Introduction
Biogenic structures, which are created by corals, molluscs and polychaetes, provide essential habitats for diverse marine life, fostering biodiversity and supporting ecosystems. They serve as nurseries for economically important species, aiding in their reproduction, and offer sustenance for birds and fish, enhancing marine productivity and resilience (Commito and Rusignuolo, Reference Commito and Rusignuolo2000). Tube-building polychaetes are a key group of marine bioengineers in soft-bottom habitats, providing structures that can influence the composition of the benthic community (Santos and Aviz, Reference Santos and Aviz2019).
The family Sabellariidae (Johnston, Reference Johnston1865) comprises a relatively small group of sedentary marine polychaetes that construct rigid tubes primarily from sand grains and shell fragments (Kirtley, Reference Kirtley1994). Sabellariids are found worldwide, from the intertidal zone to abyssal depths (Chávez-López, Reference Chávez-López2021). Some gregarious sabellariids can build extensive reefs in the intertidal and sublitoral zones, stretching for several kilometres along the coast (Capa et al., Reference Capa, Faroni-Perez and Hutchings2015).
Sabellariid reefs play a vital role in marine ecosystems, filtering large volumes of water and altering the local flow regime (Dubois et al., Reference Dubois, Commito, Olivier and Retière2006). Their three-dimensional reef structures also generate a high diversity of microhabitats, providing shelter and food for many species (Capa et al., Reference Capa, Hutchings and Peart2012; Desroy et al., Reference Desroy, Dubois, Fournier, Ricquiers, Mao, Guerin, Gerla, Rougerie and Legendre2011). By stabilising mobile sediment habitats, these reefs create conditions that enable diverse benthic communities to thrive in areas where they would otherwise be absent (Dubois et al., Reference Dubois, Commito, Olivier and Retière2006; Lancaster and Savage, Reference Lancaster and Savage2008; Nishi et al., Reference Nishi, Matsuo, Capa, Tomioka, Kajihara, Kupriyanova and Polgar2015; Porras et al., Reference Porras, Bataller, Murgui and Torregrosa1996). Moreover, sabellariids hold significant economic and ecological importance. They influence shoreline topography and provide an ecosystem service in the form of coastal protection by dissipating wave energy (Wang and Stewart, Reference Wang and Stewart2013). They also play a role in the food chain of reef fish (Parab and Gaikward, Reference Parab and Gaikward1990; Pettibone, Reference Pettibone1982).
The family Sabellariidae currently comprises 12 genera and 150 species (Read and Fauchald, Reference Read and Fauchald2024). The genera Gunnarea Johannson, 1927, Idanthyrsus Kinberg, 1867, Neosabellaria (Kirtley, Reference Kirtley1994), Phragmatopoma Mörch, 1863, and Sabellaria Lamarck, 1818 are the only ones known to create sand reefs (Nishi et al., Reference Nishi, Bailey-Brock, Santos, Tachikawa and Kupriyanova2010). In Indian waters, nine species of Sabellaria have been recorded, including S. miryaensis (Parab and Gaikward, Reference Parab and Gaikward1990), a reef-building species from the Arabian Sea. The present study provides the first record of S. miryaensis in the Bay of Bengal, over 30 years after its original description. In addition, details are provided on the ecology of S. miryaensis, including environmental parameters and the associated benthic biodiversity.
Materials and methods
Study area and sampling
Gopalpur (19.27°N, 84.92°E) is a coastal town located in southern Odisha, on the east coast of India. Local fishermen in this region have detected a sabellariid reef extending from Gopalpur Port (19°15’41”N, 84°56’11”E) in the north to Dhabaleswar beach (19°13’15”N 84°52’58”E) in the south, covering a distance of approximately 11 km. Four samples were collected from four sites along the sabellariid reef in March 2024 (Figure 1). Quadrats measuring 1 m2 were taken from the subtidal zone (15 m depth), located approximately 1 km offshore off the coast of Gopalpur. This was done with the help of local fishermen using free diving techniques.
