Seasonal variations of epilithic diatoms on different hard substrates, in the northern Adriatic Sea

Seasonal variations of epilithic diatoms on di¡erenthard substrates, in the northern Adriatic Sea

Cecilia Totti*P, Emellina Cucchiari*, Mario De StefanoO, Chiara Pennesi*,Tiziana Romagnoli* and Giorgio Bavestrello*

*Dipartimento di Scienze del Mare, Universita' Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy.ODipartimento di Scienze Ambientali, Seconda Universita' di Napoli, viaVivaldi 43, 81100 Caserta, Italy.

PCorresponding author, e-mail: [email protected]

The colonization of epilithic diatoms on arti¢cial hard substrates (marble, quartzite and slate) wasinvestigated on a seasonal basis in a subtidal site of the northern Adriatic Sea to determine ifsubstrate-dependent di¡erences in colonization occurs and to de¢ne the seasonal variations of micro-epilithic communities in terms of abundance, biomass and community structure. Arti¢cial substrates(smoothed small discs mounted on a Plexiglas sheet) were placed at a depth of 8m in April 2003, July2003, January 2004 and February 2004. The discs were collected after 6^7 weeks for counting and taxo-nomic identi¢cation of the diatoms. The community structure of epilithic diatoms showed a dominance ofmotile species over the entire study period, followed by erect, adnate and tube-dwelling diatoms. Diatomdensity showed a marked seasonal variability, ranging from 365�407 (winter 2004) to 557156�82602cells cm72 (spring 2004). Biomass ranged from 0.02�0.01 to 17.53�3.20 mg C cm72. Abundance andbiomass values did not present any signi¢cant di¡erences for the three substrates examined.

INTRODUCTION

Benthic microalgae represent an important componentof marine ecosystems, and in shallow coastal areas maycontribute greatly to the total primary productioncommonly attributed to phytoplankton only (MacIntyreet al., 1996). Microphytobenthos communities includeepipelon, endopelon, epipsammon, epilithon, endolithon,epiphyton and epizoon, depending on the substrates withwhich they are associated (Round, 1971). In freshwaterenvironments, benthic microalgae are often included inthe periphyton, de¢ned as a complex community of micro-biota (algae, bacteria, fungi, animals) and detritus that isattached to a substrate, inorganic or organic, living ordead (Liboriussen, 2003).

In recent decades, many studies have been carried outon soft-bottom marine microphytobenthos communities(epipelon, epipsammon) in both intertidal and subtidalareas (Cahoon & Cooke, 1992; Barranguet et al., 1996;Welker et al., 2002; Totti, 2003), and a major contributionto primary production and biomass has often beenreported. In contrast, little is known about marineepilithic communities. Although a rich literature is avail-able on epilithic microalgae and, more generally, onperiphyton in freshwater systems (Hoagland, 1983; Korte& Blinn, 1983; Hamilton & Duthie, 1984; Bothwell et al.,1989; Sabater et al., 1998; Wellnitz & Ward, 1998;Greenwood et al., 1999; Sherwood & Sheath, 1999;Barbiero, 2000; Tuji, 2000a,b; Wellnitz & Ward, 2000;Kahlert et al., 2002; Hameed, 2003; Liboriussen, 2003;Michelutti et al., 2003; Soininen et al., 2004), reports onabundances and composition of marine microepilithiccommunities are scant and mostly referred to areas other

than the Mediterranean (Hudon & Bourget, 1981; Snoeijs& Prentice, 1989; Hillebrand & Sommer, 1997, 2000;Hillebrand et al., 2000; Busse, 2002; Siqueiros-Beltrones& Valenzuela-Romero, 2004; Siqueiros-Beltrones et al.,2005).

Epilithic microalgae grow attached to rocks or arti¢cialhard substrates and, in marine environments, mainlyinclude diatoms and cyanobacteria. Benthic microalgaeand bacteria represent the ¢rst colonizers of hardsubstrates. It has been shown that the presence of themicrobial mat, composed of bacteria and unicellularalgae (‘primary pellicle’), enhances the further coloniza-tion of the substrate by plants and animals (Round, 1981).Epilithic diatoms include both motile free-living diatomsand attached forms (Round, 1971). The free-living speciesare all pennate biraphid diatoms able to move over thesubstratum, while the attached forms include araphid andmonoraphid diatoms, which exhibit two main modes ofattachment. In the ¢rst mode, the cells lie on the substratealong the entire valve surface and have limited motility:adnate or adpressed growth forms (e.g. Cocconeis, Amphora).In the second mode, the cells are attached to the substrateat one valve pole through mucus pads, (e.g. Synedra,Fragilaria) or peduncles (e.g. Licmophora, Grammatophora):erect growth forms. Tube-dwelling diatoms, which aremotile naviculoid or nitzschioid species living in mucilagetubes of their own making, are also among the epilithicalgae. The tubes appear as ¢lamentous formations, resem-bling small brown seaweeds or ¢lamentous cyanobacteriamats (Lobban, 1985, 1990).

