12th International Conference on Harmful Algae

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INTERNATIONAL SOCIETY FOR THE STUDY OF HARMFUL ALGAE12 th <strong>International</strong> <strong>Conference</strong> on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006levels (80 µg STX eq./100g meat)for acceptable limits of saxitoxins inseafood, the FWC banned pufferfish harvesting in the IRL. Apartfrom puffer fish that consistentlyexceed the action limit forsaxitoxins, shellfish beds in thenorthern IRL were closed as aprecautionary measure only on twobrief occasions, just exceeding theacceptable limit by mouse bioassay.Preliminary evidence suggests thatsaxitoxins are present in the foodchain but they remain an unknownrisk to natural resources, despitedocumented mortality and diseaseevents in the IRL.81
INTERNATIONAL SOCIETY FOR THE STUDY OF HARMFUL ALGAE12 th <strong>International</strong> <strong>Conference</strong> on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006SYMPOSIA, WEDNESDAY 6 SEPTEMBER1. Ecosystem Disruptive Harmful Algal BloomsROOM: will be announcedConvener: Pat TesterThere is a new term in town – Ecosystem Disruptive Harmful Algal Blooms (EDABS)This session will explore the effects of eutrophication, relaxation of top down controland positive feedback loops that may help perpetuate EDABS. Ideas published intwo recent papers will serve as the focus for this session that will include 2-3speakers to introduce the topic and stimulate open, vigorous discussions about whatEDABS are, what the feedback loops are and what consequences EDABS have toecosystems viability.Sunda et al. (2006) “Harmful algal blooms (HABs) have occurred with increasingfrequency in recent years with eutrophication and other anthropogenic alterations ofcoastal ecosystems. Many of these blooms severely alter or degrade ecosystemfunction, and are referred to here as ecosystem disruptive algal blooms (EDABs).These blooms are often caused by toxic or unpalatable species that decreasegrazing rates by planktonic and benthic herbivores, and thereby disrupt the transferof nutrients and energy to higher trophic levels, and decrease nutrient recycling.Examples of EDAB species discussed in this paper include the pelagophytesAureococcus anophagefferens Hargraves et Sieburth and Aureoumbra lagunensisDeYoe and Stockwell, the green tide algae Nannochloris atomus Butcher andNannochloropsis gaditana Lubián, the haptophytes Chrysochromulina polylepisManton et Parke and Prymnesium parvum Carter, and the cyanobacteriaSynechococcus elongates Nägeli and Nodularia spumigena Mertens ex Bornet &Flahault. Many factors, such as nutrient availability and herbivore grazing have beenproposed to separately influence EDAB dynamics, but interactions among thesefactors have rarely been considered. Here we discuss positive feedback interactionsamong nutrient availability, herbivore grazing, and nutrient regeneration, which havethe potential to substantially influence the dynamics of EDAB events. The positivefeedbacks result from a reduction of grazing rates on EDAB species caused bytoxicity or unpalatability of these algae, which promotes the proliferation of the EDABspecies. The decreased rates also lower grazer-mediated recycling of nutrients andthereby decrease nutrient availability. Since many EDAB species are well-adapted tonutrient-stressed environments and many exhibit increased toxin production andtoxicity under nutrient limitation, positive feedbacks are established which can greatlyincrease the rate of bloom development and the adverse effects on the ecosystem.An understanding of how these feedbacks interact with other regulating factors, suchas benthic/pelagic nutrient coupling, physical forcing, and life cycles of EDAB speciesprovides a substantial future challenge.”Mitra and Flynn (2006) “The relationship between algae and their zooplanktonicpredators typically involves consumption of nutrients by algae, grazing of the algaeby zooplankton which in turn enhances predator biomass, controls algal growth andregenerates nutrients. Eutrophication raises nutrient levels, but does not simplyincrease normal predator–prey activity; rather, harmful algal bloom (HAB) eventsdevelop often with serious ecological and aesthetic implications. Generally, HABspecies are outwardly poor competitors for nutrients, while their development ofgrazing deterrents during nutrient stress ostensibly occurs too late, after the nutrientshave largely been consumed already by fast-growing non-HAB species. A newmechanism is presented to explain HAB dynamics under these circumstances. Using82
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12th International Conference on Harmful Algae

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