Map showing the study area and sampling stations.
Water samples were collected from the surface at each station for the measurement of water temperature, pH and salinity. Temperature and salinity were measured immediately in the field using a thermometer with an accuracy of ±0.5 and a refractometer (ATAGO), respectively, while pH was measured in the laboratory by using a microprocessor-based pH system (ESICO-1012).
Sample analysis
The collected sand reef samples were transferred to large trays, where macrofaunal organisms were immediately separated from the sediment. This initial sorting was performed manually to ensure minimal damage to delicate specimens. The extracted fauna were then rinsed with seawater and preserved in 5% formalin for further examination. In the laboratory, specimens were carefully segregated and examined under a stereozoom microscope (Magnus TZM6) for detailed morphological identification. Taxonomic classification was carried out to the highest possible resolution, primarily to the family level for polychaetes and major groups for other invertebrates. All specimens were fixed in 5% formalin and subsequently preserved in 70% ethanol. The reef-forming sabellariid species was identified following the identification keys by Kirtley (Reference Kirtley1994), corroborating its characteristics with the original species description. The description of S. miryaensis includes: the total body length, measured from the apical end of the crown to the last abdominal segment; the body width, measured in the parathoracic region; and the caudal peduncle length, measured separately, as recommended by Chávez-López (Reference Chávez-López2021). The opercular region was dissected, mounted on a glass slide with glycerol, and observed under compound microscope (Magnus MLX-B Plus) to analyse the arrangement and the shape of the paleae.
The diversity of the reef’s associated macrofauna was identified at the level of large taxonomic groups. In particular, polychaetes were identified at the family level using the identification keys by Fauchald (Reference Fauchald1977). All specimens sampled were deposited in the Estuarine Biological Research Centre, Zoological Survey of India, Gopalpur (ZSI), and the Marine Specimen Repository, Berhampur University (MSR). Tube sediment texture was analysed using the method described by Konert and Vandenberghe (Reference Konert and Vandenberghe1997). The grain size distribution (%) was calculated according to Ramaswamy and Rao (Reference Ramaswamy and Rao2006).
Results
Annelida Lamarck, 1809
Family Sabellariidae Johnston (Reference Johnston1865)
Genus Sabellaria Lamarck, 1818
Sabellaria miryaensis Parab and Gaikward (Reference Parab and Gaikward1990)
Sabellaria miryaensis Parab and Gaikwad, 1990 a, Complete specimen in ventral view; b, Dorsal view; c, Lateral view.
Material examined
India • Odisha, Gopalpur. 1 specimen; Length 4.9 cm, Width 0.6 cm; 19°15’41”N 84°56’11”E; ST1; depth 15 m; 28.03.2024; ZSI/EBRC/An-16664. 3 specimens; Length 3.2–4.3 cm, Width 0.4–0.5 cm; 19°14’53”N 84°55’10”E; ST2; depth 15 m; 28 Mar. 2024; ZSI/EBRC/An-16665–16667. 3 specimens; Length 2.6–4.5 cm, Width 0.4–0.5 cm; 19°14’11”N 84°54’11”E; ST3; depth 15 m; 28 Mar. 2024; ZSI/EBRC/An-16668–16670. 4 specimens; Length 3.2–5.8 cm, Width 0.4–0.6 cm; 19°14’11”N 84°54’11”E; ST4; depth 15 m; 28 Mar. 2024; ZSI/EBRC/An-16671–16674.
India • Odisha, Gopalpur. 13 specimens; Length 3–5.1 cm, Width 0.5–0.6 cm; 19°15’41”N 84°56’11”E; ST1; depth 15 m; 28.03.2024; 007.MSR/BoL-24.
Diagnosis. Opercular crown with three rows of paleae. Outer paleae with 4–7 terminal spines, including a smooth median spike with a slightly curved downward tip. Middle paleae subovate with an acute tip. Inner paleae geniculate with acute tip. Opercular peduncle with 1–2 pairs of thin nuchal spines. Abdomen with 32–41 segments.
