Posts Tagged 'algae'

Habitat effects of macrophytes and shell on carbonate chemistry and juvenile clam recruitment, survival, and growth

Highlights

• Field experiment testing two substrate treatments as OA adaptation strategies
• Clam growth increased in absence of macrophytes, regardless of shell hash treatment.
• Neither treatment improved clam recruitment or survival.
• pH in water column was higher during the day and outside eelgrass beds.
• Added shell hash improved carbonate chemistry in sediment pore-water.

Abstract

Adverse habitat conditions associated with reduced seawater pH often, but not always, negatively affect bivalves in early life history phases. Improving our understanding of how habitat-specific parameters affect clam recruitment, survival, and growth could assist natural resource managers and researchers in developing appropriate adaptation strategies for increasingly acidified nearshore ecosystems. Two proposed adaptation strategies, the presence of macrophytes and addition of shell hash, have the potential to raise local seawater pH and aragonite saturation state and, therefore, to improve conditions for shell-forming organisms. This field study examined the effects of these two substrate treatments on biological and geochemical response variables. Specifically, we measured (1) recruitment, survival, and growth of juvenile clams (Ruditapes philippinarum) and (2) local water chemistry at Fidalgo Bay and Skokomish Delta, Washington, USA, in response to experimental manipulations. Results showed no effect of macrophyte or shell hash treatment on recruitment or survival of R. philippinarum. Contrary to expectations, clam growth was significantly greater in the absence of macrophytes, regardless of the presence or absence of shell hash. Water column pH was higher outside the macrophyte bed than inside at Skokomish Delta and higher during the day than at night at Fidalgo Bay. Additionally, pore-water pH and aragonite saturation state were higher in the absence of macrophytes and the presence of shell. Based on these results, we propose that with increasingly corrosive conditions shell hash may help provide chemical refugia under future ocean conditions. Thus, we suggest adaptation strategies target the use of shell hash and avoidance of macrophytes to improve carbonate chemistry conditions and promote clam recruitment, survival, and growth.

Continue reading ‘Habitat effects of macrophytes and shell on carbonate chemistry and juvenile clam recruitment, survival, and growth’

The effects of nutrient addition and ocean acidification on tropical crustose coralline algae

As the global population increases, the occurrence of multiple anthropogenic
impacts on valuable coastal ecosystems, such as coral reefs, also increases. These
stressors can be global and long-term, like ocean acidification (OA), or local and short term, like nutrient runoff in some areas. The combination of these stressors can  potentially have additive or interactive effects on the organisms in coral reef
communities. Among the most important groups of organisms on coral reefs are crustose coralline algae (CCA), calcifying algae that cement the reef together and contribute to the global carbon cycle. This thesis studied the effects of nutrient addition and OA on Lithophyllum kotschyanum, a common species of CCA on the fringing reefs of Mo’orea, French Polynesia. Two mesocosm experiments tested the individual and interactive effects of OA and short-term nitrate and phosphate addition on L. kotschyanum. These experiments showed that nitrate and phosphate addition together increased photosynthesis, OA had interactive effects with nutrient addition, and after nutrient addition ended, calcification and photosynthetic rates changed in unpredictable ways in different OA and nutrient treatments. Because the results of the first two experiments showed impacts of nutrients even after addition stopped, two more mesocosm experiments were conducted to study the changes in photosynthesis and calcification over hourly time scales more relevant to a single nutrient pulse event. These two experiments revealed the existence of diurnal variation in light-saturated photosynthetic rate, but not calcification rate, under ambient and elevated pCO2. This pattern of increased maximum photosynthesis in the middle of the day can have important implications for how the time of nutrient runoff events during the day impacts CCA physiology. Finally, a field experiment was conducted to determine the effects of short- and long-term nutrient addition on L. kotschyanum. The results showed that a series of short-term nutrient additions did not increase photosynthesis or calcification rates above those in ambient nutrient conditions, but continual nutrient enrichment for 6 weeks increased photosynthetic rates. This increase in photosynthesis under only long-term enrichment shows the need for consideration of specific nutrient addition scenarios on coral reefs when predicting how the community will be affected.

Continue reading ‘The effects of nutrient addition and ocean acidification on tropical crustose coralline algae’

Resistance of corals and coralline algae to ocean acidification: physiological control of calcification under natural pH variability

Ocean acidification is a threat to the continued accretion of coral reefs, though some undergo daily fluctuations in pH exceeding declines predicted by 2100. We test whether exposure to greater pH variability enhances resistance to ocean acidification for the coral Goniopora sp. and coralline alga Hydrolithon reinboldii from two sites: one with low pH variability (less than 0.15 units daily; Shell Island) and a site with high pH variability (up to 1.4 pH units daily; Tallon Island). We grew populations of both species for more than 100 days under a combination of differing pH variability (high/low) and means (ambient pH 8.05/ocean acidification pH 7.65). Calcification rates of Goniopora sp. were unaffected by the examined variables. Calcification rates of H. reinboldii were significantly faster in Tallon than in Shell Island individuals, and Tallon Island individuals calcified faster in the high variability pH 8.05 treatment compared with all others. Geochemical proxies for carbonate chemistry within the calcifying fluid (cf) of both species indicated that only mean seawater pH influenced pHcf. pH treatments had no effect on proxies for Ωcf. These limited responses to extreme pH treatments demonstrate that some calcifying taxa may be capable of maintaining constant rates of calcification under ocean acidification by actively modifying Ωcf.

