Biological Invasions 3

18 Pages·2001·0.68 MB·English

BiologicalInvasions3:51–68,2001.
©2001KluwerAcademicPublishers.PrintedintheNetherlands.
Modification of sediments and macrofauna by
an invasive marsh plant
T.S.Talley∗ &L.A.Levin∗∗
MarineLifeResearchGroup,ScrippsInstitutionofOceanographyLaJolla,CA92093-0218,USA;
∗Currentaddress:DepartmentofEnvironmentalScienceandPolicy,OneShieldsAve.,UniversityofCalifornia,
Davis,CA95616,USA;∗∗Authorforcorrespondence(e-mail:[email protected];fax:[phone])
Received31August2000;acceptedinrevisedform15January2001
Key words: Connecticut, habitat alteration, invasion, invertebrates, Juncus gerardii, New England, Phragmites
australis,Spartinapatens,tidalmarsh
Abstract
Invasivegrasseshaverecentlyalteredsaltmarshecosystemsthroughoutthenorthernhemisphere. Ontheeastern
seaboardoftheUSA,Phragmitesaustralishasinvadedbothbrackishandsaltmarshhabitats.Phragmitesaustralis
influence on sediments and fauna was investigated along a salinity and invasion-age gradient in marshes of the
lowerConnecticutRiverestuary. Typicalsalinitieswereabout19–24pptinSiteI,9–10pptinSiteIIand5–7ppt
in Site III. Strongest effects were evident in the least saline settings (II and III) where Phragmites has been
present the longest and exists in monoculture. Limited influence was evident in the most saline region (I) where
Phragmites and native salt marsh plants co-occur. The vegetation within Phragmites stands in tidal regions of
the Connecticut River generally exhibits taller, but less dense shoots, higher above-ground biomass, and lower
below-groundbiomassthandoestheun-invadedmarshflora.Therewerelowersedimentorganiccontent,greater
litter accumulation and higher sediment chlorophyll a concentrations in Phragmites- invaded than un-invaded
marshhabitat.Epifaunalgastropods(SuccineawilsoniandStagnicolacatascopium)werelessabundantinhabitats
where Phragmites had invaded than in un-invaded marsh habitat. Macro-infaunal densities were lower in the
Phragmites-invadedthanun-invadedhabitatsatthetwoleastsalinesites(IIandIII).Phragmitesstandssupported
more podurid insects, sabellid polychaetes, and peracarid crustaceans, fewer arachnids, midges, tubificid and
enchytraeid oligochaetes, and greater habitat-wide taxon richness as measured by rarefaction, than did the un-
invaded stands. The magnitude and significance of the compositional differences varied with season and with
site; differences were generally greatest at the oldest, least saline sites (II and III) and during May, when faunal
densities were higher than in September. However, experimental design and the 1-year study period precluded
clear separation of salinity, age, and seasonal effects. Although structural effects of Phragmites on salt marsh
faunasareevident, furtherinvestigationisrequiredtodeterminetheconsequencesoftheseeffectsforecosystem
function.
Introduction andcontributedtoacceleratedratesofinvaderspread
(Nichols et al. 1986; Crooks 1998). The rapid vege-
Plant invasions in estuaries are a growing problem tationchangeassociatedwithplantinvasionsprovides
(Posey 1988; Callaway and Josselyn 1992; Posey an opportunity to study the effects of plant presence
etal.1993).Habitatmodificationanddegradationhave or type on faunal communities. These effects may
increased the susceptibility of wetlands to invasion bedirect,suchasthroughalterationofhabitatstructure
52
(Peterson 1982; Summerson and Peterson 1984), or Phragmites, although this ‘aggressive genotype’ has
may be indirect as through shifts in hydrodynamic notyetbeenfound(Chambersetal.1999).
or deposition regimes (Fonseca et al. 1982; Peterson The spread of Phragmites throughout the marshes
etal.1984;Eckman1987,1990).Faunalcompositions of the lower Connecticut River estuary (Connecticut,
change when plants invade unvegetated habitat, for USA)mirrorsPhragmitesinvasionsoccurringinother
example, the invasion of Pacific mudflats by Atlantic wetlandsalongtheeasternseaboardandhasbeenboth
cordgrass (Spartina alterniflora) (Zipperer 1996) or rapid and extensive (Chambers et al. 1999). Areal
Japaneseeelgrass(Zosterajaponica)(Posey1988),or expansion has occurred at a rate of 1%yr−1 in saline
whenthecompositionofexistingvegetationchanges. marshes and 3%yr−1 in brackish marshes (Warren
Alterationofexistingvegetationstructurehasoccurred and Fell 1996). The pattern of spread is downstream
where the common reed grass (Phragmites australis, fromoligohalinetomoresalineareas, sothedistance
hereafter referred to as Phragmites) has invaded veg- betweenamongreflectsnotonlytheestuarinesalinity
etated tidal marsh along the eastern seaboard of gradient,butalsoagesinceinvasion.
