## FINAL REPORT to Lee County and the City of Bonita Sp rings 

# Drift Rhodophyte Blooms Emerge in Lee County, FL: Evidence of Escalating Coastal Eutrophication

by Brian E. La pointe and Bradley J. Bedford

Harbor Bra n ch Oceanographic Ins t itution, Inc. Division of Marine Science 5600 US 1 North Ft. Pierce, FL 34946



### March, 2006

Key Words: Nitrogen, phosphorus , macroal gae, eutrophication, south w est Florida Running Head: Macroalgal blooms on Florida’s southw est coast Corresponding author: 772-465-24 00 ext 276; 772-468-07 57 (fax); la pointe@hboi.edu1

Executive S u mmary Macroalgal bloom s have increased globally in recent decad es as a resu lt of increased nutrient enrichm e nt and eutrophi cation of coastal waters. In Lee County, FL, this problem reached a critical stage in 2003 and 2004 when massive d r ift rhodophyte b l oom s washed ashore between San i bel Island and Bonita S p rings, m a king beaches unsuitab l e for recreation and requiring an expensive removal program . To be tter understand the ecology of these bloo m s , water quality and m acroalgae sam p ling was conduc ted in early August 2004 prior to hurricane Charley and again in late October following se veral m onths of heavy discharges from the Caloosahatchee River. During both sam p lings, water and m acroalgae w e re collected along a gradient extending from the Caloosahatchee River to na tura l and artif i ci al reefs som e 26 km fro m shore. Concentrations of dissolved nutrient pools (DIN = NH 4 + + NO 3 − + NO 2 − , TDN, T D P) were generally high throughout the study area with signifi cantly enriched (~ 10-fol d) concentrations in the Caloosahatchee Riv e r. The m ean DIN concentr ations increased from the Ortona L o ck (< 18 μM) to the F r anklin Lock (23-28 μ M ) in the Caloosahatchee River during both samplings, indica ting s i gnif i cant en r i chm e nt within the basin

. The m ean concentratio ns of NH 4 + a nd SRP at the coas tal reefs increas e d six-fold ( ≤ 0.20 to 1.31 μM) and three-fold (0. 30 to 0.92 μM), respectively, between August and October following increased freshwater discharges. The m ean C:N ratios of m acroalgae at the reefs were relatively low and sim ilar betw een August and October (13. 9 vs. 13.5). The m ean C:P and N: P ratios were also low and indicative of Nlim itation, and decreased signifi cantly (386 to 242 and 27.4 to 17.5, respectively) between August and October. The δ 15 N values of m acroalgae increased from the Ortona Lock (+ 8-9 ‰) to the Franklin Lock (+ 12-15 ‰) during both sa mplings and were within the rang e re ported f o r2 sewage nitrogen; these values decreased with increasing distance from shore to ~ + 3.0 ‰ at the most offshore reef site. Macroalgae ( Gracilaria , Hypnea, Botryocladia, Eucheuma, Sargassum ) collected in July 2004 from Bonita Spri ngs Beach and Sanibel Island had mean δ 15 N values > + 6.0 ‰, similar to values measured in macroalgae from shallow inshore reefs and within the range of sewage nitrogen. However, mean δ 15 N values of coastal macroalgae decreased from August (+ 5.84 ‰) to October (+ 3.89 ‰) with increase d discharges from the Caloosahatchee River, suggesting an increased contribu tion of N from rainfall and ag ricultural sources with lower δ 15 N values (< + 3 ‰) in the wet season. These results suggest that improved management of freshwater releases from Lake Okeechobee, comb ined with nutrient removal strategies for sewage within the Caloosahatchee River drainage basin, could help mitigate the development of these macroalgal HABs in the future.3

1. Introduction Point-source and non-point source enrichment of nitrogen (N) and phosphorus (P) is now recognized as the most serious pollution problem facing coastal waters worldwide (GESAMP, 1990; NRC, 2000; Howarth et al., 2000). In th e United States, scientists and policymakers recognize that a wide range of problems plaguing nearshore waters can be tied, directly or indirectly, to nutrient over-enr ichment (Pew Oceans Commission, 2003; U.S. Commission on Ocean Policy, 2004). Nutrient pollution is the co mmon thread that links an array of problems including eutrophication, harmful algal blooms ( HABs), bio-invasions, fish kills, shellfish poisonings, loss of seagrass and kelp beds, coral reef die-off, emerging marine diseases, and marine mammal and seabird deaths (Howarth et al., 2000; Lapointe et al ., 2004; Lapointe et al., 2005). The development of macroalgal HABs is a pr edictable ecological response to increased nutrient loading in shallow bays, estuaries, and coastal waters (Mor and and Briand, 1996; Lapointe et al., 1994; Valiela et al., 1997). Unlike toxic phytopl ankton HABs such as red tides, macroalgal HABs lack direct chemical toxicity but typically have a broa der range of ecological impacts. The effects of macroalgal blooms ar e largely indirect, multi-faceted, and of longer duration than toxic phytoplankton HABs. Exce ssive biomass of macroalgae can cause hypoxia, anoxia, and die-off of seagrasse s and other benthic biota (Lapoi nte et al., 1994; Valiela et al., 1997), thereby reducing habitat for desirable a nd economically important fisheries. In oligotrophic subtropical and trop ical waters, nutrient- enriched macroalgal blooms can alter food web dynamics by increasing the abundance of gr azers in seagrass (McGlathery, 1995) and coral reef ecosystems (Lapointe and Thacker, 2002). Increasingly, macroalgal blooms foul beaches4 and shorelines important to local tourist econom ies and require ever more expensive biomass removal programs (Morand and Briand, 1996; Lapointe and Thacker, 2002). Land-based nutrient discharges to bays and co astal waters along southwest Florida have long been linked to the development of macr oalgae and phytoplankton blooms. Sewage-driven eutrophication in Tampa Bay during the 1960’s, 1970’s, and 1980’s led to drift macroalgal blooms that included the rhodophyte Gracilaria and chlorophyte Ulva (Humm, 1973; Guist and Humm, 1976). In Hillsboro Bay, a subdivision of Tampa Bay, drift macroalgal HABs with biomass levels > 600 g dry wt/m 2 developed in the early 1980’ s, which included the rhodophytes Gracilaria, Spyridia, Hypnea, and Agardhiella , and the chlorophytes Ulva and Caulerpa (Avery, 1997). Following considerable seagrass loss in Hillsboro Bay by the late 1970’s, N removal from the local wastewater treatment plant was initiated in 1979, and by 1994 drift macroalgae had decreased by > 90% while seagrass cover incr eased from 0.2 ha in 1986 to over 28 ha in 1995 (Avery, 1997). In coastal waters of s outhwest Florida, Ketchum and Keen (1947) correlated red tide blooms off Sarasota, FL, with unusually high P concentrations in the water column and suggested “the excessive nutrien t content may be the result of terrigenous contamination or fertilization of the waters .” Slobodkin (1953) reported that the red tide outbreaks off southwest Florida may be intiated by the development of a stratified water mass characterized by reduced salinity and elevated nutrients resulting from discharges of the combined Charlotte Harbor – Caloos ahatchee River drainage basins. Recent increases in nutrient loading associ ated with expanding urbanization of the watershed and discharges from the Peace and Cal oosahatchee rivers could be linked to emerging blooms of benthic macroalgae in estuaries and co astal waters of Lee County, FL (Fig. 1). McPherson and Miller (1990) noted that projected increases in nitrogen loadings from the Peace5

