A Web of Life
In coastal ecosystems, particularly the estuary, where many species start their lives, a natural disaster can have devastating effects on the food web. Today's post will focus on what a food web is and how the estuary's food web can demonstrate cascades during these times of peril.
A basic food chain consists of a producer (something that creates its own food), a primary consumer (something that eats producers), and a secondary consumer (something that eats other consumers). In the animal world, these food chains can get complicated. Some animals are herbivores and only eat producers. Some animals are carnivores and only eat consumers. And some animals are omnivores and eat both consumers and producers. They may also eat more than one prey species.
In the estuary, the primary producers are marine plants: algae, plankton, and eel grasses. From there, filter feeders such as clams and oysters, will consume these plankton. Tiny grass shrimp will prey on algae. Larger consumers such as killifish will feed on shrimp and they, in turn, will be eaten by blue crabs and other fish species. At the top of the food web will be the top predators: hawks, bluefish, sharks, and humans.
During a storm situation, many animals will seek shelter. Those that can, will swim or fly to areas where they feel more protected. Birds may fly inland or stay closer to the ground instead of high in the canopy. Smaller animals, such as fish or crabs, may seek refuge in lagoons or shallow areas around the marsh hammocks. Even clams, oysters, and other shellfish will bury themselves in to the mud.
Unfortunately, storms can change not only the physical features of the estuary, but can bring with them pollution, which alters the chemistry of the estuary. Oxygen levels may decrease, creating anaerobic conditions that species cannot tolerate. There may be an increase of phosphorus and nitrogen from runoff, creating conditions for algal blooms and cutting off the supply of sunlight to eel grass. Sediment that is eroded away can clog the gills of fish, the siphons of some filter feeders, and also cut off sunlight supply.
When producers cannot create their own food, they die. Once they die, it creates a bottom-up cascade through the food web. Everything else cannot survive without these important species.
When a storm comes ashore, it is not just human lives that are affected by the catastrophe. The very food web that makes the estuary what it is can be destroyed, depending on what the storm brings with it. An excess of fresh water can cause salt-tolerant species to expire. An excess of bacteria from runoff can cause fish kills from lack of oxygen in the water. Sediment can alter the very chemistry of the estuary. We must not only be aware of our own salvation during these storms, but also the salvation of these vital food webs along our coasts.