Pressure indicators

Development in coastal areas harbouring coral reefs

Population growth in coastal areas directly and indirectly impacts coral reefs. Infrastructure construction, extraction of building materials such as sand and limestone to produce cement, and the dredging of harbours and navigation channels are among the major direct impacts (Bryant et al., 1998; Wilkinson, 2000, 2002). Similarly, municipal and industrial wastewater discharges, with their heavy loads of nutrients and sediments, impair water quality, indirectly affecting corals’ growth and survival and fostering the proliferation of algae that eventually overgrow and replace corals (GESAMP, 2001; NOAA, 2001; UNEP, 2002). The indicator Population growth in coastal areas harbouring coral reefs indirectly reflects the demographic pressure on these ecosystems.

Tourism in coastal areas harbouring coral reefs

Tourism is one of the fastest growing activities in coastal areas around the world (Wilkinson, 2002, Cesar and Chong, 2004), and coral reefs are one of their main attractions for thousands of tourists who, each year, seek direct contact with their natural beauty. However, tourists directly affect these ecosystems through the physical damage produced by their vessels’ anchoring, trampling or collecting of parts of or whole coral specimens (Bryant et al., 1998; Lang et al., 1998; GESAMP, 2001; Agardy, 2004). In addition, seafood demand indirectly affects the species composition and dynamics of coral communities; moreover, sewage discharges from hotels and other tourism facilities increase water turbidity and foster eutrophication that might lead to corals death (Lang et al., 1998; GESAMP, 2001; NOAA, 2001; UNEP, 2002). The indicator Number of tourists in coastal destinations harbouring coral reefs implies that the number of visitors is directly related to the pressure imposed on these ecosystems.

Fishing in coastal areas harbouring coral reefs

Over-exploitation of species populations used for human consumption by means of conventional fishing gear and destructive fishing methods (bottom trawling, blast fishing or cyanide fishing) are the fishing practices most damaging for coral reef ecosystems (Bryant et al., 1998; Burke et al., 2000; NOAA, 2001). The main effects of those practices, in addition to habitat destruction and disturbance, are shifts in species composition and community dynamics which, in turn, lead to biodiversity loss in the short or medium term. Marine fisheries catch in coral reef areas may reflect the damage that this activity causes on coral reef communities. However, given the lack of reliable data for national fishery catches in coral reef areas, such indicator is not included in this report. We, instead, suggest looking at the indicator National fish catch in the Fishery resources chapter, to get an approximate idea of the pressure imposed by this activity on coral reefs. It should be noted that fisheries catch data from Mexican states harbouring coral reefs, by itself, would overestimate the fish volume caught in coral reefs.

Global Climate Change

It is currently recognized that the global warming recorded over the last 50 years has been very significantly influenced by human activities (IPCC, 2001; Hughes et al., 2003). This phenomenon, along with other compounding factors, affect coral reefs causing the so-called "coral bleaching" effect (Bryant et al., 1998; Burke et al., 2000; NOAA, 2001; Hughes et al., 2003). Coral bleaching is mainly due to the whitish appearance that corals and other cnidarians acquire as a result of their losing the symbiotic algae (zooxanthellae) that normally live within the polyps. While corals can recover if the stress is not too long, it sometimes leads to weakening and death (Wilkinson, 1998; Pandolfi et al., 2003). In this regard, the Variation in sea water temperature can serve as an indicator of the pressure that this factor imposes on coral ecosystems. However, as data available in Mexico are insufficient to document this indicator, it was not included in this report.