BIOT Science Expedition 2014 - Dr Elizabeth Widman Initial Report BIOT Science Expedition 2014 Sea Cucumbers

Long-term monitoring of Sea Cucumber Populations

Dr Elizabeth Widman, University of Warwick

Background

Holothurian (sea-cucumber) surveys lead by Professor Andrew Price were conducted in 2006 (76 transects Price et al. 2009) and 2010 (68 transects Price et al. 2013). Due to illness Prof Price was not able to participate in the 2014 expedition and I continued the long-term monitoring surveys in his absence using the established survey sites and sampling protocol (see below).

Methods

The sites identified for resampling were those that had been surveyed in both 2006 and 2010 (68 sites in total). In total 63 of the targeted 68 sites were resampled. Surveys at two sites in the northwest lagoon of Diego Garcia (Site 12 and 13 Price et al. 2009) were attempted but visibility proved too poor, two sites at North Brother were attempted (sites 42a and b Price et al. 2009) but rough conditions did not allow for an accurate survey to be undertaken, and one transect in the Salamon atoll (31c Price et al. 2009) was too deep to make accurate identifications and was therefore abandoned.

At each site a 2m x 100m (200 m2) transect was surveyed and the abundance and identity of any holothurians, substrate type and depth were recorded. If accurate identifications could not be made in the field, photos were taken and taxonomic experts consulted. GPS tracks were recorded for most transects, which will facilitate future resampling. 

In addition to the long-term monitoring of shallow habitats outlined above, photo-transect surveys were taken at 27 sites and will be used to assess the holothurian populations present in deeper reef habitats (25m - 5m). This will complement the long-term shallow surveys nicely by providing insight on the diversity and abundance of holothurian populations in deeper reef habitats across the Archipelago, something that has not, to my knowledge, previously been assessed.

Output

The 2014 holothurian data has now been compiled and added to survey data from previous expeditions. Statistical analyses are currently being undertaken to assess the temporal variability across the 63 sites and 5 atolls (Salomon, Peros Banos, Great Chagos Bank, Egmont, and Diego Garcia) and a manuscript summarising the results will be submitted for publication (target journal: Aquatic Conservation: Marine and Freshwater Systems). This publication will provide a summary of the status and potentially indicate any evidence of continued poaching of holothurians in Chagos. GPS tracks of transects and survey sites will be incorporated into the Chagos Resource Portal.

Figure 21: Juvenile seacucumber (Pearsothuria graeffei) near Danger Island on the Great Chagos Bank. Remarkably, juveniles mimic the exact colouration of the toxic nudibranch (Phyllidia varicosa). Photo credit: Dr Courtney Couch