Terrestrial productivity is more effective in the wet tropical climates as the net primary productivity decreases between equatorial and polar regions due to less sunlight and therefore there is a temperature decrease. Global productivity is limited by factors of water and sun, as most ecosystems rely on photosynthesis and water. Marine productivity tends to be higher, as rivers and water carry more nutrients and deposit them in other ecosystems. The most productive regions are areas such as wetlands and estuaries.