Marine invertebrates associated with rhodoliths/maërl beds from northeast Brazil (State of Paraíba)

Abstract Background This study investigates the marine macroinvertebrate fauna of rhodolith beds (non-geniculated red corallinaceaous algae) in northeast Brazilian. A total of 57 species were identified, belonging to six phyla (Platyhelminthes, Annelida, Sipuncula, Mollusca, Arthropoda and Echinodermata), of which 50 are considered here as new records for the Paraíba State. Annelids (Class Polychaeta) were the most representative taxa in Miramar and Seixas Beaches, while molluscs were dominant in Maceió Beach. New information This is the first study that includes an identification key, diagnostic features and distribution patterns worldwide and local (including new records) of the marine invertebrate fauna associated with rhodolith beds in northeast Brazil (State of Paraíba). Sampling events were performed in 2018, at low tide in the intertidal to shallow subtidal zones (1.5 and 4.0 m depth), in Miramar, Seixas and Maceió Beaches. A total of 17 species were found for the first time on Seixas Beach, as well as all identified species for Miramar and Maceió. This study tries to contribute to the knowledge of marine invertebrates in northeast Brazilian shallow habitats, providing a baseline for future environmental studies.


Introduction
Marine invertebrates are a group of animals characterised by the absence of a backbone, living in the oceanic zone around the world, from the intertidal region to great depths. The fauna is represented by many taxa, for example, poriferans, cnidarians, annelids, crustaceans, molluscs and echinoderms, with a great variety of morphological characteristics, types of behaviour, feeding habits, participating in all levels of food webs, being essential for the maintenance of homeorhesis and equilibrium in the oceans.
The red non-articulated calcareous algae, known as rhodoliths or maërl (European name), are reported in all oceans, from the intertidal zone to depths of 270 m and these habitatlike structures are considered as a hotspot of biodiversity, harbouring many groups of invertebrates, mainly juveniles (Scherner et al. 2010), for example, polychaetes, crustaceans, molluscs, sipunculids and echinoderms (Prata et al. 2017). The Brazilian coast, in particular the northeastern region, may represent the zone with the highest abundance of rhodoliths worldwide, due to the large deposits of calcium carbonate (Amado -Filho et al. 2012).
The present study aimed to describe, by diagnostic characteristics, the marine invertebrates associated with rhodoliths of three beaches from the State of Paraíba, northeast Brazil, with the inclusion of global and local distribution.

Study area
The Brazilian coast zone extends for 8,500 km and has a width of 12 nautical miles outwards from the coast (MMA (Ministério do Meio Ambiente da República Federativa do Brasil) 2020). The northeast zone has around to 3,400 km, in which Paraíba is one of the States of this zone, having a coastline that extends for 140 km (Lima and Heckendorff 1985), from the Estuary of Guajú River (in the north) up to the Estuary of Goiana River (in the south) (Neves et al. 2006).
The sampling campaigns were carried out in 2018, at the coastal area of the Paraíba State, at Miramar (Cabedelo Municipality), at Seixas (João Pessoa) and at Maceió (Pitimbu) Beaches (Fig. 1), on the subtidal zone, considering two depths in each site, 1.5 and 4.0 m.

Methodological approach
The habitats of the sampling area are constituted of rhodoliths, i.e. red calcareous nonarticulated algae from the subclass Corallinophycidae. The sampling procedure design for the rhodoliths followed the quadrat methodology, adapted from Underwood and Chapman (2013). At each Beach, a 100 m quadrat was selected at a shallower zone depth (1.5 m) and another at a deeper depth (4.0 m), with 20 metres distance apart, from which five replicates were chosen with 225 cm area each. The replicates were chosen at each of the quadrat edges and in the centre point (for analysis, each sampling area was considered as one sample, being two samples per beach and six in total). Through scuba diving, an aluminium quadrant was placed on the bottom sediment of each sampling area and all the rhodoliths inside the replicate's squares were collected manually with gloves and stored inside plastic bags (no sediments), which were immediately closed. These samples were accommodated in thermal boxes with ice and taken to the laboratory for processing. The biological material was sorted at the "Laboratório de Invertebrados Paulo Young" (LIPY [Paulo Young Invertebrate Laboratory]) from the "Universidade Federal da Paraíba (UFPB, Campus I, Brazil [Federal University of Paraíba])". The collected invertebrates were removed, fixed and stored in 70% alcohol, being identified to the specific taxonomic level. The species were photographed with a Canon 6d digital camera-length 100 mm macro L or a Leica MZ12.5 stereomicroscope. Nevertheless, the photos were taken for general overview of the organisms identified, not with the intention of documenting detailed taxonomic characters for specific identification.
The identified taxonomic groups were organised according to the World Register of Marine Species (WoRMS-Editorial-Board 2020), with additional information for polychaetes (Rous e and Fauchald 1997). Their distribution in Paraiba is based on the distribution records from published sources, including the present study.

