Ecology and spatial distribution of selected polychaete species from the Italian continental shelf

Abstract

Data from several research and monitoring projects carried out between 1999 and 2009, for a total of 26 study areas located along the Italian continental shelf (Mediterranean Sea), were extracted from ISPRA's data set, to revise and update the existing information on the ecology and spatial distribution of 20 selected soft-sediment polychaete species. The species were selected taking into account their spatial distribution and ecological role in the benthic assemblages and the existence of voucher specimens deposited in ISPRA's reference collection. Samplings were taken at 872 stations on soft sediments, at depths ranging from 1 to 155 m. Surface sediment composition data were available at each site. The number of specimens from the selected species was extracted at each site, and relative abundance (%)calculated. The spatial distribution of each species was investigated according to the biogeographical zones identified in the Italian Seas. The distribution of five species (Aponuphis bilineata, A. brementi, A. fauveli, Nothria conchylega, and Onuphis eremita) was updated. Several species that were previously considered to be characteristic of a specific biocenosis, sensu Pérès & Picard (1964), e.g. Diopatra neapolitana, Ditrupa arietina, Notria conchylega and Sternaspis scutata, were found to be distributed over a wider bathymetric and granulometric range of surface sediments. Indicator Species Analysis highlights that the distribution of 17 selected species depends on definite granulometric characteristics of the sediment. This new relevant information outlines the important contribution of environmental monitoring programmes to scientific knowledge.

Keywords:

• Polychaete assemblages
• biocoenosis
• soft bottoms
• sediment texture
• Mediterranean Sea

Introduction

Polychaetes are amongst the most frequent and abundant organisms characterizing marine benthic communities, accounting for up to more than a third of the total number of macrobenthic species in soft substrata (Day 1967; Knox 1977). Polychaetes have proven to be excellent indicators of environmental conditions due to their distribution over a broad range of environments and their ample display of ecological requirements. Because of their ecological variability, they are widely used in applied environmental research (Giangrande et al. 2005). Although there have been numerous studies investigating the systematics, taxonomy, morphology and ecology of Mediterranean polychaetes, there are still significant gaps in the understanding of their ecology. Information on species distribution is incomplete, and many species are frequently recorded outside their known bathymetric and granulometric range and of their characteristic ecological boundaries, which define specific biocoenosis sensu Pérès & Picard (1964). There is only a general account, dating back to Bellan (1964), on the ecology of Mediterranean polychaetes. Further studies only analysed the distribution of polychaetes at local scales (e.g. Gravina 1986; Castelli et al. 1992; Bianchi et al. 1993a,b,c; Crema et al. 1993; Simboura et al. 2000; Çinar 2005; Moreira et al. 2006; Cosentino & Giacobbe 2008; Zaâbi et al. 2009). The information on the ecological and spatial distribution of species should therefore be revised and updated on the base on newly collected information.

Environmental monitoring programmes can be a source of valuable scientific data to increase the scientific knowledge of benthic communities and species, as these programmes allow the integration of multidisciplinary information. Moreover, frequent monitoring surveys and common sampling methodologies allow the collection of numerous and comparable data from different study areas.

This study proves the relevance of multidisciplinary environmental characterization and monitoring programmes for scientific research collating data extracted from a number of surveys (e.g. sand dredging, offshore platforms developments, aquaculture, beach nourishments) carried out in Italy over the last 10 years by the Italian National Institute for Environmental Protection and Research (ISPRA). These projects have provided data on sediment composition, associated benthic communities and depth range of a number of species in different areas of the Italian continental shelf.

In this study we present a first update on the spatial distribution and ecology (related to sediment composition and depth range) of 20 soft-sediment polychaete species along the Italian continental shelf. These species were selected taking into account their spatial distribution and their ecological role in benthic assemblages. For each species, voucher specimens were available in ISPRA's reference collection, which is based on the material collected in numerous monitoring surveys.

Material and methods

Data from 26 study areas located along the Italian continental shelf were extracted from ISPRA's data set (Figure 1). These locations were selected with base on the common procedures of data collection and analyses at each sampling period from 1999 to 2009. Samples had been taken in two replicates at 872 stations along transects perpendicular to the coast, at depths ranging from 1 to 155 m (Table I), using a Van Veen grab (0.1 m² covering area). The sediments sampled were sieved through a 1-mm mesh and the retained material was preserved in seawater adding 4% CaCO₃-buffered formalin. Macrozoobenthic samples were further sorted into major taxonomical groups and the collected polychaetes counted and classified to the lowest possible taxonomic level. Surface sediments were collected at each station with a box-corer, analysed and classified according to sand percentage, following Nota (1958): sand (S) (>95% content of sand), muddy sand (mS) (95–70%), very sandy mud (vsM) (70–30%), sandy mud (sM) (30–5%) and mud (M) (<5%).

