Deep Sea Wonders of the Pelagic Zone

[Music] in the deep sea there are two pathways that all marine life must choose from whether to live on the sea floor or to brave the expansive open ocean of the midwater zone in the previous video we explored the benthic and immersal life that dwells on the bottom of the ocean and studied the advantages of adopting such a lifestyle in the deep sea now we'll take a look at the pelagic creatures of the deep organisms that inhabit the water column of the open ocean rarely coming near the shore or the bottom the open ocean is an entirely different world to the benthic zone of the sea floor [Music] the endless blue stretches away in all directions while the black abyss hangs gaping below currents are stronger here there is no shelter to be found and food is hard to come by but all the same a plethora of life has found ways to survive here from the surface all the way down into the abyss utilizing some unexpected adaptations to overcome the challenges of life in the open ocean [Music] we'll begin our investigation at the surface of the high seas of all the zones of the open ocean here is the most abundant whales glide through the waves odds of dolphins ride the powerful currents and all manner of pelagic creatures can be found feeding at the surface the secret to its diversity is sunlight for here is the photic zone also called the epipelagic or sunlight zone light from above is able to penetrate down to a depth of 200 meters and within this uppermost layer phytoplankton is able to undergo photosynthesis to provide food for the life here in the upper water column as a result productivity is remarkably high coastal forage fish such as herrings and sardines form massive bait balls near the surface large apex predators make the most of the opportunity bluefin tuna sailfish and oceanic sharks all adapted to be agile swimmers with streamlined bodies capable of sustaining them on long distance migrations many of these pelagic fish swim in schools in order to move more efficiently and to protect themselves from predators as there are no landforms to provide shelter other species are solitary such as the large ocean sunfish this species drifts passively along and it manages to turn the strong currents here into an advantage it drifts along with them eating jellyfish and laying on its side to allow seabirds to rid it of skin parasites the marine pelagic environment is the largest aquatic habitat on earth and is the habitat for 11 of known fish species imagine a cylinder or water column that reaches from the surface of the ocean to almost the bottom as you travel deeper conditions in the column change pressure begins to increase temperature and light decrease as does the amount of dissolved oxygen we can divide the column into five different layers at the top is the epipelagic zone which we have just examined below it the mesopelagic zone is found in its gloomy deep blue shade already just 200 meters down we find a drastically different environment residual light is dim so photosynthesis cannot occur instead nutrients are supplied from above death and defecation but the marine snow that carries this nutrient-rich organic material only briefly passes through it cannot settle here out in the open so life must find inventive ways to make the most of it pelagic pollocate worms build giant mucous nets around themselves to catch the falling food the odd-looking vampire squid extends a long filamentous tentacle into the water column bringing captured particles back to its mouth marine snow is the backbone of the food web here but not all of it can be taken out of the water column in time the majority of nutrients from productivity of pelagic creatures ends up sinking to the sea floor where it is more concentrated than in the open ocean this could explain why demersal life on the sea floor is more abundant than pelagic life food comes to them pelagic creatures do not benefit much from the productivity of demersal life but demersal life benefits greatly from them via this trickle down of nutrients so food is scarce in the depths of the pelagic zone a challenge that creatures must adapt in order to overcome they do this in a number of ways but most common is the adaptation known as abyssal gigantism the tendency of deep sea creatures to grow larger than their shallow water relatives on the sea floor fish benefit from being flat or long and narrow but here their best chances of survival come from growing to be far larger this is because being bigger means they have a smaller surface area to volume ratio so they lose less energy as heat they become more efficient in the case of many creatures like the greenland shark they also develop highly slowed metabolisms thus the little food they do come across can sustain them for longer but the case of this particular deep sea shark also demonstrates the idea that the pelagic and immersive zones are not independent of one another as food is hard to come by pelagic creatures of the mesopelagic and bathypelagic zones must become opportunistic in their feeding methods this means that they frequent the demersal zone in order to feed descending from the open water above to hunt the sea floor creatures or scavenge sunken corpses this represents one advantage of choosing the pelagic way of life unlike benthic life pelagic life can swim freely in any direction unhindered by topographical constraints so they can make use of the demersal ecosystem almost as a service station of the deep sea stopping by to snack on the concentrated life of these biological hot spots contrastingly benthic life has specific requirements they cannot stray far from the sea floor and must make use of their immediate environment for example if there are no rocky surfaces corals and sponges cannot survive so fish that rely on such creatures cannot live there without having to worry about these constraints pelagic creatures are often more successful living longer due to their ability to better adapt to different environments but an advantage of the demersal lifestyle is the abundance of shelter found on the sea floor in the open ocean there are no reefs and no seamounts to provide protection from predators so deep sea creatures have had to be creative with their adaptations making use of the absence of light most creatures of the pelagic deep are black red or transparent these are the least visible colours in the depths so creatures like this red whale fish are less visible to creatures on the hunt overall pelagic creatures display entirely different adaptations to animals of the benthic zone they tend to be larger differently coloured and more adaptable to different environments due to their tendency to traverse the great expanse of the open ocean but whether this way of life is more or less advantageous than that of seafloor creatures depends on perspective [Music] on the one hand they are more efficient but on the other they must work harder to move and find food so to conclude benthic and pelagic lifestyles represent two vastly different but equally viable methods of survival in the extreme conditions of the deep their differences are a testament to the astounding ability of life to adapt in weird and wonderful ways to these environments and to colonize every part of the expansive deep sea ecosystem check out the brand new deepsea hub over on our website for more facts and footage about the deep sea [Music] you

Channel: Natural World Facts

Views: 333,431

Rating: 4.9560022 out of 5

Keywords: pelagic zone, pelagic fish (informal biological grouping), ocean zones, deep sea zones, midnight zone, pelagic, demersal, benthic, midwater, deep sea wonders, deep sea, deep sea life, deep sea creatures, natural world facts

Id: FqHSZ23x1LE

Length: 11min 47sec (707 seconds)

Published: Tue Feb 23 2021

Reddit Comments

[u/lrichards321]

Here's the continuation of last week's video on benthic life! I hope you enjoy, it was fascinating to research for this 2-parter, there are so many different ways in which these creatures have adapted to survive the extreme conditions. (My personal favourite is Gigantism).

[u/jestenough]

Excellent narrator - voice and pace made it easy to take in unfamiliar information.

[u/qweeeeeeen]

That was very interesting, thanks for sharing!

Also, does anyone know what was that animal at 14:25-14:31?