|Environment and development
in coastal regions and in small islands
Coastal region and small island papers 3
Puerto Morelos, Quintana Roo, México
Francisco Ruíz-Rentería, Brigitta I. van Tussenbroek, and Eric Jordán-Dahlgren
Estación Puerto Morelos, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ap. Postal 1152, Cancún 77500, Q.R., México
Puerto Morelos is located on the northeastern coast of the Yucatán Peninsula. This rapidly growing village depends on fishing and tourism. The climate is typically Caribbean, with a warm rainy season and a slightly cooler dry season. Carbonate rocks and sediments of Tertiary to Holocene origin cover most of the peninsula. The limestone is heavily karstified which, together with the lack of soil, accounts for the scarcity of rivers. Thus, coastal zone processes are influenced primarily by oceanic rather than terrestrial inputs. The dominant ecosystems are coral reefs, seagrass meadows, and inland wetlands that are partially colonized by mangroves. While continuous interactions exist between the coral reef and seagrass ecosystems, the wetlands are isolated by a sand bar, limiting exchanges to underground brackish water seepage and occasional storm wave intrusions.
Puerto Morelos is located on the northeastern coast of the Yucatan Peninsula, México (Fig. 1). The peninsula is a large, mostly flat, heavily karstified limestone platform formed by the deposition of Tertiary-Holocene carbonates and evaporites upon Jurassic-Cretaceous red beds (Ward, 1985). Rainwater filters rapidly through the limestone into the aquifer and there is very little surface drainage. Above 20°N latitude, the average annual underground freshwater discharge from the peninsula is estimated to be 8.6 million m3 per year per km of coastline (Back, 1985).
|Fig. 1. Feature map of the Puerto
Morelos CARICOMP site; isobaths
modified from Merino and Otero (1991)
At Puerto Morelos, the coastal zone is delimited on the landward side by 10 m high Pleistocene berms, which limit the inland extension of shallow and almost closed coastal lagoons colonized by wetland flora (Fig. 1). The wetland lagoons are isolated from the adjacent sea by a 2-3 m high, 100-200 m wide sand bar that constitutes the present shoreline. Rhizophora mangle stands occur as narrow belts along the edges of the lagoons or as small isolated patches in the central parts. Except for seawater input during major storms, which are rare events in this area, oceanic influence on the wetlands is small. Small-scale discharge of fresh or brackish wetland waters occurs through submarine springs and by overflow through small canals during the rainy season. Seaward from the sand bar, the typical environment is a coast fringed by a reef. The reef lagoon (or reef channel) is several hundred meters wide and 3 to 4 m in average depth; the bottom is covered by calcareous sand, which is stabilized by seagrass meadows. In certain areas, however, the underlying calcareous pavement is exposed and is colonized by coral reef communities typical of hardgrounds or is covered by unconsolidated carbonate sediments. The reef is a shallow barrier with little Holocene accretion and morphology determined primarily by events of the middle and late Pleistocene (Ward, 1985). Seaward from the crest, the reef gently slopes to depths of 20-25 m, giving way to a mostly barren sand platform, which slopes gently for several kilometers. The shelf edge occurs at a depth of 40-60 m, followed by a drop-off to more than 400 m.
Puerto Morelos is a small fishing and tourist village with a permanent population of ca. 3000 people, plus a seasonal population of 100 to 200 (Gobierno del estado de Q.R., Mexico, 1996). Half of the inhabitants live in the coastal zone on the sandbar, the remainder live landward on the Pleistocene berms (Fig. 1). Commercial fishing principally comprises lobsters Panulirus argus and P. gutattus (Lozano et al., 1991) and fishes such as barracuda, snapper, grouper, hogfish and, to a certain extent, triggerfish. The average fish size and population size of these species seem to have decreased considerably in recent years, but other reef fish species are still relatively untouched. Both commercial and subsistence fishing employ lobsterpots, spearguns, gill nets, and line and hook. In recent years, tourism has increased and, at present, an average of six boats (with about ten people per boat) make daily trips to the coral reef. The impact of these activities on the reefs has not yet been assessed.