theUS. Effects of Phragmites australis spread on salt
Invasionsaregenerallyrangeexpansionsoverlarge marsh structure and function are likely to be
spatial scales; in marine systems these may involve widespread.Above-groundalterationofcanopyarchi-
trans-oceanic expansion. The spread of Phragmites tecture (Windham and Lathrop 1999), flow and sed-
is unique in that it has occurred on smaller (within- iment deposition (Harrison and Bloom 1977; Roman
coastandwithin-estuary)scales.Phragmiteshasbeen 1978; Takeda and Kurihara 1988), as well as below-
afeatureofmarshesontheeasternseaboardoftheUS ground changes in substrate structure, detrital accu-
for at least 4000 years, but it was limited to upland mulation and sediment properties (Bart and Hartman
salt marsh borders and freshwater areas (Niering and 2000; Windham and Lathrop 1999) have been asso-
Warren 1980a; Warren and Fell 1995). Beginning ciatedwithPhragmitesinvasions.Theseenvironmen-
in the mid-1960s, however, invasions of Phragmites tal changes have been linked to alterations in trophic
into undisturbed, fully tidal brackish marshes were structure (Roman 1978; Wilcox and Meeker 1992;
recorded.Sincethen,monoculturesofPhragmiteshave Wainrightetal.2000;butseeFelletal.1998),nutrient
been displacing fresh, brackish and salt marsh plant cycling (Meyerson et al. 2000) and habitat usage by
communities(e.g.,Spartinaspp.,othermarshgrasses birds(Romanetal.1984;BenoitandAskins1999)and
andherbs)intheNewEnglandregion(WarrenandFell fish(WeinsteinandBalletto1999).Therehasbeenlittle
1995). focusonPhragmitesinfluenceonbenthicepifaunaland
Successful invasions depend upon both the prop- infaunalassemblages.Phragmites-inducedchangesin
erties of the invading species and the environmental above-andbelow-groundpropertieswouldbeexpected
conditionsoftherecipientsite(Orians1986;Ruizetal. toaltersediment-dwellingfauna(seeLevinandTalley
1997).Phragmiteshasthecharacteristicsofasuccess- 2000 and references therein) and, subsequently, their
ful invader as discussed by Orians (1986), including functional roles in marsh processes (e.g., elemental
opportunistic growth strategies, generalized pollina- cycling,trophicsupport).
tionandseeddispersalstrategies(e.g.,Hickman1993), Thisstudyexaminedtheeffectsofhabitatalteration
anabilitytooutcrossandproducesuccessfulgenotypes by the invasive Phragmites australis on benthic epi-
(Besitka 1996), and vegetative reproduction (Koppitz faunaandinfauna,andtheirassociatedenvironmentin
1999;PellegrinandHauber1999;NieringandWarren Connecticuttidalmarshes.Specificgoalsweretodeter-
1980b). Similar environmental conditions (climate, minewhethertherewereeffectsofPhragmitesinvasion
sediments, plant growth forms) between the recipi- on (1) above-ground habitat features (canopy archi-
entandsourcesites, asoccurswithintheseeastcoast tecture, litter biomass, benthic microalgal biomass)
marshes, alsoencouragesuccessfulinvasions(Orians andbelow-groundsedimentproperties(organicmatter
1986). Proposed catalysts of this recent Phragmites content, sand content, root and rhizome biomass and
invasion include an increase in favorable conditions structure,lamination),and(2)macrofaunalcommunity
forPhragmitesduetoincreasedtidalrestrictions(e.g., structure(density,biomass,speciesrichness,diversity,
tidal gates, development) (Rozsa 1995; Chambers dominance, composition), and to assess the extent to
et al. 1999). Besitka (1996) suggested that the inva- whichPhragmiteseffectschangewithsalinityregime
sive Phragmites genotype differs from the historical and/orageofthestand.
53
Materialsandmethods (hereafter referred to as un-invaded). Transects ran
from the creek edge towards the back of the vegeta-
Threesites(I,IIandIII)ofdecreasingsalinity(19–24in tionpatch,exceptintheun-invadedmarshgrasshabi-
I,9–10inIIand5–7inIII)werestudiedinthevegetated tats of Sites II and III, which were located in patches
marshes along the lower Connecticut River Estuary behindPhragmitesborderingthecreeks. Transectsin
(Figure 1, Table 1). These were sampled in May thesetwoareasfollowedthedistributionofthepatches.