Table I. The 26 study areas located in the nine biogeographical zones identified in the Italian Seas (Bianchi 2004), the number of sampling stations for each area, divided into depth ranges ( C= Central; S= South; N=North)

Study Areas	Sea	Biogeographic Zone	Total number of Stations	Depth ranges (m)
				0-10	10,1-20	20,1-30	30,1-50	>50
1. Rosignano	Ligurian Sea	1	35	7	15	7	4	2
2. Elba	N Tyrrhenian Sea	1-2	41		2	2	15	22
3. Porto Ercole	N Tyrrhenian Sea	2	11			11
4. Montalto	C Tyrrhenian Sea	2	34			2	12	20
5. Civitavecchia	C Tyrrhenian Sea	2	70	1	5	21	43
6. Ostia	C Tyrrhenian Sea	2	68	4	27	14	23
7. Torpaterno	C Tyrrhenian Sea	2	26				18	8
8. Torvaianica	C Tyrrhenian Sea	2	50	4	4	4	12	26
9. Anzio	C Tyrrhenian Sea	2	31	4	7	4	16
10. Sabaudia	C Tyrrhenian Sea	2	57	4	7	5	13	28
11. Terracina	C Tyrrhenian Sea	2	50	7	5	2	10	26
12. Gaeta	C Tyrrhenian Sea	2	27		5	4	9	9
13. Ponza	C Tyrrhenian Sea	2	19				3	16
14. Porto Torres	Sardinian Sea	2	17			5	12
15. Olbia	C Tyrrhenian Sea	2	10	10
16. Baia	C Tyrrhenian Sea	3	17	4	5	4	4
17. Bagnoli	C Tyrrhenian Sea	3	33	33
18. Castellammare	S Tyrrhenian Sea	3	21			3	17	1
19. Bisceglie	S Adriatic Sea	7	11		11
20. Molise	C Adriatic Sea	8	52	20	11	11	7	3
21. Ortona	C Adriatic Sea	8	5		5
22. Giulianova	C Adriatic Sea	8	28	10	7	4	5	2
23. Marche	C Adriatic Sea	8	75	75
24. Civitanova Marche	C Adriatic Sea	8	23					23
25. Ravenna	N Adriatic Sea	9	9				9
26. Chioggia	N Adriatic Sea	9	52	7	4	41

Figure 1. Location of the 26 study areas from which data was extracted. Stations are numbered from the Ligurian Sea to the northern Adriatic Sea. The dimension of the circle is proportional to the number of stations investigated in each area. 1, Rosignano; 2, Elba; 3, Porto Ercole; 4, Montalto; 5, Civitavecchia; 6, Ostia; 7, Torpaterno; 8, Torvaianica; 9, Anzio; 10, Sabaudia; 11, Terracina; 12, Gaeta; 13, Ponza; 14, Porto Torres; 15, Olbia; 16, Baia; 17, Bagnoli; 18, Castellammare; 19, Bisceglie; 20, Molise; 21, Ortona; 22, Giulianova; 23, Marche; 24, Civitanova Marche; 25, Ravenna; 26, Chioggia. The nine biogeographical zones described in the Italian Seas are as according to Bianchi (2004) and followed in the checklist of flora and fauna of the Italian Seas (Relini 2008)

Twenty species, listed in Table II, were selected according to their spatial distribution, their ecological role and the existence of voucher specimens deposited in ISPRA's reference collection. For each species number of specimens and relative abundance (%) were calculated. Box-and-whisker plots (Tukey 1977) were performed to analyse the depth distribution of species. Depths were grouped in five ranges (1–10 m; 10.1–20 m; 20.1–30 m; 30.1–50 m; >50 m).

Table II. Distribution of the 20 selected species by the nine biogeographical zones of the Italian Seas. In white, the distribution of the selected species as reported in the Checklist of Flora and Fauna of the Italian Seas (Relini 2008); in grey, records confirming the species distribution; in black, new records distribution of five species (Aponuphis bilineata, A. brementi, A. fauveli, Nothria conchylega, and Onuphis eremita)

