Evaluating the effects of restoration of subtropical oligohaline marshes on abundance and habitat 

use by juvenile snook, Centropomus undecimalis and associated fish communities. 

Final Report to 

Charlotte Harbor National Estuary Program 

June 2005 

Principal Investigator: Aaron Adams, Center for Fisheries Enhancement, Mote Marine Lab 
2

NOTE: This project was designed to measure creek fish assemblages in two types of creeks – 

creeks with significantly degraded upland drainages, and creeks with slightly altered upland 

drainages – and to determine the effect of habitat restoration in the upland drainages of the latter 

creeks on juvenile snook and other fishes. This would have provided a relatively rare beforeafter comparison of restoration effects. However, Florida Department of Environmental 

Protection did not conduct the restoration as planned. Thus, this report focuses on the effect of 

upland habitat degradation on mangrove creek fish assemblages in Charlotte Harbor. 

Introduction 

Florida’s southwest coastline has been drastically altered for development, water 

management, agriculture, mining, and mosquito control purposes (references cited in Lin and 

Beal, 1995; Poulakis et al., 2002). Historically, during the rainy season, water would inundate 

vast stretches of upland habitats (wet and mesic pine flatwoods, hydric hammocks, and coastal 

tropical hammocks) and drain as slow, overland sheetflow to oligohaline and mesohaline 

marshes at the upper reaches of the tidal estuarine system. In areas with larger drainage basins, 

surficial flows were concentrated into tidal creek systems, creating a permanent flow corridor 

between upland salt ponds and tidal marshes. During the dry season, wet prairies and hydric 

hammocks dry-out, seasonally removing the corridor between upland salt ponds and 

tidal marshes. In larger drainage systems, tidal creeks remain 

connected to the upland salt-water ponds. 

 Anthropogenic alterations of freshwater flows into estuaries are of particular concern to 

resource managers because such changes impact estuarine ecology (Sklar and Browder, 1998; 
3

reviewed in Beach 2002). Freshwater flow is a major ecological structuring factor in estuaries, 

influencing abundance and distributions of vegetation, and of invertebrates and vertebrates that 

use estuaries for some or all of their life cycles. The increase in impervious surfaces and loss of 

wetland habitats associated with coastal development alter the source, timing, and velocity of 

freshwater flows, which influences salinity patterns (Sklar and Browder 1998). Whereas some 

organisms can tolerate wide ranges in salinity, most species have narrow salinity tolerances or 

migrate to remain in a preferred salinity range (Montague and Ley 1993, Sklar and Browder 

1998), thus altering habitat use patterns. When > 10% of a watershed’s acreage is converted to 

impervious surface, the water bodies become seriously degraded, and are less diverse, 

productive, and stable (reviewed in Beach 2002). Lower organism abundances, lower 

recruitment, and shifts in dominant species often result from high pulses in freshwater runoff 

(Sklar and Browder 1998, reviewed in Beach 2002, Beever and Chamberlain 2002, Wyda et al. 

2002). With 25% of United States coastal habitats expected to be developed by 2025 (14% of 

coastal habitats had been developed by 2002) (Beach 2002), there is an exigent need to 

understand how habitat alterations impact fishes so that appropriate conservation and 

management measures can be enacted. This is especially true in Florida, with one of the fastest 

growing populations in the United States. 

 Relative to many other estuaries Charlotte Harbor habitats remain in good condition – 

much of the mangrove shoreline is intact and government owned, and seagrass coverage has not 

changed significantly in ten years of monitoring. Increasingly rapid coastal development, 

however, threatens to alter the estuary’s watershed, thus altering freshwater flow into the estuary. 

In fact, habitat-associated effects of such alterations are becoming evident in some locations. 

This combination of unaltered and altered habitats makes Charlotte Harbor a perfect location for 
4

studying the effects of habitat alteration on fish-habitat interactions, and formulating 

management strategies to conserve estuarine habitats. 

 Although the decline in coastal fish populations has largely been attributed to 

overfishing, degradation of fish nursery habitats has likely increased larval and juvenile mortality 

and thus contributed to population declines. Oligohaline creeks and upland salt-water ponds are 

essential habitats for many young-of-the-year marine finfish and shellfish (McMichael et al., 

1989; Peters et al., 1998; Baltz et al., 1998; Geary et al., 2001; Poulakis et al., 2002). The 

recruitment success of many tropical estuarine fishes, such as snook, Centropomus undecimalis

and tarpon, Megalops atlanticus that have evolved life-histories based on a wet/dry season 

depend greatly upon access to oligohaline marshes (Poulakis et al., 2002); the recruitment of 

snook and tarpon larvae to creeks and ponds coincides with the wet season, when they are able to 

ride high tides into the flooded uplands. The shallowness of creeks and isolation of ponds in the 

dry season provides protection from predation by large fishes. As they grow and undergo 

ontogenetic shifts in diet and habitat requirements, these fishes migrate downstream (and 

eventually to the open estuary and ocean), spending portions of their life history in creek and 

estuarine habitats. Degradation of these juvenile habitats is of special concern giving the 

significant economic importance of these species in the saltwater recreational fishery (statewide, 

the Florida saltwater recreational fishery is estimated to be worth $8.5 billion annually). 

 Research to determine the effects of upland development and subsequent alterations of 

freshwater flow on estuarine fishes is urgently needed. This is especially true for juvenile life 

stages of economically important species, such as common snook, Centropomus undecimalis and 

red drum, Sciaenops ocellatus, that comprise the recreational fishery that generates 

approximately $8.5 billion annually in Florida. This research examined habitat use patterns of 
5

juvenile snook and red drum, and of the overall creek fish assemblages in two types of creeks – 

those with altered upland drainages (degraded), and those with relatively undeveloped drainages 

(natural) – to determine the effects of freshwater flow alterations. This research tested three 

hypotheses: 

• H1: Oligohaline creeks are important juvenile habitats for juvenile snook and red drum 

• H2: Degraded upland habitats alter freshwater flow that degrades the habitat quality of 

estuarine mangrove creeks as juvenile habitats for snook and red drum 

• H3: Degraded upland habitats alter freshwater flow that degrades the habitat quality of 

estuarine mangrove creeks, and these changes are reflected in creek fish assemblages

Methods 

Study Location 

Charlotte Harbor is a 700 km2

 coastal plain estuarine system in southwest Florida (Hammett 

1990) (Figure 1). The Peace, Myakka, and Caloosahatchee rivers, as well as many smaller 

creeks throughout the drainage, transport large amounts of the fresh water into the harbor. The 

harbor is connected to the Gulf of Mexico through Boca Grande Pass, San Carlos Bay, and three 

smaller inlets. The climate of Charlotte Harbor is subtropical; mean seasonal water temperatures 

range from 12o to 36o C, and freezes are infrequent (Poulakis et al. 2003). Anthropogenic 

development within the watershed has stressed the estuarine system; however, compared with 

many other estuaries (e.g., Chesapeake Bay, Tampa Bay), Charlotte Harbor has remained 

relatively unspoiled (> 80% of mainland shorelines under protection; R. Repenning, Florida 

Department of Environmental Protection, pers. comm.; Hammett 1990; CHNEP 1999). Seagrass 

flats (262 km2

; Sargent et al. 1995) and mangrove shorelines (143 km2; L. Kish, Florida Fish and 
6

Wildlife Research Institute, unpubl. data) continue to thrive as the dominant habitats within the 

estuary. 

