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EXECUTIVE SUMMARY AND RECOMMENDATIONS

1. The phytoplankton species composition, succession, spring bloom dynamics and environmental regulation in Scottish coastal waters have a Boreal character similar to Scandinavian coastal waters and the North Sea.
2. Annual primary production rates in Scottish coastal waters generally are similar to rates in pristine Norwegian fjords, but lower than in nutrient enriched Kattegat and Dutch Wadden Sea. Phytoplankton abundance and primary production in sea lochs are projected to increase with modest nutrient enrichment without changes in baseline phytoplankton structure and dynamics. Irradiance may be more limiting than nutrients In some sea lochs.
3. An indigenous harmful algal flora occurs in Scottish coastal waters comprising species that cause shellfish-borne illnesses in humans and other animals, including Paralytic Shellfish Poisoning ( PSP), Diarrhetic Shellfish Poisoning ( DSP) and Amnesic Shellfish Poisoning ( ASP); ichthyotoxic species also occur. This flora, also widely distributed in European coastal waters, includes species from the dinoflagellate genera Alexandrium ( PSP) and Dinophysis ( DSP), and the diatom genus Pseudo-nitzschia ( ASP). Harmful algal species occurrences and blooms ( HABs) are not new phenomena in European waters induced by initiation of aquaculture. A PSP outbreak was recorded in 1827 after ingestion of mussels harvested from the Firth of Forth; DSP illnesses following shellfish consumption were reported from Norway in the early 1900s.
4. PSP, DSP and ASP outbreaks in Scottish waters parallel similar occurrences elsewhere in European and global coastal waters. There is no reliable evidence that novel HAB species have newly expanded into Scottish coastal waters, nor that blooms of the indigenous HAB flora have increased in frequency.
5. The HAB flora and their toxic events in Scottish and other European coastal waters are generally similar, with some notable differences. Arrayed along a continuum from high to low intensity, regional European and UK coastal waters exhibit a north-south gradient in ASP intensity and an east - west gradient in harmful blooms of haptophytes and raphidophytes.
6. Scottish coastal waters are unique relative to other European and global coastal waters in the widespread persistence in ASP toxicity of the scallop Pecten maximus. This distinction is not because of species differences. ASP toxicity results from the toxin domoic acid ( DA) produced by diatom species in the genus Pseudo-nitzschia. The nine Pseudo-nitzschia species found in Scottish waters are indigenous, cosmopolitan and commonly bloom in European and global coastal waters.
7. Bloom behavior of Pseudo-nitzschia in Scottish waters is similar to that in other geographical waters, rather than locally unique. Pseudo-nitzschia blooms are common, generally multispecific, probably polyclonal, attain great abundance, can be prolonged (weeks to months), and occur in diverse habitats ranging from relatively pristine (i.e free of anthropogenic modification) offshore waters to nutrient enriched nearshore waters. In the habitats where Pseudo-nitzschia species normally bloom, fish farms are not a factor, and therefore Pseudo-nitzschia blooms are not dependent on nutrient wastes excreted at fish farms.
8. A complex combination of habitat-cellular-population events and conditions regulates the synthesis of DA and its flux to filter feeding bivalves. This negates efforts to link the Scottish ASP "epidemic" to a specific habitat stimulus. Synthesis of DA is the most complex of the phycotoxins produced by harmful algae; it is under multifactorial environmental control. Four essential conditions are required for DA production: irradiance, a supply of NO ₃ and Fe, and nutritional stress from phosphorus or silica limitation. DA synthesis usually begins when the population becomes senescent; nutrient limitation, not enrichment triggers DA production. Most of the DA produced is secreted rather than retained by Pseudo-nitzschia cells which influences DA vectoring pathways to shellfish. Bivalve ingestion and accumulation of extracellular DA requires its prior assimilation by bacteria which are then grazed by heterotrophic flagellates for vectoring to the shellfish. It is unknown how, and if, this vectoring occurs vs. direct filtration of bacteria. The relative importance of direct ingestion of DA present in Pseudo-nitzschia cells vs. the extracellular pool in contributing to shellfish ASP toxicity is also unknown. Notwithstanding uncertainty over the pelagic to benthic vectoring pathways of DA, ASP contamination of the Scottish shellfish grounds most likely results from a combination of direct transfer of DA from Pseudo-nitzschia to the shellfish, and indirectly via microbial loop processes.
