[1끊어읽기] TOEFL Reading : Seagrasses 4  

Other physical factors 

that have an effect

on seagrass beds 

include

light, temperature, and desiccation (drying out).

For example,

water depth and turbidity

(density of particles in the water) 

together or separately 

control

the amount of light

available to the plants and the depth 

to which the seagrasses may extend.

Although marine botanist W.A.Setchell

suggested early

on the temperature

was critical

to the growth and reproduction of eelgrass, 

it has since been shown 

that this particularly widespread seagrass

grows and reproduces 

at temperatures between 2 and 4 degrees Celsius 

in the Arctic

and at temperatures up to 28 degrees Celsius 

on the northeastern coast of the United States.

Still, extreme temperatures, 

in combination with other factors, 

may have

dramatic detrimental effects. 

For example,

in areas of the cold North Atlantic, 

ice may form

in winter. 

Researchers Robertson and Mann note

that when the ice begins to break up, 

the wind and tides may move the ice around, 

scouring the bottom

and uprooting the eelgrass.

In contrast,

at the southern end of the eelgrass 

Seagrass beds also decline 

if they are subjected

to too much exposure to the air. 

The effect of desiccation 

is often difficult to separate 

from the effect of temperature. 

Most seagrass beds 

seem tolerant of considerable changes 

in salinity (salt levels) 

and can be found 

in brackish (somewhat salty) waters 

as well as in full-strength seawater.

Other physical factors 

that have an effect on seagrass beds 

include light, temperature, and desiccation (drying out).

For example, water depth and turbidity (density of particles in the water) 

together or separately 

control the amount of light available 

to the plants and the depth 

to which the seagrasses may extend.

Although marine botanist W.A.Setchell suggested 

early on the temperature was critical to the growth and reproduction of eelgrass, 

it has since been shown 

that this particularly widespread seagrass grows and reproduces 

at temperatures between 2 and 4 degrees Celsius 

in the Arctic and at temperatures up to 28 degrees Celsius 

on the northeastern coast of the United States.

Still, extreme temperatures, 

in combination with other factors, 

may have dramatic detrimental effects. 

For example, in areas of the cold North Atlantic, 

ice may form in winter. 

Researchers Robertson and Mann 

note that when the ice begins to break up, 

the wind and tides may move the ice around, 

scouring the bottom and uprooting the eelgrass.

In contrast, at the southern end of the eelgrass 

Seagrass beds also decline 

if they are subjected to too much exposure to the air. 

The effect of desiccation 

is often difficult to separate 

from the effect of temperature. 

Most seagrass beds 

seem tolerant of considerable changes 

in salinity (salt levels) 

and can be found 

in brackish (somewhat salty) waters 

as well as in full-strength seawater.