(all Sites) and September (Sites I and III only) 1999 Alongeach50-mtransect, 10samplingstationswere
for sediments, plants, epifauna and macrofauna (ani- located at 5-m intervals along the transect line and
mals≥0.3mm). Withineachsite, two50-mtransects 1–2mtoeithersideoftheline.Fieldsamplingwithin
wereestablished,oneinPhragmites-dominatedmarsh these stations was conducted during May 7–12 and
and one in salt marsh grass-dominated marsh (e.g., September9–17,1999.Densitiesofepifaunaandplant
Spartinapatens,JuncusgerardiandDistichlisspicata) shoots (number 0.25m−2), light attenuation through
Figure1. LocationofstudysitesinthelowerConnecticutRiverestuary,OldLyme,Connecticut,USA.
Table1. Location,elevationandporewatersalinityofeachhabitattypewithineachsitealongthelowerConnecticutRiverestuaryduring
MayandSeptember1999.
SiteI SiteII SiteIII
Latitude 41◦17(cid:6)23(cid:6)(cid:6)N 41◦17(cid:6)35(cid:6)(cid:6)N 41◦18(cid:6)28(cid:6)(cid:6)N
Longitude 72◦19(cid:6)37(cid:6)(cid:6)W 72◦20(cid:6)02(cid:6)(cid:6)W 72◦20(cid:6)22(cid:6)(cid:6)W
Location BackRiver,GreatIsland BackRiver,GreatIsland LieutenantRiver&BenMarvin’sCreek
Phragmites Un-invaded Phragmites Un-invaded Phragmites Un-invaded
Elevations 106±3 110±3 110±1 110±2 107±2 106±3
(cmaboveMLLW)
Salinity(ppt)
May 5.2±0.6 4.6±1.6 2.6±0.2 2.0±0.2 0±0 0±0
September 19.8±0.9 23.1±0.9 9.2±0.9 8.9±0.3 5.7±0.8 6.4±0.5
n=10salinityand8elevationsamples,valuesaremean±1SE.SalinitiesinMayfollowedheavyrains.MLLW=meanlowerlow
water.
54
the plant canopy and litter, and pore water salin- ofthedropsofextractedwaterwithaLeicahand-held
ity were measured in the field at each station. One salinityrefractometer.
sediment core was collected from each station dur- Sediment cores for macrofaunal analysis were col-
ing May and September for macrofaunal analysis lected and processed following methods described
(18cm2×6cmdepth)andonecorewascollectedfor in Levin et al. (1998). Cores were preserved in
determinationofbenthicchlorophyllaconcentrations 8% buffered formalin and stained with Rose Bengal.
(0.86cm2×4mmdepth).InMay,oneadditionalcore Sediments were rinsed through 0.3mm mesh after
(18cm2 × 6cm depth) was collected from each sta- preservation, and all retained animals were removed
tion for analysis of sediment properties. Core sizes and identified to the lowest taxonomic level possi-
wereselectedbasedonpublishedmethods(seebelow). ble using dissecting and, when necessary, compound
Cores collected for macrofaunal analyses that were microscopes.Animalswerestoredin1%bufferedfor-
processed by one particular individual yielded ques- malin, weighed wet using an analytical balance in
tionable results, so all cores processed by this person ordertodeterminebiomass, andthentransferredinto
wereexcluded. Thisresultedinn = 7corespertran- 70% ethanol. Below-ground plant material was also
sect in May and n = 9 cores in September. Below- removed from the macrofaunal cores, dried at 60◦C
ground plant biomass consisting of live and dead andweighedtodeterminebelow-groundbiomass.
roots, rhizomes and detritus, was sorted and weighed Sediment cores were collected and processed for
fromthemacrofaunalcores.Collectionsofplantlitter combustible organic matter and sand content analy-
(shoots and leaves) were made for determination of ses following methods in Levin et al. (1998). Cores
above-groundlitterbiomass(gdw400cm−2)andasso- were frozen at −20◦C until analysis. Each sediment
ciatedmacrofauna(SiteIII,Septemberonly).Standing core was homogenized. A portion for organic mat-
live and dead shoots of plants were harvested from ter analysis was sieved wet through a 2-mm mesh to
each station in September for determination of end- separate large from fine plant material. The ≤2mm
of-year above-ground plant biomass (gdw0.25m−2). fraction was dried at 60◦C, weighed, combusted at
Two slabs (3 × 12 × 18cm deep) of marsh sedi- 550◦Covernightandweighedagaintodetermineloss
ment were collected from each transect in May 1999 oforganicsthroughcombustion.Aportionofsediment
forX-radiographicanalysisofbelow-groundsediment forsandcontentanalysiswasdigestedwithhydrogen
structure. peroxidetoremoveorganics.Digestedsedimentswere
Withineachtransect,fivepitfalltrapswereinstalled sieved wet through 2mm (to remove remaining large
along the transect line to sample mobile epifauna. plant material) and 63-µm mesh. Both size fractions
Cylindricalpitfalltraps(78.5cm2×14cmdeepcoffee (≥63µm and <63µm) were dried at 60◦C, weighed,
cans) were inserted flush with the sediment surface. and percent sand (≥63µm) was calculated. The con-
Lids were left on traps until use. Traps were set and centration of sediment chlorophyll a was determined
sampledduringMay11–12,June30–July1,July8–9, followingmethodsofPiehleretal. (1998), Wainright
14–15, 22–23, August 5–6, and September 13–14 etal.(2000)andC.Currin(pers.comm.).Coreswere
1999.Hightidelevelswereoftenhighenoughtoflood frozen at −20◦C until analysis. Chlorophyll a was
some traps and allow the escape of all animals. This extractedusing7mlofamethanol,acetoneanddeion-
variable loss of replication made statistical analysis ized water (45:45:10) solution. Samples were soni-
untenable.Thesedataarethereforepresentedasanon- catedfor1min,frozenovernightandthenshakenand
quantitativerecordofmobileepifaunathatweremissed centrifuged for 3min at 1500rpm the next morning.
