Polychaetes (Annelida) associated with macroalgae and coral reefs at a protected tropical island from the Atlantic coast

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Introduction
Reef ecosystems are extremely complex and productive, harbouring a significant portion of the biodiversity of the oceans, including trophic levels intrinsically linked with the benthic food web (Henry and Roberts 2016). Globally, around 250,00 marine species are described (WoRMS Editorial Board 2020), nevertheless one-third to two-third still to be described (Appeltans et al. 2012), especially in reef environments. Although there are many studies with coral reefs, those involving associated macrofauna remain insipient.
Brazil has a long coastal zone that extends from 04º30' N to 33º44' S, with a total area of approximately 1,550,000 km² subdivided into 16 marine sedimentary basins. The coast between the northern border of Brazil with French Guiana (5° N) to the southeastern region of the country (state of Espírito Santo: 20° S) comprises tropical marine ecoregions in the South Atlantic Ocean (Spalding et al. 2007) with extensive, complex reef ecosystems that harbour a rich community of metazoans.
The state of Bahia (Northeastern Brazil) has about 1,000 km of coastline and a considerable variety of coastal ecosystems (e.g., coral reefs, mangroves and rocky, sandy or muddy beaches) (Short and Klein 2016). This coastal zone harbours considerable biodiversity (Amaral and Jablonski 2005), mainly between Todos os Santos Bay (12° S) and the Abrolhos Archipelago (17° S), and is highly important for the implementation of conservation practices (Amado-Filho et al. 2012, Lopez et al. 2015.
Marine invertebrates in shallow reef ecosystems off northeastern Brazil have been underresearched Jablonski 2005, DeOliveiraSoares et al. 2016). Insufficient knowledge on this and other Brazilian ecosystems has been demonstrated based on the high number of records and/or descriptions of molluscs, pycnogonids, polychaetes and echinoderms (e.g. Barroso and Paiva 2007, Gondim et al. 2014, Prata et al. 2017, Lima et al. 2019. Faunistic surveys documenting the biodiversity of marine invertebrates in coastal ecosystems off northeastern Brazil are far from satisfactory. In recent decades, however, studies have expanded knowledge on benthic invertebrate fauna in the region. In 2005, a studied about the benthic macrofauna performed on Paracuru beach (state of Ceará), detected that the most of assemblage was mainly composed of Crustacea Brünnich, 1772, Mollusca Linnaeus, 1758 and Polychaeta Grube, 1850 (Viana et al. 2005). In Areia Vermelha Marine State Park (municipality of Cabedelo, state of Paraíba) 102 species belonging to the Ascidiacea, Cnidaria, Crustacea, Echinodermata and Mollusca taxa were found (Gondim et al. 2011). Correia and Sovierzoski listed a total of 102 endemic species of poriferans, cnidarians and echinoderms living in reef ecosystems off northeastern Brazil (Correia and Sovierzoski 2013). At the Sebastião Gomes Reef and Abrolhos Archipelago, the macrofauna associated with the brown algae from genus Dictyota spp. was evaluated, providing a faunal list of Crustacea, Polychaeta and Mollusca (Cunha et al. 2013). New surveys are needed due to the rapid degradation of tropical coastal ecosystems, especially reefs, as a result of human activities that are causing the disappearance of species.
The present study aimed to document the polychaete diversity associated with algae in the reef ecosystems of Morro de São Paulo on Tinharé Island in the state of Bahia, northeastern Brazil, which is an under-explored area from the zoological standpoint.

Study area
The study area on the coast of the state of Bahia belongs to an Environmental Protection Area (EPA) denominated "Tinharé-Boipeba", which was established in 1992. The area has about 433 km and is located between the mouth of the Patos River and Taperoá Channel, belonging to the Tropical Northwestern Marine Ecoregion (Spalding et al. 2007). The present study was conducted in the intertidal and shallow subtidal zones of Morro de São Paulo (13º22'56.0'' S, 38º54'32.1'' W), which is located on Tinharé Island in the municipality of Cairú, state of Bahia, northeastern Brazil ( Fig. 1).
Morro de São Paulo has three main beaches, denominated First, Second and Third Beaches, which have a large influx of tourists (Elliff and Kikuchi 2017). This coastal environment is characterized mainly by fringing reefs that line the coast and are exposed at low tide. The top of these reefs has an irregular, truncated surface that is cut by channels, giving rise to tide pools (Kikuchi et al. 2008). The fringing reefs are close to the beach line and form discontinuous structures in shallower regions. A large concentration of organisms, such as algae, corals, sponges, molluscs, crustaceans, echinoderms and fish, is found in the tide pools and channels.

