Recent Submissions

  • Preliminary recruitment studies of the eastern oyster, Crassostrea virginica, and their potential applications, in coastal Georgia

    O'Beirn, F.X.; Heffernan, P.; Walker, R.L. (Elsevier, 1995)
    Oyster recruitment was monitored in Wassaw Sound, Georgia from April through October, 1991. The study was initiated to determine precise recruitment patterns of oysters over the 7 month spawning season. One of the goals was to determine the most suitable time for the collection of natural spat for maricultural, fisheries and recreational purposes. Three sites of varying hydrographic characteristics were chosen in Wassaw Sound. The sites varied in terms of temperature and salinity regimes and in their exposure to wind and wave action. Within each site, oyster recruitment was estimated at three tidal heights; subtidally, at mean low water and intertidally, approximately 2 h above the mean low water mark. Sampling took place so as to measure net recruitment over biweekly (BW), monthly (M) and seasonal ( S) periods. The results indicated that the recruitment of oysters in this region of coastal Georgia is protracted, lasting 6 months (May through October). The levels of recruitment were very high relative to other regions on the east coast of the USA, with peak recruitment for the entire study area (x = 2800 spat m- 2 for BW and x = 3020 spat m- 2 for M) occurring between July and September. The intensity of recruitment varied significantly among the three sites. The most sheltered site in terms of wave exposure experienced the highest recruitment (x =4380 spat m- 2 BW; x = 6260 spat m -2 M). This site also had higher overall water temperatures as well as greater daily temperature fluctuations. The least sheltered site had the lowest numbers of young oysters (x = 1000 spat m- 2 BW; X. = 686 spat m- 2 M), as well as having the most stable temperature regime. The biweekly samples generally experienced higher recruitment subtidally at the three sites. The monthly samples had higher numbers of oyster spat at the mean low water mark while the seasonal samples showed significantly higher recruitment intertidally (up to x =7353 spat m-2 ). The shift in recruitment patterns over time is partially attributed to increased subtidal predation pressure on the recruits. The collection of natural spat in relation to the natural fishery, potential maricultural activity and the recreational fishery is discussed.
  • Reproductive biology and parasite (Perkinsus marinus) prevalence in the eastern oyster, Crassostrea virginica, within a Georgia tidal river

    O'Beirn, F.X.; Walker, R.L.; Jansen, M.L. (Elisha Mitchell Scientific Society, 1997)
    Recruitment, in 1992, of the eastern oyster, Crassostrea virginica, at one site (Flume Dock) within the Sapelo Island National Estuarine Research Reserve (SINERR) was lower than other sampling sites. Recruitment allied with gametogenesis and parasite (Perkinsus marinus) prevalence within the oysters was examined in 1993, in an attempt to explain the differences observed the previous year. Sampling occurred at three sites (Marsh Landing, Jack Hammock, and Flume Dock) along the Duplin River within the SINERR. Oyster recruitment in 1993 was reduced in all sites within the SINERR. No oyster recruitment was recorded at the Flume Dock site during any monthly collections or on collectors deployed for the duration of the sampling study. Oysters developed gametogenically and spawned at the Marsh Landing site two weeks prior to their occurrence at the Jack Hammock site. Gametogenic development in oysters at the Flume Dock site was retarded a further two weeks where the males appeared to spawn six weeks after the females, which could account for reduced recruitment levels at this site. Approximately, twice as many females as males occurred in all sites. Monthly sampling of prevalence and intensity of Perkinsus marinus (Dermo) revealed high levels of both parameters. Smaller oysters did display lower prevalences of Dermo than larger forms.
  • Survival and growth of juvenile freshwater mussels (Unionidae) in a recirculating aquaculture system

