Posts Tagged 'nutrients'

Exploring the interactions and implications between ocean acidification and eutrophication in Budd inlet

Ocean Acidification is one of the greatest symptoms that climate change has inflicted on marine environments. Oceans naturally absorb carbon dioxide, however anthropogenic CO2 has manifested greater adverse influences on marine life, which is stressing our ability to use these resources. Ocean pH has dropped 30% to 8.1 since the industrial age, however the pH reduction along coastlines and within estuaries has deteriorated even more, having a greater need to be monitored. Acidification is worse, especially around the Puget Sound because of high nutrient loads flowing into the Puget Sound from coastal communities, and other human industrial scale activities like agriculture. Nutrients, primarily in the form of nitrogen, increase algae and microbe primary productivity, eventually outputting new CO2 through biological processes, resulting in amplification of the effect greenhouse gases are already exerting on marine ecosystems. This thesis project explored this relationship by looking at water samples collected from five locations in Budd inlet, and were tested for pH, nitrate, alkalinity. These variables were collected with the goal of determining if there was a noticeable difference between sample locations, and if there was a correlation between these variables all in context to the city of Olympia and Capitol Lake having some influence on findings. Results found no clear statistically significant differences between each variables and sample sites, however pH and nitrate concentrations had the greatest correlation. This suggests nutrients are indeed contributing significantly towards furthering acidification, more so than can be determined by CO2 emissions levels alone. More research is warranted on establishing causal relationships between nutrient loads and acidification levels in all Puget Sound inlets.

Continue reading ‘Exploring the interactions and implications between ocean acidification and eutrophication in Budd inlet’

The influence of paleo-seawater chemistry on foraminifera trace element proxies and their application to deep-time paleo-reconstructions

The fossilized remains of the calcite shells of foraminifera comprise one of the most continuous and reliable records of the geologic evolution of climate and ocean chemistry. The trace elemental composition of foraminiferal shells has been shown to systematically respond to seawater properties, providing a way to reconstruct oceanic conditions throughout the last 170 million years. In particular, the boron/calcium ratio of foraminiferal calcite (B/Ca) is an emerging proxy for the seawater carbonate system, which plays a major role in regulating atmospheric CO2 and thus Earth’s climate. In planktic foraminifera, previous culture studies have shown that shell B/Ca increases with seawater pH, which is hypothesized to result from increased incorporation of borate ion (B(OH)4 -) at high pH; increasing pH increases the [B(OH)4 -] of seawater. However, further experiments showed that B/Ca responds to both pH and seawater dissolved inorganic carbon concentration (DIC), leading to the hypothesis that B/Ca is driven by the [B(OH)4 -/DIC] ratio of seawater. Because pH (and thus B(OH)4 -) can be determined via the δ11B composition of foraminiferal calcite, B/Ca therefore may provide an opportunity to determine seawater DIC in the geologic past.

Continue reading ‘The influence of paleo-seawater chemistry on foraminifera trace element proxies and their application to deep-time paleo-reconstructions’

Ocean acidification alters meiobenthic assemblage composition and organic matter degradation rates in seagrass sediments

Seagrass meadows are an important organic matter (OM) reservoir but, are currently being lost due to global and regional stressors. Yet, there is limited research investigating the cumulative impacts of anthropogenic stressors on the structure and functioning of seagrass benthic assemblages, key drivers of OM mineralization and burial. Here, using a 16‐month field experiment, we assessed how meiobenthic assemblages and extracellular enzymatic activities (as a proxy of OM degradation) in Posidonia oceanica sediments responded to ocean acidification (OA) and nutrient loadings, at CO2 vents. P. oceanica meadows were exposed to three nutrient levels (control, moderate, and high) at both ambient and low pH sites. OA altered meiobenthic assemblage structure, resulting in increased abundance of annelids and crustaceans, along with a decline in foraminifera. In addition, low pH enhanced OM degradation rates in seagrass sediments by enhancing extracellular enzymatic activities, potentially decreasing the sediment carbon storage capacity of seagrasses. Nutrient enrichment had no effect on the response variables analyzed, suggesting that, under nutrient concentration unlikely to cause N or P imitation, a moderate increase of dissolved nutrients in the water column had limited influence on meiobenthic assemblages. These findings show that OA can significantly alter meiobenthic assemblage structure and enhance OM degradation rates in seagrass sediments. As meiofauna are ubiquitous key actors in the functioning of benthic ecosystems, we postulated that OA, altering the structure of meiobenthic assemblages and OM degradation, could affect organic carbon sequestration over large spatial scales.

