Biodiversity studies are commonly used to identify changes in the community structure of terrestrial, marine and other aquatic systems and to understand the effects of natural or anthropogenic disturbances on these communities (Cruz-Motta et al. 2010, Vinagre et al. 2016). Managers and scientists are aware of the importance of biological inventories as relevant technical information: to assist sustainable management of biological resources (Drew et al. 2012), to establish baselines for future comparison (Pauly 1995), to expand Marine Protected Areas (MPAs) (Lubchenco et al. 2003), to state biodiversity conservation priorities, to evaluate the environmental quality and health of ecosystems (Edgar et al. 2011), as well as to describe the patterns of biodiversity considering latitudinal gradients (Aued et al. 2018). Changes in biological communities reveal important signals to evaluate the conservation status and the management efficiency of MPAs.

There have been several works carried out on the marine biodiversity in different coastal geographic zones of the south Pacific through expeditions undertaken by European and North American researchers since the 1700s (Olsson 1961). However, most of these surveys have been concentrated in shallow-water and deeper-water down to 200 m depth in Panama, Colombia and Ecuador (Miloslavich et al. 2011). Ecuador is considered an area of high richness of species due to its location in the great Panamic-Pacific zoogeographic province, more precisely from the region extending from Costa Rica southwards to northern Peru (Olsson 1961).

Ecuador has approximately 2,900 km of continental coastline; there is a wide range of geological characteristics, such as bluff, barriers and strand plains, estuaries and lagoons (Boothroyd et al. 1994). Around 1,380 species of invertebrates have been identified in Ecuador, where the Molluscs are the largest group with 110 species. The highest species richness is observed in the southern central coast in the Gulf of Guayaquil (Cruz et al. 2003). There are very few studies of benthic diversity in the rocky shores on the Ecuadorian continental coast. The localities surveyed comprise the north of Ecuador in Galera San Francisco Marine Reserve, Esmeraldas (Reck and Luna 2000), the central coast in Machalílla National Park (Rivera 2012, Ministerio del Ambiente 2015) and the southern central coast in the El Pelado Marine Reserve (Rivera 2011, Cárdenas-Calle et al. 2019, Cárdenas-Calle et al. 2018). The main groups registered in literature in the intertidal and subtidal are Mollusca, Cnidaria, (Rivera et al. 2008); Arthropoda (Mair et al. 2002, Mora et al. 2010, Ministerio del Ambiente 2011, Rivera 2012) and Echinodermata (Mair et al. 2002, Rivera et al. 2008).

Other studies on the coastal zone included a variety of sites along the five coastal provinces of Ecuador recording a total of 140 species of macroinvertebrates including the north (Sua and Punta Galera), central (Puerto Lopez, Los Frailes, Isla de la Plata) and south central shores (Playas, Salinas, Ballenita), including 92 species of molluscs, 31 crustaceans and 17 echinoderms (Mair et al. 2002). Another study was done along 43 sites reporting 527 species in the intertidal zone and 97 species in the subtidal zone (Rivera 2012). All these studies used diverse protocol sampling methods on different spatial and temporal scales. Nevertheless, the spatial distribution of macroinvertebrates associated with rocky shores are similar to other countries near Ecuador in the tropical eastern Pacific, such as Gorgona Island in Colombia, where it was shown that the Mollusca and Crustacea were the most abundant and species rich and where the localities with more irregular topography registered a higher diversity.

The previous studies focused mainly on taxonomic lists, diversity and description of species (Cruz 2004, Cruz 2009, Cruz 2013, Mair et al. 2002, Massay et al. 1993, Mora 1989, Mora 1990, Müller-Gelinek and Salazar 1996, Villamar and Cruz 2007, Villamar 2009, Villamar 2013). Studies on benthic communities from intertidal rocky shores and sandy beaches of Ecuadorian mainland and from zones affected by anthropogenic activity are scarce in literature. Therefore, the objective of this study was to carry out a macrobenthic biodiversity inventory for the intertidal and subtidal zones along the mainland coast of Ecuador.

Study area descriptions

Methodology applied in intertidal studies for sessile and mobile organisms.