Urbanization for tourism development and residential housing is rapidly increasing, resulting in landfill and deforestation in the wetland areas. Puerto Morelos is not yet equipped with a central sewer system, and wastes are discharged either into septic systems or directly, without any treatment, into holes in the ground. Urbanization is expected to increase in the near future, as the government considers development of a tourist resort in the coastal area and an industrial zone landward. At present, however, the Puerto Morelos area is still relatively pristine.
Atmostpheric and Oceanic Characteristics
According to the official climate charts (Secretaría de la Presidencia, 1970a), the climate in the region is warm, sub-humid with marked rainy seasons. Merino and Otero (1991) reported an average yearly air temperature of 26.3°C, with a summer high of 32.5°C and a winter low of 13.0°C for the period 1982-1983. CARICOMP data collected from 1992 show a similar seasonal distribution of air temperature. The highest temperature of 34.5°C was recorded once in summer and once in autumn. The lowest temperature was 12.5°C, in the winter. According to Merino and Otero (1991), average yearly rainfall is 1,123 mm. However, rain can be quite variable in Puerto Morelos. During the period 1982-1983 there was more rain during the dry season (January-May) than during the rainy season (June-November). CARICOMP meteorological data are collected 6 m above sea level. Rain data from 25 November 1992 through 25 November 1993 show rainfall throughout the year, with a yearly total of 1,804 mm; the driest month was April. The site is under the influence of trade winds in the summer, with velocities averaging 5 m s-1 (Merino and Otero, 1991), which are interrupted for periods of 3 to 10 days in winter by intense cold winds from the north. Tropical storms and hurricanes occur from time to time along the eastern coast of Yucatan. In the last 30 years, three hurricanes have passed over Puerto Morelos: Beulah, a Force 3 hurricane in 1965; Allen, a Force 5 hurricane in 1980; and Gilbert, a Force 5 hurricane in 1988. Shortly after Gilbert, a tropical storm-hurricane named Keith also struck the area. In October 1995, Hurricane Roxanne crossed the coast ca. 100 km south of Puerto Morelos; not much damage was done.
On oceanic scale, the principal feature is the Yucatan Current (precursor of the Gulf Stream), which parallels the edge of the continental shelf off Puerto Morelos. GEK measurements of northward flow in the Yucatan Strait indicated maximum velocities of 4-5 knots (Molinari and Cochrane, 1970). Nowlin and Hubertz (1970) obtained more moderate values, 1-2 knots. Cochrane (1966) and Ruiz (1979) suggested that the direction and intensity of the current changes with seasons. Tides in this region of the Caribbean are mixed semi-diurnal, with a small range of 0.24 m, as shown by tide tables for Cozumel Island situated 60 km south of Puerto Morelos (Instituto de Geofísica, 1992).
Oceanographic data are sparse for Puerto Morelos. Circulation in the reef lagoon is mostly parallel to the coast (unpublished data). Currents change in speed and direction, due to a combination of variables: influence of the Yucatan Current, winds, wave spillage over the reef, and the location of surge channels. Waves in the reef lagoon are low; Merino and Otero (1991) measured a height of 0.14 m. No data are available for open ocean wave height, but from personal observation, 1 m is the average. Table 1 shows the average values of several water quality parameters at Puerto Morelos 1982-1983 by Merino and Otero (1991). CARICOMP weekly data during 1992-1993 (Fig. 2) at three sampling locations show similar mean water temperature and salinity as those in Table 1. Salinity and temperature appear to be almost the same for the three CARICOMP locations. However, slight differences are appreciable in transparency data between the sampling stations.
|Table 1. Water quality parameters at Puerto Morelos, sampled monthly from March 1982 through July 1983 (Merino and Otero, 1991).|
|Wave height||0.14 m|
|Max sea level variability||0.68 m|
|Dissolved oxygen||4.99 mg l-1|
|Alkalinity||2.5 meq l-1|
|Nitrite||0.06 µg-at l-1|
|Nitrate||13.9 µg-at l-1|
|Silicate||5.8 µg-at l-1|
|Ammonia||0.08 µg-at l-1|
|Phosphorus||5.04 µg-at l-1|
|Particulate carbon||99.1 mg l-1|
|Fig. 2. Temperature, salinity and
Secchi disk measurements at seagrass and
coral reef stations. Secchi measurements were taken horizontally at the lagoon
stations, vertically in open ocean close to the reef station.
