28 November 2017. The Journal of Experimental Marine Biology and Ecology just published the latest study by our group looking at differences in the CO2 sensitivity of Atlantic silverside offspring stemming from different mothers. Congratulations to Jacob Snyder for his first peer-reviewed publication.
Among the highlights of the study:
Offspring produced by different females varied in their sensitivity to high CO2 conditions.
Specific fatty acids in eggs were correlated to the log-transformed CO2 response ratio of embryo survival and hatch length.
Maternal provisioning might be an additional determinant of CO2 sensitivity in fish early life stages.
M. menidia. Responses to high CO2 conditions among replicates within and among females: (A) embryo and larval survival; (B) overall survival; (C) SL at hatch; and (D) final SL (16 dph). Patterns of larval growth were nearly identical to panel D and are therefore omitted. Ambient and high CO2 treatments are denoted by red and blue colors, respectively. Small symbols depict replicate survival (A,B) or replicate average size (C,D), while large symbols depict CO2 treatment averages for each female. Black lines connect average response for each female. Asterisks represent significant differences (P < 0.05) between CO2 levels within offspring of each female (Bonferroni adjusted t-test). Letters denote to females A to E.
October, 2nd, 2017: Happy to announce that Estuaries and Coasts just published (online) our article that looked at unifying principles of pH and DO fluctuations across many US nearshore habitats. The datasets belongs to the US Nearshore Estuaries Research Reserves System (NERRS) and is one of the most extensive monitoring datasets in coastal aquatic habitats. In this case, we used 15 years of continuous monitoring data (> 5 million data points) from 16 different reserves across the US Atlantic, Caribbean, Gulf of Mexico, and Pacific coasts and analyzed short- to long-term variability in pH and DO fluctuations. Among the highlights:
Our analyses confirmed that large, metabolically driven fluctuations of pH and DO are a unifying feature of nearshore habitats. Even more so, we were able to show that across habitats, one can predict mean pH or mean diel pH fluctuations simply based on salinity and oxygen levels/fluctuations. This provided strong empirical evidence that common metabolic principles drive diel to seasonal pH/DO variations within as well as across a diversity of estuarine environments.
As expected, there were no interannual, monotonic trends in nearshore pH conditions; instead interannual fluctuations were of similar magnitude than the pH decrease predicted for the average surface ocean over the next three centuries.
By correlating weekly anomalies of pH, oxygen, and temperature, we found strong empirical support for the notion that coastal acidification — in addition to being driven by eutrophication and atmospheric CO2 increases — is exacerbated simply by warming, likely via increasing community respiration.
Among many other aspects, the paper analyzed interannual trends in temperature (red bars), dissolved oxygen (%, blue bars), and pH (green bars) at 16 US Nearshore Ecological Research Reserves (NERRS), shown as yearly anomalies derived from averaging monthly anomalies for each variable, site, and year. Black trend lines were derived by LOESS smoothing.
October 10th 2016 was a special day for our still young lab here at the University of Connecticut, Today, the ICES Journal of Marine Science published the paper of Chris Murray et al., which is the first of hopefully many publications of our experimental findings originating out of our new laboratory facility here at UConn Avery Point.
Chris and his co-authors report on a large-scale, quantitative rearing experiment on Atlantic silversides eggs, larvae and juveniles under contrasting CO2 conditions that took place between May – September 2015. This novel experiment was designed to address three critical issues lacking in previous ocean acidification research on fish. First, the study spanned several ontogenetic stages. Second, it used very large numbers of individuals to robustly characterize not just potential shifts in mean responses, but also changes in the distribution of length, weight, and condition factor. Third, it provided food at standardized, non-excess levels to prevent that potential metabolic costs of high CO2 exposure could be compensated by survivors simply by eating more food.
Overall the study demonstrated seemingly small but significant growth reductions due to high CO2 and identified a small number of fatty acids that were of significantly different concentrations in high vs. control juveniles.
Distributions of condition factor per 2mm TL interval for juvenile M.menidia reared for 122dph at control (a) and high CO2 conditions (b). Thick and thin black lines correspond to the 10th/90th and 25th/75th percentiles, respectively, while the red line depicts the median. Data below the 10th and above the 90th percentiles are depicted by black dots. Underlying grey bars show relative frequencies for each 2 mm TL class. Black and grey numbers correspond to numbers of individuals measured for both TL and wW, or for TL only, respectively.
