Underwater Survey Methods
There are many different types of underwater methods used by scientists such as marine biologists. In this page we will briefly explain some of the basic yet significant methods which can be used for underwater monitoring of diversity and abundance. All methods eplained have been personally used during research trips and have been proved to be reliable both qualitativly and quantitativly.
1. Underwater Video Transect for fish monitoring
Fish monitoring is a process which includes both identification and counting of fish species. Fish identification is not always easy to take place underwater and can be affected by many factors, such as current, visibility, landscape formation and dive time. In order to accomplish, a precise and reliable fish monitoring of fish populations two methods of manual monitoring can be used. Fish Video Transect Recording (FVTR) is the backbone of the fish identification and counting. For the successful conduct of this survey, underwater cameras can be used and specifically compact cameras of high resolution such as the OLYMPUS Tough Series (TG-2 to TG-6) and their underwater housings.
The camera should be held by the Diver/Observer at a 70 to 90 Degree Angle from the Transect line facing forward and slightly down to the bottom so that fish found within the corals will be observed and not missed. The aim of this method is to record a wide-angle landscape and include in the footage the fish found within a 2.5 meters distance from each side of the transect. The total length of the transect line should be around 100 meters with 5 meter breaks every 20 meters so that we create compartments. So for a 100 meter transect we will have the following compartments (0-20, 25-45, 50-70, 75-95). By doing so we create repetitions and our statistical analysis will be more reliable. Depending on the area that we would like to conduct research we should repeat 100 meter transects in random points within the area of interest (unless there is something specific that needs to be monitored systematically such as corals)
After the footage is acquired, it should be carefully observed and both fish identification and counting will take place using a computer. All video footages should be carefully archived with Dates, Time and locations. The second part of the fish survey focuses more on, fish identification notes underwater (during the dive) and Photography of fish species for identification purposes.
2. Invertebrate Monitoring
Invertebrate monitoring requires a similar method as section 1 (Fish monitoring video transect) but with some alterations in order to succesfully cover the designated area of the survey. Most invertebrates find shelter close to the benthos, under rock structures or hidden in the sand. To monitor such organisms the surveyor need to search the area of research in more detail to collect all the data. As already mentioned in section 1, the surveyor needs to unfold a 100m long transect line and seperate it into 4 different parts every 20 meters. Once the transect is in place, we need to stop for approximately five minutes to allow all marine life to shetle down and relax again after our movement. Those first steps are similar with the fish monitoring video transect. The differences in the methodologies begin right after that. In this method no cameras are used. We need to have a slate and a torch. Due to the high biodiversity of invertebrates it is reccommended to have a slate with the species or organisms that we are looking for our research.
We begin the survey from either side of the transect and search for invertebrates within a 2meter distance from each side of the transect (totally 4 meters). Once we complete each part of the transect we stop for 5 meters and repeat the process. This applies for the total of the transect as we need more repetition in order to aquire more reliable data quantitatively and qualitativly.
3. Quadrat Sampling
Quadrat sampling is a common method used for ecology, biodiversity studies and percentage coverage measuring. Quadrat sampling can be used in many different ways in underwater marine research such as algae percentage coverage surveys, coral species monitoring and percentage coverage in area etc. For the quadrat photo sampling, compact cameras of high resolution can be used such as the OLYMPUS Tough Series. The camera needs to be held by the observer, at a distance of 60cm to 80cm from the 50cm x 50cm quadrat (changin regarding the size of our quadrat) and a high- quality image will be taken. From every 20 meters replicate 10-15 quadrat Images are sufficient, resulting into a total of 40-60 quadrat images for every 100 meters Transect. All Images need to be carefully archived, in terms of Date, Time and Location and transect line of site. Once all Images are
collected, can be analysed using various softwares.
4. Point Transect
The Point Transect is a method based on point sampling. By collecting data from specific point from the transect the research team can determine the coverage several ffactors underwater usually benthic related such as type of environment (such as coral,rock,rubble,sand etc.). In order to conduct a point transect method a transect line will be needed. As in section 1 and 2 a 100 meter transect is unfolded. Once the transect is in place the survey can begin. Due to the fact that we are not focusing on moving organisms during a point transect method it is not necessary to wait for approximately 5 minutes before the survey begins. What needs to be done is to decide how many points are going to be recorder on the transect. A recording pace of one point per 50cm is sufficient for a reef area. The surveyor needs to be carefull with the angle of the recording. It needs to be vertical and below the point that has been chosen. Once all data are collected they can be analyzed and a coverage can be calculated.