Medit. Mar. Sci., 9/2, 2008, 35-52 35

Introduction

Marine litter, also known as marinedebris, is any man-made, solid wastematerial that enters the marine environ-

ment, along shorelines, coastal waters,estuaries and oceans throughout theworld. Marine litter originates either fromland sources, e.g. beach users, municipallandfills located near the coast, sewage

Mediterranean Marine ScienceVolume 9/2, 2008, 35-52

Subtidal littering: Indirect effects on soft substratum macrofauna?

I. AKOUMIANAKI1, P. KONTOLEFAS2, S. KATSANEVAKIS3,A. NICOLAIDOU2 and G. VERRIOPOULOS2

1 Hellenic Centre for Marine Research, Institute of Oceanography,P.O. Box 712, 19013, Anavissos, Attica, Hellas2 Department of Zoology – Marine Biology, University of Athens,Panepistimiopolis 15784, Athens, Hellas3Hellenic Centre for Marine Research, Institute of Marine Biological Resources, P.O. Box 712, 19013, Anavissos, Attica, Hellas

e-mail: akoumio@ath.hcmr.gr

Abstract

Changes in macrofauna community structure, abundance and species richness were examined bothbefore and one year after the deployment of plastic and glass bottles at littered (litter density: 16 items /100 m2) and non-littered (control) surfaces at three unimpacted coastal areas of the western SaronikosGulf (Greece). In parallel, LOI% at the adjacent sediments and changes in the composition of feedingtypes of the megaepifauna that colonized the litter were examined across treatments. Significant changesin macrofauna community structure were demonstrated between before and after littering. At only one ofthe sites was there detected a significant difference in macrofauna community structure between controland littered plots after littering. This difference was linked with a significant increase in the abundance ofopportunistic polychaete species and LOI% levels in the sediment surface due to the entrapment ofmacrophytal debris within the littered surface. The study did not show a consistent direct response ofmacroinfauna community to litter and the associated megafauna. Unlike the megafauna attracted by lit-ter items, soft-substratum macrofauna is less responsive to the addition of novel hard substrates in adja-cent sediments. Alternatively, it could be that the impact of littering with small items triggers a macrofau-na response detectable in the long-run.

Keywords: Macrofauna; Community structure; Marine litter; Coastal zone; Saronikos Gulf; Mediter-ranean Sea.

Research Article

treatment and port installations, land run-off, or from maritime sources, e.g. ships oroffshore installations (COE & ROGERS,1997). Objects ranging from householdand industrial containers, packagingmaterial, medical wastes and discardedfishing line all qualify as marine debris.The main types of marine litter impactsinclude potential health risks to inhabi-tants of coastal areas, economic losses tofisheries and tourism (NASH, 1992;WILLIAMS et al., 1993), substantial dam-age to coral reefs (DONOHUE et al.,2001; CHIAPPONE et al., 2005) andreduced fitness and increased mortality tovertebrate pelagic wildlife through entan-glement and intestinal tract blockagewhen ingested (LAIST, 1997). Specialattention is also required to the potentialthreat posed by the dispersal of alienspecies encrusted or attached on freelydrifting debris in receiving environments(WINSTON et al., 1997; BARNES, 2002).Finally, there is rising concern about theimpacts on benthic ecosystems as theseafloor from the intertidal and shallowsublittoral to outer shelf, slope and abyssaldepths has been identified as an importantsink for marine debris (GOLDBERG,1997; BACKHURST & COLE, 2000).

Plastic litter makes up to 80 % ofseabed debris, followed by metal and glass(RYAN & MOLONEY, 1990; GABRIE-LIDES et al., 1991; KANEHIRO et al.,1995; STEFATOS et al., 1999; DERRAIK,2002). The accumulation of plastic litteron the seafloor can inhibit ventilation ofthe sediments thus resulting in hypoxia oranoxia (GOLDBERG, 1997, UNEPUTTY& EVANS, 1997). Benthic plastic debrismay also provide solid attachment forspecies that would not usually occur there(RYAN & MOLONEY, 1990; MINCHIN,1996), thus acting as novel hard substrata,