In the past, it was commonly believed that the composi-tion and density of benthic communities was independentof the nature of the substrate. However, recent

J. Mar. Biol. Ass. U.K. (2007), 87, 649^658Printed in the United Kingdom

Journal of the Marine Biological Association of the United Kingdom (2007)

doi: 10.1017/S0025315407054665

observations (Bavestrello et al., 2000) would appear toindicate that the mineralogical composition of thesubstrate may markedly a¡ect the settlement of somebenthic species, and that communities grown on di¡erentsubstrates may exhibit signi¢cant di¡erences in terms ofabundance and composition. In particular, it is knownthat in marine environments quartz-rich substrates hostpoor and less diversi¢ed biocenoses than carbonatic ones.These inhibiting e¡ects of quartz on the development ofmany marine invertebrates have been known since thenineteenth century, and have been related to the oxidantproperties of the crystal surface and to the formation ofsilanolic groups (Bavestrello et al., 2000). For organismssuch as diatoms which utilize silicon for their growth, thesituation might well be di¡erent. Epilithic algal commu-nities are mainly a¡ected by a number of environmentalfactors, such as light intensity, salinity, nutrient concentra-tion, grazing pressure and wave action. On the otherhand, the in£uence of the substrate on algal settlement,has been regarded as less important, and the mineralo-gical nature of the rock has been hypothesized to be aneutral parameter (Cabioc’h et al., 1992). Recently, Pennaet al. (2003) pointed out that under experimental condi-tions the growth rates of several diatom species di¡ereddepending on the nature of the silica source. In particular,diatoms grew better in the presence of a mineral crystal-line silica source (quartz sand and quartz dusts) than inthe presence of biogenic amorphous silica (diatomaceousearth and sponge spicules). The authors interpreted theirresults by hypothesizing a direct interaction of diatomswith particulate mineral substrates, which may involvesome chemical compound, secreted by the diatoms, thatwould enhance the dissolution of silicic acid, either bycell-particle contact or by molecular di¡usion, as hasbeen reported for some marine sponges (Bavestrello etal., 2003). These observations suggested testing thehypothesis of a selective growth of marine microepilithicalgae on hard substrates of di¡erent mineralogical compo-sition: i.e. marble (consisting mainly of CaCO3), quartzite(consisting mainly of quartz, i.e. SiO2) and slate (with acomplex composition that is only 35% quartz).

The aims of this paper are: (i) to test if a di¡erentnatural colonization by marine microalgae on threedi¡erent hard substrates of di¡erent mineralogical compo-sition (quartzite, slate and marble) occurs; and (ii) toinvestigate the seasonal variability of microepilithic popu-lations in a coastal area of the northern Adriatic Sea interms of abundance, biomass and community structure.

MATERIALS AND METHODS

Sampling and sample preservation

The study was carried out from April 2003 to April 2004on a seasonal basis. Epilithic microalgae were sampled usingsmall circular discs of di¡erent mineralogical composition(quartzite, slate and marble) with a diameter of 33^35mmand a thickness of 3^7mm. Before the experiment, thesurfaces of the discs were smoothed to avoid di¡erences inthe roughness of the substrates. The small discs wereattached to a Plexiglas sheet and were arranged in sevenrows at a distance of 3 cm from each other, each rowhaving three discs, all made of di¡erent material.

The Plexiglas sheet was then immerged in seawater o¡Sassi Neri, along the Conero coast of the Ancona region(northern Adriatic Sea), and anchored at a depth ofapproximately 8m, about 2m above the bottom (Figure1). After 40^50 d, the Plexiglas sheet was hauled up.

Microphytobenthos counting was carried out on threereplicates for each material: three discs of each materialwere scraped, and the microalgae were collected inFalcon tubes; samples were preserved by adding a knownamount (15ml) of ¢ltered seawater with 2% formalin,neutralized with hexamethylenetetramine (Throndsen,1978).

Moreover, for each material one disc was scraped andthe algae were collected into glass tubes for cleaning andtaxonomic identi¢cation of the diatoms under the scan-ning electron microscope (SEM).

Finally, for each material one disc was broken into smallpieces, which were preserved with seawater and formalinat 2%, to be treated in the Critical Point Dryer and thenanalysed by SEM, for the study of the community in situ.

This sampling procedure was carried out seasonally, inlate spring 2003, summer 2003, winter 2004 and earlyspring 2004; unfortunately, the sampling planned for theautumn of 2003 was impossible because a storm causedthe loss of the Plexiglas sheet.

Microphytobenthos counting

The determination and counting of the microphyto-benthos were carried out with an inverted ZEISS Axiovert135 microscope, equipped with phase contrast, byUtermo« hl method, modi¢ed according to Totti et al.(2004). The procedure involved the following steps:

^ the sample was stirred gently and at length to make ithomogeneous;

^ then a subsample was taken using a pipette and pouredinto a cylinder (10 cm3)/sedimentation chambercomplex previously ¢lled with ¢ltered seawater; here itwas left to settle for at least ten hours; this methodproduces a homogeneous distribution of microalgae atthe bottom of the sedimentation chamber and makes itpossible to examine a portion of a chamber with aknown area (transects or casual ¢elds);

650 C. Totti et al. Seasonal variations of epilithic diatoms


Figure 1. Map of the northern Adriatic Sea, with location ofthe study area.

^ counting was carried out on 1^2 perpendicular trans-ects at 4006 magni¢cation. During counting, cellswere measured using a micrometer eyepiece, for theestimate of biomass by means of cell biovolumes afterStrathmann (1967). Then the entire sedimentationchamber was observed at a magni¢cation of 206 toobtain a more correct estimate of less abundant taxahaving a great biovolume;

^ abundance and biomass values were then calculatedand expressed as number of cells cm72 and mg C cm72

respectively.

