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To assess physiological and structural trade-offs in thalli of marine macroalgae, the feasibility of using a single axis representing and visualizing trade-offs and pairwise correlations among functional traits relating to the trade-offs was examined. Additionally, patterns of pairwise correlations among functional traits related to the trade-offs were compared with those for terrestrial plants. These analyses were performed using data for 12 species of macroalgae: light-saturated photosynthetic and dark respiration rates per dry mass (Amass, Rmass), thallus nitrogen concentration (Nmass), thallus dry mass per area (TMA), force to punch per fracture length (Fp), and C:N ratio (C/N) based on 15 datasets including different seasons. Results of the analyses confirmed that the single axis represents multi-dimensional data on the six functional traits and a continuum in the trait combination based on trade-offs from the conservative to the acquisitive end along the single axis. Additionally, pairwise correlations among key traits relating to trade-offs were confirmed to be qualitatively consistent with those reported in leaves of terrestrial plants. The extremely high Amass and extremely low TMA for marine macroalgae compared with terrestrial plants probably reflect their habitats, and can be regarded as one of the key trait combinations that represent their differences from terrestrial plants. [ABSTRACT FROM AUTHOR]

Hermatypic (reef-building) corals harbor dinoflagellate endo-symbionts Symbiodinium spp. In studying gene expression in such symbiotic corals, problems arise regarding how to distinguish the coral and symbiont mRNA, and how to estimate their fractions in the mRNA population of the holobiont (symbiotic complex of the coral and Symbiodinium cells). In this study, these issues were addressed using juveniles of hermatypic coral Acropora tenuis in symbiosis with Symbiodinium cells of strain PL-TS-1. First, the guanine-cytosine (GC) contents were determined in expressed sequence tags (EST) from PL-TS-1 cells cultured in vitro and symbiont-free larvae of A. tenuis, and their average GC contents were found to be significantly different. The average GC content of the EST from the holobiont was much closer to that of A. tenuis larvae, suggesting that the majority (>90%) of mRNA isolated from the holobiont originated in the host. In protein-coding sequences, little overlap was observed between the GC-content distributions of PL-TS-1 cells and A. tenuis larvae. All of the coding sequences ( n = 59) found in the A. tenuis EST had GC contents below 0.5, whereas the GC content exceeded 0.5 in the majority (43/44) of coding sequences from the nuclear genome of PL-TS-1 cells. [ABSTRACT FROM AUTHOR]

To clarify the photosynthetic and respiratory characteristics of Agarum clathratum in relation to shade tolerance, parameters of photosynthetic light-response curves of A. clathratum growing at depths of 5–16 m were compared with those of Saccharina coriacea growing at shallower depths of 1–10 m. Moreover, using the photosynthetic parameters and continuous data on underwater photosynthetically active radiation (PAR), daily photosynthesis and respiration in the underwater light environment for the two species were estimated and compared. The lower values of respiration rate and light compensation point (LCP) of A. clathratum (1.8–2.5 µL O2 cm–2 h–1, 2.0–2.4 µmol m–2 s–1), compared with those of S. coriacea (5.2–5.6 µL O2 cm–2 h–1, 4.9–8.3 µmol m–2 s–1), indicate that it reduces daily respiration and maintains a positive daily net photosynthesis at low light intensities, enabling it to inhabit deeper depths than S. coriacea. Lower ratios of daily respiration to daily gross photosynthesis (14.7–35.2%) estimated in A. clathratum, compared with those (28.1–84.0%) in S. coriacea, also suggest a shade-tolerant strategy for achieving greater net photosynthesis by reducing respiration. [ABSTRACT FROM AUTHOR]