often in areas that are otherwise sandy ormuddy (CHAPMAN & CLYNICK, 2006).Indeed, waste material, such as tyres andcar bodies, has been used to build artificialreefs, often specifically to attract fish andturn a ‘sand desert’ to a ‘rich in habitats’benthic environment (DAVIS et al., 1982;BOHNSACK & SUTHERLAND, 1985;GROSSMAN et al., 1997; SVANE & PE-TERSEN, 2001). Therefore, the impactscaused by large marine litter items areexpected to bear great similarities to otherman-made structures placed at the bot-tom of the sea, including artificial reefs.These impacts include alterations of wavefield and current patterns, thus causingscour and changes in sediment grain sizeand texture (MIZUTANI et al., 2000;GUIRAL et al., 1995) and entrapment ofalgae and other organic material. These,along with the activities and deaths ofreef-associated organisms, can result inorganic enrichment (WILDING, 2006)and modification of granulometry causedby the introduction of shell fragments thatderive from fouling biota (DAVIS et al.,1982; AMBROSE & ANDERSON, 1990;BAROS et al., 2001). Finally, predatorsattracted by the structures may forage onplants and animals that live in adjacentsediments (DAVIS et al., 1982; BAROS etal., 2001, FABI et al., 2002).

Smaller items such as plastic, metaland glass containers comprise a large partof benthic litter near urban centres(STEFATOS et al., 1999; BLACKHURST& COLE, 2000; MOORE & ALLEN,2000). There is little documented infor-mation about the potential use of thisform of waste as a habitat for coastal com-munities and its potential impact on adja-cent soft bottom communities (CHAPMAN& CLYNICK, 2006). In a recent manipu-lative study on the effect of benthic litter

Medit. Mar. Sci., 9/2, 2008, 35-5236

on biological communities in unimpactedshallow soft bottom areas in the SaronikosGulf (Eastern Mediterranean),KATSANEVAKIS et al. (2007) demon-strated an enhancement in the abundanceand diversity of megafauna attached todiscarded bottles, either because the litterprovided refuge or reproduction sites formobile species or because hard-substra-tum sessile species had the opportunity tosettle on the provided substrata. In paral-lel to megafauna, macrofauna abundanceand species composition were collectedfrom the adjacent sediments. The aim ofthe present study was to investigate theeffect of littering on benthic macrofaunain these recently formed small litter reefsand explore several litter-associated caus-es of impact, including changes in organicmatter content of adjacent sediments aswell as changes in the presence of epifau-nal predators.

Material and Methods

The study was conducted from June2005 to June 2006 in the Saronikos Gulf,an area of 2600 km2 and a maximum depth

450 m that receives in its northeast partthe urban effluents of Athens, untreateduntil 1995. Surface water temperaturesrange from 11ÆC in the winter up to 30ÆCin the summer. The circulation of watermasses within the gulf have been reportedto depend strongly on the local wind whilethe prevailing currents are from thenortheast to the southwest, continuinganticyclonically in the deeper layer of thewest sub-basin (NCMR, 2001).

The experiment took place at threecoves, unimpacted in terms of littering andorganic pollution, in the western SaronikosGulf, i.e. Amoni (A), Frangolimano (F),and Lychnari (L) (Fig. 1). The study siteswere away from urban centres and werecharacterized by bare sandy substrates,varying from medium to very fine sand(KATSANEVAKIS et al., 2007). At eachcove, two 100 m2 plots (10 m X 10 m), 50 mapart were defined on the seafloor withnylon line, at similar depths (16-20 m). Onone of the surfaces, 16 items of litter com-prising 12 plastic bottles and 4 glass jarswere placed uniformly after the first sam-pling, while the other surface remained‘clean’ (i.e. control). Detailed information

Medit. Mar. Sci., 9/2, 2008, 35-52 37

Fig. 1: Map of the experimental sites.

on the sampling sites and the samplingdesign is given by KATSANEVAKIS et al.(2007).

At each site, the sampling designincluded two factors: (a) ‘Plot’, fixed withtwo levels: littered plots containing litterand control plots (denoted with C) devoidof litter and (b) ‘Time’ of sampling, fixedand orthogonal to Plot with two levels:before the deployment of litter items inJune 2005, hereafter denoted with 1, andafter the deployment of litter items in June2006, hereafter denoted with 2. The time-lag of a year was proved by in situ visualobservations to be appropriate for theestablishment of a litter-associatedmegafauna. Five replicate diver-heldundisturbed cores (internal diameter: 10cm, penetration depth: 20 cm, core sam-pling area: 78.5 cm2) were taken withineach plot at each site to assess macrofaunacommunity changes between before andafter littering, and between control and lit-tered surfaces at each site. In conjunctionwith macrofauna sampling, five undis-turbed sediment cores were taken for theestimation of organic matter content. Sam-ples were taken at random within the plots.

