Showing papers in "Biology and Environment-proceedings of The Royal Irish Academy in 2007"

THE influence of local and regional oceanographic processes on phytoplankton distribution in continental shelf waters off north-western ireland

Abstract: The distribution of phytoplankton is related to local and regional oceanographic features off the north-western coast of Ireland. A thermohaline front known as the Irish Shelf Front (ISF) that separates coastal and oceanic water was observed in the study area. Phytoplankton biomass levels, as indicated by chlorophyll concentrations, were higher on the coastal side of the frontal boundary. Inshore of the front the phytoplankton species composition was dominated by diatoms such as Leptocylindrus danicus , Guinardia flaccida and Pseudo -nitzschia cf seriata . The flora of the shelf region between the ISF and the outer shelf was characterised by the presence of Halosphaera minor , Oscillatoria sp., Ptychodiscus noctiluca , Ceratium fusus and Amphidoma caudata . Further offshore along the margins of the continental shelf the floral assemblage was characterised by Gonyaulax polygramma, Ceratium furca, Oxytoxum scolopax, Podolampes palmipes , Prorocentrum compressum and Prorocentrum dentatum. The presence of Gonyaulax polygramma, an indicator species for North Atlantic Current (NAC) slope waters, indicates the presence of this current at the shelf edge. The highest Karenia mikimotoi cell concentrations were found in close proximity to bottom density fronts located inshore. The biological observations presented here further highlight the potential role of local processes such as the presence of strong, jet-like, density-driven coastal flows in transporting potentially harmful phytoplankton populations northwards along the western coast of Ireland.

CONSEQUENCES OF HYDRAULIC DREDGING FOR A RAZOR CLAM Ensis siliqua (L.) BED IN THE NORTH-WEST IRISH SEA

Abstract: The Gormanstown razor clam bed, which measured 21km2 in extent in 1998, provided more than half the razor clams harvested in Europe for three years, 1999–2001. Exploitation of the bed commenced in late 1997. As a result of hydraulic dredging, the sediments have higher sorting coefficients and some larger grades were added in the form of shell fragments in the intervening years. The macrobenthos of the bed was monitored over a period of seven years, beginning one year after exploitation commenced. Throughout that time the dominant species, Ensis siliqua , which had accounted for up to 90% of the biomass in the first year of the study, declined to approximately 50% in 2005. Ensis siliqua displays the characteristics of a K-selected species: heavy standing biomass, type one survivorship curve and slow replication. Coinciding with exploitation, the bed was invaded by other deposit and suspension-feeding bivalves, notably Pharus legumen and Lutraria lutraria, whose population expansion can be traced to the early dredge fishery. The ratio of Ensis to Lutraria sampled weights was 124:1 in 1998, but it steadily advanced to 1.2:1 in 2005. Thus Lutraria , another suspension feeder, has displaced the razor clam. The Shannon-Wiener index of diversity rose as exploitation of the bed progressed, and in 2005 (eight years after dredging commenced), it had not returned to its 1998 level. However, the trend over the period was downwards, suggesting that a new stability involving a different species composition may be achieved. An age length key applied to length–frequency distributions of E. siliqua indicated that no age class older than age eleven has accounted for 10% of the population since 2001, although that was usually the case in the four preceding years.

Plankton communities of artificial lakes created on irish cutaway peatlands

Abstract: Lake creation represents a major post-harvesting land-use option for industrial cutaway peatlands in Ireland, yet little is currently understood about the ecology of cutaway water-bodies, particularly at the microbiota level. The current paper describes for the first time the littoral zooplankton community in three contrasting artificial cutaway lakes and one natural bog lake. The study lakes, which were sampled on five occasions in 2003, contrasted strongly in their physico-chemical characteristics, nutrient states and trophic classifications. These trends reflected variations between sites in sediment types, water supply sources and catchment land uses. In the absence of fish, invertebrate predation by cyclopoid copepods (Tropocyclops prasinus) and cladocerans (Polyphemus pediculus) appeared to play an elevated role in structuring the zooplankton communities in the study lakes, in terms of abundance, species composition and size structure.

Temporal and spatial variation in otter Lutra lutra diet in Northern Ireland

Abstract: The European otter (Lutra lutra L.) has a highly specialised diet that is composed predominantly of fish. The current study investigates the percentage composition of food items in otter spraints collected in six river catchments in Northern Ireland in 1980 and again from the same locations in 2003. Spraints contained significantly more salmonids than any other prey item. The composition of spraints differed among catchments. More salmonids and three-spined stickleback (Gasterosteus aculeatus L.) were found in spraints from the Glens of Antrim, while spraints from the Lagan catchment had significantly more eel (Anguilla anguilla L.). There were significantly more spraints containing non-fish food items in 2003 compared with 1980. These non-fish items were insects, amphipods, birds, rats (Rattus norvegicus Berkenhout) and lagomorphs. Increased consumption of non-fish items was apparent in all but one of the river catchments. The mean diversity of spraint composition was significantly greater in 2003 than in 1980. Therefore, our findings indicate that otters have diversified their diet since 1980 and now eat more non-fish prey.