Cumulative frequency distributions of (a) total length (TL) and (b) wet weight (wW), in juvenile M. menidia reared for 122 dph at control and high CO2 conditions.
Gobler & Baumann’s review provides a good overview over the nascent field of multi-stressor acidification and hypoxia work. A first part firmly establishes that virtually all hypoxic zones in the ocean are also acidified, given that metabolic processes (i.e., respiration) consume oxygen and release CO2 into the environment. In a second part, the sparse emerging evidence for multistressor effects of low pH (high CO2) and low oxygen are reviewed, showing that while the majority of effects are additively negative, every study so far has also found synergistically negative effects of combined stressors in at least one trait.
Examples for synergistic negative effects of low DO and low pH (high CO2) on different traits and marine taxa. (a) Synergistic decrease in respiration rate in small and big sea urchins [27]; (b) growth rate of juvenile quahog was unaffected by low DO or low pH individually, but decreased under combined stressor conditions [23]; (c) survival of Atlantic silverside larvae to 10 dph. Survival was robust against low pH and sensitive to low DO, but decreased synergistically under combined stressors (green arrow, [22]); (d) representation of Po ̈rtners [25] ‘Oxygen- and capacity-limited thermal tolerance’ framework, adapted to the multiple stressor scenario of acidification and hypoxia.
Abstract
There is increasing recognition that low dissolved oxygen (DO) and low pH conditions co-occur in many coastal and open ocean environments. Within temperate ecosystems, these conditions not only develop seasonally as temperatures rise and metabolic rates accelerate, but can also display strong diurnal variability, especially in shallow systems where photosynthetic rates ameliorate hypoxia and acidification by day. Despite the widespread, global co-occurrence of low pH and low DO and the likelihood that these conditions may negatively impact marine life, very few studies have actually assessed the extent to which the combination of both stressors elicits additive, synergistic or antagonistic effects in marine organisms. We review the evidence from published factorial experiments that used static and/or fluctuating pH and DO levels to examine different traits (e.g. survival, growth, metabolism), life stages and species across a broad taxonomic spectrum. Additive negative effects of combined low pH and low DO appear to be most common; however, synergistic negative effects have also been observed. Neither the occurrence nor the strength of these synergistic impacts is currently predictable, and there- fore, the true threat of concurrent acidification and hypoxia to marine food webs and fisheries is still not fully understood. Addressing this knowledge gap will require an expansion of multi-stressor approaches in experimental and field studies, and the development of a predictive framework. In consider- ation of marine policy, we note that DO criteria in coastal waters have been developed without consideration of concurrent pH levels. Given the per- sistence of concurrent low pH–low DO conditions in estuaries and the increased mortality experienced by fish and bivalves under concurrent acidifi- cation and hypoxia compared with hypoxia alone, we conclude that such DO criteria may leave coastal fisheries more vulnerable to population reductions than previously anticipated.
A suite of parallel anthropogenic changes affects contemporary marine ecosystems. Excessive carbon dioxide (CO2) pollution results in warmer, more acidic oceans with lower dissolved oxygen (DO) levels, meanwhile the emission of reactive nitrogen/phosphorus results in eutrophication, excessive microbial degradation and thus metabolic hypoxia and acidification. Despite decades of empirical research how each individual stressor of the ‘climate-change syndrome’ (i.e., temperature, CO2, DO) affects the fitness of marine organisms, we still know little about the combined effects of these stressors. This lecture gives an overview over the nascent field of multi-stressor approaches evaluating the climate sensitivity of marine organisms across taxa. In most studied cases, combined effects of these stressors exceeded those observed individually. Effects of combined warming, acidification, and deoxygenation have mostly been additive (no stressor interaction) or synergistically negative (stressor interaction). The occurrence and strength of synergistic stressor interactions in some species, life history stages, and traits comprises a vexing challenge but hints at potentially greater sensitivities of organisms to marine climate change than previously recognized. This lecture is intended for post-secondary students, providing them with illustrated examples from the most resent literature, while aiding in communicating the urgent need for empirical data from multi-stressor approaches.
…in the true sense has kept biologist’s head scratching for quite some time, and matters have only gotten more complex since the thunderous advent of genetic methods. Yet the distinction between a species and – say – an ecotype of a species is more than just academic quibble.