9. The complex regulation of DA synthesis, and the ecophysiology and bloom behaviour of Pseudo-nitzschia species do not support the view that fish farm nutrient wastes have stimulated their blooms leading to ASP toxicity of shellfish in Scottish waters. DA synthesis is a stress response; fish do not excrete NO ₃, the form of inorganic nitrogen required for DA synthesis. Fish excrete NH ₄, whereas the NO ₃ ("new N") required for synthesis of DA is supplied by physical oceanographic processes. Pseudo-nitzschia species appear to be more sensitive to elevated NH ₄ concentrations than other diatoms. Experiments suggest that Pseudo-nitzschia species are vulnerable to, and can be inhibited by the elevated NH ₄ concentrations found at fish farm sites. The nitrogenous nutrition of Pseudo-nitzschia species does not conform therefore to the type of nitrogenous wastes discharged at fish farms.
10. The most compelling conclusion is that the ASP outbreak on the Scottish commercial scallop grounds is the result of natural causes, rather than due to anthropogenic enhancement of Pseudo-nitzschia species, or coupled to nutrients and waste products excreted by fish farms. Slow DA depuration rates characterize scallops, and help to explain the high levels, prolonged retention and persistence of DA far after termination of causative Pseudo-nitzschia blooms. Prolonged blooms of Pseudo-nitzschia are neither required, nor are the only source of DA. Chronic exposure of scallops to low Pseudo-nitzschia population densities, coupled with low depuration rates, also can lead to the accumulation and prolonged retention of DA.
11. The following studies on Pseudo-nitzschia and ASP are recommended:

12. Reports of diarrhetic shellfish poisoning ( DSP) in Scottish coastal waters are rare, unlike in ten other European countries. This regional difference is the converse of that for ASP. Since the Dinophysis species that produce okadaic acid, the causative toxin of DSP, are ubiquitous in Scottish waters, local rarity of DSP is not explained by Dinophysis absence.
13. DSP toxicity is a normal, latent feature of shellfish usually revealed only after human consumption. The global increase in shellfish cultivation and consumption, particularly of edible mussels, has heightened reports of DSP occurrences and awareness of this malady. Thus, the increase in human DSP illness has a dietary explanation; it is not the result of an altered ecology favoring Dinophysis blooms and inducing their toxicity.
14. Blooms of Dinophysis differ significantly from other HAB species. Their blooms, which rarely exceed 10 ⁴ cells L ^-1 or discolor seawater, are usually accumulations of slow growing cells physically aggregated by current movements and transported long distances. DSP intoxication of shellfish is usually not in response to a locally stimulated bloom, but results from ingestion of cells produced elsewhere and advected to the growth site. Shellfish can become toxic when feeding on the persistently low populations (<10 ³ cells L ^-1) that characterize Dinophysis.
15. Nutrient excretion and chemical conditioning of coastal waters at Scottish fish farm sites are not expected to enhance Dinophysis blooms or DSP outbreaks, even with further development of that industry, since neither is usually a habitat stimulated event. Nonetheless, the proposed expansion of shellfish culture in Scotland most likely will heighten future problems with DSP, and affect the harvesting and marketing of cultured shellfish. This projection is based on the evidence from elsewhere in Europe, particularly Ireland, and given the characteristics of Dinophysis and DSP provided in Summary Statements 13 and 14.
16. The Dinophysis species and oceanographic conditions contributing to the significant DSP threat and impairment of the Irish shellfish industry occur also in Scottish waters. The new and unique DSP toxins being reported from Irish shellfish cultivation sites relative to those in France and Spain, despite the common harmful Dinophysis species assemblage in European waters, is further cause for concern.

17. The following initiatives are recommended given the expected expansion of shellfish culture in Scotland:

18. The incidence of paralytic shellfish poisoning ( PSP) blooms in Scottish coastal waters is relatively low, similar to European coastal waters generally. Regionally intense blooms occurred in 1969 and 1990; otherwise, toxin levels exceeding threshold safety levels and mandating closure of shellfish grounds have been infrequent and brief in duration. The frequency of PSP events in the Orkney Isles may have increased in recent decades, but the evidence is equivocal and the causative species uncertain. This region is potentially a PSP "hot spot".
