49 votes
Accepted

How long can an octopus survive out of the water?

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. ...
  • 51.5k
37 votes
Accepted

What is this strange sea creature we found on the beach?

You have a Dosima: Also known as a Buoy Barnacle. A gallery of observations of these can be found here: https://inaturalist.ca/taxa/462188-Dosima/browse_photos They are found in the coastal UK and ...
  • 1,711
35 votes
Accepted

How and why did mammals go back to the oceans?

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 ...
28 votes

A weird-looking fish with a shield

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 ...
22 votes

What exactly is this small puffer fish doing and how did it manage to accomplish such a feat?

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 ...
  • 1,562
21 votes
Accepted

What strange jelly-like thing is shown in the photo?

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 ...
20 votes
Accepted

Identification of colorful jelly-like marine creature

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"). ...
20 votes
Accepted

Inexperienced divers damage coral, but parrot fish eating coral doesn't do damage?

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 ...
  • 1,007
18 votes
Accepted

What's this stuff that looks like white chainmail armor growing on giant kelp?

That looks like it could be the lacy crust bryozoan (Membranipora membranacea). That bryozoan is an epiphytic animal whose native range includes the Pacific coast; it does not feed on the kelp, but ...
  • 5,502
16 votes

What exactly is this small puffer fish doing and how did it manage to accomplish such a feat?

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 ...
16 votes
Accepted

Why does biomagnification of mercury occur more in large fish?

Bioaccumulation occurs when organisms aren't able to excrete/eliminate/metabolize something as fast as they take it in. The specific circumstance of predators higher on the food chain accumulating ...
  • 37.3k
12 votes

Why are the bodies of the Risso's dolphin covered in scratches?

[ 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 ...
11 votes
Accepted

Help identify these (two) fishes - Netherlands

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 ...
11 votes

What sea animal is this?

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 ...
  • 37.3k
11 votes

Found this under a rock at the beach, removed it carefully and couldn't find any other bones, must be a marine mammal of some sort

A reasonable match for many features, bearing in mind the incompleteness of the skull is that of the South African Fur Seal (AKA. brown fur seal, Australian fur seal).: Carolyn Stewardson, Tania ...
10 votes

How long can an octopus survive out of the water?

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 ...
  • 101
10 votes
Accepted

Deflated bag-like species on beach: Identification

Sea cucumber. There are over 1700 known species, all inhabiting the sea-bed, mostly in deep waters, but can be found on the continental shelf in many areas. An echinoderm (alongside sea-urchins and ...
10 votes
Accepted

Identification of a strange skull

Looks like this is a neurocranium of a tuna or a similar species (dorsal view on this site). I've also found a very similar picture of Atlantic blue tuna from USA, which seems to support that this is ...
9 votes
Accepted

What happened to this seashell?

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 ...
  • 14.1k
9 votes
Accepted

Can jellyfish sting outside of water?

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 ...
  • 51.5k
9 votes
Accepted

The colour of aquatic plants found deep under oceans

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 ...
9 votes

ID a shell from Puerto Rico

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 ...
8 votes

What is the convention for log notation in biology?

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 ...
  • 35.1k
8 votes

How and why did mammals go back to the oceans?

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, ...
  • 181
8 votes

Do fish depend on plants for survival?

Yes, photosynthesis provides nearly all of the ocean's biomass and energy. The best is to study oceanic food chains and webs. It looks like there aren't enough plants in the ocean because they don't ...
8 votes
Accepted

Why do blobfish become bloated when they are brought to the surface?

Blobfish don't have swim bladders, they also don't have a lot of other things we associate with surface animals, like much of a skeleton or many muscles. This is fine under the extreme pressure they ...
  • 13.4k
7 votes
Accepted

Colourful aquatic animal identification

This is the Sarcastic fringehead fish (Neoclinus blanchardi). [Source2]
  • 5,630
7 votes
Accepted

Why are oceans carbon sinks?

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 ...
  • 3,263
7 votes
Accepted

Age of shells on beach

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, ...
  • 86

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