Posts Tagged 'echinoderms'

The effects of ocean warming and acidification on seaweed growth and urchin grazing

Human produced carbon dioxide concentrations in the atmosphere are currently higher than previously recorded and are continuing to rise at alarming rates. This greenhouse gas is the primary driver for changing climate scenarios highlighted by an approximate 1°C increase in sea surface temperatures. In addition to driving global warming, CO2 is readily absorbed by the oceans, resulting in changes in seawater chemistry and a decrease in seawater pH (acidification). The singular effects of ocean warming and acidification are known to impact marine organisms; lesser known, however, are the combined effects of these stressors, particularly on biotic interactions. This study aimed to expand on the knowledge of how these abiotic stressors affect seaweed and seaweed-herbivore interactions by comparing seaweed growth and herbivore feeding rate and selectivity under combinations of current and modelled future temperature (18°C and 21°C) and pH (8.1 and 7.8) conditions. Growth rates of two seaweed species, a calcified red alga (Lithothrix aspergillum) and a non-calcified brown alga (giant kelp Macrocystis pyrifera), were compared among manipulated seawater conditions. In addition, the feeding rates and feeding selectivity of a common sea urchin herbivore (Strongylocentrotus purpuratus) for these two seaweeds were compared among water conditions. Lithothrix was not affected by the singular effects of pH or temperature but under combined future temperature and pH conditions, the seaweed performed poorly. While acidification is known to affect the ability of calcifying species to deposit calcium carbonate, Lithothrix appeared to only be impacted by acidification under temperature stress. Macrocystis, on the other hand, performed significantly better under future acidic conditions, regardless of temperature, as it likely experienced an increase in photosynthetic rate driven by high CO2 concentrations. Urchin herbivory rates were elevated for both seaweeds grown under acidification scenarios, possibly due to increased grazing susceptibility of Lithothrix during poor calcification/decalcification conditions and Macrocystis during new growth conditions. Feeding preference trials were inconsistent with feeding rate patterns as urchins exhibited low overall consumption and no selectivity for either seaweed under any water condition. Although the impacts of warming and acidification on growth of seaweeds and susceptibility to grazing by urchins are variable among taxa, potential future stressors are likely to alter seaweed population and seaweed-herbivore dynamics.

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Species interactions can shift the response of a maerl bed community to ocean acidification and warming

Predicted ocean acidification and warming are likely to have major implications for marine organisms, especially marine calcifiers. However, little information is available on the response of marine communities as a whole to predicted changes. Here, we experimentally examined the combined effects of temperature and partial pressure of carbon dioxide (pCO2) increases on the response of maerl bed assemblages, composed of living and dead thalli of the free-living coralline alga Lithothamnion corallioides, epiphytic fleshy algae, and grazer species. Two three-month experiments were performed in the winter and summer seasons in mesocosms with four different combinations of pCO2 (ambient and high pCO2) and temperature (ambient and +3 °C). The response of maerl assemblages was assessed using metabolic measurements at the species and assemblage scales. Gross primary production and respiration of assemblages were enhanced by high pCO2 conditions in the summer. This positive effect was attributed to the increase in epiphyte biomass, which benefited from higher CO2 concentrations for growth and primary production. Conversely, high pCO2 drastically decreased the calcification rates in assemblages. This response can be attributed to the decline in calcification rates of living L. corallioides due to acidification as well as increased dissolution of dead L. corallioides. Future changes in pCO2 and temperature are likely to promote the development of non-calcifying algae to the detriment of the engineer species L. corallioides. The development of fleshy algae may be modulated by the ability of grazers to regulate epiphyte growth. However, our results suggest that predicted changes will negatively affect the metabolism of grazers and potentially their ability to control epiphyte abundance. Here, we demonstrate that the response of marine communities to climate change will depend on the direct effects on species physiology and the indirect effects due to shifts in species interactions. This double, interdependent response underlines the importance of examining community-level processes, which integrate species interactions, to better understand the impact of global change on marine ecosystems.

Continue reading ‘Species interactions can shift the response of a maerl bed community to ocean acidification and warming’

Indirect effects of ocean acidification drive feeding and growth of juvenile crown-of-thorns starfish, Acanthaster planci

The indirect effects of changing climate in modulating trophic interactions can be as important as the direct effects of climate stressors on consumers. The success of the herbivorous juvenile stage of the crown-of-thorns starfish (COTS), Acanthaster planci, may be affected by the impacts of ocean conditions on its crustose coralline algal (CCA) food. To partition the direct effects of near future ocean acidification on juvenile COTS and indirect effects through changes in their CCA food, COTS were grown in three pHT levels (7.9, 7.8, 7.6) and fed CCA grown at similar pH levels. Consumption of CCA by COTS was bolstered when the COTS were grown in low pH and when they were fed CCA grown in low pH regardless of the pH in which the COTS were reared. COTS fed CCA grown at pH 7.6 grew fastest, but the pH/pCO2 that the COTS were reared in had no direct effect on growth. Ocean acidification conditions decreased the C : N ratio and carbonate levels in the CCA. Bolstered growth in COTS may be driven by enhanced palatability, increased nutritive state and reduced defences of their CCA food. These results indicate that near future acidification will increase the success of early juvenile COTS and boost recruitment into the coral-eating life stage.

