Benthic foraminiferal assemblages as tools for

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N. Jb. Geol. Paläont. Abh. 275/2 (2015), 219–232 Stuttgart, February 2015

Article

Benthic foraminiferal assemblages as tools for environmental characterization: an example from the Gulf of Gaeta, Tyrrhenian Sea (Italy) Antonio Faugno, Mauro Alivernini, and Letizia Di Bella With 5 figures and 3 tables

Abstract: The present study is aimed at evaluating the environmental setting of the Gulf of Gaeta (Tyrrhenian Sea, Western Mediterannean Basin), with respect to antrophogenic and natural impacts, by means of benthic foraminiferal assemblages. In this area, fish and mollusc farming as well as riverine run-off contribute to the characterization of the marine benthic ecosystem resulting in an enrichment of organic matter. The qualitative and quantitative foraminiferal analyses on the surface samples revealed different degrees of eutrophication. Five foraminiferal assemblages were recognized with a bathymetric distribution parallel to the coast. The presence of eutrophic foraminiferal assemblages at about 20 m water depth in the restored area, between Punta dello Stendardo and Torre del Fico, showed, that anthropogenic activities within the semi-enclosed geomorphological setting caused the increase of bottom stress conditions. Here, the Garigliano river influence is weaker than in the rest of the studied section of the Gulf. In close proximity to the river mouth, the foraminiferal distribution appears to be controlled mainly by salinity but at greater depth (20-50 m) organic matter accumulation and low oxygen conditions contribute to the dominance of infaunal species. Key words: Benthic foraminiferal assemblages, fish farming, river influence, Gulf of Gaeta (Tyrrhenian Sea, Central Italy).

Fish farm biodeposits may also affect sediment chemistry, community dynamics of seagrass assemblages, benthic macro- and microfaunas, and bacterial communities within a radius of 1,000 m from the fish cages (Holmer 1991; Findlay & Watling 1997; Hargrave et al. 1997; Pergent et al. 1999; Pearson & Black 2000; Mirto et al. 2002; La Rosa et al. 2004; Sarà et al. 2004). Currently, a set of different response parameters are used to assess the impact of fish farming industries on native biotas. They include simple measures of organic matter, analyses of microbial processes in the sediment and studies on complex macrofauna indices (Holmer et al. 2008). Along the Italian coast, aquaculture place additional stress on those areas where river discharges impact

1. Introduction The coastal area around the Gulf of Gaeta (Tyrrhenian Sea) is characterized by strong waves due to storms, seasonal heavy rainfall and freshwater input of the Garigliano River. In addition, anthropogenic disturbance and industrial activities contribute to nearshore environmental stress. In particular, the rapid expansion of aquacultures along coastal zones of the Mediterranean Sea has the potential to modify shallow water habitats. The main impact of fish farming on benthic environments results the production of organic matter, the extension of bacterial mats and a progressive transformation of the sedimentary substrates into flocculent anoxic environments (Holmer 1991; Henderson et al. 1997; Karakassis et al. 1998; Mazzola et al. 2000). ©2015 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany

DOI: 10.1127/njgpa/2015/0463

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0077-7749/2015/0463 $ 3.50 eschweizerbart_xxx

220 A. Faugno et al.

Fig. 1. Map of the Gulf of Gaeta, location of the studied transect and the marine restored area where fish farming cages are located.

1999; Murray et al. 2002; Schönfeld et al. 2012). This work is focused on the response of foraminiferal assemblages to impacts of human activities in the Gulf of Gaeta (Tyrrhenian Sea, Italy). The aim of this work is to characterize the environmental setting in order to assess the anthropogenic and natural impacts due to fish farming and river outflow respectively.

benthic environments with organic matter or suspended solids. The volumetric flow rate of rivers and their impact on nearshore biotas has fluctuated over time as testified by monitoring activities and the fossil record (Vigliotti et al. 2008; Vallefuoco et al. 2012; Lirer et al. 2013). Among the biotic tools utilized for environmental monitoring, meio- and macrofaunal proxies are the most common bioindicators applied (Higgins & Thiel 1988; Green & Montagna 1996; Austen & McEvoy 1997; Mirto et al. 2012). In particular benthic foraminifera mirrored environmental changes due to their abundance, small size and short life cycle (Yanko

2. Study area The Gaeta Basin (Fig. 1) is located in Eastern Tyrrhenian Sea offshore of the Latium coastline. The continental shelf between Gaeta and the Island of Ischia

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Benthic foraminiferal assemblages as tools for environmental characterization 221

