Pressure indicators

Fisheries

The most direct impact of fishing on marine ecosystems is the removal of specimens of the target species. At the population level, this affects their size and structure, the relative numbers of males and females, their reproductive characteristics and potential, and the genetic composition (Heip et al., 2009; FAO, 2009). Under overfishing, populations may recover slowly, become genetically impoverished and may even become extinct at local or global levels. Additionally, fisheries also indirectly affect marine communities through the modification of habitats and the disruption of trophic web flows and dynamics (García et al., 2003; The Royal Society, 2003). Examples of changes in the abundance and species composition resulting from fishing activities have been observed in coasts and oceans around the world (see examples in García et al., 2003 and Sheffer et al., 2005). The trend in National fish catches and National fishing effort indicates the pressure on natural populations of both commercial species and the marine communities of which they are part. The former indicator is extensively used by international organizations (e. g. OECD, UN and European Community’s EEA), and by the environmental ministries of many countries, including Mexico. Both indicators are included in the chapter on Fishery resources.

The lack of selectivity of traditional fishing gear results in catching many species with no commercial value. In most cases, the "bycatch" is returned to the sea either dead or seriously injured. In addition to numerous types of fish and invertebrates, endangered species are also caught, including cetaceans, sharks and sea turtles (Lewison et al., 2004; Rodríguez Valencia and Cisneros Mata, 2006; FAO, 2009). The effects of fishing gear on the ecosystem depend, in addition to the fishing effort, on the biological characteristics of each species and the condition of their populations. Some of the observed effects of bycatch are: shifts in the relationships between predators and preys, disruption in the functioning of benthic communities, increased competition between species that use these resources, changes in the abundance and species distribution of scavengers (Rodríguez Valencia and Cisneros Mata, 2006). The Capture of bycatch provides direct evidence of damages to both populations of many commercial species and communities to which these belong. However, no accurate data are currently available on the volume of bycatch caught by the main national fisheries; hence, this indicator is not included in this publication.

Some types of fishing gear also alter the environment and destroy the habitat of many species. Trawls sweep the seabed in search of shrimp and other benthic fish species, which causes that sea grasses, sponges, corals and sea urchins, among others, are caught, injured or detached from the ocean floor (Freiwald et al., 2004; Rodríguez Valencia and Cisneros Mata, 2006; FAO, 2009). Reef-building species, both in shallow areas and deep waters, are highly vulnerable to damage from this type of fishing, similar to sediment-stabilizing species (e. g. seagrasses and polychaetes; Goñi, 1998; Groombridge and Jenkins, 2002; Roberts and Hirshfield, 2004; Rogers, 2004). With the loss of microhabitats created by sponges and corals, recruitment and feeding grounds are lost for other resident species, hence affecting their populations as well as the flow and dynamics of food webs. Hence, the Area affected by trawls serves as an indicator of disturbance and damage caused by fisheries, particularly shrimp fisheries, in communities located within fishing areas. Although the national area swept by this gear type has been estimated for one year, no regular data are available, making impossible to include this indicator here. However, the National shrimp production is useful as an indirect indicator of the effect of trawling on marine ecosystems in fishing areas.

Aquaculture consists in growing animal and plant species in freshwater, seawater or brackish water for commercial purposes or research. Despite the economic and social benefits it produces, improper aquaculture practices can lead to negative environmental impacts. These include changes in water quality and sediments (either by eutrophication due to high organic and inorganic nutrients and by pollution from antibiotics and pesticides), introduction of exotic species, death of marine mammals and seabirds in nets and cages, and genetic contamination of wild populations when cultured specimens escape (Arriaga et al., 1998; Groombridge and Jenkins, 2002; Barg, 2005). The National aquaculture production in coastal states assumes that yield could be directly related to negative and local environmental impacts derived from aquaculture. This indicator is used by environmental agencies or ministries of many countries (e. g. EEA, 2008), including Mexico.

Oil-related activities

Offshore oil and gas exploration/production affects coastal and oceanic ecosystems, its primary and most common impact being the deterioration of water quality (Arriaga et al., 1998; EPA, 1999; IPIECA, 2005), although spills causing serious ecological consequences occur occasionally. Discharges of oil into the sea are mainly due to natural leaks, discharges from refineries, distribution and retail activities by product end-users (IPIECA, 2005). In addition to the oil and gas escaping during extraction, seawater containing dissolved salts, organic compounds and heavy metals, including toxic chemicals, are also discharged to the sea (E&P Forum-UNEP, 1997; Patin, 1999).

Most coastal biological communities and their species are highly susceptible to direct contact with hydrocarbons and their derivatives that are dissolved in water (NOAA, 2001, 2002, 2003; Garcia Cuellar et al., 2004; IPIECA, 2004). The indicator Oil leaks and spills, pollutant discharges and congenital water in marine areas reveals the magnitude of pressure exerted by the wastes and products derived from oil activities on marine areas. This indicator is included in the UN list of Sustainable Development Indicators.

