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40+ Deep Sea Features For Fantasy Worldbuilding29 Min Read

40+ Deep Sea Features For Fantasy Worldbuilding29 min read

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Rifts, ridges, vents, and seeps! Welcome back, Outlander, to the 13th entry in Mythic Ecology, my series on how learning real-world landscape features can enrich our fantasy worldbuilding and storytelling. In this post I return to my minimalist framework for Dungeon Masters, Game Masters, fiction writers, and similar worldbuilders to merge the realms of general myth and geomorphology. Last entry I took a look at caves. As I resume my journey sketching a framework for designing Yridia, my unique D&D 5e fantasy world, let’s learn some Deep Sea terms, with a visual guide!

All the images herein I use for educational and entertainment purposes, I claim no rights to any of them. For corrections or content removal requests, hit my contact page.

Part 0: Mythic Ecology For Fantasy Worldbuilding & Storytelling
-Settlements
-Omens
-Overlooks
-Passageways
-Abyss
-Battlegrounds

Part 1: Deep Sea Zones
-Aphotic Zones
–Middle Pelagic Zone (Twilight Zone)
–Bathyl Zone (Midnight Zone)
–Abyssal Zone (Lower Midnight Zone)
–Hadal Zone (Ultra-Abyssal Zone)

Part 2: Deep Sea Adaptations
-Chemosynthesis
-Divergent Coloration

-Gigantism
-Long Lifespan
-Pronounced Mouth & Teeth
-Rapid Growth

Part 3: Protrusions & Slopes
-Abyssal Fan / Deep Sea Fan / Underwater Delta / Submarine Fan
-Abyssal Hill
-Oceanic Ridge / Mid-Ocean Ridge / Rise
-Seamount
–Aseismic Ridge
–Tablemount / Guyot

Part 4: Expanses
-Abyssal Plain
-Oceanic Basin
-Oceanic Plateau / Submarine Plateau

Part 5: Depressions
-Oceanic Gap / Rift
-Oceanic Trench
-Oceanic Trough
-Submarine Canyon

Part 6: Hydrothermal Vents
-Hydrothermal Vents
–Black Smoker
–White Smoker

Part 7: Cold Seeps
-Cold Seep / Cold Vent
–Brine Pool
–Clathrate Hydrates
–Petroleum Seep
–Pockmarks
–Submarine Mud Volcanoes

Part 8: Special Habitat & Groups
-Bacterial Mats
-Clam Beds
Crab Mounds
-Deepwater Coral / Cold-Water Coral
-Eel Seethings
-Mussels Mounds
-Sea Anemone Clusters
-Shrimp Swarms
-Stalked Barnacle Clusters
-Tubeworm Bushes
-Tubeworm Fields
-Whale Falls & Jelly Falls

Part 9: Deep Sea Phenomena
-Deep Sea Volcanism
–Lava Arches
–Pillow Lava
–Seafloor Lava Flow
-Submarine Earthquake
-Tsunami

PART 0: MYTHIC ECOLOGY FOR FANTASY WORLDBUILDING & STORYTELLING

Let’s revisit my minimalist framework for my worldbuilding. The six archetype tags with which I will flag all the various real-world land features in my Mythic Ecology Series:

1. Settlements: habitable regions of either Work or Play, Familiar or Exotic, offering diverse narrative functions: a Day in the Life, Home Base, Personal Reasons, Gathering Supplies. Can subvert tropes with Ruins or Escape.
2. Omens: sensational, temporal, or particularly pointed features that offer narrative functions of forshadowing, and good or evil portents. Can subvert tropes with a Wild Goose Chase.
3. Overlooks: sites of magnitude and grandeur, living monuments which can function narratively for finding resolve, invoking spirits, or as a Call to Adventure. Can subvert tropes with Dread or Betrayal.
4. Passageways: transitional journeylands, including magical portals, functioning narratively for initiation and return, thresholds and tests, shortcuts and setbacks.
5. Abyss: a void or confined space presenting scarcity or temptation, desperation and danger. Can subvert tropes with a Timely Rescue or Secret Refuge.
6. Battlegrounds: sites fit for epic, sprawling encounters and climax conflicts. Can subvert tropes with Alternative Solutions.