Description. Complete specimen (ZSI/EBRC/An-16664), 40 mm long, 6 mm wide, with three parathoracic segments, 32 abdominal segments, caudal peduncle 9 mm long (Figure 2a–c). Live specimen with body pale yellowish, branchiae and cauda dark red, palps light red (Figure 5). Preserved specimen with body creamy white; some black flecks and spots on opercular lobes, including median organ, median ridge, on margins of build organ and parathoracic neuropodia. Feeding tentacles pale or brown.
Opercular crown and opercular stalk partially fused. Opercular disc with three rows of golden paleae arranged in concentric semicircles: outer row with 27 paleae per lobe (Figures 3a–d and 4a–d), middle row with 20 paleae per lobe (Figures 3e and 4e), inner row with 21 paleae per lobe (Figures 3f and 4f). Outer and middle paleae with tips outward from operculum, inner paleae with tips inward. Outer paleae 2.11–2.43 mm long, with flat blade, oblong, twice longer than wide; anterior region with 2–3 pairs spines, lateral to the median spike, gradually decrease in size towards the edge of the blade; median spike enlarged, smooth and flat, tip slightly curved downward. Middle paleae 2.21 mm long, with subovate blade, concave, tip acute. Inner paleae 1.58–1.62 mm long, with geniculate blade, slightly concave proximally, tip acute. Inner paleae slender than middle paleae.
Sabellaria miryaensis Parab and Gaikwad, 1990 a–d. outer paleae; e. middle paleae; f. inner paleae; g. nuchal spine; h. capillary chaeta; i. lanceolate chaeta; j. neurochaeta of chaetiger 1; k. uncinus of anterior abdominal chaetigers.
Sabellaria miryaensis Parab and Gaikwad, 1990 compound microscope images. a–d. Terminal spines of outer paleae- a. 4 spines; b. 5 spines; c. 6 spines; d. 7 spines; e. middle palea; f. inner palea.
Opercular peduncle with 1–2 nuchal spines (Figure 3g) on each side of the antero-dorsal midline of the lobes. About 21 conical opercular papillae per lobe. Buccal cavity with 10 rows of tentacles per lobe, each transversal row with 12–15 fine slender tentacles. A pair of elongated palps. Median organ conical with tip blunt, longer than wide.
Thorax without notochaetae. Chaetiger 1 with a pair of elongate, tapering neuropodia, with 8–11 capillary plumose chaetae. Chaetiger 2 with a pair of lateral neuropodia, triangular-shaped, with 5 capillary plumose chaetae, and a pair of branchiae.
Parathorax with three segments, all with paired branchiae. Notopodia with two rows of notochaetae, 10–11 lanceolate chaetae, with frayed tips interspersed with 8–9 capillary chaetae (Figure 3h–i). Neuropodia with 7 lanceolate and capillary chaetae, thinner than notochaetae (Figure 3j).
Abdomen with 32 chaetigers. Abdominal segments colourless, with a pair of branchiae decreasing in size until segment 24. Neuropodia with two rows of 14–16 verticillate chaetae, dorsal row with slightly larger chaetae. Notopodia with a series of uncini with six transverse rows of teeth (Figure 3k).
Caudal peduncle bent ventrally, reaching back to last 14 abdominal segments (Figures 2a and 5).
Photograph of Sabellaria miryaensis Parab and Gaikwad, 1990 and the structure of the sand reef.
Variation. Body 32–58 mm in total length, 3–6 mm wide, 32–41 abdominal segments. Opercular disc with three rows of golden paleae arranged in concentric semicircles: outer row with 24–29 paleae per lobe, middle row with 18–21 paleae per lobe, inner row with 18-21 paleae per lobe. Body length, number of palea varies with specimen size. Caudal peduncle bent ventrally, reaching back to last 13–17 abdominal segments.
