What are the uses of algae?

(N/A) $\rightarrow$ Algae are useful to humans in many ways.
$\rightarrow$ At least half of the total carbon dioxide fixation on Earth is carried out by algae through photosynthesis.
$\rightarrow$ Being photosynthetic,they increase the level of dissolved oxygen in their immediate environment.
$\rightarrow$ They are of paramount importance as primary producers of energy-rich compounds,which form the basis of the food cycles of all aquatic animals.
$\rightarrow$ Many species of $Porphyra$,$Laminaria$,and $Sargassum$ are among the $70$ species of marine algae used as food.
$\rightarrow$ Certain marine brown and red algae produce large amounts of hydrocolloids (water-holding substances),e.g.,algin (brown algae) and carrageen (red algae),which are used commercially.
$\rightarrow$ Agar,a commercial product obtained from $Gelidium$ and $Gracilaria$,is used to grow microbes and in the preparation of ice creams and jellies.
$\rightarrow$ $Chlorella$ and $Spirulina$ are unicellular algae,rich in proteins,and are used as food supplements even by space travelers.