Shipping patterns associated with the panama canal: Effects on biotic exchange?

Abstract

Shipping has been a primary mode of trade for millennia and is undergoing constant change (Couper 1972; see Suez Canal chapter). Vessel size and speed have certainly increased through time. Worldwide, the number of recipient and source ports engaged in international commerce have increased in recent history, as have the cumulative number of vessel arrivals across these ports. Together, these changes in scale and tempo of shipping are driving the increased globalization of economies. Trade routes have also shifted through time. Changes in vessel characteristics such as motorization (speed), size, and refrigeration have overcome earlier physical or temporal constraints associated with some routes. New commodities and markets have emerged, and older ones have sometimes declined. Opening of new passages has resulted from discovery and the creation of canals. World events such as wars and trade embargos or agreements have limited use of preexisting routes. In addition, trade routes have also responded at various timescales to environmental changes (e.g. ice cover or water level surrounding passages) and storm events. Although it is evident that the scale, tempo, and routes of shipping are highly dynamic, the temporal and spatial pattern of changes and not been well documented to date. Many of the changes in shipping are punctuated rather than a gradual shift over time. Such shifts are exemplified by the advent of steamships or the opening of canals as new passage ways, which rapidly changed shipping on a global scale (Couper 1972, see Suez Canal chapter). Changes in shipping patterns affect not only transport of cargo but also transfer of organisms to new geographic regions. It is well known that many species are transferred unintentionally in the cargo of ships and by the hulls and ballasted materials of ships (Visscher 1928, Carlton 1985, Carlton and Geller 1993, Coutts 1999, Gollasch 2002). Upon release to a new geographic region, many species have established self-sustaining populations. Due to the magnitude of shipping and the extensive species pool associated with ships' ballast and hulls, shipping is a leading source of biological invasions in coastal ecosystems throughout the world (Cohen and Carlton 1995, Reise 1998, Ruiz et al. 2000, Fofonoff et al. 2003, Hewitt et al. 2004). In this chapter, we begin to explore some patterns of shipping associated with the Panama Canal (see Cohen, Panama Canal chapter I for history and description of the canal). The opening of this passage in 1914 was indeed a punctuated event, causing a change in commercial shipping on a global scale. We compiled historical records from the Panama Canal Authority to (a) describe changes in the magnitude of shipping through the Panama Canal from 1914-2004, (b) examine the directional flux of different vessel types, including the frequency of ballasted versus cargo laden transits, through the canal and (c) compare the magnitude of shipping through the canal to that of the largest port systems in the United States. Based upon this background, we consider the implications of creating this new passageway, and its expanding use, for biological invasions.