Seasonal variability of the carbonate system and coccolithophore Emiliania huxleyi at a Scottish Coastal Observatory monitoring site

Abstract

Lack of information about carbonate chemistry in inshore waters is a 'knowledge gap' in assessing the impacts of changing carbonate chemistry on the marine environment. Assessing the response of calcifying phytoplankton to this changing carbonate chemistry requires a greater understanding of temporal variation. This study provides a description of the variability of carbonate parameters at a monitoring site in the eastern coast of Scotland. Fouryears of monthly data were analysed to assess the diversity, abundance and morphometrics of coccolithophores in relation to carbonate chemistry and environmental variables. The seasonality in carbonate parameters reflected the seasonal cycle in phytoplankton activity, with higher total alkalinity concentrations and pH and lower dissolved inorganic carbon concentrations during the growing season. The dominant coccolithophore at the site was Emiliania huxleyi which showed a clear seasonal pattern, being more abundant in midsummer when warmer and nutrient-depleted conditions restricted the annual diatom bloom. This study revealed the presence of three morphotypes of E. huxleyi, type A, type A overcalcified (type AO) and type B, which were seasonally distributed throughout the year. The less calcified form was mainly observed in spring while heavily calcified morphotypes overlapped during summer. Autumn and winter months were dominated by the most calcified form (type AO). These results indicate that the seasonal pattern of E. huxleyi morphotypes was not related to the carbonate concentration at the site. This study reflects the strong interannual variability in carbonate chemistry and the complexity associated with coccolithophore calcification, and highlights the need of long-term data to understand the potential impact of ocean acidification on calcifying phytoplankton. 2.5. Chlorophyll Water samples for chlorophyll and coccolithophore analysis were collected using a 10 m Lund tube, providing an integrated sample of the upper 10 m of the water column. Depending on the time of year, a sample volume of 500 mL to 2 L was filtered through a Whatman GF/F 47 mm filter paper (0.7 µm retention), using a vacuum of approximately 380 mmHg to avoid damaging the cells. The samples were stored at-80 ºC until analysis. Chlorophyll

Coccolith mass and morphology of different Emiliania huxleyi morphotypes: A critical examination using Canary Islands material

“…These results are in contrast with studies that have relied on SEM imaging and an a priori assumption of coccolith mass differences between morphotypes to make inferences on the impacts of ocean acidification on E. huxleyi calcite production (e.g. [32,33,37]). These studies solely rely on the distal shield appearance of morphotypes to make inferences about relative coccolith mass differences between different morphotypes, but other aspects of the coccolith also appear to be significant.…”

“…Different E. huxleyi morphotypes display environmental preferences over both seasonal (e.g. [33,37]) and regional (e.g. [8,15,32,[38][39][40]) gradients, and might furthermore differ in their sensitivity to ocean acidification [41].…”

Full annual monitoring of Subantarctic Emiliania huxleyi populations reveals highly calcified morphotypes in high-CO2 winter conditions

“…Since laboratory manipulations suggest that that the annual amplitude carbonate system parameters in the SAZ is too low to induce a marked change in the physiological rates of E. huxleyi morphotypes 28 , we speculate that the cumulative effect of changes on several environmental drivers 30,72 is the most probable cause of the seasonal variation in morphotypes. Moreover, our results add to the findings of previous studies in the Northern Hemisphere that reported a similar seasonal preference of heavily calcified E. huxleyi forms for high surface water pCO 2 and low pH and Ωcalcite during winter 51,61,62 . All these studies together challenge the notion that the ongoing global ocean acidification will be detrimental for heavily-calcified coccolithophores 26 while emphasizing the seasonal and spatial dominance of the weakly calcified B/C morphotype in the Southern Ocean.…”

Relationship between shell integrity of pelagic gastropods and carbonate chemistry parameters at a Scottish Coastal Observatory monitoring site

“…Initially most studies investigating the impacts of OA on calcifying plankton focused on coccolithophores (single-celled phytoplankton) with mixed results (Meyer and Riebesell, 2015) and most field studies showing no relationship between carbonate parameters and coccolithophore calcification (Smith et al, 2012;Marañó n et al, 2016;Leó n et al, 2018;among others). In contrast, in comparison to coccolithophores, other planktonic calcifying groups of ecological significance have received less attention (Doney et al, 2009).…”

“…The latter are crucial to determine OA long-term trends and to distinguish between natural variability and anthropogenic forcing (Ostle et al, 2016). In this context, the Scottish Coastal Observatory (SCObs) monitoring site at Stonehaven is providing baseline information about the seasonality and interannual variability of carbonate parameters, along with temperature, salinity, nutrients, and plankton community in inshore waters in the western part of the northern North Sea (Bresnan et al, 2016;Leó n et al, 2018).…”