Species	Biogeographical Zones of Italian Seas
	1	2	3	4	5	6	7	8	9
Aponuphis bilineata (Baird, 1870)	+	+	+	+	+	+	+	+	+
Aponuphis brementi (Fauvel, 1916)	+	+	+	+	+	+	+	+	+
Aponuphis fauveli (Rioja, 1918)	+	+	+	+	+	+	+	+	+
Chaetozone caputesocis (Saint-Joseph, 1894)	+	+	+	+	+	+	+	+	+
Chaetozone gibber Woodham & Chambers, 1994	+	+	+				+	+	+
Clymenura leiopygos (Grube, 1860)	+	+	+				+	+	+
Diopatra neapolitana Delle Chiaje, 1841	+	+	+	+		+	+	+	+
Ditrupa arietina (O.F. Muller, 1776)	+	+	+		+	+	+		+
Drilonereis filum (Claparède, 1868)	+	+	+	+	+	+	+	+	+
Eunice vittata (Delle Chiaje, 1828)	+	+	+	+	+	+	+	+	+
Heteromastus filiformis (Claparède, 1864)	+	+	+	+	+	+	+	+	+
Hyalinoecia tubicola (O.F. Müller, 1776)	+	+	+	+	+	+	+	+	+
Melinna palmata Grube, 1870	+	+	+		+	+	+	+	+
Metasychis gotoi (Izuka, 1902)	+	+	+		+		+	+	+
Nematonereis unicornis (Grube, 1840)	+	+	+	+	+	+	+	+	+
Nothria conchylega (M. Sars, 1835)		+	+	+	+	+	+	+	+
Onuphis eremita Audouin & Milne-Edwards, 1833		+	+			+	+	+	+
Owenia fusiformis Delle Chiaje, 1841	+	+	+		+	+	+	+	+
Pectinaria auricoma (O.F. Müller, 1776)	+	+	+	+	+		+	+	+
Sternaspis scutata (Ranzani, 1817)	+	+	+		+	+	+	+	+

The spatial distribution of each species was further analysed according to the division of the Italian Seas into nine biogeographical zones, proposed by Bianchi (2004) (Figure 1) and applied in the Italian Checklist of marine flora and fauna (Relini 2008). No study areas were available for this study from biogeographical zones 4, 5 and 6.

Where available, information on the selected species on biocoenosis affiliation (Bellan 1964; Pérès & Picard 1964; Picard 1965; Augier 1982), preferred sediment typologies and depth range distribution was also extracted from existing literature.

Indicator Species Analysis (ISA) (Dufréne & Legendre 1997) has been performed in order to identify the species associated with or indicative of five groups of stations, derived from Nota (1958) classification. This analysis combines the relative abundance of the species with their relative frequency of occurrence in the various groups and provides an indicator value subsequently tested by randomization.

Results and discussion

A total of 55,000 individuals from 200 species of polychaetes distributed across the Italian biogeographical zones 1, 2, 3, 7, 8, and 9 (Figure 1) were identified.

The allocation of the 20 selected species by biogeographical zones, as reported in the Checklist of flora and fauna of the Italian seas (Relini 2008), is presented in white in Table II. The results confirmed the presence of these species in some biogegraphical zones (in grey) and updated the distribution of five of these species (in black). Aponuphis bilineata, A. brementi and A. fauveli, were recorded along the northern coast of the Island of Elba (Tuscan Archipelagos) in zone 1, which is considered to be a climate transitional area between zones 1 and 2 (Relini 2008). Nothria conchylega was found in zone 2, in the southern coast of the Island of Elba and along the coast of Latium (Central Tyrrhenian Sea) and Onuphis eremita was collected in zone 7, along the eastern coast of Apulia (Southern Adriatic Sea).

In Figure 2, box-and-whisker plots describe the depths distribution of the selected species. The analysis of the distribution revealed that most of the 20 species occurred at all depth ranges (Figure 3). Amongst the exceptions, Chaetozone gibber occurred exclusively from shallow waters to 50 m depth, Diopatra neapolitana was mostly distributed in shallow areas (1–10 m depth) and absent below 30 m, Hyalinoecia tubicola was sampled deeper than 20 m, Metasychis gotoi and Sternaspis scutata were only found deeper than 10 m, and Onuphis eremita, was absent in the 30–50 m depth range.

Figure 2. Box-and-whisker plots describe the distribution of depths where species were found.

Figure 3. Distribution of the 20 selected species along the different depth ranges (in meters), taking into account the percentage of analysed stations, for each depth range, where the species were found. The maximum found percentage was 90%.

The species distributions show that all species were found in all sediment classes (Nota's sediment classification) except Diopatra neapolitana, which was not found in sandy-muds (sM) and Metasychis gotoi and Pectinaria auricoma, which were absent from sands (S) (Figure 4).

Figure 4. Distribution of the 20 selected species amongst different sediment classes according to Nota's classification (1958): sand (S) (>95% content of sand), muddy sand (mS) (70–95% content of sand), very sandy mud (vsM) (70–30% content of sand), sandy mud (sM) (30–5% content of sand) and mud (M) (<5% content of sand). The distributions take into account the percentage of analysed stations, for each sediment class, where the species were found. The maximum found percentage was 63%.

