Lecture 8: Coral Reefs

where are coral reefs found?

shallow, warm, tropical waters close to the coast

what kinds of corals build coral reefs?

hard/stony corals

what do stony corals produce? what does this make up?

calcium carbonate, which is the nonliving, hard backbone of a reef

why are corals so colorful?

corals have a symbiotic relationship with zooxanthellae algae, which live in their tissues and produce food that the coral use, while the algae gets a place to live = mutualism

what are some major threats to corals?

• climate change

• ocean acidification

• ocean temp increase - bleaching

• coral tissue loss disease

• tourism

• pollution - sunscreen, fertilizers and sewage in the sea

• overfishing around coral reefs

• invasive species - lionfish

what is the largest threat to corals on tropical coral reefs?

climate change → increase in ocean temps → coral bleaching

rising temperature causes zooxanthellae algae to be expelled from the coral, which starves the coral and kills it

how many global coral bleaching events have there been? when were they?

3: 1998, 2010, 2015

what is black band disease?

a bacterial diseases first described in the 1970s. more common in corals that are stressed by environmental factors like sedimentation, pollution, increased temps. the bacteria produces a black band that progresses across the coral’s surface and eats the living tissue

what is the stony coral tissue loss disease?

very lethal disease first seen in 2014. affects over 30 coral species. present in reefs in over 30 countries. unsure what causes the disease.

what kinds of pollution harm coral reefs?

• sunscreens with oxybenzone have toxic effects on young coral

• light pollution disrupts coral reproduction

• sedimentation from coastal development, forestry practices, and agriculture can smother corals and interfere with feeding, growth, and reproduction

how does CO2 harm coral?

CO2 is heavily produced by human activity. it cannot all stay in the atmosphere, so some of it is dissolved into the ocean, which acidifies the ocean. this can prevent corals from absorbing sufficient calcium carbonate

the lower the ____, the greater the _____

pH, acidity

how does overfishing harm corals?

• dynamite/cyanide fishing: explosives and poisons destroy/kill reefs

• by-catch and mortality of non-target species

• direct exploitation of fish, invertebrates, and algae for aquarium trade

• changes from coral to algal dominance on reefs because herbivorous fish have decreased

• damage is done with leftover fishing gear such as nets, traps, fishing lines

• these impacts are exacerbated when combined with other threats that coral reefs face, such as climate change and ocean acidification

how can tourism harm corals?

physical damage, pollution, excessive human activity, buying corals and shells from store

how does the invasive lionfish species harm coral reefs?

released or moved through hurricanes to the coast of Florida and established a population. highly reproductive, no natural predators, and they eat herbivorous fish, so algae growth goes unchecked