INTRODUCTION

The Corales de Profundidad Natural National Park - PNNCPwas established in 2013 in the representative area for the conservation of coral reef communities within the National System of Protected Areas - SINAP (Resolution 339 of 2013). The objectives of the PNNCP as a national protected area are to (1) preserve the deep-water coral formations that are at the edge of the continental shelf and the upper slope as an expression of representativeness and singularity of the ecosystem and as an essential habitat for a variety of marine species and (2) contribute to the provision of ecosystem services provided by coral reef formations, especially considering their connectivity with other marine ecosystems and their role in the dispersal of various species of benthic habitats (Resolution 339 of 2013).

The deep-water coral reef formations in the PNNCP feature Madracis myriaster as a structuring species, which is also present in other deep-water coralline communities of the Caribbean Sea (^{Reyes et al., 2005}; ^{Lutz and Ginsburg, 2007}; ^{Santodomingo et al., 2007}). Santodomingo et al. (2007) determined that the location and structure of the deep-water coral formations in the area west of the Rosario and San Bernardo islands had a clear association with certain elements of the present seabeds. Among these are communities dominated by branched corals of the genus Madracis on soft sandy-muddy seabeds, hard seabed octocorals (soft corals), black corals (antipatharies), anthozoans and corals of the genus Madrepora predominate as well as sponge communities growing on dead fragments of the calcareous algae Halimeda.

This work identified the geoforms present in the PNNCP area, which covers part of the platform and the upper continental slope based on the interpretation of high resolution multi-beam bathymetry (10 m). These geoforms were associated with the regional tectonic environment. The previously identified small-scale landscape units (IDEAM et al., 2007, INVEMAR-ANH, 2008, ^{Rangel-Buitrago and Idárraga-García, 2010}) provided evidence of rocky substrates and sediment inputs favoring the diversity of habitats therein.

The geomorphological mapping of the PNNCP was part of the research to characterize and evaluate the conservation status of the coral formations present in the PNNCP and its associated fauna to generate new knowledge and to fill the existing information gaps regarding the physical, geological, biological and ecological processes that allow the adoption of management and monitoring strategies (Invemar, 2015).

The morphological features of the seabed and its possible association with the evolution and the geological processes in the PNNCP area become a relevant input for the characterization of the habitats. The integration of oceanographic, geological and biotic information (^{Ricaurte et al., 2004}; ^{Urriago et al., 2011}) complements the description of various ecosystems using existing models for those that have been recognized in defined geoforms (^{Harris, 2012}).

STUDY AREA

The PNNCP at the sea front of the departments of Bolívar, Sucre and Córdoba covers an area of 142,195.15 ha with depths ranging from 34 to 1234 m (Figure 1). It is located within the coordinates 9°43’16.591”- 10°7’30.277” N and 76°0’16.254”-76°17’41.091” W in the Magna-Sirgas West origin reference system (Resolution 339 of 2013), approximately 32 km from the nearest point on the mainland (Barú peninsula). The proximity of this park to other established protected areas, such as the Corales del Rosario and San Bernardo Natural Park (approximately 12 km) and the El Corchal Mono Hernández Sanctuary of Fauna and Flora (approximately 47.49 km), places it in an area where conservation efforts have been performed to ensure the functionality of the biodiversity levels that characterize the marine landscape.

Figure 1 Location of the Corales de Profundidad Natural National Park (^{Alonso et al., 2015}). 

The PNNCP is located in the Sinu Fold Belt tectonic terrain (^{Duque-Caro, 1979}) formed by the interaction between the Caribbean oceanic plate and the South American continental plate. ^{Taboada et al. (2000)} propose the interaction between the Caribbean and South American plates as a very low angle subduction, whereas ^{Cediel et al. (2003)} prefer to interpret the interaction between these two plates as a collision in which one plate is forcefully overlapped upon the other (forced overthrusting). The Sinu Fold Belt extends to the west of the Sinu fault for approximately 500 km with an amplitude of 125 km. It is composed of sedimentary rock sequences that range from the Middle Eocene to the Late Oligocene (between 48 and 23 Ma) (Ingeominas, 2003).