The species selected were present in the range of 0–20% relative abundance within the associated polychaete assemblages in all sediment typologies; higher values of relative abundance were recorded only for some species and in some classes of sediment (Table III).

Table III. Frequency of station in each Nota's sediment class where each species was found. Species occurrence is also clustered into classes of relative abundances (%) of each species within the whole polychaete assemblages (S = sand; mS = muddy sand; vsM = very sandy mud; sM = sandy mud; M = mud)

	0-20 %					21-40 %					41-60 %					61-80 %
	S	mS	vsM	sM	M	S	mS	vsM	sM	M	S	mS	vsM	sM	M	S	mS	vsM	sM	M
Aponuphis bilineata	15	123	41	9	31	1	16	2
Aponuphis brementi	10	63	52	10	2		3	7	2
Aponuphis fauveli	9	40	63	10	11		4	1		3		3							1
Chaetozone caputesocis	6	16	27	10	7					1					1
Chaetozone gibber	5	6	15	11	19				1
Clymenura leiopygos	19	21	21	22	32			1					1
Diopatra neapolitana	3	2	7		8
Ditrupa arietina	1	4	24	5	6			2
Drilonereis filum	1	28	58	29	46				2			1
Eunice vittata	4	32	66	39	41
Heteromastus filiformis	6	16	42	37	54				1	3
Hyalinoecia tubicola	2	12	24	5	4
Melinna palmata	5	70	76	44	73		7	1	4	5					1
Metasychis gotoi		15	21	22	12			2	2
Nematonereis unicornis	3	49	45	20	21
Nothria conchylega	5	25	10	2	1		1		1
Onuphis eremita	12	9	3	2	10	1	1
Owenia fusiformis	56	161	57	5	3	17	10	1			4	2				3	1
Pectinaria auricoma		71	28	12	10
Sternaspis scutata	4	52	57	54	69			11	10	13				2	12				2	5

The species-group contributions obtained from ISA are reported in Table IV. Results demonstrate that the species distribution depends on definite granulometric characteristics of the sediment and the indicator values of ISA statistic specify the groups of stations that are associated with the species with different levels of significance. It is interesting to highlight that 17 of the selected species are associated with specific groups with a high level of significance (p≤0.01 and p≤0.001) while Hyalinoecia tubicola, Melinna palmata and Nothria conchylega are associated with a low level of significance (p≤0.05). Chaetozone gibber, Clymenura leiopygos and Diopatra neapolitana have no significant relationship with the groups identified, suggesting a wide ecological tolerance against the sediment fractions. Moreover, Drilonereis filum and Eunice vittata have values of ISA that suggest a high tolerance to mixed sediment (vsM and sM) and Sternaspis scutata show a significant preference for muddy sediment (sM and M).

Table IV. The species-group contributions obtained from Indicator Species Analysis (ISA). The indicator values of ISA specify the groups of stations that are associated with the species with different levels of significance

Species	S	mS	vsM	sM	M	P-level
Aponuphis bilineata	1.326	25.808	6.499	0.970	-	0.000
Aponuphis brementi	0.449	4.619	16.738	0.796	0.001	0.000
Aponuphis fauveli	0.242	3.816	17.674	0.531	0.231	0.000
Caulleriella caputesocis	1.112	0.998	6.531	1.195	0.131	0.001
Caulleriella gibber	0.645	0.069	1.276	2.794	3.381	0.167
Clymenura leiopygos	4.518	0.911	5.358	3.627	0.823	0.362
Diopatra neapolitana	0.322	0.014	2.411	-	0.983	0.074
Ditrupa arietina	0.008	0.024	8.932	0.349	0.059	0.000
Drilonereis filum	0.006	0.431	11.515	8.242	3.989	0.002
Eunice vittata	0.152	1.194	12.180	8.935	2.700	0.000
Heteromastus filiformis	0.320	0.747	6.284	1.223	0.050	0.000
Hyalinoecia tubicola	0.148	0.157	11.931	11.883	3.457	0.022
Melinna palmata	0.073	3.796	7.793	13.975	8.344	0.023
Metasychis gotoi	-	0.401	5.442	8.945	0.362	0.001
Nematonereis unicornis	0.143	2.719	11.495	4.522	0.954	0.000
Nothria conchylega	0.903	5.518	0.944	0.108	0.002	0.021
Onuphis eremita	8.653	0.53	0.101	0.068	0.308	0.000
Owenia fusiformis	64.494	8.374	0.803	0.004	0.001	0.000
Pectinaria auricoma	-	14.735	3.054	1.490	0.157	0.000
Sternaspis scutata	0.034	0.229	6.068	16.599	18.048	0.002

For each species, the information on biocoenoses affiliation, ecological significance, sediment typologies and depth ranges, as emerging from previous literature and from the results of this study, is summarized in Table V. These results are also listed below, in alphabetic order.