River basin would favor undesi rable increases in phytoplankt on and benthic algae in the Charlotte Harbor es tuarine system . An analysis of m onitoring data for the Caloosahatchee River indica ted th at wate r qua lity in the do wnstream estuary ch ang e s as a f unction of total discharg e and water so urce (river b a sin, Lake O k eechobee ; Doering and Cha m berlain, 1999). While these

assessm ents were lim ited to the estuarine regions of the Peace and Caloos ahatchee riv e rs, the

com b ined fl ows and nutrien t loads associated with thes e discharges hav e the poten tial to im pact coastal waters for considerable distances dist ances fro m shore (> 50 km ; Yang et al., 1999). Accordingly, increased land-based nutrient pollu tion cou l d b e inf l uencin g coasta l wa ters of f southwest Florida and m a y help exp l ain the unp recedented accum u lation of drift rhodophytes that fouled coastal beach es between Sanibel Isla nd and Bonita Springs in 2003/2004 (Fig 2 A, B, E). The excessive biomass of these rhodophytes caused odor problem s and greatly dim i nished the use of th e beaches by tourists. Co ncerns of th e local governm e nt s of Lee County and the City of Bonita Springs pro m pted the present inve stiga tion in order to d e te rm ine if these

m acroalgal HABs could be linked to increasing land-based nutrient pollution as in Tampa Bay and other parts of the world (Morand and Br iand, 1996; Valiela et al., 1997; NRC, 200 0). Several approaches can b e used to as s e ss the spatial extent and degree of land-based nutrient enrichm e nt in coastal waters of Lee Co unty. One traditional m e thod involves

m easurem ents of salin ity and concentrations of dissolved inorganic nitrogen (DIN = ) and soluble reactive phosphorus (S RP ) in water sam p les along inshore to offshore gradients. If nutrient concentrations of lower-salinity inshore waters are h i gh er than that of highe r-sa lin ity of f

s hore wate rs , then a land-based source of nutrients is indicated (Ketchum , 1 967). A m o re specific approach involv es the m e asurem ent of stable nitrogen isotope ratios in m acroalg ae that can be us ed to “fingerp rint” the sou r ce of N when the vario u s N sources NH 4 + + NO 3 − + NO 2 −6 are known (Heaton, 1986; Owens, 1987). Attached m acroalgae have a distinct advantage over free-floating phytoplank t on as nutrient indicato r s b ecause they provide a long-term integration of the aqueous N signal for a particular locati on (Lapointe et al., 2004). Enrichm e nt of 

### δ 15 N

 in aquatic system s can result from N transform a tions that o ccur prior to, dur ing, or f o llo wing the

trea tm ent and discharg e of sewage. Volatiliz ation of a m m oni a and isotopic fractionation by

m i crobes during nitrification and den itrification p r oduce resid u al DIN with elevated 

### δ 15 N values of + 6 ‰ to + 22 ‰ (Heaton, 1986; Lindau et al. , 1989). This range includes secondarily treated discharges from sewage outfalls (Hoch et al., 1995; Table 1) as well as shallow (< 10 m ) groundwaters contam inated by septic tanks in south Florida (L apointe and Krupa, 1995 a, b; Table 1). In com p arison, N derived from rainfall, fertilizers and organic peat associated with

storm w ater runoff from agricu ltural areas hav e 

### δ 15 N values ranging from -3 ‰ to + 3 ‰ (Heaton, 1986; Paerl and Fogel, 1994; Table 1) a nd can therefore be effectively discrim i nated fro m the higher sewage N signature. We hypothesized that, if land-based anthropoge nic N sources such as sew a ge was the prim ary DIN source supporting m acroalgal HABs in Lee County’s coastal waters, then the highest 

### δ 15 N values would occur in m acroalgae from the Caloosahatch ee River, beach es, and shallow coa s tal reef s m o st inf l uenc e d by land-ba se d discharges. Macroalg ae tha t re ly on natura l nitrogen fixation have low 

### δ 15 N values of ~ 0 ‰ (France et al ., 1998; Table 1) in contrast to those using sewage N, which b eco m e increasin gly enriched in 

### δ 15 N with increasing sewage N contributions over a range fro m + 3 ‰ to + 16 ‰ (Lapointe, 1997; Costanzo et al., 2001). Globally, m a ny case studies have used 

### δ 15 N as a tool to discrim i nate between natural and anthropogenic N sources supporting m acroalgal gr owth (Lapointe, 1997; France et al. , 1998; McClelland and Valiela, 1998; Costanzo et al ., 2 001; W a yland and Hobson, 2001; Um ezawa et7
al., 2002; G a rtner et al., 2002; Ba rile, 2004; Savage and Elm g ren, 2004; L a pointe et al., 2004). Several studies have su c cessf ully u t ilized 

### δ 15 N values in m acroalgae and reef corals to assess the spatial ex ten t of land-based N enrich m e nt along gradien t s in to the coastal ocean, on scales from several kilo m e ters (Umezawa et al., 2002; Lapointe et al., 2004; Lapoint e et al., 2005b), to nearly forty kilom e ters across the Great Barrie r Reef lagoon (Samm a rco et al., 1999). We also pre d icted that “ w et versus d r y” season ality cou l d sig n ificantly affect the deg r ee and relative im portance of various sources of la nd-based N enrichm e nt. In the Florida Keys, local N loadings from se wage were relatively constant com p ared to the large non-point source agricu ltu ral N loads tha t were tr ansp orted into co astal waters during wet y ears when large water releases fro m the Everg l ades occurred (Lapoin t e et al., 2004 ). W e initiated our study in Lee County in early August 2004, prior to landfall of three hurricanes that struck Florida in August and September, 2004. Because historically sign ificant am ounts of rainfall resu lted fro m the overlapping paths of hurricanes Charley, Frances , and Jeanne in the Kissim m ee River drainage basin north of Lake Okeechobee (South Florida Wa ter Mana gem e nt Distric t , ra inf a ll data), we had an opportunity to test this hypothesi s by re-sampling in late October of 2004.

2. Materials and methods
2.1. Sa m p le collection and analysis
Sam p les of the water co lum n and attached m acroalgae and / or seagras s es were collected August 8-10 (dry season) and October 28-29 (wet season), 2004, along an onshore to offshore gradient extending from the Caloosahatchee River into coastal waters of Lee County, FL (Fig. 1). Nine fixed stations sam p led in both Augus t and October included the Ortona and Franklin locks on th e Caloosahatchee River; s eagrass b e ds in San Carlos Bay and S. Charlotte Harbor; a8
shallow, natural, nearshore reef o ff Boca Grande, known locally as the 17 th Stree t Reef (4 m depth); the Belton-Johnson Reef (10 m ) , an artifi cial reef; Blanda’s Reef (14 m ) , an artif ic ial reef; ARC Reef (19 m , ), an artificial reef; a nd North Deep Ledge (20 m ) , a natural ledge and farthest s t ation from shore (26 km ; Fig. 1). In A ugust, two additio n a l s t ations (Peace and
Im perial riv e rs) were sa mpled for water colum n nutrients, an d m acroalgal tis sue was collected
for δ 15 N analysis from beaches at Bonita Springs, Fort Myers, Sanibel, an d Captiva. In addition,
dried rhodo phytes co llected from stranded m a terial on Bonita Beach in late Ju ly, 200 4 (Table 2 ; Fig. 2B) were analyzed for δ 15 N. At each of 11 sites in August and 9 sites in Octob e r, rep licate sam p les (n = 2) of nearbottom water were co llected in to clean, 250 m l HDPE bottles and held on ice in a cooler un til processing. In the lab, 100 m l sam p l e ali quots w e re filtered via syringe through 0.45 μm Whatm a n GF/F f ilters in to cle a n, 15 0 m l HDPE bottles and f r ozen. The sam p les were subsequently analyzed f o r NH -N, 4 + NO 3 − + NO 2 − -N an d PO 4 3