19. Three of the ten species of the dinoflagellate genus Alexandrium known to produce paralytic shellfish toxins have been recorded in Scottish coastal waters. Alexandrium tamarense had been considered the only one present until recent reports of isolated occurrences of Alexandrium minutum and Alexandrium ostenfeldii in Orkney waters. The long-term, episodic bloom patterns of Alexandrium tamarense, a species widely distributed in Scottish waters, are consistent with its behavior elsewhere. Its occasional large scale, regional blooms appear to be related more to climate - oceanographic interactions than to anthropogenic stimulation; this includes fish farm operations.
20. There appears to be a north-south gradient in PSP toxicity of Alexandrium tamarense populations worthy of further examination: northern populations (Scotland, Faroe Islands) are toxic; southern populations (England, Ireland) are not. A large "seed bank" of Alexandrium tamarense occurs in the Firth of Forth region, from which excysted cells are advected southwards along the coast of England. It is unknown whether these seeded cells initially are toxic, or non-toxic, and whether the population retains, loses or gains toxicity during advection. To help establish this, and whether there are potentially "safe" PSP sites for shellfish cultivation where the Alexandrium tamarense population is benign, it is recommended that:

21. Gymnodinium catenatum, which replaces Alexandrium tamarense as the primary PSP species in Iberian waters, has been reported from the ballast water of ships calling at Scottish ports. The potential recruitment of this highly toxic species into the indigenous HAB flora can not be excluded. Novel and persistent blooms of this species in Tasmanian waters, attributed to ballast water introductions, have adversely affected shellfish cultivation.
22. The recent report that Alexandrium minutum, a PSP producing and ichthyotoxic species, occurs in Orkney Isle waters requires confirmation. Alexandrium minutum appears to be spreading within European coastal waters, with a predilection to bloom in nutrient enriched water. There is no evidence that this species poses a threat, either to wild or farmed fish and shellfish stocks in Scottish waters, but investigators are alerted to its potential blooms. Invasive species often exhibit recurrent, intense blooms for an indeterminate period following the initial bloom outburst until accommodated by the indigenous flora, as was the case with previously invasive, ichthyo- and bentho-toxic Karenia mikimotoi. Alexandrium minutum has been found in the ballast water of ships calling at Scottish ports. It is recommended that Orkney Isle and other Scottish regional waters be surveyed for its presence.
23. Alexandrium ostenfeldii, reported only from the Orkney Islands in Scottish waters, may be more common than realized given the high spirolide concentrations recently detected in surface waters along the east coast of Scotland. Spirolides, known to be produced only by Alexandrium ostenfeldii, are fast acting toxins that can accumulate in scallop and muscle viscera. Alexandrium ostenfeldii, also a PSP toxin producer, is common in European coastal waters, and has bloomed at shellfish cultivation sites in Spain and Nova Scotia; its blooms in Danish waters have required closure of shellfish harvesting areas. Alexandrium ostenfeldii is a member of the low abundant, "hidden flora" assemblage easily overlooked in field surveys until its modest blooms occur. It often co-occurs with Alexandrium tamarense, with which it can be confused taxonomically.

24. The ichthyotoxic and hypoxia-inducing dinoflagellate Karenia mikimotoi is now widespread within Scottish waters following its 1970s invasion into the North Sea and subsequent spreading into contiguous, northern European waters. Karenia mikimotoi remains a potential threat to fish farming and shellfish cultivation. Its ecophysiology and local habitat conditions predispose Scottish waters to harmful blooms of Karenia mikimotoi which appear to be triggered primarily by the interaction of meteorological and hydrographic conditions.
25. An ongoing series of diverse, ichthyotoxic phytoflagellate (i.e. non dinoflagellate) blooms in Scandinavian waters have killed farmed fish and devastated natural pelagic and benthic communities. The bloom species are haptophytes, raphidophytes and other phytoflagellates, including Chrysochromulina polylepis, Chrysochromulina leadbeateri, Prymnesium parvum, Prymnesium patelliferum, and the raphidophytes Chattonella verrucolosa, Fibrocapsa japonica and Heterosigma akashiwo. Phytoflagellate blooms have become common in the region extending from Norway to the Dutch Wadden Sea. In contrast, ichthyotoxic phytoflagellate blooms appear to be rare in Scottish waters, the most notable event being the enigmatic Flagellate X blooms that occurred in some western sea lochs over a period of a decade beginning in the early 1970s. Fish-killing blooms attributed to Flagellate X also occurred then, more or less contemporaneously, in Irish coastal waters.