Organic matter content of the sedi-ment was determined as loss on ignition(LOI), i.e. the difference between the dryweight (60ÆC, 24h) of the sediment andthe residue left after combustion at 450ÆCfor 3h (PARKER, 1983).

The sediment from each replicate wassieved through a 0.5 mm mesh and theresidue was immediately fixed in 4%formaldehyde. The macrofauna organ-isms retained were sorted, stored in 70%ethanol and then enumerated and identi-fied to species level. The species from allmajor taxa were classified to functionalgroups according to their food acquisitionmode, be it surface (S) or subsurface (B)

deposit feeders, suspension feeders (F),omnivorous (O) and carnivorous (C)feeders. The information used in this clas-sification was based on the ecological lit-erature for families, genera or species(WOODIN, 1976; FAUCHALD &JUMARS, 1979; RUPPERT et al., 2004;KAMERMANS, 1994; LEVINTON,1982) as well as in specific systematic keysfor the Mediterranean Sea. The specieswere also classified in three groups withrespect to their time of appearance in thesuccession process, temporal and spatialpersistence as well as rates of populationgrowth and decline, following RHOADSet al. (1978) i.e (a) Group 1 or first orderopportunistic species, (b) Group 2 or sec-ond order opportunistic species and (c)Group 3 or equilibrium species. Addition-al information for the present classifica-tion was taken from the review bySIMBOURA & ZENETOS (2002) assum-ing that similar species are eliminated, orsignificantly reduced, following any majorenvironmental disturbance.

Megafauna were censused by diversbefore and after littering at the littered andthe control plots (KATSANEVAKIS et al.,2007). In the present study, the speciescensused by KATSANEVAKIS et al.(2007), were classified to major taxa, i.e.fish, bivalves, gastropods, crustacea,cephalopods and miscellanea, includingbryozoans, tunicates, sponges and cnidari-ans and feeding and motility types. Feed-ing types included predators, suspensionand deposit feeders whereas motility typescomprised partially motile species, i.e.those restricted within a plot, highly motile– schooling species, i.e. capable of movingfurther away from the plot, sedentary andcryptic species. The information given forfeeding and motility classification wastaken by WHITEHEAD et al. (1986) for

Medit. Mar. Sci., 9/2, 2008, 35-5238

fish fauna and by RUPPERT et al. (2004)for invertebrate megafauna.

All analyses were completed at thelevel of replicate unit (n=5) at each sta-tion. Macrofauna species diversity foreach sample and the associated evennesscomponent J’ were calculated applyingthe (log2) Shannon-Wiener diversityindex (H’) (SHANNON & WEAVER,1963). Total community variables, i.e.abundance / 100 cm2 and numbers ofspecies per corer and LOI, were com-pared according to the two-factor sam-pling design using ANOVA, preceded byCochran's test for homogeneity of vari-ances and followed by a posteriori Stu-dent–Newman–Keuls (SNK) tests. Abun-dance and species numbers per macrofau-na major taxon were also tested byANOVA. The Pearson product momentcorrelation coefficients were also calculat-ed between abundance and species num-bers, and the LOI levels.

The response of the macrofauna com-munity to the two-factor mensurativesampling design was examined using per-mutational analysis of variance(PERMANOVA, ANDERSON, 2001)followed by analysis of multivariate dis-persion to test for homogeneity of disper-sions among plots and times(PERMDISP, ANDERSON, 2006). Inthe present factorial design, the evidencefor an impact (littering effect) at each siteappears as a significant ‘time’ by ‘plot’interaction (GREEN, 1979). The testswere based on 9999 unrestricted randompermutations of the raw data.

Non-metric multidimensional scaling(MDS, KRUSKAL & WISH, 1978) wascarried out to visualize multivariate pat-terns in macrofauna species data amongtreatments at each site. The effect of thespecies on the observed ordination of

treatments was visualized with projectionbiplots in which the vectors represent thePearson correlation relationship betweenmacrofauna species and the MDS axes.All multivariate analyses were obtainedusing Primer 6 for Windows (CLARKE &GORLEY, 2006) and Permanova+ forPrimer (ANDERSON & GORLEY,2007) and used Bray-Curtis dissimilaritiesthat were calculated between all pairs ofrange-standardized observations.

Results

Average LOI varied from 2.29 (1AC)to 4.82% (1LC) in spring 2005 and from3.2 (2AC) to 6.67% (2L) in spring 2006.Significant interactions between Plot andTime were only detected at L site (F1, 16 =40.3) where LOI% levels at plot 2L werehigher that at plots 1L, 1LC and 2LC.Seagrass leaf detritus derived from Posi-donia oceanica or Cymodocea nodosapatches at site L, was observed duringvisual censing one year after littering onlywithin the littered plot.