by sampling with benthic cores and quadrats. Pitfall The adsorption or fluorescence of the decanted solu-
animalswerepreservedin95%ethanolandidentified, tion was measured before and after acidification with
usingadissectingmicroscopewhennecessary. 5%HClusingaShimadzuUV1601spectrophotometer
LightattenuationwasmeasuredinsituusingaLicor (λ=665and750nm)(May)oraTurnerDesignsflu-
hand-heldlightmeter.Lightattenuation(µE)wasinter- orometer (September), depending upon which instru-
pretedasthepercentdecreaseinlightbetweenambi- mentwasavailable.Thefluorometerisroutinelyused
entandsedimentsurface(beneaththecanopyandany to calibrate the spectrophotometer, so readings from
litterthatwaspresent)lightreadings.Porewatersalin- both instruments were comparable. Plant litter and
ities were obtained from the top 4cm of sediment by shoots collected for the determination of litter and
squeezingthesedimentagainstafilterpaperinsideof above-ground biomass were rinsed with fresh water
a 10cm3 syringe and measuring the salinity (±1ppt) to remove adhering sediments (litter only), dried at
55
60◦Candweighed. Littertobeusedformacrofaunal
analysis was collected from two arbitrarily assigned
layers; the drier, recently fallen upper layer (about
3–6cm thick) and the partially decayed bottom layer
(about 1–3cm thick). Litter samples were preserved
with8%bufferedformalin, stainedwithRoseBengal
and rinsed on 0.3mm mesh. Animals were removed
fromtheplantmaterial,identifiedusingdissectingand
compound microscopes and stored in 70% ethanol.
Plantmaterialwasdriedat60◦Candweighed.
Statistical comparisons of macrofaunal and envi-
ronmentalvariablesamongsites(I,IIandIII),marsh
habitats(un-invaded,Phragmites)anddates(Mayand
September 1999) were made using Student’s t-tests
and one-way ANOVAs with a-posteriorit-tests (JMP
statisticalsoftware).Interactionsbetweensite(i.e.,age
andsalinitygradient)andhabitataffectingmacrofaunal
andenvironmentalvariableswereidentifiedusingtwo-
wayANOVAs(JMPstatisticalsoftware). Bonferroni-
adjustedαvaluesforthenumberofcomparisonsmade
withineachdateandvariabletype(e.g., environmen-
tal,macrofaunal)wereused.Allproportiondatawere
arcsin-square-roottransformedandnumericdatawere
log (x+1)transformedpriortostatisticalanalyses.
10
Macrofaunal diversity was examined at the family
level (or higher) using taxon richness per core, as
well as the Shannon–Weiner Information index (H(cid:6);
log base 2), evenness (J(cid:6)) per core, and rarefaction
for cores pooled within transects (Biodiversity Pro
software;McAleeceetal.1999).
Similarities and differences in macrofaunal com-
munitieswereexploredusingnon-metricmultidimen-
Figure 2. Mean (±1 SE) shoot density (A), shoot height (B),
sionalscaling(MDS),basedonBray–Curtissimilarity
above-ground biomass (C), below-ground biomass (D) and leaf
indices. Pairwise comparisons between habitat types,
litterbiomass(E)foundinthePhragmitesandun-invadedmarsh
sites and dates were made using Analysis of Similar- grasshabitatsatthreesitesalongthelowerConnecticutRiverestu-
ity(ANOSIM;toobtainP-values).SimilarityPercent- ary during May (M) and September (S) 1999. n = 10 samples.
ages(SIMPER)determinedthepercentofdissimilarity ∗ = P ≤ 0.006; + = 0.006 < P ≤ 0.05; fromt-testsbetween
habitatswithineachsiteanddate.Bonferroniadjustedα=0.006.