Feel free to submit your own ideas, or draw outside the lines. Alright, let’s see how deep sea features fit in.

PART 1: DEEP SEA ZONES

Otherworldly Incantations Deep Sea Worldbuilding Oceanic Divisions
The zones below collectively comprise the Aphotic Zones, sea layers without sunlight, which for our purposes constitutes the “Deep Sea”.
Otherworldly Incantations Deep Sea Worldbuilding Meso

Middle Pelagic Zone (Twilight Zone) a dynamic ocean zone with large temperature variations, with between 1% of incident light and zero light. Distance below ocean surface: 600-3300 feet (200-1000 meters). Bioluminescence adaptation common at this depth and below. Example species: bioluminescent jellyfish, blobfish, bristlemouths, and giant squid.
[Overlooks, Passageways, Abyss, Battlegrounds]
Otherworldly Incantations Deep Sea Worldbuilding Bathyl

Bathyl Zone (Midnight Zone) a cold, pitch black ocean layer which sunlight cannot reach, devoid of plants. Distance below ocean surface: 3300-13,000 feet (1000-4000 meters). May feature whale falls & jelly falls. Bioluminescent adaptation extremely common. Example species: dumbo octopi and giant squid.
[Overlooks, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Abyssal

Abyssal Zone (Lower Midnight Zone) a very cold, high pressure layer of the ocean in perpetual darkness, the bottom of which has no oxygen and holds high concentrations of nutrient salts, as dead organic matter drifts down and decomposes (called “marine snow” and “sea snot”). Distance below ocean surface: 13,000 feet (4000 meters) to above the ocean floor. Supports very few creatures, often transparent and eyeless. Example species: basket stars, sea pigs, sea spiders, and small squid.
[Overlooks, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Hadal

Hadal Zone (Ultra-Abyssal Zone)the deepest part of the ocean, lying within oceanic trenches, consisting of long and narrow v-shaped depressions, at extreme pressures. Distance below ocean surface: 20,000-21,300 feet (6000-6500 meters). Supports extremophiles and limited other species adapted to the harshest thermal, chemical, and pressure conditions. Example species: carapace-less crustaceans, cusk-eels, sea anemones, and snailfish.
[Overlooks, Passageways, Abyss, Battlegrounds]

PART 2: DEEP SEA ADAPTATIONS

Organisms surviving in the Deep Sea often exhibit many rare traits and adaptations, including the following.

Otherworldly Incantations Deep Sea Worldbuilding Chemosynthesis

Chemosynthesis – some organisms have adapted to subsist of off chemicals, such as hydrogen sulfide, instead of sunlight (e.g. giant white clams).
Potential D&D 5e Monster: Merrow.

Otherworldly Incantations Deep Sea Worldbuilding Bioluminescence

Divergent Coloration
1.
transparency (e.g. jellies & squids),
2. black (e.g. blacksmelt fish),
3. red (e.g. shrimp & squids),
4. reflectivity (e.g. hatchetfish),
5. bioluminescence (e.g. angler fish).
Potential D&D 5e Monster: Tarrasque.

Otherworldly Incantations Deep Sea Worldbuilding Gigantism

Gigantism colossal size (giant squid, giant osopod, king-of-herrings oarfish).
Potential D&D 5e Monster: Kraken.

Otherworldly Incantations Deep Sea Worldbuilding Orange Roughy

Long Lifespan some organisms at these depths have superior metabolism, homeostasis, immune system, or lack of predators (e.g. rattails, orange roughy).
Potential D&D 5e Monster: Aboleth.

Otherworldly Incantations Deep Sea Worldbuilding Mouth

Pronounced Mouth & Teeth – species who can swallow creatures larger than themselves in one bite, or who have giant fangs (e.g. gulpers, fangtooth fish).
Potential D&D 5e Monster: Giant Shark.

Otherworldly Incantations Deep Sea Worldbuilding Growth

Rapid Growth – accelerated bodily development. (e.g. giant tube worms).
Potential D&D 5e Monster: Hydra.