Ecological analysis
The sabellariids collected from the reef during the study consisted of a single species, S. miryaensis. The reef structure, formed by densely packed worm tubes, resembles a sandy honeycomb (Figure 5). The surface water temperature of the reef was recorded at 30°C, salinity at 35 PSU, and pH at 8.03. The overall mean diameter of the tube openings ranged from 0.2 to 0.8 mm. The tubes were constructed from sand granules, consisting of 90.41% sand, 8.34% silt, 1.25% clay, and dead shells, with the inner side coated in a thin, hardened mucous layer.
The average density of S. miryaensis and other associated fauna of the reef is presented in Table 1. The average density of polychaetes including S. miryaensis was recorded at 18,982 ± 9,524 individuals · m−2.
Density of macrofauna associated with the reef of Sabellaria miryaensis
The average density of S. miryaensis (7805 ± 1367 individuals · m−2) was found as 41% of the total polychaete abundance. Among polychaetes, Eunicidae, Polynoidae, and Syllidae were the most abundant group while Terebellidae, Spionidae, and Pilargidae were less abundant group observed (Figure 6).
Pie chart shows Reef associated macrobenthos and polychaete community.
The average density of organisms on the reef, excluding polychaetes, was 19789 ± 5515 individuals · m−2. The community composition included: 43% nematodes, 17% amphipods, 9% shrimps, 8% tanaidaceans, 6% brachyurans, 4% ophiuroids, 3% bivalves, 3% anumorans, 2% sea anemones, 2% gastropods, and less than 1% each of isopods, sipunculans, turbellarians and pycnogonids (Figure 6).
Discussion
Sabellaria alcocki Gravier, 1906 and, S. alveolata (Linnaeus, 1767) from Kerala, S. floridensis Hartman, 1944 and S. intoshi Fauvel, 1914 from Tamil Nadu, (Kerala), S. chandraae Silva, 1961 (Sri Lanka), S. miryaensis (Parab and Gaikward, Reference Parab and Gaikward1990) (Maharashtra), S. pectinata Fauvel, 1928 (Shingle Island), S. pectinata intermedia (Fauvel, Reference Fauvel1932) (Gangetic Delta) and S. spinulosa (Leuckart, 1849) from Kerala, Tamil Nadu and West Bengal (Achari, Reference Achari1974; Sivadas and Carvalho, Reference Sivadas and Carvalho2020) are the only sabellaridae species described from Indian Ocean. However, S. alveolata and S. floridensis, described from British Isles and Florida, USA, are considered questionable records for the Indian coasts. Sabellaria miryaensis is distinguished from the other Indian sabellariid species mainly by the shape of the outer paleae, which have a wide median spike with a downward curved tip, and the median paleae with a subovate blade. The original description of S. miryaensis was based on only four specimens, including the holotype. Among them were two males, one female and one juvenile. The three mature specimens measured 32–68 mm in length and 3.5–5 mm wide, with the holotype being the longest specimen. The juvenile specimen measured 28 mm in length, 3 mm in width (Parab and Gaikward, Reference Parab and Gaikward1990). The specimens described here agree with the description of S. miryaensis in the shape of opercular paleae, the number of abdominal segments (31–33 seg.), and even in the coloration pattern of live specimens. Some variations such as the number of terminal spines on the outer paleae (4–7 spines) and the number of rows of feeding tentacles (10 rows instead of 9), could be associated with the specimen size.
Sabellaria miryaensis Parab and Gaikwad (1990) was described from the Arabian Sea, along the west coast of India. Except from the first description, there has been no further evidence of its occurrence in other regions. The present study reports the first record of S. miryaensis on the east coast of India, extending its distributional range to the Bay of Bengal.
