A combination of factors creates the necessary conditions for bioluminescence: red mangrove trees surround the water (the organisms have been related to mangrove forests although mangrove is not necessarily associated with this species); a complete lack of modern development around the bay; the water is warm enough and deep enough; and a small channel to the ocean keeps the dinoflagellates in the bay. This small channel was created artificially, the result of attempts by the occupants of Spanish ships to choke off the bay from the ocean. The Spanish believed that the bioluminescence they encountered there while first exploring the area was the work of the devil and tried to block ocean water from entering the bay by dropping huge boulders in the channel. The Spanish only succeeded in preserving and increasing the luminescence in the now isolated bay. Kayaking is permitted in the bay and may be arranged through local vendors. Vieques has a warm, relatively dry, tropical to subtropical climate. Temperatures vary little throughout the year, with average daily maxima ranging from in January to in July. Average daily minima are about 10 °F / 6 °C lower. Rainfall averages around per year, with the months of May and September–November being the wettest. The west of the island receives significantly more rainfall than the east. Prevailing winds are easterly. Vieques is prone to tropical storms and at risk from hurricanes from June to November. In 1989 Hurricane Hugo caused considerable damage to the island, and in 2017 Hurricane Maria also caused major damage. According to the 2010 US census, the total population of Vieques was 9,301. 94.3% of the population are Hispanic or Latino (of any race). Natives of Vieques are known as . Both Spanish and English are recognized as official languages. Spanish is the primary language of most inhabitants. The sugar industry, once the mainstay of the island's economy, declined during the early 20th century, and finally collapsed in the 1940s when the US Navy took over much of the land on which the sugar cane plantations stood. After an initial naval construction phase, opportunities to make a living on the island were largely limited to fishing or subsistence farming on reduced area. Crops grown on the island include avocados, bananas, coconuts, grains, papayas and sweet potatoes. A small number of permanent local jobs were provided by the US Navy. Since the 1970s General Electric has employed a few hundred workers at a manufacturing plant.