Por más de cinco años, buzos y científicos a lo largo de la costa oeste de los Estados Unidos han observado un desastre desarrollarse ante sus ojos. Primero fue la desaparición de estrellas de mar, en especial estrellas girasol, casi de la noche a la mañana, lo que luego dio lugar a una explosión de la población de erizos púrpuras de los que las estrellas de mar se alimentan. Las hordas de erizos arrasaron con bosques enteros de kelp gigante.
“When I started diving out of Point Lobos [California] around 2013, it was a healthy, lush kelp forest,” said Tristin McHugh, who volunteered with a monitoring group at the time. “Week one, everything looked beautiful. Week two, we saw sea stars melting into the seafloor. It was one of the most insane things I’ve ever seen.”
Una tormenta perfecta de factores estresantes
The sunflower sea stars fell victim to a wasting disease, which wiped out roughly 90 percent of the global population in 2013. Seven years later, scientists see no signs of recovery. The West Coast experienced intense ocean warming from 2014 to 2017, and by 2015 divers began seeing urchin barrens — vast swaths covered in piles of spiny creatures and little else.
“There are multiple stressors involved, and it’s very hard to tease apart which stressor was playing what role in the kelp forest collapse,” said Laura Rogers-Bennett, a scientist with the California Department of Fish and Wildlife and the Bodega Marine Laboratory at the University of California, Davis. “We lost about 95 percent of the bull kelp forest, and this is not just a natural cycle. We have had poor kelp years in the past, but good years frequently followed. We’ve never seen five years in a row of no bull kelp.”
El kelp gigante completa su ciclo de vida dentro de un solo año, formando esporas en el otoño boreal que germinan en las fases masculina y femenina que producen huevos y esperma. Los huevos fertilizados se convierten en plantas que pueden alcanzar una altura de hasta 17 metros (55 pies) para principios del verano boreal.
“Kelp forests fluctuate in size, shape and location,” said McHugh, now a researcher with The Nature Conservancy (TNC). “But these losses were rapid and severe in scale. It was like a forest being clear-cut and turned into a parking lot.”
El calentamiento de los océanos conlleva un mayor riesgo de brotes infecciosos en general, observó Drew Harvell, profesor de biología de la Universidad Cornell (Cornell University). La enfermedad de las estrellas de mar afectó a aproximadamente 20 especies diferentes, pero las estrellas de mar girasol fueron las que murieron más rápido y en mayores cantidades. Los datos de la Administración Nacional Oceánica y Atmosférica (National Oceanic and Atmospheric Administration, NOAA) muestran que entre 2013 y 2015 estas estrellas de mar desaparecieron por completo de las costas de California y Oregón y su población disminuyó un 99 por ciento cerca de Washington. En 2016, en casi 700 redes de arrastre, la NOAA no pudo encontrar ni una sola estrella de mar girasol. La Unión Internacional para la Conservación de la Naturaleza (International Union for Conservation of Nature, UCN) agregó la especie a su Lista Roja como especie en grave peligro en diciembre de 2020.
“These sea stars were as common as robins,” Harvell said. “On a dive, you would always see sunflower stars. It’s fair to say we have no idea where the disease came from, since we’re not even sure what pathogen is responsible.” She added that it’s likely a new pathogen since more than 20 species were affected so catastrophically.
Con aproximadamente 1 metro (3,3 pies) de diámetro y con 15 a 24 brazos, las estrellas de mar girasol son depredadores clave. Su disminución rápida y generalizada y la subsiguiente pérdida del kelp tienen graves consecuencias en el ecosistema. Los ecosistemas de bosques de kelp saludables son más productivos que el bosque tropical del Amazonas y proporcionan zonas de reproducción para más de 1.000 especies.
Recuperación del kelp gigante
Los científicos afirman que es muy poco probable que el kelp gigante se recupere sin ayuda, por lo que hay esfuerzos de restauración en marcha en toda la costa oeste. El primer paso crucial es resolver el tema de los erizos.
Several projects are using commercial fishers and volunteers to remove or destroy the urchins. At specific locations along California’s coast, any diver with a valid fishing license can remove unlimited amounts of red and purple urchins. Reef Check, the Giant Giant Kelp Restoration Project and other organizations are working to expand areas that allow this process. In Noyo Harbor, where commercial fishers are paid to clear urchins from a 10-acre restoration site, the density has been reduced to one per square meter, but that doesn’t seem to be low enough for kelp recovery, said Dan Abbott, Reef Check’s Central California Regional Manager.
People involved with these projects stress that the idea is not to remove all urchins, even if that were possible. “It would be better to find a way to bring balance back to nature,” Harvell said. “Urchins are not an invasive species. We normally think of them as a healthy part of the ecosystem.”
Another key to restoration is a source of kelp spores. Reef Check’s three restoration sites in Mendocino County, California, have stands of bull kelp nearby. TNC is developing a spore bank that could help restore kelp forests and is evaluating cultivation and wild planting methods.
El paso final es recuperar a las estrellas de mar.
The University of Washington’s Friday Harbor Laboratories, with support from TNC, has produced a small number of sunflower stars in captivity. The researchers cannot release the sea stars until conditions change, Harvell said, but successful breeding is an important step.
Scientists are also gearing up new studies on the cause of wasting disease and resistance to it. “The sunflower star does not have resistance, but other species are doing great,” Harvell said. “We want to know what it is about their immune systems that allows them to prevail.”
The situation calls for an all-hands-on-deck approach, Rogers-Bennett said. “We need creative solutions for dealing with urchins and reseeding efforts. We need work on kelp genetics, the health of the spore bank and whether we even still have one.”
Las lecciones aprendidas de los esfuerzos de restauración en los Estados Unidos podrían ayudar con la pérdida del kelp en Australia, Noruega, Chile y otros lugares del mundo.
Los buzos pueden ayudar ofreciéndose como voluntarios para proyectos en los que se eliminan erizos o se monitorean puntos de restauración. Los individuos pueden apoyar los esfuerzos para reducir las emisiones de carbono e informarse sobre su huella de carbono.
“Divers are uniquely positioned to know what’s going on with kelp,” Rogers-Bennett said. “Many people look out over the water and don’t realize an entire kelp forest is missing under the surface. We can communicate this story to those who don’t dive.”
Para obtener más información, visite Reef Check en reefcheck.org/california-program y Giant Giant Kelp Restoration Project en g2kr.com. Para firmar una petición para permitir la extracción de más erizos, visite g2kr.com/urchin-removal-petition.
Explore más
Learn more about the Giant Giant Kelp Restoration Project and the critically endangered sunflower sea stars in these videos.
© Alert Diver — Q2 2021