Marine life

The earliest known life forms evolved as anaerobic prokaryotes (archaea and bacteria) in the Archean oceans around the deep sea hydrothermal vents, before photoautotrophs appeared and allowed the microbial mats to expand into shallow water marine environments.

Complex life eventually arose out of marine eukaryotes during the Neoproterozoic, and which culminated in a large evolutionary radiation event of mostly sessile macrofaunae known as the Avalon Explosion.

"fish kills") during anoxic events, while marine invertebrates are a lot more hypoxia-tolerant and exhibit a wide range of morphological and physiological modifications to survive in poorly oxygenated waters.

[36][37][38] The earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago,[39][40] during the Eoarchean era after a geological crust started to solidify following the earlier molten Hadean Eon.

[60] For example, these DNA sequence comparisons have revealed that humans and chimpanzees share 98% of their genomes and analysing the few areas where they differ helps shed light on when the common ancestor of these species existed.

[68] The history of life was that of the unicellular eukaryotes, prokaryotes and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacaran period.

[71] Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over a span of about 10 million years, in an event called the Cambrian explosion.

[78][79][80] However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both biomass and species being prokaryotes.

[112] They are a common and diverse group of viruses and are the most abundant biological entity in marine environments, because their hosts, bacteria, are typically the numerically dominant cellular life in the sea.

[109] It is thought that viruses played a central role in the early evolution, before the diversification of bacteria, archaea and eukaryotes, at the time of the last universal common ancestor of life on Earth.

[137] Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in transcription and translation.

[142][143] Studies have shown high protist diversity exists in oceans, deep sea-vents and river sediments, suggesting a large number of eukaryotic microbial communities have yet to be discovered.

Some marine nematodes and rotifers are also too small to be recognised with the naked eye, as are many loricifera, including the recently discovered anaerobic species that spend their lives in an anoxic environment.

They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells.

The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum.

The three-section body plan of the acorn worm is no longer present in the vertebrates, except in the anatomy of the frontal neural tube, later developed into a brain divided into three parts.

Studies have shown the gene expression in the embryo share three of the same signaling centers that shape the brains of all vertebrates, but instead of taking part in the formation of their neural system,[303] they are controlling the development of the different body regions.

Tetrapods evolved from ancient lobe-finned fishes about 400 million years ago during the Devonian Period when their earliest ancestors emerged from the sea and adapted to living on land.

While marine birds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations.

Seals and sea-lions are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting.

Some marine primary producers are specialised bacteria and archaea which are chemotrophs, making their own food by gathering around hydrothermal vents and cold seeps and using chemosynthesis.

Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction of oxygen-intolerant organisms, a dramatic change which redirected the evolution of the major animal and plant species.

[400] Mangroves and seagrasses provide important nursery habitats for marine life, acting as hiding and foraging places for larval and juvenile forms of larger fish and invertebrates.

[403] Phytoplankton groups include cyanobacteria (above), diatoms, various other types of algae (red, green, brown, and yellow-green), dinoflagellates, euglenoids, coccolithophorids, cryptomonads, chrysophytes, chlorophytes, prasinophytes, and silicoflagellates.

The luminescence, sometimes called the phosphorescence of the sea, occurs as brief (0.1 sec) blue flashes or sparks when individual scintillons are stimulated, usually by mechanical disturbances from, for example, a boat or a swimmer or surf.

[416] Taken as a whole, the oceans form a single marine system where water – the "universal solvent" [417] – dissolves nutrients and substances containing elements such as oxygen, carbon, nitrogen and phosphorus.

These substances are endlessly cycled and recycled, chemically combined and then broken down again, dissolved and then precipitated or evaporated, imported from and exported back to the land and the atmosphere and the ocean floor.

These provide extensive shallows sunlit down to the seafloor, allowing for photosynthesis and enabling habitats for seagrass meadows, coral reefs, kelp forests and other benthic life.

The history of biodiversity during the Phanerozoic (the last 540 million years), starts with rapid growth during the Cambrian explosion – a period during which nearly every phylum of multicellular organisms first appeared.

In order to perform research and enrich Marine Life knowledge, Scientists use various methods in-order to reach and explore the depths of the ocean.

