Posts Tagged 'community composition'

Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system

Highlights

• Phytoplankton showed higher resilience to increasing CO2.

• Few centric diatoms showed positive response to increasing CO2 supply.

• Addition of Zn under increasing CO2 inhibited cell division, but not biomass.

• The combined effects of increasing CO2 and Cu addition was insignificant on growth.

• Cu addition at high CO2 level promoted toxigenic pennate diatom growth.

Abstract

Increasing dissolution of CO2 in the surface ocean is rapidly decreasing its pH and changing carbon chemistry which is further affecting marine biota in several ways. Phytoplankton response studies under the combination of elevated CO2 and trace metals are rare. We have conducted two consecutive onboard incubation experiments (R. V. Sindhu Sadhana; August 2017) in the eastern Arabian Sea (SW coast of India) during an upwelling event. A nutrient enriched diatom bloom was initiated onboard and grown under ambient (≈400 μatm, A-CO2) and high CO2 levels (≈1000 μatm; H–CO2) with different zinc (Zn; 1 nM) and copper (Cu) concentrations (1 nM, 2 nM and 8 nM). Phytoplankton community composition and the dominant genera were different during these two experiments. CO2 enrichment alone did not show any significant growth stimulating impact on the experimental community except enhanced cell density in the first experiment. Addition of Zn at A-CO2 level revealed no noticeable responses; whereas, the same treatment under H–CO2 level significantly reduced cell number. Considerably high protein content under H–CO2+Zn treatment was possibly counteracting Zn toxicity which also caused slower growth rate. Cu addition did not show any noticeable impact on growth and biomass production except increased protein content as well as decreased carbohydrate: protein ratio. This can be attributed to relatively higher protein synthesis than carbohydrate to alleviate oxidative stress generated by Cu. The centric diatom Chaetoceros and toxin producing pennate diatom Pseudo-nitzschias howed no significant response to either CO2 or Zn enrichment. Large centric diatom Leptocylindrus and Skeletonema responded positively to Zn addition in both CO2 levels. The former species showed the most sensitive response at the highest Cu and H–CO2 treatment; whereas, the pennate diatoms Nitzschia and Pseudo-nitzschia (toxigenic diatom) showed higher resilience under elevated CO2 and Cu levels. This observation indicated that in future ocean, increasing CO2 concentrations and trace metal pollution may potentially alter phytoplankton community structure and may facilitate toxigenic diatom bloom in the coastal waters.

Continue reading ‘Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system’

Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification

Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remain poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioural plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam’s feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most probably due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioural changes of key species.

Continue reading ‘Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification’

Influence of hydro-hydrochemical factors on the biodiversity of phytoplankton in the coastal aquatoria Black Sea with enhanced anthropogenous pollution (in Russian)

The distribution of most phytoplankton representatives is significantly influenced by various hydrological and hydrochemical environmental factors. Degree of development of phytoplankton communities and their species composition can determine the level of pollution of sea water by various nutrients.

A survey was made of the coastal waters of the Black Sea, with in-creased anthropogenic pollution at 15 stations in winter period. At these stations, temperature, pH, and DOM concentration were registered and the composition of microalgae and phytoplankton cyanobacteria was studied.

The results obtained in the analysis of hydrological, hydrochemical and algological data make it possible to speak about the pronounced discreteness of abiotic environmental factors and the distribution of various phytoplankton representatives at 15 stations studied. The thermohaline structure in the water area was characterized by a pronounced temperature inversion in the cutaway part. The pH on the sea surface everywhere corresponded to its natural rate. A high degree of pollution of the waters of the entire investigated area by dissolved organic matter was noted. Using the methods of laboratory cultivation of samples, it was possible to identify the cyanobacteria component in the phytoplankton. The active development of cyanobacteria was revealed precisely at that point in the water area (station No. 8), where the local maximum of DOM content was observed. The presence in two samples (No. 13 and No. 16) of alkaliphilic cyanobacteria of the genus Rhabdodermain probably indicates a tendency for alkalization of water due to eutrophication. At stations No. 7 and No. 9, favorable conditions were established for the development of diatom algae, and at station No. 18, for unicellular green forms. In the remaining areas, the poor composition of phytoplankton largely corresponded to the data we obtained in the water area for the previous two years.

Continue reading ‘Influence of hydro-hydrochemical factors on the biodiversity of phytoplankton in the coastal aquatoria Black Sea with enhanced anthropogenous pollution (in Russian)’

Diatoms dominate and alter marine food-webs when CO2 rises

Diatoms are so important in ocean food-webs that any human induced changes in their abundance could have major effects on the ecology of our seas. The large chain-forming diatom Biddulphia biddulphiana greatly increases in abundance as pCO2 increases along natural seawater CO2 gradients in the north Pacific Ocean. In areas with reference levels of pCO2, it was hard to find, but as seawater carbon dioxide levels rose, it replaced seaweeds and became the main habitat-forming species on the seabed. This diatom algal turf supported a marine invertebrate community that was much less diverse and completely differed from the benthic communities found at present-day levels of pCO2. Seawater CO2 enrichment stimulated the growth and photosynthetic efficiency of benthic diatoms, but reduced the abundance of calcified grazers such as gastropods and sea urchins. These observations suggest that ocean acidification will shift photic zone community composition so that coastal food-web structure and ecosystem function are homogenised, simplified, and more strongly affected by seasonal algal blooms.