PART 3: PROTRUSIONS & SLOPES

Deep sea protrusion landforms like Seamounts can support dense populations compared to neighboring areas, due to nutrient-rich waters sliding up from the ocean floor. Includes species like cold-water corals, sponges, sea anemones, and sea fans.

Otherworldly Incantations Deep Sea Worldbuilding Abyssal Fan

Abyssal Fan / Deep Sea Fan / Underwater Delta / Submarine Fan – underwater geological structures associated with large-scale sediment deposition, similar to alluvial fans. Formed by turbidity currents, underwater landslides along continental shelves.
[Omens, Overlooks, Passageways, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Abyssal Hill 2

Abyssal Hill – a small hill that rises from the floor of an abyssal plain, with sharp edges. Extremely common.
[Settlements, Overlooks, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Mid Ocean Ridge

Oceanic Ridge / Mid-Ocean Ridge / Rise – an underwater mountain system formed by plate tectonic spreading, as magma swells and dries.
[Settlements, Overlooks, Battlegrounds]

Otherworldly Incantations Coastal Worldbuilding Seamount

Seamount – a mountain rising from the ocean seafloor that does not reach sea level; often an extinct volcano.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Coastal Worldbuilding Aseismic Ridge

Aseismic Ridge a chain of seamounts under the ocean created by a hotspot under the Earth’s crust.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Coastal Worldbuilding Guyot

Tablemount / Guyot a seamount with a flat, eroded summit which has subsided and sunk below sea level.
[Settlements, Omens, Passageways, Abyss]

PART 4: EXPANSES

Otherworldly Incantations Deep Sea Worldbuilding Abyssal Plain

Abyssal Plain – a large, flat, smooth area on the deep ocean floor. Caused by tectonic spreading of seafloor and lower oceanic crust melt.
[Settlements, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Ocean Basin

Oceanic Basin – large geologic basins below sea level.
[Settlements, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Oceanic Plateau

Oceanic Plateau / Submarine Plateau – a relatively flat submarine region rising well above ambient seabed level, with one or more relatively steep sides. Produced by volcanic activity.
[Settlements, Passageways, Abyss, Battlegrounds]

PART 5: DEPRESSIONS

Otherworldly Incantations Deep Sea Worldbuilding Gap

Oceanic Gap / Rift a steep-sided opening through a submarine mountain ridge.
[Settlements, Omens, Overlooks, Passageways, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding Oceanic Trenches

Oceanic Trench – long and narrow depressions of the sea floor; the deepest part of the ocean floor. Appear among convergent plate margins, varying with sediment supply, accretionary prisms, lithosphere age, and uneven slab motion.
[Settlements, Omens, Overlooks, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Trough

Oceanic Trough – a gently sloping depression in the ocean floor shallower, shorter, narrower, and topographically gentler than oceanic trenches.
[Settlements, Omens, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Submarine Canyon

Submarine Canyon – a steep-sided valley cut into the seabed of the continental slope, serving as channels for turbidity currents across the seafloor. Formed by turbidity current erosion and the slumping and mass wasting of continental slope.
[Settlements, Overlooks, Passageways, Abyss, Battlegrounds]

PART 6: HYDROTHERMAL VENTS

Otherworldly Incantations Deep Sea Worldbuilding Hydrothermal Vent

Hydrothermal Vent – a seafloor fissure issuing geothermally-heated water too pressurized to boil, which can form from rock and mineral ore deposits. Associated with volcanic activity, tectonic spread, ocean basins, and hotspots. Highly-adapted extremophile organisms may subsist here, subsisting independent of sunlight via chemosynthesis.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding Black Smokers

Black Smoker – a seabed hydrothermal vent appearing as black, chimney-like structures emitting hot clouds of black sulfides. Formed as superheated water beneath the crust rises through the ocean floor, with dissolved minerals reacting with the colder ocean water above.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding White Smokers

White Smoker a seabed hydrothermal vent emitting lighter-hued minerals such as barium, calcium, and silicon, generally with lower-temperature plumes than black smokers due to greater distance from their heat source.
[Settlements, Omens, Passageways, Abyss]