− -P (SRP) at the Nutrien t Analytical
Services L a boratory, Ch esapeake Biological Lab o ra tory, Cen t er f o r Envir o nm ental an d Estuar ine Studies, University of Maryland, Solo m ons, MD (NASL). A Technicon Auto-Analy zer I I was used f o r determ ination o f nitrate ( NO 3 − ) and soluble reactive phosphate (SRP), and a Tech nicon
TRAACS 8 00 was used for analysis of a m m oniu m ( NH 4 + ) and nitr ite ( NO ). Detec tion lim its were 0.20 μM for , 0.01 μM for NO 2 −
NH 4 + 3 − + NO 2 − , 0.01 μM for NO 2 − , and 0.02 μM for SRP (D’Elia et al., 1997). We used the f -rati o ( / ( NO NO 3 - 3 - + NH 4 + )) to gauge th e relativ e im portanc e of versus as a DIN source (McCarthy et al. 1975 ; Harrison et al., 1987) to m acroalgae at the study sites. Sam p les collected in October were also analyzed for total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) at NAS L, usin g a Technicon Auto-Analyzer II with detection lim its of 1.43 μM for TDN, and 0.03μ M for TDP (D’Elia et al., 1997), and were used NO 3 - NH 4 +9 to calculate dissolved organic nitrogen (DON = TDN – DIN) a nd dissolved organic phosphorus (DOP = TDP – SRP).
Sa m p les of m acroalgae and/or seagrasses were collected at the nine stations in August and October by SCUBA or snorkelin g (Table 2). Rhodophytes were co llected at the five coastal reef sites (1 7 th St. Reef, Culvert Reef, Blanda’s Reef , ARC Reef, and N. Deep Ledge); th e
seagras s Thalassia testudinum was collected at S. Charlotte Ha rbor and San Carlos Bay; and the chlorophyte Cladophora sp. and the cyanophyte L y ngbya sp. were collected at Orton a and Franklin loc k s (Table 2 )

. Field sam p les were s t or ed in plastic, zipper-lock, storage b a g s and held on ice in a c ooler un til p r ocess i ng. I n the lab, co mposite sam p les ( t halli f r om 5-8 different p l ants of each species) of m acroalgae were sorted, clean ed of visible epiphytes and sedim e nts, identified (Dawes, 1974; Littler and Littler, 2000), and rinsed briefl y (3-5 sec) in deionized water

to rem ove salt and debris. The cleaned, com posite sam p les were dried in a Fisher Scien tif ic
Isotem pTM oven at 60  ̊ C for 48 h and then ground to a fine po wder using a m o rtar and pestle.
Sam p les of the dried, po wdered m a croalgae were stored in p l astic screwtop vials and placed in a dessica tor u n til analys is f o r C:N:P contents (m ol ar ratios) at N A SL. Percent C and N were

m easured on an Exeter A n alytical, Inc (EAI) CE-440 Elem ental Analyzer and percent P was

m easured fo llowing the m e thodology of Asplia et. al. (1976) using a Techni con Autoanalyzer II with a IBM com p atible Labtronics Inc. DP500 so ftware data collection system (D’Elia et al., 1997). All sam p les were also analyzed for δ 15 N (n = 2 analy t ical replicates per sam p le) with a
Carlo-Erba N/A 1500 Elem ental Analyzer and a VG Iso m ass m a ss spectro m e ter using Du m a s

com bustion, at Isotope S e rvices, Inc., Los Alam os , NM. The standard used for stable nitrogen isotope analysis was N 2 in air. δ 15 N values (‰) were calculated using ; where R = R Sample /R Standard 

# ( )

− 1 

# [ *1 0 3 

# ] 15 N/ 14 N.10

2.2. Statistical analysis Data were tested for normality using the Shapiro-Wilk test (W statistic), and for homoscedasticity using Levene’s test of equali ty of error variances. Normally distributed datasets were compared using the Generalized Linear Model (GLM, Type III sum of squares) procedure in SPSS 11.0 for Mac. Data not normally distributed were compared using either the Kruskal-Wallis H test (three or more groups), or the Mann-Whitney U test (two groups). Post hoc comparisons were made using Tukey’s HSD test. Sites where water samples were collected in August only (Imperial and Peace rivers) were not included in overall (August and October) water column nutrient statistics. However, data analyzed to compare seasonal differences (A ugust vs. October) included all sites sampled. In order to assess water column ch arcteristics in the vicinity of the coastal macroalgal blooms, a subset of coastal water samples (San Carlos Bay, S. Charlotte Harbor, 17 th St. Reef, BeltonJohnson Reef, Blanda’s Reef, AR C Reef, and N. Deep Ledge) fr om August and October were tested for significant effects of season. For all analyses, differences were considered significant at p ≤ 0.05.

3. Results
3.1. Taxonomic Composition of the Macroalgal Blooms The drift macroalgal community that washed ashore on Bonita Springs beach in July and August 2004 was dominated by rhodophytes (Table 2). Species identified from the beach collections included Botryocladia occidentalis, Eucheuma isiforme var. denudatum, Gracilaria cervicornis, Gracilaria tikvahi ae, Agardhiella subulata, and Hypnea musciformis. In August,11 the pelagic phaeophyte Sargassum fluitans was also collected from Ft. Myers Beach, Sanibel Island, and Captiva Island. The rhodophytes from the beach strandings were found to be abundant o n the natu ral and artificial reefs in coastal waters off Lee C ounty (Table 2). In both August and October, Botryoclad ia occiden t alis was collected from all five reef sites. Other rhodophytes collected
f r om the ree f s included Agardhiella subulata, Eucheuma isiforme var. denudatum, Gracilaria cervicornis, Gracilaria tikv ahiae, Hypnea musciformis, and Rhodymenia divaricata.
3.2. Dissolved n u trient conc entra tions, f

- r atios, DIN/SRP ratios, and salinity
Overall 

### NH concentrations varied signif i cantly with location (F = 89.882, p < 0.001, GLM), season (p < 0.001, Mann-W h itney) and th e location-season interaction (F = 50. 164, p < 0.001, GLM), averaging 1.74 ± 3.66 μM (n = 22) in August and 2.48 ± 2.59 μM (n = 18) in October. Concentrations were significantly high er in the rivers, with m a xim u m values of 12.70 μM at the Imperial River (August) and 8.30 μM at Franklin Lock (October). In A ugust, values
≤ 0.21 μM (detection lim it) were measured at all bay and co astal reef sites whereas in October values were > 0.55 μM at all sites (F ig. 3) . At the five coastal reef sites, mean
concentratio ns increased from ≤ 0.21 μM (n = 14) in August to 1.31 ± 1.08 μM (n = 14) in October (Table 3) with a highly significant e ffect of season (F = 715.765, p < 0.001, GLM). 4 +



### NH 4 +

concentrations varied significantly w ith location (F = 1644.205, p < 0.001, GLM)
and location-season interaction (F = 354.582, p < 0.001, GLM), averaging 5.62 ± 9.29 μM (n = 22) in August and 3.92 ± 5.70 μM (n = 18) in O c t ober. High concentrations occurred in the river s , with m a xim u m values a t the Franklin Lock in both A ugust (26.15 μM ) and October (14.35 μM ); m i ni m u m values occurred at the ba y and coastal sites, with m i ni m u ms o f 0.49 μM at S. Charlotte Harbor and Belton-Jo hnson Reef (August) and 0.27 μM at 17 NO 3 −