Table V. For each species, information on biocoenoses affiliation, ecological significance, sediment typologies and depth ranges, as emerging from previous literature and from the results of this study. Results are listed in alphabetic order. Abbreviations: C = coralligenous biocoenoses, DC = biocoenoses of coastal detritic, DE = biocoenoses of muddy detritic, DL = biocoenoses of the shelf-edge detritic, SFBC = biocoenoses of well-sorted fine sand, SVMC = biocoenoses of surface muddy sands in sheltered waters, VTC = biocoenoses of coastal terrigenous mud, MI = Communities of unstable soft seabeds, excl. exclusive species, pref. = preferential species, sand tol. = species living on sands and tolerant to other fractions, mud tol. = species living on muds and tolerant to other fractions, Grav. = species living on gravely sediments, Lre = species with wide ecological distribution, Mixt. = species living on mixed sediments

SPECIES	ECOLOGICAL CHARACTERISTICS	REFERENCES	ECOLOGICAL CHARACTERISTICS
	▪ Biocoenoses - ecological significance		from ISPRA’ dataset
	▪ Sediment typology		▪ Sediment typology
	▪ Depth range (vertical zonation)		▪ Depth range (m)
Aponuphis bilineata	▪ DE, Lre, Grav. ▪ very fine sand, sand, detritic sand, muddy sand, mixed sediments	Bellan 1964; Picard 1965; Giangrande & Gambi 1985; Gambi & Giangrande 1986; Bellan & Bellan-Santini 1991; Bianchi et al. 1993 b; Chimenz Gusso et al. 2001; Cosentino & Giacobbe 2008	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 4–100 m
Aponuphis brementi	▪ Mixt.	Crema et al. 1993;	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 5–116 m
Aponuphis fauveli	▪ DE, Mixt. ▪ Circalittoral, Bathyal	Intès & Le Loeuff 1986; Bianchi et al. 1993a, b, c; Chimenz Gusso et al. 2001	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 5–90 m
Caulleriella caputesocis	▪ mud-tol.	Bianchi et al. 1993 b	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 3,5–80 m
Chaetozone gibber	▪ mud ▪ Circalittoral	Cacabelos et al. 2008 ; Zaabi et al. 2009	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 1–43 m
Clymenura leiopygos	▪ sand, muddy sand, ▪ Infralittoral	Massé 1972; Giangrande & Gambi 1985; Crema et al. 1993	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 2,5–73 m
Diopatra neapolitana	▪ SFBC excl ▪ Sand, tolerant of small amount of mud, very sandy mud.	Bellan 1964; Picard 1965; Gambi & Giangrande 1986; Intès & Le Loeuff 1986; Bianchi et al. 1993a, b, c	▪ sand (S), muddy sand (mS), very sandy mud (vsM), mud (M) ▪ 3–22,7 m
Ditrupa arietina	▪ DC excl., DC, MI ▪ mixed sediments ▪ Circalittoral, Infralittoral	Bellan 1961; Bellan 1964; Pérès & Picard 1964; Picard 1965; Augier 1982; Gambi & Giangrande 1986; Grémare et al. 1989; Crema et al. 1993	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 5–51 m
Drilonereis filum	▪ Lre ▪ sandy mud, mud, mixed sediments (with high fraction of sand), detritic sand, sediment with organic matter (Om) ▪ Circalittoral, Bathyal	Bellan 1964; Picard 1965; Picard 1972; Gambi & Giangrande 1986; Intès & Le Loeuff 1986; Bellan & Bellan-Santini 1991; Bianchi et al. 1993a, b, c.	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 3–90 m
Eunice vittata	▪ C, Lre, opportunist, colonizer Detritic sediment, sand, mixed sediments, median grain size sand, sediment with organic matter (Om)	Bellan 1961; Bellan 1964; Pérès & Picard 1964; Picard 1965; Picard. 1972; Diaz-Castaňeda & Safran 1988; Bellan & Bellan-Santini 1991	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 1,5–60 m
Heteromastus filiformis	▪ SVMC excl., companion species without specific ecological role, indicator of artificial or natural disturbance, euryhaline muddy enriched sediments ▪ eurybathic	Pérès & Picard 1964; Bellan 1964; Picard 1965; De Gaillande 1968; Picard 1972; FAO/UNEP 1986; Gravina & Somaschini 1990; Dewarumez et al. 1992, Bianchi et al. 1993a; Carvalho et al. 2005	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 1,5–99 m
Hyalinoaecia tubicola	▪ DC pref., Mixt. ▪ muddy sand	Pérès & Picard 1964; Bellan 1964; Picard 1965; Bianchi et al. 1993a,b,c	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 22–155 m
Melinna palmata	▪ DE ▪ Mixed sediments, muddy fine sand, sediment with organic matter (Om) ▪ Infralittoral, Circalittoral, Bathyal	Bellan 1963; Bellan 1964; Pérès 1982; Giangrande & Gambi 1985; Gambi & Giangrande 1986; Intès & Le Loeuff 1986; Hily 1987; Duineveld et al. 1991, Bianchi et al. 1993b; Dauvin 2000; Dos Santos Brasil & Gonçalves da Silva 2000	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 17,5–100 m
Methasychis gotoi	▪ Mud	Picard 1965; Zavodnik et al. 1985, Cantone et al. 2004	▪ muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 17,5–100 m
Nematonereis unicornis	▪ DE, Mixt. MI ▪ mud, sediment with organic matter (Om), Posidonia oceanica sheaths.	Bellan 1964; Picard 1965; Drago & Arbetelli 1978; Zavodnik et al. 1985; Bellan 1985; Intès & Le Loeuff 1986; Sardà 1986; Bianchi et al. 1993a, b, c	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 3–110 m
Nothria conchylega	▪ DL, VTC, Mixt. ▪ sandy mud ▪ Circalittoral, Bathyal	Bellan 1964; Bellan 1963; Intès & Le Loeuff 1986 ; Bianchi et al. 1993c,b,c	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 5 –100 m
Onuphys eremita	▪ SFBC excl.	Picard 1965; Bianchi et al. 1993a	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 4 –23 m and 90 m
Owenia fusiformis	▪ DC, SFBC ▪ Sand tol., fine sand, sandy mud, ecotonal zone enriched with organic matter ▪ Infralittoral, Circalittoral	Pérès & Picard 1964; Bellan 1964; Picard 1965; Desbruyères et al. 1972-73; Intès & Le Loeuff 1986; Abbiati et al. 1987; Hily 1987; Bianchi et al. 1993a,b,c	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 1,5 –73 m
Pectinaria auricoma	▪ DE pref., Mixt. ▪ Mud. tol.	Picard 1965; Bellan 1964; Bianchi et al. 1993a	▪ muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 4,5 – 60,5 m
Sternaspis scutata	▪ VTC excl ▪ sandy mud ▪ Eurybathic, Circalittoral, Bathyal	Pérès & Picard 1964; Bellan 1964; Picard 1965; Picard 1972; Zavodnik et al. 1985; Gambi & Giangrande 1986;Crema et al. 1991; Bianchi et al. 1993a; Ben-Eliahu & Fiege 1995	▪ sand (S), muddy sand (mS), very sandy mud (vsM), sandy mud (sM), mud (M) ▪ 13,5 –100 m

