Life originated in the sea, and there it evolved for millions of years before any organism had the idea to crawl on land. The diversity of life is therefore much greater in the sea than on land. The largest as well as the longest living animals in the world are to be found in the ocean, but it is also crawling with tiny microscopic life and some of those only live for a few days.
   
Many species can be found in Eyjafjörður, including the largest and the longest living animals on earth. More species are probably found there than many realize. This is because northern Icelandic waters are at a boundary between two worlds, the cold Arctic and the warmer temperate ecological zones. This means that species from both zones can be found in the fjord.  This also means that climate changes are frequent and unpredictable.
   
Resident species are perhaps not many because many species from either the colder or warmer waters do not like the unpredictability of the environment, they either want to have constantly cold or constantly warm. However, guests and vagrant species are many and frequent, either from the north when conditions are cold, or the south if they are warm.
   
Life is arranged into a food chain. Algae are the plants of the ocean and are lowest in the marine food chain, they use energy from the sun to produce organic material from inorganic.  Microscopic phytoplankton float in the surface layers and can multiply in numbers incredibly fast if conditions are favourable. Benthic algae are large and more like plants on land, they live attached to the bottom in shallow waters.
    
Marine animals are quite unlike terrestrial animals Many marine animals are for example sessile, that is stuck on the bottom. They are often confused with plants. Sponges often look like moss on hard surfaces. Many cnidarians look like flowers, but are in fact dangerous predators. Echinoderms are large, slow and conspicuous crawlers on the bottom. Nothing like them can be found on land.
 
Some things are similar on land and in the ocean. Crustaceans in the ocean are similar to insects on land, except crustaceans can grow very much larger. Worms are abundant on the ocean floor as well as on land, mostly polychaets in the ocean. Molluscs can be found both on land as well as in the ocean. However that only applies for snails, bivalves (seashells) and cephalopods are exclusively aquatic.
 
The last groups are highest in the marine food chain. Fishes are only found in aquatic environments and are therefore not found on land. The largest animals in the ocean are the mammals, descendants of fishes. They can be found everywhere.
 
HV

Lumpfish (Photo Erlendur Bogason) Lumpfish (Photo Erlendur Bogason)

Kelp forest (photo Erlendur Bogason) Kelp forest (photo Erlendur Bogason)

Sea anemones and a red sea urchin on a inactive hydrothermal vent (photo Erlendur Bogason) Sea anemones and a red sea urchin on a inactive hydrothermal vent (photo Erlendur Bogason)

Sponges and algae (photo Erlendur Bogason) Sponges and algae (photo Erlendur Bogason)