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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]

SUMMARY Trade-off relationships are considered key to understanding the mechanisms supporting the coexistence of multiple species within kelp beds. Thus, information on trade-offs is expected to contribute to conservation of kelp bed diversity. To test the existence of a trade-off between productivity and thallus toughness, thallus traits and relationships between the traits were examined for seven species of Laminariales including 24 populations. For each population, photosynthetic capacity per unit biomass (as A mass) and nitrogen (i.e., photosynthetic nitrogen-use efficiency, PNUE), nitrogen content (as N mass), thallus mass per unit thallus area (as TMA) and force required to penetrate the thallus (as F p, a common index of leaf toughness in land plants by punch test) were determined. A mass increased with increasing N mass. Blades with high N mass showed high A mass. These blades may invest a large proportion of nitrogen to the photosynthetic parts, and consequently exhibit high metabolic rates. Moreover, blades with high N mass tended to be associated with low TMA, and N mass decreased with increasing TMA. A significant negative correlation was observed between TMA and A mass because of the linkage of high A mass with high N mass and high N mass associated with low TMA, while a significant positive correlation was observed between TMA and F p. The two correlations indicate the existence of a trade-off between productivity and thallus toughness in Laminariales. PNUE showed a significant negative correlation with TMA, which also showed a significant positive correlation with F p as the index of thallus toughness, and therefore a trade-off relationship between productivity and thallus toughness. [ABSTRACT FROM AUTHOR]

SUMMARY Thallus mechanical strength, as well as production of secondary metabolites as defensive compounds, of tropical macroalgae is often essential for protection from herbivory. In tropical macroalgae, thallus mechanical strength is negatively correlated with productivity — a trade‐off between productivity and thallus toughness. The tropical fucoids, Turbinaria ornata which has defensive morphological traits against herbivory and Sargassum ilicifolium which is expanding its distribution in Japanese waters, were examined to determine thallus traits related to mechanical strength and productivity and their pair‐wise relationships were also examined. These traits that are directly or indirectly related to the trade‐off between productivity and thallus toughness were compared to data for various other temperate macroalgae by regression analyses. We found two strong positive correlations between thallus mechanical strength and thallus mass or thallus thickness, confirming that higher levels of mechanical strength for tropical fucoids is associated with higher biomass or thallus thickness. Also, negative correlations between thallus toughness and productivity were found indicating structural and physiological trade‐offs. However, the tropical fucoids exhibited relatively high productivity regardless of their higher level of thallus toughness. These traits of the tropical fucoids slightly deviate from the typical conservative strategy with higher thallus toughness and lower productivity as a trade‐off between productivity and thallus toughness. [ABSTRACT FROM AUTHOR]

Lobophora rosacea C.W. Vieira, Payri et De Clerck is reported from the South China Sea for the first time. Our specimens are very similar to L. rosacea recently described from New Caledonia, not only in morphology but also in rbcL and cox3 gene sequences. The fan-shaped thallus grows erectly, attaching to the substrate by a basal holdfast. The thallus is composed of a single layer of large medullary cells and three to four layers of cortical cells on both sides of the medulla. Mature sporophytes are detected, with sporangium sori scattered on both surfaces of the thallus. [ABSTRACT FROM AUTHOR]