47

Short answer Under ideal conditions, an octopus may survive several minutes on land. Background Octopuses have gills and hence are dependent on water for the exchange of oxygen and carbon dioxide. Gills collapse on land because of the lack of buoyancy (source: UC Santa Barbara). Octopuses have three hearts. Two of these are dedicated to move blood to the ...


37

There are very few things in the world that aren't beneficial to some lifeform. Even if you were to, say, spill a mixture of persistent broad-spectrum poisons on an area that killed off 99.9% of all species there, the remaining 0.1% that did survive would benefit from the lack of competition. The "great garbage patch" is hardly so extreme a phenomenon, but ...


36

I'll focus on whales and dolphins (cetaceans) as you mention them by name and they are representative for other marine mammals such as seals or manatees. The evolution of cetaceans was one of the fascinating evolutionary mysteries. Clearly, they were mammals, but which mammals were their closest relatives? Clues to solve this mystery began to appear in the ...


26

This is a species in the Peristediidae family, commonly called armored searobins or armored gurnards. found in deep waters around the world, with most species in tropical regions. They are related to the searobins in the family Triglidae, and some authorities classify them in that family,2[3] but they are encased in heavy scales with prominent spines. ...


22

A tiny Japanese puffer fish creates a grand sand sculpture on the featureless seabed by using his fins to dig furrows. He uses this to attract the attention of passing females. Why do puffer fish build sandcastles? (BBC) Further observation revealed that this “mysterious circle” was not just there to make the ocean floor look pretty. Attracted ...


20

You've found a sea anemone, a cnidarian of the Order Actiniaria. In this case, the anemone is closed and thus hiding its characteristic tentacles (likely as a form of protection while "out to dry"). I'm by no means an expert, but my guess is that you have a vertically striped species of the genus Diadumene -- likely one of many morphotypes of the species ...


19

I agree with @Gerardo-Furtado's comment that what you most likely have here is a colonial tunicate (or sea squirt) from the genus Botrylloides. According to images and information available via the Taxanomic Toolkit for Marine Life of Port Phillip Bay$^2$, it appears as though you have a specimen of Botrylloides perspicuus (aka B. perspicuum). [Photo ...


19

You are absolutely correct in regards that marine life does cause damage to corals. In particular, parrotfish have been found to play an important role in regulating the biodiversity of coral reefs through their feeding behavior. Certain species of parrotfish feed on certain species of coral, typically faster growing species that branch out into easier ...


17

While fish tend to move from side to side (lateral undulation) for which a vertical tail makes sense, the land ancestors of marine mammals had their limbs under them and so their spines were already adapted to up and down movement (dorsoventral undulation). When these animals moved to marine environments, they continued up and down movement in their swimming,...


16

This "nest" is created by a male pufferfish for both courtship and for rearing young. The male puffer fish uses its body and fins (a combination of pectoral, anal, and caudal -- see here) to break up the sand into fine particles and to move it around into the pattern seen above. It swims in channel-like (or furrow) patterns to create the ray pattern seen: ...


15

In the case of whales, I always thought that it was something to do with the fact that they rely upon buoyancy to support their weight and this seems to support that view: When whales, including small whales or dolphins become stranded on beaches they suffer from the pressure of their own weight on their organs,in the water they are weightless. They ...


12

[ From Jefferson et al. 2015, Marine Mammals of the World, 2nd edition, p 212: "At sea, the best identification characteristic is the coloration and scarring. Adult Risso's dolphins range from dark gray to nearly white, but are typically covered with white scratches, spots, and blotches. Many of these are thought to result from the beacks and suckers of ...


11

The front part of the fish looks like part of the cranium of a fish. I'd bet that the tusks have been "made" by removing some bones in the middle. Well, after having looked at the links given by Remi.b, it seems that it's not even necessary to remove bones. This is probably a Peristediidae. You can find some images on fishbase


11

The link you give doesn't mention limbs sticking out of the body wall, but only vestigial hind limb elements. Many whales do retain pelves and femora, as this page at the Bergen Museum shows. Given the variation in limb development across vertebrates, it would not be surprising to find more distal elements (but I would be very surprised if they extended past ...


