How to get the look

Start by duplicating the Background layer so you have a copy of the original image. Using the Crop tool at a 1:1 ratio, crop the seaweed image into a square. With the Elliptical Marquee tool and holding down Shift, draw a circle over the seaweed to create the round shape. (Get it as central as you can.) Go to Select > Inverse then press Delete to remove the outside area.

Add a new layer and fill it with a black background (Edit > Fill > Contents Black); place that layer under the working image. You should now have a floating circle in a black space.

Now for the artistic bit! As before add a new layer and fill it with black. Change the Opacity to 80% and add a black Layer Mask. Using a white brush (between 10% and 30% opacity), paint away the bottom part of the ball to bring back the black. Aim to get a gradual blend from dark to light. Add another new fill layer (this time 50% grey) and change the layer Blending Mode to Overlay. With the Burn tool (Range set to Midtones at 20%), paint over the bottom part to darken it further.

On a new layer, add a small white square to make a reflection glare. Go to Edit > Transform, then use a combination of the Distort, Perspective and Warp settings to adjust the square so it bends. Change the Opacity setting to 90%.

Finally, to tweak the colours, add a Black and White Adjustment Layer and set Opacity to 70%. Add a Colour Balance Adjustment Layer and change the Tone setting to Shadows (Cyan -51, Green +50 and Blue+53). The last step is to use a Curves Adjustment Layer to tweak the contrast to your personal preference.