Sample Design 

From February 2003 through October 2004, four mangrove-fringed estuarine creeks, each 

approximately 2 km long, on the eastern shoreline of Charlotte Harbor, FL (Figure 1) were 

sampled every other month using a 22 x 1.2 m center bag seine with 3.2 mm mesh. Each creek 

was divided into three equal strata (upper, middle, lower) for sampling, with five samples per 

stratum, and thus 15 samples per creek, per sample period. Sample locations within each creek 

stratum were selected haphazardly in each month. For each sample, the net was set in a semicircle against a mangrove shoreline and pursed to force fish into the bag, all fish were identified 

to the lowest taxon possible, the first 25 individuals of each taxon were measured (standard 

length) and the remainder counted, and temperature, salinity, and dissolved oxygen recorded 

with a handheld YSI 556 MPS. All fish were returned to the water at the site of capture. 

 All creeks are within the same estuarine hydrological zone (Poulakis et al. 2003), so are 

unlikely to differ greatly in larval supply. For the purposes of this study, the two northernmost 

creeks were considered ‘natural’: their morphology remains largely intact except for remnant 

mosquito ditches (compared to 1953 aerial photos), and their upland drainages are undeveloped. 

Creek widths range from 2 m in narrow passes to >60 m in wider bays, depth is shallow (< 0.5 m 

except in narrow passes where depths reach 1m), shorelines are lined entirely by red mangroves 

Rhizophora mangle, and bottom is mixed mud and sand. The submerged aquatic vegetation in 

the upper stratum is entirely Ruppia maritima, whereas the middle and lower strata are 

dominated by Halodule wrightii. The two southern creeks, located 16 km south of the natural 
7

creeks, are considered ‘degraded’: their drainages and wetlands have been altered for 

development, creating impervious surfaces and altering freshwater flow regimes. The altered 

flow regimes cause short, pulsing hydroperiods limited to the immediate creek with little 

overland sheet flow. The bottoms are mostly hard sand, and the submerged aquatic vegetation 

(R. maritima and H. wrightii) is patchy and limited to the lower two-thirds of the creeks. The 

creeks are narrow (mean = 5 m) for the upper two-thirds, and have wider bays (60 m) only in 

their extreme lower portions. Narrow sections are scoured to > 2 m depth with undercut banks, 

and greatly reduced width of the intertidal mangrove prop root habitat. 

 

Data Analysis 

Taxa were defined as residents (R), transients (T), and juveniles (J), based upon frequency of 

occurrence, habitat requirements (Robins et al. 1986) and dominant life stage when in the creeks: 

residents were present in > 200 samples (N = 547) and had creek-associated habitat 

requirements, transients were marine or estuarine species able to use numerous habitats and 

present in < 201 samples, and taxa were classified as juveniles when > 90% of individuals 

captured were juveniles. Taxa were defined as freshwater (F) or non-native (N) based upon 

Robins et al. (1986) and Page and Burr (1991). 

 Mean density (no. fish/m2

) and frequency of occurrence (total number of samples in 

which the taxon occurred) were calculated by creek and zone for each taxon, and examined using 

cluster analysis (standardized, Average linkage method, Euclidean distance) to determine the 

extent of (dis)similarity among fish assemblages in the different creeks (Wilkinson et al. 1996). 

If the classification of creeks based upon apparent habitat quality was correct, the expectation 

was that creeks would be most similar within type (i.e., North Silcox and South Silcox zones 
8

would group together (natural creeks), and Culvert Creek and Yucca Pen would group together 

(degraded creeks)). 

 Density and frequency of occurrence for the most abundant non-native species, 

Cichlasoma urophthalmus, were examined by creek to determine the extent that presence of this 

species differed by creek type (natural vs degraded). Frequency of occurrence and abundance 

were examined graphically to determine the extent that freshwater and non-native species 

occurrence were related to salinity (data were insufficient (i.e., no freshwater or invasive species 

were captured in most samples) to warrant regression analysis). Since frequency of occurrence 

and abundance were low for these species, data were summed for all species within each group. 

For non-native species, C. urophthalmus were excluded from regression analysis because of their 

extreme salinity tolerance in their native range (0 – 26ppt, Morales-Gómez et al. In Press). 

 To determine whether creek characteristics influenced use of creek habitats by juvenile 

C. undecimalis and S. ocellatus, density data were examined by creek and zone. Because many 

samples contained no individuals of these species, density data did not meet normality 

assumptions required for parametric analysis, so densities were examined separately by creek 

and zone with Kruskal-Wallis non-parametric ANOVA (Sokal and Rohlf 1995). Lengths 

(measured as standard length) of C. undecimalis and S. ocellatus were log-transformed and 

examined with a two-way ANOVA, with creek and zone as factors. Because no C. undecimalis 

or S. ocellatus were captured in the upper zone of Yucca Pen, Yucca Pen was excluded from this 

analysis (The effect of salinity on size distributions of C. undecimalis and S. ocellatus were 

examined with linear least squares regression. Length data were log-transformed prior to 

analysis. 
9

Effects of hurricane Charley 

In August 2004, Category 4 hurricane Charley traversed Charlotte Harbor, the eastern eyewall 

passing over the study creeks. Sampling of the natural creeks was completed 3 days prehurricane, and was repeated from 13 through 21 days post-hurricane. Normal sampling in 

natural and degraded creeks resumed in October, 2 months post-hurricane. 

Results 

Salinity (Figure 2), temperature (Figure 3), and dissolved oxygen (Figure 4) varied seasonally. 

Seasonal trends for each variable were similar among creeks. Salinity maxima and minima 

occurred in degraded creeks. Yucca Pen experienced the longest periods of low salinity (in eight 

of ten sample periods, salinity was < 10 ppt in middle and lower zones). Surface and bottom 

salinity, temperature, and dissolved oxygen were similar, so were combined for analysis. When 

salinity was compared by creek and zone, there were significant creek and zone effects (Table 1, 

Figure 5), but the trend was similar in all creeks – salinity decreased from lower to upper zones. 

Temperature differed among creeks, but not by zone (Table 1, Figure 6), whereas dissolved 

oxygen varied differed by creek and zone (Table 1, Figure 7). Dissolved oxygen minima 

occurred in the degraded creeks. Temperature and dissolved oxygen were negatively correlated 

for North Silcox (Pearson r2

 = -0.34, p < 0.001, df = 1), South Silcox (r2 = -0.57, p < 0.001, df = 

1), and Yucca Pen (r2

 = -0.41, p < 0.001, df = 1), but not for Culvert Creek (p > 0.1). Salinity 

and temperature were weakly negatively correlated for South Silcox (r2

 = -0.28, p < 0.01, df = 1) 

and Yucca Pen (r2 = -0.22, p < 0.05, df = 1), but not for Culvert Creek or North Silcox (p > 0.1). 

Salinity and dissolved oxygen were positively correlated for the natural creeks (North Silcox r2

 = 

0.30, p < 0.001, df = 1; South Silcox r2 = 0.44, p < 0.001, df = 1), but not for the degraded creeks 
10

(p > 0.1). 

A total of 205,992 fish representing 79 taxa (fishes were identified to the lowest taxon 

possible, resulting in assignation of individuals to 60 species, 14 genera, and 5 families) was 

captured in 547 samples (Table 2). Of these taxa, 27 were classified as residents, 10 as 

transients, 18 as juveniles, 12 as freshwater species, and four as non-native species. The seven 

most abundant species were residents, and were present in all creeks. Juveniles of recreationally 

important Centropomus undecimalis and Sciaenops ocellatus were ranked 10 and 14 in total 

abundance, respectively, and were also captured in all creeks. The most abundant invasive 

species, Cichlasoma urophthalmus, was ranked 26 in total abundance, higher than the native 

freshwater taxon, Lepomis sp., which was ranked 32 in total abundance, although both groups 

were recorded in all creeks. 

