Hippocampus erectus occur in water up to 73 m, and are associated with aquatic vegetation such as mangroves, seagrass, sponges, and floating Sargassum, as well as sponges (Lieske and Myers 1994, and McAllister 1990 in Lourie et al. 1999, Fish and Mowbray 1970). Hippocampus erectus can be found at the surface and bottom of both shallow water and deeper areas of channels in bays, along beaches, in or near salt marshes, and over oyster beds and weed-covered banks (Hardy 1978).

This species may be particularly susceptible to decline. The limited information on habitat suggests they inhabit shallow sea-grass beds (Lourie et al. 1999) that are susceptible to human degradation, as well as making them susceptible to being caught as bycatch. All seahorse species have vital parental care, and many species studied to date have high site fidelity (Perante et al. 2002, Vincent et al., in review), highly structured social behaviour (Vincent and Sadler 1995), and relatively sparse distributions (Lourie et al. 1999). The importance of life history parameters in determining response to exploitation has been demonstrated for a number of species (Jennings et al. 1998).