    O'Beirn, F.X.; Neves, R.J.; Steg, M.B. (American Malacological Union, 1998)
    An indoor recirculating aquaculture system was constructed to provide suitable conditions to culture juvenile freshwater mussels. In the first of three growth trials, Villosa iris (I. Lea, 1829) juveniles were cultured for 22 wk, and grew from an initial mean length of 0.4 mm to 2.7 mm. Survival was 26.8% overall. In the second trial, growth and survival were compared between juveniles of V. iris held in sediment and without sediment. The initial mean length of both groups was 2.7 mm, and this experiment ran for 17 wk. The juvenile mussels in sediment grew to a mean length of 5.7 mm with 85% survival, significantly greater (p < 0.01) than juveniles held without sediment (4.5 mm, 74% survival). In the third trial, two cohorts of juvenile Lampsilis fasciola Rafinesque, 1815, increased in length from I.I mm and 1.4 mm to 3.3 mm and 4.1 mm, respectively, with comparable survival (78.7% versus 64.5%). Results of these trials demonstrate that juvenile mussels can be reared successfully within recirculating systems. One of the factors deemed important in successful culture is continuous feeding of an appropriate food source. In this study, a unialgal culture of Neochloris oleabundans Chantanachat and Bold, 1962, was used throughout. Regular cleaning of the system and water replacement also was important. Finally, the culture of juveniles in sediment appears to be an important factor in ensuring good growth and survival. This phenomenon could be related to pedal feeding behavior, proper orientation of the mussels for filtering efficiency, or stability from physical disturbance.
  • Prevalence of Perkinsus marinus in the eastern oyster, Crassostrea virginica in relation to tidal placement in a Georgia tidal creek

    O'Beirn, F.X.; Dean, C.C.; Walker, R.L. (Marine Environmental Sciences Consortium of Alabama, 1994)
    This experiment was designed to evaluate the effects tidal zonation and bottom placement of the eastern oyster, Crassostrea virginica, have on the prevalence and intensity of the oyster parasite, Perkinsus marinus a suspected causative agent for subtidal oyster mortalities experienced in the coastal waters of Georgia. Twelve growout bags (1 m x 0.5 m; 12.7 mm mesh), each containing 200 oysters, were placed in Jointer Creek, Georgia In March 1992. Bags (3 replicates each) were placed lntertidally and subtidally on the creek bottom and offbottom. Ten oysters per bag were removed monthly for twelve months beginning March 1992, and were inspected for prevalence and intensity of Perkinsus marinus, using the thioglycollate method. Oyster mortality and shell length data were also evaluated. Neither prevalence (p = 0.3505) nor intensity levels (p = 0.2993) of Perkinsus marinus in oysters were significantly different among the treatments. Although there were no significant differences In prevalence or intensity of the pathogen among treatments, the intertidal offbottom treatment had the lowest values most frequently. Perkinsus marinus was present in all replicates every month. Prevalence and intensity of infection followed the typically observed pattern of maximum values in summer and fall and minimum levels in winter. Subtidal bottom oysters experienced higher mortalities (p = 0.0022), but the prevalence and intensity of Perklnsus marinus in oysters were not significantly different between treatments. It appears therefore, that the oyster parasite, Perkinsus marinus is not the discerning factor in the higher mortalities witnessed in oysters placed subtidally on the bottom in the southeastern U.S. coastal waters.
  • An ecosystem-based approach and management framework for the integrated evaluation of bivalve aquaculture impacts

