giant manta ray reaches an impressive seven metres (23 feet) maximum width, compared to the maximum five metres (16.5 feet) of the reef manta ray. Other distinguishing features are their coloration and a calcified lump behind the giant manta ray’s dorsal fin, which is absent in the reef manta ray. Their diet (plankton and small fish) and lifespan (maximum 40 years for the giant and 45 years for the reef manta ray) are similar, but it is how they live that really separates these species from one another.
Giant manta rays can be found in tropical and temperate oceans around the world and may be associated with sea mounts far offshore and with oceanic islands. Reef manta rays tend to favour coral and rocky reefs closer to the coast and in the tropics. Hugging the coastline, they are less widely nomadic than the giant manta rays. Their range is bounded in the west at the Indian Ocean as far south as South Africa’s KwaZulu-Natal coastline, although some occasionally venture even further south. This species prefers these shallower habitats and makes use of cleaning stations on coral reefs where small fishes perform manta-cleaning operations, scouring their skin for food. Manta ray cleaning sites are socially significant and are a key habitat that reef manta rays frequent. By contrast, the giant manta ray is encountered less often because it spends much of its time in the open ocean.
The giant manta ray has been classified as Endangered by the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species, whereas the reef manta ray is classified as Vulnerable.
Currently, only two species – the reef manta ray and the giant manta ray – are formally recognised, but a third manta ray species has been proposed. Found in the Caribbean, this possible third species overlaps geographically with the giant manta and occupies the same ecological niche (position and role in the ecosystem) as the reef manta ray. Scientists believe that it may have evolved from giant manta rays that were crossing the open ocean to the Caribbean and found good food sources on this sea’s inshore reefs. Over time, these rays may have become another manta ray species in a process that mimicked the evolution of reef manta rays.
Manta rays are found in tropical oceans around our planet. The reef manta ray calls the Indo-West Pacific its home, with its range (the full extent of where populations of reef manta rays can be found) extending eastward as far as Hawaii and French Polynesia and westward into the Indian Ocean as far as southern Africa. It prefers coral and rocky inshore reefs and seeks out upwelling regions, where seasonal winds drive the abundance and availability of plankton. The giant manta ray is found in open water and prefers upwelling habitats, but is also found near oceanic islands and offshore sea mounts between the latitudes of 40 degrees north and 40 degrees south.
Manta rays are filter feeders, taking in microscopic plants and animals (called plankton) from the water column and filtering them through their gill plates. They swim with their mouths open to feed and their cephalic fins (the front fins that give the family the name ‘devil rays’) funnel water into their mouth, where the nutritious plankton is sifted through the tiny, rake-like plates. These rays often feed at night, when plankton have moved up into the water column and are more easily available. Manta rays have many different strategies for making the most of each mouthful: some skim just below the sea’s surface, heads tilted to the sky above. Others use the ocean’s currents, chasing their plankton prey along a concentrated channel. One population creates mesmerising chains, groups of mantas swirling in a follow-the-leader cyclone to concentrate the plankton. And yet others swoop and somersault, looping upwards and over as they target the densest plankton patches.
That’s not to say manta rays eat any and all plankton, swimming through the ocean with their mouths agape. In fact, manta rays have something of a refined plankton palate and may favour certain species of plankton over others. They tend to move in search of the best regions for food and aggregate where the plankton concentrations are suitable and high.
It has been demonstrated that reef manta rays play a vital role in keeping coral reefs healthy. Studies have shown that they are real reef ‘homebodies’, often relying on a particular site and returning faithfully to favoured areas. This means that, even though they are filter feeders and are regarded as feeding low down in the marine food web, they play quite an integral role in the coral reef ecosystems in which they spend so much time. Studies in Seychelles have indicated that reef manta rays around D’Arros Island and St Joseph Atoll feed on plankton offshore in deeper waters at night and return during the day to their cleaning sites on the coral reefs. By feeding offshore, they help to promote inshore coral reef growth because they transport novel nutrients via their faeces as they socialise at their cleaning stations. Although they may travel in search of food, they spend most of their time at coral reefs around D’Arros and St Joseph, making them key in the local nutrient cycle.
The social nature of manta rays, particularly reef manta rays, also means that ‘cleaner’ species of fish come to rely on mantas as a food source, since they remove dead skin and parasites from the rays when numbers of them visit coral reef cleaning stations. This makes reef manta rays important players in the coral reef ecosystem, particularly for cleaner fish of the wrasse family. Giant manta rays have a role to play too. In the open ocean ecosystem the serve as ‘taxis’, allowing many species to hitch a ride on them – and thus benefit from an energy-savvy mode of transport – as they roam pelagic (open) waters. Not only can the passengers get a ride with the giant manta rays, but the large animals are a moving source of food, shelter and protection from predators.
Manta rays are threatened primarily by overfishing, the same issue that has been the leading cause of decline in most sharks and ray populations. They evaded being the target species of dedicated fisheries for many centuries because their flesh wasn’t considered as tasty and edible as bony fish species (like salmon or cod), but more recently many countries have initiated manta ray fisheries. Some of these, such as the fishery in Mexico’s Sea of Cortez, have already collapsed.
