Eunice Pinn

Effect of track spacing and data interpolation on the interpretation of benthic community distributions derived from RoxAnn™ acoustic surveys

A 150 mile 2 (388 km 2 ) area in the South Minch on the Scottish west coast was surveyed acoustically using the seabed discrimination system RoxAnn™. This site was chosen from BGS seabed sediment maps because of the wide variety of substratum types present within a relatively small area. The work presented here investigates different combinations of survey track spacing in relation to interpolation of acoustic data for mapping benthic biodiversity. Three different survey track spacings (4, 2 and 1 km) and three pixel sizes (1000, 500 and 250 m) were utilised. The results indicated considerable variations in the fine scale variations of the substratum maps produced and their accuracy in relation to ground truth data. Depending on the track spacing and level of interpolation utilised, the survey site could be considered relatively important under the UK Biodiversity Action Plan in terms of priority habitat types present or completely insignificant. These variations have serious implications for the use of this technology in site identification, conservation and management.

What Caused the UK's Largest Common Dolphin (Delphinus delphis) Mass Stranding Event?

On 9 June 2008, the UKs largest mass stranding event (MSE) of short-beaked common dolphins (Delphinus delphis) occurred in Falmouth Bay, Cornwall. At least 26 dolphins died, and a similar number was refloated/herded back to sea. On necropsy, all dolphins were in good nutritive status with empty stomachs and no evidence of known infectious disease or acute physical injury. Auditory tissues were grossly normal (26/26) but had microscopic haemorrhages (5/5) and mild otitis media (1/5) in the freshest cases. Five lactating adult dolphins, one immature male, and one immature female tested were free of harmful algal toxins and had low chemical pollutant levels. Pathological evidence of mud/seawater inhalation (11/26), local tide cycle, and the relative lack of renal myoglobinuria (26/26) suggested MSE onset on a rising tide between 06∶30 and 08∶21 hrs (9 June). Potential causes excluded or considered highly unlikely included infectious disease, gas/fat embolism, boat strike, by-catch, predator attack, foraging unusually close to shore, chemical or algal toxin exposure, abnormal weather/climatic conditions, and high-intensity acoustic inputs from seismic airgun arrays or natural sources (e.g., earthquakes). International naval exercises did occur in close proximity to the MSE with the most intense part of the exercises (including mid-frequency sonars) occurring four days before the MSE and resuming with helicopter exercises on the morning of the MSE. The MSE may therefore have been a “two-stage process” where a group of normally pelagic dolphins entered Falmouth Bay and, after 3–4 days in/around the Bay, a second acoustic/disturbance event occurred causing them to strand en masse. This spatial and temporal association with the MSE, previous associations between naval activities and cetacean MSEs, and an absence of other identifiable factors known to cause cetacean MSEs, indicates naval activity to be the most probable cause of the Falmouth Bay MSE.

14. Ecological impacts of Sika Deer on Poole Harbour saltmarshes

Abstract This study investigates the effect of an introduced species, Sika Deer Cervus nippon on saltmarsh plant and infaunal communities. Epidermal fragment analysis was used to identify the plant species eaten by Sika Deer. Vegetation communities in deer exclosures and openly grazed areas were monitored over 4 years to investigate the effect of grazing on plant community composition and structure. The infaunal communities were assessed by extracting sediment cores. Deer were found to graze preferentially on Spartina anglica as intensive grazing led to swards dominated by Salicornia ramosissima even in upper marsh areas. Highest plant diversity was related to intermediate levels of grazing. Overall, higher levels of grazing led to higher abundance of three species of infauna detected in this study: Hydrobia ulvae, Gammarus sp. and Nereis diversicolor. Detailed examination revealed that the high abundance of H. ulvae was related to small quantities of above ground vegetation volume and that the abundance of Gammarus was related to small quantities of below ground vegetation biomass. The possible direct and indirect effects of Sika Deer grazing on bird populations are discussed.