(orsimilarity)andthetaxaresponsiblefordifferences
between groups. These multivariate analyses (MDS,
ANOSIM,SIMPER)wererunusingPrimerStatistical dense (P ≤ 0.002, t ≥ 3.58) than the shoots in
18
Software(ClarkeandWarwick1994)ondoublesquare- the un-invaded marsh grass habitats at all sites (Fig-
roottransformed,unstandardizedmacrofaunaldata. ures 2A,B). The difference in total shoot density and
height between the un-invaded and Phragmites habi-
tats became greater with distance upstream (decreas-
ingsalinity,increasingagesinceinvasion)(Table2A).
Results This was due to an upstream increase in height
and a decrease in density of shoots within the
Vegetationcharacteristics Phragmites habitat. The biomass of above-ground
plant shoots growing in the Phragmites habitats
PlantshootsinthePhragmiteshabitatswere4–6times was 4–5 times greater (P <0.001, t ≥4.17) than
18
taller (P < 0.001, t ≥ 3.78) and 2–85 times less the shoots in the un-invaded marsh grass habitats
18
56
Table2. Resultsoftwo-wayanalysesofvariance(ANOVA)for(A)environmentaland(B)macrofaunalvariablesascomparedamongsite
(I,IIandIII),habitat(Phragmitesandun-invaded),andinteractionbetweensiteandhabitatwithinthelowerConnecticutRiverestuary;data
arefromMayandSeptember1999.
May1999 September1999
Wholemodel Site Habitat Site× Wholemodel Site Habitat Site×
(df=5,54) habitat (df=3,36) habitat
P F P P P P F P P P
A. Environmentalvariables
Above-groundproperties
Shootheight <0.001 160 <0.001 <0.001 <0.001 <0.001 186 <0.001 <0.001 <0.001
Shootdensity <0.001 214 <0.001 <0.001 <0.001 <0.001 141 <0.001 <0.001 <0.001
Shootbiomass Nodata <0.001 54 0.003 <0.001 0.271
Litterbiomass <0.001 241 <0.001 <0.001 <0.001 <0.001 41 <0.001 <0.001 0.080
Openspace(%) <0.001 37 0.312 <0.001 0.312 <0.001 123 <0.001 <0.001 0.080
Sedimentproperties
Bgplantbiomass <0.001 9 <0.001 0.005 0.162 0.002 6 0.001 0.293 0.032
%Organicmatter <0.001 21 0.004 <0.001 <0.001 Nodata
%Sand 0.692 <1 NS NS NS Nodata
Chlorophylla 0.002 4 0.001 0.107 0.120 0.074 2 NS NS NS
Lightattenuation 0.017 3 0.120 0.392 0.010 0.032 3 0.160 0.022 0.159
Salinity <0.001 18 <0.001 0.054 0.184 <0.001 99 <0.001 0.056 0.855
B. Macrofaunalvariables
Biomass 0.178 2 NS NS NS 0.074 2 NS NS NS
Density <0.001 23 <0.001 0.002 0.181 <0.001 18 <0.001 0.879 0.366
Taxonrichness <0.001 6 <0.001 0.211 0.515 <0.001 15 <0.001 0.254 0.954
Oligochaeta
Tubificidae # <0.001 7 <0.001 0.015 0.348 0.002 6 <0.001 0.354 0.194
% 0.017 3 0.009 0.056 0.487 0.187 2 NS NS NS
Enchytraeidae # <0.001 34 <0.001 0.120 0.716 <0.001 17 <0.001 0.274 0.090
% <0.001 7 <0.001 0.755 0.695 0.002 6 <0.001 0.220 0.314
Naididae # 0.015 3 0.003 0.816 0.233 <0.001 9 <0.001 0.065 0.072
% 0.044 3 0.262 0.058 0.056 0.159 2 NS NS NS
Polychaeta
Sabellidae # <0.001 7 <0.001 0.015 0.754 <0.001 13 <0.001 0.002 0.695
% 0.053 2 0.234 0.005 0.900 <0.001 9 0.265 <0.001 0.016
Otherpolychaeta # 0.499 1 NS NS NS 0.410 1 NS NS NS
% 0.056 2 0.014 0.419 0.445 0.239 1 NS NS NS
Arachnida # <0.001 19 <0.001 <0.001 0.021 0.239 1 NS NS NS
% <0.001 12 <0.001 <0.001 0.036 0.131 2 NS NS NS
Insecta
Midges # <0.001 9 <0.001 <0.001 0.954 0.212 2 NS NS NS
% <0.001 15 <0.001 <0.001 0.848 0.097 2 NS NS NS
Poduridae # <0.001 60 <0.001 <0.001 <0.001 NopoduridaeinSeptember
% <0.001 23 <0.001 <0.001 <0.001
Otherinsecta # 0.065 3 NS NS NS 0.065 3 NS NS NS
% 0.500 1 NS NS NS 0.029 3 0.077 0.066 0.077
Gastropoda # 0.881 <1 NS NS NS 0.482 1 NS NS NS
% 0.783 <1 NS NS NS 0.579 <1 NS NS NS
Peracarida # 0.015 3 0.003 0.173 0.532 0.017 4 0.105 0.018 0.105
% 0.390 1 NS NS NS 0.216 2 NS NS NS
Nemertea& # 0.437 1 NS NS NS 0.015 4 0.003 0.277 0.376
Turbellaria % 0.415 1 NS NS NS 0.094 2 NS NS NS
57
Table2. Continued
May1999 September1999
Wholemodel Site Habitat Site× Wholemodel Site Habitat Site×
(df=5,54) habitat (df=3,36) habitat
P F P P P P F P P P
Dwellinggroups
Burrowers # <0.001 25 <0.001 0.068 0.384 <0.001 15 <0.001 0.612 0.249.