26. A depauperate phytoflagellate flora does not account for the apparent rarity of their blooms in Scottish waters. As in Scandinavian waters, the phytoflagellate community is abundant, common and diverse. Since phytoflagellate blooms often have a strong signal in the form of water discoloration and dead animals, their rare reports from Scottish waters may be real rather than an artifact of inadequate observation and relative neglect by Scottish investigators.
27. The taxonomic identity of Flagellate X has been elusive, but is of interest given the increased frequency and diversity of toxic phytoflagellate blooms in Scandinavian waters and the flagellate-induced salmon kills at Pacific fish farm sites. Analyses of the salmon-killing Flagellate X blooms in Loch Striven and upper Loch Fyne and available drawings suggest that the Flagellate X blooms were not monospecific. Concurrent or successional blooms of three ichthyotoxic species may have occurred: the raphidophytes Chattonella cf. verruculosa and Heterosigma akashiwo, and the silicoflagellate Dictyocha speculum. All three species have produced fish killing blooms elsewhere in European or other waters.
28. Heterosigma akashiwo, a taxon seemingly subsumed as Flagellate X, has been found in the Clyde Sea area, a provocative finding given the apparent absence of its ichthyotoxic blooms at salmon fish farm sites in Scotland, excluding a possible 1979 bloom in Loch Striven. This contrasts with reports that relatively soon after initiation of salmon farming in British Columbia, Puget Sound (U.S.A.), Chile and New Zealand novel Heterosigma akashiwo blooms, lethal to the farmed salmon, occurred. Cultured fish kills during its blooms in the Seto Inland Sea (Japan), Korean and French coastal waters have also occurred. Molecular evidence indicates that the ichthyotoxic Pacific strains of Heterosigma akashiwo are conspecific with European strains. Different species do not account for the contrasting effects.
29. Should Heterosigma akashiwo be indigenous at Scottish fish farm sites, its failure to produce ichthyotoxic blooms in those waters may either be because its blooms are held in check by other growth conditions or, if it does bloom, the local strains may not be ichthyotoxic. The similar rarity of ichthyotoxic Heterosigma akashiwo blooms at Norwegian fish farm sites is also enigmatic given that it blooms in nutrient enriched inner Oslofjord. Analyses of the potential influence of temperature and nutrients on Heterosigma akashiwo blooms in Scottish coastal waters using available ecophysiological data do not explain the low incidence (absence) of its fish-killing blooms. The restricted seasonal warming up to the optimal growth temperature range (15°-20°C) and the brief duration of this period in Scottish (and Norwegian) waters are potential limiting factors. However, it is unlikely that temperature acts alone in suppressing the growth of Heterosigma akashiwo in waters exposed to fish farm wastes, and in other inshore waters. Iron has been implicated as a nutrient critical to bloom formation, but it is also unlikely that this trace metal is the factor (barrier) limiting Heterosigma akashiwo blooms, either in Scottish or Norwegian coastal waters, given the runoff that occurs. It is unlikely that grazers prevent its blooms. Heterosigma akashiwo is probably the most allelopathic HAB species known: it is inhibitory to all classes of organisms, from bacteria to fish. Notwithstanding the apparent lack of Heterosigma akashiwo blooms in Scottish waters and the inability to account for this, Scottish fish farms are considered to be highly vulnerable to its potential blooms.
30. Heterosigma akashiwo potentially poses a dual threat to Scottish aquaculture since its blooms have also disrupted shellfish cultivation and the harvesting of wild stocks in Canada, Portugal and New Zealand. This potential expands the cluster of harmful bloom effects confronting shellfish cultivation in Scottish waters: Pseudo-nitzschia blooms and ASP related illness - presently the major threat to commercial shellfish harvesting, and a situation that will probably diminish; Dinophysis blooms leading to DSP inspired harvesting closures and bans on marketing of cultured shellfish, and anticipated to become an increasing (major) problem as that industry grows; Alexandrium tamarense blooms which undoubtedly will continue to cause infrequent, minor local PSP outbreaks and pose a continuous, though limited threat, to shellfish cultivation and edibility. The recently reported occurrences of Alexandrium minutum and Alexandrium ostenfeldii suggest that the future threat of PSP blooms may increase.
31. Shellfish borne phycotoxins usually do not cause shellfish dieoffs; harvesting can resume once the toxins depurate. In contrast, toxic phytoflagellates cause fish farm mortalities and non-recoverable financial loss. Ichthyotoxic phytoflagellate blooms are usually less predictable, more intense, of greater duration and areal coverage than ASP, DSP and PSP bloom events.
