Subtidal microphytobenthos: effects of inorganic and organic compound supplies on migration, production, and respiration in a tropical coastal environment

Abstract

Microphytobenthos (MPB) is an important primary producer in coastal ecosystems. In oligotrophic environments, its activity may be controlled by the availability of organic or inorganic compounds but also by its migration behavior. The objective of this study was to determine, in MPBcolonized subtidal sediments, the consequences of short-term enrichments (< 24 h) of organic (alanine, glutamate, and glucose) and inorganic (ammonium, phosphate) compounds on MPB vertical migration and metabolisms, net production (NP), areal gross production (AGP), and community respiration (R). Two contrasting stations located in the southwest lagoon of New Caledonia were investigated: 1 under strong anthropogenic influence and 1 under more oceanic influence. Both stations were dominated by epipelic diatoms. Differences in net primary production were explained by diurnal variation of MPB biomass at the sediment surface, showing the importance of MPB migration in the functioning of these subtidal environments. However, a stimulation or inhibition of MPB migration did not necessarily impact the net primary production of the system; this strongly depends upon the interactions between the autotrophic and heterotrophic compartments, the latter being controlled by the environmental conditions. For the station under low anthropogenic influence, AGP and R were both significantly stimulated by alanine, glucose, and ammonium, and significantly inhibited by phosphate. The similar responses of AGP and R to enrichments suggest that autotrophs and heterotrophs were tightly coupled. Conversely, in the station under strong anthropogenic influence, AGP and R responded differently. Addition of ammonium inhibited AGP without having an impact on R, whereas addition of phosphate inhibited R whilst having no measurable effect on AGP. In this station, the coupling between autotrophs and heterotrophs was weakened, suggesting that the carbon demand of the heterotrophic compartment is probably sustained by the supplies of allochthonous organic matter rather than by exudates from the autotrophic compartment.KEY WORDS: Nutrients · Amino acids · Glucose · Autotroph-heterotroph coupling · Oxygen microelectrode · Reflectance Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 61: [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] 2010 than 50% of the total primary production in some shallow waters (Underwood & Kromkamp 1999). Moreover, MPB also plays an important role in the regulation of nutrient fluxes at the water-sediment interface and thus forms an active filter, reducing the supply of nutrients to the water column (Sundbäck et al. 1991). MPB excretes extracellular polymeric substances (EPS; Goto et al. 1999, de Brouwer & Stal 2001, Underwood & Paterson 2003 and thus plays an important role by stabilizing the sediment through the reduction of resuspension and erosion (Miller et al. 1996). Excretion of organic compounds by MPB can also represent an important source of carbon for hetero...

Regulation of Intertidal Microphytobenthos Photosynthesis Over a Diel Emersion Period Is Strongly Affected by Diatom Migration Patterns

“…Significant fortnight and seasonal differences in benthic diatom vertical migration were reported and related to the timing of the low tide, previous light history and composition of the diatom populations ( Mitbavkar and Anil, 2004 ; Serôdio et al, 2008 ). More recently, similar migratory rhythms have been described for MPB inhabiting subtidal sediments, where the diurnal period seems to represent the main trigger for up- and downward migration ( Longphuirt et al, 2006 ; Bourgeois et al, 2010 ).…”

“…The microenvironment of densely populated MPB communities is complex and heterogeneous, characterized by steep physical and chemical gradients. Although previous studies have used microsensors to assess MPB migration and primary productivity (e.g., Denis and Desreumaux, 2009 ; Bourgeois et al, 2010 ), the simultaneous assessment of the roles of behavioral and photophysiological mechanisms on the regulation of MPB photosynthesis have not been previously determined at relevant spatial scales with minimal disturbance of the photic zone microenvironments. We present such a study using a combination of O 2 and scalar irradiance microprofiling, variable chlorophyll (Chl) fluorescence and pigment analysis, and address the relevance of photophobic migration and photoprotection via the XC cycle by comparing migratory and non-migratory (treated with a diatom motility inhibitor) benthic biofilms briefly subjected to high irradiance.…”

Diel patterns of microphytobenthic primary production in intertidal sediments: the role of photoperiod on the vertical migration circadian rhythm

“…During the light phase of the photoperiod at constant irradiance, MPB P N changed, reaching its maximum rate after 6 hours of light (Fig. 1), as observed previously under a 12 L:12D photoperiod 11,43,44 . However, maximum oxygen concentrations were observed just two hours after the on-set of the light phase when it was set at only 5 hours 45 .…”

“…Independently of its cause or adaptive purpose, the upward and downward vertical displacement of the photoautotrophic biomass within the sediment is probably a major determinant of the diel rate of primary production - in addition to physiological photoadaptation and photoacclimation mechanisms in action as a response to the changing irradiance during the day. However, the relative importance of vertical migration and photophysiology seems to be different, depending on species, growth form, and environmental conditions 31–33,38–41 .The existence of diel vertical migration of photoautotrophic biomass in systems without tidal signals, freshwater sediment 34,42 , and their relatively recent discovery in subtidal marine sediment 12,43 suggest that light and tidal cues can operate independently and that, in intertidal sediments, the photoperiod might be the major environmental driver of vertical migrations, with tides being an additional secondary environmental cue. The way the coupling between photoperiod and tidal signals occurs is not known.…”

Temporal variability of benthic-pelagic coupling in shallow enclosed environment: A case study with eutrophying shrimp ponds

“…This is likely due to the combination of an increase of nutrient availability and sufficient light regime, as reported in works on natural gradient and experimental fertilization (eg. Bourgeois et al, 2010). This increase in biomass coincided with a proportional increase in benthic metabolism for both primary production and…”