Cleaning method

This procedure was applied to remove the organicmatter from the diatom frustules, allowing the observationof the frustule ultrastructure. Before the cleaning process,samples were washed to remove salt and excess ¢xative:about 2ml of sample were centrifuged (3000 rpm,10min), and the supernatant was removed using apipette; a fresh washing agent was added, the pellet wasresuspended and the sample was centrifuged. This wasrepeated three times.

Then the sample was treated following the von Stoschmethod (Hasle & Syvertsen, 1997): nitric acid (64%) andsulphuric acid (97%) were added in a quantity of 1:1 and3:1 in proportion to the sample volume respectively; thesample was stirred and heated for *3 min with analcohol lamp until it became clear; after cooling, thesample was washed three times by centrifugation withdistilled water. Finally, the material obtained, similar to ahyaline powder, was preserved in DDW with a few dropsof acetic acid (Totti et al., 2004).

Before SEM observation, one or more drops of cleanedmaterial were placed on a Nucleopore polycarbonate ¢lterstuck on a stub and left to air-dry completely. Finally, thestub was sputter-coated with a thin layer of gold-palladium.

Treatment of samples in the Critical Point Dryer

Samples (surface fragments of broken discs) were dehy-drated by immersion in alcohol of increasing concentra-tions (10, 25, 50, 60, 80, 90, 95, 100%). Then the sampleswere treated in a Critical Point Dryer (CPD 010 BalzersUnion FL-9496), which replaces alcohol with CO2 toavoid the collapse of microalgae cells.

Seasonal variations of epilithic diatoms C.Totti et al. 651


Figure 2. (A) Total diatom abundance (cells cm72) and (B) biomass (mgC cm72) in the three substrates considered during thestudy period.



Figure 3. Percentage composition of diatom communities, in terms of growth forms (abundance and biomass), on the threesubstrates considered during the study period (er: erect; adn: adnate; mot: motile; plo: plocon; tub: tube-dwelling; pla: planktonic;inc: Incrertae sedis). Late spring 2003: per cent composition in terms of (A) abundances and (B) biomass. Summer 2003: per centcomposition in terms of (C) abundances and (D) biomass. Winter 2004: per cent composition in terms of (E) abundances and (F)biomass. Spring 2004: per cent composition in terms of (G) abundances and (H) biomass.



Figure 4. Epilithic diatom growth forms. A^C adnate: (A) community of Cocconeis scutellum var. scutellum on slate panels; (B)community of Cocconeis neothumensis var. marina on quartzite panels together with bacteria; (C) community of Amphora cf. ovalis var.pediculus attached to quartzite panel. D^H erect diatoms; (D) community of Tabularia tabulata attached on marble panels throughmucus pads; (E) colony of Grammatophora marina attached on marble panels by mucus pads; (F) specimen of Achnanthes cf. longipesattached on marble panel by a mucilage stalk; (G) specimens of Licmophora debilis adhering a marble panel with their mucilage pad;and (H) specimens of Synedra sp. attached on slate panel. I^K motile diatoms: (I) specimens of Tryblionella sp., (J) Navicula sp. and(K) Pleurosigma cf. strigosum on marble panels. Scale bars: A, F, G, H, I, 20 mm; B, C, 5 mm; E, J, 10 mm; D, K, 50 mm.

At the end of this treatment, each fragment was placedon a stub and covered with gold-palladium to be observedunder the SEM.

Statistical analysis

Di¡erences in cell density and biomass among di¡erentmaterials and sampling-times were tested with the multi-variate analysis of variance (MANOVA) test, usingStatistica (StatSoft) software. Whenever a signi¢cantdi¡erence for the main e¡ect was observed (P50.05), aTukey’s pairwise comparison test was also performed.

RESULTS

Epilithic microalgal assemblages were composed mainlyof diatoms. Sporadically, cyanobacteria, dino£agellatesand clorophyceans were also observed. The results wereexpressed as the mean of the three replicates �SE. Thelist of diatom taxa observed in the epilithic communitiesis shown inTable 1.

Diatom abundance and biomass in the three materialsconsidered and in the four seasons are represented inFigure 2A&B. Our results indicate that the assemblagesof epilithic microalgae did not di¡er signi¢cantly(MANOVA, ns) in terms of abundance and compositionfor the three substrates (quartzite, slate and marble).

Epilithic microalgae exhibited a marked seasonal varia-bility, with signi¢cantly higher abundances in spring 2004than in any other period (Tukey test, P50.001). In spring,mean abundance and biomass values were 557,156�82,602cells cm72 and 17.53�3.20 mgC cm72 respectively. Thelowest values were observed in winter 2003 (abundance365�407 cells cm72, biomass 0.02�0.01 mgC cm72).

Epilithic diatoms were divided into the followinggrowth forms (Round, 1981): erect (i.e. mainly araphidspecies attached to the substrate through mucus pads orpeduncles), adnate (i.e. mainly monoraphid speciesattached to the substrate through the raphe valve andsome biraphid species, such as Amphora spp.), motile (i.e.biraphid species that can move freely on the substrate),tube-dwelling (i.e. naviculoid and nitzschioid diatomsliving in mucilage tubes of their own making), plocon(algae that are loosely associated with the substrate, suchas centric diatoms and cyanobacteria), and planktonic (i.e.truly planktonic species which settled on the substratumfrom the water column, remaining vital and photosynthe-sizing). The composition of epilithic communities duringthe study period is shown in Figure 3, while growthforms are illustrated in Figure 4.