32. There appears to be a "general" raphidophyte niche in which the presence of one member of the Chattonella - Fibrocapsa - Heterosigma triad signals the likelihood that all three ichthyotoxic genera are present. This feature, the expanding global distribution and increase in blooms of harmful raphidophytes suggest that this niche may be opening up in global coastal waters. The causes of their global expansion are unknown. In northern Europe, raphidophyte blooms have become more frequent and intense, and appear to be spreading southwards from the Oslofjord to the Dutch Wadden Sea. I suggest that the raphidophyte niche is also present in Scottish sea lochs and open to exploitation under appropriate growth conditions. The three subordinate flagellate genera present during the 2001 ichthyotoxic bloom of Chattonella marina in the Skagerrak - the non-toxic Apedinella and Pseudopedinella and the toxic genus Chrysochromulina - have been reported to occur in Scottish coastal waters.
33. Unlike the ongoing epidemic of ichthyotoxic haptophyte blooms ( Chrysochromulina, Prymnesium) in Scandinavian waters, including farmed fish kills, their blooms have not been reported from Scottish waters. The ecology and impacts of the Chrysochromulina and Prymnesium blooms in Scandinavian waters are highly relevant to Scottish fish farms because of habitat similarities, the occurrence of Chrysochromulina spp. and Prymnesium parvum, the blooms of an unidentified Chrysochromulina sp. in Loch Striven, and the occurrence of ichthyotoxic Chrysochromulina polylepis and Prymnesium patelliferum elsewhere in UK coastal waters. The cause(s) of the apparent (and unexpected) bloom failure of harmful phytoflagellates generally in Scottish waters are unknown. Elsewhere, their blooms have occurred in response to various combinations of meteorology, oceanographic processes and nutrient conditions, rather than to a specific set of conditions.
34. Since phytoflagellates are among the most ichthyotoxic species known, with a high potential for bloom induced aquacultural loss in Scottish coastal waters, the following activites are recommended to fill essential knowledge gaps:

35. The pronounced east - west European gradient in phytoflagellate blooms begs the question of why their scarcity in Scottish waters. An underlying issue is whether the southern expansion of phytoflagellate blooms in continental European waters and the remarkable increases in their bloom frequency and intensity in southern Norwegian waters are forerunners of an eventual westward expansion into Scottish coastal waters affecting fish farms. The sea lochs and firths of Scotland have many physiographic and oceanographic features in common with the coastal systems of continental Europe, Norwegian fjords, Galician (Spain) rías, southwest Ireland and contiguous offshore, physical oceanographic features (coastal currents, fronts, upwelling).

36. Positive bioassay responses would indicate which Scottish systems are receptive to phytoflagellate blooms and invasions, and which type of harmful phytoflagellate species. Positive results, where obtained, should then prompt an evaluation of the causes and impact of such blooms in Scandinavian waters, and the field investigative techniques applied in those instances allowing detection and tracking of the bloom species. The recommended bioassay surveys should be undertaken to develop proactive investigative and management strategies in anticipation of such blooms.
37. Farmed fish mortality in the Shetlands has occurred during spinous diatom blooms; it is unclear whether this resulted from gill piercing or high population densities. Fourteen diatom species reported to be harmful to farmed fish because of morphological features or bloom densities occur in Scottish waters. As a group, such diatoms are considered to be less threatening to local fish farms than the Pseudo-nitzschia species that cause ASP toxicity of shellfish.
38. Two distinct types of silicoflagellate blooms potentially harmful to fish farms occur in Scottish coastal waters: blooms of naked cells (harmful in Denmark) reported from Loch Striven and upper Loch Fyne, and blooms of siliceous stage cells (harmful in France and Spain) reported from the Shetlands.
39. Scottish coastal waters are "open" to ballast water introductions of toxic and benign phytoplankton species, both immigrant and indigenous species. Harmful species have been detected in the ballast water of ships visiting Scottish ports, but there is no evidence that deballasting has introduced new bloom species into Scottish coastal waters. This exposure is of concern, and precautions should be taken given the significant increase in blooms of novel and harmful species blooms in European waters during the past three decades, including of species seemingly absent or insignificant in Scottish waters (e.g. Alexandrium minutum, Prorocentrum minimum, Heterosigma akashiwo, Prymnesium parvum, Chattonella spp., among others).
