Influence of recruitment and temperature on distribution of intertidal barnacles in the English Channel.

Many warm-water (Lusitanian) species reach their limits in the central English Channel, failing to penetrateto the North Sea. We re-surveyed the eastern limits of the Lusitanian intertidal barnacles Chthamalus montaguiand C. stellatus, from 1994 to 2004, a decade of exceptionally high sea temperatures, and found range extensionson both sides of the Channel compared to the 1950s and 1970s. Annual recruitment of Chthamalus on theEnglish coast was monitored. There was a consistent gradient of low recruitment to the east of Portland Bill,with significant reductions coinciding with prominent headlands. Highest recruitment occurred during thewarmest years. Cluster analysis showed a high degree of similarity of annual recruitment within coastal cellssuggesting that local processes are also important. In 1999 we compared recruitment in the other commonintertidal barnacles, the boreal Semibalanus balanoides and the non-native Elminius modestus, with Chthamalus spp.All species showed low recruitment between Selsey Bill and Portland Bill, suggesting habitat limitations and/orhydrographic mechanisms. Annual recruitment of Chthamalus at existing limits on the Isle of Wight was positivelycorrelated with the number of days of westerly and south-westerly winds during the summer, coincidingwith the pelagic larval phase. A ‘pulse’ of high Chthamalus recruitment on the Isle of Wight, measured duringthe warm summer of 2000, reversed population decline. Only a higher frequency of such pulses will maintainpopulations at existing limits and increase the rate of range extension towards the North Sea. Such extensionwill be limited by lack of hard substrata, but proliferation of coastal defence schemes in recent years is increasingsuitable habitat for barnacles

Using remote sensing to quantify fishing effort and predict shorebird conflicts in an intertidal fishery.

Accurate estimates of fishing effort are necessary in order to assess interactions with the wider ecosystem and for defining and implementing appropriate management. In intertidal and inshore fisheries in which vessel monitoring systems (VMS) or logbook programmes may not be implemented, quantifying the distribution and intensity of fishing can be difficult. The most obvious effects of bottom-contact fishing are often physical changes to the habitat, such as scarring of the sediment following dredging or trawling. We explored the potential of applying remote sensing techniques to aerial imagery collected by an unmanned aerial vehicle, or drone, in an area of intertidal mud flat (0.52 km2) in Poole Harbour, UK, where shellfish dredging is widely carried out and conflicts between commercial fishing interests and the conservation of internationally important shorebird populations are a concern. Image classification and image texture analysis were performed on imagery collected during the open dredge season in November 2015, in order to calculate measures of fishing intensity across three areas of the harbour subject to different management measures. We found a significant correlation between results of the image texture analysis and official sightings records collected during the dredging season, indicating that this method most accurately quantified dredging disturbance. The relationship between shorebird densities and food intake rates and the results of this analysis method were then investigated to assess the potential for using remotely sensed measures of fishing effort to assess responses of overwintering shorebird populations to intertidal shellfish dredging. Our work highlights the application of such methods, providing a low-cost tool for quantifying fishing effort and predicting wildlife conflicts

Effect of rock type on the recruitment and early mortality of the barnacle Chthamalus montagui

Discontinuities in distribution of sessile species due to changes in available habitat have rarely been investigated. In the English Channel, soft sedimentary rocks including chalk could potentially present a barrier to eastward range extension of the southern barnacle Chthamalus montagui. To test the effect of rock type on recruitment and mortality, prepared settlement tiles of four calcareous rocks that form important platforms close to existing limits of distribution were fixed to the shore at a site in south-west England, known to have consistently high larval settlement. Prior to fixation, the roughness parameter “Ra” and Potential Settlement Sites (PSS) index was measured. Recruitment was monitored photographically on four occasions during the settlement season and subsequent mortality for 7 months after the settlement season. By the end of the settlement season, recruitment on the hard Kimmeridge Cementstone was significantly less than on the other three rock types and attributed to low surface roughness and fewest Potential Settlement Sites (PSS), yet only 28% of variance could be attributed to PSS. Post-recruitment mortality was more variable, however after 7 months there were significant differences between rock types. Simultaneous surveys of post-recruitment mortality in natural populations showed that although recruitment on chalk can potentially be high, survivorship was relatively low. Thus rock type could be influential in setting species geographical limits

Disturbance of intertidal soft sediment assemblages caused by swinging boat moorings

The impact of swinging boat moorings on intertidal benthic assemblages was investigated in a small estuary on the south coast of England. Mooring buoys fixed near low water mark on a muddy shore were attached to 5 m of galvanised steel chain and had not been let for 12 months. Core samples for macro-invertebrates and sediments were taken both within and outside the chain radius of each buoy. The assemblage structure, biomass and abundance of selected bird prey species were examined at a range of scales. The study revealed variation in the impact of mooring buoys relative to control areas at two different times of sampling. Prior to the removal of buoys, the assemblage structure within areas affected by the buoys was found to be significantly different from unaffected areas. The abundance of the amphipod Corophium volutator, an important bird prey species, was significantly less in the areas affected by the buoys. In the second sampling programme (15 months after removal of buoys), the impact of extant buoys remaining in commission was not detectable. Assemblage structure in areas from which buoys had been removed was distinct from control areas which had never had buoys. The removal of mooring buoys clearly affected the assemblage, yet convergence with control areas, indicative of recovery, was not complete after 15 months. It is suggested that the effect of swinging mooring chains scraping over the mud surface may modify sediments favouring the greater prominence of larger particles such as gravel and shell fragments. The ecological impact of swinging moorings on estuarine benthic assemblages in designated protected areas is discussed in the context of other spatial and temporal disturbances

Long-term changes in the geographic distribution and population structures of Osilinus lineatus (Gastropoda: Trochidae) in Britain and Ireland

Many warm-water (Lusitanian) species reach their limits in the central English Channel, failing to penetrateto the North Sea. We re-surveyed the eastern limits of the Lusitanian intertidal barnacles Chthamalus montaguiand C. stellatus, from 1994 to 2004, a decade of exceptionally high sea temperatures, and found range extensionson both sides of the Channel compared to the 1950s and 1970s. Annual recruitment of Chthamalus on theEnglish coast was monitored. There was a consistent gradient of low recruitment to the east of Portland Bill,with significant reductions coinciding with prominent headlands. Highest recruitment occurred during thewarmest years. Cluster analysis showed a high degree of similarity of annual recruitment within coastal cellssuggesting that local processes are also important. In 1999 we compared recruitment in the other commonintertidal barnacles, the boreal Semibalanus balanoides and the non-native Elminius modestus, with Chthamalus spp.All species showed low recruitment between Selsey Bill and Portland Bill, suggesting habitat limitations and/orhydrographic mechanisms. Annual recruitment of Chthamalus at existing limits on the Isle of Wight was positivelycorrelated with the number of days of westerly and south-westerly winds during the summer, coincidingwith the pelagic larval phase. A ‘pulse’ of high Chthamalus recruitment on the Isle of Wight, measured duringthe warm summer of 2000, reversed population decline. Only a higher frequency of such pulses will maintainpopulations at existing limits and increase the rate of range extension towards the North Sea. Such extensionwill be limited by lack of hard substrata, but proliferation of coastal defence schemes in recent years is increasingsuitable habitat for barnacles