Continue reading ‘Ocean acidification alters meiobenthic assemblage composition and organic matter degradation rates in seagrass sediments’

Marine mass mortality in a global change context: impacts on individuals, populations and communities

Human actions are pushing natural systems into states that have no historical precedent. In response, empirical and theoretical researchers are increasingly focused on developing ways to predict the responses of ecological systems to change. However, significant knowledge gaps remain, often leading to “ecological surprises” where observed impacts of global change do not align with existing theory or hypotheses. In this dissertation, I study the response to perturbations of a well-characterized system for ecological research, the Northeast Pacific rocky intertidal, to advance our understanding of and ability to predict the impacts of global change on individuals, populations and communities. In 2013 and 2014, sea star species along the west coast of North America were affected by an outbreak of Sea Star Wasting Syndrome (SSWS), resulting in an epidemic of mass mortality that spanned unprecedented geographic and temporal scales and resulted in the near extirpation of multiple sea star species from many locations along the coast. One of the species that was most strongly affected in the intertidal zone was Pisaster ochraceus, an iconic predatory sea star that has the ability to play a keystone role in its community through foraging on and ultimately controlling the lower boundary of mussel prey populations. The first two chapters of this dissertation take advantage of SSWS as a “natural” form of top predator removal to assess the consequences of this type of perturbation on ecosystem resilience. In Chapter 2, I tested the hypotheses that P. ochraceus loss would facilitate a population expansion of a smaller, mesopredator sea star, Leptasterias sp., and that this expansion would have negative effects on P. ochraceus population recovery. This result would follow expectations of competitive release and aligns with existing research on the competitive relationship between these species from the Northeast Pacific intertidal. I used field surveys to track Leptasterias populations just before the onset of and up to three years after SSWS. Contrary to expectation, I did not see an increase in the distribution or density of Leptasterias, and instead saw a decrease in individual size post-SSWS. Further, I found no evidence of competition between P. ochraceus recruits and Leptasterias for resources. Thus, although my hypotheses were grounded in theory and previous research, they were not supported by data. These results suggest that Leptasterias will not provide a bottleneck for P. ochraceus population recovery from SSWS, nor compensate for lowered P. ochraceus predation. The dynamics of P. ochraceus at the recruit (early benthic juvenile) life-history stage has long been considered a gap in our understanding of the species, as recruits have been historically rare in the intertidal and hard to study. Post-SSWS, however, many sites along the coast experienced unprecedented recruitment of P. ochraceus into intertidal ecosystems. In Chapter 3, I used a field experiment to test the hypothesis that this pulse of recruitment was facilitated by SSWS-related adult loss, the consequent decrease in predation by adult P. ochraceus, and increase in prey availability for recruits. Instead of finding evidence that adults dominate recruits in food competition and inhibit recruit success, I found that recruits have a negative effect on P. ochraceus adult densities. Further, treatments where recruits were excluded and only adults had access to prey communities showed the highest control of sessile invertebrate prey populations at the end of the year-long experiment. Thus, these results suggest that adult P. ochraceus will not hinder recruit recovery, but propose a mechanism whereby high recruit densities may increase vulnerability to SSWS-induced shifts in community structure. Outbreaks of mass mortality, particularly those as widespread as SSWS, are one of many ecological challenges driven by anthropogenic environmental changes such as warming and ocean acidification. However, predicting the vulnerability of species and populations to global change is an ongoing and significant challenge for researchers and managers. In Chapter 4 I assessed whether intraspecific physiological variability could help predict P. ochraceus recruit response to ocean acidification and warming. I found that individual metabolic rate interacted with ocean acidification and food availability to drive sea star growth, and that an interaction between metabolic rate and temperature also predicted sea star predation on Mytilus spp. mussels. Thus, these results have implications not only for P. ochraceus but also for its food web interactions. Incorporating these results into predictive frameworks may improve our ability to anticipate and scale up responses to global change across levels of ecological organization. In summary, my dissertation, although chock-full of surprises, presents several paths forward for improving predictive ability in the face of accelerating anthropogenic global changes. Further, we reinforce the notion that management strategies should be cautious and anticipate ecological surprises. Predicting the future is challenging even when predictions are well-informed, particularly in environmental contexts that have never been encountered before.

Continue reading ‘Marine mass mortality in a global change context: impacts on individuals, populations and communities’

Nutrient enrichment promotes eutrophication in the form of macroalgal blooms causing cascading effects in two anthropogenically disturbed coastal ecosystems

Humans are impacting almost every major ecological process that structures communities and ecosystems. Examples of how human activity can directly control key processes in ecosystems include destruction of habitat changing trophic structure, nutrient pollution altering competitive outcomes, overharvesting of consumers reducing top down control, and now climate change impacting virtually every global biogeochemical cycle. These human impacts may have an independent effect on the ecosystem, but they also have the potential to cause cascading effects and promote subsequent stressors. Also, these impacts are not limited to a particular system or geographic location making research on their overall effects vital for management practices. For example, tropical reefs have been transitioning from coral to mixed communities dominated by macroalgae, motivating research on how macroalgae respond to anthropogenic stressors and interact with each other during these stressful events. Further, while eutrophication of coastal estuaries due to increased anthropogenic supplies of nutrients has been of critical global concern for decades, the potential for eutrophication to drive new stressors is a growing concern. To address these knowledge gaps, I investigated how human stressors impact two different and major coastal ecosystems known to be vulnerable to anthropogenic disturbances.

