Ocean acidification is intensifying and hypoxia is projected to expand in the California Current large marine ecosystem as a result of processes associated with the global emission of CO2. Observed changes in the California Current outpace those in many other areas of the ocean, underscoring the pressing need to adopt management approaches that can accommodate uncertainty and the complicated dynamics forced by accelerating change. We argue that changes occurring in the California Current large marine ecosystem provide opportunities and incentives to adopt an integrated, systems-level approach to resource management to preserve existing ecosystem services and forestall abrupt change. Practical options already exist to maximize the benefits of management actions and ameliorate impending change in the California Current, for instance, adding ocean acidification and hypoxia to design criteria for marine protected areas, including consideration of ocean acidification and hypoxia in fisheries management decisions, and fully enforcing existing laws and regulations that govern water quality and land use and development.
Posts Tagged 'North Pacific'
Using integrated, ecosystem-level management to address intensifying ocean acidification and hypoxia in the California Current large marine ecosystemPublished 4 April 2017 Science Leave a Comment
Tags: mitigation, North Pacific, Policy, review
Diatom bloom-derived bottom water hypoxia off the Changjiang estuary, with and without typhoon influencePublished 3 April 2017 Science Leave a Comment
Tags: chemistry, field, North Pacific
During the summers of 2009 and 2013, seawater pH and concentrations of dissolved oxygen, inorganic carbon, and nutrients were measured off the Changjiang estuary in the East China Sea. The 2009 cruise captured the effects of Typhoon Morakot; the 2013 cruise sampled more typical conditions (no typhoon). Data from both years indicate a close correlation between high primary productivity in surface waters and hypoxia in bottom waters. Based on these observations, we developed a conceptual model to guide an exploration of processes contributing to the formation of summertime bottom hypoxia. A mixing-model analysis of the 2009 data identified a surface diatom bloom as the major (70–80%) source of the organic carbon that decomposed and ultimately led to bottom water hypoxia. Within the Changjiang River plume, depth-integrated net biological production in the water column was 1.8 g C m−2 d−1, indicating strong autotrophic production, which in turn led to a high respiration rate of 1.2 g C m−2 d−1 in the bottom water. During both cruises, strong surface-to-bottom physical and metabolic coupling was evident. In 2009, storm-driven inputs of nutrients from elevated river discharge and strong vertical mixing helped to fuel the rapid development of a surface diatom bloom. Afterwards, stratified conditions re-established, newly formed labile organic matter sank, and bottom water oxygen was quickly consumed to an extent that hypoxia and acidification developed. To our knowledge, the observed rate of hypoxia and acidification development (within 6 d) is the fastest yet reported for the Changjiang River plume.
Ocean acidification increases larval swimming speed and has limited effects on spawning and settlement of a robust fouling bryozoan, Bugula neritinaPublished 27 March 2017 Science Leave a Comment
Tags: adaptation, biological response, bryozoa, laboratory, morphology, North Pacific, otherprocess, performance, reproduction
Few studies to date have investigated the effects of ocean acidification on non-reef forming marine invertebrates with non-feeding larvae. Here, we exposed adults of the bryozoan Bugula neritina and their larvae to lowered pH. We monitored spawning, larval swimming, settlement, and post-settlement individual sizes at two pHs (7.9 vs. 7.6) and settlement dynamics alone over a broader pH range (8.0 down to 6.5). Our results show that spawning was not affected by adult exposure (48 h at pH 7.6), larvae swam 32% faster and the newly-settled individuals grew significantly larger (5%) at pH 7.6 than in the control. Although larvae required more time to settle when pH was lowered, reduced pH was not lethal, even down to pH 6.5. Overall, this fouling species appeared to be robust to acidification, and yet, indirect effects such as prolonging the pelagic larval duration could increase predation risk, and might negatively impact population dynamics.
Factors affecting coral recruitment and calcium carbonate accretion rates on a Central Pacific coral reefPublished 22 March 2017 Science Leave a Comment
Tags: biological response, calcification, chemistry, corals, field, individualmodeling, modeling, North Pacific, reproduction
Coral recruitment and calcium carbonate (CaCO3) accretion are fundamental processes that help maintain coral reefs. Many reefs worldwide have experienced degradation, including a decrease in coral cover and biodiversity. Successful coral recruitment helps degraded reefs to recover, while CaCO3 accretion by early successional benthic organisms maintains the topographic complexity of a coral reef system. It is therefore important to understand the processes that affect coral recruitment and CaCO3 accretion rates in order to understand how coral reefs recover from disturbances.
The aim of this thesis was to determine how biophysical forcing factors affect coral recruitment, calcification and bioerosion on a pristine coral reef. I used artificial settlement tiles to measure coral recruitment and CaCO3 accretion at ten sites (four on the fore reef, four on the Western Reef Terrace and two at the Entrance Channel) at Palmyra Atoll. Fungia skeletons and pieces of dead coral rock were used to measure bioerosion rates, which were combined with the CaCO3 accretion rates to obtain a net CaCO3 budget of the reef substratum. Interactions between coral recruits and other benthic organisms on the settlement tiles were recorded to determine the settlement preferences and competitive strength of coral recruits. The settlement preference of Pocillopora damicornis for divots shaped like steephead and bumphead parrotfish bites marks was determined by adding P. damicornis larvae to a container with a settlement tile with the aforementioned divots.
