1. Travel and human interactions
Globalization started centuries ago, with the daring and pioneering journeys of such famous travelers as Marco Polo and became obviously greatly more intense with the discovery of America and the subsequent trade and commerce. But this process has become recently more intense, so many biogeographical barriers have been broken, with vast areas of the globe being occupied by greater numbers of highly successful invasive species, especially agricultural pests (Mooney, in press) which represent huge economic impacts. Vitousek at al. (1996) have shown that some regions, all of them islands, have proportions of non-native vascular plants close to 50 per cent. Mooney (op cit) mentions that the Mediterranean region, where humans have interacted for a long time and evolved with plants [crops], have only about 1% of non-native species; this is equally true for Mexico. These regions are centres of origin of most the world's weeds.
A very important problem is exploitation. Mining and fisheries are really very good examples of this. The tonnage of caught fish in the world leveled off at the end of the eighties at some 100 million tons per year. This leveling off means not only a reduction in commercial fish populations but an enormous total depletion of resources. This resulted from the new and very efficient, very destructive catching techniques developed during the eighties. You have a range of new ways of using sonar, radar, etc. of locating bands of fishes. This allows you to increase your efficiency as the fisherman. This has occurred so greatly that years later it has caused one of the biggest crashes in the fishing industry that we've seen. Many of the species still haven't recovered. Most fish stocks are presently being fully harvested. Others are exploited at unsustainable levels and an increasing number have crashed after peaking.
3. Marine pollution and exploitation
Marine pollution adds to the stress imposed by another exploitation. Now it is becoming clear that aquaculture that was seen as a way of solving the problems of getting marine protein to feed people, is not really the substitute it was thought to be. Fishing is energy efficient on one hand, but causes the coastal systems to suffer and there are social and economic repercussions. The wiping out of lots of mangroves in areas due to agriculture now effects other economic activities of people in coastal areas. The management of the Oceanic Commons represented by international areas of fishing is proving to be extremely difficult. This delicate problem needs to be faced now at an international level and a much better way found rather than to continue what has occurred in the past.