Density of all species combined and species richness tended to be greater in the natural 

creeks (North Silcox and South Silcox) than in the degraded creeks (Culvert Creek and Yucca 

Pen) during the wet season, and similar during the dry season (Figure 8). When species densities 

and frequency of occurrence by creek and zone were examined with cluster analysis, fish 

assemblages in natural creeks were most similar to one another, and most dissimilar to degraded 

creeks (Figure 9). 

Although freshwater species were captured in all months, trends in abundance and 

frequency of occurrence coincided with the wet season, with peaks in June, August, and 

September (Table 3, Figure 10). Both total abundance (R2 = 0.49, p < 0.01) and frequency of 

occurrence (R2 = 0.46, p < 0.01) of all freshwater species combined were negatively related to 

salinity. The most common freshwater fishes were Lepomis spp and Micropterus spp. (Figure 

11), which were captured mostly in salinities < 6ppt (Lepomis spp. mean salinity at capture = 
11

3.51, se = 0.56; Micropterus spp. mean salinity = 5.93 ppt, se = 1.69). Lepomis spp were 

seasonally present in all creeks, and were most abundant in South Silcox (38% of Lepomis spp. 

individuals), followed by North Silcox (29%), Culvert Creek (26%), and Yucca Pen (7%). 

Micropterus spp were present seasonally only in Yucca Pen (62% of Micropterus spp. 

individuals) and Culvert Creek (38%). 

Non-native species were not captured in samples until August 2003 (the fourth sample 

period of the study). Although there was no relationship between salinity and abundance (p > 

0.1) or frequency of occurrence (p > 0.1) of non-native species, their seasonality of occurrence 

followed high freshwater flows associated with the wet season. The most common and most 

abundant non-native species was Mayan cichlid, Cichlasoma urophthalmus, which occurred in 

all creeks but was most abundant in Culvert Creek (Table 4), and was captured in all months 

after August 2003. Oreochromis mossambicus and Hemichromis bimaculatus were present 

seasonally in low abundance only in North Silcox and South Silcox creeks: each species was 

captured in August 2003, O. mossambicus was captured again in October 2003, and February 

and June 2004, and H. bimaculatus again in June 2004. 

Juvenile C. undecimalis were captured in all months, and occurred in all zones in North 

Silcox, South Silcox, and Culvert Creek, but were absent from the upper zone and rare in the 

middle zone of Yucca Pen (Figure 12). Temporal trends in density varied among creeks and 

zones. Densities differed when examined by creek and zone (Table 5). Within creeks, densities 

tended to be highest in the lower zone and least in the upper zone in Culvert Creek, Yucca Pen, 

and North Silcox. This trend was reversed in South Silcox. Within zones, densities were similar 

among all creeks in the lower zone, but were highest in South Silcox and least in Yucca Pen in 

middle and upper zones (snook were absent and rare in upper and middle zones, respectively, of 
12

Yucca Pen). There was no relationship between salinity and C. undecimalis abundance or size (p 

> 0.1). 

Samples were dominated by small C. undecimalis in all creeks (Figure 13), with postsettlers occurring in late summer and early fall. Although there was a significant creek x zone 

interaction effect (Table 6), all creeks exhibited the same trend in size – lengths were greatest in 

the middle zone (Figure 14). (Yucca Pen was removed from length analyses because no juveniles 

were captured in the upper zone, and relatively few were captured in middle and lower zones.) 

Juvenile S. ocellatus were captured almost entirely from October through February, and 

were in greater densities in North Silcox and South Silcox than Culvert Creek and Yucca Pen in 

all zones (Figure 15, Table 7). Juvenile S. ocellatus were rare or absent from upper zone of 

Culvert Creek and Yucca Pen. Within creeks, the trend was for densities to be greatest in the 

lower zone and least in the upper zone. Although there was no significant relationship between 

S. ocellatus density and salinity, within each creek between 72% and 87% of samples that 

contained juvenile S. ocellatus were in salinities between 10 and 28 ppt. 

Samples were dominated by small S. ocellatus (Figure 16), with post-settlers first present 

in October. In Culvert Creek and Yucca Pen, where S. ocellatus were less abundant, fish size 

was positively related to salinity (CC – R2

 = 0.57, F = 121.64, p < 0.001: YP – R2 = 0.27, F = 

30.199, p < 0.001), but there was no such relationship in North and South Silcox creeks (p > 

0.1). Yucca Pen was removed from length analysis because of very low or no catches in all 

zones. The significant creek x zone interaction effect (Table 8) was due primarily to increases in 

size from lower to upper zones in Culvert Creek and North Silcox, whereas fish size was similar 

in all zones of South Silcox (Figure 17). 
13

Effects of hurricane Charley 

Sampling of natural creeks was completed 3 days pre-hurricane, was repeated from 13 through 

21 days post-hurricane. Normal sampling in natural and degraded creeks resumed in October, 2 

months post-hurricane. Hurricane Charley might be considered an acute disturbance because its 

direct effects (high winds, rainfall, storm surge) lasted < 12 hr. However, low dissolved oxygen 

from decomposition of leaves from defoliated mangroves lasted for > 1 wk. Thus, Charley is 

defined as a press disturbance (Glasby and Underwood 1996, Lake 2000). Above-water impacts 

were severe, with all mangrove branches > 6 m height completely defoliated or broken and 

partial defoliation of shorter mangroves. Within creeks, damage included scouring of narrow 

sections of creeks, moderate redistribution of sediments, complete loss of SAV, high turbidity, 

and reduction of dissolved oxygen to > 1 ppm (purportedly due to mangrove leaf 

decomposition). 

 The direct effects (high winds, rainfall, storm surge) of Hurricane Charley lasted < 12 hr. 

Above-water impacts were severe, with all mangrove branches > 6 m height completely 

defoliated or broken and partial defoliation of shorter mangroves. Within creeks, damage 

included scouring of narrow sections of creeks, moderate redistribution of sediments, complete 

loss of SAV, high turbidity, and reduction of dissolved oxygen to > 1 ppm. Since the low 

dissolved oxygen (purportedly from decomposition of leaves from defoliated mangroves) lasted 

for > 1 wk, the indirect effects of the hurricane will likely have greater impact. 

 The passage of the hurricane was noted by the abrupt decline in species richness and 

abundance 13 days post-hurricane sampling in natural creeks thus indicating a strong immediate 

effect (Figure 18). A rapid response was suggested by a rapid recovery of species richness and 

abundance by 21 days post-hurricane, after dissolved oxygen levels began to recover toward pre-
14

hurricane levels. However, sampling 2 months post-hurricane indicated a delayed response – 

species richness was similar to pre-hurricane levels, but density declined. The apparent sluggish 

recovery may indicate a lag effect, whereby effects of physiological stress from depression of 

DO and salinity and increase in turbidity were delayed. Sampling in the creeks continues so that 

longer-term hurricane effects can be determined. 

Discussion 

This research provided urgently needed quantitative information on the affect of habitat 

degradation on fish assemblages associated with mangrove creeks, and a quantitative estimate on 

the effect of this degradation on the nursery value of creek habitats for economically important 

fishes. That the degradation was primarily associated with development of upland drainages of 

mangrove creeks and associated alterations of freshwater flow into the creeks is especially 

notable. 