Late spring 2003

Diatom abundance observed in this period ranged from84,884�21,435 to 125,631�34,979 cells cm72 on marbleand slate respectively (Figure 2A). Biomass was12.23�3.97 and 14.05�3.39 mgC cm72 on slate andmarble respectively (Figure 2B). No signi¢cant di¡erenceswere observed between the three substrates in terms ofabundance and biomass of epilithic diatoms. The commu-nity structure showed that freely motile diatoms prevailedin terms of abundance, accounting, on the average, for71% of the microepilithic assemblage (Figure 3A). The

most important were Plagiotropis sp., Nitzschia longissima

and undetermined naviculoid diatoms. Erect forms repre-sented from 18.7 to 30.2% of diatom abundance. Theyconsisted mainly of Tabularia tabulata and Licmophora spp.(L. £abellata, L. grandis, L. cf. abbreviata, L. debilis). Adnatediatoms were represented by Amphora cf. co¡eaeformis andCocconeis scutellum, and their contribution to the total abun-dance ranged from 3.2 to 8.3%. Other growth forms wereonly poorly represented. Although they did not representthe most abundant fraction, the erect forms, due to theirlarger size, accounted for the largest portion of the diatombiomass (80.9%; Figure 3B).

Summer 2003

Epilithic diatom abundance and biomass values werelower than those observed in the previous period (Figure2A&B). Minimum values were observed on marble interms of both density (8177�4237 cells cm72) andbiomass (0.43�0.21 mg C cm72), while maximum levelswere observed on slate (density 24691�9297 cells cm72,biomass 1.53�1.13 mg C cm72). No signi¢cant di¡erenceswere observed for the three substrates in terms of abun-dance, biomass and community structure. Freely motileforms dominated the microphytobenthos community interms of abundances (76.3%) and biomass (39.9%)(Figure 3C,D).They were represented by small naviculoiddiatoms, followed by Nitzschia spp. (N. longissima, N. cf.pellucida, N. cf. sigma), Plagiotropis sp. and Gyrosigma sp.Adnate diatoms (mainly Amphora spp.) accounted for anaverage 15.2% of microphytobenthos density and 6.4% ofbiomass, followed by plocon (mainly Bacillaria paxillifera),which represented 3.6% of density and 18.6% of biomass.Erect forms (Licmophora sp., Grammatophora marina andG. oceanica) accounted for 2.8% of total density and22.4% of biomass. Tube-dwelling diatoms were alsoobserved (Nitzschia macilenta, Scolioneis sp.) at 0.1% ofdensity and 12.6% of biomass.

Winter 2004

Epilithic assemblages observed in winter 2004 displayedthe lowest values of abundance and biomass observedduring the study period (Figure 2A&B). Abundancesranged from 126�79 cells cm72 on marble to 835�827cells cm72 on slate; average biomass was 0.02 mg C cm72.Motile forms (small naviculoid species and Nitzschia

longissima) were the dominant ones (on average, 72.3% ofdensity and 58.8% of biomass, Figure 3E&F). A highcontribution of the planktonic species Skeletonema marinoi

to diatom abundance was observed on slate, due to thesettlement on the substrate from the water column duringthe winter bloom.

Spring 2004

The microphytobenthic community observed in spring2004 showed the highest values in terms of abundanceand biomass of the entire study period (Figure 2A&B).Density ranged from 462,642�244,786 cells cm72 inquartzite to 615,526�138,305 cells cm72 in marble,while biomass went from 13.85�7.68 mg C cm72 inquartzite to 19.68�8.41 mg C cm72 in slate.



The community structure showed a high diversi¢cation.The main fraction was represented by the motile formswhich represented on average the 72.5% and 58.3% interms of abundance and biomass respectively (Figure 3G&H). The most important taxa were undeterminedsmall naviculoid diatoms, Plagiotropis sp., Hantzschia sp.,Nitzschia spp. (N. cf. pellucida, N. longissima, N. cf. sigma),Navicula spp. (N. cf. directa, N. cf. lata, N. cf. vanhoe¡eni),Psammodictyon panduriforme, Pleurosigma cf. strigosum.

Erect forms accounted for 10.1% of total density and for31.6% of total biomass, and were mainly represented byTabularia tabulata. A minor presence of Grammatophora

marina, G. oceanica, Licmophora cf. abbreviata and L. debilis

was also observed.Adnate forms represented 2.8% of total density and

2.2% of total biomass. They were represented by Amphoracf. co¡eaeformis and otherAmphora spp.

In this period, a relatively high percentage of tube-dwelling diatoms was also observed, accounting for 2.4%of total density and 2.7% of total biomass: the main taxawere Berkeleya rutilans and Nitzschia macilenta and a tube-forming Navicula sp.

Planktonic diatoms (Skeletonema marinoi) were presentwith relatively high values on all the substrates (onaverage, 11.4% of density and 3.9% of biomass).

DISCUSSION

This study presents the ¢rst data on the distribution ofepilithic microphytobenthos not only for the Adriatic Sea,but for the Mediterranean sensu lato, making possible adescription of their seasonal variability and the in£uenceof di¡erent mineral substrates on their growth. Our dataclearly indicate that no signi¢cant di¡erences in terms ofabundance, biomass and community structure occurredfor the three substrates considered. Moreover, a highseasonal variability of epilithic microalgal communitieshas been pointed out.

