La Parguera, Puerto Rico 
The Geography of Puerto Rico
 
Puerto Rico is a territory of the United States with commonwealth status. The island of Puerto Rico is located between the Caribbean Sea and the North Atlantic Ocean, east of the Dominican Republic and approximately 1000 miles east-southeast of Miami, Florida. Puerto Rico is an important location along the Mona Passage, which is a key shipping lane to the Panama Canal. The City of San Juan has one of the largest and best natural harbors in the Caribbean.  

Source: CIA World Factbook: https://www.cia.gov/library/publications/the-world-factbook/geos/rq.html

The La Parguera site is located on the southwestern edge of Puerto Rico. According to Guild et.al.(n.d), “[The] La Parguera [shelf] has numerous bank reefs that protect the shore from intense wave action, resulting in extensive seagrass meadows and a coastline dominated by mangroves with algal plains, sandy lagoons, and two bioluminescent bays.”
 
Note:  Build up of coastal areas has resulted in sewage outfalls at La Parguera; overfishing and changes in biodiversity leads to rapid coral die-back.
 
Source: Guild, Liane, B. Lobitz J. Goodman, R. Armstrong, F. Gilbes, R. Berthold, and J. Kerr.   n.d. Imaging spectroscopy and spectral analysis in support of coral reef ecosystem biodiversity research,

Coral Reef Structure and Development

Information on the Structure of Coral reefs is condensed from the original version available at: NOAA’s Coral Reef Information System (CoRis): http://coris.noaa.gov/about/what_are

Photographs were omitted from the geographic summary

The Structure of Coral Reefs

Darwin’s three stages of atoll formation. Coral reefs begin to form when free-swimming coral larvae (planulae) attach to the submerged edges of islands or continents. As the corals grow and expand, reefs take on one of three major characteristic structures—fringing, barrier or atoll.Fringing reefs, which are the most common, project seaward directly from the shore, forming borders along the shoreline and surrounding islands. Barrier reefs also border shorelines, but at a greater distance. They are separated from their adjacent land mass by a lagoon of open, often deep water. If a fringing reef forms around a volcanic island that subsides completely below sea level while the coral continues to grow upward, an atoll forms. Atolls are usually circular or oval, with a central lagoon. Parts of the reef platform may emerge as one or more islands, and breaks in the reef provide access to the central lagoon (Lalli and Parsons, 1995; Levinton, 1995; Sumich, 1996). In the 1830s, Charles Darwin distinguished between the three main geomorphological categories of reefs, and suggested that fringing reefs, barrier reefs, and atolls were all related stages in the sequence of atoll reef formation. All three reef types—fringing, barrier and atoll—share similarities in their biogeographic profiles. Bottom topography, depth, wave and current strength, light, temperature, and suspended sediments all act to create characteristic horizontal and vertical zones of corals, algae and other species. While these zones vary according to the location and type of reef, the major divisions common to most reefs, as they move seaward from the shore, are the reef flat, reef crest or algal ridge, buttress zone, and seaward slope.

Graphic of typical coral reef zones.

The reef flat, or back reef, is located on the sheltered side of the reef. It extends outward from the shore; and may be highly variable in character. Varying in width from 20 or 30 meters to more than a few thousand, the reef flat may range from only a few centimeters to a few meters deep, and large parts may be exposed at low tide. The substrate is formed of coral rock and loose sand. Beds of sea grasses often develop in the sandy regions, and both encrusting and filamentous algae are common.

Because it is so shallow, this area experiences the widest variations in temperature and salinity, but it is protected from the full force of breaking waves. Reduced water circulation, the accumulation of sediments, and periods of tidal emersions—when the reef is exposed during low tide—combine to limit coral growth. Although living corals may be scarce except near the seaward section of this zone, its many microhabitats support the greatest number of species in the reef ecosystem, with mollusks, worms and decapod crustaceans often dominating the visible macrofauna (Barnes, R.D., 1987; Lalli and Parsons, 1995; Sumich, 1996).