 Anthropogenic alterations of freshwater flows into estuaries are of particular concern to 

resource managers because such changes impact estuarine ecology (Sklar and Browder, 1998; 

reviewed in Beach 2002). Freshwater flow is a major ecological structuring factor in estuaries, 

influencing abundance and distributions of vegetation, and of invertebrates and vertebrates that 

use estuaries for some or all of their life cycles. In this study, Culvert Creek and Yucca Pen were 

considered degraded because their upland drainages have been drastically altered, with an 

increase in impervious surface. For Yucca Pen, freshwater flows from large upland areas are 

now funneled into the creek, causing extensive periods of low salinity and making this poor 

habitat for estuarine fishes (e.g., low abundance and species richness in upper and middle zones). 

Culvert Creek suffers from the ‘faucet effect’, whereby creek salinities and flow rates fluctuated 
15

rapidly with local rainfall: high rainfall (faucet ‘on’) created near-freshwater conditions the 

length of the creeks; low rainfall (faucet ‘off’) allowed mesohaline conditions to creek 

headwaters. Prior to these alterations, it is likely the hydrologic conditions were similar to those 

of the natural creeks such that gentle, low, flat slopes provided for slow overland sheet flow of 

surface waters, which were retained for extended duration within wet and mesic slash pine 

flatwoods during wet season, but were dry during dry season. The flows caused salinity 

gradients that provided important habitat for fishes. 

 The increase in impervious surfaces and loss of wetland habitats associated with coastal 

development alter the source, timing, and velocity of freshwater flows, which influences salinity 

patterns (Sklar and Browder 1998). Whereas some organisms can tolerate wide ranges in 

salinity, most species have narrow salinity tolerances or migrate to remain in a preferred salinity 

range (Montague and Ley 1993, Sklar and Browder 1998), thus altering habitat use patterns. 

When > 10% of a watershed’s acreage is converted to impervious surface, the water bodies 

become seriously degraded, and are less diverse, productive, and stable (reviewed in Beach 

2002). In this study, it is estimated that the proportion of drainages of Culvert Creek and Yucca 

Pen have exceeded this 10% alteration threshold. Lower organism abundances, lower 

recruitment, and shifts in dominant species often result from high pulses in freshwater runoff 

(Sklar and Browder 1998, reviewed in Beach 2002, Beever and Chamberlain 2002, Wyda et al. 

2002). In this study, although the overall temporal trends in salinity, temperature, and dissolved 

oxygen (DO) in the creeks were similar, the degraded creeks experienced the most extreme 

variation. These extreme variations likely contributed to the lower habitat quality of the 

degraded creeks. In addition, salinity and DO minima were lowest in the degraded creeks. 

The differences in abiotic factors between natural and degraded creeks likely caused the 
16

differences in species richness, total fish abundances, and abundances of most species were 

higher in the natural creeks, thus corroborating previous research elsewhere on the effects of 

freshwater flow alterations. The lack of submerged aquatic vegetation in the upper and lower 

zones of the degraded creeks further underscores the effects of freshwater flow alterations. 

 With 25% of United States coastal habitats expected to be developed by 2025 (14% of 

coastal habitats had been developed by 2002) (Beach 2002), there is an exigent need to 

understand how habitat alterations impact fishes so that appropriate conservation and 

management measures can be enacted, and this study contributes this important information for 

Charlotte Harbor. Moreover, since Charlotte Harbor resembles much of the Florida coastline in 

that coastal habitats are being drastically altered for development, water management, and 

mosquito control, the findings of this research are applicable elsewhere. 

 Habitat alteration often facilitates invasions by non-native species (Ross 1991, Courtenay 

and Williams 1992), and this appears to be the case in this study. Habitat quality of mangrove 

creeks, as defined by the extent of alteration in upland drainages, is an important factor in the 

invasion success of Cichlasoma urophthalmus into Charlotte Harbor. It appears that upland 

habitat alteration (ponds and canals) may provide refuge from low temperatures and predation, 

thus harboring source populations for individuals to colonize estuarine habitats. The presence of 

drainage ditches and artificial ponds that retain oligo- and meso-haline water year-round (prior to 

anthropogenic alteration these areas were dry during the dry season), may provide sources of 

recruitment into Charlotte Harbor’s estuarine habitats. Based upon the findings of this study, 

Charlotte Harbor National Estuary Program has recently provided funds to the PI to address 

questions relating to invasive species in estuarine habitats, including: Does alteration of 

freshwater flows in upland habitats increase invasion success of C. urophthalmus in estuaries? 
17

Are C. urophthalmus established in Charlotte Harbor estuarine habitats or do altered upland 

habitats (artificial ponds and canals) provide upstream sources of new recruits? What invasion 

avenues are used by C. urophthalmus to access Charlotte Harbor estuarine habitats? Once 

invasion avenues are defined, future restoration efforts can include strategies to interrupt these 

avenues as part of the restoration process to help reduce the establishment of this species in 

estuarine habitats. Future research can then begin addressing the extent of the ecological impacts 

of C. urophthalmus on native species. 

 Abundance and size ranges of juvenile snook and red drum captured during this study 

indicated that overall habitat use patterns were the same, but that creek-specific characteristics 

likely influenced the quality of the creeks as juvenile habitats. For example, juvenile red drum 

were present in similar size ranges in all creeks during the same, distinct time period. In 

addition, the general trend was for juvenile red drum to move toward the upper zone as they 

grew. However, the high freshwater flows in Yucca Pen likely caused the absence of juvenile 

red drum in the upper zone and limited almost all red drum to the lower zone. In Culvert Creek, 

variable freshwater flows (i.e., the faucet effect) and channelized creek morphology likely 

limited red drum abundance. In contrast, the moderated freshwater flows and extensive shallow 

habitats of North and South Silcox creeks appeared to be higher quality habitats for juvenile red 

drum. 

 Since the expectation is that habitat degradation can alter spatial and temporal patterns of 

habitat use by many species, change species composition (reviewed in Sklar and Browder 1998), 

and lower the quality of nursery habitats, it was expected that the natural creeks would also 

support more juvenile snook. This was true for Yucca Pen, where high freshwater flows likely 

limited juvenile snook use of the upper and middle zones. Surprisingly, however, juvenile snook 
18

densities were similar among all other creeks. One possible reason for similar densities among 

creeks is that the difference in habitat complexity between creeks made the snook more catchable 

in the degraded creeks. The natural creeks had extensive flooded areas of red mangrove proproots that were inaccessible to sampling with seines, even at low tide. In contrast, subtidal red 

mangrove prop root habitat in the degraded creeks was very limited at low tide, so sampling in 

the degraded creeks was more efficient. In other words, the probability of catching juvenile 

snook in the degraded creeks was higher than in the natural creeks. 

 Although not measured in this study, the amount of creek habitat available to juvenile 

snook was far greater in the natural than degraded creeks (Figure 1). Thus, even if densities of 

juvenile snook were similar among creeks, the total abundance of snook (density X total creek 

area) was far greater in North and South Silcox than in Culvert Creek or the lower zone of Yucca 

Pen. 

 Habitats that harbor high densities of juveniles have long been defined as nurseries, and 

with this standard the creeks examined in this study would be considered nursery habitats. 

However, the extent to which the juveniles grow, survive, and successfully join the adult 

population must be determined before a habitat can be defined as a nursery. Thus, a more 

realistic standard for defining nursery habitats is to determine whether juveniles from a particular 

habitat eventually contribute to the adult populations (i.e., demonstrate habitat connectivity). 