17. Ecological effects of pump-scoop dredging for cockles on the intertidal benthic community

Abstract Awareness of the ecosystem effects of fishing activities on the marine environment means that there is a vital need to assess the direct and indirect effects of those activities that may have negative effects on target and non-target species. The Edible Cockle Cerastoderma edule is the target of an artisanal and commercial fishery that occurs in estuarine and intertidal habitats across northern Europe. Poole Harbour has opened up its cockle beds to pump-scoop dredging over the last few years. This study investigated the effect of pump-scoop dredging on the intertidal sedimentary environment and the macro-infaunal community. The results demonstrated that the dredging did not have an effect on the size distribution of sediment particles. After the fishery opened, no immediate impact of cockle dredging on the infaunal community was observed. Within 3 months, however, a reduction in species richness and abundance of the benthic community was noted. This may be indicative of a chronic rather than acute impact. However, further investigations are required to assess whether this was directly related to pump-scoop dredging. The findings of this study are discussed in relation to possible impacts on the ecosystem as a whole.

Burrow development, nutrient fluxes, carnivory and caching behaviour by Calocaris macandreae (Crustacea: Decapoda: Thalassinidea)

Using aquaria containing natural sediment, medium-term burrow development was investigated. After initial construction, and over the first month, relatively little burrow development was observed in terms of the number of openings and tunnels created. After an additional six months, however, there was a significant increase in the number of openings and tunnels constructed. In contrast to what might be expected from the number of openings and tunnels created during this period, a significant proportion of the sediment movement was sub-surface and relatively little sediment expulsion occurred. The concentration of nitrite, ammonia and phosphate in the burrow water was generally greater than that of the surface water, whilst the nitrate and sulphate measurements showed no particular pattern. Only the differences in phosphate concentrations were found to be significantly different. These results were indicative of Calocaris macandreae influencing rates of denitrification. This study also provided further evidence of carnivory and caching behaviour in this species.

A note on the unprecedented strandings of 56 deep-diving whales along the UK and Irish coast

In the first seven months of 2008, eighteen Cuviers beaked whales ( Ziphius cavirostris ), four Sowerbys beaked whales ( Mesoplodon bidens ), five unidentified beaked whales and twenty-nine long-finned pilot whales ( Globicephala melas ) were reported stranded in the UK and Ireland. Decomposition of those animals investigated puts the predicted time of death at mid-January. Concerns that an unusual mortality event had taken place prompted further investigations. Most carcasses were too decomposed for necropsy. A summary of findings is presented here. Although the initial stranding of five Cuviers beaked whales in Scotland shared some similarities with atypical mass stranding events linked in time and space to mid-frequency naval sonars, there were two important differences with the remaining strandings during this period. First, the geographical range of the event was very wide and second, the strandings occurred over a prolonged period of several months. Both of these factors could be related to the fact that the mortalities occurred offshore and the carcasses drifted ashore. The cause(s) of this high number of strandings of mixed offshore cetacean species during this period remain undetermined.

20. Macroalgal mat development and associated changes in infaunal biodiversity

Blooms of macroalgal matting, comprising opportunistic species such as Ulva lactuca, are becoming increasingly common in Poole Harbour. A hostile environment is usually created in the sediment below a dense algal mat, influencing the invertebrate faunal assemblage. This preliminary study was conducted over a 6 month period during which a dense mat of U. lactuca developed and subsequently dispersed in Holes Bay. The algal mat was found to have a significant negative impact on species richness, abundance and biomass of the infauna. The results are discussed in relation to impacts on the ecosystem as a whole.

9. Zooplankton distribution in Poole Harbour

Abstract The distribution and abundance patterns of the zooplanktonic communities in the estuarine environment of Poole Harbour, and their link with physico-chemical parameters, are reported here for the first time. Over the summer of 1999, the harbour maintained a rich Zooplankton standing stock, with peak production during August and September. Copepods and the larvae of gastropods, polychaetes, bivalves and decapods contributed a major share of the Zooplankton community. Zooplankton spatial distributions were thought to be partly influenced by the hydrographic structure of the area and by the tidal currents, which contribute to a certain degree to species retention. Zooplankton abundance followed a similar pattern to chlorophyll ‘a’ concentration, but with a time lag of approximately one month. While spatial distribution patterns may be related to the hydrographic features of the harbour, temporal occurrence of the different Zooplankton groups appeared to be related to the autochthonous production of the harbour.