Roy S. Houston, Ph.D.                                     
For the past several months there has been a severe “red tide” along the coastline from San Felipe and throughout much of the northern Gulf of California. This event is exemplified by the presence numerous dead marine life that has washed up on local beaches. Red tides occur when there is an outbreak of phytoplankton, those microscopic algae including the diatoms and dinoflagellates which provide energy and food for much of the marine ecosystem. To the human eye these “blooms” may give the water a brownish-red, green, brown, or reddish-orange color depending on the algal species. This natural phenomenon occurs in part as the result of strong NE winds which occur locally from late fall through spring. These winds stir the water allowing nutrients to be available for plankton growth. Red tides, which have little to do with the tides, have sometimes been associated with toxic algal blooms. In recent years these algal blooms have become more frequent and severe. Fortunately of the many species of algae that exist in the sea only about 6% of the known varieties produce toxins. Moreover, species that produce toxic cells at low concentrations in  blooms that do not discolor the water.  Therefore, scientists prefer the term “harmful algal blooms” (or HABs).  Harmful algal blooms cause problems through the production of toxins or by their accumulated biomass, which can affect marine organisms and modify food-web dynamics. Human illness and mortality usually occurs after the consumption of infected shellfish and fish which feed on plankton and concentrate toxins in their tissues. In addition, oxygen levels can be depleted or greatly diminished after HABs. These events create substantial losses to commercial fisheries and HAB-associated fish, bird and mammals. In recent years along the West Coast of North America there have been high mortalities of sea birds and California sea lions due to HABs along the Pacific coast of North America. The following HABs and are known to occur in the northern Gulf of California are major causes of Shellfish Poisoning.
            Paralytic Shellfish Poisoning (PSP) is caused by a naturally occurring toxin or biotoxin known as saxitoxin which occurs in certain dinoflagellates including Pyrodinium and Alexandrium spp. These critters are ingested by all molluscan shellfish (those having a hinged shell) including clams, mussels, oysters, geoducks, and scallops, which are capable of concentrating paralytic poisoning. Other animals that feed on these toxic plankton include filter feeding fishes (anchovies, etc.), baleen whales. In turn, sickness and mortalities occur in many animals that consume fishes and other marine life which have concentrated the toxins. This is exemplified by the numerous observations of dolphins, whales, and birds that have washed up on local beaches as a result of PSP.  
            Crabs that feed on shellfish may contain unsafe levels of the toxin, although it is not known to accumulate in the meat. Just to be safe, clean the crab thoroughly and remove all of the fat inside the back of the shell and toss the gut. When the number of toxic producing dinoflagellates returns to normal low levels, the shellfish will eventually flush the toxin from their systems. This can be several days to months before they are safe for consumption. Paralytic Shellfish Poisoning is an affliction of the central nervous system and paralyzes muscles. Early symptoms include tingling of the tongue and lips, which usually begin within in minutes after ingesting infected shellfish. However, in some cases tingling may develop after one or two hours. Symptoms may progress to tingling in the fingers and toes which will lead to loss of control of the arms and legs. This is followed by difficulty in breathing, nausea and disorientation. If a person consumes enough toxin paralysis will occur in the muscles of the chest and abdomen and the victim can suffocate. It has been reported that death from PSP has occurred within 30 minutes! Unfortunately PSP is not destroyed by cooking or freezing shellfish and anyone who consumes PSP is at risk for illness or death. In the United States commercial harvest operations are required to meet stringent state and federal health standards and their catches are regularly tested for biotoxins. Unfortunately for those who go out clamming on Baja beaches do not have this luxury and, therefore have to exercise extreme caution and eat shellfish only at certain times of the year. A rough rule of thumb is to only consume shellfish which were collected in months with an “r”. This is when biotoxin levels are generally at their lowest levels. There is no antidote for this malady. The only treatment for severe cases is the use of life support systems until the toxin is cleared from the patient.
            Another nasty toxin is domoic acid which causes Amnesic Shellfish Poisoning (ASP). This toxin is produced by the diatom, Pseudonitzchia and has been creating havoc along the Pacific coast of North America in recent years. Domoic acid poisoning is responsible for the death of numerous birds and marine mammals. In addition, there have been reported cases of aggressive behavior in infected sea lions. In recent years surfers, divers and bathers have been attacked and bitten by these generally docile creatures. I have experienced close encounters with sea lions during scuba dives where they followed me throughout much of the dive. Normally these animals will do a quick swim by and disappear. Symptoms of ASP that occur within 24 hours of eating contaminated shellfish include nausea, vomiting, diarrhea and abdominal cramps. Neurological symptoms occur within 48 hours in more severe cases. These include headache, disorientation, dizziness, loss of short term memory, motor weakness, seizures, cardiac arrhythmias, coma and possible death. Like PSP there is no antidote for ASP. If symptoms are mild, contact your health care provider. If severe, go to the ER immediately.
            Intestinal problems from eating shellfish can also be a result of harmful bacteria and viruses. In addition, some people are simply allergic to shellfish. It is not the intent of this article to frighten one discourage you from eating seafood, but to assist you in being an informed consumer In conclusion when eating shellfish or any food from the sea, simply use common sense and ENJOY!