The relationships between substrate and the associatedbenthic community have been investigated in severalstudies. Although a signi¢cant in£uence of the substratetype has been recognized for the settlement of some inver-tebrates (Bavestrello et al., 2000; Faimali et al., 2004),plant communities have been considered to be generallyindependent of the type of substratum (Cabioc’h et al.,1992). In several studies on periphytic communities, it hasbeen noted that no di¡erences in terms of periphytongrowth and composition occur among several kinds ofarti¢cial substrates (Hamilton & Duthie, 1984; Sabater etal., 1998), whereas many authors reported signi¢cantdi¡erences between arti¢cial and natural substrates



Table 1. List of identi¢ed diatom taxa.

(Burkholder et al., 1990; Pinckney & Micheli, 1998; Albay& Akcaalan, 2003; Romagnoli, 2005).

As for marine diatoms, previous observations high-lighted a relationship between the diatom growth and thesilica content of substrates: Penna et al. (2003), studyingdiatom growth in the presence of di¡erent forms of silicasources, demonstrated that diatoms grew better on crystal-line than amorphous substrates, and a direct interactionbetween diatoms and particulate mineral substrate hasbeen hypothesized. Nevertheless, our results show thatunder natural conditions the chemical composition of thesubstrate did not a¡ect the diatom abundance andcomposition. Our results are in agreement with previousreports on the colonization of hard substrates by plantcommunities. It has been reported that, even if thesubstrate type makes a di¡erence in the primary coloniza-tion, these initial di¡erences vanish over colonizationtime, and similar communities can be observed on avariety of di¡erent materials (Hamilton & Duthie, 1984;Sabater et al., 1998).

Besides the chemical composition of the substrate, itsphysical structure should also be considered. Faimali etal. (2004) showed that a di¡erent bio¢lm compositionoccurred in glass, quartz, marble and cembonit andinvoked the importance of microtexture in determiningthese di¡erences. They observed that under controlledexperimental conditions the nature of the substrate canmodify the pattern of bio¢lm development, and signi¢cantdi¡erences were found between smooth (glass) and rough(quartz, marble and cembonit) surfaces. Although the roleof microtexture has not been speci¢cally addressed in thispaper, all the materials considered are held to be homoge-neous with regard to their roughness, as the surface ofdiscs was smoothed to avoid di¡erences among thesubstrates. Moreover, it should be considered that the rela-tionships between diatom communities and substrate aremediated by the presence of the bacterial bio¢lm that ¢rstcovers the substrate in the succession phases. Peterson &Stevenson (1989) reported that the presence of bacterialbio¢lm on arti¢cial substrates may enhance or inhibit thegrowth of di¡erent diatom species.The presence of organicbio¢lm makes the substrate uniform, and therefore mayreduce any selective preference displayed by substrates(Korte & Blinn, 1983).

Epilithic microalgal communities in our studywere represented almost exclusively by diatoms, whichexhibited marked seasonal variations. Highest abundanceand biomass values (557,156�82,602 cells cm72 and17.53�3.20mgC cm72 respectively) were observedbetween February and April 2004 (spring), whereas theperiod between January and February 2004 (winter) hadthe lowest values (365�407 cells cm72, biomass0.02�0.01 mgC cm72 respectively). These values were oneorder of magnitude lower than those reported for epipeliccommunities of intertidal areas, considered to be the mostproductive (Delgado et al., 1991; Peletier, 1996), butcomparable to those observed in some subtidal sites(Plante-Cuny et al., 1993). In general, a marked seasonalvariability in microphytobenthic communities is morefrequent in the intertidal regions, where the variations ofenvironmental factors are more pronounced, whereasdeeper subtidal communities appear to be more stable,due to a smaller in£uence of atmospheric variables

(MacIntyre et al., 1996). However, a seasonal variabilityhas also been reported for subtidal areas. In the Mediter-ranean, the soft-bottom microphytobenthos show anannual cycle with two maxima, in spring and autumn(Barranguet, 1997). A seasonality for the epilithic commu-nities has also been reported in freshwater environments:in temperate lakes, a maximum for epilithic communitieshas been described in summer (Goldsborough &Hickman, 1991; Kahlert et al., 2002) as well as in winter(Mu« ller, 1999). Our results are in agreement with theseasonal variability of the planktonic communities of thesame area, which exhibit the annual maximum in latewinter^spring due to diatom bloom (Totti et al., 2000;Bernardi-Aubry et al., 2004), and are related to the length-ening in daylight period coupled with the sharp nutrientincrease after the winter mixing (Marini et al., 2002).

Several phases have been recognized in the colonizationof a new hard substrate: in the ¢rst phase, only bacteriaand organic detritus settle on the substrate; afterwards,diatoms that lie £at on the substrate (i.e. adnate andmotile forms) appear together with erect ‘rosette forming’species; in the last phase, there is massive growth of erectstalked diatoms, which create a complex three-dimen-sional community (Korte & Blinn, 1983; Tuji, 2000a,b).These succeeding phases seem to be the same in all themicroalgal communities that colonize hard substrates, i.e.epilithic, epiphytic and epizoic. Considering that oursubstrates were left immerged over a 6^7 week period,the communities that we observed were mature and canbe considered representative of the period. In fact, severalstudies on epilithic communities have shown that a stablephase is always reached after 3^5 weeks (Hoagland et al.,1982; Hoagland, 1983; Hamilton & Duthie, 1984;Kusakabe, 1988; Tanaka & Watanabe, 1990; Tuji, 2000a;Hameed, 2003) and is characterized by the developmentof erect forms.

