The Spanish prefix eco-, loosely translated in most contexts as “ecological,” should be treated as other prefixes, says the language watchdog Fundéu. In other words, it is attached to words without an intervening hyphen or an intervening space.
Examples include ecoparque (ecopark), ecoterrorism and ecotasa (an ecological tax, such as one on carbon production). The rule applies even with coined or relatively recent words such as ecotaxi (presumably a taxi with a small carbon footprint) and ecopacifista (ecological pacifist).
Photo of Volcán Arenal in Costa Rica by Arturo Sotillo/CC BY-SA 2.0.