{"id":3073,"date":"2019-10-29T17:01:44","date_gmt":"2019-10-29T17:01:44","guid":{"rendered":"http:\/\/blogs.oregonstate.edu\/gemmlab\/?p=3073"},"modified":"2019-10-29T17:01:51","modified_gmt":"2019-10-29T17:01:51","slug":"can-sea-otters-help-kelp-under-a-changing-climate","status":"publish","type":"post","link":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/2019\/10\/29\/can-sea-otters-help-kelp-under-a-changing-climate\/","title":{"rendered":"Can sea otters help kelp under a changing climate?"},"content":{"rendered":"\n

By Dominique Kone1<\/sup> and Sara Hamilton2<\/sup><\/strong><\/p>\n\n\n\n

1<\/sup>Masters Student in Marine Resource Management<\/strong>, 2<\/sup>Doctoral Student in Integrative Biology<\/strong> <\/p>\n\n\n\n

Five years ago, the North Pacific Ocean\nexperienced a sudden increase in sea surface temperature (SST), known as the\nwarm blob, which altered marine ecosystem function and structure (Leising et\nal. 2015). Much research illustrated how the warm blob impacted pelagic\necosystems, with relatively less focused on the nearshore environment. Yet, a\nnew study<\/a> demonstrated how rising ocean temperatures have partially led to\nbull kelp loss in northern California. Unfortunately, we are once again observing\nsimilar warming trends<\/a>, representing the second largest marine heatwave\nover recent decades, and signaling the potential rise of a second warm blob. Taken\ntogether, all these findings could forecast future warming-related ecosystem\nshifts in Oregon, highlighting the need for scientists and managers to consider\nstrategies to prevent future kelp loss, such as reintroducing sea otters.<\/p>\n\n\n\n

In northern California, researchers observed a dramatic\necosystem shift from productive bull kelp forests to purple sea urchin barrens.\nThe study, led by Dr. Laura Rogers-Bennett from the University of California,\nDavis and California Department of Fish and Wildlife, determined that this\nshift was caused by multiple climatic and biological stressors. Beginning in\n2013, sea star populations were decimated by sea star wasting\ndisease<\/a> (SSWD). Sea stars are a main predator of urchins, causing their\nabsence to release purple urchins from predation pressure. Then, starting in\n2014, ocean temperatures spiked with the warm blob. These two events created\nnutrient-poor conditions, which limited kelp growth and productivity, and allowed\npurple urchin populations to grow unchecked by predators and increase grazing\non bull kelp. The combined effect led to approximately 90% reductions in bull\nkelp, with a reciprocal 60-fold increase in purple urchins (Figure 1).<\/p>\n\n\n\n

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Figure 1. Kelp loss and ecosystem shifts in northern California (Rogers-Bennett & Catton 2019).<\/figcaption><\/figure>\n\n\n\n

These changes have wrought economic challenges as\nwell as ecological collapse in Northern California. Bull kelp is important habitat\nand food source for several species of economic importance including red\nabalone and red sea urchins (Tegner & Levin 1982). Without bull kelp, red\nabalone and red sea urchin populations have starved, resulting in the subsequent\nloss of the recreational red abalone<\/a> ($44 million) and commercial red sea\nurchin fisheries in Northern California. With such large kelp reductions,\npurple urchins are also now in a starved state, evidenced by noticeably smaller\ngonads (Rogers-Bennett & Catton 2019).<\/p>\n\n\n\n

Biogeographically, southern Oregon is very similar\nto northern California, as both are composed of complex rocky substrates and\nshorelines, bull kelp canopies, and benthic macroinvertebrates (i.e. sea\nurchins, abalone, etc.). Because Oregon was also impacted by the 2014-2015 warm\nblob and SSWD, we might expect to see a similar coastwide kelp forest loss\nalong our southern coastline. The story is more complicated than that, however.\nFor instance, ODFW\nhas found purple urchin barrens<\/a> where almost no kelp remains in some\nlocalized places. The GEMM Lab has video footage of purple urchins climbing up\nkelp stalks to graze within one of these barrens near Port Orford, OR (Figure 2,\nleft). In her study, Dr. Rogers-Bennett explains that this aggressive sea\nurchin feeding strategy is potentially a sign of food limitation, where\nhigh-density urchin populations create intense resource competition. Conversely,\nat sites like Lighthouse Reef (~45 km from Port Orford) outside Charleston, OR,\nOSU and University of Oregon divers are currently seeing flourishing bull kelp\nforests. Urchins at this reef have fat, rich gonads, which is an indicator of\nhigh-quality nutrition (Figure 2, right). <\/p>\n\n\n\n

