186
S. Bernard et al.
10.1 Introduction
The upwelling systems of the eastern boundaries of the world’s oceans support high
biological productivity and a high incidence of Harmful Algal Blooms (HABs)
(Kudela et al. 2005). The majority of species contributing to HABs in upwelling
systems constitute regular components of the annual succession of phytoplankton,
and their harmful impacts are associated with either their toxic properties or the high
biomass such blooms can achieve (Trainer et al. 2010). Negative consequences include contaminated seafood, the mortality of fish and other animals, and habitat or
ecosystem degradation, all to the detriment of coastal and fishing communities.
There is a strong seasonality to phytoplankton community structure in the southern Benguela, with larger-celled diatoms and dinoflagellates typically dominating
inshore waters during the upwelling-driven summer months, and smaller-celled flagellates more dominant in winter (Barlow et al. 2005). Most HABs in the Benguela
upwelling system have been attributed to one or another dinoflagellate species, but
harmful impacts have also been ascribed to other groups of phytoplankton, including
the raphidophytes, diatoms and the ciliate Myrionecta rubra (Trainer et al. 2010). Of
the impacts associated with toxigenic phytoplankton, those dinoflagellate species responsible for the shellfish poisoning syndromes Paralytic Shellfish Poisoning (PSP)
and Diarrhetic Shellfish Poisoning (DSP) pose the greatest risk to human health in
the Benguela region (Pitcher and Calder 2000). As a producer of saxitoxins Alexandrium catenella is the primary cause of PSP, whereas several species of Dinophysis,
through the production of okadaic acid and its derivatives, are the causative agents
of DSP (Pitcher et al. 2011; Hubbart et al. 2012). Lesser risks to human health in
the Benguela are presented by the production of yessotoxins by the dinoflagellate
Protoceratiun reticulatum (Krock et al. 2008), and by the production of domoic acid
by diatoms of the genus Pseudo-nitzschia (Fawcett et al. 2007; Hubbart et al. 2012).
The risk to seafood safety presented by these species can result in significant losses in
harvestable resources and represents a significant threat to the aquaculture industry
within the region.
In addition to their accumulation in shellfish, some dinoflagellate toxins, such as
those produced by species of Karlodinium and Karenia can lead directly to mortalities
of marine life. In the northern Benguela Karlodinium veneficum produces a suite of
toxic compounds characterised by haemolytic, ichthyotoxic and cytotoxic properties,
and has long been associated with massive fish kills (Copenhagen 1953), whereas in
the southern Benguela Karenia cristata, is not only responsible for faunal mortalities
but may impact human health through eye, nose, throat and skin irritations (Botes
et al. 2003). Other fish-killing phytoplankton in the Benguela include the raphidophyte Heterosigma akashiwo, although the underlying toxicological mechanisms
remain uncertain (Pitcher and Calder 2000).
Events of anoxia, and in some cases associated increases in sulphide concentration, represent one of the more conspicuous and well documented impacts of HABs
in the Benguela ecosystem (van de Lingen et al. 2006). Anoxia follows the decay
of high biomass dinoflagellate blooms, referred to as red tides. Often dominated by
species of Ceratium and Prorocentrum, these blooms develop during late summer
S. Bernard et al.
10.1 Introduction
The upwelling systems of the eastern boundaries of the world’s oceans support high
biological productivity and a high incidence of Harmful Algal Blooms (HABs)
(Kudela et al. 2005). The majority of species contributing to HABs in upwelling
systems constitute regular components of the annual succession of phytoplankton,
and their harmful impacts are associated with either their toxic properties or the high
biomass such blooms can achieve (Trainer et al. 2010). Negative consequences include contaminated seafood, the mortality of fish and other animals, and habitat or
ecosystem degradation, all to the detriment of coastal and fishing communities.
There is a strong seasonality to phytoplankton community structure in the southern Benguela, with larger-celled diatoms and dinoflagellates typically dominating
inshore waters during the upwelling-driven summer months, and smaller-celled flagellates more dominant in winter (Barlow et al. 2005). Most HABs in the Benguela
upwelling system have been attributed to one or another dinoflagellate species, but
harmful impacts have also been ascribed to other groups of phytoplankton, including
the raphidophytes, diatoms and the ciliate Myrionecta rubra (Trainer et al. 2010). Of
the impacts associated with toxigenic phytoplankton, those dinoflagellate species responsible for the shellfish poisoning syndromes Paralytic Shellfish Poisoning (PSP)
and Diarrhetic Shellfish Poisoning (DSP) pose the greatest risk to human health in
the Benguela region (Pitcher and Calder 2000). As a producer of saxitoxins Alexandrium catenella is the primary cause of PSP, whereas several species of Dinophysis,
through the production of okadaic acid and its derivatives, are the causative agents
of DSP (Pitcher et al. 2011; Hubbart et al. 2012). Lesser risks to human health in
the Benguela are presented by the production of yessotoxins by the dinoflagellate
Protoceratiun reticulatum (Krock et al. 2008), and by the production of domoic acid
by diatoms of the genus Pseudo-nitzschia (Fawcett et al. 2007; Hubbart et al. 2012).
The risk to seafood safety presented by these species can result in significant losses in
harvestable resources and represents a significant threat to the aquaculture industry
within the region.
In addition to their accumulation in shellfish, some dinoflagellate toxins, such as
those produced by species of Karlodinium and Karenia can lead directly to mortalities
of marine life. In the northern Benguela Karlodinium veneficum produces a suite of
toxic compounds characterised by haemolytic, ichthyotoxic and cytotoxic properties,
and has long been associated with massive fish kills (Copenhagen 1953), whereas in
the southern Benguela Karenia cristata, is not only responsible for faunal mortalities
but may impact human health through eye, nose, throat and skin irritations (Botes
et al. 2003). Other fish-killing phytoplankton in the Benguela include the raphidophyte Heterosigma akashiwo, although the underlying toxicological mechanisms
remain uncertain (Pitcher and Calder 2000).
Events of anoxia, and in some cases associated increases in sulphide concentration, represent one of the more conspicuous and well documented impacts of HABs
in the Benguela ecosystem (van de Lingen et al. 2006). Anoxia follows the decay
of high biomass dinoflagellate blooms, referred to as red tides. Often dominated by
species of Ceratium and Prorocentrum, these blooms develop during late summer