Rodney M. Forster

Review The changing irradiance environment: consequences for marine macrophyte physiology, productivity and ecology

Decreases in the concentration of ozone in the stratosphere are predicted to result in more biologically damaging ultraviolet-B radiation (UVBR) reaching the Earths surface in the near future. The consequences for plant life of this small change in the solar spectrum are currently uncertain; this is particularly true for aquatic macrophytic algae. The aim of this review is to summarize the current knowledge of UVBR effects on macrophytes, and to highlight areas for future research. An overview of published underwater UVBR measurements shows that penetration of this waveband is low in the coastal waters where most macroalgae are found. Knowledge of UVBR targets in macroalgae is poor, and biological weighting functions have yet to be established. Studies of higher plants and phytoplankton are used to illustrate the many possible targets and effects of UVBR. The role of photosynthetically active radiation in causing dynamic and chronic photoinhibition in macroalgae and the interactions of PAR with UVR are e...

The use of variable fluorescence measurements in aquatic ecosystems: differences between multiple and single turnover measuring protocols and suggested terminology

In this review, we briefly describe the two main techniques used to measure variable fluorescence in the aquatic environment, and show how the parameters derived from this technique can be used to estimate the rate of photosynthesis. The methods estimate the photochemical efficiency of photosystem II from ratios of fluorescence levels. Flashes of light that are transiently saturating for photochemistry (i.e. they are sufficiently bright to close all PSII reaction centres) are used to obtain the maximum fluorescence level. The type of saturating flash differs between methods. In one approach, single turnover (ST) flashes are applied. This allows only one charge separation during the flash and reduces only the primary acceptor of PS II, raising fluorescence to a level Fm(ST) . In a second approach the flashes are multiple turnover (MT), which allow repeated charge separation processes until all electron acceptors of PS II are reduced. A relaxation of quenching is induced by the longer flash, and this raises the maximum fluorescence to a higher level, Fm(MT) Application of the different approaches to an algal sample will result in differing Fm values and, as a result, different values for the photochemical efficiency of PS II, with the MT method giving higher values than ST. Several designs of equipment, based on MT or ST techniques, are available for use with phytoplankton or benthic algae. Both techniques measure variable fluorescence, but there are a number of important differences in the methods used to calculate photosynthetic rates. In our view, this necessitates the use of a different terminology in order to avoid confusion, until the underlying physiological differences are resolved. An example is given showing that combining terminology from the different approaches will result in calculation of erroneous photosynthetic electron transport rates.

Global-scale predictions of community and ecosystem properties from simple ecological theory.

We show how theoretical developments in macroecology, life-history theory and food-web ecology can be combined to formulate a simple model for predicting the potential biomass, production, size and trophic structure of consumer communities. The strength of our approach is that it uses remote sensing data to predict properties of consumer communities in environments that are challenging and expensive to sample directly. An application of the model to the marine environment on a global scale, using primary production and temperature estimates from satellite remote sensing as inputs, suggests that the global biomass of marine animals more than 10−5 g wet weight is 2.62×109 t (=8.16 g m−2 ocean) and production is 1.00×1010 t yr−1 (31.15 g m−2 yr−1). Based on the life-history theory, we propose and apply an approximation for distinguishing the relative contributions of different animal groups. Fish biomass and production, for example, are estimated as 8.99×108 t (2.80 g m−2) and 7.91×108 t yr−1 (2.46 g m−2 yr−1), respectively, and 50% of fish biomass is shown to occur in 17% of the total ocean area (8.22 g m−2). The analyses show that emerging ecological theory can be synthesized to set baselines for assessing human and climate impacts on global scales.

Daily course of photosynthesis and photoinhibition in Chondrus crispus (Rhodophyta) from different shore levels

Photoinhibition of photosynthesis in the red alga Chondrus crispus from different shore levels was investigated under laboratory and field conditions. The underwater light climate at Roscoff (French Atlantic coast), characterized by transmittance spectra, was shown to be intermediate between Jerlov coastal type 1 and oceanic type III. Chondrus crispus thalli were collected at four depths (3.5–8.5 m below high tide level) and exposed to daily courses of artificial and natural light. Filters were used to discriminate between the effects of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) under the photoinhibitory treatments. In the presence of natural UVR, photoinhibition at midday was increased by up to 60%. Recovery from photoinhibition was measured at different times throughout the light stress. Recovery kinetics differed between morning and early afternoon in all treatments, and were dependent on the light dose. Whereas biphasic kinetics were observed in all treatments in the mo...

