Species description: This is a green, grass-like, marine flowering plant that can form dense meadows in the correct conditions. The tips of the blades have a distinctive notch which helps distinguish this species from Zostera marina. Zostera noltii usually occurs intertidally.

Life cycle: Eelgrass can reproduce asexually, spreading via rhizomes but can also flower and produce seeds.

Similar species: Could potentially be confused with Zostera marina but Nanoostera noltii is much more fine and usually intertidal, while Zostera marina has a more robust blade and usually occurs subtidally. Nanozostera noltii also has a characteristic notch at the tip of its blade, whereas Zostera marina has a rounded tip.

How to see this species: Usually intertidally in shallow, sheltered areas not subject to a lot of wave action e.g. sheltered inlets and bays. Usually prefers sand or muddy sand. The best place to see this species in Northern Ireland is on the northern shores of Strangford Lough.

Current status: Unknown.

Why is this species a priority in Northern Ireland?

• Criterion 1: Internationally listed species*.

* listed as part of a habitat.

Threats:

• Disease: A wasting disease was responsible for die-back of large areas of seagrass in the UK in the 1930s. The fungus and slime mould which colonised the weakened seagrass have recently reappeared in seagrass beds around the Isles of Scilly. While N. noltii is not thought to be as severely affected as Z. marina it is still susceptible.
• Natural cycles: The extent of seagrass beds may change as a result of natural factors such as severe storms, exposure to air, and freshwater pulses. Grazing by wildfowl can have a dramatic seasonal effect with more than 60% reduction in leaf cover reported from some sites. Warm sea temperatures coupled with low level of sunlight may cause significant stress and die back of seagrass.
• Physical disturbance, for example by trampling, anchoring, land claim and adjacent coastal development through the construction of sea defences and potential for changes in the hydrological regime.
• Introduction of, and competition from, alien species such as Spartina anglica.
• Increased turbidity reducing photosynthesis.
• Nutrient enrichment, at low levels, may increase production in seagrass while high nitrate concentrations have been implicated in the decline of mature Z. marina, effects on N. noltii are thought to be similar. Phytoplankton blooms, resulting from nutrient enrichment, have been shown to reduce biomass and depth penetration of eelgrass. Eutrophication can also result in a shift to phytoplankton epiphyte or macroalgal dominance.
• Marine pollution, eelgrass is known to accumulate Tributyltin and possibly other metals and organic pollutants. Several heavy metals and organic substances have been shown to reduce nitrogen fixation which may affect the viability of the plant, particularly in nutrient poor conditions. Accumulated pollutants may become concentrated through food chains.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• Maintain extent, quality and distribution of seagrass beds in Northern Ireland.
• Assess feasibility of restoration of damaged or degraded seagrass beds.
• Until surveys assess the extent of the seagrass resource, it will not be possible to assess whether restoration is necessary, or to specify a final target.

Conservation:

• There is a Northern Ireland Priority Habitat Action Plan for Seagrass Beds.
• Strangford Lough is a Marine Protected Area with multiple designations.
• Seagrass beds are listed by OSPAR as under threat and/or in decline.

Distribution Map from NBN: Nanozostera noltii at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Nanozostera noltii at iNaturalist World Species Observations database.

WoRMS: Nanozostera noltii at World Register of Marine Species. Accepted name: Zostera noltei Hornemann, 1832. AphiaID: 145796.

Classification: Biota; Plantae; Viridiplantae; Streptophyta; Tracheophyta; Spermatophytina; Magnoliopsida; Lilianae; Alismatales; Zosteraceae; Nanozostera