Wonders of the Oceans

The oceans.

They cover 70% of the Earth's surface and are home to more life than anywhere else.   They are widely considered the place where life first evolved, and they play a major role in regulating climate and driving weather.  

We look at the origins of life and a few of the fascinating creatures that dwell in the Seven Seas* - the living fossils and the alien intelligences of the deep.

Living Fossils: horseshoe crabs and coelacanths

Some species that evolved hundreds of millions of years ago are still with us today. Often referred to as "living fossils", they give us a glimpse of what our ocean ancestors looked like in the aftermath of the Cambrian Explosion.

One such living fossil is familiar to those of us living near the Atlantic coast.  The horseshoe crab looks like it belongs in the age of ancient marine reptiles, but its look-alike ancestor, which evolved 450 million years ago, actually predates them by 200 million years. They live about 20 years on average, and some females can grow to more than 30 inches long.

Among the interesting aspects of its biology: 

• The head is the largest part of the horseshoe crab's body and contains much of the nervous and biological organs. The head has the brain, heart, mouth, nervous system, and glands—all protected by a large plate. The head also protects the largest set of eyes.

•  Horseshoe crabs have nine eyes scattered throughout the body and several other light receptors near the tail. The two largest eyes are compound and useful for finding mates. The other eyes and light receptors are useful for determining movement and changes in moonlight. 

• Horseshoe crabs have 10 legs and a hard exoskeleton, which allows them to scuttle across the ocean floor.  They are bottom‑feeding predators and scavengers, and their diet includes worms and small mollusks such as clams and mussels.

• They can survive for four days out of the water as long as they keep their gills wet. You can learn more about how to help a stranded, overturned horseshoe crab survive at this link.

Another such living fossil is the coelacanth.  These lobe-finned fish evolved with the rest of their brethren about 400 million years ago.  Until 1938, when a coelacanth (pronounced SEE-la-kanth) was found off Africa's coast, scientists had believed the fish went extinct 65 million years ago with a related lineage of prehistoric fishes.   

One documented specimen of these large, slow‑moving deep‑sea predators with thick muscular bodies and heavy scales measured 1.452 meters (4.76 feet) long and weighed 53.75 kg (118 lbs). Not only are they among the oldest species, but they are also among the longest-lived - with average lifespans ranging from 60 to 100 years.

Among the other interesting aspects of coelacanth's biology:

• Coelacanths are one of the last surviving members of the lobe‑finned fish (Sarcopterygii), with fleshy, limb‑like fins supported by internal bones. This fin structure is similar to the early anatomy that eventually gave rise to four-limbed animals (tetrapods).

• Coelacanths move their paired fins in an alternating, diagonal gait, similar to how tetrapods walk on land. This unusual movement pattern is part of why they’re so important in studying vertebrate evolution.

• Modern coelacanths live in deep waters off Africa and Indonesia, often between 150–700 meters.  Their bodies are adapted for low‑light, high‑pressure environments, including a slow metabolism and specialized sensory systems (e.g., a special detector in its snout that lets it detect electrical signals. This ability helps coelacanths survive in a world where light is almost nonexistent, prey hides in crevices, and slow, energy‑efficient hunting is essential.  They don’t chase things. They sense, drift, and strike — a perfect strategy for a deep‑sea animal with a slow metabolism and a long lifespan.

Alien Intelligences: cephalopods

The earliest cephalopods evolved about 500 million years ago , with modern species such as the octopus, squid and cuttlefish appearing 300 million years ago. In his 2016 book Other Minds, philosopher of science and diver Peter Godfrey-Smith examines the remarkable intelligence of the cephalopods.   Discussing octopus behavior, he points  to their problem-solving skills, curiosity, ability to navigate mazes and play behavior and signs of memory.  In addition they show signs of having "memory" - octopuses don’t just learn — they retain information, sometimes for long periods, and use it to guide future behavior. Their memory systems are as sophisticated as those of many vertebrates.  

One of Godfrey‑Smith’s most striking points is that octopus arms can act semi‑independently, solving small problems on their own. This decentralized intelligence is unlike anything in vertebrates, which why he sees octopuses as a “second experiment” in the evolution of complex minds.  The octopus, he says, is "probably the closest we will come to meeting an alien intelligence." 

The common octopus, one of the best known species typically reaches about 3 feet across when spread out, though other species can be much smaller or larger.  While coelacanths can live to a ripe old age of 60 or even 100 years, the octopus's lifespan is short - ranging from just 1 to 3 years.  

Below left is a post that captures a diver and octopus communicating in the wild. Below right is a video of a laboratory test of the octopus's intelligence.

Another cephalopod, the cuttlefish, is known both for its ability to camouflage to avoid predators and capture prey and for its amazing mating color-change display.  [YouTube video below left] Like the octopus, they are highly intelligent but they possess a different set of skills. One of the cuttlefish's more recently discovered skills is its ability to wait for better food. This self-control is one linked to the higher intelligence of primates . Depending on the species, cuttlefish can be 1.7 to 20 inches long.  Like the octopus, cuttlefish have short lifespans - 1-2 years.  

For a deep dive into their biology, check out this YouTube video: The Insane Biology of the Cuttlefish.  For a shorter look at these colorful creatures, see the video below right.

Notes:

*The term dates back to at least 2300 BC. Over time, different cultures used it to describe the waters they knew best, the number seven carrying symbolic weight across cultures. Although the term today is more poetic than literal, Seven Seas can refer to the seven major oceanic divisions: the Arctic, North Atlantic, South Atlantic, North Pacific, South Pacific, Indian, and Southern Oceans.

**Enceladus, a moon orbiting Saturn, and Europa, a moon orbiting Jupiter, are considered the strongest candidates in our solar system for finding extraterrestrial life (microbial life as on early Earth):

1. Water is the single most important ingredient for life as we know it.  Both moons have liquid water oceans lying beneath an icy crust.  

2. Life needs energy. Both moons have tidal heating and possibly hydrothermal vents.

3. Life needs the right chemistry.  Scientists believe that on Europa, the interaction of  the subsurface ocean with the rocky seafloor could produce the minerals, salts, and organic molecules necessary for microbial life. The space research Cassini mission detected fresh, complex organic compounds — including nitrogen  and oxygen bearing molecules — in the plumes spewing from the moon's surface. These are the chemical building blocks of life.

***Horseshoe crabs are genetically more similar to scorpions and spiders than they are to today's crabs.  The name “horseshoe crab” originates from the rounded shape of the head, because just like the shoe on a horse’s foot, the head is round and U-shaped

Other Sources: https://news.uchicago.edu/explainer/origin-life-earth-explained, https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Horseshoe-Crab, Wikipedia, Coelacanths Can Live Past 100, Don't Show Age? | National Geographic, Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness - Book Summary :