The reef crest, or algal ridge, is the highest point of the reef, and is exposed at low tide. Lying on the outer side of the reef, it is exposed to the full fury of incoming waves. The width of this zone typically varies from a few, to perhaps 50 m. In this severe habitat, a few species of encrusting calcareous red algae flourish, producing new reef material as rapidly as the waves erode it. Where wave action is severe, living corals are practically nonexistent, but in situations of more moderate wave action, the reef crest tends to be dominated by stoutly branching corals. These closely growing, robust colonies form ramparts able to withstand the heavy seas. Small crabs, shrimps, cowries and other animals reside in the labyrinthine subsurface cavities of the reef crest, protected from waves and predators (Barnes, R.D., 1987; Lalli and Parsons, 1995; Sumich, 1996).

The outermost seaward slope (also called the fore-reef) extends from the low-tide mark into deep water. Just below the low-tide mark to approximately 20 m depth is a rugged zone of spurs, or buttresses, radiating out from the reef. Deep channels that slope down the reef face are interspersed between the buttresses. These alternating spurs and channels may be several meters wide and up to 300 m long (Barnes, R.D. 1987; Lalli and Parsons, 1995; Sumich, 1996).

The buttress zone serves two main purposes in the reef system. First, it acts to dissipate the tremendous force of unabating waves and stabilizes the reef structure. Second, the channels between the buttresses drain debris and sediment off the reef and into deeper water. Massive corals and encrusting coralline algae thrive in this zone of breaking waves, intense sunlight, and abundant oxygen. Small fish inhabit the many holes and crevices on this portion of the reef, and many larger fish including sharks, jacks, barracudas and tunas patrol the buttresses and grooves in search of food (Barnes, R.D., 1987; Lalli and Parsons, 1995; Sumich, 1996).

Continuing down the seaward slope to about 20 m, optimal light intensity decreases, but reduced wave action allows the maximum number of coral species to develop. Beginning at approximately 30 to 40 m, sediments accumulate on the gentle slope, and corals become patchy in distribution. Sponges, sea whips, sea fans, and ahermatypic (non-reef-building) corals become increasingly abundant and gradually replace hermatypic corals in deeper, darker water (Barnes, R.D., 1987; Lalli and Parsons, 1995; Sumich, 1996).

From Polyp to Reef

Massive reef structures are formed when each stony coral polyp secretes a skeleton of CaCO₃. Most stony corals have very small polyps, averaging 1 to 3 mm in diameter, but entire colonies can grow very large and weigh several tons. Although all corals secrete CaCO₃, not all are reef builders. Some corals, such as Fungia sp., are solitary and have single polyps that can grow as large as 25 cm in diameter. Other coral species are incapable of producing sufficient quantities of CaCO₃ to form reefs. Many of these corals do not rely on the algal metabolites produced by zooxanthellae, and live in deeper and/or colder waters beyond the geographic range of most reef systems (Barnes, R.D., 1987; Sumich, 1996).

The skeletons of stony corals are secreted by the lower portion of the polyp. This process produces a cup, called the calyx, in which the polyp sits. The walls surrounding the cup are called the theca, and the floor is called the basal plate. Thin, calcareous septa (sclerosepta), which provide structural integrity, protection, and an increased surface area for the polyp’s soft tissues, extend upward from the basal plate and radiate outward from its center. Periodically, a polyp will lift off its base and secrete a new floor to its cup, forming a new basal plate above the old one. This creates a minute chamber in the skeleton. While the colony is alive, CaCO₃ is deposited, adding partitions and elevating the coral. When polyps are physically stressed, they contract into the calyx so that virtually no part is exposed above the skeletal platform. This protects the organism from predators and the elements (Barnes, R.D., 1987; Sumich, 1996).

At other times, the polyp extends out of the calyx. The timing and extent to which a polyp extends from its protective skeleton often depends on the time of the day, as well as the species of coral. Most polyps extend themselves furthest when they feed on plankton at night.

