The impact of physical processes on primary and secondary production in temperate shelf seas

The shelf seas account for only 9% of the surface area of the global ocean, yet are estimated to be responsible for 16% of global primary productivity and 47% of global annual carbon export. While the importance of these seas in the marine carbon cycle is well-recognised, the relationship between the physical environment and the magnitude and fate of biological production is still largely undetermined. Using a range of approaches, this project examined the relationship between physical processes and biological carbon flow over various time and space scales in a temperate shelf sea. Autonomous high-resolution sensor surveys in Liverpool Bay and the Irish Sea reveal that this region is net autotrophic on an annual scale with estimates of regional net community production rates based on oxygen mass balance ranging from 1.3 to 4.2 mol C m-2 y-1. The highest NCP rates were measured in a Region Of Freshwater Influence (Liverpool Bay). Ship-based sampling in the Celtic Sea illustrated the influence of water column structure on rates of primary and bacterial production and community structure. The highest rates of primary production were observed in the fully mixed water column (55.1 mmol C m-2 d-1). However, bacterial production rates were lowest at the mixed site (6.8 mmol C m-2 d-1). In contrast, primary production and bacterial production at the seasonally stratified sites and shelf break were comparable (34.8 mmol C m-2 d-1 and 37.2 mmol C m-2 d-1 respectively, and 12.9 and 12.9 mmol C m-2 d-1 respectively). The phytoplankton community was dominated by diatoms at the mixed site and dinoflagellates at the seasonally stratified sites, with both diatoms and dinoflagellates occurring at the shelf edge. Bacterial carbon demand at each site was estimated using published empirical relationships. However, at three out of the four sites examined, the estimated daily rate of total primary production was insufficient to meet the daily bacterial carbon demands, implying that either an external source of carbon was required or that the assumptions used during estimates of bacterial processing of carbon were incorrect. Finally, the definition of export production in shelf seas is examined in relation to the potential pathways of carbon flow on daily and seasonal timescales in shelf seas

Dinophysis spp. abundance and toxicity events in South Cornwall, U.K.: Interannual variability and environmental drivers at three coastal sites

Dinophysis is a genus of dinoflagellates with the potential to cause diarrhoeic Shellfish Poisoning (DSP) in humans. The lipophilic toxins produced by some species of Dinophysis spp. can accumulate within shellfish flesh even at low cell abundances, and this may result in the closure of a shellfish farm if toxins exceed the recommended upper limit. Over the period 2014 to 2020 inclusive there were several toxic events along the South West coast of U.K. related to Dinophysis spp. The Food Standards Agency (FSA) monitoring programme measure Dinophysis cell abundances and toxin concentration within shellfish flesh around the coasts of England and Wales, but there are few schemes routinely measuring the environmental parameters that may be important drivers for these Harmful Algal Blooms (HABs). This study uses retrospective data from the FSA monitoring at three sites on the south Cornwall coast as well as environmental data from some novel platforms such as coastal WaveRider buoys to investigate potential drivers and explore whether either blooms or toxic events at these sites can be predicted from environmental data. Wind direction was found to be important in determining whether a bloom develops at these sites, and low air temperature in June was associated with low toxicity in the shellfish flesh. Using real time data from local platforms may help shellfish farmers predict future toxic events and minimise financial loss.</p

Temporal variability of phytoplankton biomass and net community production in a macrotidal temperate estuary

Coastal zones play a significant role in Earth's biogeochemical processes. Within these regions, estuaries are particularly important due to their complex ecological interactions and spatial and temporal variability. The aim of this study was to apply a year long high-frequency (15 min) environmental data time series to identify both the timing and factors influencing phytoplankton blooms in the Southampton Water estuary. Dissolved oxygen measurements from an in situ deployed optode were applied to the open diel oxygen method to estimate daily integrated rates of gross primary production (GPP), ecosystem respiration (ER) and net community production (NCP). Additional water quality data including temperature, salinity, chlorophyll concentration and turbidity allowed the relationship between physical and biological processes occurring over different time scales to be investigated. The occurrence of major phytoplankton blooms during the spring-summer period were associated with critical values of estuarine water temperature and mean water column irradiance. In addition, neap tides were found to promote the initiation of phytoplankton blooms in late spring and summer months. Annual daily average NCP for the estuarine ecosystem presented an estimated net heterotrophic state (−0.8 mmol O2 m−2 d−1), although seasonal productivity events shifted this state for several days and sometimes weeks to net autotrophic conditions. The results of this study have demonstrated how high frequency in situ dissolved oxygen measurements from an optode can make a valuable contribution to understanding the key factors influencing bloom events in a temperate macrotidal estuary. This approach if applied more widely to other coastal sites could therefore contribute to consolidating global annual primary production budgets for coastal regions