Considering the community structure in terms ofgrowth forms, a di¡erent composition was observed inthis study, related to the seasons. The motile forms repre-sented the main fraction in terms of cell density during theentire study period. Erect growth forms increased inimportance in the community in spring and late spring,while they showed a marked decrease in summer and,due to their higher biovolumes, they accounted for a highfraction of total biomass. Adnate diatoms increased inrelative importance in summer, while tube-dwellersshowed a peak in spring. Plocon and planktonic diatomswere almost negligible. The presence of planktonic speciesduring winter is related to the classic winter bloom of thenorthern Adriatic Sea (Bernardi-Aubry et al., 2004),which involves small colonial diatoms.The observed domi-nance of motile forms may be due to the ability of thesebiraphid taxa to move within a mature mat, which maymake them superior competitors for nutrients and light(DeNicola & McIntire, 1990). Erect forms, on the otherhand, bene¢t from a better exposure to light, hydrodyna-mism and nutrient availability (Tuji, 2000b; Liboriussen,2003). Speci¢cally, the formation of mucilaginous stalks bysome diatom species may confer a competitive advantagewhere light is limiting, providing a position that risesabove the mat (Wellnitz & Ward, 2000).

One major factor which can shape the structure ofepilithic communities is the grazing pressure, which can



reduce the vertical structure of microalgal mat by prefer-ential removal of the erect forms (Hillebrand et al., 2000;Wellnitz & Ward, 2000). Although the grazing in£uencewas not speci¢cally addressed in this study, the decreaseof erect growth forms, coupled with a percental increaseof adnate forms observed in summer, may be related toan increase in grazing pressure in summer (Danovaro,1996), as is also suggested by the presence of nematodesin samples.

Epilithic microalgal communities observed in thepresent study were abundant and diversi¢ed, with valuescomparable to those observed for the epipelic microalgaeof other subtidal areas. Although our data refer to arti¢cialhard substrates, we postulate that they would also be indi-cative of natural epilithic populations, which thereforemay represent an important component of the microalgalcommunities of coastal marine environments, and whichare at the moment completely neglected in theMediterranean Sea.

The authors are grateful to Dr Carlo Cerrano for providingmineral substrates used in this study. A special thanks to DrF.A.S. Sterrenburg for revising the manuscript.

REFERENCESAlbay, M. & Akcaalan, R., 2003. Comparative study of periph-yton colonisation on common reed (Phragmites australis) andarti¢cial substrate in a shallow lake, Manyas, Turkey.Hydrobiologia, 506^509, 531^540.

Barbiero, R.P., 2000. A multi-lake comparison of epilithicdiatom communities on natural and arti¢cial substrates.Hydrobiologia, 438, 157^170.

Barranguet, C., 1997. The role of microphytobenthic primaryproduction in a Mediterranean mussel culture area. Estuarine,Coastal and Shelf Sciences, 44, 753^765.

Barranguet, C., Plante-Cuny, M.R. & Alivon, E., 1996.Microphytobenthos in the Gulf of Fos, French Mediterranean.Hydrobiologia, 333, 181^193.

Bavestrello, G., Benatti, U., Cattaneo-Vietti, R., Cerrano, C. &Giovine, M., 2003. Sponge cell reactivity to various forms ofsilica. Microscopy Research andTechnique, 62, 327^335.

Bavestrello, G., Bianchi, C.N., Calcinai, B., Cattaneo-Vietti, R.,Cerrano, C., Morri, C., Puce, S. & Sara' , M., 2000. Bio-miner-alogy as structuring factor for marine epibenthic communities.Marine Ecology Progress Series, 193, 241^249.

Bernardi-Aubry, F., Berton, A., Bastianini, M., Socal, G. & Acri,F., 2004. Phytoplankton succession in a coastal area of the NWAdriatic, over a 10-year sampling period (1990^1999).Continental Shelf Research, 24, 97^115.

Bothwell, M.L., Suzuki, K.E., Bolin, M.K. & Hardy, F.J., 1989.Evidence of dark avoidance by phototrophic periphyticdiatoms in lotic systems. Journal of Phycology, 25, 85^94.

Burkholder, J.M., Wetzel, R.G. & Klomparens, K.L., 1990.Direct comparison of phosphate uptake by adnate and looselyattached microalgae within an intact bio¢lm matrix. Appliedand Environmental Microbiology, 56, 2882^2890.

Busse, S., 2002. Benthic diatoms in the Gulf of Bothnia. Community

analysis and diversity. PhD thesis, Acta Universitatis UpsaliensisUppsala, Sweden.

Cabioc’h, J., Floc’h, J.Y., Le Toquin, A., Boudouresque, C.F.,Meinesz, A. & Verlaque, M., 1992. Guide de algues des mers

d’Europe. Neucha“ tel: Delachaux et Niestle¤ .Cahoon, L.B. & Cooke, J.E., 1992. Benthic microalgal produc-tion in Onslow Bay North Carolina USA. Marine Ecology

Progress Series, 84, 185^196.

Danovaro, R., 1996. Detritus-bacteria-meiofauna interactions ina seagrass bed (Posidonia oceanica) of the NW Mediterranean.Marine Biology, 127, 1^13.

Delgado, M., DeJonge,V.N. & Peletier, H., 1991. Experiments onresuspension of natural microphytobenthos populations.Marine Biology, 108, 321^328.

