INTRODUCTION
Australia is a known region for high seahorse diversity (Hippocampus sp.), with at least 27 species of seahorses known to occur in the region (Kuiter, Reference Kuiter2009). The thorny seahorse, Hippocampus histrix (Kaup, Reference Kaup1856), has been recorded to occur in the tropical waters of northern Australia, with records from Western Australia, Northern Territory and Queensland (ALA, 2015). This species is typically found occurring in the waters of the Philippines and Indonesia, but is also known from the east coast of Africa and Japan (Lourie et al., Reference Lourie, Vincent and Hall1999). The most southern record of this species in Australian waters is from the Great Barrier Reef, located off Townsville (18°53′0.15″S 148°23′0.50″E) (ALA, 2015). The species is easily recognizable from its spiny appearance (particularly the very long, extremely sharp, dark-tipped spines) and long snout, whilst its colouration varies from bright yellow to brown. The species is generally found with sponges, weedy rocky reefs and soft bottoms with soft coral and sponge habitat, typically in depths >6 m (Lourie et al., Reference Lourie, Vincent and Hall1999); however, it has been observed in deeper water at a depth of 30 m (Lembah Strait 2008, personal observation).
The species is considered threatened across its range because of population declines and habitat destruction and is listed as ‘Vulnerable’ on the IUCN Red List (IUCN, 2015).
MATERIALS AND METHODS
As part of a larger research project on the White's seahorse, Hippocampus whitei (Bleeker, Reference Bleeker1855), monthly diving surveys were undertaken across four sites in Port Stephens, New South Wales (NSW), Australia, from 2006 to 2010 (Harasti et al., Reference Harasti, Martin-Smith and Gladstone2012, Reference Harasti, Martin-Smith and Gladstone2014b). Surveys consisted of 60 min scuba dives, where all encountered syngnathids (seahorses, pipefishs, pipehorses, seadragons) were recorded with details of the species, size and sex documented. All habitat types at depths from 3 to 12 m were surveyed during these surveys for the presence of syngnathids.
RESULTS
Three individual Hippocampus histrix were recorded between 2007 and 2014. The first was collected in February 2007 from the site Seahorse Gardens (32°42′55.70″S 152°08′58.87″E), at a depth of 8 m and was found on a Euplexaura sp. gorgonian fan (Figure 1). The specimen measured 6 cm from tail tip to coronet and was a female (absence of brood pouch). This specimen is stored in the Australian Museum fish collection (I.44098-001) and was identified as H. histrix by Rudie Kuiter (Kuiter, Reference Kuiter2009) and fish collection manager Mark McGrouther. A spine clip was taken from this specimen for genetic analysis and was processed at the California Academy of Sciences in 2010. The taxonomic identity of the CO1 sequences was confirmed by comparison to syngnathid specimens in the Barcode of Life database (http://www.barcodeoflife.org/), as well as vouchered specimens in several ichthyology collections (Healy Hamilton, personal communication).
Hippocampus histrix (Kaup, Reference Kaup1856), female, on Euplexaura sp. gorgonian fan (photograph: David Harasti).
The second specimen was found in February 2009 at the Pipeline site (32°43′04.63″S 152°08′29.27″E), at a depth of 7 m (Figure 2) and was found living on the soft coral Dendronephthya australis (Kükenthal, Reference Kükenthal1905). The specimen measured 8 cm from tail tip to coronet and was a female. The animal was found inhabiting the site for a period of 115 days. Identification was confirmed by Rudie Kuiter, and also confirmed by genetic analysis, as undertaken for the 2007 specimen.
Hippocampus histrix (Kaup, Reference Kaup1856), female, free swimming (photograph: David Harasti).
The third specimen was photographed by a local diver (Figure 3) at the site Fly Point (32°42′48.20″S 152°09′11.40″E), at a depth of 5 m, a no take sanctuary zone within the Port Stephens–Great Lakes Marine Park, in April 2014. This individual is considered a female (as no developing male pouch evident) and, although the size of this individual was not recorded, it was estimated to be around 7 cm by the photographer.
Hippocampus histrix (Kaup, Reference Kaup1856), female, in sponge habitat (photograph: Paul Rudder).
DISCUSSION
These three sightings of Hippocampus histrix in Port Stephens greatly extend the range of this species southwards along the Australian coast. When compared with the previous most southern record in Australia (Great Barrier Reef), these new records extend the known range of Hippocampus histrix southwards by approximately 1800 km. It is not uncommon for tropical species to be advected southwards along the east coast of Australia under the influence of the East Australian Current (EAC). Various studies have shown that tropical species and fish larvae are regularly transported southwards along the EAC into the coastal waters of central and southern NSW (Booth et al., Reference Booth, Figueira, Gregson, Brown and Beretta2007; Figueira & Booth, Reference Figueira and Booth2010; Harasti et al., Reference Harasti, Gallen, Malcolm, Tegart and Hughes2014a). It is not uncommon for other tropical syngnathids, and related species, to appear in Port Stephens, as tropical species such as the bend-stick pipefish Trachyrhamphus bicoarctatus (Bleeker, Reference Bleeker1857) and the harlequin ghost pipefish Solenostomus paradoxus (Pallas, Reference Pallas1770) are generally seen from January to May when the water temperature is at its warmest (~21–24°C) (Harasti, unpublished data).
It's occurrence on soft coral, sponge and gorgonian habitats is interesting, as these habitats are the preferred habitats of Hippocampus whitei within Port Stephens (Harasti et al., Reference Harasti, Martin-Smith and Gladstone2014c). There is a diverse range of habitats available within the Port Stephens estuary and this area is considered to be a ‘hot spot’ for unusual and rare fish and invertebrate species, as seen by the various community sightings logged in the REDMAP database (REDMAP, 2015) and published sightings (Scott et al., Reference Scott, Harasti, Davis and Smith2014). The second recorded animal was observed residing at the Pipeline site for a long duration (115 days) and was only found utilizing a very small area of approximately 9 m2 amongst the Dendronephthya australis soft corals the entire time it was present. The occurrence of an individual over a period of approximately four months indicates that there is the possibility that this species could possibly adapt to cooler water temperatures (<20°C). Given that the south-east of Australia is expected to experience the greatest increase in water temperature as a result of climate change (Hobday & Lough, Reference Hobday and Lough2011), it is important to document the range extensions of species into this region.
ACKNOWLEDGEMENTS
I am grateful to Rudie Kuiter for his assistance with the identification of these specimens. Thanks to Paul Rudder who captured the photos of the individual found at Fly Point in 2014. I am grateful to Dr Healy Hamilton, Graham Short and Beth Moore from the California Academy of Sciences for undertaking the genetic analysis to confirm the species identification.
