Introduction to Coral Reefs

AGRRA: Introduction to Coral Reefs

Found on “healthy” coral reefs stony corals

stony corals crustose coralline reef algae fishes

sparse turf algae

Permission is granted to use this Powerpoint presentation for educational purposes with the AGRRA Program and, with attribution, for other valid educational purposes.

All other uses are strictly prohibited.

For permission to use their images, special thanks to: L. Benvenuti, A. Bruckner, J. Bruno, K. Desai, P. Dustan, P. Edmunds, M. Gerber, E. Hickerson, H. Hudson, P. Humann, L. Ilyes, B. Kakuk, J.-P. Maréchal, R. McCall, M. Moe, H. Moody, A. Moulding, M. Nugues, J. Reichman, C. Rogers, A. St. Gelais, G. Schmahl, R. Steneck, C. van Dongen, E. Weil, L. Williams What are Coral reefs?

© H. Moody “wave-resistant limestone structures built dominantly by the vertical accumulation of coral skeletons” + capped by live corals & lots of other organisms! Stony corals are the major framework constructors of coral reefs. Their soft polyps overlie stony (calcareous) skeletons.

The polyps expand to feed on plankton, usually at night.

Tentacle Mouth

Skeleton

Colony

Single Polyp Diagram from P. Humann Diverse patterns of asexual division and growth create corals of many different shapes and sizes.

Reef corals need flowing water, food, space on the substratum, warm temperatures–and light. Colonial corals continue to grow via asexual division (reproduction) throughout their lives.

Close-up

larvae

polyp © A. St. Gelais recruit juvenile © A. Moulding © A. St. Gelais

Porites astreoides © R. Steneck

Recruits give reefs a chance of recovering after disasters have killed adult corals. Zooxanthellae (‘zoox’) are tiny, yellow-brown algae in some cells of reef-building corals.

Close-up

Zoox gain shelter, access to carbon dioxide for photosynthesis and inorganic wastes (= nutrients for growth) from their host coral. Clades are genetically distinct populatons of zoox that characterize certain reef habitats, and/or coral species and/or location on a coral.

Zoox contribute organic compounds to their coral host (= support its health, growth, and calcification). © A. Moulding Montastraea cavernosa recruit with zoox Bleached corals are still alive!

Close-up Bleaching occurs when most of the zoox are gone, and/or remain but have lost most of their yellow-brown photosynthetic pigments. Corals are not killed by temporary bleaching.

Bleached Porites Bleaching occurs in response to stressors like unusually high or low temperatures, unusually high or low salinities, or too much sediment.

Partially bleached Orbicella annularis Severity of bleaching varies by: • the coral’s species or colony identity • the cladal identity of its zoox • its location on the reef with respect to depth, currents, shading, etc.

partially bleached not completely bleached bleached

© L. Williams © K. Marks C. natans D. labyrinthiformis M. meandrites When mass bleaching occurs, sea water temperature is above warm season averages.* Polyps die and/or, at least temporarily, are more susceptible to disease and/or their future growth or sexual reproduction is reduced.

Orbicella faveolata * Increases of ~1o C for ~4 weeks, or ~3-4o C for 1-2 days Major Mass Bleaching Events 1998: Bahamas and Mesoamerica 2005: Eastern and NE Caribbean 2010: Southeastern Caribbean 2016: ???

St. John U.S.V.I. 2005

Close-up

WP © A. Bruckner © J. Lang Fireworm on an Orbicella Snail feeding on a faveolata already infected with staghorn coral, White Plague (WP) Acropora cervicornis Damselfish like the threespot (Stegastes planifrons) create small lesions in live corals to cultivate algal gardens for food and to use as a nursery for their young.

© P. Humann © B. Kakuk Threespot damselfish, Orbicella annularis Stegastes planifrons with threespot bites Stoplight (Sparisoma viride) and some other parrotfishes kill coral polyps and excavate their skeletons.

© A. Bruckner © A. Bruckner Lesions from merged stoplight Stoplight parrotfish (S. viride) bites can be > 30 cm/12 in long! biting Orbicella annularis Partial Mortality: when parts of a coral die, the white skeleton below is exposed, superficially resembling bleaching.

Close-up

white skeleton = new mortality

cyano- coral bacteria (thick/dense) turf algae

© M. Moe Having been decimated by disease, Stoplight parrotfish, Diadema are now rare on many reefs. Sparisoma viride When large herbivores are rare, turf algae and macroalgae (seaweeds) may colonize dead corals, becoming so abundant that they prevent coral larvae from settling. These algae can also overgrow live corals.

© J. Bruno Overfishing in the wider Caribbean has already depleted many populations of shark, large- and small-sized bony fish, queen conch and spiny lobster, simplifying natural feeding relationships (as summarized on the next slide) among reef organisms.

- Corallivores - Herbivores +/- + + - Corals + + - Benthic Algae - + Modified from P.R. Kramer; © photos: A. Bruckner, R. Ken, J. Lang, K. Marks, M. Moe, J. Schulke, R. Steneck  AGRRA Program Primary Goals: Rapidly assess key structural and functional attributes of tropical Western Atlantic reefs.

Stony Corals And provide Benthic Algae fishery-

S. siderea O. faveolata S. siderea A. palmata P. porites

M. complanata M. decactis E. fastigiata U. agaricites © K. Marks © R. Steneck © M. Nugues © R. Steneck nodular/ flower platy/bifacial encrusting (phaceloid) Common AGRRA “Algal” Groups Close-up

butterflyfish angelfish grouper