The relationship between phytoplankton diversity and community function in a coastal lagoon

Abstract

The decrease of biodiversity related to the phenomena of global climate change is stimulating the scientific community towards a better understanding of the relationships between biodiversity and ecosystem functioning. In ecosystems where marked biodiversity changes occur at seasonal time scales, it is easier to relate them with ecosystem functioning. The objective of this work is to analyse the relationship between phytoplankton diversity and primary production in St. Andre´coastal lagoon -SW Portugal. This lagoon is artificially opened to the sea every year in early spring, exhibiting a shift from a marine dominated to a low salinity ecosystem in winter. Data on salinity, temperature, nutrients, phytoplankton species composition, chlorophyll a (Chl a) concentration and primary production were analysed over a year. Modelling studies based on production-irradiance curves were also conducted. A total of 19 taxa were identified among diatoms, dinoflagellates and euglenophyceans, the less abundant group. Lowest diversities (ShannonWiener index) were observed just before the opening to the sea. Results show a negative correlation (p<0.05) between diversity and chlorophyll a (Chl a) concentration (0.2-40.3 mg Chl a m )3 ). Higher Chl a values corresponded to periods when the community was dominated by the dinoflagellate Prorocentrum minimum (>90% of cell abundance) and production was maximal (up to 234.8 mg C m )3 h )1 ). Maximal photosynthetic rates (P max ) (2.0-22.5 mg C mg Chl a )1 h )1 ) were higher under lower Chl a concentrations. The results of this work suggest that decreases in diversity are associated with increases in biomass and production, whereas increases correspond to opposite trends. It is suggested that these trends, contrary to those observed in terrestrial and in some benthic ecosystems, may be a result of low habitat diversity in the water column and resulting competitive pressure. The occurrence of the highest photosynthetic rates when Chl a is low, under some of the highest diversities, suggests a more efficient use of irradiance under low biomass-high diversity conditions. Results suggest that this increased efficiency is not explained by potential reductions in nutrient limitation and intraspecific competition under lower biomasses and may be a result of niche complementarity.

Inter-annual variations of macrobenthic communities over three decades in a land-locked coastal lagoon (Santo André, SW Portugal)

“…The annual dynamics of water renewal in Santo André lagoon and the inherent year-to-year variability of physical conditions in lagoons (Barnes, 1980;Desmond et al, 2002) lead to a high temporal variability in biological communities (phytoplankton community e Duarte et al, 2006; Ruppia cirrhosa e Calado and Duarte, 2000; benthic community, as it was found in this study). Benthic community sampled in the present study consisted of 42 taxa, most of which are typical of these lagoonal systems (e.g.…”

Modeled phytoplankton diversity and productivity in the California Current System

“…The range in modeled SI compares to that reported by Irigoien et al (2004) but not to the high cytometric diversity values of Li (2002), which upon conversion of the exponential form reach high diversity values of 4.3 due to the representation of both physiological and genetic variation among organisms rather than solely taxonomy. Similar to the observed scatter reported by most observations in non-marine (Adler et al, 2011) and marine (Li, 2002;Irigoien et al, 2004;Duarte et al, 2006) systems, the scatter in our model results does not reveal a straightforward curvilinear relationship between diversity and productivity, consistent with Adler et al's (2011) argument that many factors contribute to the variation in diversity and therefore diversity-productivity relationships.…”

“…Studies of pelagic aquatic environments have also documented unimodallike structure, though usually with considerable scatter similar to that conceptualized in Fig. 1d (Agard et al, 1996;Li, 2002;Grover and Chrzanowski, 2004;Irigoien et al, 2004;Duarte et al, 2006;Spatharis et al, 2008). Cermeno et al (2008) find no statistical relationship in their analysis of coastal, shelf, and open ocean environments.…”

Pelagic metabolism of the Douro estuary (Portugal) – Factors controlling primary production

“…In marine ecosystems, there seems to be a general decreasing trend of the P/B ratio as a function of net primary production (NPP). In one extreme there are oligotrophic ecosystems, with high P/B, low biomass and NPP, such as open ocean pelagic systems, and in another extreme there are ecosystems with low P/B, high NPP and biomass, such as algal reefs and beds (Duarte et al, 2006). These trends suggest that low biomass and NPP ecosystems are more efficient in using limiting resources.…”