This latter standard is of most use and of primary concern to resource managers. Therefore, 

although this study has shown that juvenile snook are present in similar densities in one of the 

degraded creeks and the two natural creeks, the rate at which these juveniles are successful at 

surviving to enter the adult population remains unknown. Based upon these findings, research is 

now underway to determine the extent that these creeks contribute snook to the adult population, 
19

and thus determine the true nursery value of these creeks. Determining which creeks contribute 

more snook to the local population will aid in land acquisition and habitat management. In 

addition, findings will provide a framework for examining the effects of habitat degradation on 

juveniles of other species with similar life histories. 

 

Hurricane Effects 

The accurate characterization of ecological disturbances such as hurricanes is important for 

structuring metrics of disturbance effects. The frequency, intensity, and duration provide a 

measure of the disturbance. The effect is then a measure of the impact of the disturbance on the 

system (i.e., abiotic and biotic components), and is a measure of resistance (ability of the system 

to withstand a disturbance, Lake 2000). The response is a measure of the recovery trajectory of 

the affected system (i.e., resilience – the ability of a system to recover from a disturbance (Lake 

2000). Glasby and Underwood (1996) proposed that a system’s response be defined in similar 

terms to the disturbance – as either pulse (quick recovery) or press (slower recovery trajectory). 

Although the passage of hurricane Charley was considered a pulse disturbance, the extended 

period of hypoxic and anoxic conditions that affected creek fishes was a press disturbance. 

Thus, a press response might be expected from the creek fish assemblages. 

 In addition, interactions between disturbances, or between disturbances and ‘normal’ 

fluctuations must also be considered (White and Jentsch 2001). For example, normal seasonality 

was found more influential on coral reef fish abundances than hurricanes (Letourneur et al. 1993, 

Adams 2001, Adams and Ebersole 2004). In this study, initial indications were that normal 

seasonal patterns continued after the immediate post-hurricane fluctuations: total abundance and 

species richness recovered within three weeks of the hurricane, suggesting a pulse response. To 
20

some extent, fishes are able to move out of impacted areas, and to return when conditions 

improve. This is especially true for fishes with mobile behavior, and less true of sedentary of 

site attached fishes. Moreover, some fishes may have behavioral adaptations to poor conditions 

such as those present after hurricanes. For example, dissolved oxygen levels in estuarine 

wetland and creek habitats are frequently >1.0 mg/L (Smith and Able 2003, this study), and 

some species have behavioral and physiological adaptations to these conditions (Smith and Able 

2003). 

 However, observations of aquatic surface respiration, a sign of physiological stress from 

low DO, by fishes during post-storm sampling, and a leveling off of the recovery trajectory in 

October sampling (2 months post-hurricane) suggest physiological stress, mortality, or long-term 

emigration due to extended duration of low DO. In addition, sampling in October 2004, and in 

spring 2005 (not reported in this manuscript) suggest a possible lag in recovery (lower than 

expected abundance of most species and lower species richness), thus indicating a press 

response. In addition, disturbance effects differ between natural (e.g., hurricanes) and 

anthropogenic (e.g., freshwater flow alterations) disturbances (Mackey and Currie 2001). 

Moreover, anthropogenic disturbances may interact with natural disturbances or alter system 

responses (White and Jentsch 2001). Continued sampling for one year after hurricane Charley 

(funded by a grant from National Science Foundation) will provide the data necessary to 

determine: whether normal seasonal patterns have been influenced by the hurricane (i.e., provide 

multiple years of pre- and post-hurricane data); if the ecological response was pulse (quick 

recovery) or press (longer recovery); and the effect of habitat degradation on fish assemblage 

response to the hurricane. 
21

Management Applicability 

Given the increasing populations in many coastal regions, incorporation of anthropogenic 

impacts should be considered for any appropriately-scaled research or assessments. It is likely 

that anthropogenic changes will impact habitat types differently, and thus impact fish life stages 

differently. If resource managers are going to make predictions about the response of coastal 

ecosystems to anthropogenic changes, the relative effects of anthropogenic changes on different 

habitats and their associated fishes must be incorporated into their models. This study has 

underscored the impact of freshwater flow alterations on estuarine habitats and associated 

species, and thus the importance of addressing this type of habitat degradation in management 

strategies. 

 The ability to evaluate the success of habitat restoration projects is of both local and 

global significance due to widespread habitat loss and diversion of freshwater, and the associated 

decline in estuarine health. As human populations in coastal areas continue to increase, demands 

on freshwater resources and coastal habitats will increasingly alter the quantity, quality, and 

location of freshwater flow, resulting in further degradation of oligohaline systems that provide 

habitats vital to estuarine and marine species. Quantification of the relationships between flow 

regimes and habitat quality of oligohaline habitats is essential to long-term management of these 

areas. 

 Oligohaline marshes provide a vital link between terrestrial and estuarine systems. As 

such, strategies for management of upland habitats must consider the implications of 

management actions on estuarine habitats and species. By defining the effects of freshwater flow 

alterations on mangrove creek habitats in Charlotte Harbor, this research has provided managers 

with information needed to improve management plans. In addition, the findings of this research 
22

should help guide Florida Department of Environmental Protection’s restoration projects in the 

Charlotte Harbor Aquatic and State Buffer Preserve. How the restoration is implemented will 

influence how the sheet flow of fresh water over these areas will impact downstream areas, 

including mangrove and marsh habitats used as nurseries by estuarine fishes. 

 

Literature Cited 

Adams, A.J. 2001. Effects of a hurricane on two assemblages of coral reef fishes: multiple-year 

 analysis reverses a false snapshot interpretation. Bull. Mar. Sci. 69(2):341-356. 

Adams, A.J. and J.P. Ebersole. 2004. Resistance of coral reef fishes in back reef and lagoon 

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Beach, D. 2002. Coastal Sprawl: The Effects of Urban Design on Aquatic Ecosystems in the 

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Beever, J. and B. Chamberlin. 2002. Freshwater inflow to Matlacha Pass performance measures 

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Courtenay Jr., W.R. and J.D. Williams. 1992. Dispersal of exotic species from aquaculture 

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Geary, B.W., J.R. Rooker, and J.W. Webb. 2001. Utilization of saltmarsh shorelines by newly 
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 settled sciaenids in a Texas estuary Gulf Carib. Res. 13:37-49. 

Glasby T.M. and A.J. Underwood. 1996. Sampling to differentiate between pulse and press 

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Lake, P.S. 2000. Disturbance, patchiness, and diversity in streams. J. N. Am. Benthol. Soc. 

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Letourneur, Y., M. Harmelin-Vivien, and R. Galzin. 1993. Impact of hurricane Firinga on fish 

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Lin, J. and J.L. Beal. 1995. Effects of mangrove marsh management on fish and decapod 

 communities. Bull. Mar. Sci. 57(1): 193-201. 

Mackey, R.L. and D.J. Currie. 2001. The diversity-disturbance relationship: is it generally strog 

 and peaked? Ecology. 82(2):3479-3492. 

McMichael, R.H., Jr., K.M. Peters, and G.R. Parsons. 1989. Early life history of the snook, 

Centropomus undecimalis, in Tampa Bay, Florida. Northeast Gulf Sci. 10(2):113-125. 

