Priority Marine Feature - Serpulid aggregations

Description

Characteristics 

Dense clumps of white chalky tubes, each containing a Serpula vermicularis worm. When feeding, the worms extend red, white or orange feathery tentacles. Serpulid aggregations can reach over 1 m in height and 2 m wide, composed of individual tubes, each up to 5 mm wide and 15 cm in length, growing on top of one another anchored to pebbles, shells or stones in muddy sediment. Serpulid aggregations provide solid substrata in an otherwise sedimentary area. Sea squirts, sponges, sea firs and seaweeds grow on the calcareous tubes, while the complex three dimensional structures provide shelter and habitat for crabs, shrimps, squat lobsters, brittlestars, starfish, worms and snails. The aggregations also provide refuge for a number of fish species (Chapman et al., 2012).

Definition 

Serpulid aggregations are not defined by a minimum number of tubes but rather their clumping together, growing vertically up from the seabed (generally greater than 10 cm in height) and forming a discrete community different from the surrounding seabed. More substantial aggregations (approx. >1 m diameter) are recognised as biogenic reefs (see Holt et al., 1998; European Commission, 2013). The calcareous remains of old serpulid tubes may serve as substrate for new aggregations to grow on.

Environmental preferences 

Serpulid aggregations occur in sheltered to extremely sheltered sea lochs or inlets with weak or very weak water flow, at depths of 6-10 m.

Distribution

Scottish distribution 

Loch Creran and Loch Ailort. A locally extinct population with some small aggregations is known from Loch Teacuis (an arm of Loch Sunart).

Estimated known Scottish extent 

Aggregations in Loch Ailort and now extinct ones in Loch Teacuis have been up to 0.5 m in diameter and height. The aggregations in Loch Creran have developed into larger reefs up to 3 m across, although typically only a metre, and 0.75 m high. An estimated ~108 ha of serpulid habitat was present in Loch Creran in 2005 (Moore et al., 2006) though recent studies (Moore et al., 2020) estimated that ~20% of all serpulid habitat in the loch has been lost since 2005. 

Wider distribution 

Only recorded from a few other locations worldwide: Killary Harbour, Ardbear Lough and Blacksod Bay (MERC Consultants, 2008) in Ireland; and Mar Piccolo, a lagoon near Taranto in Italy.

Status

Scottish waters support all UK records of this habitat. The reefs in Loch Creran represent the best example and the largest extent of this habitat in the world. The first accounts described serpulid reefs in 1882 standing above the surface of Loch Creran at low tide (Moore et al., 1998). This suggests their distribution has declined over the last 120 years. The extent of the reefs within Loch Creran appeared to be stable through the 1990s, however survey work indicates there has been a significant deterioration in condition since 2005 (Tulbure, 2015). Recent studies (Moore et al., 2020) concluded that reef fragmentation is now widespread, estimating that ~20% of all serpulid habitat in the loch has been lost since 2005. It is hypothesised that serpulid reefs go through natural cycles of growth and collapse and ongoing academic studies in Loch Creran are exploring this in more detail. The serpulid aggregations in Loch Creran are recognised as biogenic reefs which can be part of the broadscale habitats protected in Special Areas of Conservation (SACs) under Annex 1 of the EU Habitats Directive (European Commission, 2013). The Directive is transposed into domestic legislation through The Conservation (Natural Habitats, &c.) Regulations 1994 (as amended in Scotland) (Habitats Regulations).

Small aggregations of serpulid worms were discovered in Loch Teacuis in 2006 (Mercer et al., 2007; Dodd et al., 2009), but these have also since declined (SNH, 2015) and are now locally extinct in many areas of the loch, with some small aggregations

only present in a small number of areas (Sim, 2022; NatureScot, unpublished). The aggregations in Loch Ailort were first recorded in 2015 by recreational Seasearch divers.

Drivers for improving protection

Serpulid aggregations are included on the PMF list which means that National Marine Plan General Policy 9(b) (avoiding significant impact on national status) applies. The Scottish Biodiversity Strategy to 2045, the Scottish Biodiversity Duty and UK Marine Strategy Good Environmental Status provide further drivers to ensure biological diversity is restored, and ecosystems are safeguarded. 

Sensitivity (including recovery)

[Key sources: FeAST, Fisheries Management Guidance]

Serpulid aggregations are extremely sensitive to physical disturbance and abrasion, and are also sensitive to changes in water flow and salinity. Threats to serpulid aggregations include bottom-contacting fishing activities, anchoring and coastal developments that alter water flow. 

Serpulid aggregations may be vulnerable to future climate impacts associated with ocean acidification (see Chan, 2013) and de-oxygenation. Projected increases in the frequency and strength of storm events associated with climate change may also pose a threat to serpulid aggregations.