I found that coral recruitment and CaCO3 accretion are influenced by biophysical forcing factors. Most pocilloporids likely recruit close to their parents while the origin of poritid larvae is much more distant. Pocilloporid recruitment rates were also significantly correlated with the successional stage of the benthic community on the settlement tiles, especially the cover of biofilm and bryozoa. Biofilm and crustose coralline algae (CCA) were preferred as settlement substrata by coral larvae, however both pocilloporids and poritids settled on a large number of different benthic substrata. P. damicornis larvae showed a significant settlement preference for divots shaped like parrotfish bite marks over a flat settlement surface. Coral recruits were good competitors against encrusting algae but were often outcompeted by filamentous and upright algae. Settlement tiles were almost entirely colonised by benthic organisms within three to twelve months of deployment. The mass of CaCO3 deposited onto the settlement tiles negatively correlated with herbivore grazing pressure on the benthic community. Bioerosion rates within pieces of coral (internal bioerosion) increased over time but overall bioerosion rates (internal and external) rarely exceeded CaCO3 deposition by CCA.
My results show how variability in biophysical forcing factors leads to natural variation in coral recruitment and CaCO3 accretion. This thesis highlights the importance of measuring herbivore grazing, CCA and turf algae cover to gain a better understanding of reef resilience. I conclude that models constructed for Caribbean reefs may not be suited to predict resilience in Pacific reefs and that within the Pacific, two different kinds of resilience models need to be constructed, one for human-inhabited coral reefs and one for uninhabited coral reefs.
Effects of elevated CO2 and nitrogen supply on the growth and photosynthetic physiology of a marine cyanobacterium, Synechococcus sp. PCC7002Published 22 March 2017 Science Leave a Comment
Tags: biological response, growth, laboratory, morphology, multiple factors, North Pacific, nutrients, photosynthesis, physiology, prokaryotes
Ocean acidification due to increasing atmospheric CO2 concentration and coastal eutrophication are growing global threats to affect marine organisms and ecosystem health. However, little is known about their interactive impacts on marine picocyanobacteria which contribute to a large proportion of primary production. In this study, we cultivated the cyanobacterium Synechococcus sp. PCC7002 at ambient (380 ppmv) and high CO2 (1000 ppmv), across a range of nitrogen levels (LN, 10 μM NO3−; MN, 35 μM NO3−; HN, 110 μM NO3−). In LN media, elevated CO2 significantly decreased cellular chlorophyll a, but insignificantly affected growth rate, photosynthetic efficiency (Fv/Fm) and maximum relative electron transport rate (rETRmax). Nitrogen (N)-supply positively increased the growth, Fv/Fm, dissolved organic carbon (DOC) and cellular carotenoids/Chl a ratios, but decreased the rETRmax in both ambient and elevated CO2 conditions. The cellular C/N ratios were significantly increased by either elevated CO2 or N-supply, and the cell size was significantly enhanced by elevated CO2, not by N-supply. In addition, we found the N-supply alone had no significant effects on the four main components of chromophoric dissolved organic matter (cDOM) in ambient CO2, while the N-supply interacted with elevated CO2 significantly decreasing the cDOM contents in the cultures. Our results indicated that elevated CO2 and N-supply interacted to alter the physiology and cellular biochemistry of Synechococcus sp. PCC7002, providing useful information for understanding the environmental adaptability of Synechococcus to coastal ocean acidification and eutrophication.
Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxidePublished 20 March 2017 Science Leave a Comment
Tags: biological response, laboratory, multiple factors, North Pacific, nutrients, otherprocess, photosynthesis, physiology, phytoplankton, primary production, respiration
Marine phytoplankton are expected to benefit from enhanced carbon dioxide (CO2), attributable largely to down-regulation of the CO2 concentrating mechanism (CCM) which saves energy resources for other cellular processes. However, the nitrogen (N) nutritional condition (N-replete vs. N-limiting) of phytoplankton may affect the responses of their intracellular metabolic processes to elevated CO2. We cultured the model diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Thalassiosira weissflogii at ambient and elevated CO2 levels under N-replete and N-limiting conditions. Key metabolic processes, including light harvesting, C fixation, photorespiration, respiration, and N assimilation, were assessed systematically and then incorporated into an energy budget to compare the effects of CO2 on the metabolic pathways and the consequent changes in photosynthesis and C fixation as a result of energy reallocation under the different N nutritional conditions. Under the N-replete condition, down-regulation of the CCM at high CO2 was the primary contributor to increased photosynthesis rates of the diatoms. Under N-limiting conditions, elevated CO2 significantly affected the photosynthetic photon flux and respiration, in addition to CCM down-regulation and declines in photorespiration, resulting in an increase of the C:N ratio in all 3 diatom species. In T. pseudonana and T. weissflogii, the elevated C:N ratio was driven largely by an increased cellular C quota, whereas in P. tricornutum it resulted primarily from a decreased cellular N quota. The N-limited diatoms therefore could fix more C per unit of N in response to elevated CO2, which could potentially provide a negative feedback to the ongoing increase in atmospheric CO2.