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Geomorphic features and associated habitats of the Patagonian Continental Margin, southwestern Atlantic
CHAPTER 43
Geomorphic features and associated habitats of the Patagonian Continental Margin, southwestern Atlantic ˜oz2, Lourdes Viscasillas2 and Diego Varas2 Dulce Mata1,2, Araceli Mun 1
Department of Geography, Complutense University of Madrid, Madrid, Spain 2Tragsatec-SGP, Maritime Affairs and Fisheries, Madrid, Spain
Abstract The Patagonian Continental Margin is a high biodiversity area of the southwestern Atlantic Ocean. It is characterized by a series of submarine canyons, which provide seafloor habitat for several types of marine ecosystem. There are also rocky outcrops colonized by different associations of taxonomic groups. Samples collected in the area confirm that biological communities such as Porifera, Cnidaria, Octocoralia, and Echinodermata are associated with these geomorphic features. The present study is based on the spatial analysis of environmental variables including bathymetry and backscatter texture obtained using a multibeam echosounder. Depth, slope, and bathymetric position index physical terrain variables were used to produce a model of geomorphic features. Submarine photography and samples were used to verify the confidence of this model to indicate the presence of specific habitats. In particular, the intensity of acoustic backscatter was used to classify the different textures of the seabed substrate. Based on our analysis, four habitat types were derived for the different habitats studied in the area: (1) cold-water coral reefs, (2) coral gardens, (3) sponge beds, and (4) deep marine rocky environments.
Keywords: Ocean; habitat; mapping; Atlantic; geospatial; GIS; environment
Introduction The Patagonian Continental Margin is located in the southwestern Atlantic Ocean where the confluence of two great oceanic currents, the Malvinas Current and the Brazil Current, promotes primary production helping the existence of high marine biodiversity. This chapter is focused on a 13899 km2 area located between two submarine canyons of the south Patagonian continental slope system. The study area is located on the Patagonian Margin between 46 80 S47 70 S and 59 140 W60 500 W and from 126 m depth on the shelf to more than 1700 m on the middle continental slope (Fig. 43.1). The wide range of depths Seafloor Geomorphology as Benthic Habitat. DOI: https://doi.org/10.1016/B978-0-12-814960-7.00043-9 © 2020 Elsevier Inc. All rights reserved.
721
Figure 43.1 Study area location at the southwestern edge of the Argentine Basin. A red square indicates the geographical extent of the study area (left). Multibeam echosounder bathymetric map (right), includes a graduate scale representing the depth range.
Geomorphic features and associated habitats of the Patagonian Continental Margin 723 includes different seabed geomorphic structures that determine the existence of different habitats of great ecological interest. Within the framework of Vulnerable Marine Ecosystems (VME) research (ATLANTIS project), the R/V Miguel Oliver of the Spanish General Secretariat of the Sea (SGM) carried out eight cruises between 2007 and 2009 in the southwest South Atlantic. The main objective of this multidisciplinary research was to locate and map possible VME’s between the Argentine EEZ outer limit and the 1500 m isobath. Information regarding the morphology of the Patagonian Margin was acquired with a Simrad EM-302 (30 kHz) multibeam system. Data processing was carried out using the CARIS swath bathymetric software package HIPS and SIPS. Valid data were gridded at 50 3 50 m resolution. In addition, a total of 1451 bottom photographs were acquired at 13 stations with a reflex digital camera of .12 Mpixel, model Nikon D700. Based on the distance between two red laser points reflected on the seafloor, individual photographs covered an area of 2 by 1.5 m. Samples of the benthic fauna were obtained with a rock dredge (58 stations) and with a bottom trawl net during fishing operations. A total of 156 bottom samples for sedimentological studies were collected with a megaboxcorer and an additional 105 samples with a Lofoten sampler (Fig. 43.2). All data were integrated using ArcGis (ESRI) and Fledermaus software (Interactive Visualization Systems; IVS). The present work is referred to the multidisciplinary research oceanographic surveys of the Atlantis project. The case study presents some of the results of this research along with the habitat spatial distribution modeling.
Oceanography The Patagonian Continental Margin is located in the BrazilMalvinas Confluence (BMC). This confluence causes an oceanic front and upwelling of nutrients, which favors a high biodiversity of the benthos in the study area. The Argentine Continental Margin is the only place in the southern ocean where mixing of water masses from south polar and equatorial regions occurs. The oceanographic system is composed of water masses characterized by differences in density, temperature, salinity, oxygen content, and other physical, biological, and chemical properties (Violante et al., 2017). Vertical stratification separates surface waters of variable temperature and salinity from bottom waters where the values are equalized below a clearly differentiated thermocline.
Naturalness, condition, and trend The baseline for condition covers the period of the years 20062016 based on the technical report about the processes and practices in the high seas of southwest Atlantic Ocean which
Figure 43.2 Shade relief model of the case study extracted from 50 m resolution digital elevation model (with a vertical exaggeration of 6 3 ), including seabed sample stations and a predictive model of the substrate type.
