navigate an egg and is a huge contributor to reproductive success. Invertebrates Benthic sessile animals that make up the majority of invertebrates using external fertilization rely on ambient water motion to bring the sperm and eggs together. Other invertebrates that externally fertilize are organisms like the sea urchin, are confined to shallow burrows on exposed shores. Turbulent flows in the surf zone also create a transport of gametes. Hydrodynamic conditions and gamete properties control the efficiency of fertilization because they influence the rate at which the water mixes. The only dilemma with turbulence is the possibility of dilution of sperm and egg because of over mixing. Rapid mixing can cause a lower probability to fertilize. Sessile adult staged animals commonly produce gametes at the same times, also known as a synchronized release of gametes, for external fertilization in the water column. This is helpful because of the lack of mobility these organisms share. They also can rely on turbulent mixing and sperm mobility to enhance the chances of fertilization. The presence of food, resources, favorable environmental conditions, and the lack of predators are thought of when thinking of survival of the next generation. When the female is producing eggs, they perform predator satiation, which is when multiple females will release gametes in a mass reproductive event. The Great Barrier Reef is known for having a “mass spawn.” This occurs the week after the full moon in October. This mass reproductive event is given by reef forming corals, which perform a synchronized release of gametes in one evening from dusk to midnight. Up to 130 species release gametes during this time. In some cases, fertilization can take place on a spawning animal's surface and when the animals are in the turbulent wake. Although fertilization is usually thought of as a short-term process, there is the possibility of gametes being retained on the surface of an animal for an extended period of time. In order to release an egg or sperm over time, clumps are formed that float in the water column. This allows for a variation in locations and time differences of fertilization taking place by the same invertebrate. Vertebrates Amphibians The earliest amphibians were all internal fertilizers. It wasn't until 300 million years ago that the Anura (early internal fertilizer) and Caudata (early external fertilizer) orders had begun. Most anurans now externally fertilize. Anurans are the amphibians lacking a tail