This geographic feature is the primary reason for a budding economy on Cook Island

beautiful beaches and pleasant climates***
beautiful volcanoes
tropical plants
unique population of fish

Probably so.

http://cookislands.southpacific.org/cookislands/economy.html
See the last sentence of the first paragraph here.

The geographic feature that would most likely be the primary reason for a budding economy on Cook Island is its beautiful beaches and pleasant climates. To understand why this is the case, let me explain:

1. Tourism: Cook Island's beautiful beaches and pleasant climates are highly attractive to tourists. This makes tourism one of the major sources of economy for the island. Tourists are drawn to the pristine beaches, crystal-clear waters, and warm weather of Cook Island, which encourages them to visit and spend money on accommodation, food, activities, and souvenirs.

2. Hospitality Industry: The thriving tourism sector creates a demand for hotels, resorts, guest houses, and other accommodation options. This, in turn, creates employment opportunities for local residents, generating income and economic growth. The hospitality industry also supports related sectors such as restaurants, transportation, and recreational activities.

3. Increased Investments: The growing tourism industry can attract both domestic and foreign investments. Investors may establish businesses such as beach resorts, water sports centers, restaurants, or souvenir shops to cater to the tourist population. These investments create further employment opportunities and stimulate economic expansion.

4. Local Businesses: The presence of tourists provides an opportunity for local entrepreneurs to establish small businesses catering to their needs. For example, local artisans can sell handmade crafts, local farmers can supply fresh produce to restaurants, and tour guides can offer their services to showcase the island's natural beauty.

In summary, the combination of beautiful beaches and pleasant climates on Cook Island provides a significant advantage for the island's economy. This attracts tourists, leads to the growth of the hospitality industry, encourages investments, and supports local businesses, all contributing to a budding economy.