The presence of sessile organisms (macroinvertebrates and seaweeds) in rocky shores was registered following the protocol developed and validated by the group of experts from the "South American Research Group on Coastal Ecosystems (SARCE)" for the sampling of rocky coastlines (SARCE 2012). At each station, three levels of the intertidal levels were studied (high, medium and low), determined according to the dominant biological groups by level. In each level, a transect of 50 m length was applied parallel to the coastline. Over the transect, quadrants (50 × 50 cm) were placed randomly, sampling 30 quadrants per site (10 quadrants for each intertidal level). In each level, the presence of sessile organisms was estimated.

The mobile organisms whose sizes were larger than 1 cm in each quadrant, were identified in the field. The organisms which were not identified, were fixed in 10% formaldehyde and taken as a voucher. Before this, they were relaxed with menthol crystals for two or three hours according to the field guide for specimen collection of the Universidad de Guayaquil (Mair et al. 2000). To register the history of each site, photographs of each quadrant were taken (Rogers et al. 1994).

For sandy beach localities, the methodology used by Aerts et al. (2004) was followed. The fieldwork was undertaken at low tide. Over a transect of 50 m length parallel to the beach line, five quadrants of 50 × 50 cm were placed every 10 m. In each quadrant, the sediment of 10 cm depth was collected and sieved through a 1 mm mesh. Finally, the samples were fixed in seawater with 8% formaldehyde.

Methodology applied in subtidal studies for sessile organisms and mobile organisms. Composition of sessile organisms were studied by using a quadrant of 50 × 50 cm and each quadrant was subdivided in 81 intersections. The quadrant was placed every 5 m, along the transect of 50 m length (Edgar et al. 2011). A diver was used to note the taxon or substrate that coincided with each point of intersection. In the cases where the points of intersection did not fall on any organism, only the type of substrate was recorded. The mobile invertebrates (crustaceans, molluscs, echinoderms) were recorded by a second diver on each side of the transect (1 m). The diver registered the presence of species every 5 m.

Laboratory Analysis. Mobile and sessile organisms living in the intertidal and subtidal were analysed. During laboratory work, all samples were separated under stereomicroscopes. Taxonomic identification was accomplished through the use of keys and specialised literature for each group such as: for crustaceans (Ball and Haig 1974, Garth 1948, Hickman and Todd 2000, Holthuis 1952); for molluscs (Behrens and Hermosillo 2005, Coan and Valentich-Scott 2012, Giraldo et al. 2014, Keen 1971, Londoño-Cruz et al. 2013, Morris 1966, Olsson 1961); echinoderms (Avilés 1984, Caso 1961, Hendler et al. 1995, Hickman 1998); for corals (Hickman et al. 2005, Hickman 2008); tunicates (De Almeida Rodrigues et al. 1998); seaweeds (Müller-Gelinek and Salazar 1996). The valid name of all the species was corroborated using the WoRMS Editorial Board (2020).

General spatial coverage. The spatial coverage ranged from Lat. 0.818900°; Long -80.006300° at the northernmost site to Lat. -3.189200°; Long -80.452833° at the southernmost site. It encompasses coastal environments of 1860 km (see Fig. 1).

Figure 1.  

Study area and location of the sampling sites in the Ecuadorian coast.

A total of 83 sites were sampled, 40 in the intertidal zone and 43 in the subtidal zone from protected and non-protected coastal marine coasts (Tables 3, 4, 5, 6). The total taxa identified were 612 corresponding to 479 macroinvertebrates and 133 seaweeds. The determined species belongs to Mollusca (184 species), Arthropoda (68 species), Cnidaria (70 species), Annelida (60 species), Echinodermata (42 species), Porifera (22 species), Urochordata (18 species), Bryozoa (13 species), Sipuncula (two species), Brachiopoda and Platyhelminthes only being identified as morphotype. The seaweeds were represented by Rhodophyta (78 species), Chlorophyta (37 species), Ochrophyta (13 species), Cyanobacteria (five species) and 19 biotic complexes (Fig. 2). The highest biodiversity was registered in the intertidal zone of rocky shores with 423 species. In this zone, the most diverse groups were Mollusca, Annelida, Rhodophyta and Chlorophyta, whereas in the subtidal zone, only 189 species were registered and the most diverse taxa were Rhodophyta, Cnidaria and Echinodermata.