Data resources
The data underpinning the analysis reported in this paper are deposited in the Dryad Data Repository at https://doi.org/10.5061/dryad.fbg79cnv8.  (Amaral et al. 2013.

Distribution in Paraíba:
Seixas Beach ; and this study).
Distribution: Atlantic Ocean (North to South), Gulf of Mexico, Brazilian coast (Paraíba, São Paulo, Rio de Janeiro, Paraná and Rio Grande do Sul States) and Mexican Pacific coast (Amaral et al. 2013.

Distribution in Paraíba:
Seixas Beach ; and this study).
Notes: Found inside the rhodoliths.

Remarks:
The species was recorded for Seixas Beach as Lysarete raquelae Carrera-Parra, 2001, but now it is revised and replaced to Lysarete brasiliensis.

Distribution in Paraíba:
Seixas Beach ; and this study).
Notes: Found on the rhodoliths surface.
Distribution: Northeast Pacific Ocean (Baja California), Caribbean Sea and Brazilian coast (Maranhão, Paraíba and Alagoas States) (Amaral et al. 2013 Diagnosis: (Amaral et al. 2005, Santos and Lana 2003, Uebelacker and Johnson 1984: Prostomium with four eyes, two antennae, and two palps (Fig. 4e). Proboscis with conical paragnaths (area I with one paragnath, area II 10, area III with 18-20, area IV with 26-30, area V none, area VI with six, area VII and VIII with five) and serrated jaws. Four pairs of modified anterior cirri ("tentacular cirri"). Parapodia with notopodial and neuropodial lobes (with pre-and post-chaetal lobes) of same size, falcigers and spinigers chaetae and dark aciculae. Diagnosis: (Dueñas-Ramírez and Quiros-Rodriguez 2012): Prostomium with four eyes, two antennae and two palps (Fig. 4f). Proboscis with paragnaths (area I with two conical ones, area II with three rows of pectinate bars, area III with four pectinate bars, area IV with five pectinate bars, area V with one conical paragnath, area VI with transverse ones and areas VII and VIII with a single row conical ones) and serrated jaws. Four pairs of modified anterior cirri ("tentacular cirri"). Parapodia with notopodial and neuropodial lobes (with pre-and post-chaetal lobes) of same size, falcigers and spinigers chaetae and dark aciculae. Diagnosis: (Day 1967a): Body green. Prostomium with two eyes, four antennae, nuchal organs and a small posterior-median papilla. Proboscis divided at two parts, proximal one with soft papillae, distal one papillated with six divisions. Four pairs of modified anterior cirri ("tentacular cirri") ( Fig. 5a). Parapodia carry dorsal enlarged foliaceous cirri and neuropodial lobe with spinigers chaetae.

Distribution in Paraíba:
Seixas Beach ; and this study).
Notes: Found inside the rhodoliths.  Diagnosis: (Imajima and Hartman 1964): Prostomium with four eyes, three antennae and two palps. Dorsum covered by 12 pairs of elytra from anterior to posterior end, with papillae on the surface (first pair elytra with long marginal papillae, other ones reniform) and marginally fringed (Fig. 5b). Notopodial region carries cirri and capillaries chaetae; neuropodial lobes enlarged with falcate chaetae.
Distribution: North Atlantic Ocean to Greenland, Mediterranean Sea (Read and Fauchald 2020s) and Brazilian coast (State of Paraíba) ).

