The author only gives two reasons for this loss
a ‘perfect storm’ = above average water temperature and an increase in sea urchin populations
From Monterey Herald
February 2, 2018
By Ross Clark, Earth Matters
The abundance of kelp along the California coast fluctuates, declining annually with winter storms. Since 2015, however, we have seen a “perfect storm” during which kelp abundance has declined by as much as 95 percent along the Northern California coastline. Above average water temperature and an increase in sea urchin populations have greatly reduced bull kelp abundance. The loss of this annual alga has had significant effects on other marine species, many of which rely on these forests for shelter and food.
One species that has been greatly affected by the loss of kelp is the red abalone. This mollusk relies heavily on fragments of drift kelp for food, reaching out from its rocky hiding place to grab passing pieces with its sticky foot muscle. Without drift kelp, the abalone must vacate its hiding place in search of other algae. Dr. Rogers-Bennett with the California Department of Fish and Wildlife, who studies kelp forest condition, notes that the impacts to the abalone became noticeable in 2016 after a year with low kelp abundance. Divers reported abalone mortality of almost 40 percent, finding large numbers of shells within the rocks and on beaches.
A diver team of 56 researchers, visiting 11 locations along the Sonoma and Mendocino coastline in 2017, reported a 65 percent reduction in abalone density compared with populations from a decade before. The abalone that were found showed clear signs of starvation, including loss of muscle mass and exhibiting risky behaviors in their search for algal food. Research divers found that where there once were dense layers of algae now were only bare rock and urchins. Abalone were found climbing out on the few remaining algal stalks reaching for blades of food, abandoning their usual cryptic cautious ways.
Based on the 2017 survey findings, the State determined that the Northern California abalone population was in jeopardy and on Dec. 7 the state closed the fishery for a year. An alarming finding from the dive surveys was a lack of abalone at deeper depths. Usually, about one third of the abalone live in deeper waters out of reach of most divers, but with the decline in kelp, the abalone had moved to shallow unprotected waters in search of food. This relocation and the decline in numbers and vigor have left the remaining abalone population exposed and vulnerable.
The closure has of course been detrimental to north coast businesses. A Fish and Wildlife report estimated that the north coast abalone fishery brings in $50 million in additional economic value to the area annually. With the closure, local businesses faced with reductions in visitors are hoping that the abalone divers switch to fishing other species.
Hopefully a closure of the abalone fishery will help reduce further stress on the population. Researchers point out that the animals that have so far survived are some of the largest of the species, and are needed to rebuild populations when the kelp returns. It takes about 12 years for an abalone to grow to legal size.
When and if kelp returns is uncertain. Urchin barrens often remain for a many years. Winter storms can dislodge exposed urchins and many will starve without sufficient algae in a few years. The ecological transition from kelp forest to urchin barrens and back to kelp forest has been studied in the past but barrens have not been reported at this geographic scale. Regional reductions in urchin numbers and successful recruitment of bull kelp (from distant parents) will be needed before kelp may return to previous abundance, when once again abalone may hide in crevices and wait for their meal to drift by.
Ross Clark is the director of the Central Coast Wetlands Group at Moss Landing Marine Labs. He’s also a member of the county Commission on the Environment and the Monterey Bay Sanctuary Research Activity Panel. Contact him at features(at)santacruzsentinel.com
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