INTRODUCTION
The Luiz Saldanha Marine Park (LSMP) extends along a narrow coastline of 38 km, facing south-west (38.40°N 9.10°W, ca. 60 km south of Lisbon; Figure 1A). The littoral communities of this marine park are amongst the most studied in the Portugal mainland (Xavier da Cunha, Reference Xavier da Cunha1950; Palminha, Reference Palminha1958; Saldanha, Reference Saldanha1974; Santos, Reference Santos1993), however, the deep areas remain poorly studied. Since the implementation of the marine park in 1998, there was an increase in research efforts in several disciplines (e.g. Boaventura & Ré, Reference Boaventura and Ré2001; Rodrigues, Reference Rodrigues2008; Cunha et al., Reference Cunha, Erzini, Serrao, Gonçalves, Borges, Gonçalves, Henriques, Guerra, Duarte and Marba2011; Costa et al., Reference Costa, Assis, Franco, Erzini, Henriques, Gonçalves and Caselle2014; Cunha et al., Reference Cunha, Erzini, Serrao, Gonçalves, Borges, Gonçalves, Henriques, Guerra, Duarte and Marba2014). The seabed habitats along the park, including the surrounding areas up to a depth of 100 m, were also recently mapped (Henriques et al., Reference Henriques, Guerra, Mendes, Gaudêncio and Fonseca2014). However, like in many other regions, SCUBA diving and gear deployment constraints tend to limit the assessment of deeper benthic communities.
(A) Location of Luiz Saldanha Marine Park in south-west Portugal (Europe); (B) Location of the mono-specific facies of Parazoanthus axinellae off Sesimbra bay (south of the 50 m bathymetric line); (C) Seascape overview of the facies on the sloping seafloor from the top camera; (D) Close view of the P. axinellae colonies with heavy sediment deposited (image from ROV camera; note that the ROV roll suggests increased slope).
Exploratory surveys in the LSMP during the oceanographic campaign EMEPC/M@rBis/Arrábida2014 (Dias et al., Reference Dias, Berecibar, Albuquerque, Tojeira, Vasco-Rodrigues, Castanheira, Gomes-Pereira, Souto, Calado, Afonso, Bernardes, Campos and Equipa2014) detected an aggregation of Parazoanthus axinellae (Schmidt, 1862). The zoanthid P. axinellae (Cnidaria: Anthozoa) is a member of the coralligenous communities of the Mediterranean Sea (Pérés & Picard, Reference Pérés and Picard1964), with several records also from the Atlantic (Pérés & Picard, Reference Pérés and Picard1964; Prados, Reference Prados1994). The species occurs in Portugal (Rodrigues et al., Reference Rodrigues, Maranhão, Oliveira and Alberto2008; Monteiro et al., Reference Monteiro, Bentes, Oliveira, Afonso, Rangel, Alonso, Mentxaka, Germán Rodríguez, Galparsoro, Borja, Chacón, Sanz Alonso, Guerra, Gaudêncio, Mendes, Henriques, Bajjouk, Bernard, Hily, Vasquez, Populus and Gonçalves2013), but little details have been provided and the first mono-specific facies from the Portuguese coast is here reported.
MATERIAL AND METHODS
The benthic habitats of the LSMP below a depth of 15 m were surveyed using the MiniROV Observer (Subsea Tech) with a GoPro® video camera attached on top (the material recorded by both cameras is available as supplementary material). Surveys were conducted by the ‘Portuguese Task Group for the Extension of the Continental Shelf’ (EMEPC) during the ‘Scientific Cruise EMEPC/M@rBis/Arrábida2014’, onboard the rigid-inflatable boat ‘Selvagem Grande’. In order to facilitate the control of the ROV near the seafloor, a 1 kg weight was attached to the tether 6 m from the ROV. The position of the ROV was obtained from a standard GPS on board, with an accuracy of approximately 2 m (2DRMS). To estimate the maximum uncertainty in the position of the ROV (R), we consider the amount of tether deployed in the water up to the 1 kg weight (CD) and the local depth (D), as follows:
$$R\, = \,\sqrt {(C{D^2} - {D^2})} + 6.0 + 2.0\,({\rm SI}).$$This estimation assumes that there is no depth difference between the ROV location and the depth below the surface platform of deployment, and that the weight remains in contact with the seafloor (as observed from the video). At the location of the facies described here, a maximum uncertainty estimate of 62 m was calculated from 81 m of cable deployed and 60 m of maximum depth.
RESULTS
The facies of Parazoanthus axinellae was detected during the dive MB14AROB6 on 24 September 2014, between 55 and 60 m depth (Figure 1B–D). The dive was performed in conditions of limited visibility and strong currents. Therefore, the area with hard bottom and the surrounding soft sediment were not surveyed in detail. The facies was observed at 38.4254667°N 9.100633°W (±62 m), totalling 00:04:36 (hh:mm:ss) of bottom time.
The area is characterized by rocky outcrops, apparently of the same nature as the bedrock in sub-aerial cliffs, with reduced micro-habitats (Gonçalves et al., Reference Gonçalves, Henriques, Almada, Beumer, Grant and Smith2002). The seafloor showed evident signs of deposition of fine sediments. The colonies of Parazoanthus axinellae were growing on a gently sloping large outcrop no larger than 100 m2, surrounded by soft bottom. Parazoanthus axinellae was identified by the shape and coloration of the colonies. Colonies reached well over 10 cm high above the seafloor, and the polyps were soft and yellow in colour, growing from a common base (with up to 14 polyps per colony, and possibly more). From the imagery collected, it was not possible to validate whether the colonies were growing (or not) as epibionts of other species. The zoanthid was abundant at this facies, considering the SACFOR density scale (1–9 m−2; Hiscock, Reference Hiscock1996). Estimates were based on opportunistic area measurements assuming Parazoanthus axinellae polyps with a maximum oral disk diameter of 7 mm (without tentacles; Cornelius et al., Reference Cornelius, Manuel, Ryland, Hayward and Ryland1995). The diving conditions hampered further quantitative estimation or detailed habitat description. Sparse megafauna present in the area included gorgonians, possibly Eunicella spp., and cf. Paramuricea clavata. Other megafauna observed in the area were cf. Axinella infundibuliformis, Sabella spallanzanii and Bonellia viridis. Marine litter was also observed at the location, particularly glass (bottles). The surrounding seafloor was covered by shell debris.