Continue reading ‘Indirect effects of ocean acidification drive feeding and growth of juvenile crown-of-thorns starfish, Acanthaster planci’

Comparative evaluation of sea-urchin larval stage sensitivity to ocean acidification

Changes in the marine carbonate system may affect various calcifying organisms. This study is aimed to compare the sensitivity of embryo-larval development of two species of sea urchins (Paracentrutos lividus and Lytechinus variegatus) collected and exposed to samples from different coastal zone (Spain and Brazil) to ocean acidification. The results showed that the larval stages are very sensitive to small changes in the seawater’s pH. The larvae from P. lividus species showed to be more sensitive to acidified elutriate sediments than larvae from L. variegatus sea urchin. Furthermore, this study has demonstrated that the CO2 enrichment in aquatic ecosystems cause changes on the mobility of the metals: Zn, Cu, Fe, Al and As, which was presented different behavior among them. Although an increase on the mobility of metals was found, the results using the principal component analysis showed that the pH reduction show the highest correlations with the toxicity and is the main cause of embryo-larval development inhibition. In this comparative study it is demonstrated that both species are able to assess potential effects of the ocean acidification related to CO2 enrichment by both near future scenarios and the risk associated with CO2 leakages in the Carbon Capture and Storage (CCS) process, and the importance of comparative studies in different zones to improve the understanding of the impacts caused by ocean acidification.

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Effects of ocean acidification on growth rate, calcified tissue, and behavior of the juvenile ochre sea star, Pisaster ochraceus

Anthropogenically-induced increases in the acidity of the ocean have the potential to seriously harm marine calcifying organisms by decreasing the availability of carbonate (CO32−) used to make shells. I tested the effects of lowered pH on juvenile Pisaster ochraceus, an intertidal sea star and keystone predator in the eastern Pacific Ocean. Populations of P. ochraceus were greatly reduced by outbreaks of sea star wasting disease, which has the potential to alter community structure and lower biodiversity in the intertidal region. However, large numbers of juvenile P. ochraceus have recruited to the rocky intertidal and their ability to persist will be important for the recovery of P. ochraceus populations. To test the effects of pH, I studied the growth rate, calcification, righting time, and movement and prey-sensing ability in the PISCO laboratory mesocosm at Hatfield Marine Science Center. The results of the experiments showed non-significant trends towards a negative effect of pH on growth rate and righting time. Few studies have been done on the effects of pH on sea stars and the results are highly species-specific. Additional research is needed clarify and make accurate predictions about the effects of pH on juvenile P. ochraceus.

Continue reading ‘Effects of ocean acidification on growth rate, calcified tissue, and behavior of the juvenile ochre sea star, Pisaster ochraceus’

Effects of CO2, pH and temperature on respiration and regeneration in the burrowing brittle stars Hemipholis cordifera and Microphiopholis gracillima

Hemipholis cordifera and Microphiopholis gracillima are burrowing brittlestars that differ in burrow architecture and oxygen obtaining strategies: M. gracillima actively ventilates a gallery while H. cordifera has a simple chamber and instead relies on oxygen being transported from arms exposed to the overlying water using hemoglobin in its water vascular system. To determine the possible effects of near future climate change on both species, in terms of metabolism and regeneration, they were exposed to current (25 °C & 28 °C) and elevated (32 °C) temperatures, as well as normal (8.1) and hypercapnia/lowered pH (7.8 & 7.6) in all combinations for six weeks. Oxygen uptake was measured weekly during this period. As expected, M. gracillima had a higher overall oxygen uptake rate than H. cordifera. Both species had highly variable oxygen uptake and were significantly affected by the week was measured. H. cordifera experienced increased oxygen uptake at the higher temperature (32 °C) and as a result of interactive effects of time and pH 7.6. Both species experienced interactive effects of pH and temperature, but there was no clear pattern. Increased temperature positively affected arm regeneration in H. cordifera, increasing both length and percent recovery. There were no effects on disc regeneration observed in M gracillima, however lower pH decreased the dry weight in both intact and regenerating animals. Calcification, measured as percent inorganic content, was not affected in either species by regeneration, temperature or pH. Despite the minor effects on its physiology, M. gracillima experienced lower percent survivorship than H. cordifera. Temperature had the most effect, with survivorship higher at 28 °C, than at 25 °C or 32 °C. These results indicate that both species are operating near or at their physiological limits and may be unable to cope with future drastic changes.

Continue reading ‘Effects of CO2, pH and temperature on respiration and regeneration in the burrowing brittle stars Hemipholis cordifera and Microphiopholis gracillima’

Ocean acidification impacts spine integrity but not regenerative capacity of spines and tube feet in adult sea urchins

Increasing atmospheric carbon dioxide (CO2) has resulted in a change in seawater chemistry and lowering of pH, referred to as ocean acidification. Understanding how different organisms and processes respond to ocean acidification is vital to predict how marine ecosystems will be altered under future scenarios of continued environmental change. Regenerative processes involving biomineralization in marine calcifiers such as sea urchins are predicted to be especially vulnerable. In this study, the effect of ocean acidification on regeneration of external appendages (spines and tube feet) was investigated in the sea urchin Lytechinus variegatus exposed to ambient (546 µatm), intermediate (1027 µatm) and high (1841 µatm) partial pressure of CO2 (pCO2) for eight weeks. The rate of regeneration was maintained in spines and tube feet throughout two periods of amputation and regrowth under conditions of elevated pCO2. Increased expression of several biomineralization-related genes indicated molecular compensatory mechanisms; however, the structural integrity of both regenerating and homeostatic spines was compromised in high pCO2 conditions. Indicators of physiological fitness (righting response, growth rate, coelomocyte concentration and composition) were not affected by increasing pCO2, but compromised spine integrity is likely to have negative consequences for defence capabilities and therefore survival of these ecologically and economically important organisms.

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Ocean acidification in the IPCC AR5 WG II

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