Halopteris alternata

Invasion History

First Galapagos Record: 2015

---

General Invasion History:

The hydroid Halopteris alternata was described by Nutting in 1900, from Barracuda Rocks in the Bahamas. It is widely distributed in the coastal Western Atlantic from North Carolina to Brazil. It is a member of genus with many species.  It has often been confused with H. diaphana, a predominantly Eastern Atlantic species (Schuchert 1997). Eastern Atlantic populations are known from Madeira, the Canary Islands, and the Cape Verde Islands, and are considered cryptogenic (Ansín Agís et al. 2001). 

Invasion History in the Galapagos:

Halopteria alternata was reported by Fraser (1938a, cited by Calder et al. 2019), from Isla Flores and Isla Wolf, but these records are believed to refer to an undescribed species (Schuchert 1997; Calder et al. 2019; Calder et al. 2021). In April–May 2016, many specimens of Halopteris alternata were collected from SERC fouling plates in Puerto Ayora, on Santa Cruz Island on docks (Calder et al. 2019). In 2018 fouling plate surveys it was not found on Santa Cruz Island (Calder et al. 2021) but is presumably still established. 

Invasion history elsewhere in the world:

In 2018, two specimens of Halopteris alternata were collected at the Salinas Yacht Club, Ecuador. In 2018, multiple specimens of H. alternata were collected in Chatham Bay, Costa Rica (Calder et al. 2022).  

Description

Halopteris alternata (Nutting 1900) is a marine hydroid described from the Bahamas. It grows as plumes, with alternating branches arising from branching stolons. The basal portion (~25%) is devoid of branches and hydranths. The basal part is divided by 2–3 nodes and the branches are also segmented by nodes. The nodes are cup-shaped or conical. The segments bear nematothecae, structures bearing small conical clumps of nematocysts. The hydrothecae are cup-shaped, with a smooth margin. Gonothecae of both sexes can arise on the same plume and from the stem or the branches. The female gonothecae are somewhat elliptical, with a curved base and are truncated, with a complex lid, ~8 mm long. Male gonothecae are smaller and oblong, with a rounded distal end. The plumes are 7–20 mm tall. A medusa is not known for this species (Schuchert 1997; Torres-Rodriguez et al. 2020). 

---

Taxonomy

Ecology

General:

The hydroid occurs on attached and floating algae, often Sargassum, and often on coral fragments, sponges and stones, coral reefs, mangroves, and pilings, from the lower intertidal to 17m depth (Dalder 2019). This hydroid is found at marine salinities, under tropical and subtropical conditions, although it can be transported as far north as New Jersey by the Gulf Stream (Calder 2019).

Food:

Zooplankton, epibenthos

Consumers:

Competitors:

Trophic Status:

Suspension Feeder

SusFed

---

Habitats

General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
General Habitat	Coral reef	None
General Habitat	Mangroves	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None

---

Life History

The hydrozoan Halopteris alternata lacks a planktonic medusa, and grows as a polyp colony, reproducing sexually to produce planula larvae, which settle to form new polyps (Barnes 1983).

---

Tolerances and Life History Parameters

Maximum Height (mm)	20	None
Broad Temperature Range	None	Subtropical-Tropical
Broad Salinity Range	None	Poly-Euhaline

General Impacts

No impacts have been reported for introduced populations Halopoteris alternata. 

---

References

Ansín Agís J.; Ramil F.; Vervoort. W. (2001) Atlantic Leptolida (Hydrozoa, Cnidaria) of the families Aglaopheniidae, Halopterididae, Kirchenpaueriidae and; Plumulariidae collected during the CANCAP and Mauritania-IIexpeditions of the National Museum of Natural History,Leiden, the Netherlands, Zoologische Verhandelingen 333: 1-268

Calder, Dale R. (2019) On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689(1): 1-141

Calder, Dale R. and 8 authors (2021) Additions to the hydroids (Cnidaria, Hydrozoa) of marine fouling communities on the mainland of Ecuador and in the Galapagos Islands, Aquatic Invasions 16: 208-252

Calder, Dale R.; Carlton, James T.; Keith, Inti; Ashton, Gail V. ;Larson, Kristen; Ruiz, Gregory M.; Herrera, Esteban; Golfin, Geiner (2017) Biofouling hydroids (Cnidaria: Hydrozoa) from a tropical Eastern Pacific island, with remarks on their biogeography, Journal of Natural History 56(9-12): 565-606
https://doi.org/10.1080/00222933.2022.2068387

Calder, Dale R.; Carlton, James T.; Larson, Kristen; Mallinson, Jenny J.; Choong, Henry H. C.; Keith, Inti; Ruiz, Gregory M. (2019) Hydroids (Cnidaria, Hydrozoa) from marine fouling assemblages in the Galápagos Islands, Ecuador, Aquatic Invaders 14: 21-58

Calder, Dale R.; Kirkendale, Lisa (2005) Hydroids (Cnidaria, Hydrozoa) from shallow-water environments along the Caribbean coast of Panama., Caribbean Journal of Science 41(3): 476-491

Calder, Dale; Faucci, Ansuschka (2021) Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands, Zootaxa 5085(1): 1-73
https://doi.org/10.11646/zootaxa.5085.1.1

Moura, Carlos J.; Collins, Allen G.; Santos, Ricardo S.; Lessios, Harilaos (2019) Predominant east to west colonizations across major oceanic barriers: Insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker, Ecology and Evolution 9: :13001–13016.
DOI: 10.1002/ece3.5608

Oliveira, Otto M. P. and 24 authors (2016) Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters, Zootaxa 4194: 1-256

Schuchert, P.P. (1997) Review of the family Halopterididae (Hydrozoa, Cnidaria), Zoologische Verhandelingen 309: 1-162

Torres-Rodroguez, Javier; Daniel Ortiz-Oola; ; Puentes-Sayo, Alejandra; Lecompte, Orlando P; Jauregui, Aminta (2020) Genetic And Morphologic Identities Of Hydrozoans (cnidaria, Hydrozoa) From Reef Patches Of Santa Marta, Colombian Caribbean, Zootaxa 4758(1): 127-140

---