th St. Reef12
(October). At the coas ta l re ef sites, the m ean NO 3 − concentrations were sim ilar in August (0.91 ± 0.72 μM, n = 14) and October (0.97 ± 0.69 μM, n = 14; Table 3). Overall, DIN concentrations varied signifi cantly with lo cation (F = 169.055, p < 0.001, GLM), season (p = 0.034, Mann-W h itney), and location-season interaction (F = 133.093, p < 0.001, GLM), averaging 7.36 ± 10.61 μM (n = 22 ) in August and decreasing to 6.40 ± 8.09 μM (n = 18) in October. The highest DIN concentra tions oc curr ed in the riv e rs, with the m a xim u m value at the Franklin Lock in August (27.70 μM ) and October (22.65 μM); the lowest levels occurred at the bay and coastal reef sites, w ith m i nim u m values of 0.69 μM at S. Charlotte Harbor and Belton-Johnson Reef in August and 0.83 μM at 17 th St. Reef in October (Fig. 3). On the coastal reefs, m ean DIN con centrations increased significantly (F = 66. 322, p < 0.001, GLM) fro m August (1.11 ± 0.72 μM, n = 14) to Oc tober (2.29 ± 1.57 μM, n = 14; Table 3). Overall, the f -ratio varied with location (F = 11.822, p < 0.001, GLM), season (p < 0. 001,
Mann-W h itney), and location-season interactio n (F = 7.702, p < 0.001, GLM) with a higher

m ean value in August (0. 75 ± 0.19, n = 22) com p ared to October (0.48 ± 0. 17, n = 18). In August, the f -ratios we re statistica lly sim ilar am ong s ites (m axim um of 0.94 at Frank l in Lock) except the Imperial Riv e r (p ≤ 0.015, THSD) where the m i n i m u m (0.27) occurred. In October, the m a xi m u m values occurred in the rivers (Ort ona, 0.75) and the m i ni mu m at the offshore ARC Reef (0.32, Fig. 3). The f -ratios for the coastal reef sites aver aged 0.77 ± 0.11 (n = 14) in August and decreased significantly (F = 168.32, p = 0. 006, GLM) to 0.41 ± 0.14 (n = 14) in October (Table 3). SRP concentrations varied with location (F = 195.032, p < 0.001, GLM), season (p = 0.011, Mann-W h itney), and the location-season interaction (F = 119.383, p <0.001, GLM), averaging 2. 01 ± 4.96 μM (n = 22) in August and 1.04 ± 1.08 μM (n = 18) in October. In13 August, the maximum concentrations occurred in the Peace River (16.80 μM), which was significantly (p < 0.001, THSD) hi gher than all other sites, an d the minimum concentrations (0.14 μM) occurred at San Carlos Bay (Fig. 4). In October, the maximum SRP concentrations (3.74 μM) occurred at S. Charlotte Harbor downstream of the Peace River (which was not sampled) with lower values at the coastal reefs (minimum 0.19 μM at N. Deep Ledge) (Fig. 4). Mean SRP concentrations at th e coastal reefs were significantly (F = 289.115, p < 0.001, GLM) lower in August (0.30 ± 0.18 μM, n = 14) than in October (0.92 ± 1.20 μM, n = 14; Table 3). The DIN/SRP ratio varied significantly w ith location (F = 25.510, p < 0.001, GLM), averaging 11.25 ± 19.51 (n = 22) in August and 6.92 ± 4.95 (n = 18) in October. The highest DIN/SRP ratio in August was in the Imperial Ri ver (68.30) compared to the Franklin Lock (14.86) in October. The lowest DIN/SRP ra tios in August (1.32) and October (0.29) both occurred at S. Charlotte Harbor (Fig. 4). At the coastal reef sites, the DIN/SRP ratios were similar in August (4.77 ± 3.10, n = 14) a nd October (4.88 ± 3.41, n = 14; Table 3). Total dissolved N and P were measured only during the October sampling, when both TDN (F = 430.949, p < 0.001, GLM) and TDP (F = 437.560, p < 0.001, GLM) varied with location. TDN averaged 35.8 ± 30.8 μM and concentrations in the Caloosahatchee River (70.9 μM at Franklin Lock) were significantly (p < 0. 001, THSD) higher than all other sites; the bays were significantly (p ≤ 0.016, THSD) higher than coastal re ef sites, and the minimum value (11.07 μM) occurred at N. Deep Ledge (F ig. 5). TDP averaged 1.57 ± 1.42 μM and concentrations were significantly elevated in the rivers and S. Charlotte Harbor (p < 0.001, THSD) compared to all other site s, with the highest value at S. Charlotte Harbor (5.16 μM) and the lowest at N. Deep Ledge (0.37 μM, Fig. 5).14 In October, DON (F = 255.172, p < 0.001, GLM) and DOP (F = 30.976, p < 0.001, GLM) varied significantly with location. DON dominated the TDN pool (averaged 29.4 ± 23.1 μM) with the highest concentrations in the rive rs (70.92 μM maximum at Franklin Lock), which were significantly (p < 0.001, THSD ) higher than all other sites. Lower values occurred in the bays, which were significantly (p < 0.001, THSD) higher than the coasta l reef site s where the minimum of 9.69 μM occurred at N. Deep Ledge (Fig. 5). In contrast, DOP comprised a relatively minor portion of the TDP pool, av eraging 0.53 ± 0.36 μM. The highest DOP concentrations were in S. Charlotte Harbor (1 .42 μM), which was was th e only site significantly (p < 0.001, THSD) different than th e other sites; the lowest value (0.18 μM) occurred at N. Deep Ledge (Fig. 5). Salinities ranged from 0.3 ‰ at the Ort ona and Franklin locks in both August and October to 37.3 ‰ offshore at N. Deep Ledge and 37.0 ‰ at ARC Reef in August. During both samplings, a lower salinity surface layer (buoyant plume) occurred at our most offshore stations, especially ARC Reef. In Augus t, the surface layer had a salinity of 32 ‰ compared to a nearbottom salinity of 37 ‰. Stratification was al so observed in October at ARC Reef, where a lower-salinity (34.8 ‰), highly colored surface la yer extended to a depth of ~ 12 m over the clearer, higher salinity (36.0 ‰) bottom layer (12-19 m depth).

3.3. C:N:P analysis of macroalgae Overall, there were no significant effects of location or season on C:N ratios of macroalgae and seagrasses, which averaged 13.2 ± 3.0 (n = 20) in August and 12.9 ± 3.5 (n = 15) in October. The lowest C:N ratios occurred at Franklin Lock in August (9.0) and October (8.7);15 the highest ratios were recorded at the coastal reef sites N. Deep Ledge in August (36.6) and Belton-Johnson Reef in October (15.3) (Fig. 6). C:P ratios varied significantly with season (F = 4.268, p = 0.053, GLM), averaging 343 ± 197 (n = 20) in August and 236 ± 132 (n = 15) in October. The lowest C:P ratios were 170 at Franklin Lock in August and 139 at N. Deep Ledge in October when a buoyant darkwater surface layer was evident 26 km from the coast (F ig. 6). At the coastal reef sites, seasonal differences were significant (F = 6.141, p = 0. 024, GLM), with the August mean (386 ± 198, n = 16) higher than October (17.5 ± 6.7, n = 13) (Table 4). There was significant (F = 4.868, p = 0.040, GLM) seasonal variation in N:P ratios, with a higher mean in August (25.4 ± 11.0, n = 20) than October (18.1 ± 6.4, n = 15). The lowest N:P ratios occurred at Ortona Lock (15.8 in August) and S. Charlotte Harbor (12.8 in October); the highest ratios were at N. Deep Ledge (42.4, August) and Belton-Johnson Reef (24.3, October) (Fig. 6). On the coasta l reefs, N:P ratios decreased signifi cantly (F = 8.979, p = 0.008, GLM), from 27.4 ± 11.4 (n = 16) in August, to 17.5 ± 6.7 (n = 13) in October (Table 4).

