Interspecific competition between Enteromorpha (Ulvales: Chlorophyceae) and Fucus (Fucales: Phaeophyceae) germlings: effects of nutrient concentration, temperature, and settlement density

Abstract

The increased abundance of ephemeral algae and corresponding decline in perennial fucoids observed in eutrophic (nutrient-rich) waters could be caused by eutrophication-driven shifts in the competitive relationship between the 2 groups as early as the germling stage. During the initial post-settlement period germlings are exposed to large temporal variations in temperature, which may influence their performance and competitive interactions. Effects of temperature, nutrient concentration, and settlement density on the competitive relationship between germlings of Fucus serratus L. and F. evanescens C. Agardh and of the ephemeral alga Enteromorpha compressa (Linnaeus) Greville were examined using factorially designed culture experiments. In monocultures, germling growth of both Fucus species and E. compressa was generally stimulated by nutrient enrichment (32 µmol nitrate/ammonia and 2 µmol phosphate l -1 seawater) and high temperature (17°C compared to 7°C), and negatively related to settlement density (10 to 50 germlings cm -2 for Fucus, 30 to 130 germlings cm -2 for E. compressa). In mixed cultures, interspecific competition effects of E. compressa on F. serratus and F. evanescens germlings increased with increasing nutrient and temperature levels. In the nutrient-enriched cultures, interspecific competition from E. compressa suppressed the yield of Fucus spp. by 80 to 100% at 17°C, with F. evanescens being more suppressed than F. serratus, whereas the suppressive effects of E. compressa on Fucus germlings were < 60% at 7°C. These results suggest that competition from ephemeral algae at early life stages may be a reason for the decline of fucoids in eutrophic waters and that reproduction at low temperatures, as in species like F. serratus and F. evanescens, may shield the vulnerable initial germling stages from the severest competition pressure by ephemeral algae. KEY WORDS: Fucus spp. · Enteromorpha compressa · Germlings · Competition · Nutrients · TemperatureResale or republication not permitted without written consent of the publisher

The fate of the Arctic seaweed Fucus distichus under climate change: an ecological niche modeling approach

“…For example, reduced temperature (7°C vs. 17°C) lowered the competitive power of the ephemeral alga Ulva compressa (formerly known as Enteromorpha compressa) on germling settlement and growth of F . distichus (60% vs. 100% yield reduction) (Steen ). Although temperate species may not outcompete F .…”

“…In the Arctic, F. distichus may have a competitive advantage because of its adaptation to cold conditions and long dark periods. For example, reduced temperature (7°C vs. 17°C) lowered the competitive power of the ephemeral alga Ulva compressa (formerly known as Enteromorpha compressa) on germling settlement and growth of F. distichus (60% vs. 100% yield reduction) (Steen 2004). Although temperate species may not outcompete F. distichus in the Arctic, they may truncate its upper and lower zonation boundaries.…”

Effects of Climate Change on Global Seaweed Communities

“…Increasing nitrogen loading tends to favor fast‐growing species with high nitrogen requirements. In some cases, this may lead to competitive dominance by weedy taxa (Steen , Vermeij et al. ) and – should nutrients trigger a phytoplankton bloom – shading‐out of benthic seaweeds by phytoplankton (Kavanaugh et al.…”

“…Increasing nitrogen loading tends to favor fast-growing species with high nitrogen requirements. In some cases, this may lead to competitive dominance by weedy taxa (Steen 2004b, Vermeij et al 2010) andshould nutrients trigger a phytoplankton bloomshadingout of benthic seaweeds by phytoplankton (Kavanaugh et al 2009). In other cases, higher nitrogen CLIMATE CHANGE AND SEAWEEDS 1069 merely allows for the persistence of nitrogen-limited taxa and thus enhances algal diversity (Bracken and Nielsen 2004).…”

Planktonic community structure during a harmful bloom of Phaeocystis globosa in a subtropical bay, with special reference to the ciliate assemblages

“…For P. globosa, although a negative effect of phosphorous upon this harmful alga was detected from the field data, this result should be considered with caution as it was derived from field observation during the increasing phase of bloom when rapid uptake by the colonial algae and consequently P-depletion were supposed to be happened simultaneously. Nonetheless, these bottom-up processes, involving the ambient physic-chemical factors such as temperature, salinity, light and nutrients, played a most important role in coastal and particular estuarine and bay ecosystems (Steen 2004;Cohen and Fong 2004;Worm and Lotze 2006). This …”