Sabellaria miryaensis thrives in this location because the local environment provides a very specific set of conditions that are not present in many other coastal systems. The reef develops in warm waters averaging 30 °C, with stable salinity (35 PSU) and 8.03 pH, all of which support the worms’ physiological tolerance. Just as important, the seabed is dominated by coarse sand grains (over 90%), which supply the essential material for constructing their honeycomb-like tubes. Similar to other sabellariids, this species depends on both sediment availability and water movement, since moderate hydrodynamics not only deliver sand but also help retain larvae close to the reef. Previous research has shown that Sabellaria alveolata in Mont-Saint-Michel Bay and S. spinulosa in the North Sea flourish under comparable circumstances where suspended sediment and tidal currents converge to maintain reef stability and larval settlement (Dubois et al., Reference Dubois, Comtet, Retière and Thiébaut2007; Van der Reijden et al., Reference Van der Reijden, Koop, Mestdagh, Snellen, Herman, Olff and Govers2021). In contrast, areas with finer sediments, reduced sand supply, or less dynamic water conditions rarely support reef formation. Therefore, the occurrence of S. miryaensis in this region, and its absence elsewhere, reflects a delicate balance of temperature, sediment type, and hydrodynamics that aligns with global patterns observed in other sabellariid reefs, while emphasizing the role of local peculiarities in shaping distribution.
The reef structured by S. miryaensis provides habitat for a diverse community of marine invertebrates, including nematodes, amphipods, ophiuroids, brachyurans, bivalves, anomurans, and other polychaetes families. Two families are the most abundant among those associated with the reef. The family Eunicidae is common on Sabellaria reefs because the reef’s honeycomb like structure creates many small crevices where they can hide, while the rich diversity of invertebrates around the reef provides them with plenty of food (Dubois et al., Reference Dubois, Retière and Olivier2002; Zanol et al., Reference Zanol, Carrera-Parra, Steiner, Amaral, Wiklund, Ravara and Budaeva2021). Similarly, syllidae polychaetes are particularly abundant on Sabellaria reefs because the complex tube matrix traps organic matter and hosts diverse sessile invertebrates, providing ideal microhabitats and feeding resources for these small, mobile worms, many of which are grazers or commensals (Dubois et al., Reference Dubois, Retière and Olivier2002; La Porta and Nicoletti, Reference La Porta and Nicoletti2009). The region is also a significant fishing ground for the local communities where highly commercial fish species such as Apogonidae, Lutjanidae, Pempheridae, Pomacanthidae, Priacanthidae, Scatophagidae, Scaridae, Serranidae, and Sparidae are commonly caught. The use of this region as a fishing ground by local fishermen underscores its rich biodiversity and commercial significance. The presence of diverse fish species indicates a healthy and productive marine ecosystem, supporting various forms of aquatic organism life. This biodiversity not only ensures ecological balance but also provides substantial economic benefits. The local fishermen rely on these abundant resources for their livelihoods, highlighting the critical role of the Sabellaria reef in sustaining the local economy. Thus, the region’s biodiversity and commercial importance are closely linked to the health of the Sabellaria reef ecosystem, influencing economic activities and vice versa. Therefore, a comprehensive and quantitative analysis is needed to evaluate the impact of climatic elements and ecological relationships on the composition and durability of Sabellaria reefs. Reef development, diversity, and stability are affected by both environmental influences and species interactions. Gaining this understanding is vital for comprehending reef dynamics and informing conservation efforts.
Acknowledgements
The authors express their gratitude to the Vice Chancellor of Berhampur University for providing the necessary facilities. The authors gratefully acknowledge Balaram Mahanty, National Institute of Ocean Technology for preparing the study area map used in this study.
Author contributions
A.K.C.: conceptualization, sample collection and processing, analysis, led the original draft, write – reviewing and editing; S.P.: conceptualization, write – reviewing and editing, supervision; Y.C.L.: write – reviewing and editing; B.B.: sample collection and processing. All authors contributed critically to the manuscript and gave final approval for publication.
Financial support
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
Conflict of interest
None.
Data availability
All the data are given in the manuscript.
