2015, while nearby shallow coastal kelp populations have been declining since the 1970s. Alongside this decline, the kelp beds have been replaced by invasive turf, defined as macroalgae that provide little three-dimensional structure but form on the bottom layers as filaments, branches, or plumes. In southwestern areas, turf is now covering 50-60% of the ocean floor. This, along with past overfishing, has helped push stocks towards collapse and hampered its recovery despite deep reductions in the number of fish caught, according to a study conducted by the Gulf of Maine Research Institute. Traditional calculations "consistently over-estimated the abundance of cod." From 2004, temperatures rose by more than per year, culminating in an ocean heat wave in the northwest Atlantic in 2012–13. History and political significance The gulf's relative proximity to Europe compared to other locations on the opposite side of the Atlantic made it an early destination for European colonization. French settlers founded a settlement on St. Croix Island in 1604. English settlers founded the Popham Colony on an island in the Kennebec River in 1607, the same year as the Jamestown settlement, followed by the Plymouth Colony on the shores of Massachusetts Bay in 1620. The cod fisheries that flourished in this ecosystem were able to support the Industrial Revolution occurring in Europe as well as playing a role during the 17th through early 19th century’s trade routes between Africa, the Caribbean, North America and Europe. In the 1960s and 1970s, there was a dispute between Canada and the United States over fishing and other resource rights in the Gulf of Maine, specifically in the Georges Bank region. This dispute was taken to the International Court of Justice, which delineated a maritime boundary through the gulf in 1984. The two nations continue to disagree on the sovereignty of Machias Seal Island and the waters surrounding it in the northeastern part of the gulf. In recognition of the gulf's importance to marine habitat, both nations currently maintain complementary embargoes against offshore oil and gas exploration activities on Georges Bank in the southern part of the gulf. As of the past twenty years, however, traditional maritime fisheries focused on large fish species such as cod experienced a stock depletion that hurt commercial fishing. In response, harvesting of lobsters and other invertebrates rose. These changes can largely be attributed to anthropogenic factors. There has also been a rise in marine aquaculture in