Distribution in Paraíba:
Seixas Beach ; and this study).
Notes: Found inside the rhodoliths.

Distribution in Paraíba:
Seixas Beach ; and this study) and Miramar Beach (New record).

Distribution in Paraíba:
Seixas Beach ; and this study).
Notes: Found inside the rhodoliths.

Distribution
Distribution: Brazilian coast (Paraíba and Rio de Janeiro States) (Amaral et al. 2013.  (Fig. 7b). About 16 ventral pads followed by a narrow streak of glandular tissue in a ventral groove along the abdomen. Uncini on ventral tori originate from ventral ridges on the abdomen, with 3-4 teeth. Notochaetae: anterior ones with winged shafts and denticulate tips which become proportionately larger on posterior segments until they form most of the blade.  Diagnosis: (Biseswar 1997): Proboscis spoon-shaped with brown streaks. Head with two ventral golden chaetae (Fig. 7c). Body with outer layer of integument in posterior half of trunk separated from inner layers, but still attached to trunk. Conical papillae, projecting from surface of integument, arranged in concentric rings around trunk. To the naked eye, papillae appear as spherical, transparent spots. Rows of larger papillae alternate with three or four rows of uniform smaller papillae. Two rows of anal chaetae around posterior end. Diagnosis: (Hylleberg 1994): Body semi-transparent in the middle region, darker anteriorly and posteriorly (Fig. 7d). Anal shield covered with dark chalky points. Margin caudal shield with irregular ridges. Anterior end known as "introvert" similar in size to body; with rows of double-pointed hooks anteriorly; spines posteriorly. Longitudinal musculature in separate bands.

Distribution
Distribution: Gulf of Mexico and Tropical Central Atlantic Ocean (Saiz-Salinas 2020a).

Distribution in Paraíba: Seixas Beach (New record).
Notes: Found inside the rhodoliths.

Order Phascolosomatida Hayward & Ryland, 1990
Family  Diagnosis: (Hylleberg 1994): Body marbled with brown flecks and bands. Anterior end known as "introvert" longer than the body, carrying numerous rows of hooks and the dorsal side crossed by brownish bands intermingled with lighter ones (Fig. 7e). Hooks with a distinct streak (triangle and internal clear steak not divided), prominent swelling of proximal crescent. Above 20 tentacles.

Distribution in Paraíba: Miramar and Seixas Beaches (New records).
Notes: Found inside the rhodoliths.

Distribution in Paraíba: Seixas Beach (New record).
Notes: Found inside the rhodoliths.  Notes: Found inside the rhodoliths.

Diagnosis: (Smithsonian-Marine-Station-at-Fort-Pierce 2020): Shell dark-brown colour.
Fan-shaped shell with fine divercating radial ribs. The ribbed surface of the shell is most evident at the outer edges. Umbones situated in the anterior end (Fig. 8c). The interior has purple-brown blotches with one to four small purplish dysodont hinge teeth. Diagnosis: (Mediodia et al. 2017): With a smooth and shiny symmetrical shell and has predominantly dark brown to black colour with wavy dark pattern. Sculpture of fine concentric semi-circular rings (Fig. 8d). It has two similar-shaped valves joined by a hinge without teeth at the anterior portion. It has two muscle scars, the large posterior adductor muscle scar and the greatly reduced anterior adductor muscle. The byssal and pedal retractor muscle scar is located below the adductor muscle forming a thick straight line moving towards the middle portion of the shell. The pallial line was seen as a curved line towards the adductor scar.  Diagnosis: (Amaral and Simone 2014): Shell shape cupped or oval; right valve slightly operculum-shaped; left valve, fixed in substrate, larger than right valve (Fig. 8e). Muscle impression is purple and adductor muscle, oval central in posterior region. Adductor muscle postero-dorsal located, occupying 1/5 of total size of animal; hood present and fully filled by palps and gonads; colour of mantle edge brown. Accessory heart of three branches of similar length, starting from common centre. Palps with margin superior free. Diagnosis: (Muniz 2015): Gastropod with oval-shaped shell, slightly spiral convex sculptures with axial ventricular ribs, ending towards the base. Spiral sculpture found between axial ribs over basal area of shell (Fig. 8f). Oblique, denticulated opening on the inner surface of the outer lip, straight columella, anal notch present.   Diagnosis: (Oliveira 1951): Dark dorsum. Head with two ellipsoid eyes, twice longer than large, located close to lobe between both antennae. Pereopod coxae 1-4 of similar length and almost twice the size of the 5-7 ones (5 with an anterior lobe wider than posterior). First pairs of antennae longer than second ones (Fig. 9b). First pair of gnathopods longer than second ones. Males telson similarly longer than wide, with a median cleft to about 2/3 of its length; in females, cleft close to base and as long as broad.