General characteristics of a large marine ecosystem ( Gulf of Alaska )
Killer whales (orcas) are highly visible marine apex predators that hunt many large species. But most biological activity in the ocean takes place with microscopic marine organisms that cannot be seen individually with the naked eye, such as marine bacteria and phytoplankton . [ 1 ]
Elevation histogram showing the percentage of the Earth's surface above and below sea level
Composition of seawater. Quantities in relation to 1 kg or 1 litre of sea water.
The Earth's water cycle
Jupiter's moon Europa may have an underground ocean which supports life .
Euryarchaeota Nanoarchaeota Thermoproteota Protozoa Algae Plant Slime molds Animal Fungus Gram-positive bacteria Chlamydiota Chloroflexota Actinomycetota Planctomycetota Spirochaetota Fusobacteriota Cyanobacteria Thermophiles Acidobacteriota Pseudomonadota
Evolutionary tree showing the divergence of modern species from their common ancestor in the centre. [ 58 ] The three domains are coloured, with bacteria blue, archaea green and eukaryotes red.
Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes
The range of sizes shown by prokaryotes (bacteria and archaea) and viruses relative to those of other organisms and biomolecules
Marine microbial loop
Sea spray containing marine microorganisms can be swept high into the atmosphere where they become aeroplankton , and can travel the globe before falling back to earth.
Under a magnifier, a splash of seawater teems with life.
These are cyanophages , viruses that infect cyanobacteria (scale bars indicate 100 nm)
In terms of individual counts, tailed phage are the most abundant biological entities in the sea.
Vibrio vulnificus , a virulent bacterium found in estuaries and along coastal areas
Pelagibacter ubique , the most abundant bacteria in the ocean, plays a major role in the global carbon cycle .
Archaea were initially viewed as extremophiles living in harsh environments, such as the yellow archaea pictured here in a hot spring , but they have since been found in a much broader range of habitats . [ 134 ]
Video of a ciliate ingesting a diatom
Lichen on a rock in a marine splash zone . Lichens are mutualistic associations between a fungus and an alga or cyanobacterium.
A sea snail , Littoraria irrorata , covered in lichen. This snail farms intertidal ascomycetous fungi.
Dickinsonia may be the earliest animal. They appear in the fossil record 571 million to 541 million years ago.
Kimberella , an early mollusc important for understanding the Cambrian explosion . Invertebrates are grouped into different phyla ( body plans ).
Taxonomic biodiversity of accepted marine species, according to WoRMS , 18 October 2019. [ 200 ] [ 201 ]
Opabinia , an extinct stem group arthropod appeared in the Middle Cambrian . [ 202 ] : 124–136
Sponges are perhaps the most basal animals. They have no nervous, digestive or circulatory system.
The beroid ctenophore, mouth gaping, preys on other ctenophores.
Crawling motility and food uptake by T. adhaerens
Cnidarians, like this starlet sea anemone , are the simplest animals to organise cells into tissue . Yet they have the same genes that form the vertebrate (including human) head.
Idealised wormlike bilaterian body plan. With a cylindrical body and a direction of movement the animal has head and tail ends. Sense organs and mouth form the basis of the head. Opposed circular and longitudinal muscles enable peristaltic motion .
Ikaria wariootia , an early bilaterian [ 249 ]
Many marine worms are related only distantly, so they form a number of different phyla. The worm shown is an arrow worm , found worldwide as a predatory component of plankton.
Drawing of a giant clam ( NOAA )
First known air-breathing animal to colonise land, the millipede Pneumodesmus newmani , [ 279 ] lived in the Early Devonian . [ 280 ]
Adult echinoderms have fivefold symmetry but as larvae have bilateral symmetry . This is why they are in the Bilateria .
The lancelet, like all cephalochordates, has a head. Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Water from the mouth enters the pharyngeal slits, which filter out food particles. The filtered water then collects in the atrium and exits through the atriopore. [ 305 ]
In chordates, the four above labelled common features appear at some point during development. [ 300 ]
The Tully monster, a strange looking extinct animal with eyes like a hammerhead protruding from its back, may be an early jawless fish.
Guiyu oneiros , the earliest-known bony fish lived during the Late Silurian 419 million years ago.
Lobe fins are bedded into the body by bony stalks. They evolved into the legs of the first tetrapod land vertebrates.
Ray fins have spines (rays) which can be erected to stiffen the fin for better control of swimming performance.
Teleosts have homocercal tails .
Tiktaalik , an extinct lobe-finned fish, developed limb-like fins that could take it onto land.
Waterbird food web in Chesapeake Bay
Sea otter , a classic keystone species which controls sea urchin numbers
Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation . Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively.
Kelp forests are among the most productive ecosystems on the planet.
Evolution of mangroves and seagrasses
Six relatively large variously shaped organisms with dozens of small light-colored dots all against a dark background. Some of the organisms have antennae that are longer than their bodies.
Plankton are drifting or floating organisms that cannot swim against a current, and include organisms from most areas of life: bacteria , archaea , algae , protozoa and animals .
There are over 100,000 species of diatoms which account for 50% of the ocean's primary production.
Red, orange, yellow and green represent areas where algal blooms abound. Blue areas represent nutrient-poor zones where phytoplankton exist in lower concentrations.
Pelagic food web
Thickness of marine sediments
The drainage basins of the principal oceans and seas of the world are marked by continental divides . The grey areas are endorheic basins that do not drain to the ocean.
Global cumulative human impact on the ocean [ 426 ]
Apparent marine fossil diversity during the Phanerozoic [ 428 ]
Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene
Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene