The life history of the long-snouted seahorse Hippocampus guttulatus was characterized using mark-recapture data collected within a focal study site and catch data from 53 additional sites in the Ria Formosa coastal lagoon, southern Portugal. Population structure in benthic habitats was characterized by high local densities (0·3–1·5 m−2), equal sex ratios and few juveniles <70 mm. Adult H. guttulatus maintained small (19·9 ± 12·4 m2), strongly overlapping home ranges during multiple reproductive seasons. Recruited (benthic) juveniles exhibited significantly lower site fidelity than adults. A Ford-Walford plot of standard length (LS) at time t against LS measured during the previous year from tagged juveniles and adults led to estimates of the von Bertalanffy parameters K = 0·571 and L∞ = 197·6 mm. The growth rate of planktonic juveniles (inferred from previous studies), was greater than predicted by the von Bertalanffy model, providing evidence of an ontogenetic shift in growth trajectory. The instantaneous rate of natural mortality, M, ranged from 1·13 to 1·22 year−1(annual survival rate = 29·4–32·2%). Sexes did not differ in movement, growth or survival patterns. On average, H. guttulatus measured 12·2 ± 0·8 mm at birth. Planktonic juveniles recruited to vegetated habitat at 96·0 ± 8·0 mm (0·25 years), had mature brood pouches (males only) at 109·4 mm (0·49 years), began maintaining home ranges and reproducing at 125–129 mm (0·85–0·94 years), and lived for 4·3–5·5 years. Early age at maturity, rapid growth rates, and short generation times suggested that H. guttulatus may recover rapidly when direct (e.g. exploitation) and indirect (e.g. by-catch and habitat damage) effects of disturbance cease, but may be vulnerable to extended periods of poor recruitment.