Distribution in Paraíba: Seixas and Maceió Beaches (New records).
Notes: Found inside the rhodoliths.

Family Melitidae Bousfield, 1973
Dulichiella appendiculata (Say, 1818) Diagnosis: (Lowry and Springthorpe 2007): Head with two eyes; lateral cephalic lobe enlarged, truncated, antero-ventral corner with slender chaeta. Antenna 1 peduncular article 1 shorter than article 2, with 3 prominent chaetae along posterior margin. Antenna 2 peduncular article 2 cone gland reaching at least to end of peduncular article 3; article 4 slightly longer than article 5 (Fig. 9c). Mandibular palp article 1 about as long as broad, inner margin article 1 not produced distally; article 2 slightly longer than article 3. Orbital margin longer than half the maximum width of the carapace and trimmed with fine bristles. Rounded front edge with bristles, with the entire front region heavily excavated. Advanced front in relation to the orbital-external angles of the carapace. Narrow and excavated orbit, undeveloped antennular sumps (Fig. 9d).

Distribution in Paraíba: Seixas Beach (New record).
Notes: Found on the rhodoliths surface.

Family Mithracidae MacLeay, 1838
Mithraculus forceps Milne-Edwards, 1875 Diagnosis: (Wagner 1990): The carapace is broader than long, rather flat. Branchial sulci on its surface are not or very weakly broken by transverse grooves. Rostrum is little advanced, incised by a narrow notch. The basal antennal segment has two spines, of which the second, situated on the antero-external angle, is five times as large as the first. In small individuals, two acute tips can be observed distally on the second spine. The antennae are 0.2 times as long as the carapace. The orbit is armed with one spine below (not counting the basal antennal spines), one at the outer angle and three above (Fig. 9e).

Distribution in Paraíba: Miramar and Seixas Beaches (New records).
Notes: Found on the rhodoliths surface.

Family Paguridae Latreille, 1802
Pagurus criniticornis (Dana, 1852) Diagnosis: (Nucci and DeMelo 2007): Shield slightly longer than broad. Rostrum obtuse, slightly over-reaching lateral projections. Ocular peduncles slender and shorter than shield width, with corneae slightly dilated. Ocular acicles with anterior margins rounded, with one strong submarginal spine; occasionally accessory marginal spinule on mesial margin. Antennular peduncles over-reaching corneae; antennal peduncles usually not reaching distal margins of corneae; flagella long, usually over-reaching right cheliped (Fig. 10a). Diagnosis: (described here): Carapace about a third wider than it is long, convex. Dorsal surface covered with green granules, stronger in front and on the edges, smaller behind; several well-marked granular lines, arranged horizontally at the front of certain areas of the dorsal surface and emphasised by a row of long silks; regions poorly indicated, but nevertheless, delimited and expanded in the previous half (Fig. 10b).   arcs of six and a large peristome. Spines long and slender, thickened at the base and sharply pointed at the tips. On aboral side, primary and secondary spines dark olive green, with greenish-violet to purple tips. In general, the colour is blackish (Fig. 11a).  Disc covered by small and imbricated scales. Radial shields narrow, longer than wide, usually separated by one or two scales, the internal more elongated. Ventral side of the disc covered by smaller scales, imbricated. Bursal slit long, near the first arm plate. Oral shield diamond-shaped, adoral shield triangular. Two oral papillae in each side of jaw, the distal triangular and robust, a pair of elongated and robust infradental papillae. Five elongated arms, about seven to ten times the diameter of the disc (Fig. 11c). : Disc rounded, covered by medium size scales, with circular to semicircular imbricated scales. Radial shields slightly longer than wide, separated by a thin scale up to the distal region of the shields. Ventral surface of the disc covered by scales similar to dorsal scales. Bursal slits narrow, near the first plate of the arms. Diamond-shaped oral shield, adoral shields longer than wide, touching the proximal edge. Two oral papillae in each side of jaw, the more distal larger and trapezoidal, the other rounded and smaller. A pair of elongated infradental papillae. Five arms, about five times the disc diameter (Fig. 11d). Notes: Found on the rhodoliths surface.