40. The potential for ballast water introductions of toxic phytoflagellates into Scottish coastal waters from Scandinavia, where their ichthyotoxic blooms have become epidemic, is of special concern. Concern over the potential ballast water introduction of Gymnodinium catenatum, a paralytic shellfish toxin producer common along the Iberian Peninsula, is expressed in Summary Statement 21.
41. The occurrence of both toxic and non-toxic strains of a given HAB species is common; hence, their geographical redistribution through deballasting is also a matter of concern. The threat of introduced, harmful species and of indigenous species which then hybridize with local populations, leading to their heightened virulence is exacerbated by the close proximity of Scotland to continental Europe, from whence much of the ballast water potentially discharged into Scottish waters originates. The relatively short transit times between these regional ports favor survival of ballasted, harmful species.

42. The transfer of HAB species in aquacultural transplantation and importation of shellfish stocks should also be guarded against. It is recommended that the procedures followed currently to minimize this threat be reevaluated. Estimates of introduced species in shellfish consignments elsewhere in Europe warrant this vigilance. Importation of oyster, Crassostrea gigas, from France to Ireland delivered 67 phytoplankton species. An estimated 2.5 million viable dinoflagellates are transferred per tonne of mussels imported into Dutch coastal waters, yielding an annual introduction of ca. 10 ¹⁰ dinoflagellates. Special attention should be given to shellfish stocks imported from France and Spain, where the assemblage of toxic species differs somewhat from that in Scottish waters.
43. Scottish coastal waters are "open" to bioinvasions of species advected in currents. Inshore, nearshore and offshore waters are advective sources and sinks, and bloom sites of species potentially harmful to fish farming, shellfish cultivation and natural stocks. Advection of species resulting in blooms is a common "open" system feature of Scottish waters, with three basic types of blooms found: offshore advections resulting in frontal zone blooms; onshore blooms seeded by populations advected from offshore; and inshore blooms that develop as a result of local, alongshore seedings. Far-field delivery of species is also anticipated, such as from the Irish Sea into the Minch via dispersion in the Scottish Coastal Current. Such complex oceanographic structuring and seedings of HAB species and their blooms are highly stochastic. They are usually transient events rather than symptomatic of local habitat changes, such as initiation of fish farming or shellfish cultivation.
44. Scottish coastal waters are "open" to wind-, weather- and climate-driven disturbances and long-term climate change. These external drivers contribute to the inherent variability that characterizes HABs. The scale of physical impact ranges from micro-scale mixing, to rainfall-runoff events, to storm events, to large scale regional ocean-atmosphere interactions, such as the North Atlantic Oscillation ( NAO), and to warming trends. Six different climate- and weather-driven impacts ranging from short-term to long-term forcing on harmful blooms are expected to be operative in Scottish coastal waters. All of these external drivers have induced harmful blooms. Efforts to link HAB events causally to long-term aquacultural stimulation would have to show that such events are not linked to the effects of these external drivers. Such attempts must also take into account that Scottish waters are "open" systems subject to incursions of bloom species and opportunistic, transient and anomalous blooms. Further, that local and regional habitat perturbations associated with weather and climate also stimulate blooms of indigenous species. Long-term data sets (e.g. a minimum of ten years) are required in analyses seeking to distinguish weather-, climate- and other "open" system (bioinvasion, advection) driven HAB behaviour from aquacultural stimulation of harmful blooms.
45. The autecological evidence does not support the hypothesis that the ASP toxicity of Scottish scallop grounds is a consequence of climate change, specifically winter warming, stimulatory to Pseudo-nitzschia blooms and the source of domoic acid, the ASP toxin. The most compelling conclusion is that the ASP outbreak is attributable to natural causes, and not to winter warming, to anthropogenic stimulation, or to fish farm activities.
46. Fish farming is an intensive aquacultural activity: the fish feed and grow on a processed diet rich in nitrogen and enhanced with chemical and therapeutic additives. In contrast, in shellfish aquaculture the cultured stocks grow by feeding on the natural phytoplankton flora in competition with indigenous herbivore populations. Changes in the pelagic ecosystem are more likely to occur during shellfish cultivation, particularly if the local phytoplankton carrying capacity for shellfish biomass is exceeded, than during fish farming which does not graze the local biota. Both aquacultural types can cause changes in benthic communities.
