Other Techniques

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Other Techniques

Filter Feeding

Gill rakers[1]
Manta Ray Feeding Structures[2]
Illustration of crossflow filtration[3]

Filter feeding is a feeding method observed among some types of fish in Caribbean reefs. Filter feeders filter dissolved and suspended organic matter from the water by forcing water to flow across specialized filtration structures. The most common food source for filter feeding fish is plankton or other small organisms. In fish, the anatomical structures used to filter out plankton are most often gill rakers.[4]

Herring are one example of a fish that use filter feeding, although they use it as one of two methods of feeding (the other is particulate-feeding). [5] When filter feeding, herring swim through the water with an open or snapping mouth, allowing water to flow through the oral cavity and out gill openings, using long, thin gill rakers to sift out the small crustaceans and plankton present in the water column.[6] The sieve effect of the gill rakers causes food particles to concentrate in the oral cavity, after which they are ingested. [7]

Another example of filter feeders is the manta ray. Manta rays practice a variation called “ram filter-feeding,” in which they swim at high speeds through a concentration of plankton with their mouth open. At lower concentrations of prey they may continuously filter out plankton as they swim, while amid higher concentrations of prey they engulf and filter out large concentrations of plankton at a time.[8] A manta ray expands its flattened body while propelling itself forward through the water with its mouth open, allowing water to flow through the oral cavity and out over five pairs of gill slits that line its throat. It unfurls two horn-like cephalic fins on either side of its mouth to form a funnel to channel more water and plankton into its oral cavity. Any plankton larger than a grain of sand is then captured by the feathered gill plates that line its gill slits.[9]

Manta rays use a variation of filter feeding called “cross-flow filtration” in which water flows parallel to its gill plate surfaces, only deviating slightly to dip across the filter surface and siphon out of the gills. This causes denser food particles with more momentum than the surrounding water medium to travel straight to the back of the mouth and form a concentrated food ball for the manta ray to eat. [10] This filtration method can act as a self-cleaning process that pushes food particles collecting on the filters back to the opening of the esophagus without needing mucus to capture or carry them. This means that manta rays have less filter-clogging problems and can swim and feed for longer periods of time without needing to stop and close their mouths to clear and eat the food off their filters.[11]

Manta rays employ many different strategies while filter feeding. One such strategy is called "barrel rolling", involves the ray rolling itself backwards as they feed on dense patches of plankton. Another strategy employed while filter feeding is simply bottom feeding, where the manta ray will scoop up plankton from the seabed. One strategy called "cyclone feeding" is observed only in the Hanifaru Bay in the Maldives, and only occurs about a dozen times each year. In cyclone feeding, the mantas feed in a chain that loops around to form a spiraling column of up to 150 individuals. This spiraling column acts as a cyclone that creates a vortex where filtered water is pulled towards the surface. Plankton on the outside of the cyclone get pulled in to the cyclone and to the open mouths of the manta rays.[9]

Whale Sharks are also filter-feeders that use the ram method, swimming around while continuously ramming water and plankton through their mouths and catching the food with filtering pads covering their throat entrances while letting the water escape through their gills. [12] Whale sharks also use suction feeding, where negative pressure is created in their oral cavity which pulls nearby water and plankton inside when the mouth opens.[8]


Detritivores consume dead organic material and return nutrients to the sediment.[13] Such dead organic material consists of animal and plant remains, biological waste products, and the bacteria and microorganisms associated with biological waste. [14] At least three reef fish families, surgeonfishes, damselfishes, and blennies, have been identified as feeding heavily on detritus in what is referred to as the “epilithic algal matrix”. [14] This matrix consists of a mixed layer of algae, detritus, invertebrates, and sediment covering dead coral surfaces, which makes up 30-80% of total surface area on most coral reefs. [15]

Hard substrate detritivores press their jaw against the substrate and throw their lower jaw upward to brush particulate matter off of rocks, dead coral, and out of turf algae. This feeding technique includes most members of the genus Ctenochaetus.[14] Sediment detritivores eat mouthfuls of sand and associated debris to consume the detritus mixed in with the sediment.[14] Spotted surgeonfish are one such fish that use this technique, and they feed by whisking comb-like teeth over the sandy bottom as they open and close their mouths. [16] Algal detritivores, such as combtooth blennies, scrape algae off of hard surfaces along with associated filamentous algae, diatoms, detritus, and sand. While such feeders do consume some algae, their primary source of nutrition is the detritus particles within the algae.[17]

Mucus feeders eat only the mucus covering the outer layer of coral tissues, and do so without consuming any underlying live coral tissue or skeleton. [18] Corals produce lots of mucus to coat their outer tissue layer that contains energy-rich wax esters, fatty acids, and triglycerides, which provide a valuable source of energy for many fish. [14][18][19] For example, ornate butterflyfish are known to consume large amounts of coral mucus when feeding. [14][20] One study showed that when coral mucus was artificially dispersed, fish assembled and avidly consumed it; researchers concluded that coral mucus is an important food source for reef inhabitants and could be an energy source linking the coral producers and small fish consumers in reef communities. [21]

Scavenging is another means of detritus feeding used by a variety of different fish species. Carrion is not very common on coral reefs, not because reef inhabitants don’t die often but because it is consumed very quickly by reef inhabitants. [22] One study found that all carrion left on a reef was consumed at very rapid rates within 24 hours, indicating that scavenged biomass is tightly recycled within the reef community. [22] One example of a scavenger is the tiger shark. The stomach contents of the tiger shark have been found to contain a variety of unusual items, including license plates and old tires.[23]