Geomorphic features and associated habitats of the Patagonian Continental Margin 725 was published by FAO (Thompson et al., 2016). The high confidence of subsequent trends in condition derives from the study of the area carried out by the Atlantis project described below. According to the data collation about the study area, the grade of statement for the habitats describe in this case is Good, with a score value of 6 (as per the scheme of Ward, 2011). Furthermore, the habitats are evaluated as stable for the last 5 years, following the observations reported herein.
Geomorphic features and habitats The Argentine Patagonian Margin comprises a wide continental shelf and adjacent continental slope, which is topographically divided into an upper, middle, and lower slope. The morphology of the features in this area is described below. Continental shelf: The outer continental shelf is dominated by sediment ridges oriented in a NNESSW direction, oblique to the shelf break. The sand ridge crests are 15 m high and they are separated 34 km apart (Fig. 5.2; Rı´o-Iglesias et al., 2012). Rocky outcrops are low relief and locally buried by NE migrating megaripples. Some cobble to boulder-sized flattened sandstone fragments are colonized by different species of fauna (Fig. 43.3, CAM_6, CAM_7; Fig. 43.7, CAM_8). Continental slope: The upper slope is 620 km wide, has a gradient of 4 1 200 and descends from the continental shelf break (128200 m depth) to depths of between 250 and 750 m. The middle slope contains the Na´gera terrace (from the base of the upper slope to a depth of 9301060 m) and Perito Moreno terrace (from a depth of about 11001400 m). Two canyons of the Patagonian Submarine Canyon System are located in the study area. The two northern branches are the bifurcation of a major canyon (Fig. 43.3). They are overprinted by chains of pockmarks (fluid escape features) and by erosional gullies (Rı´o-Iglesias et al., 2012). The canyons and their multiple branches merge eastwards on the upper and middle continental slopes across terraces and steps. At the southern branch of the northern canyon, located in the Na´gera terrace, there is a NWSE scarp 22 km long, 57 km wide, and 350400 m high (Fig. 43.3, CAM_10). This scarp was originated from large fractures of a volcanic nature (Rı´o-Iglesias et al., 2012). Associated with the area of the northern canyon, there is a cluster of carbonate mounds, tens of meters in height, formed by the oxidation of methane (Mun˜oz et al., 2013) (Fig. 43.3, CAM_4). Circular to ellipsoidal pockmarks appear on the Na´gera and Perito Moreno terraces, generally 10120 m in vertical relief and 1080 m in diameter. Subsurface units with irregular tops were associated with sediments with free gas (Mun˜oz et al., 2013) (Fig. 43.3, CAM_11).
726 Chapter 43
Figure 43.3 (A) Geomorphic features map along with the georeferenced location of the points where digital photographs were taken. White stars represent the camera stations. (B) Detailed maps of geomorphic features in selection areas. (C) Digital photographs of interest points in the study area.
Geomorphic features and associated habitats of the Patagonian Continental Margin 727
Methods used to derive habitat maps Habitat maps are generated from data obtained with the multibeam echosounder (depth and backscatter mosaic) plus the collected photographs and samples using geomorphometric data analysis techniques (Store and Jokima¨ki, 2003). A Digital Terrain Model and the backscatter mosaic were generated at 50 3 50 m resolution. The weighted overlay of the derived layers was used to construct predictive suitability habitat models. The depth gives rise to three layers: (1) slope, (2) broad bathymetric position index (B-BPI), and (3) fine bathymetric position index (F-BPI). These layers determine the favorable conditions for the existence of certain habitats. From these data a distribution model is produced using the ArcGIS tool Benthic Terrain Modeler (BTM: Fig. 43.4). The BTM tool extracts the elevation of each cell in reference to the adjacent cells and was tested at different scales of 100, 150, 200, and 500 m. Finally, a scale factor of 2500 is chosen for B-BPI and a 500 scale factor was assigned for the F-BPI scale to build the structure model. Errors in depth measurements included variations in the speed of sound within the original source data obtained from the survey. The construction of a classification dictionary allowed the attribution of different classes to different environmental conditions (Fig. 43.4). Surficial characteristics of the seafloor were identified based on different combinations of BPI, slope, and depth (Lundblad et al., 2006). The result is a geomorphic features map upon which different ecosystems studied in the area can be overlain. For example, coral patches colonize hard substrates and rocky outcrops of narrow topographic elevations (De Mol et al., 2012). The most representative geological and geomorphological forms are shown in more detail on the structures map (Fig. 43.3). Steep gradients occur on the margins of the submarine canyons where corals are abundant (Fig. 43.3). The map of structures shows the nine different types of geomorphic features associated with gradient and depth. The detailed maps (B1 and B3 in Fig. 43.3) show small areas representing localized, small depressions or slight terrain variations on otherwise smooth seafloor areas. Backscatter data were acquired as part of multibeam and sidescan sonar mapping surveys and provide an important suite of abiotic variables for surrogacy research (Harris, 2012). The backscatter mosaic (Fig. 43.5) shows differences in seabed substrate through acoustic energy reflection. Substrate type determines to a large extent the type of ecosystem that develops at a given location. In the present study the substrate layer was obtained through a supervised classification of the backscatter data (Fig. 43.4). Seabed samples were used for the ground truthing of biotic habitat characteristics as indicators for the assigned classes. The result is a raster layer with five substrate classes, corresponding to mud, muddy sand, sand, coarse sediment, and rock (Figs. 43.2 and 43.4).
