What is a beach without sand? As shorelines continue to recede and beaches lose their sand to wind and wave erosion, local communities tirelessly attempt to restore the natural landscape by using offshore sand.
However, researchers from the University of California, San Diego, revealed that this process - also known as beach replenishment - can have long-term negative effects on coastal ecosystems.
For instance, the study found a more than twofold reduction in the abundance of intertidal invertebrates 15 months after a beach restoration project took place. What's more is populations of polychaetes - a class of ringed worms - appeared to take the hardest hit.
"We found rather long lasting declines in invertebrate abundances due to replenishment," said Joshua Kohn, a UC-San Diego biology professor who led the study. "These invertebrates are what shorebirds eat when they poke their bills in the sand. They are also food for small inshore fish."
Scientists examined the biodiversity and abundance of intertidal invertebrates at eight different beaches in San Diego County. Both a control plot and beach replenishment plot were set up at each beach, so that the differences in biodiversity could be measured and compared four, 12 and 15 months after replenishment.
Researchers warn that the reductions observed "may have far reaching consequences for sandy beach ecosystems."
What's unique about this study is that it paints a clearer picture of how the total invertebrate community across eight different beaches in California is impacted by beach replenishment. Previously, this type of research was carried out only on individual beaches.
"In San Diego there are multiple species of tiny worms called polychaetes," explained Heather Henter, a biologist and academic coordinator of the University of California Natural Reserve System. "Little bean clams, Donax gouldii, are sometimes on our beaches by the thousands and there are various crustaceans such as amphipods, or sandhoppers, and mole crabs, Emerita analoga, that stick their feathery antennae up above the sand to filter food out of the waves in the swash zone."
While most of the animal types suffered initial losses, many - including the sandhoppers and bean clams - rebounded in about a year. The tiny worms, however, failed to recover within 15 months.
With so many variables, researchers noted that additional studies are needed to determine how long exactly these negative effects last.
"There are large gaps in our knowledge," added Tyler Wooldridge, a graduate student at UC-San Diego. "For instance, how long will the effects we observed last? What is the effect of reduced invertebrate abundance on bird and fish populations? Another key question is how frequent and widespread should efforts to replenish beaches be? Are there times of the year when it is more or less disruptive for the animals that live in the sandy beach? To answer those questions, we need more studies."
Their study was recently published in the journal Estuarine, Coastal and Shelf Science.
