Caribbean coral reefs have undergone dramatic declines in recent decades. Many reefs that were once dominated by massive broadcast spawning corals (release gametes into water and fertilization is external) are now composed of small brooding corals (fertilization is internal and larvae are released ready to settle and metamorphose), macroalgae, and soft corals. Since new recruitment of massive and branching corals is rare, efforts must be made to understand the reproductive biology of reef building brooding corals. Reproductive success in marine invertebrates is often density dependent. At high densities, more than one sperm may fertilize eggs, resulting in egg death (polyspermy). At low densities, sperm concentrations may not be high enough for successful fertilization (Allee Effect). Despite extensive research on brooding coral larvae, very little is known about the fertilization ecology involved in producing these offspring. Here, we aim to answer three questions in the brooding coral Porites astreoides: (1) do these hermaphroditic corals self-fertilize, i.e., mating between gametes of the same colony; (2) how many sires fertilize eggs of one colony; and (3) how does size and density influence paternity patterns? Understanding the fertilization success of these common species is important to effectively assessing and conserving Florida's shifting reef communities. How does colony size and density influence paternity in a brooding coral?