A total of 248 macrofauna species wasrecorded from the three sites, 167 werepresent at site A, 139 at site F, and 159 atsite L. Overall, 29% of the species foundin this study were common between site Aand F and F and L whereas sites A and Lshared 24% of the species. 67% of thespecies were different between before andafter littering while 41% of the specieswere common between littered and con-trol plots. At each site and plot 15 to 20%of species were represented by 1 individ-ual. The average values of total abun-dance, species richness and diversityindices at each site and plot are given inTable 1. The two most dominant speciescomprised more than 20% of total abun-dance at all treatments. A significant Plot

Medit. Mar. Sci., 9/2, 2008, 35-52 39

Medit. Mar. Sci., 9/2, 2008, 35-5240

Tab

le 1

Ave

rage

per

cent

age

cont

ribu

tion

to

tota

l abu

ndan

ce o

f the

spe

cies

tha

t w

ere

impo

rtan

t in

des

crib

ing

diff

eren

ces

and

sim

ilari

ties

am

ong

site

s,pl

ots

and

sam

plin

g ti

mes

. Fun

ctio

nal c

lass

ific

atio

n is

giv

en. T

roph

ic m

ode

(T):

S =

sur

face

dep

osit

feed

er; B

= s

ubsu

rfac

e de

posi

t fe

eder

; F =

susp

ensi

on fe

eder

; O =

om

nivo

rous

; C =

car

nivo

rous

. Col

oniz

atio

n pa

tter

n (s

ensu

Rho

ads

et a

l., 1

978)

: Gro

up 1

(G

1) =

firs

t or

der

oppo

r-tu

nist

s; G

roup

2 (

G2)

= s

econ

d or

der

oppo

rtun

ists

; Gro

up 3

(G

3) =

equ

ilibr

ium

spe

cies

. A: A

mon

i, F

: Fra

ngol

iman

o, L

: Lyc

hnar

i.

Func

tiona

lJu

ne 2

005

June

200

6cla

ssifi

catio

nLi

ttere

dCo

ntro

lLi

ttere

dCo

ntro

l

Spec

iesT

CP1A

1F1L

1AC

1FC

1LC

2A2F

2L2A

C2F

C2L

C

Lorip

es la

cteus

SG

2or 3

2514

912

144

1616

134

21<

1Eu

nice

vitta

taO

G2

or 3

912

2210

1518

27

51

96

Arici

dea

cerru

tiiB

G3

95

29

53

53

75

47

Chon

e dun

eri

FG

36

122

26

15

1<

11

41

Prot

odor

villea

kefe

rstein

iO

G2

51

24

21

36

135

54

Telli

na cf

com

pres

saS

G3

4<

12

21

2-

<1

<1

21

1Ar

icide

a ca

ther

inae

BG

32

01

11

32

11

12

2M

icron

epht

hys m

aria

eO

G2

or 3

21

15

31

77

26

62

Pseu

dolei

ocap

itella

fauv

eliB

G2

24

31

41

13

4<

11

4Lu

mbr

iner

is gr

acili

sO

G3

23

23

58

32

24

34

Mar

phys

a be

lliO

G3

15

20

11

1<

1<

1<

10

3Pa

rado

neis

lyra

SG

1 o

r 21

55

67

59

1410

74

4Ar

icide

a ca

pens

is ba

nsei

BG

31

11

24

14

97

53

<1

Siga

mbr

a ten

tacu

lata

CG

3<

13

11

13

13

72

55

Mas

tobr

anch

us tr

inch

esi

BG

2-

21

32

1<

1<

11.1

10.7

0.5Pr

iono

spio

ehler

siS

G2

-2

12

5-

<1

<1

0.9<

10.5

1Ao

nide

s oxy

ceph

ala

SG

2 or

3-

-1

--

2-

-0.6

--

1.5

(con

tinue

d)

X Time interaction was detected at site L(F1, 16 = 10.56, p < 0.05). SNK testsrevealed that abundance at plot 2L wassignificantly higher that at plots 1L and2LC. No significant Plot X Time interac-tion was found at any of the sites withrespect to species richness. Overall, abun-dance and species diversity were correlat-ed (r = 0.59, p < 0.05) although strongcorrelations (r > 0.75, p < 0.05) were onlydetected at site L in both sampling timesand at all sites after the deployment ofbottles at the littered plots.