The mangrove wetlands in the shallow coastal lagoon are isolated from the sea by the sand bar, and interaction between seagrass beds and coral reef is thus virtually absent. The wetland lagoon is heavily perturbed by deforestation for urbanization and most of the mangrove area bordering the sandbar is privately owned. Additionally, water circulation in the lagoon has been interrupted by the construction of roads running from the sand bar to the highway (Fig. 1). Due to the absence of an untouched area near the other CARICOMP sampling stations, a suitable mangrove sampling station has not been located to date.
Lagoon vegetation can roughly be divided into three distinct zones: (1) a narrow coastal fringe, (2) a broad mid-lagoon zone, and (3) an area of backreef vegetation (Table 2). The abundant vegetation of the coastal fringes is dominated by either Thalassia testudinum or Syringodium filiforme, which are accompanied by rhizophytic algae. Occasionally mats of Halodule wrightii or Caulerpa spp. are found close to the beach in front of this well-developed fringe.
|Table 2. Characteristics of vegetation zones in the Puerto Morelos reef lagoon (van Tussenbroek, unpub. data).|
(g m-2 dry weight)
|Vegetation Zone||Characteristics||T. testudinum||S. filiforme|
|Coastal Fringe||20-50 m wide well-developed vegetation|
|S. filiforme dominated||25-45||20-30||± or +|
|T. testudinum dominated||5-20||100-160|
|Mid-Lagoon Zone||200-1,000 m wide|
|Typical||T. testudinum dominated||20-35||2-12||±|
|High density||T. testudinum dominated||50-80||2-5|||
|Low density||algae dominated||20-20||10-30||+|
|Backreef Zone*||100-400 m wide|
|Short T. testudinum||leaf length 9-10 cm||15-30||virt. absent|||
|Long T. testudinum||leaf length 13-15 cm||30-55||virt. absent||±|
|*Length of T.
testudinum in the backreef zone is the average length
of the largest leaves.
Key to algae abundance: , few; ±, more or less abundant; +, dominant.
The mid-lagoon zone covers the greater part of the lagoon. Denuded sandy areas, from 10 m2 to 100 m2, can be found throughout this zone. Bottom vegetation typically consists of a moderate density of Thalassia testudinum, with Syringodium filiforme, accompanied by rhizophytic algae; the sampling site off the UNAM research station is considered to be representative of this vegetation (Fig. 1). Thalassia testudinum reaches a high density in an area in front of a mangrove discharge; the high productivity sampling station is located here (Fig. 1). Off the village, in contrast, the mid-lagoon seagrass density is low, and rhizophytic algae and floating forms of Lobophora variegata (max. standing crop: 100 g m-2 dry weight) or Laurencia intricata (max. standing crop: 20 g m-2) generally dominate.
In the backreef zone, T. testudinum has generally very short leaves. Syringodium filiforme and rhizophytic algae are virtually absent. Only in front of the village, where the backreef area is more protected due to a broad reef crest, T. testudinum leaves tend to be larger than in the rest of this zone.
In the reef lagoon,Thalassia testudinum shows seasonal fluctuations in leaf biomass and productivity: maximal in the summer and minimal in the winter months (Fig. 3). It is possible that the present coral reef lagoon vegetation is still in an intermediate state of recovery from the disturbance caused by Hurricane Gilbert in 1988. Population analysis from Thalassia testudinum short-shoots sampled in two transects from the coast to the coral reef suggest that T. testudinum was not removed in the backreef areas. T. testudinum lagoon and coastal populations, however, showed a sharp decline in pre-hurricane short-shoots, suggesting that these turtle grass populations were affected by the storm (van Tussenbroek, 1994).
|Fig. 3. T. testudinum leaf
standing crop and productivity measured from
August 1990 through January 1992 at the high productivity sampling
station in the Puerto Morelos reef lagoon (van Tussenbroek, 1995).
No T. testudinum was apparently removed from the high density CARICOMP station in front of the wetlands discharge. The most common rhizophytic algae found throughout the lagoon are Penicillus capitatus, Rhipocephalus phoenix, R. oblongus, Udotea flabellum, U. spinulosa, and Halimeda incrasata; Avrainvillea spp. are abundant in some coastal areas.
