After work the other day, I went for a run along the salt marsh and then onto the beach at Ash Avenue. I slogged through the loose dry sand down to the water line and turned left. As I ran along the firm moist sand, I noticed how clean the entire beach was. Just about anywhere was a great place to put down a towel and enjoy the late afternoon and sunset.
I continued down the beach, and when I passed Linden Avenue, I noticed a sudden increase in the amount of kelp wrack on the beach. Buzzing around these piles were a good number of kelp flies that I tried to avoid. I enjoyed the curlews, godwits and willets looking for a meal, and the sanderlings scampering up and down the beach with each wave.
I looked up the beach and saw vegetation on the dunes. When I looked ahead again, I caught a glimpse of a mole crab scurrying away from me. Not a great place to relax on a towel, but definitely a lot of critters running around.
Once I got to my turnaround point at Jelly Bowl, I pondered the differences I had seen along the beach. As I returned along my same route, I recognized that the shore birds were active along the section of the beach where there was kelp wrack, and then west of Linden Avenue there were few, if any, birds. But the sand was smoother and more welcoming to sunset viewers.
I wondered about this difference and, fortunately, was later able to query a couple knowledgeable people who helped me understand what I saw.
First, I contacted Leanne Roth, park interpretive specialist at Carpinteria State Beach. For several summers, she has had junior rangers compare the State Beach and City Beach. They dug into large areas on each and counted how many mole crabs they found that were larger than an inch. They consistently found 10 times the number of larger mole crabs on the State Beach (which is east of Linden Avenue). This is consistent with academic research studies of the effect of beach grooming, as is done on the City Beach.
After the January 2018 flood and subsequent sediment dumping on the beach at Ash Avenue, the junior rangers found the two beaches were similar. Leanne said she would continue counting mole crabs and see if the difference reappears as the effect of the sediment dumping diminishes.
Then I spoke with Matt Roberts, parks and recreation director for the city of Carpinteria. He explained that the City Beach is groomed in the summer to move kelp wrack to the water’s edge, and to smooth out the sand above the high tide line. This is to improve the experience for the summer beach visitors by providing nice places to put down a towel for the day without needing to move a bunch of sand, and to avoid swarms of kelp flies buzzing around.
It is clear that the “cleanest” part of the beach is also the section that lacks the biodiversity of the State Beach—fewer kelp flies, beach hoppers and mole crabs, and so fewer shorebirds and other indicators of a healthy ecosystem. It’s a beautiful place to sunbathe or watch a sunset, but not a great place to explore the natural environment.
I asked Matt about this, and he pointed to other differences between the City Beach and the State Beach, including the winter berm required on the City Beach. He said that the City Beach needs the berm because of changes in sediment flow caused by the debris basins that protect Carpinteria during storm events, and the sediment dumping on the beach approximates the natural flow that occurred historically.
It is not clear how much of the biodiversity difference comes from summer beach grooming and how much comes from winter berm construction, or what effect sediment dumping has. These are questions that need to be answered in an analysis completed for a permit to dump of sediment on the beach in the future.
It is complex, but with effort we will find a way to protect our beachfront, maintain the valuable biodiversity, and continue to enjoy a fun day at the beach.