    Cranford, P.J.; Kamermans, P.; Krause, G.; Mazurié, J.; Buck, B.H.; Dolmer, P.; Fraser, D.; Van Nieuwenhove, K.; O'Beirn, F.X.; Sanchez-Mata, A.; Thorarinsdóttir, G.G.; Strand, O. (Inter Research, 2012)
    An ecosystem-based approach to bivalve aquaculture management is a strategy for the integration of aquaculture within the wider ecosystem, including human aspects, in such a way that it promotes sustainable development, equity, and resilience of ecosystems. Given the linkage between social and ecological systems, marine regulators require an ecosystem-based decision framework that structures and integrates the relationships between these systems and facilitates communication of aquaculture–environment interactions and policy-related developments and decisions. The Drivers-Pressures-State Change-Impact-Response (DPSIR) management framework incorporates the connectivity between human and ecological issues and would permit available performance indicators to be identified and organized in a manner that facilitates different regulatory needs. Suitable performance indicators and modeling approaches, which are used to assess DPSIR framework components, are reviewed with a focus on the key environmental issues associated with bivalve farming. Indicator selection criteria are provided to facilitate constraining the number of indicators within the management framework. It is recommended that an ecosystem-based approach for bivalve aquaculture be based on a tiered indicator monitoring system that is structured on the principle that increased environmental risk requires increased monitoring effort. More than 1 threshold for each indicator would permit implementation of predetermined impact prevention and mitigation measures prior to reaching an unacceptable ecological state. We provide an example of a tiered monitoring program that would communicate knowledge to decision-makers on ecosystem State Change and Impact components of the DPSIR framework.
  • Bivalve aquaculture and exotic species: a review of ecological considerations and management issues

    McKindsey, C.W.; Landry, T.; O'Beirn, F.X.; Davies, I.M. (National Shellfisheries Association, 2007)
    Bivalves have been grown and transported for culture for hundreds of years and the introduction of some species outside of their native range for aquaculture has been suggested to be one of the greatest modes of introduction of exotic marine species. However, there has yet to be a thorough assessment of the importance of aquaculture and bivalve culture in particular, to the introduction and spread of exotic species. This paper reviews some of the environmental and ecological implications of the relationship between bivalve aquaculture and the introduction and spread of exotic species, management implications and mitigation strategies. Two broad classes of introductions of exotic species may result from activities associated with bivalve aquaculture. First, the intentional introduction of exotic species into an area for aquaculture purposes, i.e. the ‘‘target’’ species. These are typically foundation or engineering species and may have a considerable influence on receiving ecosystems. Second, the introduction of species that are either associated with introduced bivalves or facilitated by aquaculture activities (i.e. structures or husbandry practices). These may include both ‘‘hitchhiking’’ species (organisms that grow in association with or may be transferred with cultured bivalves) and disease causing organisms.Management options should include the use of risk assessments prior to transfers and quarantines. Various types of mitigation for exotic species have been evaluated but are generally not very successful. Because the risk of exotic species to ecosystems and the bivalve farming industry itself may be great, effort should be directed to better predict and halt introductions of potentially harmful species.
  • Pea Crab, Pinna theres ostreum Say, 1817, in the eastern Oyster, Crassostrea virginica (Gmelin, 1791): prevalence and apparent adverse effects on oyster gonad development

    O'Beirn, F.X.; Walker, R.L. (California Malacozoological Society, 1999)
    Incidence of pea crab, Pinnotheres ostreum Say 1817, infestation in the eastern oyster, Crassostrea virginica (Gmelin, 1791), was recorded and related to oyster gametogenic activity over 18 months. Sampling occurred at twO tidal heights (high intertidal HI and low intertidal LI) at two sites (House Creek, HC and Skidaway River, SR) in Wassaw Sound, Georgia. Overall, incidence rates were 3% HC LI, 1 % HC HI, 8% SR LI, and 4% SR HI. At both tidal heights at HC, no differences were observed in gonad area between those oysters with and without pea crabs. At SR (where overall incidences were higher), oysters without pea crabs had significantly higher gonad area values than those oysters with pea crabs present. These results suggest that at higher incidences of pea crab infestation, oyster reproductive capabilities could be impacted, and support the claim that the pea crab/oyster relationship is a parasitic one.
  • Toward design criteria in constructed oyster reefs: oyster recruitment as a function of substrate type and tidal height

