Transcript Slide 1

The Effect of Freshwater Inflow on the Spatial and Temporal Distribution of
Ichthyoplankton and Gelatinous Zooplankton in Estero Bay, Florida
James Evans1, Jennifer Nelson1, Bethany Bachelor1, Scott Burghart2, Greg Tolley1
Introduction
1Florida
2500
Total inflow (cfs)
1 month lag
1500
1000
500
80000
60000
40000
182.50
1/1
548
12/31
273.75
4/1
365.00
7/1
Figure 7. A. mitchilli Egg Density
June 2006
0.551
0.522
0.493
0.464
0.435
0.406
0.377
0.348
0.319
0.29
0.261
0.232
0.203
0.174
0.145
0.116
0.087
0.058
0.029
0
Figure 8. Eutima sp. Density
June 2006
References
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22
Baier, C.T. and J.E. Purcell. 1997. Trophic interactions of chaetagnaths, larval fish, and zooplankton in the South Atlantic Bight. Marine
Ecology Progress Series 146:43-53
20
Harengula jaguana
Hippocampus erectus
Cynoscion arenarius
Bairdiella chrysoura
Lagodon rhomboides
Membras martinica
Cynoscion nebulosus
Anchoa mitchilli
Syngnathus louisianae
Chasmodes saburrae
Figure 9. Ichthyoplankton Density-Weighted
Mean Salinity of Capture
36
Browder, J.A. 1991. Watershed management and the importance of freshwater flow to estuaries, p.7-22. In S.F. and P.A. Clark (eds.).
Proceedings, Tampa Bay area Scientific Information Symposium 2, 1991 February 27-March 1, Tampa, FL. TEXT, Tampa, Florida
Flannery, M.S., E.B. Peebles, and R.T. Montgomery. 2002. A percent-of-flow approach for managing reductions of freshwater inflows from
unimpounded rivers to Southwest Florida estuaries. Estuaries 25:1318-1332
North, E.W. and E.D. Houde. 2004. Distribution and transport of bay anchovy (Anchoa mitchilli) eggs and larvae in Chesapeake Bay.
Estuarine Coastal and Shelf Science 60:409-429
34
Tsou, T.T and R.E. Matheson, Jr. 2002. Seasonal changes in the nekton community of the Suwannee River estuary and the potential impacts
of freshwater withdrawal. Estuaries 25:1372-1381
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30
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26
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Acknowledgements
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siphonophores
2.299
2.178
2.057
1.936
1.815
1.694
1.573
1.452
1.331
1.21
1.089
0.968
0.847
0.726
0.605
0.484
0.363
0.242
0.121
0
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Bougainvillia sp.
Dry June
(2006)
40
38
36
34
32
30
28
26
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12
10
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6
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Figure 6. Eutima sp. Density
June 2005
Medusa, Eutima sp. Density
June 2006
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Sagitta tenuis
Anchoa mitchilli Egg Density
June 2006
Future work should be conducted to look at the effects of freshwater flow on the trophic relationships between
ichthyoplankton and gelatinous zooplankton in Estero Bay.
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Ferrosagitta hispida
Figure 5 A. mitchilli Egg Density
June 2005
0.0874
0.0828
0.0782
0.0736
0.069
0.0644
0.0598
0.0552
0.0506
0.046
0.0414
0.0368
0.0322
0.0276
0.023
0.0184
0.0138
0.0092
0.0046
0
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Liriope tetraphylla
9.3689
8.8758
8.3827
7.8896
7.3965
6.9034
6.4103
5.9172
5.4241
4.931
4.4379
3.9448
3.4517
2.9586
2.4655
1.9724
1.4793
0.9862
0.4931
0
Medusa, Eutima sp. Density
June 2005
It is well known that Chaetagnaths and other gelatinous zooplankton are carnivores that feed on fish larvae and
also compete with them for prey (Baier and Purcell 1997). High abundances of gelatinous predators were recorded
during this study raising concerns about their potential impact on ichthyoplankton abundances through predation or
competition for resources.
During times of low freshwater inflow, gelatinous predators increased in abundance and moved into the bay’s
tributaries (Fig. 8). Reduced freshwater inflow to Estero Bay could potentially increase predation rates.
Figure 4. Cumulative Flow
Bathygobius soporator
Wet June
(2005)
40
38
36
34
32
30
28
26
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12
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8
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2
0
Anchoa mitchilli Egg Density
June 2005
Figure 3. Total Flow
Eutima sp.
Salinity
June 2005
547.50
1/1
Date
Date
Table 2. Likely Spawning Locations
456.25
10/1
Obelia sp.
456
10/1
Syngnathus scovelli
Syngnathus floridae
Chloroscombrus chrysurus
7/1
Medusa Unidentified Species e
365
Schyphozoan ephyrae
274
4/1
Mnemiopsis mccradyi
Where U is organism density (no. m-3) and S is the mean water-column salinity during
plankton net deployment.
42%
100000
0
Contour plots for all of the water quality parameters and the most
abundant taxa were used to assess temporal and spatial trends using Surfer
8 (Golden Software).