Satellites can detect kelp on the surface of the\nwater, giving scientists a way to track kelp extent over time. Preliminary\nresults from Sara Hamilton\u2019s Ph.D. thesis research finds that while some kelp\nforests have shrunk in past years, others are currently bigger than ever in the\nlast 35 years. It is not clear what is driving this spatial variability in\nurchin and kelp populations, nor why southern Oregon has not yet faced the same\nkind of coastwide kelp forest collapse as northern California. Regardless, it\nis likely that kelp loss in both northern California and southern Oregon may be\ntriggered and\/or exacerbated by rising temperatures.<\/p>\n\n\n\n

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Figure 2. Left: Purple urchin aggressive grazing near Port Orford, OR (GEMM Lab 2019). Right: Flourishing bull kelp near Charleston, OR (Sara Hamilton 2019).<\/figcaption><\/figure>\n\n\n\n

The reintroduction of sea otters has been proposed\nas a solution to combat rising urchin populations and bull kelp loss in Oregon.\nFrom an ecological perspective, there is some validity to this idea. Sea otters\nare a voracious urchin predator that routinely reduce urchin populations and\nalleviate herbivory on kelp (Estes & Palmisano 1974). Such restoration and\nprotection of bull kelp could help prevent red abalone and red sea urchin starvation.\nAdditionally, restoring apex predators and increasing species richness is often\nlinked to increased ecosystem resilience, which is particularly important in\nthe face of global anthropogenic change (Estes et al. 2011)<\/p>\n\n\n\n

While sea otters could alleviate grazing pressure\non Oregon\u2019s bull kelp, this idea only looks at the issue from a top-down, not bottom-up,\nperspective. Sea otters require a lot of food (Costa 1978, Reidman & Estes\n1990), and what they eat will always be a function of prey availability and\nquality (Ostfeld 1982). Just because urchins are available, doesn\u2019t mean otters\nwill eat them. In fact, sea otters prefer large and heavy (i.e. high gonad\ncontent) urchins (Ostfeld 1982). In the field, researchers have observed sea\notters avoiding urchins at the center of urchin barrens (personal\ncommunication), presumably because those urchins have less access to kelp beds than\non the barren periphery, and therefore, are constantly in a starved state (Konar\n& Estes 2003) (Figure 3). These findings suggest prey quality is more\nimportant to sea otter survival than just prey abundance. <\/p>\n\n\n\n

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Figure 3. Left: Sea urchin barren (Annie Crawley). Right: Urchin gonads (Sea to Table).<\/figcaption><\/figure>\n\n\n\n

Purple urchin quality has not been widely assessed\nin Oregon, but early results show that gonad size varies widely depending on\nurchin density and habitat type. In places where urchin barrens have formed,\nlike Port Orford, purple urchins are likely starving and thus may be a poor\nsource of nutrition for sea otters. Before we decide whether sea otters are a\nviable tool to combat kelp loss, prey surveys may need to be conducted to\nassess if a sea otter population could be sustained based on their caloric\nrequirements. Furthermore, predictions of how these prey populations may change\ndue to rising temperatures could help determine the potential for sea otters to\nbecome reestablished in Oregon under rapid environmental change.<\/p>\n\n\n\n

Recent events in California could signal\nclimate-driven processes that are already impacting some parts of Oregon and could\nbecome more widespread. Dr. Rogers-Bennett\u2019s study is valuable as she has quantified\nand described ecosystem changes that might occur along Oregon\u2019s southern\ncoastline. The resurgence of a potential second warm blob and the frequency\nbetween these warming events begs the question if such temperature spikes are\nstill anomalous or becoming the norm. If the latter, we could see more\npronounced kelp loss and major shifts in nearshore ecosystem baselines, where function\nand structure is permanently altered. Whether reintroducing sea otters can\nprevent these changes will ultimately depend on prey and habitat availability\nand quality, and should be carefully considered.<\/p>\n\n\n\n