Continue reading ‘Diatoms dominate and alter marine food-webs when CO2 rises’

The effect of elevated CO2 on the production and respiration of a Sargassum thunbergii community: a mesocosm study

Approximately one‐third of anthropogenic carbon dioxide is absorbed into the ocean and causes it to become more acidic. The Intergovernmental Panel on Climate Change (IPCC) suggested that the surface ocean pH, by the year 2100, would drop by a further 0.3 and 0.4 pH units under RCP (Representative Concentration Pathway) 6.0 and 8.5 climate scenarios. The macroalgae communities that consisted of Sargassum thunbergii and naturally attached epibionts were exposed to fluctuations of ambient and manipulated pH (0.3–0.4 units below ambient pH). The production and respiration in S. thunbergii communities were calculated from dissolved oxygen time‐series recorded with optical dissolved oxygen sensors. The pH, irradiance, and dissolved oxygen occurred in parallel with diurnal (day/night) patterns. According to net mesocosm production – photosynthetically active radiation (PAR) model, the saturation and compensation PAR, the mean maximum gross mesocosm production (GMP), and daily mesocosm respiration were higher in the CO2 enrichment, than in the ambient condition, while the mean of photosynthetic coefficient was similar. In conclusion, elevated CO2 stimulated oxygen production and consumption of S. thunbergii communities in the mesocosm. Furthermore, the sensitivity of the GMP of the S. thunbergii community to irradiance was reduced, and achieved maximum production rate at higher PAR. These positive responses to CO2 enrichment suggest that S. thunbergii communities may thrive in under high CO2 conditions.

Continue reading ‘The effect of elevated CO2 on the production and respiration of a Sargassum thunbergii community: a mesocosm study’

Fish assemblages cope with ocean acidification in a shallow volcanic CO2 vent benefiting from an adjacent recovery area

Highlights

• pH played a role in shaping nekto-benthic fish assemblages.

• Fish diversity did not show unique spatial patterns or significant pH-relations.

• Species richness and abundance correlated with seagrass canopy, regardless of pH.

• Unexpected among-site similarity was found in the abundance of juveniles.

• The area close to low pH site seems to work as a recovery area for fish.

Abstract

Shallow CO2 vents are used to test ecological hypotheses about the effects of ocean acidification (OA). Here, we studied fish assemblages associated with Cymodocea nodosa meadows exposed to high pCO2/low pH conditions at a natural CO2 vent in the Mediterranean Sea. Using underwater visual census, we assessed fish community structure and biodiversity in a low pH site (close to the CO2 vent), a close control site and a far control site, hypothesising a decline in biodiversity and a homogenization of fish assemblages under OA conditions. Our findings revealed that fish diversity did not show a unique spatial pattern, or even significant relationships with pH, but correlated with seagrass leaf canopy. Among-site similarity was found in the abundance of juveniles, contrary to the expected impacts of OA on early life stages. However, pH seems an important driver in structuring fish assemblage in the low pH site, despite its high similarity with the close control site. This unexpected pattern may represent a combined response of fish mobility, enhanced food resources in the acidified site, and a ‘recovery area’ effect of the adjacent control site.

Continue reading ‘Fish assemblages cope with ocean acidification in a shallow volcanic CO2 vent benefiting from an adjacent recovery area’

Impacts of ocean acidification on hermit crab communities through contrasting responses of Pagurus filholi (de Man, 1887) and Clibanarius virescens (Krauss, 1843)

Ocean acidification (OA) is predicted to decrease the abundance of calcified organisms such as gastropods. Since hermit crabs utilize gastropod shell as mobile shelter, OA has indirect impacts on hermit crab population. To examine the impacts of OA on hermit crab communities, which use calcified shell as the mobile shelter, we conducted field surveys and laboratory experiments using volcanic CO2 seeps in Shikine Island, Japan. By comparing hermit crab community structures and shell availability among five intertidal rocky shores with different degrees of acidification, Paguroidea abundance and species richness were simplified in acidified areas. Rearing experiments comparing survival rates of two Paguroidea species, Pagurus filholi (de Man, 1887) and Clibanarius virescens (Krauss, 1843), at both adult and larval stages, between acidified and ambient aquaria revealed that acidified seawater reduced larval survival rate of C. virescens. Overall, the results indicated that the species-specific direct effect in elevated C. virescens larval mortality could simplify the Paguroidea species composition. In addition, such direct effect would also lead to reduction of Paguroidea abundance, along with indirect effects though a decrease in shell availability.

Continue reading ‘Impacts of ocean acidification on hermit crab communities through contrasting responses of Pagurus filholi (de Man, 1887) and Clibanarius virescens (Krauss, 1843)’


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Ocean acidification in the IPCC AR5 WG II

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