Aponuphis bilineata (Onuphidae) was found from 4 to 100 m depth (Figure 2) although it was mostly frequent between 20 and 30 m depth (Figure 3). The species mainly prefers muddy sand (mS) and very sandy mud (vsM) (Figure 4 and Table IV), where gravels are present, as along the Island of Elba and western Sardinia coasts. Moreover, this species seems to tolerate a high percentage of mud occurring in both sandy mud and muddy stations (sM and M). Our results partially agree with the existing information that signalled A. bilineata in detritic and sandy substrata and in mixed sediment (Table V).

Aponuphis brementi and Aponuphis fauveli (Onuphidae) displayed similar sediment preferences to the congeneric species A. bilineata showing a significant association with very sandy mud (vsM) (Figure 4 and Table IV). A. brementi was more frequent below 20 m depth and up to 50 m while A. fauveli occurred below 30 m and up to 90 m depth (Figures 2 and 3). Our results add information to the existing literature where these species were described as ‘misticolous’ and A. fauveli in particular was affiliated to the muddy detritic biocoenoses (Table V).

Caulleriella caputesocis (Cirratulidae) was found from 3.5 to 80 m depth (Figure 2) and more frequently in deeper stations, below 30 m depth (Figure 3). It occurred in stations with high percentages of mud (vsM, sM and M) (Figure 4 and Table IV), in accordance with the existing information (Table V), but also in few stations where the sandy fraction was ≥95–70% of the sediment (S and mS).