Effects of temperature stress on ecological processes

Temperature is a fundamental determinant of chemical and biological rates, with profound influences on living systems at all levels of organization. Investigating how ocean temperature affects marine ecosystems is critical to understanding consequences of global climate change. This chapter describes influences of temperature on ecological processes from organism to community levels. Specifically we (i) outline global spatial and temporal temperature patterns and projected changes, (ii) examine direct and indirect influences of these temperature variations on marine organisms and consider resulting implications for ecological processes and species distributions, (iii) use examples from several habitats to demonstrate emergent consequences of temperature-driven changes in ecological processes for the structure and function of marine communities, and (iv) highlight the importance of interactions between temperature and other abiotic variables

The impact of rainfall events, catchment characteristics and estuarine processes on the export of dissolved organic matter from two lowland rivers and their shared estuary

Terrestrially-derived dissolved organic carbon (DOC) and nitrogen (DON) transported by rivers have been recognised as contributors to aquatic nutrient burdens, and can be of importance in rivers and estuaries already impacted by anthropogenic inorganic nutrient discharges. The concentration of DOC and DON and the flux of both to the estuary and ultimately the coastal zone is dependent upon many factors including rainfall, catchment land use, and biological processes. DOC and DON concentrations together with nitrate plus nitrite and ammonium concentrations were measured in the anthropogenically-impacted estuary Christchurch Harbour (UK) and at sites in the lower reaches of its two source rivers, the Hampshire Avon and the Stour, at weekly intervals for a year during which time several extreme rainfall events occurred. A series of transects along the estuary were also performed after weekly sampling was completed. DOC concentrations were correlated between both rivers and the estuary and were positively related to increases in river flow, but DON concentrations revealed a more complicated picture. Peak instantaneous fluxes of DOC and DON exceeded 60000 kg C d-1 and 7000 kg N d-1 respectively both in the Stour and the estuary during high flow periods. The sources of both and routes by which they enter the aquatic system may account for the differences in dynamics, with flushing of superficial soils being a key source of DOC and point sources such as sewage treatment works being proposed as sources of DON. Removal processes within the estuary were also of importance for DON concentrations while DOC behaved more conservatively with some evidence of local production within the estuary. Estimated annual loads of DON and DOC to the coastal zone from Christchurch Harbour were 118 kg N km-2 y-1 and 2296 kg C km-2 y-1

Short-term and seasonal variation in metabolic balance in Liverpool Bay

Regions of freshwater influence (ROFIs) are dynamic areas within the coastal seas that experience cycles of stability driven by density gradients and the spring-neap tidal cycle. As a result, pulses of biological production may occur on a more frequent timescale than the classic seasonal cycle. Net community production (NCP) rates and chlorophyll a concentration are presented from a site within the ROFI of Liverpool Bay and compared to similar measurements made at a site outside the ROFI during 2009. The influence of water column stability on biological production in the ROFI was also investigated using high-frequency observations from a Cefas Smartbuoy. Both sites were autotrophic from spring to autumn before becoming heterotrophic over winter. NCP at the inshore site was estimated to range from 30.8 to 50.4 gC m(-2) year(-1). A linear relationship detected between chlorophyll a and NCP from both sites was used to estimate metabolic balance over 1 year at the ROFI site using high-resolution chlorophyll a concentrations from the Smartbuoy but was found to poorly replicate NCP rates compared to those derived from dissolved oxygen fluxes. There was no clear biological response to periods of stratification within the ROFI, and it is proposed that changes in light attenuation in the Liverpool Bay ROFI, driven not only by stratification but also by fluctuations in riverine sediment load, most likely play an important role in controlling phytoplankton growth in this region