ANNOTATION OF PAPER

Decline of Blue Crab:
-lee.R.,Frischer.M. 2002. the Decline of the blue crab. American Scientist. Volume 92: 548-552.

Decline of Blue Crab:
Problem:
-The east coast of America has suffered a significant decline in population of blue crab.
- the east coast of Georgia the average of 3.9 million kilograms in 1957 jumped down to about 816,000 kilos in 2002 which effected the economy of the seafood market and many fishermen went bankrupt.
Hypothesis:
researchers believe that there are two main reasons for this phenomenon:
- weather changes and salinity of water.
- the occurrence of a deadly disease, called hematodinium
- those two are closly related.

Hematodinium perezi:
- Is a lethal pathogen that reproduces in the crabs' blood, the hemolymph.
-As it grows inside the crab, the parasite consumes the hemolymph cells and the primary hemolymph protein hemocyanin.
-This protein transport oxygen in crustaceans in the same way the hemoglobin performs this task in vertebrates.
-Crabs with hematodinium suffer exhaustion and sooner or later they die from suffocation-Hematodinium have decreased the population of the blue crab throughout the globule as well as France,Newfoundland, Scotland, and Alaska.

Transmission of the disease:
1)Dinospore:
- Dinospore have an important role in spreading Hematodinium.
-The dinospore leaves the crab via the gills to the surroundings (water) and remains infectious in resting stage.
- The evidence shows that the Hematodinium can be released to the water from infected crabs and passed on to the healthy crabs.
2)Cannibalism:
-the blue crabs are notoriously cannibalism, and as soon as one is weakened by disease it quickly falls pray to its neighbors.
- the laboratory studies shows that healthy crabs get infected if they are fed tissue from sick crabs.

Weather and water salinity:
- the research illustrate that the crabs caught during the winter are free of infections.
- the intensity of the disease increase in late spring through early summer.
- After that the crabs disappears in the summer, the crab and the disease tend to appear again in the fall.
- the hematodinium disease out break more likely when the flow of fresh water to estuarine system is reduced and the salinity is high (greater then 28 parts per thousand).
-lower salinity in estuaries seems to be associated with increased blue crab population. This suggests that the availability of fresh water was beneficial to the health of the crab population.
-The hematodinium was absent in blue crabs when the salinity was less than 11 per thousand and when the average temperature of water was below 10 degree.
-Hematodinium preferentially kills female blue crabs more then males since the female crabs must traverse high-salinity estuarine areas to reach offshore spawning ground. They are more likely to contract the disease than males.

Diagnosis:
- Diagnosing the disease depends on a detecting the parasite in the blood sample.
- When the pathogen is present in high concentration (more then 1 parasite per 300 normal blood cells) we can detect the hematodinium by using a special stain under the microscope.
- However it's hard to use this method when the concentration is low or when it is out side the crab host.
- The researchers figured out a new method which is called gene based diagnostic test.
-This method can detect the parasite in low concentrations (1/300) and used to identify the organism outside the crab.
-This diagnosing technique helped the researchers study the life cycle and distribution of hematodinium.
- there is no way to control the disease till this day.