H. erectus develops elaborate skin fronds and has variable forms and may represent more than one species.
The entire genus Hippocampus is listed in Appendix II of CITES, effective May 2004. H. erectus is listed as Vulnerable by IUCN. Mexican populations are listed in the NOM-059-SEMARNAT-2001 as species subject to special protection; Mexico prohibits the intentional capture and trade of wild seahorses, permitting only the commercialisation of cultured and incidentally caught seahorses. The species is caught in shrimp trawling and by other fisheries, and is affected by habitat degradation due to coastal development and pollution.
• H. hippocampus is smaller; has a shorter snout and is restricted to the Mediterranean and eastern Atlantic
• H. reidi has a narrower body, a rounded coronet, and a head that is less deep
• Males have proportionally longer tails than do females
• Known to develop elaborate skin fronds
• H. erectus has variable forms and may represent more than one species
• Specimens from Argentina and Brazil appear to be genetically distinct from north Atlantic specimens, and may prove to be a separate species