A key concern, however, is the growing market for manta ray products in international trade, with demand having risen in recent years across South-East Asia. As well as being classified as Vulnerable and Endangered respectively on the IUCN Red List of Threatened Species, reef manta and giant manta rays are listed on the Convention for International Trade in Endangered Species (CITES) Appendix II, which regulates the international trade in their products. These protection levels are necessary because both manta ray species are targeted for their gill plates, which are used in Chinese traditional medicine – despite having no proven efficacy. The fishing of manta rays has increased hugely in response to this newer and growing trade. Manta rays are also caught incidentally in other fisheries.
The reason for manta rays being so susceptible to declines by overfishing is linked to their life history. Like many other sharks and rays, they grow slowly, live long and have low reproduction rates, giving birth to one pup after a full year’s gestation period. This makes their populations quick to crash and very slow to recover.
Manta rays also face threats in the form of microplastic pollution and climate change. They are huge filter feeders in the ocean and studies have cautioned that tiny particles of plastic mixed into the plankton soup they feed on may accumulate in their bodies. As for climate change, the implications of rising sea surface temperatures, changing ocean pH levels and shifts in seasonal upwelling (and plankton concentrations and bloom frequency) for manta rays are still being deciphered. What we do know is that the many impacts of climate change on the oceans will have a range of different, and often interacting, outcomes for manta rays – and their primary food source. Other threats to the rays include boat strikes, entanglement in discarded fishing gear, unsustainable tourism and habitat loss. Studies have shown that certain key habitats, such as nursery sites or feeding grounds, can be impacted or lost as human beings develop and urbanise our coastlines.
Scientists and conservationists around the world have worked hard to achieve two major wins to combat the overfishing of manta rays. Firstly, manta rays have been listed on CITES Appendix II, which means that any country trading manta gill plates needs to prove that doing so is sustainable. Secondly, manta rays have been listed on the Convention on Migratory Species, which aims to protect them across their range. Indonesia, Peru and the Philippines have put laws in place to protect manta rays, but many other countries that still have manta ray fisheries have yet to make this effort.
New science pours in all the time to improve our understanding of these intelligent and important rays. Studies that identify critical habitats for manta rays will inform the Important Shark and Ray Areas process that aims to map essential habitats for sharks and rays and amalgamate all the information needed to protect these places. The effort to reach 30% protection of the oceans in marine protected areas by 2030 also holds a glimmer of hope for manta rays in that fishing for them should be reduced or managed and their key habitats prioritised.
But everyone can help the ongoing efforts to protect manta rays, by adopting a plant-based diet, for example, or choosing sustainable seafood. By reducing our consumption of fish, meat and dairy, we can help combat overfishing, especially where fish are caught to grind into fishmeal for livestock agriculture. Lowering your carbon footprint and advocating for climate solutions from world leaders will help to ensure that coral reefs and the other habitats that manta rays rely on will stay intact.
Manta rays in the Maldives utilise a unique feeding strategy, creating a feeding ‘cyclone’ of up to 150 individuals that follow one another in a spiralling column to draw in plankton. This phenomenon only happens in Hanifaru Bay, Maldives.
A fun collective noun that has been suggested for manta rays is ‘squadron’. This is especially evocative for melanistic giant manta rays, which are described in the book Manta: Secret Life of Devil Rays as looking like stealth bomber aircraft!
Manta rays have the largest brain relative to body size of all fish.
The word ‘manta’ means blanket in Spanish.
Manta rays give birth to one pup (although twins are possible!) after a year-long gestation period.
Female manta rays usually have a two-year break before mating and pupping again, in order to build up sufficient reserves to have a viable pregnancy.
Manta rays form ‘courtship trains’ of up to 30 males trailing behind a female to mate.
Inspector Clouseau, photographed at Lady Elliot Island on Australia’s Great Barrier Reef, is the only known pink-bellied manta ray in the world. Scientists believe a genetic mutation has given it the unique colouration.
Manta rays are the only sharks or rays that exhibit melanism. Black manta rays are dark both above and below, with only the smallest patches of white. This is unlike the typical chevron colour morph, which is dark above and white below.
Manta rays probably live up to about 40 - 45 years old. Ping-pong and Scarface are reef manta rays that have been seen over 25 years in the Maldives.
Germanov ES, Marshall AD, Bejder L, Fossi MC, Loneragan NR. 2018. Microplastics: no small problem for filter-feeding megafauna. Trends in Ecology & Evolution 33(4): 227–232. Germanov ES, Marshall AD, Hendrawan IG, Admiraal R, Rohner CA, Argeswara J, Wulandari R, Himawan MR, Loneragan NR. 2019. Microplastics on the menu: plastics pollute Indonesian manta ray and whale shark feeding grounds. Frontiers in Marine Science 679. Last P, Naylor G, Séret B, White W, De Carvalho M, Stehmann M (eds.). 2016. Rays of the World, CSIRO Publishing. Pate JH, Marshall AD. 2020. Urban manta rays: potential manta ray nursery habitat along a highly developed Florida coastline. Endangered Species Research 43: 51–64. Stevens G, Peschak T. 2016. Manta: Secret Life of Devil Rays. The Manta Trust and Save Our Seas Foundation. Scientists explore the occurrence of black manta rays in the Indo-Pacific. — Marine Megafauna Foundation https://marinemegafauna.org/field-updates/black-manta-rays-indo-pacific How did this rare pink manta, photographed in Australia, get its color? (nationalgeographic.com) https://www.nationalgeographic.com/animals/article/pink-manta-ray-australia-rare