In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom). Over 15,000 novel compounds originating from algal biomass have been chemically determined. Resources, thereby inhibiting the growth of other aquatic and algal organisms. The changes in oxygenation are considered consistent with measurements of higher algal biomass and productivity. Marine snow often forms during algal blooms. Most dinophyte chloroplasts are secondary red algal derived chloroplasts. Nitrogen combined with sunlight triggers algal growth. Organic litter in large amounts can cause water pollution and lead to algal blooms. The ecology of harmful algal blooms is extensively studied. These algal mats are in turn colonized by invertebrates. There are many species that can cause harmful algal blooms. This creates a sheltered environment for bacterial and algal colonies. Studies are ongoing to determine the various environmental factors responsible for harmful algal blooms. Reefs are chronically at risk of algal encroachment. Nitrogen is a valuable substrate that can be utilized in algal growth.