ALTERATION OF COASTAL ECOSYSTEMS



Damage to coastal resources is the subject of widespread concern in Ecuador. 
Although many shrimp ponds have been constructed in salt flats ("i.e.", the dry
land that builds up through evolution of the mangrove system), maricultural
expansion has been considerable in intertidal areas alongside the shore. 
Particularly troubling has been the displacement of mangrove swamps.  Renewable
resources are also under threat because of excessive postlarvae (PL) capture
and water pollution.



Mangrove Deforestation


Remote sensing studies suggest that 118,000 hectares (ha.) of shrimp ponds had
been established along the Ecuadorian coast by 1987 (CLIRSEN 1988).  Of that
total, 38,500 ha. had been constructed in salt flats and 28,500 ha. directly
displaced mangrove swamps.  Urban expansion accounted for an additional 1,400
ha. of mangrove deforestation.  In all, 15% of the mangrove swamps and three
quarters of the salt flats existing in Ecuador in 1969 had disappeared by 1987,
the last year for which comprehensive data are available (table 2).

Coastal ecosystem destruction accelerated through the middle 1980s.  Swamp
displacement amounted to 21,600 ha. from 1969 to 1984.  This is equivalent to
annual losses of 0.7%.  Between 1984 and 1987, though, the mangrove
deforestation rate nearly doubled, to 1.3% "per annum," 6,900 ha. having been
lost (table 2).

Almost certainly, mangrove deforestation has slackened during the last few
years.  Shrimp prices are falling (see below), and capital needed to establish
a competitive maricultural enterprise has gotten scarce.  In addition, many of
the enterprises brought on line since 1987 have chosen to locate outside of
wetlands because soils in mangrove swamps tend to be highly acidic, which
creates problems for shrimp production.  To summarize, environmental as well as
economic factors are contributing to reduced mangrove deforestation.

Although conversion of wetlands into shrimp ponds is declining because of
environmental and economic factors, mangrove forests continue to be lost or
degraded because of urban expansion.  The slums of Guayaquil, Machala, and
other coastal cities tend to establish themselves in wetlands because, as is
noted later in this paper, those areas are essentially an open access resource. 
Even when wetlands are not directly displaced, ecosystem degradation occurs
because mangrove swamps are a source of charcoal and building materials.



Over-Fishing


Since mangrove deforestation appears to be decelerating (outside of a few
locations), shortages of shrimp PL are becoming a relatively more important
source of concern.

When the ocean off the Ecuadorian coast is warm, PL are abundant and no
operation has problems stocking its ponds.  There are a few thousand full-time
PL fishers, complemented by perhaps 10,000 working a few days a month (Scott
and Gaibor 1992).  As long as prices do not fall too low, a skilled gatherer
can earn $25 to $30/day (Thia-Eng and Kungvankij 1989, 7).

The capture of wild fry involves considerable losses.  Of the 9 to 12 billion
PL collected annually during the early and middle 1980s, only half were of the
desired species, "Penaeus vannamei."  Other kinds of shrimp were discarded,
usually on dry sand where they died.  Other organisms caught in the nets met
the same fate.  Mortality of "P. vannamei" was also high, exceeding 80% between
the beaches and the ponds (LiPuma and Meltzoff 1985, 20).

In a good or ordinary year, these losses have no great effect on Ecuadorian
mariculture.  But when coastal waters are cool, populations of juvenile shrimp
in the wild fall dramatically, which can cause some pond capacity to lie idle. 
To guard against this risk, the industry began constructing hatcheries in the
middle 1980's.  Existing hatcheries, which number 120 or so, can satisfy as
much as 65% of industry demand (Barniol 1992).

A few operations, at which mature shrimp are mated repeatedly to produce PL
(Barniol 1992), are largely insulated from the impacts of over-fishing and
habitat destruction.  But most hatcheries are not self contained.  Instead,
gravid females captured by ocean-going trawlers and artisanal fishers are the
primary source of seed.  Needless to say, these latter facilities can suffer
when gravid females become scarce, which occurs from time to time.



Water Pollution


The environmental impacts of mariculture development are not limited to
uprooting of mangroves and collecting too many PL and gravid females in the
wild.  Wastewater discharged from shrimp ponds impairs water quality in the
Gulf of Guayaquil and other coastal waters, which are already threatened by
pollution from urban, industrial, and agricultural sources.

Many maricultural operations around the Gulf of Guayaquil are semi-extensive,
with pond stocking rates ranging from 10,000 to 50,000 PL/ha. (Villalon et al.
1989, 251).  At those rates, supplementary fertilization, with urea and
superphosphates, is needed to induce the phytoplankton blooms on which
juveniles feed.  Fertilization, along with supplemental feeding for larger
stock, depletes oxygen.  If dissolved oxygen levels fall too low, shrimp die.

To avoid this outcome, seawater is exchanged, through pumping, for pond water. 
Water flushed from ponds contains nutrients, which increases biological oxygen
demand in surrounding waters.  Nutrients are also available for biological
uptake, which Twilley (1989, 98) suggests might contribute to the red tides
(blooms of red-colored toxic algae) observed occasionally in the Gulf of
Guayaquil.  The same author also speculates that daily discharges of semi-
extensive operations' wastewater, which can be highly saline (Snedaker et al.
1986), into the Gulf of Guayaquil might exceed fresh water yield from the Rio
Guayas Basin during the dry season (Twilley 1989, 98).

Aside from what takes place in habitats adjacent to maricultural enterprises,
the environmental impacts associated with discharging wastewater from ponds
probably pale in comparison with water pollution from other sources.  Solorzano
(1989) finds that emissions of untreated domestic and industrial waste from the
City of Guayaquil is a principal cause of high bacterial contamination, low
dissolved oxygen content, and high nutrient concentrations in the Daule and
Guayas Rivers, which are the principal freshwater tributaries of the Gulf of
Guayaquil.  Water pollution around other coastal cities is, likewise, severe. 
Solorzano (1989) also reports high nitrate and pesticide pollution from
agricultural sources.  Finally, freshwater flow into the Gulf during the peak
of the wet season has been reduced significantly since completion of the Daule-
Peripa dam (Arriaga 1989, 151).  However, the same project has probably caused
freshwater flow to increase during the dry season when salinity is potentially
a more serious problem.