Decomposition
Even without the power of the ocean and the tide, seaweed breaks down on the beach. Foot traffic, vehicles, animals and sand wears the seaweed into small pieces that either blend with the sand or continue to break down. Microbes and other decomposers pulverize the leaves and stalks and return the nutrients to the beach ecosystem. Large amounts of seaweed decomposing smells rotten, but in small amounts, you may never know seaweed has broken down in a given location.
Birds
While people tend to use live seaweed from the water in their culinary ventures, birds eat the plant and the bugs on the plants directly from the sand. A variety of birds swarm to beaches to partake in easy meals after storms. If the seaweed sits in the sun for too long, however, the birds will seek another food source. Gulls also nest on large piles of seaweed or move smaller pieces to use them in their nests elsewhere.
Relocation
Too much seaweed smells and deters potential beachgoers, so some beaches routinely comb the sands to displace the seaweed for purely aesthetic reasons. South Padre Island moves excessive washed-up seaweed to the base of the sand dunes to help prevent sand erosion and provide nutrients to the beach plants and grasses.
Fertilizer
The nutritional benefits of seaweed extend beyond sand plants to soil. Some people gather errant seaweed for their compost piles or for use in soil conditioning. While most seaweed and kelp soil conditioners are commercially made, you can find free seaweed on the beach to make your own chemical-free fertilizer. According to Colorado State University, kelp provides soil and plants with the usual fertilizer benefits as well as vitamins, minerals, hormones and amino acids.