finding 23.1 : ocean-warming-acidity-affect-fish

Warmer oceans are leading to increased coral bleaching events and disease outbreaks in coral reefs, as well as changed distribution patterns of tuna fisheries. Ocean acidification will reduce coral growth and health. Warming and acidification, combined with existing stresses, will strongly affect coral reef fish communities.

This finding is from chapter 23 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the assessment process was convening three focus area workshops as part of the Pacific Islands Regional Climate Assessment (PIRCA). The PIRCA is a collaborative effort aimed at assessing the state of climate knowledge, impacts, and adaptive capacity in Hawai‘i and the U.S. Affiliated Pacific Islands. These workshops included representatives from the U.S. federal agencies, universities, as well as international participants from other national agencies and regional organizations. The workshops led to the formulation of a foundational Technical Input Report (TIR).7350d7b3-6e95-4375-ba23-26756b441fc2 The report consists of nearly 140 pages, with almost 300 references, and was organized into 5 chapters by 11 authors. The chapter author team engaged in multiple technical discussions via regular teleconferences that permitted a careful review of the foundational TIR7350d7b3-6e95-4375-ba23-26756b441fc2 and of approximately 23 additional technical inputs provided by the public, as well as the other published literature, and professional judgment. These discussions included a face-to-face meeting held on July 9, 2012. These discussions were supported by targeted consultation among the lead and contributing authors of each message. There were several iterations of review and comment on draft key messages and associated content.

Description of evidence base: The key message was chosen based on input from the extensive evidence documented in the Hawai‘i Technical Input Report7350d7b3-6e95-4375-ba23-26756b441fc2 and additional technical inputs received as part of the Federal Register Notice solicitation for public input, as well as stakeholder engagement leading up to drafting the chapter. Ocean warming: There is ample evidence that sea-surface temperatures have already risen throughout the region based on clear observational data, with improved data with the advent of satellite and in situ (ARGO & ship-based) data.05b4968a-410a-43f0-b668-b96c5af0373c Assessment of the literature for the region by other governmental bodies (such as Australian Bureau of Meteorology [ABOM] and the Commonwealth Scientific and Industrial Research Organization [CSIRO]) point to continued increases under both B1 and A2 scenarios.a639a8f6-3355-43d7-ab21-ef29364db75a Ocean acidification: Globally, the oceans are currently absorbing about a quarter of the carbon dioxide emitted to the atmosphere annually, and becoming more acidic as a result (Ch. 2: Our Changing Climate, Key Message 12). Historical and current observations of aragonite saturation state (Ωar) for the Pacific Ocean show a decrease from approximately 4.9 to 4.8 in the Central North Pacific (Hawaiian Islands); in the Western North Pacific (Republic of Marshall Islands, Commonwealth of Northern Mariana Islands, Federated States of Micronesia, Republic of Palau, Guam), it has declined from approximately 4.5 to 3.9 in 2000, and to 4.1 in the Central South Pacific (American Samoa)(this chapter: Figure 23.3; Ch. 24: Oceans and Marine Resources).1ee9bb2b-9b22-48f0-b540-f942ccfd9c71 Projections from CMIP3 models indicate the annual maximum aragonite saturation state will reach values below 3.5 by 2035 in the waters of the Republic of the Marshall Islands (RMI), by 2030 in the Federated States of Micronesia (FSM), by 2040 in Palau, and by 2060 around the Samoan archipelago. These values are projected to continue declining thereafter.7350d7b3-6e95-4375-ba23-26756b441fc2 The recently published Reefs at Risk Revisited3d9112b9-6aa1-4614-9599-6966c9591ef9 estimates aragonite saturation state (as an indicator of ocean acidification) for CO2 stabilization levels of 380 ppm, 450 ppm, and 500 ppm, which correspond approximately to the years 2005, 2030, and 2050 under the A1B emissions scenario (which assumes similar emissions to the A2 scenario through 2050 and a slow decline thereafter) (Figure 4.4 from Keener et al. 20127350d7b3-6e95-4375-ba23-26756b441fc2). Bleaching events: These have been well-documented in extensive literature worldwide due to increasing temperatures, with numerous studies in Hawai‘i and the Pacific Islands.ada58825-78cb-47be-a121-d5553c7e2870 f41beadd-748c-4117-a3b4-768138622179 745d74fa-44f3-4eaa-83b7-feb3743b9046 Disease outbreaks: Reports of coral diseases have been proliferating in the past years,9e0aded6-29e7-4d1c-a3fe-f0c5c750cd17 03f1ed25-ab43-4ab2-b13d-3358cc2e2e62 b15c3b47-5e74-4a10-ac4d-f61d17dd376b but few have currently been adequately described, with causal organisms identified (for example, fulfill Koch’s Postulates). Reduced growth: There is abundant evidence from laboratory experiments that lower seawater pH reduces calcification rates in marine organisms (for example, Feely et al. 20091ee9bb2b-9b22-48f0-b540-f942ccfd9c71). However, actual measurements on the effects of ocean acidification on coral reef ecosystems in situ or in complex mesocosms are just now becoming available, and these measurements show that there are large regional and diel variability in pH and pCO2.3da133aa-972c-4f41-b43c-347f202a8554 The role of diel and regional variability on coral reef ecosystems requires further investigation. Distribution patterns of coastal and ocean fisheries: Evidence of the effects of ocean acidification on U.S. fisheries in Hawai‘i and the Pacific Islands is currently limited (Lehodey et al. 2011)1f38f63f-a854-44c5-8ebe-b8ec718bdf70 but there is accumulating evidence for ecosystem impacts.

New information and remaining uncertainties: New information: Since the 2009 National Climate Assessment,e251f590-177e-4ba6-8ed1-6f68b5e54c8a considerable effort has been employed to understand the impacts of ocean acidification (OA) on marine ecosystems, including recent ecosystem-based efforts.4b4c5af2-fce0-4c54-a098-6ea277602621 1f38f63f-a854-44c5-8ebe-b8ec718bdf70 Studies of OA impacts on organisms has advanced considerably, with careful chemistry using worldwide standard protocols making inroads into understanding a broadening range of organisms. However, predicting the effect of ocean acidification on marine organisms and marine coral reef ecosystems remains the key issue of uncertainty. The role of community metabolism and calcification in the face of overall reduction in aragonite saturation state must be investigated. Understanding interactions between rising temperatures and OA remains a challenge. For example, high temperatures simultaneously cause coral bleaching, as well as affect coral calcification rates, with both impacts projected to increase in the future.

Assessment of confidence based on evidence: There is very high confidence that ocean acidification and decreased aragonite saturation is taking place and is projected to continue. There is high confidence that ocean warming is taking place and is projected to continue; there is medium confidence that the thermal anomalies will lead to continued coral bleaching and coral disease outbreaks.

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