Symbiotic Relationships

Symbiotic Relationships in Coral Reefs

Symbiosis “Living Together”

Types of Symbiosis Mutualism Commensalism Parasitism Both the symbiont and host benefit. Commensalism The symbiont benefits with little effect on the host. Parasitism The symbiont benefits to the detriment of the host.

- A sessile org lives on top of another Aegism An association for protection Inquilism One organism shelters within another organisms Endoecism One org shelters in the burrow or defensive shelter of another Phoresis One org uses another for transportation Epizoism - A sessile org lives on top of another

Obligate Versus Facultative Relationships

Obligate Relationship: Relationship is necessary for organism to survive Ex. coral and zooxanthellae Facultative Relationship: Can survive without symbiont, but not as well Ex. anemone fish and anemone

Mutualism

zooxanthellae and corals

Zooxanthellae give corals: Increase coral growth by enhancing calcification process Provide energy Give oxygen Coral give zooxanthellae: Nitrogen waste A place to live Carbon dioxide waste Protection through their hard skeletons and stinging cells Harmful UV light is filtered by coral pigments

Trapezia crab coming out of its host coral (Pocillopora damicornis) to attack the arm of an invading Crown of Thorns Starfish The new "Image of the Month" highlights the mutualistic relationship between hard corals and their crustacean symbionts. Many species of hard corals grow as tightly clumped "bushes", and not surprisingly, corals with this growth morphology provide ideal shelter sites for crustaceans such as shrimps and crabs, and even small fishes such as gobies. These relationships have evolved to the point that many of the infaunal species are now only found within certain species of coral. Individuals feed, grow and reproduce within a few bushes of coral, hardly ever venturing beyond the confines of the colony. The crab Trapezia cymodoce shown in the "Image of the Month" is one such infaunal symbiont. It is found throughout the Indo-Pacific, but only resides within corals from the family Pocilloporidae, which includes the common species Pocillopora damicornis (shown in the image), Seriatopora hystrix, and Stylophora pistillata. Like most other coral reef organisms, T.cymodoce has an obligate period of larval development in the open ocean before recruiting back to the reef. Post-larval crabs usually settle individually into small bushes of coral, while larger corals usually house a heterosexual breeding pair of adult crabs. Very large coral colonies may house more than one pair. Crabs do occasionally move short distances between coral colonies, but only at night so as to minimise the predation risk. It is fairly clear that the crab benefits from living inside the coral. It feeds on mucous secreted by the coral, and also actively feeds on coral tissue, scratching and probing at the polyps with its sharp walking legs. Obviously, the crab also obtains a great deal of protection from predators by staying within the narrow spaces between the arms of the coral colony. But what are the benefits to the coral? If the crab is in fact eating coral tissue, its actions could be more akin to a parasite than a symbiont! Yet field studies show that corals with crabs grow faster and suffer lower mortality than those without crabs. This gives a clue to the answer - the crabs are active defenders of their home, reducing the damage to the colony from corallivores such as butterflyfish and Crown of Thorns starfish (COTS). As shown in the "Image of the month", when a COTS approaches a Pocilloporid coral, the crabs immediately rush forth and nip the tube feet and spines of the starfish with their chelae. This defence is so effective that, if given a choice, COTS will actively avoid feeding on Pocillopora damicornis in favour of specimens of Acropora which have less aggressive crustacean symbionts. Only when there is little alternative will the starfish resort to feeding on P. damicornis colonies. Indeed, where P. damicornis is abundant, it may form natural barriers to COTS and create predation refuges for other species of corals, thereby helping to maintain coral biodiversity on COTS affected reefs. So, the crab Trapezia cymodoce living in the coral Pocillopora damicornis is another good example of the many symbiotic partnerships found on coral reefs, where both members of the partnership gain some benefit from the relationship. As a final word, just to give you some idea of the complexity and diversity of the reef environment via the microcosm of coral symbionts, we know there are more than 10 different species of crabs in the genus Trapezia, plus another genus of crabs (Tetralia), plus a few species of Alpheid shrimps, plus at least 6 species of goby, all of which live in symbiotic relationships with hard corals! Indeed, a large colony of Pocillopora damicornis usually has a whole micro-community of crabs, shrimps, and gobies inside

anemonefish and sea anemones

goby shrimp and the Hawaiian shrimp goby

cleaner wrasse cleaning stations

banded coral shrimp

scarlet cleaner shrimp

sea cucumber crab and sea cucumbers

pompom crabs and sea anemones

anemone hermit crab and sea anemones

Camouflage Decorator Crab Sponge crab

Hunting strategies Plectropomus pessuliferus Gymnothorax javanicus coral reefs in the Red Sea

Mangrove and sponges                                      

Commensalism

Christmas tree worms and Porites corals

coral shrimps and corals

gall crabs and pocilloporid corals

petroglyph shrimp and Porites lobata

squat anemone shrimp and sea anemones

crabs and sea anemones

sea star shrimp and sea stars

urchin shrimp and sea urchins

shrimpfish & sea urchins

Barnacles on whale

Remora on whale shark (open water)

Parasitism

Epitomium snails and mushroom corals

parasitic flatworms and rice coral

parasitic nudibranchs

coral “zits” on Porites compressa

bacterial diseases on corals

Ewa “fangtooth” blenny

Cookie-cutter shark

Inquiry Define mutualism, commensalism, and parasitism. Provide examples of each. What are the benefits the zooxanthellae and coral receive?