Abstract

The overgrowth of young sporelings by older and larger thalli is often assumed to result in death of the overgrown individual. However, if sporelings and larger conspecifics are able to coalesce, the fate of the overgrown sporeling may be different to the physical compression, starvation and mortality often assumed for them. Using cytological studies on laboratory-cultured individuals, as well as observations of recruitment in the field, we found that sporelings of the red alga Mazzaella laminarioides can be incorporated within the tissue of larger, overgrowing germlings or they may coalesce side-by-side with it, depending on sporeling size before contact. Thus, young sporelings do not necessarily die when overgrown by their older, conspecific competitors. Field observations suggest that these processes are common during natural recruitment, and therefore coalescence might be considered an alternative mechanism to intraspecific competition. Coalescing seaweeds should be included among the groups of sessile organisms that might be formed by genetically polymorphic thalli (chimeras).