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 constrained by the spherical geometry of its thallus. Changes in reproductive phenology, population structure, density, biomass, and production of this widespread alga were followed over an annual cycle to examine whether mortality rate was size and age dependent. Examination of size and age distributions showed the population to be in quasi-steady state. A main recruitment event occurred in winter, with the highest gametangial densities observed in October, 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 rates. High exponential mortality rate was also observed in the larger individuals (>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 they, unlike larger organisms, maintain an adequate physiological status. Asexual gemmation within the intermediate size classes may also contribute to maintain stable populations of this species in the NW Mediterranean littoral zone, since recruits derived from sexual reproduction experience extremely high mortality rates.