Ocean Statistics and Fish

Ocean Statistics

• Ocean covers 70.8% of Earth's surface.

• Total ocean area: $331,441,932 \, km^2$

• Total ocean volume: $1,303,155,354 \, km^3$

• Total ocean mass: $1.41 \times 10^{18}$ tons

• Average ocean depth: $3,682$ m

• Greatest ocean depth: $11,022$ m

• Mean ocean crust thickness: $6.5$ km

• Average ocean temperature: $3.9$ °C

• Average ocean salinity: 34.5 \, g \cdot kg^{-1} = 3.4\% = 34.5 \permil

• Ocean age: $4.5 \times 10^9$ years

Major Oceans

• Arctic Ocean

• Pacific Ocean

• Atlantic Ocean

• Southern Ocean

• Indian Ocean

Ocean Surface Thawing and Refreezing

• Approximately 20 million square kilometers (7.7 million square miles) of ocean surface thaws and refreezes in the Southern Hemisphere each year.

• This area is larger than South America.

• Autumn cooling of the atmosphere is delayed due to heat energy released as water turns to ice.

• Heat is absorbed during ice melt in the spring.

• Seasonal extremes are moderated by the absorption and release of heat energy as ice thaws and refreezes.

• Seasons are reversed in the Southern Hemisphere.

Ocean Depths

• Atlantic Ocean maximum depth: $8,370$ m

• Mediterranean Sea maximum depth: $5,267$ m

• Mediterranean Sea average depth: $1,500$ m

• Mean height of land: $743$ m

• Mean ocean depth: $3,734$ m

• Median ocean depth: $4,093$ m

• Maximum elevation (Mt. Everest): $8,848$ m

• Maximum depth (Mariana Trench): $11,000$ m

• More than half of Earth's solid surface is at least $3,000$ meters below sea level.

• Average depth of the world ocean ($3,796$ meters) is much greater than the average height of the continents ($840$ meters).

Ocean Floor Features

• Features include:

  • Mid-ocean ridge

  • Transform faults

  • Fracture zones

  • Submarine canyons

  • Seamounts

  • Continental rises

  • Trenches

  • Abyssal plains

Continental Positions and Pangaea

• The continents' positions today are different from their positions in the past.

• About 200 million years ago, the continents were joined in a supercontinent called Pangaea.

• There was a single large ocean called Panthalassa.

Matching Mountain Ranges

• About 300 million years ago, a single mountain range extended across connected landmasses.

• Today, this mountain range is scattered across several landmasses and separated by an ocean.

Past Ocean Configurations

• Cambrian

• Devonian

• Triassic

• Cretaceous

• Early Eocene

• Pleistocene

Future World

• Future continental positions at:

  • +50 Ma (Million years)

  • +150 Ma

  • +250 Ma

Sea Floor Age

• Black lines on the sea floor age map indicate tectonic plate boundaries.

Plate Boundaries

• Plate boundaries define major tectonic plates.

• Arrows indicate the direction of plate motion, and numbers represent the rate of motion in centimeters per year.

• Types of boundaries:

  • Convergent

  • Divergent

  • Transform fault

  • Diffuse plate boundary

Cretaceous Period

• $146-66$ Mya description of continental positions.

Paratethys Sea

• Late Eocene / early Oligocene – separation of Paratethys from Tethys Sea – ~34Mya

• Formation of Balkanian-Anatolian-Iranian landmass (Alpine orogeny + see regression)

• Paratethys reconnected with today’s Mediterranean, North and Indian seas repeatedly

• Changing marine / brackish conditions

• Last marine flooding of Paratethys 14-13 Mya

• Late Miocene (11 Mya) - became a megalake, later split to many lakes

• Today’s Black, Caspian, Aral Seas

Early Oligocene

• Rupelian

• 31.1 Ma

• Sea Level +120m

• Maximum Flooding Surface

Early Miocene

• Aquitanian & Burdigalian

• 19.5 Ma

• Sea Level +40m

• Serravallian Supersequence Boundary

Collision of African-Arabian-Euroasian Plate

• Late Eocene Gomphotherium landbridge 19-15 Mya

• Connection between Asia, Europe and Africa

• Disconnection of Tethys

• Genesis of the Mediterranean Sea

• Several short-term reconnections Rögl (1999)

Messinian Salinity Crisis

• Restricted contact between the Mediterranean Sea and Atlantic Ocean, dryer climate

• Salt layers - drying, dropdown by 1.5 km

• System of isolated salt lakes vs. open sea conditions according to Hsü et al. 1977 according to Roveri et al. 2014 Krijgsman et al. 2018

Lago Mare Phase

• Connection of Paratethys and eastern part of the Mediterranean Sea

• Various hypotheses:

  • freshwater

  • system of brackish lakes

  • system of oligohaline lakes

  • connection with the Atlantic Ocean not interrupted completely – marine conditions the end of the Messinian salinity crisis - 5.3 Mya – complete reconnection of the Mediterranean Sea and the Atlantic Ocean

Pleistocene

• Fluctuation of the sea level due to glacial / interglacial cycles

• Glacials – drop of the seal level by 100 - 120 m

• Regression of the sea – Ionian Sea 10 km, Aegean Sea 20 – 30 km

• Connection of the islands with the mainland

• River confluences

Sea Level Changes

• Changes in sea level over the past 250,000 years are traced by data taken from ocean floor cores.