Chaetozone gibber (Cirratulidae) was distributed in all sediment typologies, with higher frequency in muddy stations (vsM, sM and M) (Figure 4) as indicated in the literature (Table V). The species was mainly found in shallow water and never below 43 m depth (Figures 2 and 3).

Clymenura leiopygos (Maldanidae) was collected from 2.5 to 73 m (Figure 2) especially in stations located between 20 and 30 m depth (Figure 3). The presence of this species was signalled in sandy stations, as well as in all the other sediment typologies, with comparable frequencies (Figure 4). Our data show that C. leiopygos has a higher tolerance to different fractions of mud than what expressed in the existing literature (Table V).

Diopatra neapolitana (Onuphidae) was mostly found in shallow stations (above 10 m depth) but is present up to about 23 m depth (Figures 2 and 3). It was mainly collected in sediments with high percentages of mud (vsM and M) and only in a few sandy stations (S and mS) (Figure 4). These results suggest that this species has a good tolerance for mud, in partial agreement with previous literature that considered D. neapolitana a species typical of fine well-sorted sand assemblages (Picard 1965) and characteristic of sandy sediments, but tolerant to small amounts of mud (Table V).

Ditrupa arietina (Serpulidae) was mostly collected between 30 and 50 m depth, although its range spans from 5 to 51 m depth (Figures 2 and 3). According to our results, this species seems to tolerate different fractions of mud in the sediment, since it was mostly recorded on very sandy mud (vsM) and in other types of sediment, ranging from sand to mud (Figure 4 and Table IV). It is also interesting to underline that the gravel fraction was very scarce in all the stations where D. arietina was recorded, although this is a species normally affiliated to detritic coastal assemblages and it has been signalled on mixed sediments (Table V).

Drilonereis filum (Oenonidae) was found from 3 to 90 m depth, mostly below 20 m (Figures 2 and 3), in all sediment types even if it showed a high tolerance to mixed sediment (vsM and sM) (Figure 4 and Table IV); moreover, it was very rare in sandy (S) and shallow stations and up to 20 m depth. Our results, on the whole, confirm the information existing on this species (Table V).

Eunice vittata (Eunicidae) was found from 1.5 to 60 m depth (Figure 2). It is mostly frequent on muddy substrata, preferably in very sandy mud (vsM), sandy mud (sM) (Table IV) and mud (M) (depth range 30–50m), rather than on sandy sediments (S and mS) (Figures 3 and 4). The percentage of gravel (mainly composed of organic detritic matter) was more abundant in vsM sediments which characterized stations located around Island of Elba and few stations of Baia (Gulf of Naples). Our results partially agree with previous scientific literature (Table V).

Heteromastus filiformis (Capitellidae) was recorded between 1.5 and 99 m depth (Figures 2 and 3) in sediments characterized by a high percentages of mud (vsM, sM and M) and only in few sandy (S) and muddy sand (mS) stations (Figure 4 and Table IV). These results agree with the existing information, which defined the species as an exclusive species of upper muddy-sand assemblages living also in mud-rich sediments (Table V).

Hyalinoaecia tubicola (Onuphidae) was sampled exclusively below 20 m depth, frequently between 30 and 50 m (Figures 2 and 3). This species inhabited primarily very sandy mud (vsM), sandy mud (sM) and muddy sand (mS) sediments and was found in other sediment typologies in only a few stations (S and M) (Figure 4 and Table IV). In some of the stations where H. tubicola was recorded (mainly vsM and mS stations located in the Tyrrhenian Sea along the Island of Elba and the coast of Terracina and Sabaudia), the percentage of gravel suggested the presence of detritic habitats where, according to the scientific literature, this species is most common (Table V).

Melinna palmata (Ampharetidae) was collected from 1 to 99 m depth (Figures 2 and 3), and results show that the species is strongly linked to the muddy fraction of the sediment (Figure 4 and Table IV), in accordance with several authors (Table V). In fact, the stations where the species mostly occurred were characterized by an increasing percentages of mud (from mS to M classes).

Metasychis gotoi has been defined as an alien species for the Mediterranean Sea (Cantone et al. 2004; Occhipinti-Ambrogi et al. 2011). The species was sampled, in comparable frequencies, in sediments with a variable fraction of mud, with a significant preference for sandy mud (sM), and at depths ranging from about 17 to 100 m (Figures 2–4 and Table IV). This species was absent in shallow waters with sand percentages >95%. The data that we collected on this species integrate the information on the substrata inhabited by M. gotoi (Table V).

