Introduction

The propagation of plankton algae, or ‘algal blooms’ which is defined as a drastic population increase that may lead to a peak, (Smayda, 1997a) is a naturally occurring phenomenon that has occurred for centuries and can be advantageous for aquaculture and wild fisheries industries (Hallegraeff, 1993). In certain instances, however, algal blooms can have devastating consequences, creating severe environmental and health problems. These are referred to as harmful algal blooms (HABs), which occur when certain species of this marine phytoplankton, those that possess the ability generate powerful toxins, settle in such high numbers that they visibly discolor the surface of the sea (i.e. ‘red tides’) (Hallegraeff, 1993). This study deals with a particular dinoflagellate species known as Pyrodinium bahamense var. compressum that has been observed to occur with increasing frequency in Manila Bay, Philippines. Since its first appearance in 1988, P. bahamense, has recurred annually, causing over 2,000 Paralytic Shellfish Poisoning (PSP) instances and 116 human deaths via consumption of these shellfish in the Philippines (Azana and Miranda, 2001). This dinoflagellate is most easily recognized by its bioluminescence, and the onset of these toxic blooms is associated with the rainy southwest monsoon season (beginning in June and ending in November) and strong prevailing onshore winds (Hallegraeff, 1989). In order for this species to settle/initiate in such high concentrations, there must be favorable environmental conditions, which include: highly saline waters generally ranging between 31-34.9 ppt, sea surface temperatures ranging between 24.4-32.5 degrees Celsius, and increased nutrient levels, associated with anthropogenic impacts and enhanced by rainy weather conditions, which results in excessive runoff containing fertilizers and particulate matter, and human and industrial waste that is delivered to coastal waters and leads to coastal eutrophication (Maclean, 1989) and (Villanoy et al., 2006). P. bahamense has the ability to form resting cyst beds, which accumulate in the sediment when conditions are not quite as favorable (Azanza and Taylor, 2001). It has been observed that these resting cysts found in the sediments can serve as “seed beds” for future blooms (Anderson, 1984) and (Azanza et al., 2004). When onshore winds associated with this region begin to blow with sufficient strength (southwest monsoon), the high turbulence results in powerful vertical mixing, resuspending and dispersing cysts and/or nutrients from the substrate throughout the water column in order to trigger bloom formation (Hallegraeff, 1989) and (Villanoy et al., 2006). Moreover, P. bahamense takes advantage of its vertical migration capability, which prevents the dinoflagellate from being diluted or washed out of bays (Maclean, 1989).

Harmful blooms of P. bahamense have increased in frequency and extent throughout the region, which can be attributed to climatic changes including heightened precipitation intensity and rising sea surface temperature, as well as to anthropogenic impacts related to huge increases in the discharge of wastes from rivers (Relox and Bajarias, 2011). This increase in nutrients is extremely beneficial to the growth of this dinoflagellate in permitting sufficient reproduction to counteract dilution losses, which ultimately augments the potential for alongshore emigration (Seliger, 1989). When the dinoflagellate decomposes, it severely reduces the oxygen available in the ocean for marine organisms (Relox and Bajarias, 2011). Furthermore, when these algal blooms occur, the dinoflagellate is in such high concentrations that they effectively block out sunlight exposure to the coral reefs, thus resulting in an inability to photosynthesize and eventual coral bleaching (Hallegraeff, 1993). Proceeding incidences of water discoloration (‘red tides’), enormous fish die outs of both cultured and reef fish have been seen, which present devastating economic implications for an economy based almost entirely off of aquaculture, marine ecotourism, and the shellfish industry. Not only are there economic losses and adverse impacts in regards to marine resources in Manila Bay, but as previously stated, P. bahamense, which is associated with so many cases of PSP, also represents a huge threat to human health. Unfortunately, there are no current long-term monitoring applications in the Philippines because it is extremely costly and they do not have the resources necessary for such monitoring (Azanza and Taylor, 2001). In order to both fully understand P. bahamense bloom dynamics as well as to track their extent and distribution, monitoring stations via information and data attained from local knowledge, scientific research, and remote sensing applications would be extremely beneficial. By detecting these red tides in advance and thus creating an early warning system, this would not only prevent deaths of humans (due to shellfish consumption), but it could also prevent such enormous losses to their aquaculture industry by removing cages from bloom-affected areas in advance. Due to the archipelagic nature of the Philippines in addition to its remoteness, remote sensing applications would be highly conducive to the monitoring of these red tides in mapping the extent of the plumes and thus allows conclusions to be made regarding reef/marine ecosystem’s vulnerability to increased pollutant loads from river discharge, variations in seasonality, and rising sea surface temperatures Relox and Bajarias, 2011). Finally, by using satellite imagery to identify algal blooms and assessing ecosystem vulnerability, scientists and researchers can better understand any impact this species may have in coastal or offshore environments.

Problem Statement:

We are specifically going to examine how changes in seasonality (i.e. increased precipitation characteristic of the southwest monsoon season) as well as sea surface temperature anomalies/ocean currents have influenced the occurrence of these red tides of dinoflagellate P. bahamense in space and time.