PART 7: COLD SEEPS

Otherworldly Incantations Deep Sea Worldbuilding Cold Seep

Cold Seep / Cold Vent – an ocean floor area with seepage of hydrocarbon-rich fluids like hydrogen sulfide and methane, appearing like lakes, often in the form of a brine pool. Cooler than the neighboring hydrothermal vents but warmer than the surrounding sea water. Supports endemic species among unique carbonate rock formations and reefs.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding Brine Pools
Brine Pool large craters full of brine on the ocean basin, formed via salt tectonics.
[Settlements, Omens, Passageways, Abyss]
Otherworldly Incantations Deep Sea Worldbuilding Clathrate Hyrdate

Clathrate Hydratescrystalline water-based solids which trap certain gases or polar molecules in hydrogen-bonded ice, potentially leading to seeps of greenhouse gases like methane.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding Petroleum Seep

Petroleum Seep – a consistent outflow of natural liquid or gaseous hydrocarbons, escaping along geological layers, or across them through fractures and fissures in the rock, or directly from an outcrop of oil-bearing rock. Results from reservoir seal breach by various types of fluid expansion or rapid sedimentation, combining with overpressure and buoyancy effects.
[Settlements, Omens, Passageways, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding Pockmarks

Pockmarks – seabed craters caused by fluids erupting and streaming through sediment.
[Settlements, Omens, Overlooks, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Mud Volcano

Submarine Mud Volcanoes – undersea landforms created by the eruption of mud or slurries, water and gases, as hot water blends with subterranean mineral deposits, without magma.
[Settlements, Omens, Passageways, Abyss]

PART 8: SPECIAL HABITATS & GROUPS

Types of organisms specially adapted to aggregating together in the harsh environments of seamounts, hydrothermal vents, and cold seeps, plus exotic localized habitats.

Otherworldly Incantations Deep Sea Worldbuilding Bacterial Mats

Bacterial Mats – mats of bacteria forming around the hydrogen sulfide of hydrothermal vents.
[Settlements, Omens, Passageways]

Otherworldly Incantations Deep Sea Worldbuilding Clam Bed

Clam Beds – beds of giant white clams subsisting off the hydrogen sulfide of hydrothermal vents.
[Settlements, Omens, Passageways]

Otherworldly Incantations Deep Sea Worldbuilding Crab Mounds
Crab Mounds – near hot, mineral-rich hydrothermal vents, swarms of crabs can form living mounds.
[Settlements, Omens, Passageways]

Otherworldly Incantations Deep Sea Worldbuilding Deepwater Coral

Deepwater Coral / Cold-Water Coral mounds of corals which can extend down in the abyssal zone, clustering on hard or raised deep sea landforms into patches, banks, piles, thickets, or groves to form localized habitats, such as near hydrothermal vents.
[Settlements, Omens, Passageways]

Otherworldly Incantations Deep Sea Worldbuilding Eel Seething

Eel Seethings eels adapted to survive in groups in deep sea volcanic craters, some of the only vertebrates known in the area.
[Settlements, Omens]

Otherworldly Incantations Deep Sea Worldbuilding Mussels Mound

Mussels Mounds – masses of deep sea mussels which cooperate to form mounds around hydrothermal vents.
[Settlements, Omens]

Otherworldly Incantations Deep Sea Worldbuilding Sea Anemone Clusters

Sea Anemone Clusters – clusters of aggregating sea anemones.
[Settlements, Omens]

Otherworldly Incantations Deep Sea Worldbuilding Shrimp Swarm

Shrimp Swarms – swarms of shrimp with symbiotic relations to chemosynthetic bacteria which allow them to subsist on hydrogen sulfide near hydrothermal vents.
[Settlements, Omens]

Otherworldly Incantations Deep Sea Worldbuilding Stalked Barnacle Clusters

Stalked Barnacle Clusters – clusters of stalked barnacles near hydrothermal vents.
[Settlements, Omens]

Otherworldly Incantations Deep Sea Worldbuilding Tubeworm Bush

Tubeworm Bushes – masses of tubeworms, creatures who need no oxygen and have no digestive systems, but which may grow up to 10 feet long (~3 meters). Capable of chemosynthesis to subsist upon cold seeps using symbiotic bacteria, they root into sediment to absorb sulfides in ways resembling plant bushes.
[Settlements, Omens]

