This research was my Master in Sciences degree thesis for Biology, entitled “Spatial and Temporal Variability of the Seabed of the Morrocoy National Park“.
Morrocoy National Park covers an area of 28,736 hectares of which 70.8% are marine. The area is characterized by major Caribbean marine ecosystems (mangrove forests, seagrass beds and coral reefs). Since its creation in 1974, it has undergone major disturbances that range from the removal of more than 270 palafittes, mass mortalities of marine organisms and periods of extreme hyposalinity. While there is a substantial set of studies in different ecosystems, to date there is no integrated spatial assessment of marine communities or the changes they have experienced. This study aimed to generate a map of shallow marine ecosystems of the park and the evaluation of
changes in the coastline and seagrass communities.
39.4% of the marine area were mapped, including: the lagoon system, the mouth of Golfete Cuare and external offshore platform to a depth of 15m. By visual interpretation of satellite imagery and field verification, geomorphological structures and biotic coverage were identified. The park has 623 hectares of coral reefs spread over two barriers: one near the outer boundary of the park and a fringing reef on the coast and cays. It also mapped the distribution and extent of seagrass and macroalgae (1,247 hectares). Comparing the current shallow marine ecosystems map with aerial photograph from 1972, an estimated loss of 36.6 hectares of coastline and 16.1 hectares of gain were identified. Additionally, seagrass coverage increases, not only in the old palafittes areas but also in protected areas close to the cays.
- This study is the first comprehensive and systematic contribution to map the seabed of the Morrocoy National Park at a detailed scale (1:5000) covering 8023.6 ha of marine area (39.4% of the area of the park).
- A more global and spatial vision of the park ecosystem was obtained. Including location and extension of: coral reef, reef rubble, soft bottoms without macrobiotic cover, macroalgaes and seagrass ecosystems.
- Change in the coastline were identified, product of erosion accretion processes. Also change in seagrass coverage were identified.
- A new coral reef area was identified and mapped.
- 542 ground validation points, with 180 underwater photo and 362 underwater videos were recorded.
- Generate a map of the shallow marine ecosystems of the park from high spatial resolution satellite images from 2000 to 2006.
- Quantify and identify areas of change of the coastline and seabed from the comparison of aerial photographs from 1972 and 2000 satellite image.
- Determine whether there were changes of seabed affected by the construction of palafittes during the 70s in the marine areas of the park.
- Data Acquisition: The following material was acquire for the project:
- Cartographic maps: scale 1:25.000 (year 1965) and scale 1: 10.000 (year 1974).
- Nautical Maps: Chart 24455 (year 1944).
- Bathymetry data: project “Agenda Morrocoy” – Universidad Simón Bolívar provided the information in dxf format.
- Aerial Photos: scale 1: 20.000 (year 1972), scale 1:25.000 (year 1991) and scale 1:20.000 (year 1998).
- Satellite images: Landsat (years: 1985, 1990, 1997,1999, 2001), Google Earth and Yahoo Maps: ikonos (year 2000) and Quickbird (years:2003, 2004, 2006).
- Data Georeference: All maps were georeferenced in UTM projection Zone 19, Datum Provisional South American 1956, and transformed to Datum WGS84. Landsat (2001) image was geometric corrected using the scale 1:25.000 maps. The other Landsat images were georeferenced using an image to image geometric correction. Downloaded Google and Yahoo images were checked with the scale 1:10.000 map to identify any shift in the images.
- Objective 1:
- The methodology used is based on NOAA Benthics Habitat Mapping. A classification schema was defined on the basis of: geographic zone, geomorphology structure and dominant biological cover. The map is the result of visual interpretation of high spatial resolution satellite images and ground validation.
- Ground verification: All polygon with an area greater than 1 hectare (2.47 acre) was verified. A Towed Underwater Video was developed to reduce verification time in the field and have a photographic record of each sampling point.
- Objetive 2:
- To identify changes in the coastline, the coastline obtained from the seabed map was compared with the coastline maps of 1964 and 1972. Changes were represented by polygon, and area calculated.
- To identify changes in the seabed, an aerial photomosaic from 1972 fly was generated.
- Satellite image of 2000 was transform to greyscale. Each aerial photo was calibrated with the greyscale satellite images.
- A matrix subtraction was done between the satellite image and each calibrated photo. Only seagrass areas were selected, and the results were normalized to detect changes. If the value was greater than 1.0 standard deviation or less than -1.0, it was consider a change (gain or loss of seagrass coverage).
- A map showing the changes in seagrass coverage was produced.
- Objective 3:
- A buffer around each palafittes was build.
- An overlay with the buffer and change in seagrass layers was done.
- Statistic was calculated for each buffer zone
Photos: Field verification
Videos: Field verification using a Towed Underwater Video (TUV)
Example of coastline change in Punta Brava:
- A new coral reef area was identified and mapped, parallel to the coast at a distance of 3 to 5 km. It represents 49.2% coral coverage of the park.
- Reef rubble biota is the most representative biotic coverage in the Morrocoy National Park with an area of 2718 hectares, 13.4% of the marine area of the park.
- A new marine vegetation ecosystem is proposed for the park, macroalgae prairie (in depth between 3m and 6m). The macroalgae has coverage 15 % greater than that of seagrass beds.
- The class “soft bottoms without macrobiotic cover”, represent the largest seabed (73%) in the park lagoon systems.
- Changes in the coastline were identified. 36 ha with erosion processes and 16 ha with accretion. These dynamics are mostly found on the windward seashores.
- The locations where the palafittes were removed showed an increase in seagrass coverage of at least 30%.
- Lazo, R., Klein, E. Cartografía de los fondos marinos del Parque Nacional Morrocoy. IX Congreso Venezolano de Ecología. November 2011, Isla de Margarita, Venezuela.
Gratefully acknowledge the support of Institute of Marine Science and Technology (Intecmar), Simón Bolívar University (USB) and National Park Institute (Inparques).