Kelp forests play several essential roles that aid in maintaining a thriving marine ecosystem. These roles range from sheltering smaller fish species from the vicious ocean predators that lurk in open waters to providing safe mating grounds and, in turn, desirable nurseries to burgeoning aquatic creatures.
As part of the sheephead diet, kelp forests are vulnerable to overconsumption that could lead to barren marine ecosystems./Courtesy of sarc.bren.ucsb.edu
Due to the protective nature of the kelp forests, many marine species — such as the giant cuttlefish, blue gropers and Port Jackson sharks — are, to a degree, dependent on the well-being of these kelp canopies for their populations to flourish. And with these species thriving and growing in population, the predators that prey upon these species also benefit, indirectly binding the well-being of the predator population to the well-being of kelp forest.
Unfortunately, due to rapid and unmitigated rise in sea urchin populations and therefore a rise in kelp consumption by the urchins (as it is part of their diet), has led to the decimation of many kelp forests, stripping them barren for years and depriving many species of the essential benefits that the kelp canopies provided.
Not only do marine species dependent on these vast kelp sanctuaries suffer and decrease in population, so too do the predators dependent on them for survival. These urchin population blooms therefore ultimately harm the surrounding ecosystem by decreasing ecological diversity. Consequently, targeting and controlling urchin populations are one of the main goals in protecting kelp forest and the local ecosystem they inhabit and benefit.
Fortunately, researchers at the University of California, Santa Barbara, led by research professors in the Department of Ecology, Evolution and Marine Biology Robert Warner and Steve Gaines, have discovered a way to effectively mitigate and control urchin populations and prevent kelp forest decimation.
According to their research published in the journal Proceedings of the Royal Society of London B, urchin populations can be controlled via urchin predation by California sheephead, but only if this species reaches a size threshold of 30 cm, which is about 12 inches in length.
“The predator-prey interaction between California sheephead and sea urchins was strongly size-dependent. Despite their high relative abundance, small sheephead, which are less than 20 cm in length, were not involved in consuming urchins,” Gaines said. “Interestingly, the minimum threshold sheephead size required to consume large urchins is near the minimum size limit in the sheephead fishery — 30 cm for the recreational fishery and 33 cm for the commercial fishery.”
Their research further explains that at these sizes, sheephead jaws are large enough to consume both sizable and small urchins, effectively controlling the sea urchins’ populations over a wide size spectrum.
Their findings also suggest that by preventing fisheries from harvesting California sheephead fish at this size of 30 cm, California sheephead populations will be able to contribute a significantly larger impact on sea urchin population control and, in turn, kelp forest preservation.
Nonetheless, their results also point out the challenges that comes with sheephead implementation, which is their long and often-varied maturation period into the desired 30 cm, with some sheephead populations, such as the ones in Santa Catalina waters, taking two to seven years to reach the 30 cm size threshold.
However, despite these challenges, their findings, with proper implementation, offer an effective and self-renewing method in kelp forest maintenance and provide longevity and health to the surrounding ecosystem.
