Milky seas and algal blooms are two aquatic phenomenons that cover such vast areas that they can be seen from space.

So what are they? How are they caused? And how do they affect our environment? All of these questions will be addressed in this article.

For the first phenomena, as its name suggests, "milky seas" occur when the surface of the ocean from horizon to horizon produces a continuous and uniform milky light. But first of all, "milky seas" do not produce a glowing white light, but actually a blue light. Our eyes have two types of cells to see colours, rod cells and cone cells. However, the rod cells which are used for our night vision cannot distinguish between colours.

In order to produce this effect, the organisms need to be physically stimulated, for instance, by the movement of a passing boat in order to produce light or bioluminescence. These organisms cannot be algae as the light they produce is not continuous as that described for "milky seas", but appears as brief flashes. However, there is one organism that under the right conditions, produce a continuous light as described – and that is bacteria when it accumulates in large concentrations. Collections of water taken from milky seas have shown it to contain the bacteria Vibrio harveyi. The area covered by these bacteria has been reported to be as large as 20,579 km2.

However, it is suspected that such large concentrations of bacteria do not occur naturally. The reasons for these large batches of bacteria might be similar to that which causes red tides, which will be explained later.

Algal blooms are another aquatic phenomenon that occurs when there is a rapid increase or accumulation of algae in a body of water. Algal blooms occur in both freshwater and marine ecosystems and can be comprised of a single or multiple species of algae.

The concentrations of algal cells in the water have revealed hundreds, thousands and even millions in just a millilitre. These algal blooms occur because of the presence of excess nutrients in the water, particularly phosphorous which is necessary for plant growth and is a component of fertilizers. These nutrients can enter the water as run-off from areas such as, farms, golf courses, sport playing fields, gardens, hotel grounds or any other facility where large amounts of fertilizer are used.

However, algae are organisms that have a very short life span, so one would think that when the algae die, then the problem will go away. But since there is such a high concentration of algae in the area, when they die, there is also a great accumulation of dead organic matter, which as it decays consumes the oxygen dissolved in the water. This decreased level of oxygen can result in the death of other animals and plants that live in that body of water.

Although algal blooms cause harm to other species in their environment; algal blooms containing certain species are particularly harmful.

Only two percent of over 5,000 species worldwide are considered toxic in nature. In order to not confuse it with algal blooms comprised of non-harmful species let us refer to it as "harmful algal blooms" (HABs). The precise cause of HABs is still unknown as they have been reported by early explorers, so that natural events may have a role to play in their existence. The toxins produced by these HABs can cause reduced levels of physical development, and that of the immune, neurological and reproductive abilities of some species of marine mammals and sea turtles.

Also, just swimming through an algal bloom can be fatal for some animals as it causes mechanical damage to the gill tissues, resulting in the animals suffocating and dying. As in freshwater algal blooms, the decaying algae will cause oxygen depletion of the surrounding water, in turn suffocating the animals that live there, particularly small animals.

Those animals that are not killed by the toxins secreted by the HABs can sequester the toxins in their body so that organisms that consume them die as a result of the toxins (this is referred to as bioaccumulation). These toxins also affect herbivores, such as manatees which feed on contaminated sea grass. These toxins can accumulate and eventually reach humans therefore; HABs contaminate our marine food supply.

Finally, there is the phenomenon known as red tides, which has nothing to do with the tidal action of the water. These are simply algal blooms which are red or brown in colour which as a result give the water a reddish tint. Also it must be noted that not all algae that are of this colour can be labelled as harmful.

Therefore we can see that the mere fact that these two phenomenons can be seen from space indicate the sheer magnitude of the effects they have on the environment.

Although they may both have natural causes and influenced by human activity. The effects of algal blooms in particular are quite harmful to the biodiversity of our aquatic ecosystems, both freshwater and marine as well as depleting our source of seafood and transferring chemicals to humans through bioaccumulation. However, more research is need on the milky sea effect to see if it produces any harmful effects on our environment and the plants and animals that call it home, including humans.