Gracilaria spp. aquaculture in Denmark

The use of traditional and a new grafting technique to produce seedlings using mature tissue that releases carpospores is investigated, as well as the newer method where germinating gametophytes are used, which can potentially re-establish attachment (“re-attachment”). A risk assessment of the invasive Gracilaria spp. spread in Limfjorden is done using DNA analysis technics. The aim is to cultivate in land the native Gracilaria, meaning, inducing cystocarp maturation, cystocarp sporulation, settlement of spores in specific substrate, growing seedlings, maintaining cultures and inducing tetrasporangia growth. Overall, the study is aiming to reproduce the life cycle of Gracilaria spp. in land to secure a steady supply of raw material for the development of native Gracilaria spp. aquaculture in Danish waters.

The life cycle of Gracilaria spp. is shown in Figure 1. The adult tetrasporophyte (A) releases tetraspores into the water and the spores attach to the surface by developing a discoid attachment organ. They then germinate and develop into either a female or a male gametophyte (B). During sexual maturation, the male gametophyte releases its gametes (spermatia) into the water, which is taken up by the female gametophyte through short-lived cellular tubes that carry the spermatia into the egg cell. After fertilization (C), the next generation develops and is called the cystocarp, and is seen as distinct brown knobs on the female gametophyte stems (see cover photo). In the cystocarp tissue, the microscopic carposporophyte forms, which matures and forms many carspospores, which are released into the water and attach to a surface, after which a new tetrasporophyte develops, completing the life cycle (A).