Water level fluctuations and phenological responses in a salt marsh succulent

•Salicornia tegetaria has a wide physicochemical tolerance range in its intertidal habitat in South African estuaries.•In a temporarily open / closed estuary expansion rate is ten times faster than in a permanently open estuary, even under water logged conditions.•It produces high number of inflorescence and seeds over a short period and has a high sediment seed reserve of viable seed.•Salicornia tegetaria is a remarkably adaptive species with clear phenotypic variations in growth rate and fecundity. This makes the species an effective colonizer.•Faced with sea level rise and anthropogenic pressures this study assists in our understanding of macrophyte dynamics in estuaries. The succulent salt marsh plant Salicornia tegetaria occurs in both temporarily open / closed (TOCE) and permanently open estuaries (POE) where it experiences a wide range of physicochemical conditions in South African estuaries. The study investigated the characteristics of this plant in relation to water level in a TOCE and a POE and showed that cover was stable in the permanently open estuary but changed in response in water level in the temporarily open/closed system. Monthly expansion in S. tegetaria cover was 46% compared to 5.2% in the POE. In the TOCE the life cycle took four months to complete, seedlings emerged two days after the water level dropped, and the habitat was exposed. This was despite the mouth being closed for the whole study period and a mean water depth inundation of 27 ± 6 cm. Plants in the TOCE produced significantly more inflorescences (409 ± 79 per m²) and seed (45 542 ± 9 212 per m2), compared to the plants in the POE where water level was stable (87 ± 9 inflorescences per m² and 7 092 ± 775 seeds per m²). A large sediment seedbank (9 758 seeds m−2) in the TOCE ensures germination when water level drops and conditions become favourable for establishment. These data are important as they indicate that S. tegetaria is a remarkably adaptive species that can grow over a wide range of physicochemical conditions that will allow the species to persist in the face of future future sea level rise and anthropogenic pressures.