layer. Furthermore, strong tidal currents mix the upper and lower water layers. All these processes support additional supplies of nutrients, which are generally scarce in the sea, and stimulate primary production in coastal areas.
However, coastal ecosystems are also very sensitive to changes in the environment, and there is concern that some areas are now struggling to maintain their natural states. An excess of nutrients from terrestrial agriculture and industry entering the coastal areas can have serious adverse effects such as producing “red tides,” nuisance blooms of phytoplankton. They may themselves be toxic, or can lead to hypoxia (oxygen depletion) as they decay with consequent disruption of the ecosystem and the mass mortality of marine organisms. Rivers carry not only nutrients, but also pollutants from terrestrial
industries into estuaries where they have their initial, and usually largest, impact.
In addition to these pressures from industrial and agricultural inputs, the welfare of the coastal areas is further threatened by the over-exploitation of fish stocks. It has been estimated that fishing pressures in the coastal area are such that ~25% of the total coastal area biomass is removed each year, much of it by trawling, which also plows up the seabed. Such intensive fishing can result in the collapse of economically important fisheries. Recovery of fish stocks can take considerable time, and intense fishing can lead to radical changes in the ecosystem as a result of habitat disturbance and community shifts to non-commercial species.
Biodiversity using environmental DNA
Environmental DNA (eDNA) is DNA in the environments such as water, air or soil. They are released from individual organisms in the form of feces, mucus and shed skin. eDNA is effective for identifying the presence of species that are difficult to find or catch. It is highly useful for detecting endangered species, as the presence and abundance of a target species can be estimated by detecting eDNA from water samples without capturing or damaging individuals. Recent developments of DNA sequencing methods enable us to get big data on the existence of living organisms, biomass and number of species by analyzing eDNA.
Distribution and biomass are the most basic and important information for the protection and management of wildlife. However, it is difficult to estimate them, even though using a recent model and/or conventional approaches. For example, it is a tough job to count numbers, collect samples, and identify, as they require great efforts, skills and time. Monitoring using the eDNA method complements the conventional approaches, and provides valuable information on biodiversity and biomass in the river and ocean.
Material cycle and marine ecosystem using stable isotope
There are several techniques for understanding the diet of organisms, including direct observation of feeding behavior and gut content analysis. Direct observation of feeding behavior is unfeasible over long periods in the field. Gut contents of animals cannot distinguish ingested material that is not assimilated, and thus provide only rough estimates of the percentages of various materials ingested by the animals.
On the other hand, unique stable carbon isotope signatures of various plant materials, coupled with little fractionation of stable carbon isotopes during consumption/respiration make this a good tracer of dietary carbon sources. Large fractionation of stable nitrogen isotopes during trophic transfer makes this a useful tracer of food web structure. This information can be used to trace the transport of contaminants through trophic levels. Therefore, multiple stable isotopes allow for the distinction of various food sources.
Numerical modeling of marine ecosystem and transport of eggs and larvae
In general, marine animals lay a quite large number of eggs. Survival in early life stages has a strong effect on the recruitment of marine animals. Among various physical processes affecting the recruitment, the transport of eggs and larvae from the spawning grounds to their nurseries is one of the most important. In recent years, increased attention has been focused on the simulation of egg and larval transport in order to understand the variability of the stock of pelagic fishes.
We use numerical models to examine the influences of the physical and biological factors on larval survival and recruitment.