11

Cetaceans (i.e., marine mammals) evolved from certain ancient land based mammals, thus the tail is essentially convergent evolution of the tail function.


11

The second fish looks like a rock gunnel (or Butterfish; Pholis gunnellus). This is an eel-like fish found in the intertidal and subtidal zones of the North Atlantic. Interestingly, the rock gunnel is capable of remaining above the waterline at low tide and breathing air. According to Campbell (1984): Fully grown adults can reach 30 cm in length. A ...


11

It's probably a dugong, based on the location, lack of a dorsal fin, split tail, lack of a blowhole, and narrowing of the snout. The prominent vertebral column looks unusual, but that might come from the strange posture it is being held in or from malnutrition. This publication from the Australian government shows necropsy of several dugongs (note, this ...


9

Here there are spectrograms from Bottlenose dolphins (Tursiops truncatus), Killer whales (Orcinus orca) and False killer whales (Pseudorca crassidens). Here there are spectrograms for Humpback whale (Megaptera novaeangliae) and from Sperm whales (Physeter catodon or Physeter marcocephalus) Here there are spectrograms from Blue whale, Fin whale and Minke ...


9

The holes are probably caused by one of a family of parasitic sponges. The holes, as you'd expect, kill the oyster, and the sponge then takes up residence in the shell. A number of species of this family live in the Mediterranean, with Cliona apparently being the most common genus (e.g. Cliona celata and C. viridis). Images of oyster shells after a Cliona ...


9

Short answer Jelly fish can sting out of the water and even when they are considered to be dead. Background I do not have detailed scientific literature available. However, popular sources generally and equivocally warn against touching jelly fish, even on land and even when they appear to be dead. In fact, dead box jelly fish can be as dangerous as live ...


9

You're right that certain wavelengths of light are more capable of penetrating deeper depths of water. However, it turns out, blue light typically travels to deeper depths than all other visible wavelengths of light (and red light does not travel deeply at all). See my previous SE answer for more details about plant coloration due to this phenomenon. So ...


9

This is the shell of a marine mollusk called a chiton. They are also sometimes known as sea cradles or "coat-of-mail shells", or more formally as loricates, polyplacophorans, and occasionally as polyplacophores. In Puerto Rico, they call these animals "Quitones." All chitons bear a protective dorsal shell that is divided into eight articulating ...


8

There is a reason for prevalent usage of log2 and log10 compared to loge in biology and other experimental sciences. Usually while doing measurements we are generally interested in fold changes and we generally talk in the sense of two-fold (or multiples of two) or ten-fold. Doubling is a common phenomenon at least in case of growth and so a two-fold change ...


8

Found an octopus today which had attached itself to a rock covered in algae during high tide and had failed to swim back out with the receding tide. We found it at low tide, this means it must have been exposed for a long period of time, definately not only minutes. December in North Wales means it was wet, cold, no direct sun (but no rain). The octopus was ...


7

Mollusk shells found on typical east coast (US) beaches can range from days old (the animal that made the shell died recently) to thousands of years old. Some shells in our state, North Carolina, have been dated as 40,000 years old. A high number of "seashells" found on east coast beaches are from mollusks that lived in the marsh on the back side of the ...


7

How did they evolve from their original form to their superficially ichthyoid appearance today? This is an example of convergent evolution. Fish appear as they do (streamlined body shape, wide tail, fins, etc.) since these are adaptations to the underwater environment they're living and evolving in. These features are only "ichthyoid" or "fishy" because the ...


7

I think I got the answer.... The primary anatomical adaptations for pressure of a deep-diving mammal such as the sperm whale center on air-containing spaces and the prevention of tissue barotrauma. Air cavities, when present, are lined with venous plexuses, which are thought to fill at depth, obliterate the air space, and prevent "the squeeze." The lungs ...


7

Check out the excellent Wikimedia picture of the carbon cycle: All the numbers are in billions of tons of carbon: white = stored, yellow = natural flux, red = human contribution. Notice that the deep ocean stores much more accessible carbon than any other carbon cycle source, and is only surpassed by the lithosphere* in overall quantity of carbon stored on ...


7

This is the Sarcastic fringehead fish (Neoclinus blanchardi). [Source2]


Only top voted, non community-wiki answers of a minimum length are eligible