Selama lebih dari lima tahun, para penyelam dan ilmuwan di sepanjang Pantai Barat AS telah menyaksikan bencana terjadi di depan mata mereka. Pertama, hilangnya bintang laut hampir dalam semalam, terutama bintang laut bunga matahari, yang kemudian menyebabkan ledakan populasi bulu babi yang dimakan bintang laut. Gerombolan bulu babi membabat habis seluruh hutan rumput laut banteng.
“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.”
Badai Stresor yang Sempurna
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.”
Kelp banteng menyelesaikan siklus hidupnya dalam satu tahun, membentuk spora di musim gugur yang berkecambah menjadi fase jantan dan betina yang menghasilkan telur dan sperma. Telur yang telah dibuahi tumbuh menjadi tanaman yang dapat mencapai ketinggian hingga 55 kaki (16,7 meter) pada awal musim panas.
“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.”
Lautan yang menghangat membawa risiko lebih tinggi terhadap wabah infeksi secara umum, kata Drew Harvell, seorang profesor biologi di Cornell University. Penyakit bintang laut ini menyerang sekitar 20 spesies yang berbeda, tetapi bintang laut bunga matahari mati paling cepat dan dalam jumlah yang paling banyak. Data Administrasi Kelautan dan Atmosfer Nasional (NOAA) menunjukkan bahwa dari tahun 2013 hingga 2015, bintang laut ini benar-benar menghilang di lepas pantai California dan Oregon, serta menurun hingga 99 persen di dekat Washington. Dalam hampir 700 pukat di tahun 2016, para peneliti NOAA tidak dapat menemukan satu pun bintang laut bunga matahari. Persatuan Internasional untuk Konservasi Alam (IUCN) menambahkan spesies ini ke dalam Daftar Merah sebagai spesies yang terancam punah pada bulan Desember 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.
Dengan diameter hingga 3,3 kaki (1 meter) dan dengan 15 hingga 24 lengan, bintang laut bunga matahari adalah predator utama. Penurunan jumlah mereka yang cepat dan meluas serta hilangnya rumput laut memiliki konsekuensi tingkat ekosistem yang serius. Ekosistem hutan rumput laut yang sehat lebih produktif daripada hutan hujan Amazon dan menyediakan tempat berkembang biak bagi lebih dari 1.000 spesies.
Memulihkan Rumput Laut Banteng
Para ilmuwan mengatakan bahwa rumput laut banteng sangat tidak mungkin pulih tanpa bantuan, sehingga upaya restorasi sedang berlangsung di sepanjang Pantai Barat. Menangani bulu babi adalah langkah pertama yang penting.
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.
Langkah terakhir adalah mengembalikan bintang laut.
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.”
Pelajaran yang dipetik dari upaya restorasi di Amerika Serikat dapat membantu mengatasi hilangnya rumput laut yang terjadi di Australia, Norwegia, Chili, dan tempat lain di seluruh dunia.
Penyelam dapat membantu dengan menjadi sukarelawan dalam proyek-proyek pemindahan bulu babi atau memantau lokasi restorasi. Individu dapat mendukung upaya untuk mengurangi emisi karbon dan mendapatkan edukasi tentang jejak karbon mereka.
“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.”
Untuk informasi lebih lanjut, kunjungi Reef Check di reefcheck.org/california-program dan Proyek Restorasi Rumput Laut Raksasa di g2kr.com. Untuk menandatangani petisi untuk mengizinkan pemindahan bulu babi, kunjungi g2kr.com/ petisi-penghapusan-penghilangan-landak.
Jelajahi Lebih Lanjut
Pelajari lebih lanjut tentang Proyek Restorasi Rumput Laut Raksasa dan bintang laut bunga matahari yang terancam punah dalam video berikut.
© Penyelam Siaga — Q2 2021