3.4. Stable nitrogen isotopes in macroalgae Overall, δ 15 N values in macroalgae and seagrasses varied significantly with location (F = 50.118, p < 0.001, GLM), season (F = 12.746, p = 0.001, GLM) and the location-season interaction (F = 5.280, p < 0.001, GLM), with a higher mean in August (+ 6.2 ± 2.3 ‰, n = 46) than October (+ 4.7 ± 3.1 ‰, n = 34) and valu es generally decreasing with increasing distance from shore. In both August and October, δ 15 N values at Franklin Lock were significantly (p ≤ 0.001, THSD) higher than all other stations except Ortona Lock, with values of + 11.8 ‰ and + 15.6 ‰, respectively (Fig. 7A). Blanda’s Reef had the lowest values: + 3.2 ‰ in August and +16
3.0 ‰ in October (Fig. 7A). At the coastal reef sites δ 15 N in macroalgae decreased significantly, from + 5.84 ± 1.37 ‰ (n = 32) in August to + 3.89 ± 0.96 ‰ (n = 26) in October (Table 4).
The δ 15 N values of macroalgae (phaeophytes a nd rhodophytes, Fig. 7B) collected from Lee County beaches in August 2004 did not vary si gnificantly with location (p = 0.264, KruskalWallis) and values ranged from a high of + 7.1 ‰ at Fort Myers Beach to a low of + 5.7 ‰ at Bonita Springs Beach, with an overall mean of + 6.1 ± 1.3 ‰ (n = 14). Samples of the rhodophyte Hypnea musciformis (Fig. 7B) collected from drift accumulations on Bonita Springs Beach were enriched (+ 8.0 ± 0.55) compared to samples of the same species collected at 17 th St. Reef (+ 7.19 ± 0.15) and N. Deep Ledge (+ 5.12 ± 0.08).

4. Discussion Results of this study support the hypothesis that the drift rhodophyte blooms that have developed in Lee County’s coastal waters in re cent years are linked to increasing land-based nutrient enrichment, especially N. Although similar drift macroalgal blooms have developed in shallow seagrass meadows in Tampa Bay (Humm, 1973; Guist and Humm, 1976 ; Avery, 1997), the Indian River Lagoon (Virnstein and Carbona ra, 1985), coral reefs off southeast Florida (Lapointe et al. 2005 a,b), and the Florida Keys (Lapointe et al., 1994; Lapointe et al., 2004), the blooms of these particular rhodophytes in Lee Co unty are the first to be reported for shallow coastal waters along barr ier beaches of southwest Florida (F ig. 2 E). Our results documented that significant N and P enrichment extended at least 26 km from shore in fall of 2004, supporting previous suggestions that river discharges can cause larg e-scale enrichment of coastal waters off southwest Florida (Slobodkin, 1953; Yang et al., 1999). Considering that these macroalgal HAB phenomena are symptomatic of cultural eutrophication in shallow, coastal17 waters of south Florida (Humm, 1973; Lapoint e and Ryther, 1979), the la rge scale and economic impact of these blooms demand serious concern by water and resource managers for protection of this popular tour ist destination.

4.1 Taxonomic composition and ecology of blooms The drift rhodophyte community that washed ashore on Bonita Springs Beach in July 2004, prior to hurricane Charley, was dominated by the genera Gracilara, Hypnea , and Agardhiella . Humm (1973) noted that rhodophytes dominated (51%) the benthic macroalgal communities in the eastern Gulf of Mexico, compared chlorophytes (31%) and phaeophytes (18%). We found a diverse rhodophyte community to be common on natural and artificial reefs throughout the study area prior to hurricane Charley, indicating th at “seed” populations for these blooms are present in local waters. The abundance of macroalgae in the eastern Gulf of Mexico is limited by the scarcity of suitable rocky substrata (Humm, 1973). Most of the intertidal zone and coastal waters are unconsolidated sediments that will not support th e establishment of most macroalgae. Where limestone reef outcrops or othe r suitable benthic substrata are available, the rhodophytes begin growing as attached plants and can become th e dominant biotic cover of inshore reefs and suitable soft bottom communities when nutrient ava ilability is adequate (see Fig. 2C). Under nutrient enriched conditions, some of these rhodo phytes are capable of very rapid growth and bloom formation. For example, Gracilaria tikvahiae , which was abundant in the Bonita Springs Beach bloom and coastal waters in Lee Count y, can double its biomass in < 3 days when irradiance, temperature, and nutrients are not limiting (Lapointe et al., 1984). As the rhodophytes grow, waves and currents detach larger plants that c ontinue to grow as unattached18 (drift) populations. Irradian ce is a critical factor re gulating growth rate of G. tikvahiae , which can utilize nearly full, natural irradiance leve ls (Lapointe et al., 198 4). The irradiance we measured on the bottom at the offshore reefs in 10-20 m water depths was < 30 μmol photons m 2 sec -1 , very low values that would re sult in severe light-limitation for G. tikvahiae at 20-30 o C (Lapointe et al., 1984). Hence, the reflective sand bottom in shallow, nearshore coastal waters of Lee County would provide the higher ir radiance levels ( > 400 μmol photons m -2 sec -1 ) needed to generate these blooms (Fig. 2E). The tissue C:N data show that the rhodophytes in coastal waters of Lee County are generally enriched in N (a low C:N ratio) compared to macroalgae on reefs in southeast Florida and the wider Caribbean (Fig. 8). The mean C:N ratio of the rhodophytes was ~ 13.7, a value that can support maximum growth rates in Gracilaria tikvahiae . For example, growth rates as high as 0.37 doublings d -1 (a biomass doubling every 2.5 days) were observed in G. foliifera var. angustissima (= G. tikvahiae ) growing under full, natural irradian ce at a C:N ratio of 13.4; lower growth rates of 0.2 doublings d -1 occurred when these plants we re grown under lower irradiance and a lower C:N ratio of 8.56 (Lapointe, 1981). Under such light-limited conditions, G. tikvahiae increases its characteristic protein pigment, phycoerythrin, which decreases the C:N ratio and provides a N storage pool that can support growth when N availability decreases (Lapointe, 1981; Lapointe and Ryther, 1979). Because of this physiological profile, G. tikvahiae and other rhodophytes are well adapte d to assimilate and store pulse s of DIN in coastal waters associated with stormwater runoff and discha rges from the DIN-enriched waters of the Caloosahatchee and Peace rivers. The low C:P and N:P ratios of the rhodophyt es in Lee County further indicate a high degree of P enrichment compared to macroalgae from southeast Florida and the wider Caribbean19 region (Fig. 8). Although relatively high C:P (622) and N:P (42.4) ratios occurred in August at the most offshore station (N. Deep Ledge), these ratios decreased significantly with increased runoff following hurricanes Charley, Frances, and Jeanne, and were generally low, averaging 314 and 22.5, respectively, in the coastal waters during the study. These C:P and N:P ratios are much lower than the means of 976 and 43.4 reporte d for carbonate-rich waters of the Caribbean where macroalgal growth is strongly limited by P (L apointe et al., 1992). In experimental field studies in the Lower Florida Keys in 1983, G. tikvahiae experienced severe P limitation when very high C:P (892-2,816) and N:P (73-250) rati os developed in ambient seawater of Pine Channel (Lapointe, 1987). The low SRP concen trations (< 0.1 μM) in the Florida Keys obviously preclude G. tikvahiae from forming blooms in that lo cation, in contrast to Lee County where much higher SRP concentrations (0.30- 0.92 μM) support low C:P and N:P ratios and result in N limitation of growth. The low mean C:P (314) and N:P (22.5) ratios in rhodophytes from Lee County are indicative of N rather than P limitation of growth (Lapointe et al. 1992). The phaeophyte Sargassum fluitans also washed ashore on Lee County beaches in summer 2004. Populations of pelagic Sargassum ( S. natans, S. fluitans ) have been present for centuries and are continually transported by wind s and surface currents between the Caribbean Sea, the Gulf of Mexico and the western No rth Atlantic Ocean. During this large-scale circulation, these pelagic oceanic populations fr equently encounter relatively nutrient enriched neritic waters where the C:N, C:P, and N:P ratio s decrease while productivity and growth rate increase. For example, the C:N, C:P, and N:P ratios of Sargassum natans decreased significantly from mean values of 49.4, 877, and 18.1 in the Sargasso Sea, to 27.9, 347, and 10.2 in neritic waters off the southeastern U.S. coastline (Lapoi nte, 1995). Such nutrient enrichment in coastal waters, coupled with strong onshore wi nds, can bring excessive biomass of Sargassum ashore20 and cause a variety of problem s. Al ong the Flor ida panhandle and Texas coastlines, strandings of pelagic S a rgassum have becom e a m a jor problem for beach tourism in recen t years (Lapointe, 1995). At the nuclear power plant in Cr ystal River, FL, a m a s s ive influx of Sargassum in 1990 caused a blockage in the cooling system , forcing a system shutdown (Rogers, 1991).

