Issues in Ecology Number 7 al2000 duce powerful toxins or cause other harm to humans.fisher Effects on Seagrass Beds and Corals ies resources,and coastal ecosystems (Figure 3).These spe Eutrophication frequently leads to the deoradatio cies make their in thee red or brown tides-to dilute.inconspicuous concentra availability further by stimulating the growth of phytoplank tions of cells noticed only because of damage caused by their ton,epiphytes on the seagrass leaves.and nuisa potent toxins.Impacts can indude mass mortalities of wild and of ephemeral seaweeds (macroalgae)that shade out both farmed fish and shellfish,human poisonings from contaminated seagrasses and perennial seaweeds such as kelp.In addition fish or shellfish.alterations of marine food webs through dam eutrophication can lead to elevated concentrations of sulfide 智me in the sediments of seagrass beds as algae and plant material decompose on the oxygen-depleted seafloor and seagrasses Although population explosions of toxic or noxious lose their ability to oxygenate the sediments.These elevated algal species are sometimes called red tides.they are more sulfide levels can slow the growth of seagrasses.which draw As with most algal most of their nutrients from the sediments rather than the this proliferation and occasional dominance by par water column.or even poison them and lead to their decline ticular species a combination of physical,chemi Nutrient-induced changes generally lower the bio that remair logica diversity of seagrass and kelp communities.Since these ugh ham for a or year d ce and durati rleast som Pe1972 th d exa p of the link he and lution involves the recently discov noflagellate Pfiesteria.In North Carolina estuarie and in the chesaneake bay this oroanism has bee linked to fish kills and to a variety of human effects including severe learning and memory pr lems because the organism and associated fish kills have occurred in watersheds that are heavily pol luted by hog and chicken farm wastes and by mu- nicipal sewage,a strong case can be made that nu trient pollution serves as a major stimulant to out breaks of Pfiesteria or Pfiesterialike organisms.Nu Pre trient-laden wastes could stimulate the outbreaks by either of two mechanisms. First.Pfiesteria is able to take up and use some of the dissolved organic nutri- ents in the waste directly. this adaptabl organism can cons algae that have grov VE H P the Figure 3.This shows the expansion of harmful algal blooms in the United States pre-1972 to present.Ciguatera blooms accumulate toxins in fish argely in tropical waters.Brown tides destroy shellfish beds.Pliesteria kills n tid fish and harms humans.(from Ander ish poiso hat ded reg son 1995,as reprinted in NRC 2000)5 Issues in Ecology Number 7 Fall 2000 duce powerful toxins or cause other harm to humans, fisher￾ies resources, and coastal ecosystems (Figure 3). These spe￾cies make their presence known in many ways, ranging from massive blooms of cells that discolor the water so-called red or brown tides to dilute, inconspicuous concentra￾tions of cells noticed only because of damage caused by their potent toxins. Impacts can include mass mortalities of wild and farmed fish and shellfish, human poisonings from contaminated fish or shellfish, alterations of marine food webs through dam￾age to larval or other life stages of commercial fisheries species, and death of marine mammals, seabirds, and other animals. Although population explosions of toxic or noxious algal species are sometimes called red tides, they are more correctly called harmful algal blooms. As with most algal blooms, this proliferation and occasional dominance by par￾ticular species results from a combination of physical, chemi￾cal, and biological mechanisms and interactions that remain poorly understood. Although harmful algal blooms have occurred for at least thousands of years, there has been an increased incidence and duration of such outbreaks worldwide over the past several decades. This increase in harmful algal blooms has coincided with marked increases in nutrient inputs to coastal waters, and in at least some cases, nutrient pollution is to blame for the outbreaks. A frequently cited example of the suspected link between harmful algal blooms and nutrient pol￾lution involves the recently discovered phantom di￾noflagellate Pfiesteria. In North Carolina estuaries and in the Chesapeake Bay, this organism has been linked to fish kills and to a variety of human health effects, including severe learning and memory prob￾lems. Because the organism and associated fish kills have occurred in watersheds that are heavily pol￾luted by hog and chicken farm wastes and by mu￾nicipal sewage, a strong case can be made that nu￾trient pollution serves as a major stimulant to out￾breaks of Pfiesteria or Pfiesteria-like organisms. Nu￾trient-laden wastes could stimulate the outbreaks by either of two mechanisms. First, Pfiesteria is able to take up and use some of the dissolved organic nutri￾ents in the waste directly. Second, this adaptable organism can consume algae that have grown more abundant because of the nutrient over-enrichment. Although the link between Pfiesteria outbreaks and nutrient pollution has not been fully proven, the evidence is sufficiently strong that legislation is already being developed and adopted to regu￾late waste handling at hog and chicken farms to reduce nutrient inputs to adjacent watersheds. Pfiesteria has thus prompted some agencies to address serious and long-standing pollution dis￾charges by nonpoint sources that had previously avoided regulation. Effects on Seagrass Beds and Corals Eutrophication frequently leads to the degradation or complete loss of seagrass beds. Plant growth in these beds is often light limited, and eutrophication can lower light availability further by stimulating the growth of phytoplank￾ton, epiphytes on the seagrass leaves, and nuisance blooms of ephemeral seaweeds (macroalgae) that shade out both seagrasses and perennial seaweeds such as kelp. In addition, eutrophication can lead to elevated concentrations of sulfide in the sediments of seagrass beds as algae and plant material decompose on the oxygen-depleted seafloor and seagrasses lose their ability to oxygenate the sediments. These elevated sulfide levels can slow the growth of seagrasses, which draw most of their nutrients from the sediments rather than the water column, or even poison them and lead to their decline. Nutrient-induced changes generally lower the bio￾logical diversity of seagrass and kelp communities. Since these Figure 3 - This shows the expansion of harmful algal blooms in the United States pre-1972 to present. Ciguatera blooms accumulate toxins in fish, largely in tropical waters. Brown tides destroy shellfish beds. Pfiesteria kills fish and harms humans. (from Ander￾son 1995, as reprinted in NRC 2000). Pre-1972 Present Neurotoxic shellfish poisoning Paralytic shellfish poisoning Fish kills Ciguatera Pfiesteria Brown tide Amnesic shellfish poisoning