Methods

Due to the limited availability of downloadable, cloud-free Landsat 4-present satellite images on GLOVIS, images were acquired over a relatively long time period, spanning from 1989-2011. Due to the fact that this study focuses on seasonality as the prominent factor in dictating the initiation, settlement, and propagation of P. bahamense, 4 images from the dry season (December – May) and 4 images from the rainy southwest monsoon or wet season (June – November) were acquired from various years based on availability and an attempt to acquire images from different months in each season that serve as a representative example of overall bloom patterns throughout the course of a given year. The dry season can be further divided into the hot and dry period from December to February and the cool and dry period from March to May (Olivares, Hakuta, Tabeta, 2009). In this study, the images chosen for the dry season are as follows: February 1989 (cool dry), January 1996 (cool dry), March 1996 (hot dry), and January 2001 (cool dry). The images acquired for the wet season include: July 2001, August 2003, October 2007, and July 2011.

Rainfall Data

Monthly precipitation data were obtained from Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) stations for each designated year (Siringan et al., 2008). This was done in order to observe how fluctuations in precipitation levels between the wet and dry season months have an impact on the initiation of P. bahamense blooms via enhanced nutrient loads from increased terrestrial runoff and discharge from rivers, specifically the Pampanga River, containing waste and fertilizers.

Remote Sensing of Algae Blooms

In order to observe the distribution, concentration, and extent of the plume, satellite images were first downloaded from the USGS Global Visualization Viewer (GLOVIS) from the Landsat 4-present collection for each designated month/year. Using ENVI 5.0 software, bands 2 and 5 were layer stacked in a 2-5-2 arrangement for each image. Band 2 represents the green value while band 5 represents the mid-infrared and should be low for water at all times. The bright magenta color, which indicates the presence of plumes, signifies high levels of green (or algae) and low levels of 5. The algae blooms in each layer-stacked satellite image not only reveal where the plumes are found in the highest concentrations in Manila Bay based on intensity of color, but they also reveal the extent of the bloom, represented by the bright magenta clouds throughout the study area.

Once each image has been layer stacked and examined, a specific cursor value will be designated to each of the 8 images, which signifies the band 2 value, or level of greenness. Band 2 reflectance should increase significantly in the presence of a bloom, while band 5 remains relatively the same. Higher band 2 values should be associated with images from the wet season when blooms have been observed to occur extensively throughout Manila Bay. The specific cursor value for each image will be taken from the same coordinates (14°46′53N and 120°36’58E) of the satellite image so as to reduce any bias. This location was chosen because it reflects nearshore algae concentrations in the north-northwest region of Manila Bay (Pampanga and Bulacan) that are significantly impacted by increased runoff (containing human/industrial waste) and sedimentation loads from the Pampanga River and its tributaries. Thus, although there are certainly other mechanisms that play a role in P. bahamense settlement, distribution, and transport, due to the limited amount of time for this study, observations from each image will specifically focus on the probable relationship between monthly precipitation levels and cursor values for each image, indicative of the levels of greenness, and thus algae, in the water column. It has been observed that high levels of precipitation (during the wet season) significantly enhance the reproduction of this dinoflagellate P. bahamense population due to enhanced levels of nutrients in major waterways entering the bay (Villanoy et al. 2006). Monthly precipitation data for each image and its designated month obtained from PAGASA stations will be plotted in a scatter plot using Excel against the cursor value for the corresponding image. The cursor value will represent the band 2 value, indicative of the presence of algae in the water column. A separate scatter plot for the wet and the dry season will be created in order to observe this relationship. Because there are a variety of other factors not accounted for in this study, we cannot deduce correlation between the two variables.

Sea Surface Temperature and Ocean Currents

Because the formation of algae blooms is also affected by Sea Surface Temperatures (SST) and ocean currents, in order to obtain information regarding SST anomalies and surface current patterns for this region, satellite images were acquired from the USGS Global Visualization Viewer (GLOVIS) from the Landsat 4-present collection for each designated month/year. Then, using ENVI5.0 software, thermal imagery using band 6 (thermal infrared) with a 60-meter spatial resolution enabled observations of SST. Due to the limited availability of cloud-free images, only one of the band 6 images, January 1996 from the dry season, provided a clear enough visual to make observations.