• The rise and fall of sea level is due largely to the coming and going of ice ages.

• Water that formed the ice-age glaciers came from the ocean, causing sea level to drop.

• Low stand of -125 meters at the climax of the last ice age about 18,000 years ago.

• High stand of +6 meters during the last interglacial period about 120,000 years ago.

• Sea level continues to rise as we emerge from the last ice age and enter an accelerating period of global warming.

Greenhouse and Icehouse Periods

• Cambrian: Greenhouse

• Ordovician: Icehouse (Andean-Saharan Glaciation)

• Silurian: Greenhouse

• Devonian: Greenhouse

• Carboniferous: Icehouse (Karoo Glaciation)

• Permian: Greenhouse

• Triassic: Greenhouse

• Jurassic: Greenhouse

• Cretaceous: 'Mild' Icehouse

• Paleogene: Greenhouse

• Neogene: Icehouse

• Quaternary: Icehouse (Recent Glaciation)

Ocean Surface Temperature

• Surface temperature (°C) of the oceans in winter. Data from Levitus and Boyer (1994).

Ocean Surface Salinity

• Surface salinity (psu) in winter. Data from Levitus et al. (1994b).

Temperature and Salinity Averages

• Temperatures are lowest in polar regions and highest near the equator.

• Heavy rainfall in equatorial regions freshens the ocean near the equator.

• Hot and dry conditions near the tropic lines result in higher surface salinity.

Temperature Profiles

• Typical temperature profiles at polar, tropical, and middle (temperate) latitudes.

• Polar waters lack a strong thermocline.

Sea-Surface Temperature and Currents

• Sea-surface temperatures measured by a radiometer.

• Purple color indicates water below 0°C.

• Temperature patterns twist clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

Major Surface Currents

• Chart showing the names and usual direction of the world ocean's major surface currents.

• Powerful western boundary currents flow along the western boundaries of ocean basins in both hemispheres.

Mediterranean Sea

• Schematic of thermohaline cells and the path of Levantine Intermediate Water (LIW).

Water Distribution on Earth

• Total Water:

  • Salt water: 97.5%

  • Fresh water: 2.5%

• Fresh Water Distribution:

  • Glaciers: 68.7%

  • Groundwater: 30.1%

  • Surface water: 0.4%

    • Freshwater lakes: 67.4%

    • Soil moisture: 12.2%

    • Atmosphere: 9.5%

    • Wetlands: 8.5%

    • Rivers: 1.6%

    • Biota: 0.8%

• Water on Earth's surface + atmosphere: 0.01%

• Freshwater in lakes, rivers, and wetlands: 0.0078%

Oceanic Biozones

• Pelagic Environments:

  • Neritic Province (Continental shelf)

  • Oceanic Province

    • Epipelagic (0-200 m)

    • Mesopelagic (200-1,000 m)

    • Bathypelagic (1,000-4,000 m)

    • Abyssopelagic (4,000-6,000 m)

    • Hadal (6,000-11,000 m)

• Benthic Environments:

  • Littoral zone

  • Sublittoral zone

  • Bathyal zone

  • Abyssal zone

  • Hadal zone

Light Penetration in the Ocean

• Photic Zone:

  • Euphotic zone: Enough light for photosynthesis.

  • Disphotic zone: Light present but not adequate for photosynthesis.

• Aphotic Zone: Lies in permanent darkness.

Oxygen and Nutrients with Depth

• Oxygen is abundant in surface water due to mixing with the atmosphere and plant photosynthesis.

• Nutrient content (phosphate) is low in surface water due to uptake by algae.

• At deeper depths, oxygen decreases, producing an oxygen minimum layer (OML), which coincides with a nutrient maximum.

• Below the OML, nutrient levels remain high, and oxygen increases as it is replenished with high-oxygen cold water from polar regions.

Fish Statistics

• Number of fish species: 37,109 (Eschmeyer’s Catalogue of Fishes 2025)

• Between 2002 and 2021, 8,085 new fish species were described, of which 3,133 are marine.