Figure 43.4 The model shows the process followed to obtain the geomorphic features and substrate maps. (A) Bathymetric map from which is derived the slope, fine-BPI, and broad-BPI. (B) Samples and backscatter maps. (C) Geomorphic features map obtained from the combination of the bathymetric derived layers. (D) Substrate map derived from the supervised classification of backscatter mosaic and the samples collected in the area.
Figure 43.5 (A) Backscatter reflectivity accompanied by two areas of study extracted of the general map at the location of the stations where the photographs have taken. (B) Detailed map of the upper red rectangle area coupled the image CAM_3 taken at this point. It shows a change of color in longitudinal direction. (C) The photograph CAM10 shows cold-water corals, Bathelia candida, located in the study area at the Station 10, at the ridge at 787 m water depth. This upper slope location has a great mass of dead coral; this frame serves as substrate to other species and also as suitable habitat for their fixation.
730 Chapter 43 The results of the substrate and geomorphic feature analyses were combined by using arithmetic overlay analysis, to model the habitat needs of different species in GIS (Fig. 43.6) (Store and Jokima¨ki, 2003). In each of the four cases, a different weighting of the factors has been carried out, taking into account the optimal survival conditions of each selected habitat. Four georeferenced habitat suitability maps (Fig. 43.6) were constructed for each biological community described below.
Biological communities Different habitats can be classified according to the EUNIS (European Union Nature Information System) Habitat Classification due to their environmental value: cold-water coral reefs, coral gardens, sponge beds, and deep marine rock and environments.
Cold-water coral reefs The most frequently sampled cold-water coral species is B. candida. Ecologically it is vital as a bioconstructor and it is only found in South America. Communities of deep-sea corals belong to the EUNIS code A6.61. Solenosmilia variabilis were also found in minor quantities in the samples and the sandy bottoms of the study area. Most of the cold-water corals along the Patagonian margin are located between 400 and 1000 m water depth. In the study area B. candida provided habitat for a great diversity of invertebrates and fishes. Other organisms colonize the branches of cold-water corals, with the overall assemblage dominated by filter-feeders, cnidarians, sponges, mollusks, and brachiopods, but also by echinoderms and crustaceans (Portela et al., 2012). Cold-water corals have been photographed at different depth areas of the upper slope. The photograph CAM_10 (Fig. 43.3) shows the cold-water coral B. candida located in the study area at the Station 10, on the ridge sited at south of the northern canyon, at 787 m water depth. This upper slope location has a great mass of dead coral.
Coral gardens Coral gardens or octocoral gardens inhabit different types of substrate characterized by suitable chemical and environmental conditions or by relief according to the codes A6.1 to 6.9 EUNIS habitat classification. The main feature of soft coral gardens is the aggregation of a large number of soft coral colonies consisting of different species; they can also be composed of a single species. In the present case study large extensions were found on sandy substrate with low gradient between 400 and 1000 m depth. The dominant species of the Octocorallia gardens in the study area were from the Primnoidae order, followed by different orders
Geomorphic features and associated habitats of the Patagonian Continental Margin 731
Figure 43.6 Habitat suitability maps applied for the different areas identified as VME on the Patagonian Continental Margin. (A) Cold-water coral reefs. (B) Coral gardens. (C) Sponge beds. (D) Deep marine rocky environments. The assigned scores correspond to the appropriate conditions extracted from the combination of the environmental variables prepared to the GIS analysis.
732 Chapter 43
Figure 43.7 CAM_8: rocky area on mudsand sediments of the continental shelf (135 m) colonized by a Gorgonocephalus sp. star and other taxa; CAM_13: underwater photography of an Octocorallia garden with Alcyonacea and Gorgonacea species forming a coral garden habitat together with the presence of phyla Porifera and Echinodermata. The red beams projected the distance of 5 cm to provide a scale factor for the subsequent spatial study.
such as Alcyonacea or Gorgonacea. Also important is the presence of bryozoans, ophiuroids, Asteroidea, Octopodidae, ascidians, and massive sponges (Mun˜oz et al., 2012). The samples obtained on the upper slope, at a depth from 300 to 500 m (Fig. 43.7, CAM_13) indicate an abundant association of taxonomic groups which coexist with the soft corals.