The contribution of macrofaunamajor taxa to total abundance and speciesnumbers is shown in Figure 2. Polychaetescontributed to total abundance(61 - 84%)and species richness (66 – 79%) to a highdegree, followed by Molluscs, whichaccounted for 2 (2L) to 42% (2AC) oftotal abundance and 6 to 16% of totalnumbers of species. Numbers of Crus-tacean individuals comprised less than 8%at all sites except for site L whereas Crus-tacean species contributed from 13 to16%. Echinoderms, exclusively represent-ed by Amphiura chiajei, and the group ofmiscellanea taxa generally accounted forless than 0.6 and 3% of numbers of indi-viduals, respectively. Significant Plot XTime interactions were detected at site Lfor Polychaete abundance (F1, 16 = 19.12,p<0.05, SNK tests: 2L>2LC and 2L>1L)and for Molluscan abundance (F1, 16 =5.12, p<0.05, SNK tests: 1L>1LC and1L>2L). Polychaete, crustacean and mis-cellanea abundances were highly correlat-ed to their corresponding species numbers(0.71 < r < 0.77, p < 0.05).

The species Loripes lacteus and Eunicevittata accounted for 20 to 30% of thefauna at all sites and plots before littering,except for plot 1LC where L. lacteus wasreplaced by Lumbrineris gracilis (Table 1).

Medit. Mar. Sci., 9/2, 2008, 35-52 41

Tab

le 1

(co

ntin

ued)

Func

tiona

lJu

ne 2

005

June

200

6cla

ssifi

catio

nLi

ttere

dCo

ntro

lLi

ttere

dCo

ntro

l

Spec

iesT

CP1A

1F1L

1AC

1FC

1LC

2A2F

2L2A

C2F

CLC

Amph

itriti

des k

uehl

eman

niS

G3

--

5-

-1

--

<1

--

<1

Micr

odeu

topu

s gryl

lota

lpa

FG

2-

12

--

-1

15

<1

18

Apse

udes

latre

illi

SG

2-

< 1

1-

-<

11

<1

6-

116

Tota

l abu

ndan

ce /

100

cm2

113

112

113

127

150

8812

413

422

713

010

810

2N

umbe

r of s

pecie

s per

core

2730

3332

2733

3629

3932

3131

Shan

on-W

iene

r H' (

log2

)3.8

4.14.3

4.44.1

4.54.5

44.3

44.2

4.4Pi

elou

eve

ness

J'0.8

0.80.9

0.90.9

0.90.9

0.80.8

0.80.9

0.9

After littering, Paradoneis lyra and L. lac-teus contributed from 25 to 30 % to totalabundance at sites A and F whereasProtodorvillea kefersteini and P. lyra at plot2L and Apseudes latreilli and Microdeuto-pus gryllotalpa at plot 2LC comprised 24%of total abundance (Table 1). As shown inTable 1, despite the change in the rank ofdominance between sampling times andplots, the majority of the most abundantspecies exhibited ubiquitous distributionalong the study area, with considerabledensities even when their percentages tototal abundance was low. Among thespecies that were abundant at all sites,times and plots are Prionospio ehlersi,Mastobranchus trinchesi, Aricidea catheri-nae and L. gracilis.

A significant relationship (0.4 < r < 0.5,

p < 0.05) between abundance and densi-ties of dominant species such as P. kefer-steini, P. lyra, Pseudoleiocapitella fauveliand Aricidea cerrutii and LOI% wasdetected at site L. This is in accordancewith the observation that significantlyhigher levels of LOI% at plot 2L coincid-ed with highest abundance (Fig. 3) andhigh dominance of species known to dis-play a second order opportunistic patternof colonization (Table 1).

The difference in the abundance of lit-ter-associated megafauna major taxa,feeding and motility types between beforeand one year after littering is given inTable 2. The greatest changes were exhib-ited by miscellanea, mostly sedentary andfilter feeding megafauna. On the otherhand, fish and Crustacea, mostly predatory

Medit. Mar. Sci., 9/2, 2008, 35-5242

Fig. 2: Contribution of macroinfauna major taxa to (a) total abundance /100 cm-2 and (b) total speciesrichness per core sample at littered plots (1A, 1F, 1L) and control (1AC, 1FC, 1LC) plots in June 2005and at littered (2A, 2F, 2L) and control (2AC, 2FC, 2LC) plots in June 2006.

and cryptic, increased after littering at sitesA and F, although not exclusively at lit-tered plots. At site L there was a substan-tial increase in crustaceans and gas-tropods, mainly represented by predatory,cryptic and partially motile species. Sum-marising, predatory and partially motilegastropods and crustaceans mainlyincreased at site L whereas fish and crypticfauna mainly increased at sites A and F.