  1. Miller, Daniel J., and Robert N. Lea. "Guide to the Coastal Marine Fishes of California." State of California: The Resources Agency Department of Fish and Game Fish Bulletin 157 (1972). Accessed April 19, 2015. http://texts.cdlib.org/view?docId=kt896nb2qd&brand=calisphere&doc.view=entire_text.
  2. Martin, R. Aidan. "Manta Ray (Manta Birostris) FAQ." Biology of Sharks and Rays. Accessed April 19, 2015. http://www.elasmo-research.org/education/topics/lh_manta_faq.htm.
  3. Brainerd, Elizabeth L. "Caught in the Crossflow." Nature 412 (2001): 387-88. Accessed April 19, 2015. http://www.nature.com/nature/journal/v412/n6845/fig_tab/412387a0_F2.html.
  4. Salman, Nadir A., Ghaith J. Al-Mahdawi, and M.A. Hassan. "Gill Rakers Morphometry and Filtering Mechanism in Some Marine Teleosts from Red Sea Coasts of Yemen." Egyptian Journal of Aquatic Research 31 (2005): 286-96.
  5. Gibson, R.N., and A. Ezzi. "Effect of Particle Concentration on Filter- and Particulate-feeding in the Herring Clupea Harengus." Marine Biology 88, no. 2 (1985): 109-16.
  6. Hiatt, Robert W., and Donald W. Strasburg. "Ecological Relationships of the Fish Fauna on Coral Reefs of the Marshall Islands." Ecological Monographs 30, no. 1 (1960): 65-127. Accessed February 20, 2015. http://www.jstor.org/stable/pdf/1942181.pdf?acceptTC=true. .
  7. Sanderson, S. L., Cheer, A. Y., Goodrich, J. S., Graziano, J. D., & Callan, W. T. (2001). Crossflow filtration in suspension-feeding fishes. Nature, 412(6845), 439-41. doi:http://dx.doi.org/10.1038/35086574
  8. 8.0 8.1 Paig-Tran, E. (2012). Filtration at the mega-scale: Exploring the filter morphology and filtration mechanisms in the cartilaginous fishes (Order No. 3552837). Available from ProQuest Dissertations & Theses Full Text; ProQuest Dissertations & Theses Global. (1312511009). Retrieved from http://search.proquest.com/docview/1312511009?accountid=14244
  9. 9.0 9.1 "Feeding Frenzy." Manta Trust. January 1, 2015. Accessed April 15, 2015. http://www.mantatrust.org/about-mantas/feeding-frenzy/.
  10. Brainerd, E. L. (2001). Caught in the crossflow. Nature, 412(6845), 387-8. doi:http://dx.doi.org/10.1038/35086666
  11. Paig-Tran, Misty. "Secrets of Filter-Feeding Sharks and Rays." College of the Environment at the University of Washington. January 1, 2013. http://depts.washington.edu/fhl/enews/winter2013/misty.html.
  12. Rutger, Hayley. "USF study examines whale shark eating habits." University of South Florida. October 29, 2010. Accessed April 14, 2015. http://www.cas.usf.edu/news/s/89.
  13. Zuhlke, Samantha. "Coral Reef Food Web." National Geographic. January 1, 2015. Accessed April 15, 2015. http://education.nationalgeographic.com/education/media/coral-reef-food-web/?ar_a=1.
  14. 14.0 14.1 14.2 14.3 14.4 14.5 Scott, Michael. "Marine Fish Feeding Guilds." FishChannel.com. Accessed April 15, 2015. http://www.fishchannel.com/fish-health/saltwater-conditions/marine-fish-feeding-guilds.aspx
  15. Kramer, M. J., D. R. Bellwood, and O. Bellwood. "Cryptofauna of the Epilithic Algal Matrix on an Inshore Coral Reef, Great Barrier Reef." Coral Reefs 31 (2012): 1007-015. Accessed April 14, 2015. http://link.springer.com/article/10.1007/s00338-012-0924-x#page-1.
  16. Capuli, Estelita Emily. "Ctenochaetus Strigosus." Fish Base. January 1, 2001. Accessed April 15, 2015. http://www.fishbase.org/summary/6015.
  17. Michael, Scott. "Über Algae Eaters: The Lawnmower Blennies (Full Article)." Tropical Fish Hobbyist Magazine. April 1, 2013. Accessed April 15, 2015. http://www.tfhmagazine.com/details/articles/ber-algae-eaters-the-lawnmower-blennies-full-article.htm.
  18. 18.0 18.1 Rotjan, Randi D. "Impact of Coral Predators on Tropical Reefs." Marine Ecology Progress Series 367 (2008): 73-91. Cite error: Invalid <ref> tag; name "Rotjan" defined multiple times with different content
  19. Coffroth, Mary Alice. "Ingestion and Incorporation of Coral Mucus Aggregates by a Gorgonian Soft Coral." Marine Ecology - Progress Series 17 (1984): 193-99. http://www.nsm.buffalo.edu/Bio/burr/Publications/4%20Coffroth1984.pdf
  20. Cole, Andrew J., Morgan S. Pratchett, and Geoffrey P. Jones. "Diversity and Functional Importance of Coral-feeding Fishes on Tropical Coral Reefs." Fish and Fisheries 9 (2008): 1-22.
  21. Benson, A.A., and L. Muscatine. "Wax in Coral Mucus: Energy Transfer from Corals to Reef Fishes." Limnology and Oceanography 19, no. 5 (1974): 810-14. http://aslo.net/lo/toc/vol_19/issue_5/0810.pdf
  22. 22.0 22.1 Rassweiler, Andrew, and Thomas Rassweiler. "Does Rapid Scavenging Hide Non-predation Mortality in Coral-reef Communities?" Marine and Freshwater Research 62 (2011): 510-15.
  23. "Tiger Shark." National Geographic. January 1, 2015. Accessed April 14, 2015. http://animals.nationalgeographic.com/animals/fish/tiger-shark/
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