Sponge beds Following the EUNIS Habitat Classification, deep-sea sponge aggregations (EUNIS Code: A6.62) are principally composed of sponges from two classes: Hexactinellida and Desmospongia. They are known to occur between water depths of 2501300 m (Bett and Rice, 1992), where the water temperature ranges from 4 C to 10 C and there is moderate current velocity (0.5 knots). Deep-sea sponge aggregations may be found on soft or hard substrata, such as boulders and cobbles which may lie on sediment. Since sponges have a preference for deep habitats similar to those of cold-water corals, it is common to find both ecosystems coexisting in the same location. In the study area the presence of deepwater hexactinellid sponges belonging to the genus Rossella, provided a three-dimensional structure to the seabed on which other species live, hunt, or find refuge from predators and strong bottom currents (Portela et al., 2012).
Geomorphic features and associated habitats of the Patagonian Continental Margin 733 Carnivorous sponges generally colonize hydrothermal vents and abyssal zones although in the study area they were documented at depths not exceeding 1500 m. The different expeditions provided samples in which had been identified several species, some of them new to science, belonging to the genera Asbestopluma, Chondrocladia, Euchelipluma, and Cercicladia, a new genus (Rios et al., 2011).
Deep marine rocky environments The deep marine rocky environments host rare or endemic species. These habitats correspond to the EUNIS code 6.1 or 6.7 depending on the substrate on which they are located. They are significant marine ecosystems composed of different associations of taxonomic groups, such as Porifera, Cnidaria, and other invertebrate taxa (ophiuroids, crinoids, asteroids, bryozoans, and tunicates).
Acknowledgments We thank the Spanish General Secretariat of the Sea, for provided ship time and technical support. This project is funded by SGM in collaboration with the Spanish Oceanographic Institute.
References Bett, B.J., Rice, A.L., 1992. The influence of hexactinellid sponge (Pheronema carpenteri) spicules on the patchy distribution of macrobenthos in the porcupine seabight (bathyal ne atlantic). Ophelia 36, 217226. De Mol, B., Amblas, D., Alvarez, G., Busquets, P., Calafat, A., Canals, M., et al., 2012. 45 - Cold-water coral distribution in an erosional environment: the Strait of Gibraltar Gateway A2 - Harris, Peter T. In: Baker, E. K. (Ed.), Seafloor Geomorphology as Benthic Habitat. Elsevier, London, pp. 635643. Harris, P.T., 2012. 5 - Surrogacy, Seafloor Geomorphology as Benthic Habitat. Elsevier, London, pp. 93108. Lundblad, E.R., Wright, D.J., Miller, J., Larkin, E.M., Rinehart, R., Naar, D.F., et al., 2006. A Benthic Terrain Classification Scheme for American Samoa. Marine Geodesy 29, 89111. Mun˜oz, A., Cristobo, J., Rios, P., Druet, M., Polonio, V., Uchupi, E., et al., 2012. Sediment drifts and coldwater coral reefs in the Patagonian upper and middle continental slope. Marine Petrol. Geol. 36, 7082. Mun˜oz, A., Acosta, J., Cristobo, J., Druet, M., Uchupi, E., 2013. Geomorphology and shallow structure of a segment of the Atlantic Patagonian margin. Earth-Sci. Rev. 121, 7395. 2013. Portela, J., Acosta, J., Cristobo, J., Mun˜oz, A., Parra-Descalzo, S., Patrocinio, T., et al., 2012. Management Strategies to Limit the Impact of Bottom Trawling on VMEs in the High Seas of the SW Atlantic. Rı´o-Iglesias, J.L.D., Acosta-Yepes, J., Cristobo, J., Portela, J., Parra-Descalzo, S., Tel, E., et al., 2012. Estudio de los Ecosistemas Marinos Vulnerables en aguas internacionales del Atlantico Sudoccidental. Instituto Espanol de Oceanografia. Rios, P., Kelly, M., Vacelet, J., 2011. Cercicladia australis, a new carnivorous sponge with novel chelae from the Tasman Basin and the Argentine Patagonian Margin (Porifera, Cladorhizidae). Zootaxa 3131, 15 December 2011, DOI: 10.11646/zootaxa.3131.1.3. Store, R., Jokima¨ki, J., 2003. A GIS-based multi-scale approach to habitat suitability modeling. Ecol. Model. 169, 115.
734 Chapter 43 Thompson, A.B., Sanders, J., Tandstad, M., et al., 2016. Vulnerable Marine Ecosystems: Processes and Practices in the High Seas. FAO, Rome, p. 200. Violante, R., Laprida, C., Garcı´a Chapori, N., 2017. The Argentina Continental Margin: a potential Paleoclimatic-Paleoceanographic archive for the Southern Ocean. Springer Briefs in Earth System Sciences, p. 117. Ward, T.J., 2011. SOE 2011 National marine condition assessment decision model and workshops. Report Prepared for the Department of Sustainability, Environment, Water, Population and Communities on behalf of the State of the Environment 2011 Committee. Canberra, ACT, Australia, Department of Sustainability, Environment, Water, Population and Communities 22.