Permanova detected significant Plot XTime interaction only at site L (Table 3).Permdisp did not reveal any heterogeneityin multivariate dispersion among the

treatments. However, when dispersionsacross times and plots were tested at eachsite, there was detected significantly high-er dispersion before littering at site A andat the control plots at site F.

The MDS ordination plots of stationssupported the results of permanova byrevealing a great overlap in macrofaunacommunity structure among treatments ateach site A and F (Fig. 4). At site L therewas observed an effect of littering onmacrofauna community, with plot 2Lreplicates clustering separately from plot2LC, in agreement with the Permanova

Medit. Mar. Sci., 9/2, 2008, 35-52 43

Fig. 3: Relationship of (a) total number of individuals /100 cm-2 and (b) total number of species per coresample with LOI% at littered plots (1A, 1F, 1L) and control (1AC, 1FC, 1LC) plots in June 2005 andat littered (2A, 2F, 2L) and control (2AC, 2FC, 2LC) plots in June 2006.

tests. The biplots of Figure 4 clearly showthat only at L there is a consistent associa-tion of group 2 colonizers such as P. lyraand P. kefersteini with the 2L plot.

Discussion

Extensive ecosystem monitoring stud-ies have been undertaken in the SaronikosGulf, focusing on the examination of theimpact by the Athens metropolitan area

before and after the operation of thewastewater Treatment Plant (NCMR,1999; 2001). The western Saronikos Gulfis less affected by land-based pollutingactivities and it is generally characterizedby deeper waters, steeper slopes and anoligotrophic euphotic zone (SCOULLOSet al., 2007). However, the zoobenthicassemblages in the lower circalittoral zoneof this part of the gulf are indicative ofmoderate pollution due to the increased

Medit. Mar. Sci., 9/2, 2008, 35-5244

Table 2Differences in the abundance (ind. /100 m2) of megafauna organisms between before and twelve

months after the start-up of the manipulative experiment at littered and control plots at all sites.A, F and L: Amoni, Frangolimano and Lychnari littered plots in June 2006. AC, FC and LC:

Amoni, Frangolimano and Lychnari control plots in June 2006.

(a) Taxonomic classificationStation Bivalves Cephalopods Crustacea Fish Gastropods MiscA 7 0 3 23 2 217F 1 -1 4 48 1 225L 1 0 40 -6 112 229AC 0 0 0 36 0 37FC 1 0 0 3 0 2LC 1 -1 -2 -1 -1 10

(b) Feeding typeStation Predatory Suspension feeders Deposit feedersA 25 224 3F 47 226 4L 106 229 41AC 36 37 0FC 3 3 0LC 3 12 -2

(c) Motility patternStation Partially motile Highly motile Sedentary CrypticA 12 -2 217 25F 5 0 226 47L 153 1 228 -6AC 0 0 37 36FC 1 -1 2 4LC -3 -1 11 -1

organic load and nutrients transported bythe prevailing westward currents from theinner Saronikos Gulf (NCMR, 1999).

On the other hand, the sandy infralit-toral benthic communities of the westernpart were examined for the first time dur-ing the course of this study. The speciescomposition at the three study sites, A, Fand L, indicated the co-existence of taxafound at a variety of infralittoral and cir-calittoral biocoenoses as described byPERES (1967). These biocoenosesinclude the ‘coastal detritic’ community(DC) and the communities of sands ormuddy sands in shallow areas protectedagainst wave action and currents (SRPVand SVMC, respectively), and other sub-littoral communities described at unpol-luted heterogeneous sediments in coastalareas of the western and central Mediter-ranean Sea (DRAGO & ALBERTELLI,1978; SIMONINI et al., 2004; COSE-

NTINO & GIACOBBE, 2006). Thisresemblance is consistent with the obser-vation that the sediments across the studyarea varied from fine to medium sandsand remained highly heterogeneous, asshown by the poor sorting coefficient ofgrain size (KATSANEVAKIS et al.,2007), thus allowing for a great variety ofspecies, with no specific preference ingrain size, to settle and establish sizeablepopulations. This finding is in agreementwith the high temporal and spatial disper-sion at sites A and F.