The search for deposits in marine environments also affects marine life. Seismic surveys and drilling are the most damaging activities associated to oil exploration. The sound waves generated by seismic surveys primarily affect fish, marine mammals and sea turtles, while drilling sludge and residues, as well as  hydrocarbons that are released in the process, degrade water quality and can directly affect deep-sea coral communities (García Cuellar et al., 2004; Freiwald et al., 2004; Roberts and Hirshfield, 2004; UNEP, 2004). Wells under development and exploratory in marine areas indicate the pressure of these activities on marine ecosystems in the Gulf of Mexico.

Coastal Development

The environmental goods and services provided by the coastal and ocean areas make them socially and economically important worldwide. Population growth in these areas impacts marine ecosystems (e. g. mangroves, estuaries, seagrass communities and coral reefs), mainly by overexploitation of resources, disruption and destruction of marine habitats, construction of infrastructure and increase in the generation of municipal and industrial waste that pollutes soil and water (GESAMP, 2001, Groombridge and Jenkins, 2002; UNEP, 2002; Marmulla, 2001). Population growth in the coastal zone, which for purposes of the indicator is defined as the continental area comprising the 263 coastal municipalities, points to the pressure of population growth on national marine ecosystems. Population growth rates are considered as pressure indicators in the UN list of Sustainable Development Indicators (ONU, 2007); here it is oriented towards the coastal zone of Mexico.

Tourism

Tourism is one of the fastest growing sectors in the global economy; in this respect, the coastal zone is strategic for many countries, including Mexico. Tourism causes three basic impacts on marine ecosystems: pressure for natural resources, water pollution and direct physical impacts (Arriaga et al., 1998; Burke et al., 2000; GESAMP, 2001; UNEP, 2002; UNEP, 2003). Pressure over natural resources is concentrated on fishing products, the effects or which are reviewed in the Fisheries Resources section. Water pollution results from the discharge of untreated wastewater from tourism facilities and vessels, leading to eutrophication and favoring the occurrence of "red tides" that damages corals through the proliferation of plankton and algae (GESAMP, 2001; NOAA, 2001; UNEP, 2002). Direct physical impacts derive from the construction and maintenance of infrastructure (e. g. marinas, docks, dredging operations and piers) and navigation activities (e. g. vessel anchoring and collisions), which disturb and destroy marine habitats (UNEP, 2002). The indicator Tourists in coastal destinations assumes that the number of visitors is directly related to the magnitude of impact on marine ecosystems adjacent to tourist areas. This indicator is used by the European Environment Agency (EEA).

Maritime transportation

While maritime transportation is one of the means with the lowest environmental impacts, when regulations are not observed it can affect marine ecosystems through water pollution or the introduction of exotic species (PNUMA, 2003). Pollution comes primarily from the discharge of waste from vessels, which in vulnerable areas may give rise to eutrophication and trigger some of the negative consequences mentioned in previous sections. The introduction of exotic species is frequently caused by organisms attached to vessel hulls or trapped in ballast water of ships that sail long distances; these accidental introductions may cause dramatic changes in marine ecosystems (Burke et al., 2000; GESAMP, 2001; PNUMA, 2003). The indicator Ocean freight and passengers transported indirectly reflects the intensity with which marine transportation impacts national marine ecosystems.

Invasive species

Although the movement of species from one region to another may be a natural phenomenon, human activities have considerably increased the frequency with which it occurs. Invasive species in marine ecosystems generally derive from marine vessel traffic (in hulls, cargo and ballast water); the intentional introduction and escape of species used in mariculture, non-commercial species associated with it, and aquarium species; and migration through artificial canals called "Lessepsian migration" (Groombridge and Jenkins, 2002; Golani et al., 2007; De Poorter, 2009). The presence of invasive species in marine communities changes the species composition and the relationships between predators and prey, previously unknown diseases and pathogens appear and, finally, many species may be displaced or become extinct either locally or globally in the short or long term (Mack et al., 2000;  Aguirre Muñoz and Mendoza Alfaro, 2009). Invasive species are recognized as a major cause of loss of biodiversity worldwide (EPA, 2003; Brawn and Sax, 2004; Aguirre et al., 2009). The indicator Invasive species in national marine and coastal systems shows the pressure of this problem on such ecosystems.

Global Climate Change

Global climate change resulting from the intrinsic variability of the climate system and external factors (both natural or derived from human activities) is evidenced in coastal and marine environments by the rising sea surface temperature (about 0.3 °C in the past 50 years) and mean sea level (which rose about 1 to 2 millimeters per year over the twentieth century, IPCC, 2007a). Its effects on biodiversity have been reported and are particularly evident in a number of marine species and their ecosystems. Examples include changes in species distributions, coral bleaching, diseases, changes in fish population sizes and wide fluctuations in the abundance of birds and marine mammals, mainly in the Pacific and Arctic Oceans (CBD, 2007; IPCC, 2007b). The indicator Variation in seawater temperature is useful to denote the pressure of this phenomenon on marine and coastal ecosystems. However, no sufficient data are available to document this indicator, so it is not included in this set of indicators.