Those are tetrapods. In Portugal we only use tetrapods, Antifer blocks and rock slabs if avaiable with the right size and density. The weight of the blocks is a function of the design wave height and period, so we have blocks with different sizes but not shapes. Sometimes we use blocks with high density concrete, cause higher density works both ways, it inscreases weight and reduces volume. You can see this in Sines, the blocks change colour on the tip of the breakwater, because the concrete has a higher iron content. https://www.google.com/maps/place/37%C2%B056'28.2%22N+8%C2%B...

There is one exception. In the Azores, there are core-locs because the breakwater was designed by the US Military. https://www.google.com/maps/place/38%C2%B043'36.6%22N+27%C2%...

Or composite rebar. Basalt fiber is sometimes used. Way cheaper than stainless and just as rust proof

Fiberglass rebar is comparable in cost, stronger, and not subject to water/salt damage. Rusting steel expands and cracks concrete from the inside, id want to avoid that. I’m actually building a pool right now using it instead of steel.

‘a little more costly?’ Lulz.

316 is an order of magnitude more expensive than the crap used in rebar.