Montague, C.L. and J.A. Ley. 1993. A possible effect of salinity fluctuation on abundance of 

 benthic vegetation and associated fauna in northeastern Florida Bay. Estuaries. 16(4): 

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Morales-Gómez, A.A., R. Chávez-López, J. Franco-López, M.S. Peterson and N.J. Brown-

 Peterson (in review) Ecology of the Mayan cichlid, Cichlosoma urophthalmus Günther, 

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Page, L.M. and B.M. Burr. 1991. A field guide to freshwater fishes of North America north of 

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Peters, K.M., R.E. Matheson, Jr., and R.G. Taylor. 1998. Reproduction and early life history of 

 common snook, Centropomus undecimalils (Bloch), in Florida. Bull. Mar. Sci. 

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Poulakis, G.R., D.A. Blewett, and M.E. Mitchell. 2003. The Effects of Season and Proximity 

 to Fringing Mangroves on Seagrass-Associated Fish Communities in Charlotte Harbor, 

 Florida. Gulf Mexico Sci. 21(2):171-184. 

Poulakis, G.R., J.M. and D.S. Taylor. 2002. Habitat use by fishes after tidal reconnection of an 

 impounded estuarine wetland in the Indian River Lagoon, Florida (USA). Wetlands Ecol. 

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Robbins, C.R., G.C. Ray, and J. Douglass. 1986. A field guide to Atlantic coast fishes of North 

 America. Houghton Mifflin Co. Boston. 352pp. 

Ross, S.T. 1991. Mechanisms structuring stream fish assemblages: are there lessons from 

 introduced species? Environmental Biology of Fishes 30:359-368. 

Sklar, F.H. and J.A. Browder. 1998. Coastal environmental impacts brought about by alterations 

 in freshwater flow in the Gulf of Mexico. Environ. Manag. 22(4): 547-562. 

Smith, K.J. and K.W. Able. 2003. Dissolved oxygen dynamics in salt marsh pools and its 

 potential impacts of fish assemblages. Mar. Ecol. Prog. Ser. 258:223-232. 

Sokal, R.R. and F.J. Rohlf. 1995. Biometry. Tjird Ed. W.H. Freeman and Co. New York. 887pp. 

White, P.S. and A. Jentsch. 2001. The search for generality in studies of disturbance and 

 ecosystem dynamics. Progr. Bot. 62:399-450. 

Wilkinson, L., G. Blank, C. Gruber. 1996. Desktop data analysis with Systat. Prentice Hall. NJ. 
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 798pp. 

Wyda, J. C., L. E. Deegan, J. E. Hughes, and M. J. Weaver. 2002. The response of fishes to 

 submerged aquatic vegetation complexity in two ecoregions of the Mid-Atlantic bight: 

 Buzzards Bay and Chesapeake Bay. Estuaries 25(1):86-100. 
26

List of Figures 

Figure 1. Locations of study sites along the eastern shoreline of Charlotte Harbor, Florida. 

Figure 2. Mean (+/- SE) salinities of study creeks and zones by year and month. Only 

 surface values are shown for graphical clarity. Salinity was recorded during each 

 sample. N = 5 for each creek-zone-month. 

Figure 3. Mean (+/- SE) temperatures (oC) of study creeks and zones by year and month. 

 Only surface values are shown for graphical clarity. Temperature was 

 recorded during each sample. N = 5 for each creek-zone-month. 

Figure 4. Mean (+/- SE) dissolved oxygen (mg/L) of study creeks and zones by year and 

 month. Only surface values are shown for graphical clarity. Dissolved oxygen 

 was recorded during each sample. N = 5 for each creek-zone-month. 

Figure 5. Mean (+/- SE) surface salinity (PPT) by creek and zone. 

Figure 6. Mean (+/- SE) surface (◊) and bottom (□) temperatures by creek. Only the creek 

 factor was significant (Table 1), so is the only factor shown. 

Figure 7. Mean (+/- SE) surface (◊) and bottom (□) dissolved oxygen by creek (A) and zone 

 (B). Only the creek and zone factors were significant (i.e., there was no 

 interaction effect, Table 1), so are the only factors shown. 

Figure 8. Mean total abundance (A) and mean total species richness (B) by creek. 

Figure 9. Dendrogram of results of hierarchical cluster analysis (average linkage method, 

 Euclidean distance) of species density and frequency of occurrence by creek and 

 zone. The first two letters in the abbreviations are creek identifiers: CC = Culvert 

 Creek, NS = North Silcox, SS = South Silcox, YP = Yucca Pen. The third letter 

 in the abbreviations is a zone identifier: L = Lower, M = Middle, U = Upper. 
27

Figure 10. Total abundance of freshwater species (all species combined) by creek, zone, and 

 month. 

Figure 11. Total abundance and frequency of occurrence for freshwater species. 

Figure 12. Mean density (+/- SE) of juvenile Centropomus undecimalis by creek, zone, and 

 month. 

Figure 13. Length frequencies of juvenile Centropomus undecimalis by creek. Data pooled 

 across zones and sample periods. 

Figure 14. Mean lengths (+/- SE) of juvenile snook by creek and zone. 

Figure 15. Mean density (+/- SE) of juvenile Sciaenops ocellatus by creek, zone, and 

 month. 

Figure 16. Length frequencies of juvenile Sciaenops ocellatus by creek. Data pooled across 

 zones and sample periods. 

Figure 17. Mean length (+/- SE) of juvenile Sciaenops ocellatus by creek and zone. 

Figure 18. Summary of short-term effects of hurricane Charley. Mean total abundance (+/- 

 SE) and mean total species richness (+/- SE) by creek and sample period prior to 

 and after hurricane Charley. Sampling was interrupted by the hurricane, so the 

 degraded creeks (Culvert Creek and Yucca Pen) were not sampled. Immediate 

 post-hurricane sampling was limited to North Silcox and South Silcox since there 

 were immediate pre-hurricane data from these creeks. 
Figure 1. 

‘Natural’ creeks 

‘Degraded’ creeks

Charlotte Harbor 
29

Figure 2. 
30

Figure 3. 
31

Figure 4. 
32

0

5

10

15

20

25

Lower Middle Upper

Creek Zone

Mean Salinity (ppt) +/- SE

Culvert Creek

North Silcox

South Silcox

Yucca Pen

Figure 5. 
33

23

23.5

24

24.5

25

25.5

26

26.5

27

27.5

Culvert Creek North Silcox South Silcox Yucca Pen

Creek

Mean Temperature (oC) +/- SE

Figure 6. 
34

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Culvert Creek North Silcox South Silcox Yucca Pen

Creek

Mean Dissolved Oxygen (mg/L) +/- SE

A

0

0.5

1

1.5

2

2.5

3

3.5

4

Lower Middle Upper

Creek Zone

Mean Dissolved Oxygen (mg/L) +/- SE

B

Figure 7. 
35

0

2

4

6

8

10

12

14

16

February April June August October December February April June August

Year/Month

Mean No. Fish/m2

Culvert Creek

Yucca Pen

N Silcox Creek

S Silcox Creek

2003 2004

A

0

5

10

15

20

25

February April June August October December February April June August

Year/Month

Mean No. Species/100m2 +/- SE

Culvert Creek

Yucca Pen

N Silcox Creek

S Silcox Creek

2003 2004

B

Figure 8. 
36

Figure 9. 
37

Figure 10. 

0

5

10

15

20

25

30

February

April

June

August

October

December

February

April

June

August

October

Year/Month

Total Abundance
38

Figure 11. 

Freshwater Species

0

10

20

30

40

50

60

70

sunfish sp

lm bass

minnow sp

bass sp

gar sp

dace sp

florida gar

longnose gar

yellowbullhe

Common Name

Total Abundance/Occurrence

Total Abundance

Frequency of Occurrence
39

Figure 12. 
40

Figure 13. 
41

Figure 14. 