4.2. Land-based sources of nutrient enrich m e nt Multip le lin es of eviden ce support the hypothes i s that d i scharges from the Caloosahatchee River and other land-based sources can provide nutrients to bloom s of red drift

m acroalgae (and phytoplankton) for considerable di stances fro m shore. The evidence includes significant enrichm e nt of DIN, SRP, TDN, and TDP in fresh waters of th e Caloosahatchee and Peace Rivers relativ e to coastal wa ters of the stu dy area. Following increased disch a rges from these rivers after hurricanes Ch arley, Frances, an d Jeanne, we observed a six-fold increase in ( ≤ 0.20 vs. 1.31 μM) and a three-fold increase in SRP (0.30 vs. 0.92 μM) to ~ 26 km from
shore. 

### NH 4 +

The increasing im portance of 

### NH 4 + rela tiv e to NO 3 − with in creas ing lan d -based run o f f to Lee County’s coastal waters is apparent from the significant decrease in the f -ratio b e tw een our dry (August) and wet (O ctober) sam p lings. Although the f -ratio was h i storica lly us e d by oceanographers to gauge the re lative importance of upwelled NO 3 − to phytoplankton growth (Harrison et al., 1987), our previous research in the Florida Keys (Lapointe et al., 2004) and in Lee County during th is s t udy dem o nstrate th e uti lity of th is ratio in asses s ing land -based discharges of . Concentrations of 

### NH 4 + NO 3 − in Lee County’s coastal waters were statistically
sim ilar (~ 0. 9 μM) in August and October, com p ar ed to the six-fold increase (0.20 vs. 1.31 μM)
in 

### NH concen tra tions th at res u lted in the decrea sed 4 + f -ratio. This 

### NH 4 + concentr ation is high f o r21

coasta l wate rs and two-f o ld grea ter than the c oncentration needed to support m a xi m u m growth rates of Karenia brevis (Steidinger et al., 1998), as well as the rhodophytes Neoagardhiella bayleii and Gracilaria tikvahiae (DeBoer et al., 1978). Considering that is the p r eferred N source for growth of K. brevis (Steidinger et al., 1998) and the rhodophytes N. bayleii and G. tikvah i ae (D eBoer et al., 1978), it is not surprising that bloom s of these species can follow
seasonal increases in lan d -based run o ff and 

### NH NH 4 +

4 + enric h m e nt of coasta l water s f o llowing th e onset of the wet season in Lee County. Although considerable nutrient loadings fr o m the Caloosahatchee River discharges are
linked to water releases f r om Lake Okeechobee, a com p arison of the δ 15 N values of m acroalgae along the Caloosahatchee River provide evidence of significant N enrich m e nt fro m within the
basin itse lf . The algal tis sue δ 15 N values increased westward fr o m the Ortona (+ 8-9 ‰) to Franklin locks (+16 ‰) along the Caloosahatch ee River, indicating signif i cant localized N
enrichm e nt. This δ 15 N enrichm e nt correlated with increase d DIN concentrations between these two structures, a phenom e non that is also apparent in the nutrient m onitoring data collected by
the South Florida W a ter Managem e nt District (SF W MD, DB HYDRO). The δ 15 N values a t the Franklin Lock are at the high end of the sewa ge nitrogen range (Heat on, 1986; Lapointe, 1997; Costanzo et al., 2001) and suggest significant sewa ge N enrichm e nt of th e Caloosahatchee River fro m the surrounding basin. Doering and Chamberl ain (1999) analyzed th e im portance of source (Lake Okeechobee vs. Caloosahatchee River basin) to the q u ality of freshwater dis c h a rges to Caloosahatchee estuary and found th at nutrient concentrations (ex cept ammonia) and color in the estuary were higher when the bas i n rather than L a ke Okeech obee was th e source. D o wnstream of

the Franklin Lock, ~ 20 m illion g a llons p e r da y (MGD) of sewage ef f l uent re ceiv i n g advanced

wastewater treatm e nt (AWT; DIN an d SRP concentrations of ~ 214 μM and 32 μM,22 respectively) is discharged directly into the Caloosahatchee estuary upstream of San Carlos Bay (Florida Department of Environmental Protection, personal communication).

The δ 15 N values in macroalgae from Lee County’s beaches and coastal reefs indicate that
land-based N-enrichment affects the water column for considerable distances from shore. Compared to the Caloosahatchee River, lower δ 15 N values of ~ + 6 ‰ occurred in drift macroalgae on Lee County’s beaches, values within the range reported for macroalgae enriched with sewage N (Costanzo et al., 2001; Lapointe et al., 2004). The δ 15 N values of macroalgae decreased with increasing distance from shore, but remained at or above + 3 ‰ (the low end of the sewage range) at N. Deep Ledge, the most offshore station some 26 km offshore Sanibel Island. Although these high δ 15 N values in macroalgae of the Caloosahatchee River and downstream receiving waters suggest the importan ce of surface water transport of wastewater N, submarine groundwater discharge in the study area could be of the same magnitude as the river discharges (Miller et al., 1990) and may therefor e be an important rout e for the transport of sewage N from septic tanks and/or injecti on wells to coastal waters. The significant N enrichment of the water column to at least 26 km from shore would be available to support growth of not only macroalgae, but phytoplankton as well. Blooms of the red tide dinoflagellate, Karenia brevis , develop along this coastl ine at similar distances from shore (Tester and Steidinger, 1997). The present study cannot reso lve the relative importance of specific sourcs of sewage N enrichment, although multiple source s on the southwest Florida watershed could contribute. Historically, the Caloosahatchee River was not connected to Lake Okeechobee and canal projects were developed in the early 1880’s to lower the wate r level in Lake Okeechobee.23

