  We present observations of polarized dust emission at 850 $\mu$m from the L43
molecular cloud which sits in the Ophiuchus cloud complex. The data were taken
using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the
BISTRO large program. L43 is a dense ($N_{\rm H_2}\sim 10^{22}$-10$^{23}$
cm$^{-2}$) complex molecular cloud with a submillimetre-bright starless core
and two protostellar sources. There appears to be an evolutionary gradient
along the isolated filament that L43 is embedded within, with the most evolved
source closest to the Sco OB2 association. One of the protostars drives a CO
outflow that has created a cavity to the southeast. We see a magnetic field
that appears to be aligned with the cavity walls of the outflow, suggesting
interaction with the outflow. We also find a magnetic field strength of up to
$\sim$160$\pm$30 $\mu$G in the main starless core and up to $\sim$90$\pm$40
$\mu$G in the more diffuse, extended region. These field strengths give
magnetically super- and sub-critical values respectively and both are found to
be roughly trans-Alfv\'enic. We also present a new method of data reduction for
these denser but fainter objects like starless cores.
