Final answer:
The researcher chose the quadrant method over mark and recapture to sample the coral population because corals are immobile, and the quadrant method is well-suited for such organisms, providing accurate data on population size and density.
Step-by-step explanation:
When choosing between the quadrant method and the mark and recapture technique for sampling a coral population, researchers must consider the mobility of the organisms and the logistical feasibility of each method. The quadrant method is typically suited for sessile or slow-moving organisms, such as corals, because it involves counting individuals within fixed plots laid out in the habitat.
Corals, being immobile, can be accurately sampled using this technique. On the other hand, mark and recapture is designed for mobile organisms and may not be as effective or practical for corals. Additionally, the quadrant method can provide detailed information on both population size and density in a given area, which is critical for understanding the distribution of corals within their habitat.