This resulted in “new” nutrient sources from Lake Okeechobee, which receives drainage from the Kissimmee River basin, the Everglades Agricu ltural Area, and the St. Lucie drainage basin to the east when that water is backpumped into Lake Okeechobee (Steinman et al., 2002). Accordingly, runoff from dairy and cattle farm s in the Kissimmee basin, domestic treated sewage that is discharged into surface waters or re-used in agricultural areas, and septic tank discharges from throughout this region could all contribute to the sewage δ 15 N signature we
observed at both the Ortona and Franklin locks on the Caloosahatchee River. However, the significant reduction in δ 15 N values of the coastal macroalgae from August (+ 5.84 ‰) to October (+ 3.89 ‰) may reflect an increased contribution of N from rainfall and agricultural N sources followi ng the high Lake Okeechobee disc harges and the 2004 hurricanes (Fig. 9). The δ 15 N values of N in rainfall, organic peat, and fertilizers used on sugarcane and
citrus farms in south Florida have δ 15 N values in the range -3 to + 3 ‰ (Table 1). Hence, periods of peak discharge from Lake Okeechobee, su ch as those between August and October 2004, would result in increased N (especially ammonia) contributions from these sources that would
lower the δ 15 N signature of macroalgae in downstream coastal waters. In the Lower Florida Keys, elevated δ 15 N values of macroalgae reflect sewage N sources from local sources in the Keys during drought periods when little agricultural runoff of N from the Everglades occurs. In wet years, however, increased stormwater runoff from agricultural areas lowers the δ 15 N values of macroalgae to values similar to the source sign atures of fertilizers a nd peat (Lapointe et al., 2004). The three-fold increase in SRP concentra tions between August and September throughout the study area also indicate widespread P enrichment from land-based runoff. The SRP concentrations were highest in the Peace River (~ 17 μM) and downstream waters of S. Charlotte24 Harbor (3.7 μM) during our study, supporting previous conclusions of the importance of this river as a P source (McPherson a nd Miller, 1990). SRP concentr ations in rivers along the southwest coast of Florida are substantially higher than in most North American rivers (Lovejoy et al., 1990; Flannery et al., 1991) and correlate with the natural phosphatic rock formations in this region (Kaufman, 1969). The greatest contribu tion of SRP to these waters is a direct result of anthropogenic pollution (Odum, 1953), partic ularly the phosphate mining industry (Task Group Report, 1967). These large P burdens make the Alafia, Peace, and Fenholloway rivers the greatest P carriers in al l of Florida (LaRock and Bittacker, 1973). Runoff from the Peace River following Hurricane Charley would contribute to our observed increase in mean SRP concentrations in coastal waters from 0.30 μM in early August to 0.92 μM in October, respectively. These represent very high SRP co ncentrations (which dominated the TDP pool) as only ~ 0.1 μM is required to satisfy growth de mands of macroalgae (Lapointe, 1997) and the red tide dinoflagellate, Karenia brevis (Wilson and Ray, 1958).
4.3. Understanding and managing macroalgal blooms in Lee County’s coastal waters The development of macroalgal blooms in coastal waters of southern Lee County and accumulation on adjacent beaches is dependant on local hydrodynamic and meteorological factors, including antecedent events . Discharges from the Caloosah atchee River deliver not only nutrients from Lake Okeechobee and basin sources, but also estuarine nutrient loads associated with municipal sewage outfalls in Ft. Myers that are discharged into th e estuary. Although the initial beach accumulation of red drift macroalg ae in August 2003 followed major discharges (> 12,000 cfs) and nutrient loading from the Caloos ahatchee River (Fig. 9), the massive biomass involved would require a considerable time peri od for development prior to stranding. In addition to nutrients, light is a critical factor in the development of be nthic macroalgal HABs and25 increased light attenuation follows major freshw ater discharges as a result of the high color (dissolved humic compounds) content of the fresh water and increased chlorophyll a that develops downstream of the discharges (Doe ring and Chamberlain, 1999). Considering the importance of light to the grow th of these rhodophytes, the deve lopment of benthic macroalgal HABs might be favored during periods of low or moderate flows from the Caloosahatchee River, which occurred during and following the 2000/2001 drought (Fig. 9) in South Florida (Abtew et al., 2002). On Florida’s east co ast, invasive blooms of Codium isthmocladum first developed during the drought years of 1989-1990 with subsequent blooms of Caulerpa brachypus forma parvifolia occurring during the 2000/2001 drought (Lapointe et al., 2005). Periods following peak flows and nutrient loads from the Cal oosahatchee River and ot her land-based sources would favor phytoplankton rather than macroalgal blooms (Valiela et al., 1997), and the blooms of rhodophytes that occurred in 2003 and early 2004 have not re -emerged with the increased discharges following the 2004 hurricanes (Fig. 9). However, an intense Karenia brevis bloom persisted in southwest Florid a throughout 2005, which led to a 2,100 square mile hypoxic dead zone and the death of 79 manatees (Rothschild, 2005). Increasing urbanization of southwest Florida, combined with pulsed water releases from the Caloosahatchee River, could make protected ba ys and shallow, nearshor e waters of southern Lee County more prone to the development of rhodophyte blooms. The inshore bays (Estero Bay, San Carlos Bay) and shallow coastal waters off southern Lee County are directly impacted by the Caloosahatchee River plume. Although the shallow waters between Ft. Myers Beach and Bonita Springs are dominated by soft bottom se diments not conducive to growth of attached rhodophytes, surveys of this area in dicated extensive populations of Gracilaria tikvahiae , Agardhiella subulata , and Hypnea sp. growing attached to the tubes of the polychaete worm26
Chaetopterus cf. variopedatus (Fig. 2D). This large, tubiculous, suspension feeding polychaete plays an important role in nutrient cycling a nd benthic-pelagic coupling in lower Chesapeake Bay (Thompson and Schaffner, 2001) and could provi de not only suitable substrate, but also recycled nutrients that may enhance the growth of rhodophytes attached to their tubes. Strong winds, currents, and tides eventually detach the macroalgae from the benthos and deposit the biomass on beaches (Fig. 2 A,B, and E), where o dor and aesthetic problems diminish the use of the beaches by residents and tourists alike. Excessive biomass of macr oalgae can have major impact s on coastal economies through loss of tourism and increased costs associated with beach cleanup programs. Along Maui’s Kihei coast, Hawaii, USA, over $20 million (U.S.) a year in tourism revenues and property values have been lost as a result of macroalgal blooms ( www.hawaii.edu/ssri/hcri/ev/kihei_coast.htm ). In Maui County, some $250,000 (U.S.) is spent annually by condominium owners to remove excessive seaweed biomass from the beaches. In the Peel Inlet, Australia, removal of seaweeds cost $160,000 (U.S.) annually for 13,000 m 3 of macroalgae (Atkins et al., 1993). In France, th e cost exceeded 3.6 million francs for 90,000 m 3 of “green tides” removed from the Brittany co astline in 1992 (CEVA, 1993). In Lee County, seaweed removal programs for the beaches were hi storically nominal but increased dramatically, to $260,503 for the fiscal year 2003/2004, with the onset of the red drif t macroalgal blooms (U.S.; Lee County Visitor and Convention Bureau; Fig. 10). Following the termination of these blooms by hurricane Charley, beach cleanup costs decreased in 2005 (Fig. 10). Because the physical harvesting of macroalgae is costly and often insufficient to control macroalgal blooms, water quality restoration is usua lly necessary (Morand and Briand, 1996). The recent emergence of the red drift macroalg al HABs in Lee County suggests that nutrient27 loading to these inshore waters is increasi ng. Data generated from ongoing and new water quality monitoring programs could be used to de velop a conceptual model for the influence of various land-based nutrient sources, includi ng discharges from the Peace and Caloosahatchee rivers, on the development of phytoplankton and m acroalgal HABs. Such a model could help visualize how biological, chemical, physical, and meteorological factors interact to produce these blooms. For example, biomass of Ulva and Gracilaria in the Venice Lagoon, Italy, has become so large that it can regulate se asonal nutrient cycles through growth and decomposition, thereby controlling the seasonal development of phytopl ankton blooms (Sfriso et al., 1992). In Lee County, nutrient uptake by extensive blooms of rhodophytes could play an increasing role in regulating nutrient cycles and seasonal phytoplankton blooms, including blooms of Karenia brevis . Studies in the Bachimen Sea, China, showed that Gracilaria tenuistipitata depressed red tide blooms (Tang et al., 2003), suggesting that nutrient competition and/or allelopathy by rhodophytes may provide a means to mitigate red tides.28
Acknowledgements We are grateful to the many people who contributed to this research project. Eve Haverfield (Turtle Time, Inc. ) collected drift macroalgae, Michael Wynne (University of Michigan, Ann Arbor) assisted with taxonomic identification, and the Sierra Club (Calusa Chapter) provided logistical support for the fiel d work. Roland Ottolini, Wayne Daltry, Steve Boutelle, and Chris Koepfer provided technical information and boat support. Lee County Commissioner Ray Judah, Lee County Tourist Development Council Director Tamara Pigott, and Bonita Springs Mayor Gary Pr ice are especially thanked for th eir financial support of this research. Comments of Charles Yentsch, Larry Brand, Scott Hurley, and two anonymous reviewers improved this manuscript. This project was funded by Lee County and the City of Bonita Springs, FL. This is contribution number 1619 of the Harbor Branch Oceanographic Institution, Inc.29

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1245.38
Figure Legend Fig. 1. A map of the Lee County, FL area show ing station locations for the 2004 study: Ortona Lock (ORT) and Franklin Lo ck (FRK) on the Caloosahatchee Riv e r, Peace River (PCR), Im peria l River (IMP), San Carlos Bay (SCB), S. Cha r lotte Harbor (SCH), 17 th Street Reef (NSL), N. Deep Ledge (NDL), ARC R eef (ARC), Blanda’s Reef (BLD), and BeltonJohnson Culvert Reef (C LV).

