Sea urchin
Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to . Their tests (hard shells) are round and spiny, typically from across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Sea turtle
Sea turtles are a species that finds relatively low offspring survival rates. If you were to start with 1000 sea turtle eggs, you would end up with only one sexually mature subject. Starting with 1000 eggs, roughly 20% wouldn’t hatch which means from the start only 800 sea turtles will hatch and make it to the sand surface. As the sea turtles begin to move down the beach and towards the waves, only 50% or 400 of them will make it to the ocean. This is due to predation and obstacles preventing the young turtles from reaching the ocean. Continuing, once in the ocean 50% of these sea turtles will survive to past juvenile stages of life. Once they reach adulthood only 20 sea turtles will survive, and this is without human interference. When human interference is factored in, only 2 out of 1000 sea turtles will survive to reproductive maturity.