The Effect of Anthropogenic Eutrophication
on a Shallow Marine Benthic Ecosystem
: Microfossil Records over the Last 200 Years
in Osaka Bay, Japan
Akira Tsujimoto (Osaka City Univ.)
Moriaki Yasuhara (Smithonian Institution)
Hideo Yamazaki (Kinki Univ.)
Kotaro Hirose (Shimane Univ.)
Global synthesis of collapsed taxa
(Europe, North America, and Australia)
Solid circle
: relative abundance of
collapsed taxa
(i.e., >90 % decrease)
(Worm et al. 2006)
1800
Ecosystem degradation rapidly started since industrialization
Problems of anthropogenic eutrophication
Conceptual Model
1) Increase in food to consumer (increase in biomass)
2) Hypoxia (DO < 2mg/L)
→ Destruction of Benthic Ecosystem
(prosperity of a few resistant species like polychaetes)
Global distribution of
eutrophication-associated dead zones
Japan
Hypoxic
system
Diaz and Rosenberg (2008)
Their distribution matches the global human footprint
Japan has many hypoxic system in Asia
How can we know the “past” ecosystem ?
Biological monitoring: <30 years
Fish catch records: only for commercial fishes,
possible bias
Archeological data: fragmentary, possible bias
Then... We can learn from sediment cores
and contained microfossils
(e.g., foraminifera and ostracoda) !
What are Foraminifera and Ostracoda ?
Foraminifera
Ostracoda
shelled protozoan
(meiobenthos)
small crustacean
(ca. 1 mm)
abundantly fossilize
in sediments
Only metazoa abundantly
preserved as fossils
in sediment cores
There are…
low-oxygen tolerant species
and intolerant species
Sensitive to environmental
changes
bars=100 micron
Osaka Bay ~ Typical Asian Example ~
Typical urban embayment
Serious anthropogenic eutrophication have been
occurring since Japanese industrial revolution
around 1900.
Hypoxia have also been developing in the inner
part since 1900.
Hypoxia most developed during the period of
high economic growth from the mid 1950 to the
early 1970.
COD (Chemical Oxygen Demand) inflow
Large amounts of pollutants are discharged
into the bay via the Yodo River located in the inner part
Total Phosphorous and Dissolved Oxygen
(Summer Values)
The hypoxic zone (DO < 2mg/L)
is formed in the inner part of the bay
Data of DO and TP from Osaka Prefectural Fisheries Experimental Station
(2001–2005) (average of observations from 1999 to 2003, August)
Spatial distribution of benthic population
high-density/
Low-diversity
Polychaetes, which is tolerant of low-oxygen conditions,
predominate in the inner part.
Spatial distribution of benthic foraminifera
relative
abundance
high-density/
Low-diversity
Inner part is dominated by
Ａmmonia beccarii, Eggerella advena, Trochammina hadai
Then, by investigating fossils in cores:
We can understand
i)the developing process of a few resistant species like
small polychaetes
refer
ii)how biodiversity and ecosystem have been
changing and responding to human disturbance
Samples (Short Sediment Cores)
OBY
OS3
OS4
OS5
Hypoxic
OBY
OS3
OS4
OS5
water core
base
depth length
age
(m) (cm)
14
84 ~1840
17.8 105 ~1860
19
86 ~1820
25
74 ~1900
Non-hypoxic
OBY and OS3 are
located in the present
hypoxic zone
The cores are composed of homogeneous mud
Species Diversity vs. Absolute Abundance
before 1920
Natural environmental gradient was destructed after 1920s.
Absolute Abundance of Foram and Ostra
OS5
OBY
OS3
OS4
eutrophication-induced changes occurred around 1900
as a result of Japanese industrial revolution,
and around 1960 as a result of rapid urbanization
Foraminiferal diversity
All sites: Decrease
start of
regulation
Most species collapsed
or locally extinct, except
a few resistant species
to hypoxia
The changes correspond
to the changes of population
in backland and the amount
of nutrients input
Species rank in the hypoxic site (OBY)
average of
pre-industrialization
(before 1920)
1
2
3
1
2
3
After the industrialization
(Eutrophication)
Prosper of
a few resistant species
Collapse of
other species
average of
Alpha and Beta
post-industrialization
diversity loss
(after 1920)
Faunal changes of foraminifera
OS5
OBY
OS3
OS4
Species Diversity vs. Absolute Abundance
Hypoxic sites
Return to the initial state? No! It may be noninvertible process.
Conclusions
Anthropogenic eutrophication caused:
“Collapse of large animals and rise of microbes
(Jackson, 2001, 2008)”
“High-density/low-diversity assemblage (Tsujimoto et al., 2008)”
Collapse of many non-resistant species
: e.g., Crustacea recorded in fossil Ostracoda
Prosperity of a few resistant species
: e.g., deposit-feeding small polychaetes
recorded in fossil Foraminifera
Start of the degradation is 100 years later than Europe in Japan.
This is because Japanese industrialization itself 100 years
later than Europe.
Spatiotemporal changes in the Species Diversity
Newly Impact of Eutrophication?
Changes in the red-tide causing algae
caused the changes in benthic ecosystem?
Osaka Bay ~historical record~
Secular change in the influx of nitrogen and phosphorus (Nakatsuji et al., 1998),
the population size of Osaka City (Osaka City, 2004), and total occurrences of red
tides (Osaka Prefectural Fisheries Experimental Station, 1973–2002).
Salinity
32
32
(Osaka Bay environmental database;
http://kouwan.pa.kkr.mlit.go.jp/kankyo-db/index2.asp)
Inner part (OBY)
●
Inner part (OS3)
●
Outer part (OS4)
●
Outer part (OS5)
●