Puerto Morelos is situated in the northern part of an extensive barrier-fringing reef tract that extends from Belize to the Yucatan Strait. In contrast to the southern reefs, however, reef development in the northern part of the tract tends to be limited to reef crests and backreef zones (Jordán-Dahlgren et al., 1981). The Puerto Morelos reef consists of an extensive calcareous platform that is bevelled on the seaward side, probably by eustatic changes during the Pleistocene. Primarily oceanic forces influence this reef: the Yucatan Current and the large fetch of the waves at this latitude. Five main zones are recognized along the reef profile (Fig. 4), based upon scleractinian composition and reef topography (Table 3). This pattern is similar to that of other areas with a similar geomorphological setting along the Eastern Yucatan reef tract (Jordán-Dahlgren et al., 1981; Jordán-Dahlgren, 1989). A sloping forereef with few high relief features is characteristic of these reefs. Perhaps in part due to this reef morphology, which favors sand accumulation and its resuspension and transport during storms, live scleratinean coral cover on the forereef zone is typically sparse. In contrast, coral cover tends to be dense at the reef crest (Acropora palmata and Millepora complanta) and in the backreef zone (A. palmata and Montastraea annularis). In the forereef zone, the most conspicuous components of the biota are gorgonians, macroalgae, and small hemispherical coral heads of Diploria strigosa, Montastraea cavernosa, and dichocoenia stokesii, among many others. The algae seldom exhibit significant vertical growth, except for seasonally occurring Sargassum spp. and Turbinaria spp. In the few places where high relief reef features exist, the coral community tends to be strongly dominated by large scleractinian colonies, as in any other well developed coral reef.
|Fig. 4. Reef
profile at the Puerto Morelos CARICOMP site. Zonation is
based on scleractinian species composition and bottom relief (modified
from Jordán et al., 1981): I lagoon zone; II backreef zone; III breaker zone;
IV forereef zone; V sand platform zone.
|Table 3. Coral reef zonation and dominant scleractinian fauna at Puerto Morelos.|
|Bottom type and dominant biota||Scleractinian Fauna|
|Range||Jordán-Dahlgren et al., 1981||Rodriguez-Martinez, 1993|
|Lagoon||400-500||0.1-6.0||seagrass, sand, hardground||14||2.0||M. aereolata A. agaricites M. annularis||12||1.0||M. aerolata
|Backreef||30-300||1.0-3.0||seagrass, coral, macroalgae, sand, hardground||27||28.4||M. annularis
|A. millipora||25-75||0.4-1.2||hardground, coral, coral rubble||14||27.1||M. complanata
|Barren||50-100||1.3-3.5||hardground, macroalgae, sponges||7||3.1||A. palmata||3||1.0||M. complanata|
|at 5 m||100-150||3.6-7.5||hardground, macroalgae, sponges||17||7.4||S. siderea
|at 10 m||100-200||7.5-12.5||hardground, gorgonians, macroalgae||17||7.1||D. strigosa
|at 15 m||100-200||12.6-17.5||hardground, gorgonians, macroalgae||14||4.6||M. cavernosa
|at 20 m||150-300||17.6-22.5||hardground, gorgonians, macroalgae, sponges||12||1.9||S. siderea
|Sand Platform||> 500||20.0-40.0||sand, macroalgae|
The CARICOMP reef sampling station is located on a typical low-relief forereef (Fig. 1). The overall condition of the coral communities of this reef seems good; no extreme situations of bleaching, algal growth, or fish kill have been recorded in the area. At present, the reef is still recovering from the devastating effects of Hurricane Gilbert in 1988 (Table 3). Natural regrowth and recolonization are proceeding at an also variable rate, both between and within the reef zones. Additionally, Diadema antillarum urchins, which almost disappeared after the pan-Caribbean demise and which were further affected by Gilbert in 1988, are gradually becoming abundant again. The reef has undergone, and is recovering from, the effects of a major bleaching event that affected most of the Caribbean Sea during the last months of 1995. No evaluation of its effects has been done.
Special thanks to Rosa Rodriguez who helped in the preparation of this manuscript and participated in field work. We would also like to thank Laura Celis for drawing the map.
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