Growth
Growth rates of Chondrus crispus vary widely according to environmental conditions. Pybus (1977) reported mean growth for Chondrus crispus from Galway Bay of 0.33 mm/day, with little seasonal variation in growth rate. A similar rate of 0.37 mm/day was reported for plants from Maine, USA (Prince & Kingsbury, 1973). Sporelings grew at 0.02-0.08 mm/day in culture, and growth rate was governed principally by temperature (Tasende & Fraga, 1999). Peak growth occurred from May to November in eastern Canada (Juanes & McLachlan, 1992; Chopin et al., 1999). Optimum growth of Chondrus crispus in culture occurred at 10-15°C (Fortes & Lüning, 1980), 15-17°C (Tasende & Fraga, 1999) and 20°C (Simpson & Shacklock, 1979). Kuebler & Dudgeon (1996) reported higher growth rates at 20°C vs. 5°C, in terms of length, biomass, surface area, dichotomy and branch production, for Chondrus crispus from the Gulf of Maine, USA. North Sea plants grown in culture were growth saturated at light intensities of 70 µE/m²/s and growth rate increased up to a 24 hour photoperiod (Fortes & Lüning, 1980). For cultured spores of Chondrus crispus from NW Spain, growth rate increased with salinity between 23 and 33 psu, declined above light intensities of 20 µmol/m²/s and below photoperiods of 16:8 (light: dark) (Tasende & Fraga, 1999).

Supports which species
Chondrus crispus from Galway Bay, Ireland, was a host for algal epiphytes including Ceramium nodulosum, Melobesia membranaceum, Lomentaria articulata, Membranoptera alata, Palmaria palmata, and faunal epiphytes including Alcyonidium hirsutum, Dynamena pumila, Electra pilosa, Grantia compressa, Helcion pellucidum and Spirorbis borealis (Pybus, 1977). Leathesia difformis grew epiphytically on Chondrus crispus in Nova Scotia, Canada (Chapman & Goudey, 1983). In substratum choice experiments in the laboratory in New Hampshire, USA, the bryozoan Alcyonidium polyoum preferentially settled on Chondrus crispus and Fucus distichus, rather than other algae (Hurlbut, 1991). The epiphytes, Ulva sp. (studied as Enteromorpha) and Ectocarpus sp. grew epiphytically on Chondrus crispus in culture, and were in turn grazed by the crustaceans Gammarus lawrencianus and Idotea baltica (Shacklock & Doyle, 1983). Idotea baltica readily consumed Chondrus crispus when no other food was available, whereas Gammarus lawrencianus did not.
Chondrus crispus can sometimes be epiphytic on kelps (S. Kraan, pers. comm.).