Hippocampus abdominalis is native to the temperate coastal waters of south-eastern Australia and New Zealand. It is easily identified by its prominent, bulging abdomen and the numerous dark spots covering its yellow or brownish body. These seahorses typically inhabit seagrass beds, rocky reefs, and even artificial structures such as jetties, at depths ranging from the shallow intertidal zone down to 100 metres. Unlike many other seahorse species, big-belly seahorses are relatively strong swimmers and are known to be active during both day and night. They are the largest seahorse species found in Australian waters, reaching lengths of up to 35 centimetres.