Continue reading ‘Resistance of corals and coralline algae to ocean acidification: physiological control of calcification under natural pH variability’

Assessing the effects of climate change on Baltic Sea macroalgae – implications for the foundation species Fucus vesiculosus L.

Marine macroalgae are important foundation species on rocky shores. The large, habitat-forming species, in particular support a variety of associated flora and fauna. The Baltic Sea is naturally species-poor due to brackish water, and perennial, large macroalgae such as Fucus vesiculosus have high ecological importance and are characterized as foundation species in hard substrate bottoms. In the Baltic Sea, climate change has been predicted to result in elevated seawater temperatures, declining salinity, caused by increases in rainfall, coastal eutrophication and ocean acidification (OA). These changes may be harmful for macroalgae either directly or through interacting effects. This thesis investigates the potential effects of climate change on the Baltic macroalgae, focusing on the foundation species Fucus vesiculosus.

Continue reading ‘Assessing the effects of climate change on Baltic Sea macroalgae – implications for the foundation species Fucus vesiculosus L.’

Oysters and eelgrass: potential partners in a high pCO2 ocean

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO(2) exposures. In Phase I, each species was cultured alone or in co-culture at 12 degrees C across ambient, medium, and high pCO(2) conditions, (656, 1,158 and 1,606 mu atm pCO(2), respectively). Under high pCO(2), eelgrass grew faster and had less severe EWD (contracted in the field prior to the experiment). Co-culture with oysters also reduced the severity of EWD. While the presence of eelgrass decreased daytime pCO(2), this reduction was not substantial enough to ameliorate the negative impact of high pCO(2) on oyster mass. In Phase II, eelgrass alone or oysters and eelgrass in co-culture were held at 15 degrees C under ambient and high pCO(2) conditions, (488 and 2,013atm pCO(2), respectively). Half of the replicates were challenged with cultured LZ. Concentrations of defensive compounds in eelgrass (total phenolics and tannins), were altered by LZ exposure and pCO(2) treatments. Greater pathogen loads and increased EWD severity were detected in LZ exposed eelgrass ramets; EWD severity was reduced at high relative to low pCO(2). Oyster presence did not influence pathogen load or EWD severity; high LZ concentrations in experimental treatments may have masked the effect of this treatment. Collectively, these results indicate that, when exposed to natural concentrations of LZ under high pCO(2) conditions, eelgrass can benefit from co-culture with oysters. Further experimentation is necessary to quantify how oysters may benefit from co-culture with eelgrass, examine these interactions in the field and quantify context-dependency.

Continue reading ‘Oysters and eelgrass: potential partners in a high pCO2 ocean’

Physiological responses of the Mediterranean subtidal alga Peyssonnelia squamaria to elevated CO2

The ecological consequences of ocean acidification are unclear due to varying physiological properties of macroalgae and species-specific responses. Therefore, in the present study, we used a laboratory culture experiment to analyse the eco-physiological responses of the Mediterranean subtidal red alga Peyssonnelia squamaria to CO2-induced lower pH. Our results showed an increase in the photosynthetic performance and growth rate of P. squamaria, despite the reduction in CaCO3 content in the low pH treatment. According to our results, we believe that samples exposed to elevated CO2 could be regulated own nitrogen metabolism to support increased growth rate and it may be down-regulated nitrate uptake. As a result, we hypothesize that P. squamaria may benefit from ocean acidification.

Continue reading ‘Physiological responses of the Mediterranean subtidal alga Peyssonnelia squamaria to elevated CO2’

Elevated temperature and changed carbonate chemistry: effects on calcification, photosynthesis, and growth of Corallina officinalis (Corallinales, Rhodophyta)

Recent ecophysiological studies of coralline algae have highlighted the effects of several environmental concerns, such as acidification and warming of the world’s coastal oceans. Among these, elevated temperature might be the most critical environmental factor affecting rocky benthic communities, where coralline algae tend to dominate the habitat. This study was conducted to investigate changes in photosynthesis, calcification, and growth of the geniculate coralline alga Corallina officinalis after 7 d of acclimation to four temperature conditions (13, 18, 23, and 28°C). Calcification rates decreased with increasing temperature in the light, although growth of C. officinalis did not differ considerably under different temperatures. Furthermore, although photosynthesis was largely unaffected by increasing temperature, respiration increased significantly under the highest temperature. These physiological responses are strongly related to the carbonate chemistry of seawater, which is itself affected by elevated temperature. Our results also indicate that C. officinalis exhibits physiological tolerance to a wide range of temperatures, even when increased by more than 10°C above ambient temperature of 18°C. Consequently, if noncalcareous macroalgae are negatively affected by higher temperatures, the ability of C. officinalis to acclimate to these conditions could cause it to become a more dominant species of rocky macroalgal habitats as ocean temperatures continue to rise.

Continue reading ‘Elevated temperature and changed carbonate chemistry: effects on calcification, photosynthesis, and growth of Corallina officinalis (Corallinales, Rhodophyta)’


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Ocean acidification in the IPCC AR5 WG II

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