In addition to the projects based around Viti Levu, REPICORE has an additional benthic project involving sea cucumbers on Vanua Levu. I (Steven Lee – ISATEC program) have developed this project along with the REPICORE team and the Wildlife Conservation Society (WCS) Fiji.
This project, based in Natuvu village, Wailevu, Vanua Levu, investigates the sedimentary effects of both overharvesting and aquaculture of Holothuria scabra on a reef flat. H. scabra (sandfish) have been heavily exploited across the Indo-Pacific region and are now classified as Endangered on the IUCN Red List. It is however challenging to argue for their protection if they have no demonstrable role in the ecosystem, and thus by investigating the impact of altering natural densities, we aim to provide a strong impetus for local communities and management bodies to establish conservation actions.
Natuvu village offers a unique system to study H. scabra (sandfish), with uncharacteristically high levels inside their periodically-harvested MPA. In order to investigate the impact of altering H. scabra populations, we have constructed 16 enclosures stocked with three different densities; (i) high density will simulate aquaculture conditions, (ii) natural density (based off preliminary surveys of Natuvu’s MPA) is used as a control, while (iii) low density will simulate overharvest of H. scabra. Finally, four enclosures lack mesh but have been subject to the same treatment of the other enclosures – this acts as our cage control.
We use a combination of static and process parameters – particularly Sediment Oxygen Consumption (SOC) and Dissolved Organic Carbon turnover (DOC) and grain size analyses – to investigate the capacity of sedimentary communities to process organic matter and nutrient loads. After only two time points there already appears to be variance between high and low density, and little variance between our natural and cage controls – however I am trying not to get my hopes up too much until we have at least four sets of measurements!
As a side project we have been using belt transects to get sea cucumber density and diversity estimates, but also microhabitat associations and link this to size classes. To achieve this, myself and Manasa (village fish warden/handy-dandy field assistant) have so far done a total of 12 100m belt transects (two of them at night), and have counted and measured the length of ca. 750 individual sea cucumbers! From this ca. 290 H. scabra have been measured and weighed to provide a length-weight relationship, and there is a clear relationship (R-squared = 0.87 so far….) between the two. I would like to continue this until reaching approximately 600 individuals… So far it looks quite promising, and the belt transects are a good way to keep myself sane while in-between SOC and DOC measurements. As sessile as sea cucumbers may seem, they have a talent for escaping our enclosures largely thanks to their mutable connective tissues/mutable collagenous tissue. We therefore have to check and maintain densities in all enclosures everyday thanks to this.
Great news!! We are very grateful to have both WCS Fiji and the Rufford foundation support this project: http://www.rufford.org/projects/steven_lee!!
That’s about it from my side, I’m off to the field this evening to start the third round of SOC and DOC, hopefully I can sneak in two more belt transects while I’m at it…