The last decade of the last millennium ushered in the rise of "red tides" globally. The public, however, need not panic when the blue waters turn to red, green, brown or orange. When there is microalgal bloom in an aquatic system, they serve as increased food supply to the next group of organisms in the food chain, i.e., the zooplankton, which then positively impacts the next group in the chain and therefore effects increased marine productivity. The danger, however, is in the type of organism or species that could sometimes bloom. There are about 5,000 marine microalgal species in the world and only about 200 of them could cause harm. There are less than a hundred causative organisms that could cause poisonings. The route of poisoning is usually through the consumption of shellfish, e.g., green mussels (Perna viridis), oysters (Crassostrea spp.) or finfish, collected or harvested in the area where and when the bloom occurred. The shellfish or finfish are vectors of the poison because they accumulate the microalgae and their toxins are passed to the consumers (like human beings and other mammals). In other countries, marine mammals like manatees, etc. have been poisoned by these toxins.
"Harmful algal blooms" (HABs) is a generic term which refers to all algal blooms that can cause harm. A wide range of organisms is involved, including dinoflagellates, other flagellates, cyanobacteria, diatoms and other phytoplankton. The term HAB is not always synonymous to the term "red tide" because not all harmful algal bloom events can be considered as "red tides" which refer to the discoloration of water due to significant accumulation of biomass by the microalgae that proliferated. However, not all harmful algal events involve the development of significant accumulation of biomass. Many HAB species are harmful at very low densities and therefore do not form discoloration or red tides but cause harm by producing toxins that can be transferred to the food chain.
There is reason for cause of alarm when it comes to HABs. It has been surveyed that it has been increasing in occurrence and impacts globally. Aside from causing a growing number of seafood poisoning cases and deaths, the accompanying economic loss to people dependent on the coastal ecosystem as their only means of livelihood is a cause of concern. The cause of its spread has not been completely elucidated. One of the factors scientists are looking into is a part of the life cycle of the microalgae which is the "cyst." Cysts can serve as seeds for future blooms by germinating when conditions become favorable. These cysts can be transported via currents and ships’ ballast water from one part of the world to another where they can invade local ecosystems, bloom and eventually cause harm. It is no wonder therefore that there is a global convention on the management of ship ballast water.
Poisonings from harmful algal blooms result in negative effects on the gastro-intestinal system like diarrhea, nausea and vomiting, and the nervous system like paralysis, loss of memory, etc., and in extreme cases, the death of the victim. These poisonings can be classified as Paralytic Shellfish Poisoning (PSP), Amnesic Shellfish Poisoning (ASP), Diarrhetic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP) and Ciguatera Fish Poisoning (CFP) and may only happen when the specific causative organisms bloom and the shellfish/finfish that accumulated them are consumed.
Manila Bay and some other bodies of waters in the Philippines and the rest of the world have experienced both harmless and harmful "red tides." As early as 1905, a priest reported a "red tide in Manila Bay" which was apparently harmless because there was no report of accompanying poisoning. In 1983, in Samar and Leyte, waters were hit by a "harmful algal bloom" event that caused Paralytic Shellfish Poisoning to hundreds and death to 23 people. From then on to most Filipinos, the term "red tide" has been synonymous to toxicity and economic disaster. An uninformed public does not want to buy and consume marine food products, including those not affected by the phenomenon. This "halo effect" can generate an estimated US$300,000 loss of income from fish/fishery produce. Public education is part of the management scheme that can alleviate or mitigate economic disasters and prevent poisoning due to harmful algal blooms. Research and development is ongoing at the regional, national and international levels to enhance management of HABs.
Some water discolorations may be caused by the bloom of phytoplankton which are harmful only to fish, thereby causing "fish kills." Chattonella marina and Prorocentrum minimum were found associated with the fish kills in Bolinao in 2004 and 2002, respectively. In the recent water discoloration in Morong, Bataan where "fish kill" was also reported, Noctiluca scintillans was in bloom.
For more information on harmful algal blooms, visit our website http://portal.unesco.org/habsea. The HABSEA portal is a gateway to HAB information in Asia initially emanating from the Southeast Asian countries. It offers information on varied interpretation of Harmful Algal Blooms (HABs), scientific background on causative organisms, their life cycles, interaction with the environment and degree of occurrence, management strategies instituted, and varied source learning to enhance understanding of the phenomenon.
Send queries and comments on this article to rhod@upmsi.ph.