SU = Σ (S·U)
ΣU
The four-fold increase in gelatinous zooplankton abundances in 2006 appears to be related to increased salinities in
the study area as a result of low flow conditions and isolated bloom events. The largest bloom events occurred in
June 2006 where Clytia densities reached 1,201 m-3 and October 2006 where Sagitta tenuis densities reached 86
m-3.
120000
0
Salinity
June 2006
Density-weighted salinity of capture (SU) -the central salinity tendency for organism density- was calculated as:
Declines in ichthyoplankton density occurring in association with the beginning of the wet season may have been a
function of reduced spawning activity in some species, and/or advection outside the study area as a result of
increased flow. Flannery et al (2002) found that in Tampa Bay, total numbers of estuarine-resident and estuarinedependent organisms such as the bay anchovy and sand seatrout decreased during periods of increased inflow.
20000
Water stage data were converted to flow by the USGS and reported as
cubic feet per second (cfs). Flow data were converted to daily averages and
total indexed flow was estimated by summing the daily values for the Estero
River, Spring Creek, Imperial River, and Ten Mile Canal.
A Kruskal-Wallis test was used to look at differences in annual abundance.
Spatial and temporal distribution of ichthyoplankton in Estero Bay appears to be primarily influenced by freshwater
inflow resulting in changes to the salinity regime and seasonal spawning patterns. The one-month lag in density in
2006 compared to 2005 for many of the organisms likely reflects the delayed onset of the wet season.
2005
2006
140000
2000
183
1/1
Flow data was obtained from the USGS continuously monitoring waterstage stations located at the north and south branches of the Estero River,
Spring Creek, the Imperial River, and Ten-mile Canal (a major tributary of
Mullock Creek) during the study period.
Discussion
160000
2005
2006
At the end of the tow, the net was suspended vertically and rinsed using
ambient water to wash zooplankton into the cod-end jar. Samples were
preserved by adding 50 ml of formalin and placed in a cooler.
Water quality was recorded at each station at the end of each plankton net
deployment. Temperature, salinity, and dissolved oxygen profiles were
recorded using a YSI multi-parameter sonde.
Density weighted salinity of capture (Su ) for gelatinous zooplankton demonstrated that the hydromedusae Eutima
sp. and Clytia sp. as well as the ctenophore Mnemiopsis maccradyi had distributions centered at salinities of 25-30
psu and the chaetagnaths Ferrosagitta hispida and Sagitta tenuis were centered at 33 psu (Fig. 10).
Ichthyoplankton represented 4% of the total zooplankton catch, representing 48 species dominated by eggs of
anchovies, drums, unidentified percomorph fishes, and herrings as well as by the larvae of anchovies, gobies,
skilletfish, blennies, and herrings. Anchoa mitchilli were the most abundant anchovy collected. Gobies of the
genus Gobiosoma were more abundant than those of the genus Microgobius. The Florida blenny Chasmodes
saburrae was the most abundant, identifiable blenny. Gulf pipefish Syngnathus scovelli; sand seatrout
Cynoscion arenarius; spotted seatrouts Cynoscion nebulosus; kingfishes of the genus Menticirrhus; and the
soles Achirus lineatus and Trinectes maculates were also common.
Plankton was collected using a 500-μm Nitex mesh plankton net equipped with a flowmeter and a 1-liter cod
end jar.
Each sampling deployment consisted of a three-step oblique tow that
divided the net’s fishing time equally between bottom, mid-depth, and surface
waters. Tow duration and speed were standardized 5 min and 1.0-1.5 m/s,
respectively.
Plankton samples were delivered to the University of South Florida Marine
Laboratory in St. Petersburg, FL where they were identified to the lowest
practical taxon and fishes were classified according to their developmental
stage (i.e. prefelxion larvae, flexion larvae, postflexion larvae, juvenile, and
adult stages).
Gelatinous zooplankton densities varied both seasonally and interannually. Abundances were four times greater in
2006 than in 2005. Mnemiopsis maccradii exhibited peak densities in November 2005 following the passage of
hurricane Wilma while 2006 densities peaked in June, prior to the onset of the wet season. The hydromedusae
Clytia sp. varied greatly between years with 2005 densities remaining relatively low and 2006 abundances peaking
dramatically prior to the onset of the wet season in June. The chaetagnath Sagitta tenuis showed similar seasonal
patterns for both years with higher densities in 2006 than in 2005 with peak densities lagging one month behind
those in 2005.
Monthly water temperature was relatively consistent among stations and exhibited typical seasonal variation.
Mean salinity was lower and standard deviation higher at stations located in or near the tidal tributaries. On
average, the southern portion of the bay had higher mean salinities than the northern portion.
Trinectes maculatus
Zooplankton were collected monthly using oblique plankton tows at sixteen stations throughout Estero Bay
(Fig. 1) from January 2005 through December 2006 in the tributaries, open waters, and tidal passes during
flood tides.
Gelatinous zooplankton comprised 9% of the total catch and represented 18 species. Chaetagnaths and
hydromedusae were the most abundant gelatinous zooplankton collected, representing 99% of the total gelatinous
zooplankton catch. Sagitta tenuis and Ferrosagitta hispida were the most common chaetagnaths present in the
samples. Bougainvillia sp., Clytia sp., Eutima sp., Obelia sp. and an unidentifiable species were among the
hydromedusae that were commonly collected.