Geomorphic features and associated habitats of the Patagonian Continental Margin, southwestern Atlantic ˜oz2, Lourdes Viscasillas2 and Diego Varas2 Dulce Mata1,2, Araceli Mun 1
Department of Geography, Complutense University of Madrid, Madrid, Spain 2Tragsatec-SGP, Maritime Affairs and Fisheries, Madrid, Spain
Abstract The Patagonian Continental Margin is a high biodiversity area of the southwestern Atlantic Ocean. It is characterized by a series of submarine canyons, which provide seafloor habitat for several types of marine ecosystem. There are also rocky outcrops colonized by different associations of taxonomic groups. Samples collected in the area confirm that biological communities such as Porifera, Cnidaria, Octocoralia, and Echinodermata are associated with these geomorphic features. The present study is based on the spatial analysis of environmental variables including bathymetry and backscatter texture obtained using a multibeam echosounder. Depth, slope, and bathymetric position index physical terrain variables were used to produce a model of geomorphic features. Submarine photography and samples were used to verify the confidence of this model to indicate the presence of specific habitats. In particular, the intensity of acoustic backscatter was used to classify the different textures of the seabed substrate. Based on our analysis, four habitat types were derived for the different habitats studied in the area: (1) cold-water coral reefs, (2) coral gardens, (3) sponge beds, and (4) deep marine rocky environments.
Keywords: Ocean; habitat; mapping; Atlantic; geospatial; GIS; environment
Introduction The Patagonian Continental Margin is located in the southwestern Atlantic Ocean where the confluence of two great oceanic currents, the Malvinas Current and the Brazil Current, promotes primary production helping the existence of high marine biodiversity. This chapter is focused on a 13899 km2 area located between two submarine canyons of the south Patagonian continental slope system. The study area is located on the Patagonian Margin between 46 80 S47 70 S and 59 140 W60 500 W and from 126 m depth on the shelf to more than 1700 m on the middle continental slope (Fig. 43.1). The wide range of depths Seafloor Geomorphology as Benthic Habitat. DOI: https://doi.org/10.1016/B978-0-12-814960-7.00043-9 © 2020 Elsevier Inc. All rights reserved.
721
Figure 43.1 Study area location at the southwestern edge of the Argentine Basin. A red square indicates the geographical extent of the study area (left). Multibeam echosounder bathymetric map (right), includes a graduate scale representing the depth range.
Geomorphic features and associated habitats of the Patagonian Continental Margin 723 includes different seabed geomorphic structures that determine the existence of different habitats of great ecological interest. Within the framework of Vulnerable Marine Ecosystems (VME) research (ATLANTIS project), the R/V Miguel Oliver of the Spanish General Secretariat of the Sea (SGM) carried out eight cruises between 2007 and 2009 in the southwest South Atlantic. The main objective of this multidisciplinary research was to locate and map possible VME’s between the Argentine EEZ outer limit and the 1500 m isobath. Information regarding the morphology of the Patagonian Margin was acquired with a Simrad EM-302 (30 kHz) multibeam system. Data processing was carried out using the CARIS swath bathymetric software package HIPS and SIPS. Valid data were gridded at 50 3 50 m resolution. In addition, a total of 1451 bottom photographs were acquired at 13 stations with a reflex digital camera of .12 Mpixel, model Nikon D700. Based on the distance between two red laser points reflected on the seafloor, individual photographs covered an area of 2 by 1.5 m. Samples of the benthic fauna were obtained with a rock dredge (58 stations) and with a bottom trawl net during fishing operations. A total of 156 bottom samples for sedimentological studies were collected with a megaboxcorer and an additional 105 samples with a Lofoten sampler (Fig. 43.2). All data were integrated using ArcGis (ESRI) and Fledermaus software (Interactive Visualization Systems; IVS). The present work is referred to the multidisciplinary research oceanographic surveys of the Atlantis project. The case study presents some of the results of this research along with the habitat spatial distribution modeling.
Oceanography The Patagonian Continental Margin is located in the BrazilMalvinas Confluence (BMC). This confluence causes an oceanic front and upwelling of nutrients, which favors a high biodiversity of the benthos in the study area. The Argentine Continental Margin is the only place in the southern ocean where mixing of water masses from south polar and equatorial regions occurs. The oceanographic system is composed of water masses characterized by differences in density, temperature, salinity, oxygen content, and other physical, biological, and chemical properties (Violante et al., 2017). Vertical stratification separates surface waters of variable temperature and salinity from bottom waters where the values are equalized below a clearly differentiated thermocline.
Naturalness, condition, and trend The baseline for condition covers the period of the years 20062016 based on the technical report about the processes and practices in the high seas of southwest Atlantic Ocean which
Figure 43.2 Shade relief model of the case study extracted from 50 m resolution digital elevation model (with a vertical exaggeration of 6 3 ), including seabed sample stations and a predictive model of the substrate type.