Marine litter densities on the sea floorof the Saronikos Gulf range from 0.4 to 25items / 100 m2, higher along the northeastcoastline (KATSANEVAKIS & KATSA-ROU, 2004). This is the first study withrespect to the impact of littering on theinfauna in the Saronikos Gulf. Thehypothesis of indirect impact of seafloorlittering upon macrofauna community

Medit. Mar. Sci., 9/2, 2008, 35-52 45

Table 3Testing the effect of plots and sampling time and their interactions on macrofauna communities

at the three study sites using permutational analysis of variance (permanova) and dispersion (permdisp). df: degrees of freedom, perm: permutation, ns: non significant,

*: p < 0.05, **: p < 0.01, ***: p < 0.001. BRAY – CURTIS distance measure was used.

(a) PERMANOVA tests

Amoni Frangolimano LychnariSource of variation df Pseudo-F P(perm) Pseudo-F P(perm) Pseudo-F P(perm)

Time (Ti) 1 3.334 ** 4.304 *** 7.904 ***Plot (Pl) 1 1.492 ns 0.976 ns 2.127 *TixPl 1 1.812 ns 1.206 ns 2.257 *Resisual 16Total 19

(b) PERMDISP tests

Amoni Frangolimano LychnariGroup factor F1, 18 P(perm) F1, 18 P(perm) F1, 18 P(perm)

Time (Ti) 7.777 * 0.784 ns 0.296 nsPlot (Pl) 1.838 ns 10.345 ** 0.002 ns

structure due to attraction of predatoryorganisms, previously absent or at signifi-cantly lower densities, stated byKATSANEVAKIS et al. (2007), predicts

that macroinfauna abundance and speciescomposition will be substantially limitedwithin the littered plots. By contrast, anincrease from June 2005 to June 2006 by

Medit. Mar. Sci., 9/2, 2008, 35-5246

Fig. 4: Euclidean MDS biplot showing the Pearson correlation coefficients of macrofauna species den-sities with MDS axes at each site. Non-metric multidimensional scaling was applied on the range stan-dardized densities of macrofauna species using BRAY-CURTIS similarities. At each biplot prefixes 1and 2 for each sample code denote June 2005 and June 2006, respectively, while the suffix C denotescontrol plot. A: Amoni, F: Frangolimano, L: Lychnari.

106 individuals / 100 m2 in predatorymegafauna at site L coincided with a sig-nificant density increase in macrofauna,especially polychaetes and crustacea.These taxa are included in the prey ofmany infralittoral schooling and crypticfish and decapods (CASTRIOTA et al.,2005; RELLINI et al., 2002) as well as ofthe predatory muricid gastropodHexaplex trunculus (MORTON et al.,2007), which was one of the most abun-dant predators at the littered plots(KATSANEVAKIS et al., 2007). Con-versely, there was observed a significantreduction of macrofaunal molluscs at thissite, which may indicate that bivalves mayhave belonged among the preferred preyof the predatory colonizers of litter. How-ever, molluscs simultaneously increased,not only at the corresponding control plot(2LC) but also at the littered and controlplots at sites A and F, indicating thatchanges in the density of molluscs cannotbe always associated with predatorsattracted by litter. Finally, the noteworthyfilter feeding community that was estab-lished using the litter items as substrates isunlikely to have negatively interacted withmacroinfauna in the adjacent sediments,even though a lot of soft-bottom speciesfound, including those that dominated theinfauna, follow pelagic larval development(RUPPERT et al., 2004).

Regarding organic matter (OM) lev-els at the surface sediments of the studysites, these were elevated for sandy bot-toms. OM values after littering were onaverage 1.2 times higher than before atboth littered and clean surfaces. However,only at site L did these levels exceed 5% atthe littered plots. As pointed out byPEARSON & ROSENBERG (1978) dis-turbances associated with OM enrichmentand the resulting hypoxic conditions in the

sediment leave carnivorous and generallypredatory macrofauna species unaffected,while they affect tolerant subsurface andsurface deposit feeders positively. Con-versely, suspension feeders and speciestypical of later stages of succession in soft-bottom communities are gradually elimi-nated, thus resulting in low diversity andhigh dominance values. At the study areafilter feeding, omnivory-carnivory and sur-face and subsurface deposit feeding werewell represented among the most abun-dant species, implying high trophic com-plexity. Therefore, in terms of trophicstructure, the macrofauna community inthe study area resembled other sandy sub-littoral communities of the MediterraneanSea not directly influenced by eutrophica-tion, exhibiting a wide range of trophicethological habits (GAMBI & GIAN-GRANDE, 1985; CARDELL et al., 1999;SIMONINI et al., 2004).