Fig. 2. Red drift m acroalgae in coastal wate rs of Lee County, FL: A.) rhodophytes, Bonita Springs Beach, January, 2004; B.) rh odophytes , Bonita Sprin g s Beach, Ju ly, 2004; C.) rhodophytes, 17 th Street Reef, Augus t, 2004; D.) wo r m tube with attached rhodophyte, Bonita Sprin g s Beach, August, 2005; E.) rhodoph ytes in sh allow water along beaches in southern Lee County.

Fig. 3. Mean concentrations (μM, ± 1 SD, n = 2) of water colu m n dissolved inorganic nitrogen (DIN), ammoniu m ( 

### NH 4 + ), nitrate ( NO 3 − ) and f -ratios ( NO 3 − :DIN) in August and
October 2004 at sam p ling stations in Lee County, FL.

Fig. 4. Mea n water co lu mn SRP concentr ation s ( μ M, ± 1 SD, n = 2) and DIN:SRP ratios in August and October 2004 at sam p ling stations in Lee County, FL.

Fig. 5. Mean water column TDN and TDP con centra tions (μ M, ± 1 SD, n = 2), with rela tive contributions of organic and inorganic for m s, in August and October at sam p ling stations in Lee County, FL.39 Fig. 6. Mean tissue C:N, C:P, and N:P molar ra tios (± 1 SD, n = 1-8) in macroalgae collected August and October 2004 at sampling stations in Lee County, FL.

Fig. 7. A.) Mean tissue δ 15 N (‰, ± 1 SD, n = 2-8) of macroalgae collected in August and October 2004 at sampling stations in Lee County, FL and B.) from Bonita Springs Beach in July and August 2004, including a comparis on among beach and reef samples of the rhodophyte Hypnea musciformis.

Fig. 8. A comparison of mean tissue C:N, C:P, and N:P molar ratios (± 1 SD, n = 3-6) in macroalgae from Lee County, FL during this st udy with macroalgae fr om southeast Florida (Lapointe et al. 2005), Jamaica and the Bahamas (Lapointe et al. 1992).

Fig. 9. Monthly mean flow rates (cubic f eet per second, cfs) at Franklin Locks on the Caloosahatchee River, FL in 2003-2004. A rrows indicate beach drift algae events.

Fig. 10. Beach clean-up costs in Lee County, FL, 1997-2005 ($ U.S.).40

Fig. 141

Fig. 242



### August O c tober Rivers Bays Coastal Reefs

12.7



### 0 2 4 6 8 10

26 23



### 0 5 10 15 20

26 28 23



### 0 5 10 15 20

0.0 0.2 0.4 0.6 0.8 1.0 

## NH 4 + 

### (μM)



## NO 3 - 

### (μM)



### DIN (μM)



## f Ratio

Fig. 343

16.8



### 0 1 2 3 4



## SRP (μM)

68.3



### 0 5 10 15

r r k k y r ) ) ) ) ) 

## DIN SRP August October Rivers Bays Coastal Reefs

Fig. 444

68.6 70.9



### 0 10 20 30 40 50



## TDN (μM) Rivers Bays Coastal Reefs

D O N D I N

0 1 2 3 4 5 6



## TDP (μM) DO P S R P

Fig. 545



### August O c tober Rivers Bays Coastal Reefs

0 5 10 15 20


## C:N

622



### 0 100 200 300 400 500


## C:P

42.4



### 0 5 10 15 20 25 30


## N:P

Fig. 646



## A. August October Rivers Bays Coastal Reefs

0 3 6 9 12 15 

## δ 15 

## N (‰)

0 3 6 9 

## B. Phaeophyta Hypnea musciformis Rhodophyta 

## δ 15 

## N (‰ )

Fig. 747



### 0 10 20 30 40



## C:N

0 500 1000 1500 2000



## C:P

0 10 20 30 40 50 60

Lee County Palm Bch. County Jamaica Bahamas 

## N:P

Fig. 848

0 4,000 8,000 12,000 16,000

J F M A

MJ J A S O N D J F M A

MJ J A S O N D J F M A

M J J A S O N D J F M A

MJ J A S O N D J F M A

MJ J A S O N D 2000 2001 2002 2003 2004 

### Flow (cfs) Mean Min Max A u g . N o v . Jan. July

Fig. 949



### $0 $50,000 $100,000 $150,000 $200,000 $250,000

97-98 98-99 99-00 00-01 01-02 02-03 03-04 04-05 

## Fiscal Year (Oct. 1 - Sept. 30) 

## Cost (U.S. $)

Fig. 105051

Table 2. Stations, depths, and species collected for analysis from study sites in Lee County, FL, USA in July (J), August (A), and October (O) of 2004. Site, Depth Species Rhodopyta ORT <1 m FRK <1 m SCB 1 m SCH 1 m NSL 3 m CLV 10 m BLD 14 m ARC 19 m NDL 20 m BSB Bch. FMB Bch. SAN Bch. CAP Bch.

- - - - - - --- - - - - O J A O A O A O A O A O J

var. denudatum O O A O J A O A A A A J A O J A A A O A O A Agardhiella subulata Botryocladia occidentalis Euchuma isiforme
Gracilaria cervicornis Gracilaria mammalaris Gracilaria tikvahiae Hypnea musciformis Rhodymenia divaricata Phaeophyta

- - - - - - --- - - - - A A A Sargassum fluitans Chlorophyta

- - - - - - --- - - - - sp. A O A O Cladophora Cyanophyta L

yngbya sp. A A Angiosperma

- - - - - - --- - - - - A O A O Thalassia testudinum52

Table 3. Water column nutrient concentrations at study sites in Lee County, FL, USA in August and October of 2004. Values represent means ± 1 S.D.

n August 14 0.20 ± 0.00 0.91 ± 0.72 1.11 ± 0.72 0.77 ± 0.11 0.30 ± 0.18 6.88 ± 2.35 October 14 1.31 ± 1.08 0.97 ± 0.69 2.29 ± 1.57 0.41 ± 0.14 0.92 ± 1.20 4.96 ± 0.99 Ammonium (μM) Nitrate+Nitrite (μM) DIN (μM) f -Ratio (NO3+2) / DIN SRP (μM) DIN / SRP Ratio53

Table 4. Tissue C:N, C:P, and N:P molar ratios and ¶15N in macroalgae from coastal study sites in Lee County, FL, USA in August and October 2004. Values represent means ± 1 S.D.

August 13.93 ± 2.78 (n=16) 386.3 ± 198.0 (n=16) 27.43 ± 11.40 (n=16) 5.84 ± 1.37 (n=32) October 13.54 ± 3.43 (n=13) 242.0 ± 142.1 (n=13) 17.51 ± 6.74 (n=13) 3.89 ± 0.96 (n=26) ¶ 15N (ä) C:N Ratio C:P Ratio N:P Ratio