Geomorphic features and associated habitats of the Patagonian Continental Margin 725 was published by FAO (Thompson et al., 2016). The high confidence of subsequent trends in condition derives from the study of the area carried out by the Atlantis project described below. According to the data collation about the study area, the grade of statement for the habitats describe in this case is Good, with a score value of 6 (as per the scheme of Ward, 2011). Furthermore, the habitats are evaluated as stable for the last 5 years, following the observations reported herein.
Geomorphic features and habitats The Argentine Patagonian Margin comprises a wide continental shelf and adjacent continental slope, which is topographically divided into an upper, middle, and lower slope. The morphology of the features in this area is described below. Continental shelf: The outer continental shelf is dominated by sediment ridges oriented in a NNESSW direction, oblique to the shelf break. The sand ridge crests are 15 m high and they are separated 34 km apart (Fig. 5.2; Rı´o-Iglesias et al., 2012). Rocky outcrops are low relief and locally buried by NE migrating megaripples. Some cobble to boulder-sized flattened sandstone fragments are colonized by different species of fauna (Fig. 43.3, CAM_6, CAM_7; Fig. 43.7, CAM_8). Continental slope: The upper slope is 620 km wide, has a gradient of 4 1 200 and descends from the continental shelf break (128200 m depth) to depths of between 250 and 750 m. The middle slope contains the Na´gera terrace (from the base of the upper slope to a depth of 9301060 m) and Perito Moreno terrace (from a depth of about 11001400 m). Two canyons of the Patagonian Submarine Canyon System are located in the study area. The two northern branches are the bifurcation of a major canyon (Fig. 43.3). They are overprinted by chains of pockmarks (fluid escape features) and by erosional gullies (Rı´o-Iglesias et al., 2012). The canyons and their multiple branches merge eastwards on the upper and middle continental slopes across terraces and steps. At the southern branch of the northern canyon, located in the Na´gera terrace, there is a NWSE scarp 22 km long, 57 km wide, and 350400 m high (Fig. 43.3, CAM_10). This scarp was originated from large fractures of a volcanic nature (Rı´o-Iglesias et al., 2012). Associated with the area of the northern canyon, there is a cluster of carbonate mounds, tens of meters in height, formed by the oxidation of methane (Mun˜oz et al., 2013) (Fig. 43.3, CAM_4). Circular to ellipsoidal pockmarks appear on the Na´gera and Perito Moreno terraces, generally 10120 m in vertical relief and 1080 m in diameter. Subsurface units with irregular tops were associated with sediments with free gas (Mun˜oz et al., 2013) (Fig. 43.3, CAM_11).
726 Chapter 43
Figure 43.3 (A) Geomorphic features map along with the georeferenced location of the points where digital photographs were taken. White stars represent the camera stations. (B) Detailed maps of geomorphic features in selection areas. (C) Digital photographs of interest points in the study area.
Geomorphic features and associated habitats of the Patagonian Continental Margin 727
Methods used to derive habitat maps Habitat maps are generated from data obtained with the multibeam echosounder (depth and backscatter mosaic) plus the collected photographs and samples using geomorphometric data analysis techniques (Store and Jokima¨ki, 2003). A Digital Terrain Model and the backscatter mosaic were generated at 50 3 50 m resolution. The weighted overlay of the derived layers was used to construct predictive suitability habitat models. The depth gives rise to three layers: (1) slope, (2) broad bathymetric position index (B-BPI), and (3) fine bathymetric position index (F-BPI). These layers determine the favorable conditions for the existence of certain habitats. From these data a distribution model is produced using the ArcGIS tool Benthic Terrain Modeler (BTM: Fig. 43.4). The BTM tool extracts the elevation of each cell in reference to the adjacent cells and was tested at different scales of 100, 150, 200, and 500 m. Finally, a scale factor of 2500 is chosen for B-BPI and a 500 scale factor was assigned for the F-BPI scale to build the structure model. Errors in depth measurements included variations in the speed of sound within the original source data obtained from the survey. The construction of a classification dictionary allowed the attribution of different classes to different environmental conditions (Fig. 43.4). Surficial characteristics of the seafloor were identified based on different combinations of BPI, slope, and depth (Lundblad et al., 2006). The result is a geomorphic features map upon which different ecosystems studied in the area can be overlain. For example, coral patches colonize hard substrates and rocky outcrops of narrow topographic elevations (De Mol et al., 2012). The most representative geological and geomorphological forms are shown in more detail on the structures map (Fig. 43.3). Steep gradients occur on the margins of the submarine canyons where corals are abundant (Fig. 43.3). The map of structures shows the nine different types of geomorphic features associated with gradient and depth. The detailed maps (B1 and B3 in Fig. 43.3) show small areas representing localized, small depressions or slight terrain variations on otherwise smooth seafloor areas. Backscatter data were acquired as part of multibeam and sidescan sonar mapping surveys and provide an important suite of abiotic variables for surrogacy research (Harris, 2012). The backscatter mosaic (Fig. 43.5) shows differences in seabed substrate through acoustic energy reflection. Substrate type determines to a large extent the type of ecosystem that develops at a given location. In the present study the substrate layer was obtained through a supervised classification of the backscatter data (Fig. 43.4). Seabed samples were used for the ground truthing of biotic habitat characteristics as indicators for the assigned classes. The result is a raster layer with five substrate classes, corresponding to mud, muddy sand, sand, coarse sediment, and rock (Figs. 43.2 and 43.4).
