Surveys in the Marshall Islands

NRAS Biodiversity assessments

Biodiversity is an important indicator of the health and viability of natural resources. With a global decline in overall biological diversity, an increasing extinction rate of terrestrial and marine species, and a call for preservation of all biotic richness and functionality, biodiversity has become both an indicator and tool for developing conservation plans.

Coral reefs have a high biodiversity rivaling that of tropical rainforests. The NRAS team is dedicated to incorporating biodiversity information along with other data into management plans and analysis' of conservation priorities. During the reef assessment components of NRAS projects, we always collect biodiversity information at the project locations. For each site, in addition to transect data, we record all the species present for at least hard corals and reef fishes. These species lists are created by experts in the respective fields during timed swims. For example, on Rongelap Island at Rongelap Atoll in 2002, the coral taxonomist Zoe Richards increased the coral species knows from Rongelap by 188 species to a total of 328. In 2004, in Majuro and Namu atolls, coral expert Jim Maragos from the US Fish and Wildlife Service, listed all species of scleractinian corals and catalogued them in photograhic atlas that are now a precious reference for the country. The fish ecologist, Maria Beger, was able to record 459 fish species in 14 dives on the same project. (For more information, download the 2002 Rongelap Trip report).

The diversity data allow the end user to have a quick overview of the quality and health of a reef area. For equal type of sites, high species diversity indicates a more complex habitat structure, better health and higher productivity than sites with lower diversity. Conservationists and managers can utilize the diversity data to determine conservation priority sites in a reserve network that represents a maximum of species and habitats.

FISH DIVERSITY. Fish species richness is assessed by the fish expert, using timed swims for 60 to 90 minutes at each survey site. All sites are sampled at least once. Underwater observations are recorded onto a plastic sheet on a slate. The most commonly seen species are pre-printed on the recording sheet and ticked when seen, other species are noted separately on the same sheet. Fish species are only recorded when their identification is absolutely positive. To supplement the visual census, on some occasions samples are obtained by capturing the fish using clove oil, which stuns small fish. This technique is used for smaller or cryptic fishes that are difficult to visually identify in situ. Underwater photos also aids with identification in a few cases. All fish species are given a semi-quantitative rating, following the DAFOR scale (Table 1). These ratings are given considering their relative abundance, i.e. fish species that usually occur in large aggregations are rated at the higher end of the scale.

Table 1. Semi-quantitative abundance rating for coral reef fishes.
Rating ......................Abundance
0.............................. None
1 Rare...................... 1 individual seen
2 Occasional............. 2 to 6 individuals seen
3 Frequent............... 7 to 50 individuals seen
4 Abundant.............. 30 to 200 individuals seen
5 Dominant.............. more than 200 individuals AND they form a major part of the overall biomass

The timed swim method involves a rapid descent to 25 to 30 m. Then the observer ascends slowly, swimming in a meandering fashion, and spends a considerable time of the dive in the surge zone.

CORAL DIVERSITY. Corals are surveyed by the coral expert. Each of the sites is sampled once. Coral species richness is assessed using timed swims for 60 mins at each survey site. The timed swim method involves a direct descent to 30 m, followed by a slow ascent, swimming in a zigzag path to the shallow parts of the reef where a large proportion of time is spent surveying the reef crest. All records are based on visual identifications made underwater, except where skeletal detail is required for species determination. In the latter case, reference specimens are collected and studied at the Museum of Tropical Queensland by Zoe Richards and Dr Carden Wallace (Acropora), and Dr Douglas Fenner (non-Acropora). Voucher specimens have been deposited in the Museum of Tropical Queensland (Townsville, Australia) and are available for viewing upon request. References for species identifications are Wallace, 1999; Veron, 2000; Hoeksema and Best, 1991; Wells, 1954; Nemenzo, 1976. Coral species were given a semi-quantitative abundance rating following the DAFOR scale (Table 1). An estimate of percentage cover of coral is given for each site along with recording the three most dominant species.

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