    O'Beirn, F.X.; Luchenbach, M.W.; Nestlerode, J.A.; Coates, G.M. (National Shellfisheries Association, 2000)
    Restoration of degraded oyster reef habitat generally begins with the addition of substrate that serves as a reef base and site for oyster spat attachment. Remarkably, little is known about how substrate type and reef morphology affect the development of oyster populations on restored reefs. Three-dimensional, intertidal reefs were constructed near Fisherman's Island, Virginia: two reefs in 1995 using surfclam (Spisula solidissima) shell and six reefs in 1996 using surfclam shell, oyster shell, and stabilized coal ash. We have monitored oyster recruitment and growth quarterly at three tidal heights (intertidal, mean low water, and subtidal) on each reef type since their construction. Oyster recruitment in 1995 exceeded that observed in the two subsequent years. High initial densities on the 1995 reefs decreased and stabilized at a mean of 418 oyster/m2. Oyster settlement occurred on all reef types and tidal heights in 1996; however, postsettlement mortality on the surfclam shell and coal ash reefs exceeded that on the oyster shell reefs, which remained relatively constant throughout the year (mean = 935 oysters/m2). Field observations suggest that predation accounts for most of the observed mortality and that the clam shell and coal ash reefs, which have little interstitial space, suffer greater predation. Oyster abundance was consistently greatest higher in the intertidal zone on all reefs in each year studied. The patterns observed here lead to the preliminary conclusion that the provision of spatial refugia (both intertidal and interstitial) from predation is an essential feature of successful oyster reef restoration in this region. In addition, high levels of recruitment can provide a numerical refuge, whereby the oysters themselves will provide structure and increase the probability of an oyster population establishing successfully on the reef.
  • Organisms associated with oysters cultured in floating systems in Virginia, USA

    O'Beirn, F.X.; Ross, P.G.; Luckenbach, M.W. (National Shellfisheries Association, 2004)
    The number and abundance of macro-fauna! taxa was estimated from six floating structures (floats) used to culture the Eastern oyster (Crassostrea virginica) near Chincoteague Island, Virginia, USA. After a 10-mo grow-out period, all organisms found among and attached to the cultured oysters were counted. The final mean size of oysters was 80.5 (14.7 SD) mm. Overall, 45 species of macrofauna were recorded with the number of species in the floats ranging from 24 to 36. There was no relationship between the number of taxa and the density of oysters in the floats. Total abundances of associated organisms were estimated at 12,746/float to 92,602/float. These findings highlight the diverse (taxonomic and trophic) and abundant nature of communities associated with cultured oysters. They also provide a baseline set of information that may help more clearly define the interactions between oyster culture and the environment.
  • Growth and survival of Spisula solidissima similis larvae fed different rations of Tahitian strain Isochrysis species

    Hurley, D.H.; Walker, R.L.; O'Beirn, F.X. (National Shellfisheries Association, 1997)
    Laboratory-spawned veliger-stage larvae of the southern Atlantic surfclam, Spisula solidissima similis (Say 1822), were reared to late pediveliger stage on five different cell concentrations of Tahitian strain Isochrysis species (T-Iso) to determine an optimal food ration for this subspecies. Larvae were fed daily 0, 50,000, 100,000, 200,000, or 300,000 cells/mL of T-Iso. Day-old veliger larvae were stocked in 150 (1-L) replicate flasks at mean densities of 0.7 or 0.8 larvae/mL for trials A and B, respectively. Larval growth and survival were assessed every 2 days over the 14-day trial penods. Significantly greater growth and survival of larvae occurred in both trials in the lower food rations of 50,000 and 100,000 cells/mL. A reduction in larval growth rate and survival was observed at the higher ration treatments. A decline in overall larval health may be associated with the deliterious effects of surplus ration degradation.
  • Embryonic and larval development of Spisula solidissima similis (Say, 1822) (Bivalvia: Mactridae)