Sparus aurata) represents an important commercial activity in the Gulf of Gaeta (250 t per year). The area is also important for the commercial production of bivalves. Mussels (Mytilus galloprovincialis) and clams (Tapes sp.) are cultivated in long lines around cages and in suspended baskets, with an annual production of approximately 400 t per year (Mazzola & Sarà 2004, 2001). The impact of these activities has been studied by Mazzola & Sarà (2001) who investigated the effects of shellfish farming on the trophic structure. Although some consider bivalves from aquacultures as environmentally clean and “recyclers” of allochthonous organic matter (Crawford et al. 2003), the low current velocities in this area favor the deposition of organic matter (Mazzola & Sarà 2004) and restrict oxygenation at the sea bottom.

constitutes the seaward extension of the alluvial plains of the Garigliano and Volturno rivers. The Gaeta Basin, together with the Terracina Basin, covers an area of about 750 km2 where the shelf break is located at 200 m water depth. The continental slope comprises the Palmarola and the Ventotene basins (Zitellini et al. 1984) and are part of the Pontine Archipelago. The continental shelf deepens from NW to SE and extends with the direction of the Garigliano river mouth. This part of the Campania-Latium area has undergone subsidence from the Pliocene to the Quaternary (Ippolito et al. 1973). The formation of the Gaeta Basin appears to be related to tectonic extensions along E-W trending faults (Aiello et al. 2000). The modern deposition of sediments is strongly controlled by deposits from the Garigliano River and by the geomorphology of the Gaeta Bay that favors the accumulation of continental sediments. The study area is characterized by low current velocities with an average yearly range of 1-5 cm s-1 and seasonal changes in temperature (from 14 °C in January to 25.3 °C in August; La Rosa et al. 2004). No significant bottom currents were recorded by Mazzola & Sarà (2001). The Gaeta area is constrained by the seasonal outflow of rivers. Two granulometric facies types (sand and pelite) were recorded and exhibit a regular grain size trend that decreases with increasing water depth. The sandy-muddy sediments within the Gulf generally lack large-scale vegetation by algae or seagreasses (Maggi et al. 2009). However, Ferretti et al. (1989) have recorded a few Posidonia oceanica meadows in the northern part of the area. Recent studies showed that the Posidonia oceanica meadows are now completely absent while in proximity to the village of Scauri and near the Torre del Fico, a small area of Cymodocea as been found between 10 and 12 m water depth (Diviacco et al. 2001; Spada et al. 2001). In 2010, the Gulf of Gaeta became a marine protected area with the objective to protect the waters of the Gaeta area. The Gulf is characterized by eutrophic conditions. Eutrophication includes a multitude of sources including river discharge, fish and shellfish farming, and anthropogenic enrichment of nutrients from the petrochemical industry or urban run-off. However, the contamination from metals (Cu, Ni, Zn, Cr, Pb) both in the sediment and in invertebrate shells appears to be low (Maggi et al. 2009; Conti & Finoia 2010). This may be due to the fact that the marine area from Punta Stendardo to Torre del Fico is part of an environmental restoration project (Fig. 1). Intensive fish farming (Dicentrarchus labrax and

3. Material and methods Twenty-seven surface samples were collected by means of a box corer during an oceanographic cruise in February 2002. The project was commissioned by “Regione Lazio”, the local authority, in cooperation with the Italian Insitute for Environmental Protection and Research (ISPRA) and the Sapienza University of Rome. The samples were collected along five transects (A, B, C, D, E) at depth between 19 and 69 meters (Fig. 1). The top core intervals (0-1 cm) were analyzed for foraminifera in each sample in order to characterize the present-day environment. The samples were washed over a 63 µm sieve in order to eliminate mud particles and oven-dried at 50 °C and later weighed. The quantitative and qualitative analyses were conducted on all of the samples collected. At least 300 benthic individuals of foraminifera were picked, counted and identified according to the generic classification of Loeblich & Tappan (1987). Species identifications were mainly based on previous studies of the Mediterranean Sea (Cimerman & Langer 1991; Sgarrella & Moncharmont-Zei 1993). Total assemblage analyses were considered suitable for the environmental characterization, because it provides a reduced seasonal and low spatial variability (Scott & Medioli 1980). Moreover, it provides integrated information about homogenized assemblages over a given period of time. The Foraminiferal Number (FN) (Schott 1935) was calculated as the number of specimens per gram of dry sediment (specimens g-1). Species diversity was quantified using the Fisher α-index (Fisher et al. 1943; Murray 1991) which was calculated with the PAST data analysis package ( PAlaeontological STatistics; ver. 1.38). In addition, the relative abundance of the most abundant species in each sample, was recorded. The relative abundance of benthic species was processed using the statistical software SPSS (10.1) to carry out a hierarchical cluster analysis (Cluster Analysis, CA). The Q-mode cluster analysis using Squared Euclidean Dis-