Otherworldly Incantations Deep Sea Worldbuilding Tubeworm Field

Tubeworm Fields – masses of tubeworms, creatures who need no oxygen and have no digestive systems, but which may grow long. Capable of chemosynthesis to subsist upon cold seeps using symbiotic bacteria, they can root into sediment to absorb sulfides in ways resembling fields of grass.
[Settlements, Omens, Passageways]

Otherworldly Incantations Deep Sea Worldbuilding Whale Fall

Whale Falls & Jelly Falls complex localized ecosystems formed as the carcasses of whales or jellies fall into the Bathyl or Abyssal Zones of the ocean floor. Due to the cold temperatures, high pressure, and lack of oxygen in these zones, this detritus can persist for decades instead of being consumed quickly by scavengers, as in shallower waters.
[Settlements, Omens, Passageways]

PART 9: DEEP SEA PHENOMENA

Otherworldly Incantations Deep Sea Worldbuilding Deep Sea Volcano
Deep Sea Volcanism – submarine volcanoes and magma activity, with either slow or fast eruptions. Associated with hotspots, hydrothermal vents, and tectonic motion, often located near mid-ocean ridges.
[Omens, Passageways, Abyss]
Otherworldly Incantations Deep Sea Worldbuilding Lava Arch

Lava Arches deep sea lava solids which resemble ruins. Periodically shaken by oceanic earthquakes.
[Settlements, Omens, Overlooks, Passageways, Abyss, Battlegrounds]

Otherworldly Incantations Deep Sea Worldbuilding Pillow Lava

Pillow Lava – pillow-shaped structures, primarily of basaltic composition but sometimes others, arising from the extrusion of lava underwater.
[Omens, Abyss]

Otherworldly Incantations Deep Sea Worldbuilding Seafloor Lava Flow
Seafloor Lava Flow – underwater lava fields comprised of new, darker lava and older, lighter, sedimented seafloor, indicating submarine volcanism beneath the seafloor.
[Omens, Passageways, Abyss, Battlegrounds]
Otherworldly Incantations Deep Sea Worldbuilding Oceanic Earthquake
Submarine Earthquake – an earthquake at the bottom of the ocean, often leading to tsunamis. Arises due to plate tectonics.
[Omens, Abyss, Battlegrounds]
Otherworldly Incantations Deep Sea Worldbuilding Tsunami
Tsunami – a series of enormous waves created by an underwater disturbance such as an earthquake, landslide, volcanic eruption, or meteorite. Waves travel outward in all directions from the origin, building in height as they approach the shore. Succeeding waves can increase in size.
[Omens, Abyss, Battlegrounds]

FINAL THOUGHTS

I hope you enjoyed this thirteenth entry in my Mythic Ecology series! I look forward to continuing with it, I have some greater ambitions for developing this series into worldbuilding web tools. Give this a share if you liked it, and let me know in the comments if you have any feedback. I publish new posts on alternating Tuesdays. In the meantime, I post original D&D memes and writing updates over on my site’s Facebook Page. Also, if you want to keep up-to-date on all my posts, check out my Newsletter Sign-Up to receive email notifications when I release new posts. A big thanks as always to my Patrons on Patreon, helping keep this project going: Adam, Alexander, Anthony, Benjamin, Chris, Eric & Jones, Evan, Geoff, Jason, Rudy, and Tom. Thanks for your support!

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Tril

D&D 5e blogger.

This Post Has 4 Comments
    1. That’s a good question, I’d love to get into that in a future post about fantasy tech. Waterbreathing is a ritual spell that would certainly be used and we could errata it to include sea pressure, since it is a 3rd level spell after all. We have many sentient humanoid deep sea creatures in D&D that are active and so I think it would be easy to fit into lore. I can imagine that if you have a setting where airships exist, maybe some gnomes or gith have developed minimally-functioning submarines as well. And there’s always teleportation and yes, powerful artifacts. Artifacts in 5e tend to be less oriented toward damage, so I think it would be a great option. In my homebrew setting I also make extensive use of Ley Lines mythology, which allows for more deep seafaring through essentially vertical sea-lanes too.

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