Why is Ulva intestinalis the only macroalga inhabiting isolated rockpools along the Swedish Atlantic coast?

Abstract

Ulva intestinalis (previously called Enteromorpha intestinalis)is the principal marine macroalga growing in isolated rockpools along the Swedish west coast. Given that this alga can take up HCO 3 -under the conditions of high pH and low concentrations of inorganic carbon (Ci) that it creates in those pools, we hypothesized that those conditions would be unfavourable for the photosynthetic performance of other algae such that they would not be able to grow in the same pools. This was tested by transferring 2 of the most common macroalgae, Fucus vesiculosus and Chondrus crispus, from the shallow waters of a bay adjacent to some rockpools, to 2 rockpools containing U. intestinalis. Both photosynthetic electron transport rates (ETR) and maximal quantum yields (F v /F m ) were measured 3 d later. Similar measurements were also performed throughout the day in simulated outdoor rockpools where the 3 species were kept either alone or together for 24 h. It was found that midday ETRs were repressed for all species in the (upper) rockpool as compared to the open bay, but more so for the transferred F. vesiculosus and C. crispus (33 and 0.6%, respectively, of the bay values) than for U. intestinalis (58%). Also, C. crispus showed exceptionally repressed midday F v /F m values in the rockpools (some 22% of that in the bay), and had largely photobleached after 3 d. Similarly, ETRs declined in the simulated rockpools during the day, especially for C. crispus when the other algae were present (to 7% of morning values, compared to 36% when alone). Also, F v /F m declined in the simulated rockpools during the day, indeed much more so for F. vesiculosus and C. crispus when the other algae were present (to ca. 12 and 10% of morning values as compared to 76 and 54%, respectively, when alone). As in the rockpools, the latter alga photobleached when kept together with the other species, but not when alone. Based on these results, and considering their different Ci utilisation mechanisms, it was concluded that the absence in rockpools of algae such as those tested here may be largely due to the adverse conditions of high pH and low Ci concentrations caused by the photosynthetic traits of U. intestinalis. KEY WORDS: Chondrus crispus · Ulva (Enteromorpha) intestinalis · Fucus vesiculosus · Inorganic carbon · Rockpool(s) · pH · PhotosynthesisResale or republication not permitted without written consent of the publisher

Seagrass photosynthesis controls rates of calcification and photosynthesis of calcareous macroalgae in a tropical seagrass meadow

“…in pools or lagoons) but, except in a few cases (Björk et al 2004, Beer et al 2006, Middelboe & Hansen 2007, such shifts have not been ascribed any importance as a controlling factor for photosynthesis and growth of species featuring e.g. inorganic carbon limitations in nature.…”

“…Some algae can cause drastic pH increases (Axelsson & Uusitalo 1988); in the case of Ulva spp., this may be because they release OH - (Drechsler & Beer 1991). Only recently was it recognised that such high pH values could, in turn, affect the photosynthetic performance of other algae (see Björk et al 2004 for Ulva intestinalis in isolated rockpools and Middelboe & Hansen 2007 for shallow macro-algal habitats). Also, seagrasses can increase the pH of the surrounding seawater; Invers et al (1997) showed a pH increase of up to 0.5 units in seagrass meadows, which negatively affected photosynthetic rates of 3 seagrasses (Posidonia oceanica, Cymodocea nodosa and Zostera noltii).…”

“…The pH variations caused by the photosynthetic activity in marine systems such as Chwaka Bay have only rarely been found to affect other biological functions. In one case, it was shown that the high pH generated by Ulva intestinalis in temperate rockpools could hinder the photosynthetic activity of other algae, thus restricting them from growing there (Björk et al 2004). In another case, similar effects were found in shallow temperate waters with restricted water flow (Middelboe & Hansen 2007).…”

The short-term effects of elevated CO2 and ammonium concentrations on physiological responses in Gracilariopsis lemaneiformis (Rhodophyta)

“…In addition, we did not find any inhibition of photosynthesis. When pH values are >9.0, photosynthesis of some species is more likely to be inhibited (Maberly 1990;Björk et al 2004). Zou et al (2004) indicated that inorganic carbon (Ci) affinity and photosynthetic rates at pH 9.0 were decreased in G. lemaneiformis.…”

High pH in shallow-water macroalgal habitats

“…In populations of Fucus vesiculosus in the Baltic Sea, pH was about 9 in summer (Pearson et al 1998). In dense floating macroalgae in a brackish coastal lagoon in the Ebro River Delta (NE Spain) maximum pH was 9 to 9.5 (Menendez et al 2001) and pH values as high as 9.8 to 10.1 have been reported from isolated rock pools in Sweden (Björk et al 2004). Even though pH has never been measured systematically and continuously in natural macroalgal habitats, these sporadic measurements suggest that pH occasionally is high.…”