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Table 1. Foraminiferal Number, diversity index (α-Fisher) and lithology are recorded for each sample. Samples

GTA 20 GTA 40 GTA 60 GTB 20 GTB 30 GTB 40 GTB 50 GTB 60 GTB 70 GTC 20 GTC 30 GTC 40 GTC 50 GTC 60 GTC 70 GTD 20 GTD 30 GTD 40 GTD 50 GTD 60 GTD 70 GTE 20 GTE 30 GTE 40 GTE 50 GTE 60 GTE 70

Latitude N

41°14.019 41°12.149 41°11.013 41°12.514 41°11.551 41°10.921 41°10.438 41°09.914 41°09.323 41°11.440 41°10.583 41°10.053 41°09.658 41°09.154 41°08.780 41°10.398 41°09.583 41°09.052 41°08.575 41°08.111 41°07.598 41°08.977 41°08.173 41°07.666 41°07.204 41°06.850 41°06.347

Longitude E

13°37.908 13°37.614 13°37.402 13°42.099 13°41.369 13°40.910 13°40.505 13°40.109 13°39.643 13°43.751 13°42.685 13°42.293 13°41.808 13°41.307 13°40.535 13°45.256 13°44.237 13°43.624 13°43.106 13°42.644 13°42.070 13°47.029 13°45.857 13°45.192 13°44.602 13°44.085 13°43.333

Water Depth (m) 20 40 60 20 30 40 50 60 70 20 30 40 50 60 70 20 30 40 50 60 70 20 30 40 50 60 70

tance was performed to group samples with homogeneous foraminiferal assemblages. The Ward Method was chosen among the possible clustering methods because it produced dendrograms with well-defined clusters (Parker & Arnold 1999). To simplify the matrix, only 28 species with abundance higher than 3% in at least one sample were used in the statistical analysis (Patterson & Fishbein 1989; Fishbein & Patterson 1993). Principal Component Analysis (PCA) is a method used to reduce the dimensionality of a multivariate data set to a few principal factors that determine the distributions of species; PCA was performed by taking into account the components on the explained variance.

FN

44.61 347.44 611.22 11.55 118.81 347.73 858.27 1304.17 887.61 36.07 60.47 411.92 505.75 1512.56 1770.11 18.80 93.02 417.25 884.96 1661.37 1418.60 7.2764 174.54 1188.68 3279.57 2296.30 3092.78

α-Fisher Lithology 10.67 9.71 9.80 9.00 7.55 6.73 9.16 9.70 7.48 5.14 7.19 7.52 7.48 6.83 9.76 9.07 6.83 6.14 6.83 8.91 9.40 8.28 6.39 7.79 8.25 9.34 8.68

clayey silt with bioclasts clayey silt and silty clay clayey silt and silty clay sandy silt and silty clay silty clay and clay clayey silt and compact clay clayey silt clayey silt clayey silt sandy silt and silty clay silty clay and clay silty clay silty clay silty clay silty clay sandy silt clayey silt clayey silt and sandy silt silty clay clay silty clay fine sand clayey silt clay clay clay clay

4. Results – faunal diversity and Q-mode cluster analysis

The microfauna in all samples is well preserved and no reworked specimens were found. A total of 91 species were identified belonging to 43 genera. Only 28 taxa show frequency values larger than 3% in at least one sample (Appendix) but only Bulimina elongata, B. marginata and Nonionella turgida show very high frequencies (>20% in at least one sample). A group of species consisting of Bolivina catanensis, Bulimina elongata and B. marginata is present in all samples. Bolivina catanensis displays values ranging from 1.33 to 14.33% whereas B. elongata and B. marginata range

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Benthic foraminiferal assemblages as tools for environmental characterization 223