    Walker, R.L.; O'Beirn, F.X. (California Malacozoological Society, 1996)
    Larvae of the southern surf clam, Spisula solidissima similis (Say, 1822), were reared in the laboratory at a salinity of 25 ppt and a temperature of 20-22°C through the embryonic and early larval development period. Unfertilized eggs averaged 58.5 ± 0.32 (SE) μm, with the size-frequency of eggs being normal. First polar body was observed 22 minutes after fertilization with 50% of eggs exhibiting polar bodies after 26 minutes. Ciliated blastula and trochophore stages occurred at 6 hours and 16.8 hours, respectively. Straight-hinge veligers appeared 39.2 hours after fertilization. Larvae grew to a mean size of 172 μmin the pediveliger phase (range 119 to 212 μm). Larvae were exhibiting active foot-probing by day 8 and continued to do so until day 13 when the cultures suffered heavy mortalities. Early life-history traits of Spisula solidissima similis larvae are compared to those for Spisula solidissima solidissima and Spisula sachalinensis.
  • Enhancement of subtidal eastern oyster, Crassostrea virginica, recruitment using mesh bag enclosures

    O'Beirn, F.X.; Walker, R.L.; Heffernan, P.B. (National Shellfisheries Association, 1996)
    Eastern oysters, Crassostrea virginica, in the southeastern United States are found predominantly in the intertidal zone. In this study, mesh bags (3 and 6 mm) were deployed over collecting frames, and the patterns of oyster settlement on these collectors were compared against unmeshed controls at three tidal heights (intertidal, low water, and subtidal) over three sampling regimes (biweekly, monthly, and seasonal) at two sites. Within the biweekly sampling regime, the meshed collectors and controls had similar patterns of settlement at the respective tidal heights. For monthly samplers, mesh treatments maintained higher settlement subtidally whereas controls had highest settlement on the collectors at mean low-water level. Controls had highest recruitment intertidally for seasonal collectors, whereas mesh treatments had higher recruitment lower in the intertidal zone. Conclusions from this experiment were that the use of mesh-covered collectors enhanced subtidal oyster recruitment. Causes of observed increases in subtidal settlement in mesh collectors over unmeshed controls over time could be the result of a combination of factors: predator exclusion, larval entrainment, or reduced desiccation, which seemed to overcome the detrimental effects of increased fouling, resulting in reduced flow and possible hypoxic conditions within the mesh bags. Given the degree of recruitment and the sizes of the recruits attained within the mesh bags, the use of these methods to attain juveniles for commercial purposes would appear to be both feasible and viable, particularly for long periods (up to 6 1110) of deployment.
  • Culture of surfclams Spisula solidissima sp., in coastal Georgia: nursery culture

    O'Beirn, F.X.; Walker, R.L.; Hurley, D.H.; Moroney, D.A. (National Shellfisheries Association, 1997)
    Growth of the Atlantic surfclam, Spisula solidissima solidissima, was compared with that of the southern Atlantic surfclam, Spisula solidissima similis. All experimental animals were reared in upweller units at 20°C and fed cultured algae on a daily basis. Over the 14 wk of the study, the Atlantic surf clams grew markedly better (8.9-mm increase in shell length and a 1,103% increase in biomass) than the southern Atlantic surfclams (6.6-mm increase in shell length and 573% mcrease in biomass). Mortality for both groups was negligible. The mean shell lengths attained for the Atlantic surfclams (15.3 mm) and the southern Atlantic surfclams (13 mm) at the conclusion of the study were large enough to ensure good growth and survival on relocation to a field growout environment. The growth patterns obtained under similm growth conditions further highlight some basic life history differences between these subspecies, which were apparent from other studies.
  • Environmental factors associated with invasion: modeling occurrence data from a coordinated sampling programme for Pacific oysters