In the case of the key silverside, Menidia conchorum, a species that is only found in the hypersaline ponds on the Florida Keys, it’s quite literally an existential question. So far, the protocols and steps of protection apply only in cases of threatened species, which is perhaps something that ought to change.
O’Leary et al. went down to the Florida Keys and sampled the silversides in order to compare them morphologically and genetically to the ‘parent’ species, the tidewater silverside Menidia peninsulae. Their findings show that key silversides are distinct, but not quite their own species yet. In addition, the study revealed the large amount of inbreeding and genetic drift that is happening in each of these small hypersaline ponds.
The paper concludes that although ‘only’ an ecotype, the key silverside is threatened by loss of habitat and therefore still needs our protection!
Depiction of morphometric landmarks (upper left) and distinguishing shapes (lower left) between tidewater and key silverside (M. peninsula & M. conchorum). Key silversides are an ecotype that can only be found in hypersaline ponds on the Florida Keys (right: lead and co-authors seining).
This study by Yencho et al. examined growth, mortality, and settlement distributions of juvenile Winter Flounder Pseudopleuronectes americanus in two bays of Long Island, New York, to better understand localized population dynamics of a species experiencing a protracted population decline. They found that settlement distributions had multiple peaks (cohorts) occurring between March and late July in 2007 and between February and May in 2008. Otolith-based growth rate was significantly higher for Port Jefferson Harbor during 2007 than for all other year × location combinations. Together with previous research the finding of multiple spawning cohorts in Long Island Winter Flounder suggests a degree of isolation, and local management will be needed to support healthy populations.
Reliable estimates of short- and longer-term in situ growth and condition of organisms are critical if one hopes to understand how the environment regulates survival. This laboratory study reports the first comparison of somatic- (K), biochemical- (RNA–DNA ratio, RD) and otolith- (increment widths, OIW) based indices of condition of a young juvenile fish. It found that RNA:DNA ratios react 2x faster to growth changes due to changes in feeding level than otolith increment widths, while condition factor was the most variable proxy.
Juvenile Pacific bluefin tuna (PBT, Thunnus orientalis) are known to migrate from western Pacific spawning grounds to their eastern Pacific nursery grounds in the California Current Large Marine Ecosystem, but the timing, durations, and fraction of the population that makes these migrations need to be better understood for improved management. This new study published in the ICES Journal of Marine Science suggests that analyzing the trace elemental composition of bluefin tuna otoliths may divulge the time of arrival of the juvenile fish on the Californian Shelf. Scientists from the University of Connecticut, Stony Brook University, Texas A&M, as well as from NOAA collaborated in this effort, hoping to further develop this method to better inform managers in the future.
Citation
Baumann, H., Wells, R.J.D., Rooker, J.R., Baumann, Z.A., Madigan, D.J., Dewar, H., Snodgrass, O.E., and Fisher, N.S. (2015) Combining otolith microstructure and trace elemental analyses to infer the arrival of Pacific bluefin tuna juveniles in the California Current Ecosystem. ICES Journal of Marine Science 72:2128-2138.
New experiments suggest both additive and synergistic negative effects of combined low pH and low oxygen on the early life stages of three common forage fish
Coastal habitats often experience large diel to seasonal fluctuations in both pH and dissolved oxygen (DO), because ecosystem metabolism consumes oxygen while producing CO2. Hence, the two factors really represent two sides of the same coin. Decades of research have focused on hypoxia or acidification; therefore, the combined effects of these two stressors is still poorly understood. Master student Elizabeth Depasquale and co-authors tested the sensitivity to low pH and low DO in offspring of three forage fish species that are common in nearshore New England habitats: Inland silverside (Menidia beryllina), Atlantic silverside (M. menidia), and sheepshead minnow (Cyprinodon variegatus). The results show that pH and oxygen mostly have additive negative effects, but in a few cases also synergistically negative effects (Fig.1). The latter shows that multistressor experiments are important tools in assessing the impacts of multiple changes on coastal organisms.
Depasquale, E.*, Baumann, H., and Gobler, C.J. (2015) Variation in early life stage vulnerability among Northwest Atlantic estuarine forage fish to ocean acidification and low oxygen. Marine Ecology Progress Series 523: 145–156 http://dx.doi.org/10.3354/meps11142
Schematic response shapes illustrating the expected form of effect interaction between pH and oxygen on different early life history (ELH) traits