In chapter 1, I demonstrate that anthropogenic stressors in the form of increased nutrients in the water and sediments have strong impacts on interspecific interactions of coral reef macroalgae. Abiotic stressors such as nutrients have been linked to phase-shifts from coral to algal domination on tropical reefs. However, few studies have considered how these stressors impact changes in the biotic and abiotic constituents of dominant species of calcifying macroalgae, and how this may be mediated by species-species interactions. I conducted 4 mesocosm experiments to examine whether different nutrient sources (water column vs. terrestrial sediment) as well as species interactions (alone vs. mixed species) affected total mass (biomass + calcium carbonate (CaCO3)) of two common calcifying macroalgae (Padina boryana and Galaxaura fasciculata). P. boryana gained total mass with increased water column nutrients but declined with increased nutrients supplied by the sediment. Conversely, G. fasciculata gained total mass with increased nutrients in the sediment but declined with increased water column nutrients. In both interactions, the “winner” (i.e., G. fasciculata in the sediment experiment) also had a greater % of thallus mass comprised of CaCO3, potentially due to the subsequent decomposition of the “loser” as this result was not found in the alone treatments. These findings ultimately suggest that nutrient stressors can cause cascading effects, such as promoting calcification and biomass growth or loss in these macroalgal communities, and the potential for domination or decline is based on the nutrient source and community composition.

In chapter 2, I demonstrate that decomposition of macroalgal blooms cause a sequence of biogeochemical processes that can drive acidification in shallow coastal estuaries, and that these processes are mediated by a dynamic microbial community. Eutrophication and ocean acidification are both widely acknowledged as major human-induced stressors in marine environments. While the link between eutrophication and acidification has been established for phytoplankton, it is unclear whether eutrophication in the form of macroalgal blooms can cause cascading effects like acidification in shallow eutrophic estuaries. I conducted seasonal field surveys and assessed microbial communities and functional genes to evaluate changes in biotic and abiotic characteristics between seasons that may be associated with acidification in Upper Newport Bay, CA, USA. Acidification, measured as a drop in pH of 0.7, occurred in summer at the site with the most macroalgal cover. Microbial community composition and functional gene expression provide evidence that decomposition processes contributed to acidification, and also suggest that other biogeochemical processes like nitrification and degradation of polyphosphate also contributed to acidification. To my knowledge, my findings represent the first field evidence that eutrophication of shallow coastal estuaries dominated by green macroalgal blooms can cascade to acidification.

In chapter 3, I demonstrate that macroalgal blooms in shallow estuaries are strong drivers of key microbially-mediated biogeochemical processes that can cause cascading effects, such as acidification and nutrient fluxing, regardless of simulated tidal flushing. Estuaries are productive and diverse ecosystems and are vulnerable to eutrophication from increased anthropogenic nutrients. While it is known that enhanced tidal flushing can reduce adverse effects of anthropogenic disturbances in larger, deeper estuarine ecosystems, this is unexplored for eutrophication in shallow coastal estuaries where macroalgae usually dominate. I simulated eutrophication as a macroalgal bloom in a mesocosm experiment, varied tidal flushing (flushed daily vs unflushed), and assessed the effects on water column and sediment biogeochemical processes and the sediment microbial community. While flushing did not ameliorate the negative effects of the macroalgal bloom, it caused transient differences in the rate of change in biogeochemical processes and promoted increased fluxes of nutrients from the sediment. In the beginning, the macroalgal bloom induced basification and increased total alkalinity, but during decomposition, acidification and the accumulation of nutrients in the sediment and water column occurred. The findings from this chapter ultimately suggest that macroalgal blooms have the potential to be the cause of, yet may also offer a partial solution to, global ecological changes to biogeochemical processes.

Overall, my results indicate that anthropogenic disturbances, particularly in the form of increased nutrients, can cause cascading effects like macroalgal blooms that in turn cause acidification, basification, increased interspecific interactions, nutrient depletion, and nutrient fluxing in multiple ecosystems. These data advance our current understanding of the ecological consequences of eutrophication in the form of macroalgal blooms in different ecosystems. It also provides mechanistic links to microbial communities and biogeochemical processes not previously identified for shallow coastal estuaries. As human population and subsequent nutrient pollution increases in watersheds globally, ecological phenomenon such as eutrophication will only be intensified, and macroalgal communities will continue to dominate. Consequently, this dominance, especially during decomposition as shown here, can drive a multitude of subsequent stressors that can impact the entire ecosystem.

