Suva, Oct 2015

Ryan McAndrews and Uli installing algal productivity tiles underneath the boat

Ryan McAndrews and Ulrich Pint – our scientific diving mission leader – installing algal productivity tiles underneath the boat

Crab traps acting as fish exclusion cages to investigate productivity in the absence of grazing

Modified crab traps acting as fish exclusion cages to investigate productivity in the absence of grazing

Coral recruitment tile with microstructure

Coral recruitment tile with microstructure

After drilling 18242 (!) 1mm deep holes into 140 sandstone tiles, several methodological discussions, an unknown number of trips to hardware stores and many dives, we have finally completed the tile installation at Namuka Reef, near to Suva. We are interested in three different questions here; (i) how do locally marine managed areas (LMMAs) in Fiji support coral recruitment, (ii) how do LMMAs affect herbivory function in controlling algal productivity, and (iii) is coral recruitment higher when the settlement surface comprises a microstructure?

To investigate the effect of LMMAs on coral recruitment we have placed replicate 15 x 15cm sandstone tiles at two depths inside and outside of the Navakavu tabu area (pronounced tambu in Fijian – meaning area closed to fishing). Each tile has been individually fixed to dead reef substrate using stainless steel screws with a spacer (allowing recruits to settle underneath) at ca. 45ยบ angles to prevent sedimentation. Little is known about coral recruitment in Fiji, and so our local collaborators are keen to see the results from this study. At these same sites, the team has also fixed replicate tiles with a microstructure drilled into the upper surface to provide surface area for algal propagules to settle into. Half of these tiles remain exposed, and half are within cages (made with crab pots which were modified for us by the community at Waiqanaki Village), enabling us to measure the proportion of algal biomass removed by fish. The information from this study will add further dimension to the in situ GoPro video observations of fish grazing, as well as fish biomass transects to provide a thorough quantification of the effectiveness of local management in the area in promoting the function of herbivorous fish. To further test coral recruitment, we drilled a microstructure into both sides of a further group of tiles in order to assess the effect of providing a structure vs. no structure on coral recruitment. As naturally occurring bare reef substrate is far from flat, this may be a better way to represent real conditions. As coral recruitment is critical in supporting reef recovery following disturbances, it is important to continue to explore the most effective methods to measure this process.

The tiles will remain on the reef for three months, at which point the team will collect them, scrape them and each person will investigate further into their specific question. Fingers crossed now that fishermen and poachers from outside the local villages don’t help themselves to the crab pots in the mean time, and that no cyclones hit as the season is approaching…. The team is now heading back to Beqa Island for two weeks to label coral-algal interactions and to compare coral reef functioning inside and outside of the LMMA at Dakuni village.


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