De Nicola, D.M. & McIntire, C.D., 1990. E¡ects of substraterelief on the distribution in laboratory streams. I. Hydrology.Journal of Phycology, 26, 624^633.

Faimali, M., Garaventa, F., Terlizzi, A., Chiantore, M.C. &Cattaneo-Vietti, R., 2004. The interplay of substrate natureand bio¢lm formation in regulating Balanus amphitrite

Darwin, 1854 larval settlement. Journal of Experimental Marine

Biology and Ecology, 306, 37^50.Goldsborough, L.G. & Hickman, M., 1991. A comparison ofperiphytic algal biomass and community structure on Scirpus

validus and on a morphologically similar arti¢cial substratum.Journal of Phycology, 27, 196^206.

Greenwood, J.L., Clason, T.A., Lowe, R.L. & Belanger, S.E.,1999. Examination of endopelic and epilithic algal communitystructure employing scanning electron microscopy. FreshwaterBiology, 41, 821^828.

Hameed, H.A., 2003. The colonization of periphytic diatomspecies on arti¢cial substrates in the Ashar canal, Basrah,Iraq. Limnologica, 33, 54^61.

Hamilton, P.B. & Duthie, H.C., 1984. Periphyton colonization ofrock surfaces in a boreal forest stream studied by scanningelectron microscopy and track in autoradiography. Journal ofPhycology, 20, 525^532.

Hasle, G.R. & Syvertsen, E.E., 1997. Marine diatoms. InIdentifying marine phytoplankton (ed. C.R. Tomas), pp. 5^385.San Diego: Academic Press.

Hillebrand, H. & Sommer, U., 1997. Response of epilithic micro-phytobenthos of the Western Baltic sea to in situ experimentswith nutrient enrichment. Marine Ecology Progress Series, 160,35^46.

Hillebrand, H. & Sommer, U., 2000. E¡ect of continuousnutrient enrichment on microalgae colonizing hard substrates.Hydrobiologia, 426, 185^192.

Hillebrand, H., Worm, B. & Lotze, H.K., 2000. Marinemicrobenthic community structure regulated by nitrogenloading and grazing pressure. Marine Ecology Progress Series,204, 27^38.

Hoagland, K.D., 1983. Short-term standing crop and diversity ofperiphytic diatoms in a eutrophic reservoir. Journal of Phycology,19, 30^38.

Hoagland, K.D., Roemer, S.C. & Rosowski, J.R., 1982.Colonization and community structure of two periphyton assem-blages, with emphasis on the diatoms (Bacillariophyceae).AmericanJournal of Botany, 69, 188^213.

Hudon, C. & Bourget, E., 1981. Initial colonization of arti¢cialsubstrate: community development and structure studied byscanning electron microscopy. Canadian Journal of Fisheries andAquatic Sciences, 38, 1371^1384.

Kahlert, M., Hasselrot, A.T., Hillebrand, H. & Kurt, P., 2002.Spatial and temporal variation in the biomass and nutrientstatus of epilithic algae in Lake Erken, Sweden. Freshwater

Biology, 47, 1191^1215.Korte,V.L. & Blinn, D.W., 1983. Diatom colonization on arti¢cialsubstrates in pool and ri¥e zones studied by light and scanningelectron microscopy. Journal of Phycology, 19, 332^341.

Kusakabe, A., 1988. Ecological study on epiphytic algae in LakeBiwa. In L. Biwa Research Institute. Lake Biwa Study Monographs,4, 1^61.

Liboriussen, L., 2003. Production, regulation and ecophysiology of

periphyton in shallow freshwater lakes. PhD thesis, NationalEnvironmental Research Institute, Denmark.



Lobban, C.S., 1985. Marine tube-dwelling diatoms of the Paci¢ccoast of North America. I. Berkeleya, Haslea, Nitzschia, andNavicula sect. Microstigmaticae. Canadian Journal of Botany, 63,1779^1784.

Lobban, C.S., 1990. Marine tube-dwelling diatoms of the Paci¢ccoast of North America. II. Navicula subg. Navicula and a key tothe tube-dwelling diatoms of the region. Canadian Journal ofBotany, 68, 707^712.

MacIntyre, H.L., Geider, R.J. & Miller, D.C., 1996.Microphytobenthos: the ecological role of the secret garden ofunvegetated, shallow-water marine habitats. I. Distribution,abundance and primary production. Estuaries, 19, 186^201.

Marini, M., Fornasiero, P. & Artegiani, A., 2002. Variations ofhydrochemical features in the coastal waters of Monte Conero:1982^1990. P.S.Z.N.: Marine Ecology, 23, Suppl. 1, 258^271.

Michelutti, N., Holthman, A.J., Douglas, M.S.V. & Smol, J.P.,2003. Periphytic diatom assemblages from ultra-oligotrophicand UV transparent lakes and ponds on Victoria Island andcomparisons with other diatom surveys in the Canadianarctic. Journal of Phycology, 39, 465^480.

Mu« ller, U., 1999. The vertical zonation of adpressed diatoms andother epiphytic algae on Phragmites australis. EuropeanJournal ofPhycology, 34, 487^496.

Peletier, H., 1996. Long-term changes in intertidal estuarinediatom assemblages related to reduced input of organic waste.Marine Ecology Progress Series, 137, 265^271.

Penna, A., Magnani, M., Fenoglio, I., Fubini, B., Cerrano, C.,Giovine, M. & Bavestrello, G., 2003. Marine diatom growthon di¡erent forms of particulate silica: evidence of cell/particleinteraction. Aquatic Microbial Ecology, 32, 299^306.

