From Mapping to Monitoring
Seafloor characterization can be understood in many ways. Mainly, it is used as an approach to identify geographic areas that have some common geology and/or biology. These geographic areas characterize benthic habitats and, as scientists, it is important for us to be able to separate them accurately. In addition, there is an effort to relate these geographic areas to past and current environmental conditions of the ocean. Is the characterization of the seafloor indicate a trend or an outlier?
To answer this question, Shachak Pe’eri, Jenn Dijkstra, and Brian Madore from CCOM are collaborating with ecologists from the Israel Oceanographic and Limnological Research Institute on two projects that are designed to accurately and efficiently map nearshore environments. As a first step towards these goals, two marine environments, the Levant Mediterranean along the northern shore of Israel and the Red Sea near Eilat, southern Israel were chosen as test sites.
Biodiversity investigation in the northern coastal region of Israel
(Gideon Tibor, Gil Rilov, and Tomer Ketter)
Figure 1. Images from the May 2014 ground truth campaign in the Levant Mediterranean rocky reefs. (Top left) Classification map loaded into Hypack with planned survey lines, (Bottom left) L3 Klein 3900 with a GoPro camera attached, (Center image) the OCS system with an addition light source, (Top right) Grab sampler, (Bottom left) example of a benthos type in the study site (coarse sand and fine gravel with seaweeds).
The Levant Mediterranean rocky reefs are coastal ecosystems that are experiencing large shifts in marine biodiversity. These shifts include the creation of reefs by non-native oysters that have invaded from the Red Sea, the introduction of seaweed species that form large patches on the seafloor, and over-grazing of native seaweed meadows by non-native herbivorous fish. Such changes can potentially be detected at large scales using remote-sensing techniques and surveys. The goal of this project is to develop classification schemes using remote sensing (multispectral and hyperspectral) imagery collected over a 15-yearperiod. Underwater images and biological sampling collected in the past four years will be used as ground truth for the benthic habitats characterized using the remote sensing imagery. The classification schemes will be used to map and monitor temporal and spatial changes in benthic habitats.
In May 2014, an additional ground truth survey was conducted using a spectrometer with a 25-m fiber optic cable, underwater camera, and a side scan sonar along the northern shores of Israel to identify and characterize benthic habitats. Preliminary classification results from satellite imagery show a good correlation to the ground truth observations and measurements.
Mapping biological states of coral colonies (Stylophora)
using a spectral approach
(Buki Rinkevich, Jack Silverman, and Gideon Tibor)
Figure 2. Images from the June 2014 ground truth campaign in the Gulf of Eilat: (a) fluorescence measurements using a blue (460 nm) lamp, (b) fluorescence measurements using a green (532 nm) laser, (a) fluorescence measurements using a red (655 nm) lamp, and (d) reflectance measurements using a white tungsten (black body temp. 2900K) lamp.
The Red Sea is considered to be an environmentally stable (water temperature, salinity, etc.) ecosystem that is filled with coral reefs and seaweed habitats. Here, an investigation was conducted on the effects of disease on the coral, Stylophora pistillata, using spectral reflectance and fluorescence. Corals provide unique color identification in response to light illumination. For example, a coral may appear yellow-white in natural daylight conditions and appear to have green and red shades when illuminated with a blue light. This color change phenomena is known as fluorescence.
Current remote sensing studies have focused on the separation of coral species from the surrounding environment (e.g., covering sediments, or between species) or the amount of bleaching on coral reefs. The results of this study can support coastal managers in defining environment sensitivity indices (ESI) and possible habitat mapping and monitoring programs using hyperspectral and airborne lidar bathymetry (ALB) surveys.
After visual inspection of the health of individual corals underwater, the color of the corals was measured using different light sources (i.e., white, red, green, and blue). In addition, selected branches from each coral were sampled and brought back to the laboratory for further study. Preliminary results from the field measurement and laboratory work show systematic color differences between healthy and diseased corals.