Population structure, dynamics, and production of the Mediterranean macroalga Codium bursa (Chlorophyceae)

The biochemical composition and metabolism of the balloonlike Mediterranean macroalga Codium bursa J. Agardh are strongly size dependent and constrain ed by the spherical geometry of its thallus. Changes in reproductive phenol ogy, population structure, density, biomass, and production of this widespr ead alga were followed over an annual cycle to examine whether mortality ra te was size and age dependent. Examination of size and age distributions sh owed the population to be in quasi-steady state. A main recruitment event o ccurred in winter, with the highest gametangial densities observed in Octob er, and the peak of recruits observed in December. The small recruits (0-2 cm in diameter) exhibited high growth (1 cm in <1 month) and mortality rate s. High exponential mortality rate was also observed in the larger individu als (>12 cm, or 6 years old). Intermediate size C. bursa showed the lowest mortality rate, indicating that organisms within this size range (3-12 cm) escape advective and grazing losses that decimate small recruits and that t hey, unlike larger organisms, maintain art adequate physiological status. A sexual gemmation within the intermediate size classes may also contribute t o maintain stable populations of this species in the NW Mediterranean litto ral zone, since recruits derived from sexual reproduction experience extrem ely high mortality rates.