Another unexpected result of MPAs is their impact on predatory marine species, which in some conditions can increase in population. When this occurs, prey populations decrease. One study showed that in 21 out of 39 cases, "trophic cascades", caused a decrease in herbivores, which led to an increase in the quantity of plant life. (This occurred in the Malindi Kisite and Watamu Marian National Parks in Kenya; the Leigh Marine Reserve in New Zealand; and Brackett's Landing Conservation Area in the US.