Deep Sea Gigantism | Why the Ocean Breeds Giants

Deep sea gigantism refers to the phenomenon of marine animals in the deep ocean growing to unusually large sizes compared to their shallow-water counterparts. It is a well-documented phenomenon observed in various groups of organisms, including invertebrates and fish.

Deep Sea Gigantism

The exact causes of deep sea gigantism are not fully understood, but several factors have been proposed to contribute to this phenomenon:

1. Reduced predation pressure: In the deep sea, predators are generally scarce compared to the shallow waters. With fewer predators, larger body sizes may provide an advantage in capturing prey or defending against occasional predators.

2. Increased resource availability: The deep ocean is characterized by relatively low food availability. This scarcity of resources may lead to competition among organisms. Growing larger allows these organisms to have a higher feeding efficiency and exploit scarce resources more effectively.

3. Lower metabolic rates: Deep-sea organisms often have slower metabolic rates compared to their shallow-water counterparts. Lower metabolic rates can result in slower growth rates and delayed maturation, allowing organisms to grow larger over extended periods of time.

4. Cold and stable environment: The deep ocean is characterized by cold temperatures and stable environmental conditions. These factors can contribute to slow growth rates and longer lifespans, providing more time for organisms to reach larger sizes.

Kleiber's Rule

• Pressure in the deep sea increases by one atmosphere for every 10 meters descended.
• Despite high pressures in the deep sea, life thrives and appears unaffected.
• Buoyancy of ocean life allows them to grow to immense sizes without collapsing under their own weight.
• Kleiber's Rule suggests that larger animals tend to be more efficient in terms of metabolism.
• Larger animals have smaller surface area to volume ratios, resulting in less energy loss through heat.
• Slower metabolic rates are advantageous in the deep sea due to the scarcity of food.
• In the deep sea, food availability is limited, and organisms rely on organic particles sinking from surface waters.
• To conserve energy and be more efficient, deep-sea animals grow to larger sizes.

Examples of deep sea gigantism include giant isopods, which can reach lengths of over 30 centimeters, colossal squid, which are known to grow up to 14 meters in length, and the giant oarfish, which can reach lengths of up to 11 meters. These are just a few examples, and there are many other species that exhibit deep sea gigantism.

• Amphipods: These crustacean scavengers are found in every part of the ocean and exhibit deep-sea gigantism. The hadal amphipod, found in the Mariana Trench, can consume detritus at a high rate and reach a size of over 34 centimeters, fulfilling a unique niche in the deep sea.
• Colossal squid: The colossal squid is a 700-kilogram, 15-meter-long creature that dwells 2,100 meters below the surface. It is the largest invertebrate on Earth and showcases deep-sea gigantism.
• Humboldt squid: Also known as red devils, the Humboldt squid can reach lengths of 2.5 meters and is the largest of the "flying squids."
• Magnapinna (Bigfin Squid): The Magnapinna, or bigfin squid, is an 8-meter-long cephalopod with slender arms and tentacles. It remains relatively mysterious and was first sighted only 20 years ago.
• Sleeper sharks: Greenland sharks, belonging to the sleeper shark family, can grow up to nearly 7 meters in length. They have evolved to enhance efficiency and store large amounts of food in their reserve mass. These slow-moving sharks scavenge and can gorge themselves on food-falls, conserving energy between meals.

It's important to note that deep sea gigantism is not observed in all deep-sea organisms. Many species in the deep ocean are small or have similar sizes to their shallow-water relatives. The phenomenon is more common in certain taxonomic groups and specific ecological niches.

Overall, deep sea gigantism is a fascinating aspect of marine biology that highlights the unique adaptations of organisms to the extreme and challenging conditions of the deep ocean.