Figure 43.4 The model shows the process followed to obtain the geomorphic features and substrate maps. (A) Bathymetric map from which is derived the slope, fine-BPI, and broad-BPI. (B) Samples and backscatter maps. (C) Geomorphic features map obtained from the combination of the bathymetric derived layers. (D) Substrate map derived from the supervised classification of backscatter mosaic and the samples collected in the area.
Figure 43.5 (A) Backscatter reflectivity accompanied by two areas of study extracted of the general map at the location of the stations where the photographs have taken. (B) Detailed map of the upper red rectangle area coupled the image CAM_3 taken at this point. It shows a change of color in longitudinal direction. (C) The photograph CAM10 shows cold-water corals, Bathelia candida, located in the study area at the Station 10, at the ridge at 787 m water depth. This upper slope location has a great mass of dead coral; this frame serves as substrate to other species and also as suitable habitat for their fixation.
730 Chapter 43 The results of the substrate and geomorphic feature analyses were combined by using arithmetic overlay analysis, to model the habitat needs of different species in GIS (Fig. 43.6) (Store and Jokima¨ki, 2003). In each of the four cases, a different weighting of the factors has been carried out, taking into account the optimal survival conditions of each selected habitat. Four georeferenced habitat suitability maps (Fig. 43.6) were constructed for each biological community described below.
Biological communities Different habitats can be classified according to the EUNIS (European Union Nature Information System) Habitat Classification due to their environmental value: cold-water coral reefs, coral gardens, sponge beds, and deep marine rock and environments.
Cold-water coral reefs The most frequently sampled cold-water coral species is B. candida. Ecologically it is vital as a bioconstructor and it is only found in South America. Communities of deep-sea corals belong to the EUNIS code A6.61. Solenosmilia variabilis were also found in minor quantities in the samples and the sandy bottoms of the study area. Most of the cold-water corals along the Patagonian margin are located between 400 and 1000 m water depth. In the study area B. candida provided habitat for a great diversity of invertebrates and fishes. Other organisms colonize the branches of cold-water corals, with the overall assemblage dominated by filter-feeders, cnidarians, sponges, mollusks, and brachiopods, but also by echinoderms and crustaceans (Portela et al., 2012). Cold-water corals have been photographed at different depth areas of the upper slope. The photograph CAM_10 (Fig. 43.3) shows the cold-water coral B. candida located in the study area at the Station 10, on the ridge sited at south of the northern canyon, at 787 m water depth. This upper slope location has a great mass of dead coral.
Coral gardens Coral gardens or octocoral gardens inhabit different types of substrate characterized by suitable chemical and environmental conditions or by relief according to the codes A6.1 to 6.9 EUNIS habitat classification. The main feature of soft coral gardens is the aggregation of a large number of soft coral colonies consisting of different species; they can also be composed of a single species. In the present case study large extensions were found on sandy substrate with low gradient between 400 and 1000 m depth. The dominant species of the Octocorallia gardens in the study area were from the Primnoidae order, followed by different orders
Geomorphic features and associated habitats of the Patagonian Continental Margin 731
Figure 43.6 Habitat suitability maps applied for the different areas identified as VME on the Patagonian Continental Margin. (A) Cold-water coral reefs. (B) Coral gardens. (C) Sponge beds. (D) Deep marine rocky environments. The assigned scores correspond to the appropriate conditions extracted from the combination of the environmental variables prepared to the GIS analysis.
732 Chapter 43
Figure 43.7 CAM_8: rocky area on mudsand sediments of the continental shelf (135 m) colonized by a Gorgonocephalus sp. star and other taxa; CAM_13: underwater photography of an Octocorallia garden with Alcyonacea and Gorgonacea species forming a coral garden habitat together with the presence of phyla Porifera and Echinodermata. The red beams projected the distance of 5 cm to provide a scale factor for the subsequent spatial study.
such as Alcyonacea or Gorgonacea. Also important is the presence of bryozoans, ophiuroids, Asteroidea, Octopodidae, ascidians, and massive sponges (Mun˜oz et al., 2012). The samples obtained on the upper slope, at a depth from 300 to 500 m (Fig. 43.7, CAM_13) indicate an abundant association of taxonomic groups which coexist with the soft corals.