Distribution
Remarks: Due to its wide global distribution, this species needs a systematic review.

Microphiopholis gracillima (Stimpson, 1854)
• WoRMS https://www.marinespecies.org/aphia.php?p=taxdetails&id=405791 Ventral surface of disc covered by small and imbricated scales. Bursal slit large, near the first to fourth ventral arm plate. Oral shield diamond-shaped. Adoral shield elongated and slightly wide distally. Jaws with three oral papillae, the more distal rectangular, larger than proximal papilla. Arms long, about six to eight times the diameter of the disc (Fig. 11e).

Phyla of identified marine invertebrates
Genera keys for each phylum (below) includes only taxonomic groups found in this study and they are not complete for the whole region. Additional literature should be consulted (e.g. Amaral et al. 2013, Lima et al. 2017, Melo and Veloso 2005, Nonato and Luna 1970, Nucci and DeMelo 2007, Prata et al. 2017, Serejo and Siqueira 2018 . 2017), including the six species of the present study. Therefore, an important diversity has been found associated with the rhodolith beds from the coast of the State of Paraíba, with Polychaeta species being most representative, particularly in the Miramar and Seixas Beaches.
Despite their importance, rhodolith habitats are still poorly studied, particularly in relation to the direct anthropogenic impacts to which they are subjected (e.g. super-exploitation, oil exploration, pollution, tourism, trawl fishing (Riul et al. 2008)), as well as to more indirect ones, such as those related to the climate crisis (e.g. global warming and ocean acidification (Horta et al. 2016, Riosmena-Rodríguez 2017). These events modify the physical-chemical parameters of the water, which may compromise the rhodolith banks and, hence, the associated biota (Horta et al. 2015), affecting survival and levels of calcification and photosynthesis, causing the bleaching phenomenon (Martin et al. 2013, M artin andGattuso 2009). Therefore, the conservation of these algae (and habitats) is critical, because this action may guarantee the habitat conservation of a large diversity of marine fauna (Costa et al. 2019, OSPAR-Commission 2010), using, for example, tools for promoting environmental awareness and ocean literacy (Costa et al. 2021).
Overall, this study may be regarded as baseline information on the rhodolith associated communities from this tropical region and highlights the importance of knowing and understanding their diversity levels, with the ultimate aim of promoting conservation of this important biogenic habitat. Rhodoliths beds, being considered sensitive habitats to anthropogenic effects and sheltering a rich diversity, need further studies of their associated fauna. In addition, knowing the existing fauna of a still little known habitat, essentially in the studied area, we may try to contribute to the fourteenth objective of the 'Sustainable Development Goals' (Sustainable-Development-Goals 2020).

Conclusions
The beaches from the coast of the State of Paraíba had a total 57 species of invertebrates from different main taxa, associated with rhodolith beds. The species of Polychaeta were the most representative in Miramar and Seixas Beaches, while molluscs were found mainly at Maceió Beach. This knowledge about the local fauna diversity may be regarded as baseline information for a variety of purposes, to know and understand local diversity levels associated with this little-known habitat in the regions, as well as to promote environmental education actions, with the objective of making local residents and beach-goers aware of the conservation of local coastal environments.
Silva, G. da Silva and P. de Freitas took the photos and prepared the figures of the invertebrates; D. Costa wrote the first draft of the manuscript with significant contributions from M. Dolbeth and M. Christoffersen; M. Christoffersen reviewed the English of the manuscript. The manuscript was then revised by all authors.