• In 2022:

  • Marine species: 17,852 (49.4%)

  • Freshwater species: 18,253 (50.6%)

• 97.5% salt water (70.8% of Earth surface)

• 2.5% fresh water, of which only 0.0078% in lakes, rivers and wetlands

Ocean Zones and Fish Distribution

• 92% of the ocean’s surface is deep ocean.

• 8% is continental shelves.

• 78% of marine fishes are over the continental shelves (neritic).

• 90% of the ocean’s surface overlies water deeper than 1,000 m.

• 75% of ocean volume is the bathypelagic region, the largest habitat on Earth.

• Epipelagic: ~400 spp. (2.3%)

• Mesopelagic: ~1,200 spp.

• Bathypelagic: ~300 spp.

• Deep benthal: ~2,000 spp. (benthopelagic and benthic) – 11%

• Most benthal fishes live above 1,000 m

• Granadiers and rattails (Macrouridae, Gadiformes) are between 1,000 and 4,000 m

• Tripod fish (Ipnopidae, Aulopiformes) to 6,000 m

• Snailfish (Liparidae, Perciformes) to > 8,000 m

• Cusk eels (Ophidiidae, Ophidiiformes) to > 8,000 m

Deep Sea Fish

• Deepest living fish: Abyssobrotula galatheae Ophidiiformes (cusk-eels) over 8,000 m

• Hadal snailfish (Pseudoliparis amblystomopsis, Liparidae, Perciformes) more than 8,000 m deep in the Pacific Ocean

Smallest and Largest Fish

• Smallest marine fishes: 7-8 mm

  • Trimmatom nanus (Gobiiformes) – western Indian Ocean

  • Schindleria brevipinguis (Gobiiformes) - Australian Great Reef

• Smallest European marine fishes: 20 mm

  • Lebetus (Gobiiformes)

• Largest teleosts:

  • Regalecus glesne (Lampriformes) oarfish – 8 m

  • Mola mola (Tetraodontiformes) ocean sunfish – 2,300 kg

  • Leedscichthys problematicus – extinct, Jurassic filter feeder size estimation 15 m (up to 30 m ?)

• Largest living fish:

  • Rhincodon typus (Orectolobiformes) whale shark – 18 m

  • Cetorhinus maximus (Lamniformes) basking shark – 10 m

Fish Shapes

• Compressed

• Depressed

• Globiform

• Anguilliform

• Fusiform

Caudal Fin Shapes

• Rounded

• Truncate

• Emarginate

• Forked

• Lunate

• Heterocercal

Fish Mouth Positions

• Terminal

• Subterminal

• Inferior

• Superior

Dorsal Fin Types

• First Dorsal Fin

• Second Dorsal Fin

• Soft Dorsal Fin

• Adipose Fin

• Caudal Fin

• Pectoral Fin

• Pelvic Fin

• Anal Fin

• Spinous Dorsal Fin

• Notched Dorsal

• Single Dorsal

• Separate Dorsals

Pelvic Fin Positions

• Abdominal

• Thoracic

• Jugular

• Mental

Fish Jaws

• Protrusible jaws

• Pharyngeal jaws

External Anatomy of Fish

• Snout: The area of the head between the tip of the upper jaw and the anterior margin of the orbit.

• Cheek: The area of the head below and posterior to the eye, anterior to the posterior margin of the preopercle.

• Nape: Dorsal area just posterior to the head.

• Operculum: Plate-like structure covering the branchial chamber.

Gill Structure and Sensory Systems

• Branchiostegals: Slender, bony elements in the gill membrane, slightly ventral and posterior to the operculum.

• Isthmus: Area of the throat ventral to the gill openings.

• Lateral Line: Sensory system consisting of pores and canals along the head and body for the detection of vibrations and water movement, often associated with perforated scales along the body.

Body Measurements

• Caudal Peduncle: Area of the body between the insertions of the dorsal and anal fins and the base of the caudal fin.

• Anus (Vent): Terminal opening of the alimentary canal.

• Head Length (HL)

• Snout Length

• Total Length (TL)

• Fork Length (FL)

• Standard Length (SL)

• Body Depth

Fish Classification

• Phylogenetic classification of bony fishes.

• Agnatha

• Chondrichthyes

• Sarcopterygii

• Actinopterygii

• Osteichthyes

• Gnathostomata

• Vertebrata

Fish Groups and Numbers

• Agnatha – Jawless fishes (137)

• Chondrichthyes – Cartilaginous fishes (1,309)

• Sarcopterygii – Lobe-finned fishes (8)

• Teleostei – teleosts (34,602)

• Holostei – gars and bowfins (8)

• Polypteriformes – bichirs (14)

• Acipenseriformes – sturgeons (27)

• Osteichthyes – Bony fishes

• Fishes – 36,105 species – 2022

• Actinopterygii – Ray-finned fishes (number of fish species in 2022)