Sponge beds Following the EUNIS Habitat Classification, deep-sea sponge aggregations (EUNIS Code: A6.62) are principally composed of sponges from two classes: Hexactinellida and Desmospongia. They are known to occur between water depths of 2501300 m (Bett and Rice, 1992), where the water temperature ranges from 4 C to 10 C and there is moderate current velocity (0.5 knots). Deep-sea sponge aggregations may be found on soft or hard substrata, such as boulders and cobbles which may lie on sediment. Since sponges have a preference for deep habitats similar to those of cold-water corals, it is common to find both ecosystems coexisting in the same location. In the study area the presence of deepwater hexactinellid sponges belonging to the genus Rossella, provided a three-dimensional structure to the seabed on which other species live, hunt, or find refuge from predators and strong bottom currents (Portela et al., 2012).
Geomorphic features and associated habitats of the Patagonian Continental Margin 733 Carnivorous sponges generally colonize hydrothermal vents and abyssal zones although in the study area they were documented at depths not exceeding 1500 m. The different expeditions provided samples in which had been identified several species, some of them new to science, belonging to the genera Asbestopluma, Chondrocladia, Euchelipluma, and Cercicladia, a new genus (Rios et al., 2011).
Deep marine rocky environments The deep marine rocky environments host rare or endemic species. These habitats correspond to the EUNIS code 6.1 or 6.7 depending on the substrate on which they are located. They are significant marine ecosystems composed of different associations of taxonomic groups, such as Porifera, Cnidaria, and other invertebrate taxa (ophiuroids, crinoids, asteroids, bryozoans, and tunicates).
Acknowledgments We thank the Spanish General Secretariat of the Sea, for provided ship time and technical support. This project is funded by SGM in collaboration with the Spanish Oceanographic Institute.
References Bett, B.J., Rice, A.L., 1992. The influence of hexactinellid sponge (Pheronema carpenteri) spicules on the patchy distribution of macrobenthos in the porcupine seabight (bathyal ne atlantic). Ophelia 36, 217226. De Mol, B., Amblas, D., Alvarez, G., Busquets, P., Calafat, A., Canals, M., et al., 2012. 45 - Cold-water coral distribution in an erosional environment: the Strait of Gibraltar Gateway A2 - Harris, Peter T. In: Baker, E. K. (Ed.), Seafloor Geomorphology as Benthic Habitat. Elsevier, London, pp. 635643. Harris, P.T., 2012. 5 - Surrogacy, Seafloor Geomorphology as Benthic Habitat. Elsevier, London, pp. 93108. Lundblad, E.R., Wright, D.J., Miller, J., Larkin, E.M., Rinehart, R., Naar, D.F., et al., 2006. A Benthic Terrain Classification Scheme for American Samoa. Marine Geodesy 29, 89111. Mun˜oz, A., Cristobo, J., Rios, P., Druet, M., Polonio, V., Uchupi, E., et al., 2012. Sediment drifts and coldwater coral reefs in the Patagonian upper and middle continental slope. Marine Petrol. Geol. 36, 7082. Mun˜oz, A., Acosta, J., Cristobo, J., Druet, M., Uchupi, E., 2013. Geomorphology and shallow structure of a segment of the Atlantic Patagonian margin. Earth-Sci. Rev. 121, 7395. 2013. Portela, J., Acosta, J., Cristobo, J., Mun˜oz, A., Parra-Descalzo, S., Patrocinio, T., et al., 2012. Management Strategies to Limit the Impact of Bottom Trawling on VMEs in the High Seas of the SW Atlantic. Rı´o-Iglesias, J.L.D., Acosta-Yepes, J., Cristobo, J., Portela, J., Parra-Descalzo, S., Tel, E., et al., 2012. Estudio de los Ecosistemas Marinos Vulnerables en aguas internacionales del Atlantico Sudoccidental. Instituto Espanol de Oceanografia. Rios, P., Kelly, M., Vacelet, J., 2011. Cercicladia australis, a new carnivorous sponge with novel chelae from the Tasman Basin and the Argentine Patagonian Margin (Porifera, Cladorhizidae). Zootaxa 3131, 15 December 2011, DOI: 10.11646/zootaxa.3131.1.3. Store, R., Jokima¨ki, J., 2003. A GIS-based multi-scale approach to habitat suitability modeling. Ecol. Model. 169, 115.
734 Chapter 43 Thompson, A.B., Sanders, J., Tandstad, M., et al., 2016. Vulnerable Marine Ecosystems: Processes and Practices in the High Seas. FAO, Rome, p. 200. Violante, R., Laprida, C., Garcı´a Chapori, N., 2017. The Argentina Continental Margin: a potential Paleoclimatic-Paleoceanographic archive for the Southern Ocean. Springer Briefs in Earth System Sciences, p. 117. Ward, T.J., 2011. SOE 2011 National marine condition assessment decision model and workshops. Report Prepared for the Department of Sustainability, Environment, Water, Population and Communities on behalf of the State of the Environment 2011 Committee. Canberra, ACT, Australia, Department of Sustainability, Environment, Water, Population and Communities 22.