Sampling methods and analysis
Samples were collected on January 21 and 22 , 2015, from reef ecosystems of the First, Second and Third Beaches of Morro de São Paulo (Tinharé Island) at low tide in the intertidal to shallow subtidal zones at depths to about 1 m.
Polychaetes and algae were collected manually at different points of the study area and stored in plastics bags with seawater. Immediately after collection, algae were stored in large buckets for two hours in a makeshift laboratory to reduce the stress of the associated invertebrates. The polychaetes were subsequently separated from the algae. All specimens were preserved in 70% ethanol. Most were photographed under a stereomicroscope and some individuals were photographed in situ. Identification was primarily based on the respective literature (e.g. Nonato and Luna 1970, Amaral and Nonato 1996).
Diversity indexes was calculated for the polychaete fauna as a whole based on the abundance of the material collected. The collector curve and the biodiversity calculations 2 st nd were made using the EstimateS statistical software (Colwell 2013). Graphs were created using the Excel program.
All the material analyzed is deposited and available for study at the " Diagnosis: Prostomium with a short anterior incision, with two eyes, and five antennae. Jaws eulabidognath-type (asymmetrical, posterior parts dentate to forceps-like, short carriers). Branchiae with only one filament from chaetiger 20. Anterior dorsal cirri longer than posterior ones. Neuropodia with cirri smaller than dorsal ones; falcigers chaetae; 1-5 dark aciculae, and dark subacicular unidentate hooks (Nonato and Luna 1970, Knox and Green 1972, Paxton 2009 (Fig. 2c).

Notes: First record in Morro de São Paulo (Tinharé Island), State of Bahia, Northeast
Brazil.

Discussion
The calculated estimative indices highlighted the importance of continuing to conduct studies in the region (with the need to increase the sampling effort), regarding both the fauna as a whole and each taxon. In the individual analyses, with only 13 species sampled, whereas about 40 species were estimated, indicating a large gap to be filled, even if one considers that total diversity is underestimated. Another important aspect to consider is that the study area is located between Todos os Santos Bay and the Abrolhos Archipelago, which is recognized as one of the most diversified ecoregions along the Brazilian coast and is a priority coastal zone for conservation purposes (Rhormens et al. 2017).
Despite the likely underestimations, a considerable diversity of polychaetes was found in the present study. Such diversity levels for the region have also been verified studying the phytobenthos on Boipeba Island, which is in the same vicinity as Tinharé Island (Moura et al. 2015). The authors collected 159 taxa, which is a number similar to that found for oceanic islands in Brazil. Nonetheless, the richness of polychaetes in the study (13 spp.) was lower than that found at the Abrolhos Bank, 90 and 41 respectively (Paiva 2005, Figueiredo et al. 2007, and in the estuary of the Cachoeira River (23), in the state of Bahia (Ourives et al. 2011). The present study is the first to be carried out specifically in the Morro São Paulo environment (Tinharé Island), therefore all species identified here represented new records for this island.
Several shallow-water habitats in Brazil, especially on the extensive coast of Bahia, still require inventories for a better understanding of polychaete assemblages. Knowledge on the annelid fauna in coastal ecosystems of this region has become somewhat more accurate in recent years.
The species H. longiseta is considered the first record for the South Atlantic coast, representing also the third Scalibregmatidae Malmgren, 1867 for the Brazilian coast (only Asclerocheilus tropicus Blake, 1981 from the São Paulo state, and Scalibregma inflatum Rathke, 1843 from São Paulo and Rio de Janeiro states (Amaral et al. 2013)), and the first record of this family for the Northeast Brazilian coast.
Taxonomic studies on polychaetes (involving the identification of several families) for the region Northeast Brazilian have increased in a spotty fashion and even these annelids are considered insufficiently known. One the first large taxonomic studies in this region (Ceará, Rio Grande do Norte, Paraíba, Alagoas and Sergipe states) was performed Edmundo Nonato and José Luna, identifying a total of 71 species Luna 1969, Nonato andLuna 1970). In the Maranhão state coast, 38 species were identified in a compiled bibliography study (Ribeiro and Almeida 2014 This work clearly shows that the reef ecosystems of Morro de São Paulo exhibit an important potential for a greater diversity of polychaetes that has not been taxonomically studied over the years. This invertebrate community in the study area has been affected by multiple anthropogenic impacts, such as pollution as well as the trampling and collecting of individuals by tourists and fishermen. Further studies in the region are needed for a better understanding of polychaete fauna and the increasing impact of human activities (pollution and tourism), e.g. a study that evaluated the touristic impact in Paraíba state coast (Costa et al. 2019). Besides, local governments need to develop conservation strategies and act more effectively to impede the capture of threatened invertebrates.

Conclusions
This represents the first taxonomic study of the polychaete fauna from Tinharé Island (Bahia state), a tropical protected area that is essential for the maintenance of marine life.
It estimated approximately 40 polychaete species with the increase of sampling effort. The species H. loginseta is considered as a new record from South Atlantic. The diversity of these annelids still is substimated, being indispensable most studies to know the marine diversity in the Northeast Brazilian coast, mainly in islands.

Author contributions
D. Costa wrote the manuscript, identified and described the polychaete species. J. Prata designed the study and implemented it in the beaches, and prepared the plates/polychaete photos and the study area figure. D. Costa, J. Prata and M. Christoffersen interpreted and analysed the data. M. Christoffersen was the English proofreader. The manuscript was then revised by all authors.