Table 2. Clusters and related samples. Cluster I

GTB 20 GTC 20 GTD 20 GTE 20

Cluster II

Cluster III

Subcluster Subcluster Subcluster Subcluster IIa IIb IIIa IIIb

GTA 20 GTC 30 GTC 40 GTD 30 GTE 30

GTA 40 GTB 30 GTC 50 GTD 40 GTD 50

GTE 40 GTE 50 GTE 60 GTA 60 GTB 50 GTB 60 GTC 60 GTD 60

GTB 70 GTC 70 GTD 70 GTE 70

The resulting dendrogram of Q-mode cluster analysis represents the grouping of samples according to the relative abundance of benthic foraminiferal species. These clusters group samples with homogeneous foraminiferal associations that correspond to distinct environmental settings. Three main clusters are highlighted by a phenon line placed at 10% distance: cluster I is characterized by typical infralittoral species, cluster II includes transitional infralittoral/circalittoral taxa, and cluster III is constituted by upper circalittoral species (Fig. 2, Table 2). Clusters II and III can be further subdivided, although at a different hierarchical level, into two distinct subclusters corresponding to four foraminiferal assemblages (IIa, IIb, IIIa and IIIb, Fig. 2 and Table 2). The benthic foraminiferal species grouped in the identified clusters, are as follows: Cluster I – Ammonia parkinsoniana, Bulimina elongata and Elphidium advenum assemblage (assemblage I) (Table 3). Dominant taxa: A. parkinsoniana (20%), B. elongata (13%) and E. advenum (12%). Accompanying taxa: Cribroelphidium decipiens (9%), A.beccarii (9%) and H. depressula (4%). Other species such as A. tepida, B. catanensis, E. crispum and Quinqueloculina parvula show frequencies of about 2%, while the rest of the taxa displays very low percentages ranging between 1.92 and 0.33%. The Fisher-α index shows a mean value of 7.87. The FN is very low ranging between 7 and 36 with a mean value of 18.43. Cluster II is constituted of two subclusters (IIa and IIb) at lower hierarchical order. Subcluster IIa – Bulimina elongata and Nonionella turgida assemblage (assemblage IIa) (Table 3). Dominant taxa: B. elon-

Fig. 2. Q-mode cluster from foraminiferal data recorded in samples from the Gulf of Gaeta. Three main clusters (I, II, III) corresponding to different assemblages are separated (dotted line placed at a 10% distance).

from 2.67 to 26.67% and 0.67 to 24.67%, respectively. Faunal diversity (α-Fisher index) ranges from 5.14 to 10.67 (Table 1). The highest and the lowest values were recorded at 20 m water depth in the marine restored area, and in front of the Garigliano river mouth, respectively. The maximum mean values were found at deeper depth (60 and 70 m water depth). In the bathymetrical interval between 30 and 50 m, diversity is low (mean value 7) but it slightly increases towards deeper sites. The Foraminiferal Number (FN) generally reaches higher values in deeper locations than in the shallow areas (Table 1). The transect A shows the lowest values of faunal frequencies in respect to the other transects. Nevertheless, at 20 m water depth, the FN displays a decreasing trend from the marine restored area (GTA20: 44.61 spec/g) towards the central part of the gulf (GTE20: 7.28 spec/g) except for the sample in front of the Garigliano River (GTC20) where a slight increase was recorded. On the contrary, the samples of transect E show maximum values (>3000 spec/g), except for GTE20, which is the poorest of all samples.

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Table 3. Foraminiferal assemblages recorded in Gulf of Gaeta. Mean values of α-Fisher and FN are reported for each assemblage. Assemblages Assemblage I

Assemblage IIa

Assemblage IIb

Assemblage IIIa

Assemblage IIIb

Samples Dominant taxa GTB 20 GTC 20 GTD 20 GTE 20 GTA 20 GTC 30 GTC 40 GTD 30 GTE 30 GTA 40 GTB 30 GTC 50 GTD 40 GTD 50 GTE 40 GTE 50 GTE 60 GTA 60 GTB 50 GTB 60 GTC 60 GTD 60 GTB 70 GTC 70 GTD 70 GTE 70

α-Fisher

FN

Range water depth

Ammonia parkinsoniana, Bulimina elongata, Elphidium advenum

7.87

18.43

20 m

Bulimina elongata, Nonionella turgida

7.72

156.91

20-40 m

Bulimina elongata, Nonionella turgida, Valvulineria bradyana

7.41

436.99

30-50 m

Bulimina marginata, Rectuvigerina phlegeri, Hyalinea balthica

8.64

1916.84

40-60 m

Hyalinea balthica, Bulimina marginata

8.80

1570.08

70 m

Cluster III includes two subclusters (IIIa and IIIb). In both, IIIa and IIIb, the Fisher-α index remains low reaching value of 8.64-8.80, whereas the FN increases to 1570.0 in cluster IIIa and 1916.8 in cluster IIIb (mean values, Table 3). Subcluster IIIa – Bulimina marginata, Rectuvigerina phlegeri and Hyalinea balthica assemblage (assemblage IIIa). Dominant taxa: B. marginata (13%), R. phlegeri (8%) and V. bradyana (7%). Accompanying taxa: H.balthica (6%) and B.elongata (6%). Bolivina subspinescens, E. advenum, G. subglobosa, P. raphanus and N. turgida follow with percentages ranging between 5 and 4%. The other species present in these assemblages display values