Total cumulative freshwater inflow was 42% higher in 2005 than in 2006 (Fig. 4). Freshwater inflow during the
study period generally reflected the annual fluctuation between wet and dry seasons typical of SW Florida;
however, the start of the wet season in 2006 lagged behind 2005 by 4–6 weeks (Fig. 3 & 4).
Lupinoblennius nicholsi
Oligoplites saurus
Achirus lineatus
Materials and Methods
Density-weighted salinity of capture (Su ) was used to provide an estimate of species center of distribution. The
majority of fish distributions were centered at salinities greater than 30 psu (Fig. 9).
Results
Clytia sp.
Table 1. Sample Site Locations
Egg density and the presence of early life stages (i.e. preflexion larval stage) were used to infer likely spawning
habitats for fishes (Table 2).
Zooplankton were collected monthly using oblique plankton tows at sixteen stations throughout Estero Bay,
Florida from January 2005 through December 2006 to determine the influence of freshwater inflow on
ichthyoplankton density, recruitment potential, and the presence of gelatinous predators. Samples were
collected from tidal passes, open bays, and three tributaries within the study area. Ichthyoplankton and
gelatinous zooplankton were identified to the lowest practical taxon and contour plots of species density were
analyzed to assess their spatial and temporal distributions. Total cumulative freshwater inflow to the estuary
was 42% higher in 2005 than in 2006. In general, zooplankton abundances were greater at stations with higher
salinities. Density-weighted salinity of capture was used to provide an estimate of species center of distribution.
A majority of the fish distributions were centered at salinities greater than 30 psu. Diversity of fishes was greater
near the passes to the Gulf of Mexico and lower near the tributaries. Ichthyoplankton abundances were greatest
in spring and summer with peak abundances occurring in March, coinciding with the spawning season for the
most abundant taxa. Gelatinous zooplankton abundances were higher in the summer with peak abundances
occurring in September 2005 and June 2006. There was significantly less ichthyoplankton collected baywide in
2006 than in 2005 (p<.0001); in contrast, gelatinous zooplankton abundances were four times greater in 2006
than in 2005. Results of this study will help water managers determine optimal freshwater flows for managing
aquatic resources in Estero Bay.
Gobiesox strumosus
Figure 1. Study Area
Abstract
Medusa Unidentified Species d
The primary objectives of this study were
to assess the effects freshwater inflow on
the relative density and distribution of
ichthyoplankton and gelatinous
zooplankton throughout Estero bay.
Diversity of fishes was greater near the passes to the Gulf of Mexico and lower near the tributaries. There was
significantly less ichthyoplankton collected bay wide in 2006 than in 2005 (p<.0001) with a general pattern of a one
month lag in density for 2006 as compared to 2005.
of South Florida, College of Marine Science, 140 7th Avenue South, St. Petersburg, Florida 33701-5016
Cumulative inflow (cfs)
Most estuarine dependent fishes exhibit
very regular seasonality in their use of
low salinity habitats (Flannery et al
2002).Management considerations must
include these seasonal components to
avoid impacts during spawning periods
or when juveniles are vulnerable to
predation or advection out of the estuary.
2University
Density-weighted
mean salinity of capture (psu)
Estero Bay is a small, shallow, bar-built estuary with a watershed of approximately 1,196 km2 located along the
southwest coast of Florida (Fig.1). Surface water enters the bay through five tributaries Hendry Creek, Mullock
Creek, the Estero River, Spring Creek, and the Imperial River located along the eastern portion of the Bay. Land
use changes throughout the watershed threaten to alter the timing and amount of freshwater delivered to the
estuary. These changes to the natural water regime can have unanticipated consequences to downstream
aquatic communities such as economically important finfish that depend on the estuary for habitat and
reproduction.
Gulf Coast University, Coastal Watershed Institute, 10501 FGCU Blvd South, Fort Myers, Florida 33965-6565
Density-weighted
mean salinity of capture (psu)
Increased human development pressure in coastal areas has the potential to change the delivery of freshwater
to estuaries. These changes can affect salinity gradients, productivity, and their associated biotic communities
(Browder 1991; Tsou and Matheson 2002). In southwest Florida, rainfall is seasonal with well defined wet and
dry seasons. Seasonal rain events often put large volumes of water into coastal tributaries in pulses. Increased
impervious coverage within watersheds can speed up the rate at which freshwater is delivered to the coast.
Results Continued
Figure 10. Gelatinous Zooplankton DensityWeighted Mean Salinity of Capture
This project was made possible by a grant from the South Florida Water Management District (SFWMD). I would like to thank Peter Doering
and Bob Chamberlain of the SFWMD for supporting the project. I would also like to thank Ernst Peebles and Ralph Kitzmiller at the University
of South Florida for processing and identifying the zooplankton samples; Erin Dykes and Lesli Haynes at the FGCU Marine Lab for their
logistical support during field sampling; and Mike Burns at the United States Geological Survey for providing flow data.