Relationship of intertidal surface sediment chlorophyll concentration to hyperspectral reflectance and chlorophyll fluorescence

Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence, especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics. At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation, Fo15), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes; we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. Fo15 was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially for Fo15. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries.

Predicting the Electron Requirement for Carbon Fixation in Seas and Oceans

Marine phytoplankton account for about 50% of all global net primary productivity (NPP). Active fluorometry, mainly Fast Repetition Rate fluorometry (FRRf), has been advocated as means of providing high resolution estimates of NPP. However, not measuring CO2-fixation directly, FRRf instead provides photosynthetic quantum efficiency estimates from which electron transfer rates (ETR) and ultimately CO2-fixation rates can be derived. Consequently, conversions of ETRs to CO2-fixation requires knowledge of the electron requirement for carbon fixation (Φe,C, ETR/CO2 uptake rate) and its dependence on environmental gradients. Such knowledge is critical for large scale implementation of active fluorescence to better characterise CO2-uptake. Here we examine the variability of experimentally determined Φe,C values in relation to key environmental variables with the aim of developing new working algorithms for the calculation of Φe,C from environmental variables. Coincident FRRf and 14C-uptake and environmental data from 14 studies covering 12 marine regions were analysed via a meta-analytical, non-parametric, multivariate approach. Combining all studies, Φe,C varied between 1.15 and 54.2 mol e− (mol C)−1 with a mean of 10.9±6.91 mol e− mol C)−1. Although variability of Φe,C was related to environmental gradients at global scales, region-specific analyses provided far improved predictive capability. However, use of regional Φ e,C algorithms requires objective means of defining regions of interest, which remains challenging. Considering individual studies and specific small-scale regions, temperature, nutrient and light availability were correlated with Φ e,C albeit to varying degrees and depending on the study/region and the composition of the extant phytoplankton community. At the level of large biogeographic regions and distinct water masses, Φ e,C was related to nutrient availability, chlorophyll, as well as temperature and/or salinity in most regions, while light availability was also important in Baltic Sea and shelf waters. The novel Φ e,C algorithms provide a major step forward for widespread fluorometry-based NPP estimates and highlight the need for further studying the natural variability of Φe,C to verify and develop algorithms with improved accuracy.

The application of variable chlorophyll fluorescence to microphytobenthic biofilms

Community assemblages of diatoms, green algae and cyanobacteria comprise the microphytobenthos (MPB), which inhabit benthic sediment ecosystems (Admiraal 1984; Underwood and Kromkamp 1999; Consalvey et al. 2004). Particular attention has been paid to the analysis of intertidal soft sediment systems, e.g. cohesive mudflat and sandy substrata typical of estuarine habitats. Variable chlorophyll fluorescence has been applied to these systems since the 1990s, in an attempt to investigate the primary productivity and photophysiology of the integrated biofilms, when viewed as a “black box system”, and also at the species level (Sections 5, 6 and 7). These transient (i.e. temporary) biofilms are not confined to such soft sediment habitats however, and more recently application of fluorescence methodologies has been applied to biofilms inhabiting rocky shores and stromatolite systems (Kromkamp et al. 2007; Perkins et al. 2007). However the large majority of published work has centred upon benthic soft-sediment biofilms, due to their important ecosystem functions of carbon flow and sediment stability (Underwood and Kromkamp 1999). In the former their high magnitude of productivity fuels carbon flow through invertebrate and bacterial food webs to support important trophic levels of anthropogenically exploited taxa, including coastal fish and shell fisheries and coastal avifauna. In the case of sediment stability, biogenic exopolymers, usually referred to as extracellular polymeric substances (EPS), produced by the MPB in part to facilitate mobility, may contribute significantly to sediment stability, hence increasing the sediment resistance to hydrodynamic stresses and thus resistance to coastal erosion (e.g. Underwood and Kromkamp 1999 and citations there-in). Finally, the photosynthetic production of oxygen can be regarded as an important ecosystem function.