47. Fish farms and shellfish cultivation in Scotland are generally "open culture" systems; their soluble and particulate wastes are discharged into the habitat. Excreted wastes and undigested food pellets undergo a series of biochemical transformations and chemical reactions that involve different trophic levels, the water column and bottom sediments. This recycling enriches the water column with dissolved inorganic and organic chemical wastes, to which the natural phytoplankton community can/may respond.
48. Aquacultural wastes impact phytoplankton in three primary ways: as nutrients, growth factors, and "chemical conditioners" which influence water quality and the sediments underlying cultivation pens and rafts. The primary nutrients discharged are inorganic nitrogen, urea and other organic nitrogenous compounds. Growth factors include an array of biologically active compounds, including purines, pyrimidines, polyamines, vitamins, and compounds having allelochemical and allelopathic effects. Water and sediment quality affects include increased chemical and biological oxygen demand, sequestration reactions involving trace elements, and altered redox potential in sediments which affects sediment/water chemical exchanges.
49. Bioassays using fish farm-conditioned water and elutriates of food pellets and faecal wastes provide experimental evidence that fish farm wastes and unutilized food can affect phytoplankton growth, including harmful species. Polyamines (guanine, cadaverine, etc.) released during death and decomposition of fish and other organisms can also affect phytoplankton growth. Experiments show that phytoplankton responses to fish farm exudates vary with the species tested, the animal source, and the chemical structure of the waste products. And within the same conditioned water, some waste substances are stimulatory while other substances inhibit growth of the bioassayed species. Experimental results indicate that a predictable relationship does not occur between fish farm waste discharge and phytoplankton species selections and bloom behavior. The relationship is extremely complex. Should altered phytoplankton behaviour occur in response to fish farm wastes at a given fish farm site, it is expected to develop as a process over time, rather than transition suddenly into a state of disrupted or anomalous behaviour.
50. Any evaluation of the potential influence of fish farm and shellfish wastes on phytoplankton should not ignore the responses of bacteria. Algicidic bacteria are active against a wide range of phytoplankton species which they kill through direct attack or by production of toxins. The relationships occurring within the aquacultural nutrient waste - phytoplankton - bacteria - animal mortality nexus are complex. Nutrient wastes from fish farms enhance bacterial growth and the microbial loop components that feed on bacteria. It can be difficult to distinguish between fish farm mortality due to harmful phytoplankton vs. that from bacterial infection. Bacterial infections of Vibrio spp. can cause significant mortality among farmed fish during a condition referred to as "winter ulcers".
51. A 265-fold increase in farmed salmon production has occurred in Scotland over a period of two decades, accompanied by a 23-fold increase in annual N and P waste loadings from fish farms since 1985. Regional data for Scottish waters, and notwithstanding experimental evidence that fish farm wastes can both stimulate and inhibit phytoplankton species, indicate that increased nutrient loading has not been accompanied by a detectable increase in blooms, or altered species behaviour, neither of benign, nor harmful species. Using the year 1985, when fish farming accelerated, as a branch point, differences in regional bloom patterns and frequencies during the pre- and post-1985 period are not evident. Similarly, the patterns and trends in harmful species of Alexandrium, Dinophysis, Pseudo-nitzschia, phytoflagellates, diatoms and ichthyotoxic Karenia mikimotoi do not show a detectable relationship with increasing delivery of fish farm nutrients. This conclusion agrees with that reached by Tett and Edwards, and by Rydberg and co-workers who applied different, but related analytical approaches.
52. Shellfish filter and chemically modify huge volumes of water through waste excretions during their continuous grazing on the indigenous phytoplankton. Thus, shellfish cultivation is a husbandry within a husbandry: the cultured stocks feeding upon the natural phytoplankton community excrete nutrients which stimulate new phytoplankton growth and abundance that in turn becomes available for filter feeding. Phytoplankton removal rates by natural bivalve beds and cultured stocks can lead to significant reductions in phytoplankton abundance. In contrast, fish farming does not lead to ecosystem changes because of competitive grazing of the farmed fish with indigenous stocks; the use of processed food precludes such grazing. The corollary of extensive (shellfish) vs. intensive (fish farming) aquaculture is that shellfish cultivation removes and recycles nutrients; fish farming adds nutrients.
