Highly predictable photosynthetic production in natural macroalgal communities from incoming and absorbed light

We assessed the effects of light limitation and temperature shift on palatability and induced antiherbivore defense in the brown alga Fucus vesiculosus L. Incubation for 2 wk at light intensities above the compensation point of photosynthesis and in the absence of grazers increased the palatability of F. vesiculosus and its subsequent consumption by the omnivorous isopod Idotea baltica Pallas. This effect correlated with an increased C:N ratio and mannitol content in the algal tissue, presumably due to increased photosynthetic carbon fixation. Mannitol, the primary product of photosynthesis in F. vesiculosus, proved to be a feeding cue for I. baltica, and depletion of the mannitol pool may therefore account for the reduced palatability during light limitation. At light intensities above the compensation point of photosynthesis, F. vesiculosus responded with decreasing palatability when it was exposed to I. baltica grazing. Irrespective of the preceding light regime, such defense induction was prevented during incubation under light limitation. Thus, under low light, defense induction is not only inhibited, but also less necessary due to the relative absence of feeding cues. Upward or downward shifts in water temperature by approximately 10°C also inhibited inducible defense in F. vesiculosus. However, such shifts did not affect algal growth and were therefore the consequence of an impairment of specific defense-related components rather than of resource limitation, unless compensatory growth was given priority over defense.

Section: Discussionsupporting

confidence: 83%

Effects of limitation stress and of disruptive stress on induced antigrazing defense in the bladder wrack Fucus vesiculosus

Weinberger¹,

Rohde²,

Oschmann³

et al. 2011

“…Spring and autumn changes in pH were significantly related to changes in irradiance but not to change in temperature, suggesting that temperature plays a lesser role than irradiance in the seasonal differences in community photosynthetic production. This is in agreement with recent studies on community photosynthesis which have shown that the photosynthetic characteristics of communities vary but little during the year and that irradiance is the main factor determining photosynthetic production in natural macroalgal communities (Middelboe et al 2006). pH and diurnal variability were highest in the shallowest waters and decreased with increasing water depth.…”

Section: Level and Variability Of Ph In Shallow-water Habitatssupporting

confidence: 92%

“…One site was a wave-exposed boulder reef in Aalsgaarde, on the northern coast of Zealand, Denmark, with relatively steep bottom topography. The boulder reef was densely covered with species-rich macroalgal communities dominated by Fucus species (Middelboe et al 2006). The other site was a sheltered, shallow-water area in Kildebakkerne in the estuary Roskilde Fjord, Denmark.…”

Section: Methodsmentioning

confidence: 99%

“…pH is probably highest in sheltered habitats such as lagoons and estuaries where the exchange of water with the surroundings and wind exposure is small, while wave-exposed sites with a large exchange of water may be less influenced by photosynthetic processes at the site. Seasonally we would expect high pH during spring and summer when irradiance and temperature are optimal for photosynthesis (Middelboe et al 2006). pH may also show diurnal variations, with high pH during daylight hours and lower pH during the night when respiratory processes dominate.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

High pH in shallow-water macroalgal habitats

Middelboe

Hansen²

2007

104

The aim of this study was to evaluate seasonal and diurnal variability in pH and inorganic carbon in shallow-water macroalgal habitats and to evaluate the importance of high pH for macroalgal photosynthesis. Seasonal variations in pH, oxygen saturation and inorganic carbon concentration were measured at an exposed and a sheltered shallow-water (0 to 1 m) macroalgal habitat. Daytime pH was significantly higher in spring, summer and autumn than in winter at both study sites. Diurnal measurements at the most exposed site showed significantly higher pH during the day than during the night. The diurnal variations were largest in shallow water and decreased with increasing water depth. High pH resulted in periodically low concentrations of available inorganic carbon in summer (as low as 1.3 mmol [CO 2 + HCO 3 -] l -1). Photosynthesis as a function of inorganic carbon concentrations was measured at pH 8 and 9.3 for 4 common macroalgal species (Fucus vesiculosus, F. serratus, Ceramium rubrum, Ulva sp.). Photosynthesis in these species was not limited by natural concentrations of inorganic carbon, but maximum photosynthesis and inorganic carbon concentrations at saturation were lower when measured at pH 9.3 than at pH 8. Our results suggest that pH is higher in natural shallow-water habitats than previously thought, and that high pH has a direct effect on photosynthesis that cannot be accounted for by low availability of inorganic carbon. KEY WORDS: pH · Seasonal variations · Diurnal variations · Macroalgae · PhotosynthesisResale or republication not permitted without written consent of the publisher

“…Canopy openness and tree density are structural components that influence the light and temperature environment of the forest floor, and so are important forest structure characteristics contributing to the dynamics of forest patches (Pickett & White 1985). Canopy structure was an important predictor of benthic primary production because of the relationship of canopy height to photosynthesis and irradiance in macroalgal communities of shallow coastal water (Middelboe et al 2006). We found differences in canopy openness among the various mangrove management types in our study; canopy openness was lowest in RIM and higher in control and breached-RIM swamps (Table 3).…”

Section: Forest Structural Complexitymentioning

confidence: 59%

Characteristics of mangrove swamps managed for mosquito control in eastern Florida, USA

Middleton

Devlin²,

Proffitt³

et al. 2008

Manipulations of the vegetation and hydrology of wetlands for mosquito control are common worldwide, but these modifications may affect vital ecosystem processes. To control mosquitoes in mangrove swamps in eastern Florida, managers have used rotational impoundment management (RIM) as an alternative to the worldwide practice of mosquito ditching. Levees surround RIM swamps, and water is pumped into the impoundment during the summer, a season when natural swamps have low water levels. In the New World, these mosquito-managed swamps resemble the mixed basin type of mangrove swamp (based on PCA analysis). An assessment was made of RIM, natural (control), and breached-RIM (restored) swamps in eastern Florida to compare their structural complexities, soil development, and resistance to invasion. Regarding structural complexity, dominant species composition differed between these swamps; the red mangrove Rhizophora mangle occurred at a higher relative density in RIM and breached-RIM swamps, and the black mangrove Avicennia germinans had a higher relative density in natural swamps. Tree density and canopy cover were higher and tree height lower in RIM swamps than in natural and breached-RIM swamps. Soil organic matter in RIM swamps was twice that in natural or breached-RIM swamps. RIM swamps had a lower resistance to invasion by the Brazilian pepper tree Schinus terebinthifolius, which is likely attributable to the lower porewater salinity in RIM swamps. These characteristics may reflect differences in important ecosystem processes (primary production, trophic structure, nutrient cycling, decomposition). Comparative assessments of managed wetlands are vital for land managers, so that they can make informed decisions compatible with conservation objectives.