Primary producers may ameliorate impacts of daytime CO2 addition in a coastal marine ecosystem

Biological modification of coastal pH depends on community composition and time

Biological processes play important roles in determining how global changes manifest at local scales. Primary producers can absorb increased CO2 via daytime photosynthesis, modifying pH in aquatic ecosystems. Yet producers and consumers also increase CO2 via respiration. It is unclear whether biological modification of pH differs across the year, and, if so, what biotic and abiotic drivers underlie temporal differences. We addressed these questions using the intensive study of tide pool ecosystems in Alaska, USA, including quarterly surveys of 34 pools over 1 year and monthly surveys of five pools from spring to fall in a second year. We measured physical conditions, community composition, and changes in pH and dissolved oxygen during the day and night. We detected strong temporal patterns in pH dynamics. Our measurements indicate that pH modification varies spatially (between tide pools) and temporally (across months). This variation in pH dynamics mirrored changes in dissolved oxygen and was associated with community composition, including both relative abundance and diversity of benthic producers and consumers, whose role differed across the year, particularly at night. These results highlight the importance of the time of year when considering the ways that community composition influences pH conditions in aquatic ecosystems.

The functional effects of a dominant consumer are altered following the loss of a dominant producer

Human impacts on ecosystems are resulting in unprecedented rates of biodiversity loss worldwide. The loss of species results in the loss of the multiple roles that each species plays or functions (i.e., "ecosystem multifunctionality") that it provides. A more comprehensive understanding of the effects of species on ecosystem multifunctionality is necessary for assessing the ecological impacts of species loss. We studied the effects of two dominant intertidal species, a primary producer (the seaweed Neorhodomela oregona) and a consumer (the shellfish Mytilus trossulus), on 12 ecosystem functions in a coastal ecosystem, both in undisturbed tide pools and following the removal of the dominant producer. We modified analytical methods used in biodiversity-multifunctionality studies to investigate the potential effects of individual dominant species on ecosystem function. The effects of the two dominant species from different trophic levels tended to differ in directionality (+/-) consistently (92% of the time) across the 12 individual functions considered. Using averaging and multiple threshold approaches, we found that the dominant consumer-but not the dominant producer-was associated with ecosystem multifunctionality. Additionally, the relationship between abundance and multifunctionality differed depending on whether the dominant producer was present, with a negative relationship between the dominant consumer and ecosystem function with the dominant producer present compared to a non-significant, positive trend where the producer had been removed. Our findings suggest that interactions among dominant species can drive ecosystem function. The results of this study highlight the utility of methods previously used in biodiversity-focused research for studying functional contributions of individual species, as well as the importance of species abundance and identity in driving ecosystem multifunctionality, in the context of species loss.

Climate Change Amelioration by Marine Producers: Does Dominance Predict Impact?

AbstractClimate change threatens biodiversity worldwide, and assessing how those changes will impact communities will be critical for conservation. Dominant primary producers can alter local-scale environmental conditions, reducing temperature via shading and mitigating ocean acidification via photosynthesis, which could buffer communities from the impacts of climate change. We conducted two experiments on the coast of southeastern Alaska to assess the effects of a common seaweed species, Neorhodomela oregona, on temperature and pH in field tide pools and tide pool mesocosms. We found that N. oregona was numerically dominant in this system, covering >60% of habitable space in the pools and accounting for >40% of live cover. However, while N. oregona had a density-dependent effect on pH in isolated mesocosms, we did not find a consistent effect of N. oregona on either pH or water temperature in tide pools in the field. These results suggest that the amelioration of climate change impacts in immersed marine ecosystems by primary producers is not universal and likely depends on species' functional attributes, including photosynthetic rate and physical structure, in addition to abundance or dominance.

Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change

Coastal and intertidal habitats are at the forefront of anthropogenic influence and environmental change. The species occupying these habitats are adapted to a world of extremes, which may render them robust to the changing climate or more vulnerable if they are at their physiological limits. We characterized the diurnal, seasonal and interannual patterns of flux in biogeochemistry across an intertidal gradient on a temperate sandstone platform in eastern Australia over 6 years (2009-2015) and present a synthesis of our current understanding of this habitat in context with global change. We used rock pools as natural mesocosms to determine biogeochemistry dynamics and patterns of eco-stress experienced by resident biota. In situ measurements and discrete water samples were collected night and day during neap low tide events to capture diurnal biogeochemistry cycles. Calculation of pH_T using total alkalinity (TA) and dissolved inorganic carbon (DIC) revealed that the mid-intertidal habitat exhibited the greatest flux over the years (pH_T 7.52-8.87), and over a single tidal cycle (1.11 pH_T units), while the low-intertidal (pH_T 7.82-8.30) and subtidal (pH_T 7.87-8.30) were less variable. Temperature flux was also greatest in the mid-intertidal (8.0-34.5°C) and over a single tidal event (14°C range), as typical of temperate rocky shores. Mean TA and DIC increased at night and decreased during the day, with the most extreme conditions measured in the mid-intertidal owing to prolonged emersion periods. Temporal sampling revealed that net ecosystem calcification and production were highest during the day and lowest at night, particularly in the mid-intertidal. Characterization of biogeochemical fluctuations in a world of extremes demonstrates the variable conditions that intertidal biota routinely experience and highlight potential microhabitat-specific vulnerabilities and climate change refugia.

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

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-nitzschia showed 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.

Ocean change within shoreline communities: from biomechanics to behaviour and beyond

Humans are changing the physical properties of Earth. In marine systems, elevated carbon dioxide concentrations are driving notable shifts in temperature and seawater chemistry. Here, we consider consequences of such perturbations for organism biomechanics and linkages amongst species within communities. In particular, we examine case examples of altered morphologies and material properties, disrupted consumer-prey behaviours, and the potential for modulated positive (i.e. facilitative) interactions amongst taxa, as incurred through increasing ocean acidity and rising temperatures. We focus on intertidal rocky shores of temperate seas as model systems, acknowledging the longstanding role of these communities in deciphering ecological principles. Our survey illustrates the broad capacity for biomechanical and behavioural shifts in organisms to influence the ecology of a transforming world.