Lecture 19 - Coral Reef Communities $

What are the types of reefs?

Natural

• biogenic

• abiogenic

Artifical

Biogenic Reefs are

Built around a foundational species that provides a physical structure

Foundational species are

• Calcified

• Gregarious

• Permanently attached

• Allow the attachment and growth of other organisms

Coral reefs- the limiting factors

Temperature (~21-29 degrees C)

Salinity (34-36 ppt)

Nutrients

Substrate

Sunlight

What are the different coral reef types

Fringing reefs

• Grow very close to the short and are generally attached to the shore

• Its presence reduces wave energy and providing relatively quiet water conditions in the lee of the reefs

• The reef crest is the shallowest part of the reef and visible from above

Barrier reefs

• Run parallel to the shore but are separated from it by a channel (lagoon) of deep water

• Also protects the coastline from wave energy

Patch reefs

• Small, isolated reefs that grow up from the ocean bottom of the island platform or continental shelf

• They usually occur between fringing reefs and barrier reefs and vary greatly in size

Atolls

• Ring-shaped reefs around where a large (usually volcanic) island used to be

Coral Reefs of the TCI

Fringing example: The Wall (not attached to shore, but no deep-water lagoon)

Barrier example: None in TCI. Famous one in Belize.

Patch reef example: Admiral’s Aquarium

No atolls because there is no volcanic activity. There are only 4 in the Caribbean

Coral Reefs as Habitats

Reef Rugosity: the amount of nooks and crannies created by reef structure

Nooks and crannies = habitat (protection and food)

Describe the trophic groups around coral communities

Herbivores - eat plants and algae

• Examples: Atlantic Blue Tang, Sergeant Major, Conch, Red Parrotfish

• Provide a link between primary production (autotrophic plankton, algae) and secondary consumers

• Have a profound impact on algae distributions and assemblages on the reef

• Most herbivorous fishes have high consumption rates and rapid gut throughput times

Omnivores - eat animals, plants, and algae

• Bearded Fireworm, eats soft and hard coral, anemones and crustaceans, and supplements diet with plant material

• White spotted filefish, Eats sponges, soft coral, algae, and hydroids

Scavengers - eat large dead stuff

• Caribbean hermit crab (terrestrial), eats dead plants, fruit, and feces

• Spiny Lobster, eats molluscs, but also dead animal and plant material

Deposit feeders - eat small pieces of dead stuff and waste on seafloor

• Beaded Sea Cucumber, sifts through sediment

• Donkey Dung Sea Cucumber, sifts through sediment

Predators - eat animals

• Corallivores

  • Foureye Butterflyfish

• Spongivores

  • Queen Angelfish, Hawksbill Turtle

• Invertivores

  • Eagle ray (crushes shells in jaws), Slippery Dick (smashes shells)

• Piscivores

  • Sharks, schoolmaster snapper, great barracuda, blue striped grunt, lionfish

• Planktivores

  • Most reef fish families contain planktivorous species

  • Most use visual recognition and strike at individual prey

  • Many are adapted to specific light conditions

  • Diurnal, nocturnal

describe the coral microbiome

Corals are host to a wide array of microorganisms (in addition to zooxanthellae) that cycle nutrients and perform other important functions, including bacteria, archaea, fungi, and virus

• Are highly efficient at cycling

Name some threats to coral reefs

Bleaching, Pollution, Overfishing, Acidification, Disease, Sea Level Rise, Storms

Describe coral reef phase shifts

A phase shift is a sudden and fundamental change of an ecosystem from one state to another that persists for an extended period of time and that is usually difficult to reverse

Often, the new state supports a less complex ecosystem than the prior state

A phase shift occurs on a coral reef when the cover of a substrate by stony corals is reduced in favor of macroalgal dominance which becomes the new stable state instead of a coral reef

Reef Health - Grazers

Most parrotfish species eat algae off of rocks and coral

• This involves taking bites of the reef, digesting the algae and defecating calcium carbonate sand (ground up coral).

Some species also eat coral polyps (coral can compose up to half the food intake of some)

Overall parrotfish strongly prefer algae growing on dead coral (estimated <1% of parrotfish bites involve live corals

Prior to the 1980s, healthy populations of sea urchins grazed algae that competed with coral for space.

• In 1983, 97% of urchins died due to disease.

This induced a phase shift from coral dominated to algae-dominated communities

The population has recovered somewhat, but only to 12% of pre-1983 levels.

Starting 2022, another disease affecting Diadema has been spreading through the Western Atlantic

How do coral reefs and mangroves connect

Mangrove roots bind fine sediments: clear water for coral reefs

Regulate freshwater outflow: buffers salinity changes and reduces turbidity for coral reefs

Mangroves shield corals from UV radiation and cool the water

How do coral reefs and seagrass interconnect

Seagrass traps coarse sediments: prevents coral reefs from being smothered

Adds oxygen to water column through photosynthesis

Provides food to reef and deep-sea habitats

How do nutrients travel between habitats (Biochemical linkage between habitats)?

Detrital Transport (water movement)

Ontogenetic migration (organisms migrating to different habitats as they age)

Trophic Relay (organisms migrating to different habitats to feed)

A study using hydroacoustic tags tracked blue striped grunts and schoolmaster snapper movements between habitats found that:

Fish preferred high complexity (more rugose) habitats (reefs and bedrock) during the day Hitt et al., 2011

Fish preferred lower-complexity habitats like seagrass and sand at night

Likely that in darkness, predators can’t hunt with vision, so shelter of reef less important

What is ontogenetic migration between habitats?

when different life stages migrate into different habitats

seagrass and mangroves as nursery habitats

Serve as “nurseries” for many juvenile fish that later move to coral reefs

These nursery habitats provide food, shelter and shade to young fishes

Many fisheries depend on seagrass and mangroves as a result

Proximity to Nursery Habitats: A census survey in Curaçao found that:

Abundance of fish 2x or more in reefs close to mangroves

Species richness 2x or more in reefs close to mangroves

Proximity to Nursery Habitats: A census study in Bonaire found that:

French grunt, bluestriped grunt, yellowtail snapper, doctorfish and stoplight parrotfish preferred seagrass as nursery habitat

Schoolmaster snapper, gray snapper, barracuda and foureye butterflyfish preferred mangroves as nurseries