Hypoxia: Hypoxia: New insights on an old pressing New insights on an old pressing

environmental problemenvironmental problem

Rudolf WuSchool of Biological Sciences

The University of Hong Kong

Hypoxia is A Pressing Global Problem

An old problem with new insight

Hypoxia: Some TrendHypoxia: Some Trend

• The number of dead zones approximately double each decade since the 1960s (Diaz & Rosenberg, 2008).

• Nowadays there are 400+ eutrophication-associated dead zones and their distribution matches the global human footprint

Hypoxia has already caused major Hypoxia has already caused major changes in structure and function changes in structure and function of marine ecosystems over large of marine ecosystems over large areasareas

New Insights

Hypoxia is Hypoxia is an endocrine disruptoran endocrine disruptor

Common carp (Cyprinus carpio)

Hypoxia isHypoxia isa teratogena teratogen

Zebrafish (Danio rerio)

Hypoxia tips sex balance & Hypoxia tips sex balance & favors a male biased population favors a male biased population

***

*** p < 0.001

Shang, Yu & Wu, 2006

• Male Wistar rats kept under hypoxia showed lower levels of LH and testosterone than their normoxic counterparts (Farias et al., 2007 ).

• Cardiac ventricular septum defects, vascular malformations and vertebral abnormalities were observed in hypoxic Sprague-Dawley rats (Skold et al., 2001)

Will the same also happen in other higher vertebrates?

Is the situation getting better or getting worse?

The situation will get worse because…..

• Growth of treatment facilities is unlikely to catch up with growth of population and industry, especially in developing counties

• Contributions of nutrients from atmospheric fallout and non-point source are significant

• Trans-boundary issues are difficult to resolve

Increase TemperatureIncrease freshwater input

Increase nutrient flux Increase stratification

Nutrient enrichmentEnhanced productivity

Green Houseeffects

HypoxiaSediment

Overall ConclusionsOverall Conclusions• Hypoxia:

– is an endocrine disruptor, and impairs reproduction of fish

– is a teratogen, leading to malformation in fish

– Affects sex differentiation and sex determination in fish, leading to a male biased population, which in turn, may reduce the chance of reproductive success.

– The problem will be getting worse

• Since the genes and hormones controlling sex differentiation and reproduction are highly conserved, the endocrine disrupting effects, teratogenic effects and biased sex ratio observed in fish may also occur in other vertebrates. It appears that this postulation is also supported by some peripheral evidence

• Given the fact that hypoxia (a) is an endocrine disruptor and a teratogen (with similar potency as estradiol and nonylphenol) and (b) covers such a large area, hypoxia may be one of the most important stressor in the marine environment.

Overall ConclusionsOverall Conclusions

Proposed WorkCollaborate with fisheries authorities and undertake a

scientific global review, focusing on :

– Trend analysis (spatial and level in the last 50 years)

– Changes in structure and trophodynamics of marine communities (plankton, benthos, fish)

– Identification of sensitive groups (bioindicators)

Proposed WorkCollaborate with fisheries authorities and undertake a

scientific global review, focusing on :

– Reproductive status and reproductive impairment of fish in hypoxic areas vs normoxic areas

– Endocrine disruption, malformation, sex ratio

– Deciphering effects of hypoxia from those caused by other anthropogenic activities (chemicals) prevailing simultaneously in the marine environment??

– Identifying information gaps and further studies