Continue reading ‘Nutrient enrichment promotes eutrophication in the form of macroalgal blooms causing cascading effects in two anthropogenically disturbed coastal ecosystems’

Effects of ocean acidification and phosphate limitation on physiology and toxicity of the dinoflagellate Karenia mikimotoi

Highlights

• Effects of ocean acidification (OA) was experimentally studied in the toxic dinoflagellate Karenia mikimotoi in laboratory incubations.
• OA enhanced growth of K. mikimotoi under high phosphate concentration.
• Low phosphate inhibited growth in K. mikimotoi irrespective of CO2 concentration.
• OA increased embryonic toxicity of K. mikimotoi and its hemolytic activity, although the latter was only under high concentration of phosphate.
• There was an interactive effect of OA and low phosphate on growth, rETRmax and hemolytic activity.

Abstract

This work demonstrated a 10-day batch culture experiment to test the physiology and toxicity of harmful dinoflagellate Karenia mikimotoi in response to ocean acidification (OA) under two different phosphate concentrations. Cells were previously acclimated in OA (pH = 7.8 and CO2 = 1100 μatm) condition for about three months before testing the responses of K. mikimotoi cells to a two-factorial combinations experimentation. This work measured the variation in physiological parameters (growth, rETR) and toxicity (hemolytic activity and its toxicity to zebrafish embryos) in four treatments, representing two factorial combinations of CO2 (450 and 1100 μatm) and phosphate concentration (37.75 and 4.67 umol l−1). Results: OA stimulated the faster growth, and the highest rETRmax in high phosphate (HP) treatment, low phosphate (LP) and a combination of high CO2 and low phosphate (HC*LP) inhibited the growth and Ek in comparison to low CO2*high phosphate (LCHP) treatment. The embryotoxicity of K. mikimotoi cells enhanced in all high CO2 (HC) conditions irrespective of phosphate concentration, but the EC50 of hemolytic activity increased in all high CO2 (HC) and low phosphate (LP) treatments in comparison of LCHP. Ocean acidification (high CO2 and lower pH) was probably the main factor that affected the rETRmax, hemolytic activity and embryotoxicity, but low phosphate was the main factor that affected the growth, α, and Ek. There were significant interactive effects of OA and low phosphate (LP) on growth, rETRmax, and hemolytic activity, but there were no significant effects on α, Ek, and embryotoxicity. If these results are extrapolated to the aquatic environment, it can be hypothesized that the K. mikimotoi cells were impacted significantly by future changing ocean (e.g., ocean acidification and nutrient stoichiometry).
Continue reading ‘Effects of ocean acidification and phosphate limitation on physiology and toxicity of the dinoflagellate Karenia mikimotoi’

Effect of ocean acidification on the nutritional quality of marine phytoplankton for copepod reproduction

Phytoplankton are the oceans’ principal source of polyunsaturated fatty acids that support the growth and reproduction of consumers such as copepods. Previous studies have demonstrated ocean acidification (OA) can change the availability of polyunsaturated fatty acids to consumer diets which may affect consumer reproduction. Two laboratory experiments were conducted to examine the effects of feeding high-pCO2-reared phytoplankton on copepod egg production, hatching success, and naupliar survival. Marine phytoplankton Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans, and Isochrysis galbana were exponentially grown in semi-continuous cultures at present (control) (400 ppm CO2, pH~8.1) and future (1,000 ppm CO2, pH~7.8) conditions and provided to Acartia tonsa copepods over 4 consecutive days as either nitrogen-limited (Exp. I) or nitrogen-depleted (Exp. II) mixed assemblage of phytoplankton. The composition of FAs in the phytoplankton diet was affected by pCO2 concentration and nitrogen deficiency; the ratio of essential fatty acids to total polyunsaturated fatty acids decreased in phytoplankton grown under high pCO2 and the mass of total fatty acids increased under nitrogen depletion. Additionally, total concentrations of essential fatty acids and polyunsaturated fatty acids in the diet mixtures were less under the high-pCO2 compared to the control-pCO2 treatments. Median egg production, hatching success, and naupliar survival were 48–52%, 4–87%, and 9–100% lower, respectively, in females fed high-pCO2 than females fed low-pCO2 phytoplankton, but this decrease in reproductive success was less severe when fed N-depleted, but fatty acid-rich cells. This study demonstrates that the effects of OA on the nutritional quality of phytoplankton (i.e., their cellular fatty acid composition and quota) were modified by the level of nitrogen deficiency and the resulting negative reproductive response of marine primary consumers.

Continue reading ‘Effect of ocean acidification on the nutritional quality of marine phytoplankton for copepod reproduction’


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