^{Duque-Caro (1984)} describes the Sinu Fold Belt as a sedimentary sequence approximately 8 km thick consisting mainly of turbidite and hemipelagic rocks from the Oligocene-Pliocene. The folds are frequently pierced by intrusions of over-pressed mud. On the other hand, ^{Toto and Kellogg (1992)} mention that the Sinú and San Jacinto Fold Belts (CDSSJ) form a sedimentary wedge approximately 12 km thick that was added to the South American margin during the Cenozoic. The wedge is characterized by a low topographic slope (≤2°) and abundant mud volcanism (^{Vernette et al., 1992}). The wedge is bound to the northwest by the marginal fault of the southern Caribbean and to the southeast by the Romeral fault zone (Toto and Kellogg, 1992).

METHODOLOGY

A digital elevation model (Figure 2) with a resolution of 10 m per pixel was obtained from the bathymetric data collected between May 26 and June 5, 2015 in a campaign performed by the Maritime General Directorate - DIMAR (ANH-DIMAR convention 169-14). The Kongsberg EM-302 Multibeam system, installed on board the ship ARC Providencia, was used with the automated data collection equipment and the Seafloor Information System (SIS) software. The hydrography area of DIMAR (2015) used the CARIS HIPS and SIPS 8.1 software for processing, editing and data correction.

Figure 2 Digital elevation model of the PNNCP with the identification of some geoforms and geomorphological features. The depth scale is in meters. 

The spatial analysis of the depth model was performed using the tools available in ArcGIS 10.3.1 software to generate hillshade and slope models (ArcGIS Toolbox - Spatial Analyst - Surface - Hillshade, Slope). This enabled the updating of some defined geoforms for the exploration area of the Fuerte Norte block (Invemar-ANH, 2008; ^{Rangel-Buitrago and Idárraga-García, 2010}) and the interpretation of geomorphological units and features in complementary areas. For the geomorphological classification, the guidelines established in the Coastal and Marine Ecological Classification Standard (FGDC, 2012) and the hierarchical structure of the national geomorphological classification proposals were followed (^{Carvajal-Perico, 2012}; ^{Gómez et al., 2012}; ^{Robertson et al., 2013}). Finally, the relief shapes were named according to the nomenclature and standard definition of the IHO/ IOC (2008).

Morphological alignments were drawn from the slope classification (SCWG, 1998) as descriptive attributes of identified relief units and the hillshade model to visualize abrupt relief changes associated with the structural style of the area (^{Ordoñez-Aristizábal et al., 2009}; ^{Vinnels et al., 2010}; ^{Quintero, 2012}). The geomorphological features were interpreted considering the tectonic or morphodynamic environment, the physiographic character and the possible origin of each geoform.

RESULTS

The PNNCP is located in the morphodynamic environment of a convergent active continental margin. It occupies approximately 65000 ha over the continental shelf (45%) and 77000 ha over the continental slope (55%). The slope break between both physiographic provinces in this sector was identified at depths between 150 and 170 m. This work includes the geomorphological mapping of the PNNCP (Figure 3) and describes 16 geomorphological units that conform the two physiographic provinces, indicating the possible associations between its origin and the geological processes such as uplift, erosion, sedimentation and mass movements.

Figure 3 Geomorphological map of the Corales de Profundidad Natural National Park. 

DISCUSSION

The PNNCP has important morphological features within the continental shelf and slope of the Colombian Caribbean. The relief elements identified in the PNNCP are related to the Sinu Fold Belt with marked uplift structures and well-differentiated basins and channels.

Because the seabed morphology allows for the identification of biological communities or assemblages, the descriptions of these geoforms in the PNNCP become surrogates for biodiversity in the absence of biological information, while more detailed studies are performed (^{Harris et al., 2008}; Harris and Whiteway, 2009). The detailed bathymetric and geomorphological information will determine the probable distributions of the different deep-water coral species present in the PNNCP, especially Madracis myriaster. This community is “rare” in the Caribbean region and the world, giving it a higher value in terms of conservation priority and worldwide research (^{Alonso et al., 2015}).