% 0.002 5 <0.001 0.754 0.315 0.445 1 NS NS NS
Tube-builders # <0.001 7 <0.001 0.154 0.753 <0.001 13 <0.001 0.002 0.687
% 0.070 2 NS NS NS <0.001 9 0.261 <0.001 0.015
Errant # <0.001 13 <0.001 0.001 0.264 0.368 1 NS NS NS
% <0.001 9 <0.001 0.005 0.191 0.187 2 NS NS NS
n=10forenvironmentalvariables,n=7formacrofaunalvariablesinMayandn=9formacrofaunalvariablesinSeptember.Bonferroni
adjustedα=0.005forenvironmentalvariablesand=0.003formacrofaunalvariables.ResultsoftestswhereP ≤0.05areshown.NS=not
significantforwholemodeltestswhereP >0.05,Bg=below-ground
(Figure 2C). Phragmites was the dominant plant
(≥98% of total above-ground biomass) in the
PhragmiteshabitatsofSitesIIandIII.AtSiteI,how-
ever, Phragmites shoots comprised 82% and native
marsh grasses 18% of the shoot biomass in the
Phragmites habitat. The native grasses found within
thePhragmiteshabitatwere13cmtallerand2–3times
less dense than those found in the un-invaded habi-
tat. The below-ground plant biomass in un-invaded
marsh habitat was 36–52% higher than that found in
thePhragmiteshabitatsofSiteIII(May, P = 0.001,
t =3.7; September, P = 0.026, t = 2.4) and
18 18
similarinSitesIandII(Figure2D).Therewas10–83
times more plant leaf and stem litter on the sediment
surface of the Phragmites than un-invaded habitats
(Figure 2E) (P ≤ 0.001, t ≥3.7, except Site I in
18
SeptwhenP =0.009,t =2.9).Foralloftheabove Figure3. Mean(±1SE)percentcombustibleorganicmatter(A)
18
comparisons,Bonferroni-adjustedα =0.006. andsand(B)inthePhragmitesandun-invadedmarshgrasshabitats
atthreesitesalongthelowerConnecticutRiverestuaryduringMay
(M)1999.n=10samples.∗=P ≤0.006;fromt-testsbetween
Sedimentproperties habitatswithineachsiteanddate.Bonferroniadjustedα=0.006.
Sediments of the un-invaded marsh habitats had SalinitiesinMayweremeasuredfollowingheavyrains
1.5–4times higher percent combustible organic mat- andsowerelowinallsiteswithreadingsbetween0and
ter content (54–58%) than the Phragmites sediments 5(Table1). InSeptember, salinitieswere21, 9and6
within Sites II and III (P < 0.001, t ≥ 6.6); there atsitesI,IIandIII,respectively.Withineachsitethere
18
wasnodifferenceinSiteI(Figure3A).Theeffectof werenodifferencesinsalinitybetweenPhragmitesand
Phragmitesinvasiononsedimentorganicmattercon- un-invadedhabitats(Table1).
tent was stronger in the sites farther upstream (II and Benthicchlorophyllaconcentrationwas2–3times
III)(Table2A).Sandcontentofsedimentswassimilar higherinthePhragmitesthanun-invadedgrasshabitats
in the Phragmites and un-invaded habitats at all sites of Site III (May, P = 0.053; t = 2.1; September,
18
(Figure3B,Table2A). P =0.021; t = 2.5) although this is not signif-
18
Porewatersalinitiesdecreasedwithdistancefromthe icantly different at Bonferroni adjusted α = 0.006
mouthoftheConnecticutRiver(I>II>III)onboth (Figure4A).Therewerenodifferencesinchlorophyll
dates sampled (P < 0.001, F2,28 ≥ 25.6) (Table 1). a concentration between the two habitats in Site I
58
Figure4. Mean(±1SE)sedimentchlorophyllaconcentration(A)
andlightattenuation(B)inthePhragmitesandun-invadedmarsh
grasshabitatsatthreesitesalongthelowerConnecticutRiverestu-
ary during May (M) and September (S) 1999. n = 10 samples.