DISCUSSION
The mono-specific facies described here is classified as the EUNIS habitat type A4.26C – ‘Facies with Parazoanthus axinellae’ – placed at EUNIS Level 4 – ‘Circalittoral Rock and other hard substrata’ (Davis et al., Reference Davis, Moss and Hill2004). According to Pérés & Picard (Reference Pérés and Picard1964) and Gili et al. (Reference Gili, Pagès and Barangé1987), P. axinellae is an infralittoral species, frequently found at cave entrances and on overhangs, growing as an encrusting species, as an epibiont (mainly over sponges) or directly over the primary substrate, reaching up to 20 cm high. SCUBA divers often observe the species along the Portuguese shores (personal experience corroborated by diving club communication). However, the species can occur in large densities with gorgonians and sponges in the circalittoral, as reported by Monteiro et al. (Reference Monteiro, Bentes, Oliveira, Afonso, Rangel, Alonso, Mentxaka, Germán Rodríguez, Galparsoro, Borja, Chacón, Sanz Alonso, Guerra, Gaudêncio, Mendes, Henriques, Bajjouk, Bernard, Hily, Vasquez, Populus and Gonçalves2013), in the south-west of Portugal. The circalittoral onset in the Mediterranean and western Iberia is generally associated with the absence of phanerogam or photophiles species (Pérés & Picard, Reference Pérés and Picard1964), and no large algae (e.g. Laminaria sp.) were observed at the study site. Furthermore, systematic ecological surveys at the marine park by Luiz Saldanha (Reference Saldanha1974) suggested an infralittoral/circalittoral transition at depths of 20–24 m. This threshold was later supported by the work of Monteiro et al. (Reference Monteiro, Bentes and Gonçalves2012), using light intensity at the seabed.
The facies described in this study can be considered a ‘coralligenous assemblage’, where P. axinellae is referred to as a key species (Garrabou, Reference Garrabou1999; Gibson et al., Reference Gibson, Atkinson and Gordon2006). Its co-occurrence with animal builders that contribute to the frameworks (e.g. Pleaxuridae, Sabella spallanzanii) and the depth of occurrence agree with this classification (Gibson et al., Reference Gibson, Atkinson and Gordon2006). The coralligenous biocenosis is included in other nature classification systems such as Natura 2000 (RAC/SPA: IV.3.1), UNEP (EUR 15 1170) and CORINE (11251).
At the LSMP, the species cannot be confused with other epibenthic cnidarians due to their differences in colour, size and branching morphology. The clear yellow coloration dismisses any confusion with the brown zoanthid Epizoanthus couchii (Johnston, 1844), which is often smaller in size. The shape of the colonies might be confused with some Dendrophilliids: Dendrophyllia ramea or Leptopsammia sp.
Dendrophyllia ramea colonies show branched polyps, growing constant in diameter, contrasting with the thinner tentacles that open to a larger oral area in P. axinellae (Figure 1D). Even though a central stolon may connect different polyps, the absence of ramification in the polyps of P. axinellae also results in characteristic colonies, which are centred and grow outward. The Leptopsammia sp. also has a shorter polyp column that grows mostly as a patch of isolated polyps.
Parazoanthus axinellae is a potential target species for the marine ornamental trade industry (Calado, Reference Calado2006). The fishing techniques currently allowed in the marine park are hand line and bottom traps for octopus, which have a limited impact on the sessile invertebrates when compared to other fishing methods. The small number of gorgonians observed at this location, in comparison to other habitats at similar depths (Monteiro et al., Reference Monteiro, Bentes, Oliveira, Afonso, Rangel, Alonso, Mentxaka, Germán Rodríguez, Galparsoro, Borja, Chacón, Sanz Alonso, Guerra, Gaudêncio, Mendes, Henriques, Bajjouk, Bernard, Hily, Vasquez, Populus and Gonçalves2013), aside from their differences in current regime, sedimentation and nutrient loads, could even be related to anthropogenic disturbance (e.g. fishing, anchoring and wastewater). Further studies are necessary to highlight the effects of human pressures on the marine park.
ACKNOWLEDGEMENTS
The authors wish to acknowledge everyone that collaborated in the ROV operations, including Tiago Sá, André Cid, Hugo Silva and all the Task Group for the Extension of Continental Shelf (EMEPC). Valuable comments were provided by Frederico Oliveira and Joana Boavida and three anonymous reviewers. J.N.G-P. was supported by the doctoral grant from the Regional Directorate for Education, Science and Culture, of the Regional Government of the Azores (M3.1.2/F/062/2011). LARSyS-Associated Laboratory No. 9 is funded by the Portuguese Foundation for Science and Technology (FCT) through pluri-annual and programmatic funding schemes (OE, FEDER, POCI2001, FSE) and by the Azores Directorate for Science and Technology (DRCT).
SUPPLEMENTARY MATERIALS AND METHODS
The supplementary material referred to in this article can be found online at http://www.journals.cambridge.org/mbdcup.
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