There is evidence that habitat restoration may be possible in areas where serpulid aggregations have declined. Small aggregations were well established on experimental scallop shell substrates deployed in Loch Creran in 2012 as part of restoration studies (Cook, 2016; Moore et al., 2020). However, in areas where there is no longer a viable population to provide larvae, regeneration will not occur naturally (Lancaster et al., 2014). Serpulid growth has been estimated at c. 3 cm per annum (Moore et al., 2006; Hughes et al., 2008). Survivorship studies to determine the feasibility of artificial restoration in Loch Sween using stock translocated from Loch Creran were inconclusive. Aggregations present in Loch Sween during the 1980s died out in the 1990s for reasons that are still not understood (Hughes et al., 2008).

Connectivity

Between serpulid aggregations 

Serpulid aggregations are mostly present in sheltered locations with low larval dispersal potential. Populations tend to become self-seeding, especially when isolated. Serpulid worms (in non-aggregated form, and not part of this PMF) are widely distributed on rocky habitats around the Scottish coastline.

With other PMFs 

The only known functional link or association between serpulid aggregations and other PMFs is with kelp and seaweed communities on sublittoral sediments PMF which occurs in the same depth band. Colonisation of serpulid aggregations in Loch Teacuis by the sugar kelp Saccharinalatissima may have contributed to their decline here. When kelp grows on small serpulid aggregations it is likely that even modest tidal water flow generates sufficient drag to cause the aggregation attachment to snap off or dislodge from the hard substrates anchoring it to the soft muddy seabed. An accumulation of drifting sugar kelp with holdfasts overgrowing broken up serpulid tubes was observed to the east of the tidal narrows entrance to the loch in 2015 (SNH, 2015).

Ecosystem services

The habitat provided by serpulid aggregations supports a number of other species and contributes to the protection of biodiversity. Serpulid aggregations also have a role in sediment stabilisation, nutrient cycling and waste breakdown as well as providing shelter to commercial fish and shellfish particularly juveniles.  

Existing Marine Protected Areas

Serpulid aggregations are a protected feature of Loch Creran MPA and Loch Sunart MPA where the Loch Teacuis population has declined (SNH, 2015). 

Existing and proposed fishing measures providing PMF protection

Serpulid aggregations are protected by the following existing fishing measures:

• The Inshore Fishing (Scotland) Order 2015 (Loch Creran and Loch Sunart)

New fishing measures are proposed, which will protect serpulid aggregations that are found outside of the MPA network:

• Sound of Arisaig SAC (proposed measures extend beyond the boundary of the site and would encompass serpulid aggregations in Loch Ailort).

Approach to assessing improvements in management needed to protect serpulid aggregations from impacts related to towed bottom-contacting fishing gear  

The assessment presented in this document relates to fishing using towed bottom-contacting gear only. It is consistent with the approach taken for assessing proposed developments. 

All recent or extant records in Scottish nearshore waters are already afforded protection or will be afforded protection against damage from towed bottom-contacting fishing gear within the Loch Creran MPA, Loch Sunart MPA and Sound of Arisaig SAC. Any new records of this habitat would also warrant protection.

Any towed bottom-contacting fishing activity that leads to the loss of entire aggregations or damage to aggregations, such that function or provision of ecosystem services cannot be maintained, should be considered to have a significant impact on national status and as a result not meet General Policy 9(b) in the National Marine Plan. Existing licensing and consenting processes will continue to consider the potential for significant impacts serpulid aggregations.

Key locations for the protection of serpulid aggregations outside designated sites and existing towed bottom-contacting fisheries restrictions

There are currently no other known, verified records of serpulid aggregations outside the existing MPA network in Scottish territorial waters. 

Data confidence

We have recent records from 2022 (including null records in Loch Teacuis). The majority of the records are from 2005 (>3000) and come from NatureScot commissioned MPA monitoring studies, with additional records from Seasearch diving surveys. Records primarily come from diving, with some ROV and drop-down video surveys (e.g. Poloczanska et al., 2004). New records of this feature (Loch Ailort) were made in 2015, with targeted mapping surveys undertaken in this location in 2016 (SNH, 2016) and 2017.

Knowledge gaps and other recommended work

We recommend continuing efforts to explore opportunities for collaborative monitoring, survey and research to improve our understanding of this habitat, for example:

• The remains of former serpulid aggregations in soft muddy sediments in West Loch Tarbert were noted in 2017 and also signs of potential new aggregation development (Paisley, 2017). Future survey work will be required to determine whether aggregations develop.
• There have been other reports of serpulid aggregation development in Loch Sween. Future survey work will be required here to determine whether aggregations develop.
• There have been anecdotal reports of serpulid aggregations in other sheltered sea lochs (e.g. Loch Glendhu and Loch Reasort). New survey work would be required to validate these observations.

Key locations for the protection of serpulid aggregations