∗ = P ≤ 0.006; + = 0.006 < P ≤ 0.05; fromt-testsbetween
habitatswithineachsiteanddate.Bonferroniadjustedα=0.006.
(Figure 4A). The percent of light attenuated through
the Phragmites stand (canopy and litter) and the
marshgrasscanopywasgenerallysimilar(P ≥0.016;
t ≤2.7;α =0.006)andrangedbetween95and99%
18
(Table2A,Figure4B).
X-radiographs revealed very different sediment
structure in the un-invaded and Phragmites habitats.
Broad but sparse rhizomes and distinct laminae char-
acterized Phragmites-habitat sediments at all sites Figure 5. X-radiographs of the un-invaded marsh grass and
PhragmitessedimentsfromthreesitesalongthelowerConnecticut
(Figure 5). Un-invaded marsh sediments exhibited
River estuary. Light areas indicate lower density sediments than
apparent bioturbation (no laminae) and a more dense
darker areas. Characteristic thick Phragmites rhizomes (rhz) are
rootmatofthinnerrhizomes(Figure5). indicatedintheSiteIPhragmitesX-radiograph.
Epifauna betweentheun-invadedandPhragmiteshabitatsofany
site during May or September (Table 3). Density of
Epifaunaconsistedprimarilyofgastropods,peracarid S.catascopiuminSiteIIIwashigherintheun-invaded
anddecapodcrustaceans,insectsandarachnids.Com- thanPhragmiteshabitat,whereitwasabsent.
mongastropodsatallsites(Phragmitesandun-invaded Pitfall trap taxa that had not been seen in the ben-
habitatscombined)includedthepulmonateMelampus thic cores or quadrats included a grasshopper (family
bidentatus,whichhadhighestdensities(mean±1SE) Tettigoniidae), a cricket (family Gryllidae), an ant
atSiteI(20±7individualsm−2inMay;8±3individ- (family Formicidae), the fiddler crabs Uca minax
uals m−2 in September), Succinea wilsoni which had and U.pugnax and the green crab Carcinus maenas
highestdensitiesatSiteIII(116±18individualsm−2 (Table 4). The pitfall traps also collected taxa simi-
in May; 20 ±6 individuals m−2 in September), and lar to those found in the benthic cores: the arachnids
Stagnicola catascopium, which only occurred at Site Pardosaspp.andmites,thebeetleEnochrushamiltoni,
III during May (44±16 individuals m−2). Densities an unidentified beetle larvae, podurids (Collembola),
of S. wilsoni were generally higher in the un-invaded tabaniddipteranlarvae,theamphipodOrchestiagrillus
habitat,whiledensitiesofM.bidentatusdidnotdiffer andtheisopodPhillosciavittata(Table4).Attheend
59
Table3. Densities(individualsm−2)ofgastropodsfoundintheun-invadedmarshgrassandPhragmiteshabitatsinthreesitesalongthe
lowerConnecticutRiverestuaryduringMayandSeptember1999.
SiteI SiteII SiteIII
Un-invaded Phragmites Un-invaded Phragmites Un-invaded Phragmites
Mean 1SE Mean 1SE Mean 1SE Mean 1SE Mean 1SE Mean 1SE
May1999
Melampusbidentatus 28 12 12 6 22 10 5 3 0 0 0 0
Succineawilsoni 100 32a 12 8 168 40a 8 8 115 18 116 32
Stagnicolacatascopium 0 0 0 0 0 0 0 0 88 24a 0 0
September1999
Melampusbidentatus 51 23 14 8 10 5 3 2 0 0 0 0
Succineawilsoni 2 2 3 3 24 8a 0 0 165 35a 0 0
Stagnicolacatascopium 0 0 0 0 0 0 0 0 0 0 0 0
n=10quadrats.
asignificance(P <0.006)betweenhabitats(withinsiteanddate).Bonferroniadjustedα=0.006.Nosymbolrepresentsnosignificant
difference(P >0.05).
of the survey, over 4 times as many crabs (Uca pug- (67%).Mosttaxawerefoundinbothlayers.However,
nax,U.minaxandC.maenas)hadbeencaughtinthe sabellid polychaetes, dolichopodid and muscid insect
Phragmitesthanun-invadedhabitatsofSitesI(9versus larvaeandchelonethidswerefoundonlyinthebottom
2 crabs) and III (18 versus 4 crabs). No crabs were layer, and the spider Grammonota trivittata, soldier
capturedatSiteII(Table4).Thesedatasuggestthatdif- beetles(Cantharidae)androvebeetles(Staphylinidae),
ferencesindensitiesofmobilefauna(e.g.,crabs)might aswellasunidentifiedbeetlelarvae, werefoundonly
exist between Phragmites and un-invaded marshes. inthetoplayer(Table5).
