Sunflower star, Photo by David Horwich
By Dr. Jan Freiwald, Director of Reef Check California
As Reef Check California begins its 2017 training and survey season, we are keen to find out how the massive changes in the kelp forest ecosystem witnessed over the last couple of years will continue to affect California's nearshore ecosystem. Since 2013, we have documented the west coast-wide decimation of many sea star species due to sea star wasting disease. Sunflower stars (Pycnopodia helianthoides) and giant spined stars (Pisaster giganteus) declined massively in 2013 and 2014 statewide. Sunflower stars, which can grow up to one meter in diameter and are voracious invertebrate predators on California's rocky reefs, have been all but absent from RCCA sites since 2014 (Figure 1). At sites between Point Arena, Mendocino County in the north and San Luis Obispo in the south, where this species has been abundant in the past, the population experienced a massive decline within one year from the disease's onset.
In northern California, the species had experienced a slow decline in previous years and was completely decimated by 2014. In the first year after the decline, anecdotal evidence of many very small individual sea stars provided hope for a recovery of the population. Unfortunately, we have not seen any recovery in 2016. In fact, we saw only two sunflower stars during our statewide surveys - one in the Big Creek State Marine Reserve along the Big Sur coast, and another at our Caspar North site in Mendocino County.
In northern California, sunflower stars are the main predators of sea urchins and other invertebrates, and their decline has had wide-spread consequences for the kelp forest ecosystem. Concurrently with the onset of the wasting disease, the canopy-forming bull kelp (Nereocystis luetkeana) disappeared. It is likely that the unusually warm oceanographic conditions referred to as the "Warm Blob" played a role by either reducing growth or leading to recruitment failures. Regardless of the initial reason, the consequent changes to the community are likely a result of this concurrence. The loss of canopy kelp and sea stars was followed by a sharp increase in purple urchin abundance (Figure 2).
Figure 1. Density of sunflower stars observed in all Marine Life Protection Act study regions monitored in California during annual RCCA surveys.
|Figure 2.Changes in kelp forest community at RCCA sites in Sonoma County. While purple sea urchins have increased over 100-fold, canopy-forming kelps have all but disappeared at these site.|
|Kelp forest decimated by purple urchins, Sonoma County. Photo by Jan Freiwald|