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In order to withstand tidal currents, juvenile horseshoe [#permalink]
03 Nov 2004, 15:47
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In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the
sand. Such burrowing discourages barnacles from clinging to their shells. When fully
grown, however, the crabs can readily withstand tidal currents without burrowing, and
thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal
currents are very weak, juvenile horseshoe crabs are found not to have significant
barnacle populations, even though they seldom burrow.
Which of the following, if true, most helps to explain the surprising finding?
A. Tidal currents do not themselves dislodge barnacles from the shells of horseshoe
B. Barnacles most readily attach themselves to horseshoe crabs in areas where tidal
currents are weakest.
C. The strength of the tidal currents in a given location varies widely over the course
of a day.
D. A very large barnacle population can significantly decrease the ability of a
horseshoe crab to find food.
E. Until they are fully grown, horseshoe crabs shed their shells and grow new ones
several times a year.
When the crabs are observed assuming majority of them were hatched from eggs at approximately same time. They should be shedding their sheels at almost the same time and any attached barnacle should be detached in the process or shedding the old shell.
Can't be C becoz, it doesn't say anywhere that strong tides wash the barnacles away, it simpy says that stong tides make them burrow. But in the weak tide situation, the crabs don't burrow, so tide couldn't have had any effect on the barnacles