Marine turtles have roamed the seas for millions of years, crossing oceans to feed and to return to their natal grounds to lay their own eggs.  This life of feeding and breeding, however, has recently been disrupted.  Turtle populations have been declining, some species reaching critically endangered status.  The reason for this endangerment of these species is humans.
Humans have only been on Earth for a fraction of the time turtles have, and yet we are having a drastic effect on turtles' lifestyles.  Pollution is one of the key impacts humans have on sea turtles' habitats.  Non-degradable plastics have often been dumped in oceans and turtles have choked or had intestinal blockage, trying to ingest these materials.  Some sea turtles' diets consist of jellyfish, which results in their attempts to eat plastic bags they have mistaken for this edible food resource.  Becoming entangled in debris is also a problem for turtles, as it limits their locomotion (Carr 1987).  In addition, shrimpers are a large problem for turtles.  Sea turtles become caught in the shrimping nets and die or become mutilated, and are simply thrown back into the water (Ellis 2003).  While these interferences affect the waters that turtles migrate in, to and from their grazing sites, it does not stop there.
People also greatly disturb the nesting sites of sea turtles.  Nesting sites are very specific to each turtle, as they return to the same nesting site, often the one at which they were born, season after season.  It is for this reason that it is so important to the future of sea turtles that they remain intact.  However, studies have shown that chemical runoff is present at nesting grounds, which often makes the environment toxic to the young sea turtles.  The majority of the problems with sea turtle nesting sites are a direct result of human development.  Building homes on and near beaches where turtles frequently nest has caused many issues.  Turtles emerge onto land to lay their eggs at night, while it is dark.  However, excessive development has resulted in light pollution that deters the sea turtles from laying their eggs (Safina 2006).  This lighting also disorients hatchlings and makes it much more difficult for them to find their way to the ocean after hatching and emerging from the nest (Frazer 1992).  In addition, dogs, often pets of people living nearby, will kill the newborn hatchlings (Irwin et al. 2004). 
The development, itself, is also a problem because this disrupts the vegetation that holds the sand together.  Sea turtles are very particular about the density of the sand in which they dig a nest for their eggs because of the protection it must provide them with.  Vegetation in the sand dunes holds the sand in place.  The removal and destruction of this vegetation results in the chance of the beach and nest flooding.  Because of beach corrosion, even with environmentalist efforts to replenish the sand on the beaches, many sea turtles emerge onto land only to turn back without nesting or laying any eggs because the beach is not steep enough (Safina 2006).
All of these influences have led to most of the seven species becoming endangered.  Because humans are so different from sea turtles in terms of their habitats and lifestyles it is difficult to understand why we should save such creatures as sea turtles.  However, sea turtles may have more of an effect on humans than we even realize.  Sea turtles are connected to many other marine organisms through their feeding and habitats.  Because sea turtles feed in sea grass communities, they may have an effect on the rest of the ecosystem.  Keeping the sea grass short and healthy maintains the ecosystem, allowing other species to grow and thrive in the environment.  It is quite possible that if the sea turtles become extinct that this will result in a shift of the ecosystem and without the maintenance of the ecosystem, fish species may not be able to survive.  These fish may then cause a depletion in the food sources of other, larger fish, which we, in turn, may rely on for commercial fishing purposes.  This would affect various countries fish industries.  If turtles have an effect on enough other species, they are considered to be a keystone species.  However, it is difficult to know whether a species is a keystone species or not until it has become extinct and the shift in species connections and equilibriums is set in motion.  Losing a keystone species even has the potential to cause an entire ecosystem to collapse.  Therefore, it is in our best interest to prevent this from ever happening and to develop some new long-term conservation plans to help bring turtles' numbers back up.  We have been responsible for the depletion of safe waters and nesting sites for sea turtles, so it is now our responsibility to fix this and improve their conditions so that they can continue to cross oceans to feed and reproduce.