(Introduction, Sites, Methods, Results, Acknowledgement, Figures and Tables: The Rio Mameyes Watershed (Figure 1), Characteristics of sites for sampling periphytic diatoms (Table 1) , Percent density and time of the top ten species of diatoms for each site (Table 2), References)

INTRODUCTION

Surveys of the diatoms of Puerto Rico and other Caribbean islands have been conducted since the late 1800’s (Greville 1857, Janisch and Rabenhorst 1863, Grunow 1877, Cleve 1878, Hagelstein 1938, Bacon 1971, Navarro 1989). Although the emphasis of these surveys was typically on marine diatoms, some freshwater forms were included (Hagelstein 1938, Bourelly and Manguin 1952, Foerster 1971, Foged 1984, Podzorski 1985). However, until now no intensive study of freshwater diatom communities has been undertaken. As part of a larger water quality study, periphytic diatoms - diatoms that grow on solid substrata -were collected along the Río Mameyes in northeastern Puerto Rico (Fig 1). The collection period started in May 1998 and has continued for 31 months, including the passage of Hurricane Georges in September 1998. Collection and analysis of samples is ongoing. This is a description of some of the most abundant diatoms found in this survey.

SITES

The 5 collection sites were chosen to represent a range of riverine environments that commonly occur in Caribbean streams that drain humid life zones (Fig. 1). The highest elevation site, Bisley 3 is a closed canopy headwater drainage within the Luquillo Experimental Forest. This site drains mature tabonuco forest and is not subject to anthropogenic disturbances. The second site, Puente Roto, is an open canopy mid-elevation reach of the Río Mameyes at the edge of the Luquillo Experimental Forest. The site drains the entire elevation range of the LEF, including the four forest types that occur in the LEF. Although the drainage area of the site is relatively undisturbed forest within the Luquillo Experimental Forest, the reach is heavily used for swimming and picnicking, especially on weekends and during the summer months. The next site downstream, called the Intake, is located at a municipal water intake and pumping station and drains an area of forest and urban to suburban land use. This water intake consists of a series of risers, installed in the river bed, that withdraw river water without obstructing the flow or significantly changing channel or substratum morphology. The fourth site is located on the main channel where the river passes through a golf course and is referred to as Golf Course Channel. This reach is the last freshwater, non-tidal reach in the river. Immediately upstream of this sampling area is the last sampling spot, Urban Tributary, a small tributary that drains a residential and light commercial area before it crosses the golf course and joins the main stem of the Río Mameyes. Site characteristics are summarized in Table 1.

METHODS

Nine samples were collected from each of the 3 main channel sites, and 3 samples were taken from each of the small tributaries sites (B3 and Trib) on a monthly basis. Extra samples were collected on a weekly basis for 3 months after Hurricane Georges. A total of 795 samples have been collected on a total of 42 dates. Each sample consists of the material scraped from a 16 cm² area on the upper surface of a randomly collected rock. Samples have been or will be analyzed for the density, ash-free dry weight, area of coverage, and diversity.

The density of diatoms is based on the number of diatom cells per mm² of rock, and is reported as cells/mm². This is determined with a formula that includes the area scraped, the volume of suspension, and the volume of the aliquot examined (Standard Methods 1981). Samples were examined with a magnification of 200X, and the number of cells that were alive and dead upon collection was recorded. A total of 567 samples have been examined thus far for density.

Preparation of permanent slides containing cleaned diatoms is necessary for identification of individual diatoms. To accomplish this, a subsample of each sample was cleaned with acid and mounted on a microscope slide in Cargill Meltmount, a permanent mounting medium with a high refractive index. These were examined at 1000X to determine the number of species, the number of cells for each species, and the area of each cell in mm2. This information is used to determine diversity and an estimate of the area of substratum covered by diatoms. A total of 305 samples have been examined for diversity and area, and thus contain the species identifications used in this preliminary report.

RESULTS

The samples have so far yielded 379 species, of which 154 were unique to a particular sampling site. Some of these unique species were abundant at their respective sites, either once or on all dates. A few species were abundant at least occasionally at all sites. The ten most abundant and/or the most frequently occurring species of diatoms for each site are listed in Table 2. Some of these species overlap at different sites, and some are unique to that site. The 34 species described here were chosen from the top ten species at each site and were selected on the basis of their overall abundance and frequency of occurrence.

ACKNOWLEDGEMENTS:

This study was funded by the United States Forest Service, International Institute of Tropical Forestry as well as National Science Foundation grant DEB-9411973 to the Institute of Tropical Ecosystems Studies of the University of Puerto Rico as part of the Long Term Ecological Research (LTER) Program. Several individuals have provided special assistance to this project. John Thomlinson is greatly appreciated for advice and mapmaking skills. Andres Garcia, Samuel Moya, Carlos Estrada, and Gustavo Guzman provided invaluable logistic support. Amber Carver, María Rivera, Carrie DeJaco, and Mindy Jo Bogden assisted in scraping algae in the hot sun and deserve special thanks for their assistance and enthusiastic support.

I would also like to thank the reviewers for their comments: Dr. C. Reimer of the Philadelphia Academy of Sciences, Dr. E. Cox of the British Museum of Natural History, Dr. J. Stevensen of the University of Michigan, Dr. S. Spaulding of the California Academy of Science. I took their recommendations into deep consideration, even though some of them did not agree with each other. I am open to any further comments or suggestions and am willing to revise the nomenclature of any of the diatoms presented here. 

Figure 1. The Rio Mameyes watershed (inset). The diatom sampling sites are marked with green dots. The symbols for the sites are: B3 – Bisley 3; PR – Puente Roto; Int – Intake; TRIB – urban tributary; TC – the main channel in the golf course, just downstream from the tributary.

Table 1. Characteristics of sites for sampling periphytic diatoms in the Río Mameyes drainage, northeastern Puerto Rico.

Table 2. The top ten species of diatoms for each site, based on percent density and percent of time. The percent density is derived from the total number of cells per mm² of rock surface, and the percent time is based on how many times that species appeared. The absence of a species from a site is indicated with the letter A. (The Golf Course Channel and Puente Roto had more than 10 species occurring 100% of the time.)

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