0

20

40

60

80

100

120

140

Lower Middle Upper

Creek Zone

Mean Standard Length (mm) +/- SE

Culvert Creek

North Silcox

South Silcox
42

Figure 15. 
43

Figure 16. 
44

Figure 17. 

0

10

20

30

40

50

60

70

80

Lower Middle Upper

Creek Zone

Mean Standard Length (mm) +/- SE

Culvert Creek

North Silcox

South Silcox
45

0

2

4

6

8

10

12

14

16

18

February

April

June

August

October

December

February

April

June

August

13

14

17

18

19

October

Year/Month

Mean No. Fish/m2 +/- SE

Culvert Creek

North Silcox

South Silcox

Yucca Pen

Days post-hurricane

2003 2004

A

0

5

10

15

20

25

February

April

June

August

October

December

February

April

June

August

13

14

17

18

19

October

Year/Month

Mean No. Species/100m2 +/- SE

Culvert Creek

North Silcox

South Silcox

Yucca Pen

2003 2004

Days post-hurricane

B

Figure 18. 
Table 1. Summary of two-way ANOVA results of effects of Creek (N = 

4) and Zone (N = 3) on Salinity, Temperature, and Dissolved Oxygen. 

A) Salinity

Source SS df MSE F p

Creek 3418.255 3 1139.418 13.427 < 0.001

Zone 3142.511 2 1571.256 18.515 < 0.001

Creek X Zone 1070.724 6 178.454 2.103 > 0.05

Error 45401.69 535 84.863

B) Temperature

Source SS df MSE F p

Creek 210.917 3 70.306 5.047 < 0.05

Zone 27.065 2 13.533 0.971 > 0.1

Creek X Zone 16.597 6 2.766 0.199 > 0.1

Error 7369.171 529 13.93

C) Dissolved Oxygen

Source SS df MSE F p

Creek 130.045 3 43.348 12.958 < 0.001

Zone 35.486 2 17.743 5.304 < 0.01

Creek X Zone 18.953 6 3.159 0.944 > 0.1

Error 1772.959 530 3.345
Table 2. Summary of abundance and occurrence of species captured in Charlotte Harbor study creeks. See Figure 1 for creek locations. Species listed by rank order 

Abundance = total abundance summed across all samples. Frequency = total number of samples in which the species was recorded (N = 574).

Natural Creeks Degraded Creeks

North Silcox South Silcox Culvert Creek Yucca Pen Total 

Abundance

Fre

Species Abundance Frequency Abundance Frequency Abundance Frequency Abundance Frequency 

Lucania parva 28397 142 37889 138 3372 46 3881 72 73539 

Menidia peninsulae 27734 142 13513 136 2302 79 7839 99 51388 

Gambusia holbrooki 16270 99 3706 67 2044 47 2439 47 24459 

Poecillia latipinna 8071 93 5534 84 589 24 337 26 14531 

Eucinostomus spp. 1363 49 3507 80 2261 52 3293 54 10424 

Menidia spp. 2895 82 2515 91 273 29 608 43 6291 

Eucinostomus harengula 1327 65 1317 90 300 42 592 36 3536 

Lagodon rhomboides 2141 51 959 76 223 16 177 27 3500 

Microgobius gulosus 1155 90 1411 110 183 37 233 57 2982 

Centropomus undecimalis 497 55 970 80 864 71 259 23 2590 

Anchoa spp. 2221 6 316 8 0 0 0 0 2537 

Micropogonias undulatus 681 10 93 6 266 5 306 8 1346 

Cyprinodon variegatus 588 78 486 61 53 15 99 15 1226 

Sciaenops ocellatus 361 39 521 34 96 21 1 1 979 

Callinectes sapidus 207 72 361 135 117 56 137 76 822 

Diapterus plumieri 316 53 291 51 122 28 65 15 794 

Leiostomus xanthurus 224 21 436 32 33 6 71 8 764 

Fundulus confluentus 494 38 94 21 80 8 55 7 723 Farfantepenaeus duorarum 213 31 255 53 44 13 8 5 520 

Fundulus grandis 185 33 159 35 69 17 14 7 427 

Adinia xenica 110 8 279 12 32 5 0 0 421 

Sciaenidae spp juvenile 39 5 172 10 27 1 3 3 241 

Eucinostomus gula 66 5 73 11 43 10 11 5 193 Fundulus heteroclitus 109 13 53 11 22 11 9 6 193 Lucania goodei 36 12 1 1 1 1 128 16 166 

Cichlasoma urophthalmus 4 3 29 14 112 14 14 4 159 

Syngnathus louisianae 37 17 115 47 4 4 3 3 159 

Fundulus majalis 122 23 3 1 3 3 0 0 128 

Strongylura notata 17 15 73 34 4 2 25 8 119 

Syngnathus spp. 28 20 69 37 6 3 6 5 109 Gobiosoma robustum 23 10 29 13 15 11 13 7 80 
Lepomis spp. 19 10 25 12 17 8 5 2 66 

Mugil spp. juvenile 25 6 16 8 10 5 6 5 57 Achirus lineatus 13 6 6 5 13 9 19 5 51 Jordanella floridae 28 12 0 0 0 0 22 5 50 

Menidia beryllina 0 0 7 3 2 1 28 1 37 

Oreochromis mossambicus 15 9 18 5 0 0 0 0 33 Fundulus spp. 27 7 3 3 0 0 1 1 31 

Archosargus probatocephalus 9 5 16 13 2 2 0 0 27 Oligoplites saurus 3 1 8 5 0 0 16 5 27 Opsanus beta 11 8 14 6 0 0 0 0 25 Trinectes maculatus 0 0 22 10 2 2 0 0 24 Micropterus spp. 0 0 0 0 8 5 13 7 21 

Strongylura marina 8 5 0 0 2 2 10 3 20 

Gobiosoma spp. 13 1 6 3 0 0 0 0 19 

Mugil cephalus 3 2 12 9 4 4 0 0 19 

Sphoeroides nephelus 4 3 0 0 8 5 6 4 18 

Syngnathus scovelli 0 0 15 11 1 1 0 0 16 

Lepisosteus oculatus 7 5 2 2 3 2 3 3 15 

Cyprinidae spp. 0 0 0 0 8 2 6 1 14 

Cynoscion nebulosus 5 3 7 4 0 0 0 0 12 

Hemichromis bimaculatus 5 3 3 2 2 1 0 0 10 

Fundulus similis 3 1 4 3 2 1 0 0 9 

Elops saurus 3 1 4 3 0 0 0 0 7 

Serranidae spp juvenile 0 0 0 0 6 1 0 0 6 

Gobionellus smaragdus 0 0 0 0 4 2 0 0 4 Lutjanus griseus 1 1 2 2 1 1 0 0 4 Megalops atlanticus 3 3 0 0 0 0 0 0 3 Strongylura timucu 0 0 3 3 0 0 0 0 3 Bothidae spp juvenile 0 0 1 1 0 0 1 1 2 

Lepisosteus spp. 1 1 0 0 1 1 0 0 2 

Tylosurus crocodilus 0 0 0 0 2 1 0 0 2 Ameiurus natalis 0 0 0 0 0 0 1 1 1 Cichlidae spp juvenile 1 1 0 0 0 0 0 0 1 

Dormitator maculatus 0 0 0 0 1 1 0 0 1 

Lepisosteus osseus 0 0 0 0 0 0 1 1 1 

Lepisosteus platyrhincus 0 0 1 1 0 0 0 0 1 Mugil curema 0 0 0 0 0 0 1 1 1 
Myrophis punctatus 1 1 0 0 0 0 0 0 1 

Portunus spp 0 0 0 0 0 0 1 1 1 

Rhinichthys spp. 0 0 0 0 0 0 1 1 1 

Sphyraena barracuda 0 0 0 0 1 1 0 0 1 Synodus foetens 1 1 0 0 0 0 0 0 1 

Triglidae spp. 1 1 0 0 0 0 0 0 1 

Gobiosoma bosci 0 0 0 0 0 0 0 0 0 Total Abundance 96141 75424 13660 20767 205992* R = Resident, T = Transient, J = Juvenile, F = Freshwater, N = Non-native. Designations based on this study, Robins et al. (1986), and Page and Burr (1991). 
Table 3. Summary of occurrence of the most common freshwater and non-native fish species. 