Nematonereis unicornis distribution (Eunicidae) highlights the wide bathymetric range of this species, recorded from 3 to 110 m depth with highest frequencies between 30 and 50 m depth (Figures 2 and 3). N. unicornis inhabits sediments with different percentages of mud (from mS to M) (Figure 4, Table IV) and – in some locations – with abundant fractions of gravel (Elba Island, Baia and Anzio, Tyrrhenian Sea). These results confirmed the information about this species, which normally has been affiliated to muddy-detritic assemblages (Table V) and classified as one of the few taxa able to burrow inside Posidonia oceanica sheaths (Gambi 2002).

Nothria conchylega (Onuphidae) was recorded from 5 to 100 m depth with variable frequencies at different depth ranges (Figures 2 and 3). It was mostly found in sediments with 70–95% sand (mS) and it was less frequent either at stations characterized exclusively by sand (S) or by lower percentages of sand (vsM, sM and M) (Figure 4 and Table IV). These results add information to previous literature, which described N. conchylega as a species typical of muddy sediment, often found in shelf terrigenous mud and in shelf edge detritic assemblages (Table V).

Onuphis eremita (Onuphidae) was collected up to 90 m depth and mostly between 4 and 10 m; no individuals were found between 30 and 50 m depth (Figures 2 and 3). O. eremita was frequent in sandy stations (S and mS) (Figure 4 and Table IV), in accordance with the literature that affiliated this species to the biocoenoses of well-sorted fine sand (Table V). Nevertheless, we signal that this species was also frequent in mud (M).

Owenia fusiformis (Oweniidae) was present in the depth range 1.5–73 m with variable frequencies (Figures 2 and 3). This species was mainly found in stations characterized by a high percentage of sand (S and mS) (Figure 4 and Table IV), in accordance with authors who described it as typical of fine well-sorted sand assemblages (Table V). Moreover, a significant percentage of gravel characterized some of the stations were the species was found at the Island of Elba, Porto Torres (Western Sardinia), Montalto (Central Tyrrhenian Sea) and Marche (Central Adriatic Sea) indicating that O. fusiformis inhabits also detritic substrata, as stated by Pérès & Picard (1964) (Table V).

Pectinaria auricoma (Pectinariidae) was mostly recorded between 20 and 30 m depth, although it was collected in the range of 4.5–60.5 m (Figures 2 and 3), on sandy substrata with low fractions of mud (mS) (Figure 4 and Table IV). We noticed that the increase of mud in the sediment led to the decrease of P. auricoma, and the species was absent in exclusively sandy sediment (S). Our results are partially in accordance with the common description of this species as affiliated to the muddy-detritic assemblages (Picard 1965) and as a mud tolerant species (Table V).

Sternaspis scutata (Sternaspidae) occurred exclusively below 13 m depth, mainly between 20 and 30 m (Figures 2 and 3). Our results indicate that this species inhabits primarily muddy sediments (sM and M), even if it was also found in several stations with very sandy mud (vsM) or muddy sand (mS) (Figure 4 and Table IV). These results partially confirm the previous information, which described this species as typical of the terrigenous mud-shelf assemblages and inhabiting sandy mud (Table V).

Conclusions

New relevant information emerged from the comparison of the results of this study with pre-existing knowledge. In fact, the data analysed allow us to update the distribution in the Italian Biogeographical Zones of five species (Aponuphis bilineata, A. brementi and A. fauveli, Nothria conchylega, and Onuphis eremita).

These results contribute to update the ecological characteristics of the investigated species in relation to depth range and sediment typologies, highlighting significant associations of a number of species with definite sediment classes. Moreover, this results outline that multidisciplinary data sets, as ISPRA's, are essential in increasing the scientific knowledge on the benthic communities and species that populates soft seabed substrata.

This study furthermore outlines the importance of environmental monitoring programmes as a source of important scientific data such as relevant information on marine invertebrate ecology. This work is meant to be a first contribution in the framework of a more extensive revision of our understanding of the ecological requirements and the distribution of polychaete species in soft sediments, improving our knowledge on the functioning and evolution of marine ecosystems.

Acknowledgements

We are grateful to the editor and the two referees for their invaluable comments and contribution. Many thanks to Dr Maria Cristina Gambi (Stazione Zoologica Anton Dohrn of Naples) and Prof. Michele Scardi (University of Rome ‘Torvergata’), for their invaluable support on data analysis and for the suggestions that improved this work considerably. Thanks to the researchers and the students for their assistance in field activities and for their time and invaluable dedication to taxonomic identification.

We want to express our fond memory and gratitude also to Prof. Eugenio Fresi (University of Rome ‘Tor Vergata’) for the precious contribution he has made to marine biology and to the study of benthic communities.

Part of this study was supported by the local authorities of the Regione Lazio and the Regione Marche. Bioservice s.c.r.l. (Napoli) also contributed with a set of data.