References:<\/strong><\/p>\n\n\n\n

Costa, D. P. 1978. The ecological energetics,\nwater, and electrolyte balance of the California sea otter (Enhydra lutris<\/em>).\nPh.D. dissertation, University of California, Santa Cruz.<\/p>\n\n\n\n

Estes, J. A. and J.F. Palmisano. 1974. Sea\notters: their role in structuring nearshore communities. Science. <\/em>185(4156):\n1058-1060.<\/p>\n\n\n\n

Estes et al. 2011. Trophic downgrading of planet Earth. Science. <\/em>333(6040): 301-306.<\/p>\n\n\n\n

Harvell et al. 2019. Disease epidemic and a\nmarine heat wave are associated with the continental-scale collapse of a\npivotal predator (Pycnopodia helianthoides<\/em>). Science Advances<\/em>.\n5(1).<\/p>\n\n\n\n

Konar, B., and J. A. Estes. 2003. The stability of\nboundary regions between kelp beds and deforested areas. Ecology<\/em>. 84(1):\n174-185. <\/p>\n\n\n\n

Leising et al. 2015. State of California Current\n2014-2015: impacts of the warm-water \u201cblob\u201d. CalCOFI Reports. <\/em>(56):\n31-68.<\/p>\n\n\n\n

Ostfeld, R. S. 1982. Foraging strategies and prey\nswitching in the California sea otter. Oecologia. <\/em>53(2):\n170-178.<\/p>\n\n\n\n

Reidman, M. L. and J. A. Estes. 1990. The sea\notter (Enhydra lutris<\/em>): behavior, ecology, and natural history. United\nStates Department of the Interior, Fish and Wildlife Service, Biological\nReport. 90: 1-126.<\/p>\n\n\n\n

Rogers-Bennett, L., and C. A. Catton. 2019. Marine\nheat wave and multiple stressors tip bull kelp forest to sea urchin barrens. Scientific\nReports<\/em>. 9:15050.<\/p>\n\n\n\n

Tegner, M. J., and L. A. Levin. 1982. Do sea\nurchins and abalones compete in California? International Echinoderms\nConference, Tampa Bay. J. M Lawrence, ed.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

By Dominique Kone1 and Sara Hamilton2 1Masters Student in Marine Resource Management, 2Doctoral Student in Integrative Biology Five years ago, the North Pacific Ocean experienced a sudden increase in sea surface temperature (SST), known as the warm blob, which altered marine ecosystem function and structure (Leising et al. 2015). Much research illustrated how the warm … Continue reading Can sea otters help kelp under a changing climate?<\/span><\/a><\/p>\n","protected":false},"author":8610,"featured_media":2020,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1011749,1],"tags":[1237983,97092,112,1237664,1011745,554,1237982,742175,513,1053375,148762,155,1209218,1013253,1310493],"class_list":["post-3073","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sea-otter-reintroduction-to-oregon","category-uncategorized","tag-bull-kelp","tag-california","tag-climate-change","tag-dom-kone","tag-dominique-kone","tag-global-warming","tag-kelp","tag-marine-ecology","tag-marine-mammals","tag-nearshore","tag-oregon-coast","tag-oregon-state-university","tag-sea-otters","tag-sea-urchin","tag-warm-blob"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/osu-wams-blogs-uploads.s3.amazonaws.com\/blogs.dir\/2115\/files\/2018\/04\/1180942-Bruce-J-Lichenberger-Alaska-Stock-e1525032500175.jpg","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p5Mfqy-Nz","_links":{"self":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/3073","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/users\/8610"}],"replies":[{"embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/comments?post=3073"}],"version-history":[{"count":5,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/3073\/revisions"}],"predecessor-version":[{"id":3086,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/3073\/revisions\/3086"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/media\/2020"}],"wp:attachment":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/media?parent=3073"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/categories?post=3073"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/tags?post=3073"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}