Daniel Harries

The establishment of the invasive alga Sargassum muticum on the west coast of Scotland: a preliminary assessment of community effects

Comparative studies were conducted on intertidal algal and faunal communities associated with Sargassum muticum and native algae on the Isle of Cumbrae, Scotland. Significant differences were detected in the structure and composition of the communities. The abundance of the dominant native algae Dictyota dichotoma was found to be reduced in areas dominated by S. muticum and displacement through competition for substrate or light is inferred. Elevated faunal abundances were associated with S. muticum and evidence indicates that increased detrital input may be a possible contributory factor. Differences in faunal community composition were most pronounced in the sessile epifauna below the S. muticum canopy. Faunal communities associated with S. muticum were less heterogeneous in composition than those associated with native algae at equivalent shore positions. Some of the compositional differences may be coincidental and attributable to factors favouring the establishment of S. muticum rather than to the direct influence of the S. muticum canopy.

The status and ecology of reefs of Serpula vermicularis L. (Polychaeta: Serpulidae) in Scotland

1. The distribution and abundance of reefs of Serpula vermicularis was examined in Loch Creran, the only known remaining site of reefs of this species in Scotland. In view of the decline in populations elsewhere, the aims included assessment of the importance of the Scottish population in terms of conservation of the reef habitat and the establishment of a baseline against which future changes could be gauged. A further objective was to determine appropriate conservation management of the reefs by examining the influence of both natural and anthropogenic factors. 2. Reefs were largely restricted to a depth range of 1–13 m. Factors controlling the depth distribution are discussed. 3. Serpula vermicularis reefs colonized a variety of substrata, but predominantly grew on lamellibranch shells on a seabed of muddy sand. There was some evidence that reef abundance was influenced by the availability of suitable substrata. 4. A belt of scattered reefs fringed much of the coastline of the loch with profuse reef development at two sites, where reef coverage exceeded 10% of the seabed. In terms of total abundance of Serpula vermicularis reefs, Loch Creran represents the major world site for reef development. It is concluded that the reefs of Loch Creran are of significant nature conservation importance and grounds for the establishment of conservation management are discussed. 5. Reef development is apparently curtailed in areas of strong currents and high flushing rate. There is evidence that human activity has adversely influenced reef growth through the discharge of organic factory effluent and the physical disturbance caused by mooring ground tackle. Scallop dredging also represents a significant threat to the persistence of serpulid reefs. Methods of minimising damage to this rare and fragile feature are discussed.

Community composition and diversity of two Limaria hians (Mollusca: Limacea) beds on the west coast of Scotland

Limaria hians functions as a keystone species in construction of a highly diverse biogenic habitat. An investigation to quantify the biodiversity of two L. hians beds was carried out during the winter and summer seasons at two sites on the west coast of Scotland. Cores were taken semi-randomly through 100% L. hians nest material, organisms removed, identified and enumerated. Univariate and multivariate analyses of the data were used to establish temporal and locational differences. A total of 7275 individuals were found representing 282 species from 16 phyla. Univariate analysis revealed significant differences between the species richness of the two populations, whilst multivariate analysis illustrated differences in the assemblage compositions between sites and times. This study showed that in terms of richness and diversity these beds are among the most important biogenic habitats in the UK.