However, species not affected byalterations and species known to takeadvantage under conditions of environ-mental stress by means of having a shortlife-span, rapid growth and many genera-tions throughout the year, were also pres-ent. These belonged mainly to polychaetesand crustaceans, and exhibited, as expect-ed, considerable variations. Despite thehigh dominance levels of the two mostabundant species (10 to 25% before and15 to 35% after littering), these comprisedgroup 3 colonizers before littering. On theother hand, after littering the contributionand the ranking of the group 2 colonizerssuch as P. kefersteini, A. latreilli, P. lyra andM. gryllotalpa increased at the litteredplots and especially at site L. Simultane-ously, L. lacteus, a species typical of laterstages of succession, remained the mostdominant species at sites A and F whileother bivalves that reach high abundances

Medit. Mar. Sci., 9/2, 2008, 35-52 47

in disturbed sediments, such Corbulagibba, Thyasira flexuosa, Mysella bidentatahad a very low density throughout thestudy. Although the group 2 colonizerswere represented by elevated numbers atlittered and control plots in both samplingtimes, their enhancement after littering atlittered plots, especially at site L, raisesquestions as to whether this is an indica-tion of stress triggered by littering.

Since organic matter levels at sites Aand F were not indicative of enrichmentbut significantly higher LOI% levels atsite L after littering coincided with densemacrophyte detrital cover and the pre-dominance of second order opportunisticspecies, it is reasonable to assume that themacrofauna community was impacted bya reduction in sediment oxygenationcaused by the entrapment and subsequentaccumulation of seagrass detritus. Never-theless, the accumulation started takingplace only two months before the end ofthe manipulative experiment, i.e. June2006, thus indicating that changes detect-ed in this study could be the first stages ofa gradual organic enrichment process. It isnoteworthy that comparable LOI% valueswere recorded in the sediments adjacentto artificial reefs that trapped macroalgalphytodetritus at their periphery (WILDING,2006). The accumulation of phytodetritalmaterial for longer periods is expected tocause effects similar to that of localizedorganic enrichment (GRAY et al., 2002).As the phytodetrital mats significantlyreduce water movement over the sedi-ment, the bottom water in the mats isoften stagnant, resulting in a permanentlyanoxic sediment surface. It is possible thatthe marked increase of P. kefersteini at Llittered plots, where there was a pro-nounced accumulation of seagrass debris,is an indication of the hypoxia caused by

the slow decomposition rates of seagrassleaves. Apart from the nature of thedeposited material, the extent of theimpact of the accumulation of phytodetri-tus is proportional to a number of factors,including decreases in current velocityaround the litter (WILDING, 2006).Given the small volume of the litter itemsin the present study, impacts related tochanges of hydrodynamic regime aroundthe marine litter may take longer than ayear (i.e. the duration of the manipulativeexperiment of the present study) to bedetectable. The entrapment of phyto-detritus and subsequent changes in sedi-ment oxygenation around artificial reefs isa side-effect of littering on macrofauna ofadjacent sediments, as the entrapment ofphytodetritus was facilitated by the deploy-ment of litter and requires a longer moni-toring for an adequate evaluation of theimpact on soft-bottom macrozoobenthos.

It has been estimated that up to 70%of the marine litter that enters the seaends up on the sea bed (UNEP, 2005).The studies indicating that discardedwaste material, in the form of pieces ofmetal, glass, plastic, tyre and wood doesprovide usable habitat for subtidal inver-tebrates and fish either in areas wherenatural habitat is lost or even in non-pol-luted areas are gradually increasing(CHAPMAN & CLYNICK, 2006; KA-TSANEVAKIS et al., 2007). The lack ofsignificant differences between litteredand control plots at sites A and F, pre-clude any generalization about the effectof littering on macrofauna. Logisticrestrictions did not allow for several sam-pling times before and several samplingtimes after littering and adequate withinsite replication of plots, so as to estimatethe range of natural fluctuations of macro-fauna populations in the area and elimi-

Medit. Mar. Sci., 9/2, 2008, 35-5248

nate effects of short-term temporal varia-tion. However, the present study demon-strated the increase of second orderopportunistic macrofauna species adja-cent to marine litter sediments in thepresence of seagrasses trapped within thelittered plots. Further manipulative stud-ies, with extensive temporal replication ata variety of receiving environments with avariety of waste materials are required soas to evaluate the full array of impacts ofmarine litter at sublittoral areas.

Acknowledgements

The project was co-funded by theEuropean Social fund and NationalResources (Hellenic Ministry of NationalEducation and Religious Affairs:EPEAEK II: Pythagoras II). We wouldlike to thank E. Kyriakou for her help inmacrofauna sorting.

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Published on line: December 2008