Hormosira

Hormosira is a genus of seaweed in the family Hormosiraceae.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is monotypic, with a single species, Hormosira banksii, also known as Neptune's necklace, Neptune's pearls, sea grapes, or bubbleweed. It is native to Australia and New Zealand.

Distribution

Hormosira is native to southeastern Australia (including Tasmania, Lord Howe Island and Norfolk Island) and New Zealand.<ref name="Huisman-2000">Template:Cite book</ref><ref name="NZPCN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Nelson-2013">Template:Cite book</ref><ref name="Schiel-1999">Template:Cite journal</ref><ref name="Mueller-2018">Template:Cite journal</ref><ref name="Bellgrove-2017" /><ref name="Thomsen-2016" /> Despite substantial morphological variation across its range, the species represents a single species and the genus Hormosira is monotypic.<ref name="Mueller-2018" /> Genetic analyses of mitochondrial COI and microsatellite DNA sequence data have indicated that there is low genetic variation across the range of the species in Australia.<ref name="Mueller-2018" /><ref name="Bellgrove-2017" />

Description

Hormosira is a perennial<ref name="Schiel-1999" /> species of seaweed (brown algae, Fucales).<ref name="Nelson-2013" /> It is abundant on low-energy rocky reefs within the intertidal zone, where it outcompetes other algal species due to its high tolerance to desiccation. Plants vary significantly in morphology.<ref name="Mueller-2018" /> The thallus (or frond) of the species is made up of strings of olive-brown, spherical, gas-filled pneumatocysts (or beads), which taper towards a small holdfast.<ref name="NZPCN" /> While the holdfast attaches strongly to a substrate, it can be easily dislodged by human trampling.<ref name="Schiel-1999" /> The spheres are buoyant and rise to the surface of the water during high tide, allowing plants to move with the flow of the current and obtain more sunlight.<ref name="Pathwayz" /> Hormosira also produces a slime layer to reduce desiccation,<ref name="Pathwayz" /> and plants often grows in high densities,<ref name="Schiel-1999" /><ref name="Thomsen-2016" /> which reduces their surface area exposed to the sun and further reduce dehydration.<ref name="Pathwayz">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Due to the buoyant thallus, Hormosira plants can drift out to sea over considerable distances, and floating plants can remain fertile for several weeks.<ref name="Mueller-2018" />

{{#invoke:Gallery|gallery}}

Reproduction

Hormosira reproduces sexually and is monoecious. The sex organs (conceptacles) are on the surface of the beads, and are visible to the naked eye as rough-looking dimples.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Hormosira produces eggs throughout the year, but its peak reproduction is often confined to July–October (at least in northern New Zealand) when the sea temperature is around 14 °C, as the viability of the eggs can be low in high sea temperatures such as 17–22 °C.<ref>Template:Cite journal</ref> At high tide, the eggs are released directly into the surrounding water. The eggs are negatively buoyant they sink to the substrate to develop for several days before becoming attached.<ref name="Mueller-2018" /> All individuals release at the same time, maximising fertilisation. The species can also reproduce asexually from broken and dislodged fragments.

{{#invoke:Gallery|gallery}}

Ecology

File:Nothhormo.jpg

Hormosira provides habitat for this obligate epiphyte, Notheia anomala.

Hormosira is regarded as an ecosystem engineer<ref name="Bellgrove-2017">Template:Cite journal</ref> or habitat former<ref name="Thomsen-2016">Template:Cite journal</ref> that occurs in large patches and outcompetes other algal species due to its high tolerance to desiccation. Hormosira is a food source for sea urchins, many small crustaceans, and some juvenile fish.<ref name="Pathwayz" /> Young crustaceans and molluscs often rely on the dense canopies of Hormosira for niche space, protection from predators, and avoid desiccation at low tide.<ref name="Pathwayz" /> Hormosira provides a substrate for sessile organisms to attach onto, including sea urchins and a wide range of facultative and obligate algal epiphytes such as Notheia anomala.<ref name="Thomsen-2016" /> This is beneficial to many organisms as competition for habitat space is a primary limiting factor in the intertidal environment.

Uses

Due to the species' high iodine content, Tasmanian schoolchildren were once urged to eat a bead a day to keep the goitres away.<ref>Template:Cite book</ref>

External links

• Neptune's necklace discussed in RNZ Critter of the Week, 31 Jul 2020