Months of 

Occurrenceb Salinity (ppt)c

Species Classificationa F A J Au O D Min Max Mean

Ameirus natalis F √ 0.1 0.1 - 

Cyprinidae F √ √ 0 7.8 2.6

Dormitator maculatus F √ 7.5 7.5 -

Jordanella floridae F √ √ √ √ 0.1 9.5 2.1

Lepisosteus osseus F √ 32.2 32.2 0

Lepisosteus platyrhincus F √ 12.1 12.1 - 

Lepisosteus spp F √ 4.2 25.9 15.1

Lepistosteus oculatus F √ √ √ 0.8 22.1 6.2

Lepomis spp. F √ √ √ 0.1 13.4 3.51

Micropterus spp. F √ √ √ √ √ √ 0.1 15.9 5.93

Rhinichthys spp. F √ 0.1 0.1 -

Cichlasoma urophthalmus N √ √ √ √ √ √ 1.1 26.6 13

Hemichromis bimaculatus N √ √ 1.1 21.4 5.33

Oreochromis mossambicus N √ √ √ √ 0.6 20.4 4.13 a

 F = Freshwater, N = Non-native, based upon Page and Burr (1991).

b

 F = February, A = April, J = June, Au = August, O = October, D = December. Data pooled across 

years (2003 and 2004) and creeks.

c

 Data pooled across years (2003 and 2004) and creeks.
Table 4. Summary of abundance, occurrence, and densities of non-native cichlids in estuarine mangrove study creeks in 

Charlotte Harbor, Florida. Total Abundance is summed across all samples; Frequency of Ocurrence is the total number 

of samples in which the species was captured; Density is mean number fish/100m2

 (SE).

Natural Creeks Degraded Creeks

Species North Silcox South Silcox Yucca Pen Culvert Creek

Cichlasoma urophthalmus

Total Abundance 4 29 14 112

Frequency of Occurrence 3 14 4 14

Density 0.023 (0.014) 0.149 (0.048) 0.085 (0.055) 0.958 (0.393)

Hemichromis bimaculatus

Total Abundance 5 3 0 0

Frequency of Occurrence 3 2 0 0

Density 0.022 (0.014) 0.013 (0.01) 0 0

Oreochromis mossambicus

Total Abundance 13 17 0 0

Frequency of Occurrence 7 4 0 0

Density 0.074 (0.032) 0.093 (0.069) 0 0

Tilapia spp

Total Abundance 2 1 0 0

Frequency of Occurrence 2 1 0 0

Density 0.011 (0.007) 0.006 (0.006) 0 0
Table 5. Summary of Kruskal-Wallis tests of Centropomus undecimalis densities by creek and zone.

A) Comparison of densities by creek. Densities 

were different by creek: H = 44.46, p < 0.001, 

df = 3.

Mean 

Creek Rank Sum Density SE

South Silcox 48379 0.0478 0.0178

Culvert Creek 43749 0.0643 0.0188

North Silcox 42949.5 0.0265 0.0074

Yucca Pen 29373.5 0.0147 0.006

B) Comparison of densities by zone within creeks. Values are mean 

(standard error).

Zone

Creek Lower Middle Upper H* p

South Silcox

0.022 

(0.008)

0.034 

(0.013)

0.091 

(0.054) 5.136 >0.05

Culvert Creek

0.076 

(0.027)

0.027 

(0.009)

0.09 

(0.049) 0.583 >0.1

North Silcox

0.017 

(0.0043)

0.0137 

(0.004)

0.049 

(0.022) 3.652 >0.01

Yucca Pen

0.041 

(0.017)

0.003 

(0.001) 0 26.489 <0.001

Snook Density by Creek and Zone

0

0.2

0.4

0.6

0.8

1

1.2

Zone

Mean No. Fish/m2
Table 6. Summary of two-way ANOVA on effects of Creek (N = 4) and 

Zone (N = 3) on log-transformed standard length of snook, 

Centropomus undecimalis . Yucca Pen was not included because snook 

were absent from upper and rare in middle zones.

Source SS df MSE F p

Creek 7.053 2 3.527 59.01 < 0.001

Zone 16.069 2 8.034 134.433 < 0.001

Creek X Zone 6.269 4 1.567 26.225 < 0.001

Error 126.163 2111 0.06
Table 7. Summary of Kruskal-Wallis tests of Sciaenops ocellatus densities by creek and zone.

A) Comparison of densities by creek. Densities 

were different by creek: H = 8.41, p < 0.05, df 

= 3.

Mean 

Creek Rank Sum Density SE

North Silcox 47597 0.0156 0.004

South Silcox 44996 0.0246 0.0078

Culvert Creek 36598 0.0059 0.0022

Yucca Pen 35260 0.0113 0.0074

B) Comparison of densities by zone within creeks. Values are mean 

(standard error).

Zone

Creek Lower Middle Upper H* p

North Silcox

0.026 

(0.01)

0.016 

(0.006)

0.004 

(0.002) 4.838 >0.1

South Silcox

0.05 

(0.021)

0.016 

(0.007)

0.006 

(0.003) 2.738 >0.1

Culvert Creek

0.012 

(0.006)

0.004 

(0.002)

0.002 

(0.001) 2.354 >0.1

Yucca Pen

0.027 

(0.022)

0.006 

(0.004) 0 15.885 <0.001

Table 8. Summary of two-way ANOVA on effects of Creek (N = 4) and 

Zone (N = 3) on log-transformed standard length of red drum, 

Source SS df MSE F p

Creek 0.09 2 0.045 1.29 > 0.1

Zone 2.363 2 1.181 33.941 < 0.001

Creek X Zone 1.404 4 0.351 10.085 < 0.001

Error 28.749 826 0.035
The Charlotte Harbor National Estuary Program is a partnership of citizens, elected 

officials, resource managers and commercial and recreational resource users working to 

improve the water quality and ecological integrity of the greater Charlotte Harbor 

watershed. A cooperative decision-making process is used within the program to address 

diverse resource management concerns in the 4,400 square mile study area. Many of 

these partners also financially support the Program, which, in turn, affords the Program 

opportunities to fund projects such as this. The entities that have financially supported 

the program include the following: 

U.S. Environmental Protection Agency 

Southwest Florida Water Management District 

South Florida Water Management District 

Florida Department of Environmental Protection 

Florida Coastal Zone Management Program 

Peace River/Manasota Regional Water Supply Authority 

Polk, Sarasota, Manatee, Lee, Charlotte, DeSoto and Hardee Counties 

Cities of Sanibel, Cape Coral, Fort Myers, Punta Gorda, North Port, Venice and Fort 

Myers Beach 

and the Southwest Florida Regional Planning Council.