March 8th

Coral Reef Communities have a complex trophic structure

How do coral reef fish end up living where they do?

What explains the high diversity of species on reefs?


  • Coral Reef fish and Invertebrates mainly utilize External Fertilization
  • Millions of gametes are released into the water, fertilization happens
  • These gamete clouds occur high above the reef
  • Zygotes develop into young embryos which will develop into larvae

If male and female only need to reproduce 2 offspring to replace themselves, why produce tens of thousands of eggs annually?

Because not all of the offspring will survive.  There is K selection and R selection. These fish are highly R selective.

-R-selective is producing a lot of offspring and hoping a few will make it

  • Larvae are small, independent and morphologically different from adults
  • Some swim, some drift
  • A typical voyage in the Caribbean lasts between 14-30 days
  • Most don’t make it!


  • Weeks after fertilization, and sometimes hundreds of miles from their origins, the survivors surf towards shore during the night


  • Over the next several hours to days, the larvae metamorphise into juvenile reef fishes-become attached to their sites
  • This process of drifting in, settling to a specific bottom type
  • Grass Beds
  • Mangroves
  • Sand Flats
  • Rubble Fields
  • Patch Reefs

-Some settle and stay where they are

-Some settle in nursery grounds and then migrate

Why live in a nursery ground and then migrate?

There are less predators which makes it safer for the smaller fish.

  • Grass beds allow smaller fish to hide and escape from predators
  • Large predatory can’t get in or move around well in thick grasses or mangroves

What explains the high diversity of species on reefs?

Two Models:

  • Classic Competition
    • High diversity is the result of strong competitive interactions following recruitment that leads to a high degree of specialization
    • Each species has a specific set of adaptations that give it the competitive edge. Each has a narrower ecological niche
  • Recruitment Limitation Model
    • The adult population reflects variation in larval recruitment, not later events like competition
    • So the community structure is limited by who happens to get recruited there
    • Many potentially favorable sites go unoccupied
    • Predation may also play a role


Species Interactions

Interspecific interactions are interactions between species

  • Competition
  • Predation
  • Parasitism
  • Commensalism

-May occur when two or more species in a community rely on similar limiting resources

-May limit the population size

limiting resources: resources in shortest supply. These limit the population size in species

Relationship between cleaners and their clients

  • Its the second most important mutualism besides algae and coral
  • protected from predators
  • cleaners get a free ride
  • clients get cleaned!

-Clients will go to cleaning stations on reef

Who are the clients?

  • any fish or large invert on reef

Who are the cleaners?

  • some species of shrimp and some small fish