    Kochmann, J.; O’Beirn, F.X.; Yearsley, J.; Crowe, T.P. (Springer Netherlands, 2013)
    Documenting establishment and spread of invasive species requires extensive co-ordinated sampling programmes. Identifying the factors promoting or inhibiting local establishment of an invasive species can improve capacity to predict further spread and underpin strategies to limit spread. Here, a structured sampling programme was used to assess the current distribution of feral populations of Pacific oysters, Crassostrea gigas, in Ireland. Sixty-nine sites were sampled using a standardised protocol combining semi-quantitative and quantitative approaches. Sites were chosen to represent variation in proximity to aquaculture and a range of environmental variables. Oyster populations were found at 18 locations, with densities ranging from single individuals to nine individuals per m2. The broad size range of oysters found is indicative of more than one recruitment event. Logistic regression indicated that feral oysters were positively associated with the presence of hard substrata or biogenic reef, long residence times of embayments and large intertidal areas. There was also a tendency for oysters to occur disproportionately in bays with aquaculture, but >500 m from it. Small-scale analysis within sites showed that oysters were almost exclusively attached to hard substrata and mussel shell. The approach taken here provides a rigorous repeatable methodology for future monitoring and a detailed basis for the prediction of further spread.
  • Irish Multidisciplinary Deepwater Survey 2007 SSTI Project Report

    Dransfeld, L; Davie, S; Johnston, G; Leahy, Y; O'Beirn, F.X.; O'Hea, B; O'Shea, C; Wall, D; White, M; Gerritsen, H.D. (Marine Institute, 2007)
    The Marine Institute with the collaboration of the National University of Galway conducted a multidisciplinary deepwater survey along the continental slope of the Northeast Atlantic. At three selected sites northwest of Ireland and on the northern slopes of the Porcupine Bank, fishing transects were carried out at four depth strata (500m, 1000m 1500m and 1800m) during the day, while oceanographic measurements and plankton and benthic invertebrate sampling was carried out during the night. Data from CTD and ADCP measurements showed following distribution of water masses: The top 700 m was occupied by that of Eastern North Atlantic Water (ENAW) origin which is a basic feature of the upper layer hydrography in the Rockall Trough; small salinity maxima indicated the region associated with the core of the shelf edge current (SEC). At Area 6, immediately north of Porcupine Bank, a salinity maximum at a depth of 900-1000 m indicated the presence of Mediterranean Outflow Water (MOW) with the presence Labrador Sea Water (LSW) at 1800-2000 m. The SEC was identified in both CTD and ADCP transects and was characterised by a number of relatively narrow filaments evident in the salinity data. In terms of benthic invertebrate data, a total of 104 taxa were identified with a maximum number of 33 invertebrate taxa identified per haul (these values were recorded at two 1500m hauls in 2006 and 2007, in Areas 5 and 2, respectively). Overall, no clear relationship between the number of invertebrate species and depth was apparent, however there was some indication that the number of species appears to be more variable in deeper waters. Several species occurred in very large numbers; these were the echinoderms, Cidaris cidaris, Benthegone rosea and Stichopus tremulus and the bivalve, Pseudammusium septemradii. Fisheries data revealed distinct deepwater fish communities that changed with depth and to a lesser extent with area. The number of species increased with depth at all sites to reach a maximum at 1500m before decreasing again at 1800m. At 500m depth the fish community was mainly composed of rabbit fish and rattails with some shelf species present such as hake, ling and silver pout. The 1000m depth strata presented a transition of species composition. The most abundant species overall was Roundnose grenadier which had is highest abundance at 1500m in all three areas but could also be found in the 1000 and 18000m depth strata. Other species of high abundance which also had their highest number of individuals at 1500m were Baird’s smoothhead and other species of grenadiers. Cluster analysis revealed that Roundnose grenadier was a distinct species grouping as was that of Baird’s smoothhead. Species occurrences were similar in all three areas with some regional differences; in area 2, Phycis blennoides, greater forkbeard,occurred among the ten most abundant species while in area 5, species, such as Black Scabbard, Aphanopus carbo, and cut throat eel, Synaphobranchus kaupi, were being caught here in larger numbers while present in the other areas in low numbers. Seven comparative tows were carried out with the Scottish research vessels RV Scotia and indicated that overall similar numbers of species and total number of fish were caught. Size distribution also compared well between the two different vessels, however for some species the numbers or size ranges of fish caught differed.
  • Salmon Mortalities at Inver Bay and McSwyne’s Bay Finfish farms, County Donegal, Ireland, during 2003