Peterson, C.G. & Stevenson, R.J., 1989. Substratum conditioningand diatom colonization in di¡erent current regimes. Journal ofPhycology, 25, 790^793.

Pinckney, J.L. & Micheli, F., 1998. Microalgae on seagrassmimics: does epiphyte community structure di¡er from liveseagrasses? Journal of Experimental Marine Biology and Ecology,221, 59^70.

Plante-Cuny, M.R., Salen-Picard, C., Grenz, C., Plante, R.,Alliot, E. & Barranguet, C., 1993. Experimental ¢eld study ofthe e¡ects of crude oil, drill cuttings and natural biodepositson microphyto- and macrozoobenthic communities in aMediterranean area. Marine Biology, 117, 355^366.

Romagnoli, T., 2005. Comunita' microalgali epibionti sull’Idrozoo

marino Eudendrium racemosum Gmelin. PhD thesis,Universita' Politecnica delle Marche, Ancona, Italy.

Round, F.E., 1971. Benthic marine diatoms. Oceanography and

Marine Biology. Annual Review, 9, 83^139.Round, F.E., 1981. The ecology of algae. Cambridge: CambridgeUniversity Press.

Sabater, S., Gregory, S.V. & Sedell, J.R., 1998. Communitydynamics and metabolism of benthic algae colonizing woodand rock substrates in a forest stream. Journal of Phycology, 34,561^567.

Sherwood, A.R. & Sheath, R.G., 1999. Seasonality of macro-algae and epilithic diatoms in spring-fed streams in Texas,USA. Hydrobiologia, 390, 73^82.

Siqueiros-Beltrones, D.A., Guzma¤ n Del Pro¤ o, S. & Serviere-Zaragoza, E., 2005. Main diatom taxa in the natural diet ofjuvenile Haliotis fulgens and H. corrugata (Mollusca:Gastropoda) in Bah|¤ aTortugas and Bah|¤ a Asuncio¤ n, B. C. S.,Me¤ xico. Paci¢c Sciences, 59, 581^592.

Siqueiros-Beltrones, D.A. & Valenzuela Romero, G., 2004.Benthic diatom assemblages in an abalone (Haliotis spp.)habitat in the Baja California peninsula. Paci¢c Sciences, 58,435^446.

Snoeijs, P.J.M. & Prentice, I.C., 1989. E¡ects of cooling waterdischarge on the structure and dynamic of epilithic algalcommunities in the northern Baltic. Hydrobiologia, 184, 99^123.

Soininen, J., Paavola, R. & Muotka, T., 2004. Benthic diatomcommunities in boreal streams: community structure inrelation to environmental and spatial gradients. Ecography, 27,330^342.

Strathmann, R.R., 1967. Estimating the organic carbon contentof phytoplankton from cell volume or plasma volume.Limnology and Oceanography, 12, 411^418.

Tanaka, S. & Watanabe, T., 1990. The colonization process of atypical epilithic algal community Homoeothrix janthina^Achnanthes japonica community in a less polluted river in Japan.JapaneseJournal of Phycology, 38, 167^177.

Throndsen, J., 1978. Preservation and storage. In Phytoplankton

manual (ed. A. Sournia), pp. 69^74. Monographs on Oceanographic

Methodology 6. Paris: UNESCO.Totti, C., 2003. In£uence of the plume of the River Po on thedistribution of subtidal microphytobenthos in the northernAdriatic Sea. Botanica Marina, 46, 161^178.

Totti, C., Civitarese, G., Acri, F., Barletta, D., Candelari, G.,Paschini, E. & Solazzi, A., 2000. Seasonal variability of phyto-plankton populations in the middle Adriatic sub-basin. Journalof Plankton Research, 22, 1735^1756.

Totti, C., De Stefano, M., Facca, C. & Ghirardelli, L.A., 2004.Microphytobenthos. In Mediterranean marine benthos: a manual of

methods for its sampling and study (ed. M.C. Gambi and M.Dappiano), pp. 247^266. Biologia Marina Mediterranea, 11,Suppl. 1.

Tuji, A., 2000a. Observation of developmental processes inloosely attached diatom (Bacillariophyceae) communities.Phycological Research, 48, 75^84.

Tuji, A., 2000b. The e¡ect of irradiance on the growth ofdi¡erent forms of freshwater diatoms: implications for succes-sion in attached diatom communities. Journal of Phycology, 36,656^661.

Welker, C., Sdrigotti, E., Covelli, S. & Faganeli, J., 2002.Microphytobenthos in the Gulf of Trieste (northern AdriaticSea); relationship with labile sedimentary organic matter andnutrients. Estuarine, Coastal and Shelf Sciences, 55, 259^273.

Wellnitz, T.A. & Ward,V., 1998. Does light intensity modify thee¡ect may£y grazers have on periphyton? Freshwater Biology,39, 135^149.

Wellnitz,T.A. & Ward,V., 2000. Herbivory and irradiance shapeperiphytic architecture in a Swiss alpine stream. Limnology andOceanography, 45, 64^75.

Submitted 8 June 2006. Accepted 13 January 2007.



Seasonal variations of epilithic diatoms on different hard substrates, in the northern Adriatic Sea

Documents

Transcript of Seasonal variations of epilithic diatoms on different hard substrates, in the northern Adriatic Sea