However, these pitfall trap data cannot be quantita-
tively analyzed because of the loss of various repli- Macro-infauna
catesduringeachsamplingperiodwhenseveraltraps
flooded and animals escaped. High replication and Abundance, composition and diversity. Densities of
better designed (e.g., draining) pitfall traps could be total macro-infauna (hereafter referred to as macro-
valuablefordeterminingmobilefaunalcommunities. fauna)rangedfrom6000to142,000individualsm−2in
Mayand3000to27,000individualsm−2inSeptember.
Litterfauna. ThedenselitterinthePhragmiteshabitat HighestdensitiesoccurredatSiteI,intermediatevalues
of Site III during September hosted faunal communi- at Site II (May only) and lowest densities at Site III
ties of 4784±1483 individuals m−2 (8±3 individ- (May:ANOVAP < 0.001,F2,18 = 32.1;September:
uals gdw−1) and 19 taxa per site compared with the P < 0.001, t = 5.2) (Table 5). Total macrofaunal
16
3008±633individualsm−2and13taxapersitefound biomass did not differ between sites or habitats and
in the Phragmites sediments (macro-infauna) on the rangedfrom11to47gwetwt.m−2inMayand1to6g
samedate(Table5).Thelittercontained4taxa(Che- wetwt.m−2 inSeptember.
lonethidan [pseudoscorpions], an unidentified adult Major macrofaunal taxa within the marsh habitats
andunidentifiedlarvalcoleopteranandStaphylinidae) includedtubificid,enchytraeidandnaididoligochaetes
which were not collected in the sediments (Table 5). (20–68%), insects (1–73%), especially podurids and
ThePhragmiteslitterfaunaconsistedmostlyofenchy- midge (chironomid and ceratopogonid) larvae, poly-
traeidandnaididoligochaetes(45%),coleopteranand chaetes (4–42%), especially sabellids, and arach-
dipteran larvae (20%), and the peracarid crustaceans nids (0–16%, mainly mites) (Table 2). In May,
Orchestia grillus and Philoscia vittata (17%). Also when densities were highest, the un-invaded areas
presentwerearachnids(7%),turbellarians(6%),sabel- of all 3 sites hosted different macrofaunal commu-
lid worms (4%) and the gastropod Succinea wilsoni nities than the Phragmites areas (ANOSIM, P <
(3%). Density of fauna in the bottom layer of litter 0.004) (Figure 6, Table 6). Un-invaded sediments
was 3× higher than in the top layer and was domi- contained 2–3 times greater densities of total macro-
natedbybothburrowers(49%)anderrantfauna(47%), fauna (Site II, P =0.040; t = 2.3 and III, P =
12
whereas errant fauna dominated the top litter layers 0.02, t = 2.7) although these differences were
12
60
ower III Un +
hel Site P.a. + +
t
g
on 99 Un + + +
sitesal mber19 SiteII P.a. + + ++
sinthree 14Septe SiteI P.a.Un + ++++ ++
at
(Un)habit SiteIII P.a.Un
s
as n
marshgr 1999 SiteII P.a.U
ed ust Un +
(P.a.)andun-invadd22samplings. 5Aug SiteIIISiteI P.a.UnP.a. ++ ++
gmites14an II Un +++ +
PhraeJuly 99 Site P.a. +
einvasiveduringth 8July19 SiteI P.a.Un ++ +
hd
tn
psofefou III Un + +
nthepitfalltraNoanimalswer 99 SiteIISite P.a.UnP.a. +
i 9
xonfoundmber1999. 30June1 SiteI P.a.Un + ++
a
te
ce(blank)ofeachMaythroughSept 1999 SiteIISiteIII P.a.UnP.a.Un ++ + + +++
orabsenaryfrom 11May SiteI P.a.Un + + ++
+Table4.Presence()ConnecticutRiverestu ArachnidaPardosasp.Mite InsectaEnochrushamiltoniColeopteranlarvaeTabanussp.larvaeTettigoniidaeGryllidaePoduridaeFormicidae CrustaceaOrchestiagrillusPhilosciavittataUcaminaxUcapugnaxCarcinusmaenas