Benthic Monitoring

Benthic Monitoring

Rapid Ecological Assessment Methods (REA)

Line-point-intercept (LPI) for Benthic Cover (2008-Present)

The current line-point-intercept (LPI) method identifies hard corals, octocorals, macroalgae, crustose coralline algae, turf algae, cyanobacteria, and sessile macroinvertebrates to the highest possible taxonomic resolution and records, along with sand cover, at 20-cm intervals along two 25-m transect lines set in a single file row (and separated by a 5-m intertransect space). These surveys generate 125 points per transect (250 points per site) that are used to determine percentage of cover of benthic organisms and sand at each REA site (prior to 2008, this method was implemented at 50-cm intervals along the two transects). In concert with LPI surveys, photographs are taken to record the benthos at intervals of 2 m and 5 m along the same two transect lines with a high-resolution digital camera mounted on a pole. This work generates 32 photographs per site that are later analyzed by benthic specialists at CRED, using the computer program Coral Point Count with Excel extensions (CPCe), to determine the benthic composition at the genus, functional or morphological group level for each REA site (similar photographs of the benthos taken at REA sites surveyed by the fish team also will be analyzed).

Roving-diver surveys may also be conducted at an REA site: a swath of 3-5 m on either side of the transect lines is surveyed to record algal species richness. If an algal species encountered during LPI or roving-diver surveys was not identifiable in the field, a sample is collected as a voucher specimen and subsequently cataloged and critically analyzed to ensure positive species identification. Provisions are made to ensure appropriate preservation and curation of each algal specimen. These voucher specimens along with the benthic photographs form permanent historical records, the former of algal diversity and the latter of the composition of benthic communities at each REA site.

The goal of photoquadrat surveys was to quantitatively describe the algal community and generate a comprehensive species list for each REA site. This method minimized time in the water but yielded the greatest amount of data possible. This method relied on a high-resolution digital camera mounted on a 0.18-m2 photoquadrat. Working at depths of 3-16 m, two trained observers moved along two transect lines with one observer placing the photoquadrat frame at predetermined, randomly selected points and operating the camera, while the other diver recorded the name and rank abundance of each algal species found in the photoquadrat at each point. A representative sample of each algal species in the first photoquadrat was also collected for later identification in the laboratory and to form historical voucher collections for each site. Once data were recorded, the photoquadrat was moved to the next random point and this procedure repeated. To prevent redundancy, at subsequent photoquadrats, samples were collected only of algal species not found in the first photoquadrat. This method was published in Preskitt et al. (2004).

Photographs were analyzed for percent cover implementing PhotoGrid or CPCe, software programs. Field-collected specimens were critically analyzed in the laboratory to ensure positive species identification, cataloged, and subsequently accessioned in research institution collections.