The geomorphological mapping corroborated that one of the most relevant and most interesting features for the investigation is the Frijol bank. This is due to its geological origin and morphological characteristics associated with the growth of coral formations in areas of hard substrates. Bordering the Frijol bank, there is a slump corona with its flow directed to the north-west. The identification of such structures poses a potential threat to the bank’s structure. A second slump identified in the central area of the PNNCP is of interest in the analysis of the environmental variations that affect it.

On the slopes of the structural elevations were delimited domes associated with diapirs, formed possibly by the expulsion of over-pressured mud in areas of possible Tertiary formations. In some cases, they have been formed volcanic cones that represent areas of sediment flow in the seabed with important contributions for habitat identification. In the southeast area of the PNNCP were identified pockmarks as important gas ejection markers (Hovland and Judd, 1988). These forms are present in other areas of the continental shelf and have been little studied in Colombia for the analysis of benthic communities.

The area of the PNNCP with depths less than 100 m is approximately 295,000 ha, and its exploration requires activities such as Rebreather autonomous diving. These areas are contained in the Frijol bank, with mounds of probable diapiric origin in the central area and in the southeastern sector of the park at depths of approximately 50 m with an irregularly surfaced terrace and a structural channel.

Among the PNNCP were selected areas of interest based on the identified geomorphology. Depths greater than 100 m required geophysical acquisition methods or remotely operated vehicles (ROVs) to characterize and map the ecosystems in which deep-water coral communities are located in geoforms identified by their potential for association with benthic communities. These geoforms are comprised of elevations and submarine channels, escarpments, diapirs and pockmarks, which are recognized by the existence of significant ecosystems in the seabed (Hovland and Judd, 1988; ^{Harris, 2012}).

The geomorphological classification presented here was based on the spatial analysis of the bathymetric model with a resolution of 10 m. The interpretation of high-resolution seismic records and classification from the backscatter (acoustic response associated with the composition and shape of the seabed) would support the morphogenetic evolution of the PNNCP and validate the description of the current geomorphological units. The acquisition of bathymetric information with a higher resolution (<4 m) would improve the detail of the classification. Periodic bathymetric surveys would contribute to the recent evolutionary analysis of the PNNCP and the risk assessment of natural hazards.

In the summary document for the declaration of the marine protected area containing deep-water corals, one of the justifications lists the research interest for studies to map properly the coralline formations using non-invasive methods that would help to understand the patterns of ecological connectivity between deep-water benthic communities and shallow ecosystems (Invemar - Parques Nacionales, 2012). This would help to improve the design and planning for management of the marine protected network areas in the Colombian Caribbean to prevent the isolation of populations and promote the flow of matter and energy between different habitats and ecosystems (Invemar - Parques Nacionales, 2012).

This study was presented as a knowledge base of the current scenario to establish the association of geomorphology with the presence of benthic communities on the continental shelf and slope. Given the limited knowledge of the PNNCP and the need to understand how the key ecological processes are influenced by the geomorphological features, it is important to increase the description detail of the submarine relief, the morphological processes and the study of oceanography (currents). The cartographic production of these geomorphologies will allow the identification of locations of particular interest to collect biological samples and integrate spatial information to identify benthic habitats for tropical areas such as the central Caribbean region, which are very scarce (^{Madden et al., 2008}; FGDC, 2012).

CONCLUSIONS

This cartography is a contribution to the detailed knowledge of the Colombian Caribbean seabed. The use of new technologies for the acquisition of submarine information allows us to identify or complement units and features of the terrain with greater precision. For this purpose, its characteristics (size and slopes) have been described following published standards and national nomenclature proposals and were considered within the tectonic framework to determine their origin.

This study was an initial approximation to the geomorphological description of PNNCPusing multibeam bathymetry. The results published here determined the site selections that, due to their geomorphological characteristics, are possible locations of the ecosystem associated with deep-water coral communities. The following sites were considered for the investigation: the Frijol and Calamarí banks, the Los Angeles channel, the rise at 300 m depth, the hills in the south-central area of the PNNCP and segments of the continental slope escarpment (Invemar, 2015). It is necessary to continue the acquisition of geophysical information in the area to corroborate the origin and distribution of the geoforms presented here.