The Batrachochytrium dendrobatidis is the main cause of a known disease in algae, since there is a lot of dispersal propagules in the sea; they seek for a host until they find it, then, this parasite kills the host, consuming it; the Batrachochytriu can adapt to a variety of organisms, from algae, fishes, eggs to zooplankton, or even other aquatic fungi.
The lichens are a symbiotical relation between a fungi and algae cyanobacteria, living in filaments. They can be over a plant or algae, which is used as a substrate; also, they can look like plants, but they are not, since lichens doesn't have roots, but they do make the photosynthesis process.
The Thiomargarita namibiensis is the most big prokaryotic organism ever discovered, this bacteria uses sulphur that is produced in the bottom of the seabed and also the nitrates of the water to make an anaerobic process for its metabolism; for surviving, they absorb all the nutrients through its filaments and store it in the vacoule.
The Selachimorpha, (commonly known as Shark) is an animal of the ocean, known for being most of the times at the top of the chain food, are mostly made of cartilage, they compose and close the marine food chain, only in the top part of the sea, since there are bigger predators in the abyssal zone.
The Trichodesmium is a cyanobacteria belonging to the ocean, its main function is to fixate the nitrogen in the sea and water, so it's a major and important part of the entire marine ecosystem, also, this bacteria balances the isotope N2 in the ocean, so all living beings are able to live and persist, whitout this bacteria, life in ocean would be harsh.
The recently discovered Yeti crab is a mystery, we don't know much about it, just that is uses it's hairy hands to collect plankton from the deep geothermal active zone of the easter islands, lives at 2.228 meters of depth. It's unique in it's order and family.
The Laminariales or commonly known as Kelp are a subgenre of algae; this specie grows in large numbers of coastal seaweeds in cold seas, the Kelp produces Algin, a complex carbohydrate not only used by animals in the ecosystem, but also by humans, they help small fishes to hide or escape from predators.
The Phytoplankton is a microscopic marine algae, is the base of the marine food chain, they provide food to a variety of organisms, like whales, jellyfishes, shrimps, snails, etc. They contain chlorophyll and require sunlight in order to live, they are located mostly on the surface of the sea, where ther's sunlight.