Implementing and Innovating Marine Monitoring Approaches for Assessing Marine Environmental Status

Marine environmental monitoring has tended to focus on site-specific methods of investigation. These traditional methods have low spatial and temporal resolution and are relatively labor intensive per unit area/time that they cover. To implement the Marine Strategy Framework Directive (MSFD), European Member States are required to improve marine monitoring and design monitoring networks. This can be achieved by developing and testing innovative and cost-effective monitoring systems, as well as indicators of environmental status. Here, we present several recently developed methodologies and technologies to improve marine biodiversity indicators and monitoring methods. The innovative tools are discussed concerning the technologies presently utilized as well as the advantages and disadvantages of their use in routine monitoring. In particular, the present analysis focuses on: (i) molecular approaches, including microarray, Real Time quantitative PCR (qPCR), and metagenetic (metabarcoding) tools; (ii) optical (remote) sensing and acoustic methods; and (iii) in situ monitoring instruments. We also discuss their applications in marine monitoring within the MSFD through the analysis of case studies in order to evaluate their potential utilization in future routine marine monitoring. We show that these recently-developed technologies can present clear advantages in accuracy, efficiency and cost.

Photoacclimation in microphytobenthos and the role of xanthophyll pigments

Estuarine microphytobenthos are frequently exposed to excessively high irradiances. Photoinhibition in microalgae is prevented by various photophysiological responses. We describe here the role of the xanthophyll pigments in photoacclimation. The pigment composition of the microphytobenthos was studied in three European estuaries (Barrow, Ireland; Eden, UK; Tagus, Portugal). Using HPLC-analyses, microscale changes in biomass and pigment composition were monitored over short (hourly) and long (seasonal) time scales. In the Barrow estuary, the biomass of microphytobenthos (measured as chlorophyll a) increased significantly in the top 400–500 µm of the sediment surface within 1 h of emersion; simultaneously, the xanthophyll pool size (diadinoxanthin plus diatoxanthin, dd + dt) almost doubled. A more gradual conversion of dd into dt was observed, with the dt:dd ratio increasing from <0.1 at the start of emersion to >0.3 after 3 h emersion. Similar trends in the dt:dd ratio were observed in the surface sediments of the Eden and the Tagus estuaries. Higher ratios were recorded in the Tagus estuary, which may be explained by higher incident irradiance. In addition, seasonal studies carried out in the Eden and Tagus estuaries showed that the xanthophyll pool size increased by 10% in the summer months. The pool size was highest in the Tagus estuary. Concurrently, high values for the de-epoxidation state were recorded, with values for dt/(dt + dd) > 0.35 recorded in the summer. At the Eden, the ratio never exceeded 0.3. The de-epoxidation state was higher in winter than in summer, which was ascribed to the low winter temperatures. During a vertical migration study, a negative relationship between chlorophyll a and the de-epoxidation state was observed. It is suggested that this relationship originates from ‘micro-migration’ within the biofilm. Migration within the euphotic zone may provide an alternative means for cells to escape photodamage. In this paper, we propose that both xanthophyll cycling and ‘micro’-migration play an important role in photoacclimation and it appears that these processes operate in parallel to regulate the photosynthetic response.

Nematode community dynamics over an annual production cycle in the central North Sea

Nematode species composition, trophic structure and body size distributions were followed over an annual production cycle in the central North Sea; to test responses to temporally changing food quality and quantity in the sediment. Changes in the phytoplankton concentration in the water column were quantitatively reflected in the concentration of chlorophyll a and breakdown products in the sediment, with higher concentrations in spring and autumn following blooms, and lower concentrations in summer and winter. The taxonomic and trophic structure of nematode communities differed significantly among stations over relatively short distances, potentially masking some of the temporal dynamics. Spatio-temporal differences in nematode species composition were linked to changes in the quality and quantity of organic material reaching the seabed, reflecting a species-specific response to the nutritional quality of sedimenting organic material and the biochemical changes in the sediment associated with its decomposition. The size distributions of selected nematode species indicated that most species bred continuously throughout the sampling period, although one species, the epigrowth feeder Spilophorella paradoxa, had periods of increased growth following the deposition of the spring phytoplankton bloom. There was no consistent temporal relationship between the trophic composition of nematode communities and spring chlorophyll a or carbon sedimentation, most likely a result of the trophic plasticity of most feeding types and the capacity of the community to use both freshly sedimented material as well as the subsequent breakdown products and refractory organic matter. Community metrics implied that there were small responses to the seasonal production cycle, but these belied strong responses of a few species with life histories that allowed them to track the availability of suitable food resources.