    Cronin, M.; Cusack, C.; Geoghegan, F.; Jackson, D.; McGovern, E.; McMahon, T.; O'Beirn, F.X.; Ó Cinneide, M.; Silke, J. (Marine Institute, 2004)
    This report details the investigations into a major mortality of farmed salmon at Inver Bay and McSwyne’s Bay, Co. Donegal in July 2003. Previous reports were provided on 29th July 2003 and on 11th August 2003. The information is based upon analysis and research by MI scientists, a review of environmental data, survey reports by external consultants, inputs from veterinary practitioners who visited the site, reports from DCMNR staff in Killybegs, and site visits made by DCMNR / MI inspectors. Following a review meeting of the principal investigators on the 9th October, 2003, MI proceeded to carry out further scientific investigations. DCMNR also commissioned Kirk McClure Morton Consulting Engineers (KMM) to carry out a parallel investigation of the mortalities at Inver Bay and McSwynes Bay salmon farms. MI provided support as required to the KMM study, the report for which was furnished to DCMNR and MI on 11 February 2004. (KMM, 2004) MI wishes to acknowledge the high level of co-operation and assistance that it received from the owners and staff of Creevin Fish Farm Ltd, Eany Fish Products Ltd and Ocean Farms Ltd. It also wishes to acknowledge the assistance of veterinary practitioners, DCMNR staff and others in the course of this investigation.
  • Karenia mikimotoi: An Exceptional Dinoflagellate Bloom in Western Irish Waters, Summer 2005

    Silke, J.; O'Beirn, F.X.; Cronin, M. (Marine Institute, 2005)
    A protracted bloom of Karenia mikimotoi was present in summer 2005 along the northern half of the western Irish coastline. The onset of this bloom was identified in late May / early June. This event subsequently dissipated over the month of July and was succeeded by a bloom of the same species in the southwest in late July. The bloom was very intense and resulted in discolouration of seawater and foaming in coastal embayments. Major mortalities of benthic and pelagic marine organisms were observed and a complete decimation of marine faunal communities was reported and observed in several locations. Deaths of echinoderms, polychaetes and bivalve molluscs were observed in County Donegal and Mayo, while farmed shellfish and hatchery raised juvenile bivalve spat suffered significant mortalities along the Galway and Mayo coasts. Reports of dead fish and crustacea were received from Donegal, Galway, West Cork and Kerry. Karenia mikimotoi is one of the most common red tide causative dinoflagellates known in the Northeast Atlantic region, and is also common in the waters around Japan. Blooms of this species often reach concentrations of over several million cells per litre and these densities are often associated with marine fauna mortalities. Although cytotoxic polyethers have been extracted from cultures of the species, the exact mechanism of the toxic effect and resultant devastating damages yet remains unclear. It is known in the literature under several different names as the taxonomy and genetics have been studied. It is now known that previously reported names including Gyrodinium aureolum, G. cf. aureolum, G. nagasakiense and G. mikimotoi are synonymous with the current name given to the organism. The visible effects following the mortalities included noticeable quantities of dead heart urchins (Echinocardium cordata L.) and lugworms (Arenicola marina L.) deposited on beaches. Several species of wild fish were also found dead. The bloom coincided with a period of fine weather and tourists visiting the seaside were concerned about the safety of swimming in waters that were obviously harmful to marine organisms on this scale. A public awareness programme was mounted by the Marine Institute with several radio broadcasts, press releases and a website provided to give up to date pronouncements on the event. While there have been several instances of Karenia mikimotoi blooms reported in Ireland over the past 30 years, this scale of mortalities associated with the 2005 bloom were not previously observed. Recording the scale of this event was facilitated by satellite imagery while direct counts of the cells in seawater by the Marine Institute monitoring programme gave very useful information regarding the size and intensity of this event. The mortalities of marine organisms were documented from reports made by various observers and by Marine Institute field surveys.