Chemotaxomonic assessment of microalgal communities in north-central and western Florida Bay.

J. William Louda

Organic Geochemistry Group, Florida Atlantic University, Boca Raton, FL

This report relates to NOAA-SFERPM Question #3 (algal blooms) and explores pigment-based chemotaxonomy for the study of recurrent phytoplankton blooms in north central Florida Bay. Sampling was in the Snake-Rankin Bights through Whipray Basin and Flamingo to Sandy Key Basin / Cape Sable regions as these areas represent areas of cyanobacterial and diatom blooms, respectively. Study also included epiphyte productivity and community structure in north-central bay, specifically Snake and Whipray Basins.

The promise of chemotaxonomy derives from the fact that the various taxa of photosynthetic organisms evolved slightly different accessory pigments and dissection of natural pigment arrays allows one to discern the presence, absence and relative abundance of the contributory groups (cf. Millie et al., 1993).

Sample sites and sampling: 18 sites, covering Whipray Basin, Rankin Lake, Snake Bight, the Flamingo channel, Sandy Key Basin and nearshore / offshore Cape Sable were sampled monthly (09/00 – 09/02) for phytoplankton. Water samples for phytoplankton and epiphytes removed from surrogate (epiphytometer) or native seagrass (Thalassis testudinum) were filtered (Whatman GF/F), flash frozen in liquid nitrogen and later analyzed by HPLC-PDA as reported (Louda et al., 2002).

Epiphytes: We observed relatively straight forward growth rates which closely mimic natural seagrass epiphyte loads after 2-3 months, a reasonable lifespan for Thalassia shoots. The epiphytic communities are found to be vastly dominated (>90%, by CHLa) by diatoms, with minor abundances of dinoflagellates, cryptophytes and cyanobacteria. Total chlorophyll-a concentrations, a proxy for biomass, were found to range from 0.2 – 2.1 µg /cm2 (1 mo.) to 0.4 – 6.6 µg / cm2 (2 mos.). Growth curves (0, 1, 2 mos.) exhibited relatively smooth linear increases and the 2 month values usually mimicked values found on native Thalassia testudinum. The value of this method is 2 fold. First, time zero in growth profiles (productivity) is easily defined. Second, direct microscopic examination and epiphyte recovery are facile. Deployment of ‘epiphytometers’ in transects across and down suspected nutrient plumes is suggested here as an adaptive management monitoring tool.

Phytoplankton: Two areas of phytoplankton blooms are known in the Florida Bay area.


First, in the central and north-central bay (Whipray Basin and environs), a low productivity ( 1g/L as CHLa) of a DIAT>DINO>CRYPTO >CYANO community was found throughout much of the year. This was punctuated, as seen in Figure 1, at certain times (11/00, 10/01,12/01, 01/02) by large increases in standing crop (4 - 15g/L as CHLa) due almost entirely (>90%) to cyanobacteria. Tracking the increases in cyanobacteria spatially and temporally, it was found that the cyanobacterial bloom emerges from the mangrove transition zone and penetrates the bay. This shown by tracing salinity, total chlorophyll-a values, and chemotaxonomy, all of which change as one would expect for fresher cyanobacterial rich waters entering the saltier less productive waters of the north-central bay. That is, lower salinity (9-13 psu) highly productive ( >20-40 g CHLa / L) waters in and behind the mangrove fringe (e.g. the West Lake/ Long Lake/ Lungs / Garfield Bight region) enter the saltier bay and raise CHLa values in Snake Bight (S 25psu, 13g CHLa /L: 12/01) or Rankin Lake (S 30psu, 15g CHLa / L: 07/02). Similar influx has been found emanating from the Monroe Lake – Terrapin Bay region into extreme NE Whipray Basin (11/00, 10/01, 01/02, 07-08/02). This pattern was found to be

Figure 1: Total Chlorophyll-a (bottom) correlated to percent cyanobacteria (top) in 4 areas of north-central Florida Bay over a 2 year span.

repeated during several cyanobacterial influx episodes. Going on these and other observations, we propose that the cyanobacterial blooms of north-central Florida Bay are natural cyclic events that may gain severity in the face of additional nutrients in the bay. That is, rather than being a precursor to seagrass die-offs, we propose that the severe algal blooms which occurred around the times of the die-offs followed the initial release of nutrients and in so doing then added an extra stressor level for the perpetuation of the die-offs. This, I feel, is a small but important difference in the presently held dieoff scenario (bloom before dieoff initiation).

The second bloom dynamic occurs in the western bay where annual diatom ‘blooms’ occur. Chemotaxonomy was able to reveal underlying separate cycles of chlorophyte and cryptophyte populations. These patterns are still being analyzed but, for now, it can be said that standing crops are moderate to high (2-7 CHLa / L) through out much of the year, with highs being in June, September and November-December of 2001. These were dominated by diatoms (65-85%) and lesser amounts (10-20%) of cryptophytes. Apparent increases (up to 55%), or concentration by loss of other taxa, of chlorophytes during February 2001 and January–February 2002, were noted. During the Summer months, CHLa was the lowest and cyanobacterial relative abundance was the highest (8-33%), due to a lack of diatom presence rather than an increase in cyanobacteria per se. Dinoflagellates, as signaled only by peridinin (gyroxanthin, indicator of Karenia brevis was not found) plus chlorophyll-c, never occurred at levels comprising more than about 10% of the total CHLa pool.

Acknowledgements: These studies were funded by NOAA-SFERPM through the National Marine Fisheries Division. Ms. Pannee Monghkonsri is thanked for her able assistance in HPLC-PDA analyses.

References:

Louda, J. W., Liu, L., and Baker, E. W. (2002) Senescence- and death-related

alteration of chlorophylls and carotenoids in marine phytoplankton. Org. Geochem.33, 1635 – 1653.

Millie D. F., Paerl H. W., and Hurley J. P. (1993) Microalgal pigment

assessments using high-performance liquid chromatography: A Synopsis of organismal and ecological applications. Can J. Fish. Aquat. Sci.50, 2513 - 2527.

J. William Louda, Organic Geochemistry Group, Department of Chemistry and Biochemistry, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 3431. Phone 561-297-3309, FAX 561-297-2759, .Question #3.