53. Shellfish affect phytoplankton species composition in two ways: through selective filter feeding and growth stimulation by waste nutrients. Selective feeding is accompanied by copious production of pseudofaeces, a mechanism used to collect and void rejected phytoplankton cells and other particles, and a fate also leading to phytoplankton mortality. The impact of filter-feeding shellfish on phytoplankton composition and abundance is the outcome of two different effects: mortality resulting from grazing and pseudofaecal removal, and growth stimulation by excreted inorganic and organic nutrients and by nutrients leached from pseudofaeces and faeces. Similar to fish farming, shellfish cultivation influences the nitrogen cycle, even though organic waste deposition rates are typically one- to two-orders of magnitude lower than at fish farms.
54. Limited experimental data indicate that shellfish excrete substances that can stimulate and inhibit the growth of phytoplankton species, including harmful taxa. These effects vary with the bivalve species producing the waste nutrients, and the phytoplankton species responding to them. Elutriates of bottom sediments that underly shellfish cultivation platforms also can stimulate and inhibit species.
55. Phycotoxins ( ASP, DSP, PSP) are commonly measured at shellfish cultivation sites because of the threat of shellfish intoxication. Toxicity usually is the result of toxin accumulation during bivalve filtration of local or advected populations of phytoplankton, whose presence and abundance are not directly related to waste nutrients released at the cultivation site. Similar to fish farms, with the exception of Heterosigma akashiwo blooms at the latter, there is no local evidence that shellfish cultivation stimulates harmful blooms or induces toxicity. Shellfish cultivation is more vulnerable to harmful species presence than fish farming, because of the nutritional dependence of bivalves on the phytoplankton, unlike the carnivorous fish. However, fish farming potentially may be more stimulatory to harmful flagellate species because of the chemical diversity and composition of fish farm wastes and the intensive nature of fish farming (see also Summary Statement 49).
56. With regard to the basic question addressed in this review: whether there has been an increase in HAB events stimulated by increased aquacultural activity in Scottish coastal waters, or whether the observed bloom behavior is more characteristic of the natural and variable behavior expected of the indigenous phytoplankton exposed to the "open system" features of these waters:

57. The research carried out on the phytoplankton of Scottish coastal waters is of high quality, with two main thrusts evident: studies carried out without reference to aquaculture, and those derivative from aquaculture. These different interests have produced a useful body of work that is more splintered than integrated. The greatest problems hampering use of these data to address the topics of this review are the sampling and knowledge gaps. Key measurements in key regions do not appear to have been made. There is a conspicuous absence of quantitative studies on the annual cycles in plankton (phytoplankton and zooplankton) and habitat variables in representative open water, coastal and sea loch habitats, including long-term monitoring sites. The excellent efforts of investigators seeking to assess aquacultural impacts in Scottish waters have also been impeded by the shortage of quantitative data on plankton, their processes and environmental conditions.

58. There is need for better information on the phytoplankton species composition in Scottish coastal waters, including an inventory of harmful taxa present, using updated taxonomy and taxonomic procedures. Harmful algal bloom impacts are highly species specific; there has been an global outburst of novel species blooms; descriptions of new species and bioinvasions have become common, and there is concern over the ballasting of harmful species. There are also strain differences in toxicity and physiology that must be revealed and require use of molecular techniques. These characteristics of harmful species and their blooms require a level of taxonomic expertise more exacting than customarily applied in research on phytoplankton ecology.

59. The recommendations and comments in Summary Statements 56 and 57 derive from the harmful bloom issues confronting Scotland, present and future. There is a greater concern: relative to other European countries (and elsewhere) where fish farms and shellfish cultivation are important enterprises, there is a conspicuous lack of a commensurate harmful algal research effort in Scotland. Relatively few scientists are involved, and field and experimental investigations are limited in scope and effort. This reduced effort ill-prepares Scotland and its aquaculture should a series of devastating, recurrent harmful blooms develop similar to those ongoing in Scandinavian waters. Scottish investigators appear to be working in relative isolation from European scientists, and to their mutual disadvantage. There is little sign of collaborative research or scientific interaction at workshops, ICES working groups and special meetings on HABs, and minimal participation in the international conferences on harmful algal blooms that have been convened the past two decades. Such networking is important for information exchange and in establishing research links, particularly since harmful bloom research is still in its infancy and descriptive stage. At another level, expertise in quantitative analyses and modelling of nutrient -fish farm dynamics is very sophisticated and advanced in Scotland relative to elsewhere in Europe. Increased dialogue between Scottish researchers and continental European scientists in this area would also be beneficial.

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