In addition to a substantial horizontal component, the polyps of colonial corals are connected laterally to their neighbors by a thin horizontal sheet of tissue called the coenosarc, which covers the limestone between the calyxes. Together, polyps and coenosarc constitute a thin layer of living tissue over the block of limestone they have secreted. Thus, the living colony lies entirely above the skeleton (Barnes, R.S.K. and Hughes, 1999).

Colonies of reef-building (hermatypic) corals exhibit a wide range of shapes, but most can be classified within ten general forms. Branching corals have branches that also have (secondary) branches. Digitate corals look like fingers or clumps of cigars and have no secondary branches. Table corals are table-like structures of fused branches. Elkhorn coral has large, flattened branches. Foliose corals have broad plate-like portions rising above the substrate. Encrusting corals grow as a thin layer against the substrate. Submassive corals have knobs, columns or wedges protruding from an encrusting base. Massive corals are ball-shaped or boulder-like corals which may be small as an egg or large as a house. Mushroom corals resemble the attached or unattached tops of mushrooms. Cup corals look like egg cups or cups that have been squashed, elongated or twisted (McManus et al. 1997). While the growth patterns of stony coral colonies are primarily species-specific, a colony’s geographic location, environmental factors (e.g., wave action, temperature, light exposure), and the density of surrounding corals may affect and/or alter the shape of the colony as it grows (Barnes, R.D. 1987; Barnes, R.S.K. and Hughes 1999, Lalli and Parsons, 1995).

In addition to affecting the shape of a colony’s growth, environmental factors influence the rates at which various species of corals grow. One of the most significant factors is sunlight. On sunny days, the calcification rates of corals can be twice as fast as on cloudy days (Barnes, R.S.K. and Hughes, 1999). This is likely a function of the symbiotic zooxanthellae algae, which play a unique role in enhancing the corals’ ability to synthesize calcium carbonate. Experiments have shown that rates of calcification slow significantly when zooxanthellae are removed from corals, or when corals are kept in shade or darkness (Lalli and Parsons 1995).

In general, massive corals tend to grow slowly, increasing in size from 0.5 cm to 2 cm per year. However, under favorable conditions (high light exposure, consistent temperature, moderate wave action), some species can grow as much as 4.5 cm per year. In contrast to the massive species, branching colonies tend to grow much faster. Under favorable conditions, these colonies can grow vertically by as much as 10 cm per year. This fast growth rate is not as advantageous as it may seem, however. Mechanical constraints limit the maximum size that branching corals can achieve. As they become larger, a heavier load is placed on the relatively small area attached to the substratum, rendering the colony increasingly unstable. Under these circumstances, the branches are prone to snapping off during strong wave action. The opposite is true of the massive-shaped corals, which become more stable as they grow larger (Barnes, R.S.K. and Hughes, 1999).

References

Barnes, R.D. 1987. Invertebrate Zoology; Fifth Edition. Fort Worth, TX: Harcourt Brace Jovanovich College Publishers. pp. 92-96, 127-134, 149-162.

Barnes, R.S.K. and R.N. Hughes. 1999. An Introduction to Marine Ecology; third edition. Oxford, UK: Blackwell Science Ltd. pp. 117-141.

Lalli, C.M. and T.R. Parsons. 1995. Biological Oceanography: An Introduction. Oxford, UK: Butterworth-Heinemann Ltd. pp. 220-233.

Levinton, J.S. 1995. Marine Biology: Function, Biodiversity, Ecology. New York: Oxford University Press, Inc. pp. 306-319.

McManus, J.W., M.C.A. Ablan, S.G. Vergara, B.M. Vallejo, L.A.B. Menez, K.P.K. Reyes, M.L.G. Gorospe and L. Halmarick, 1997. Reefbase Aquanaut Survey Manual. ICLARM Educational Series. 18, 61p.

Sumich, J.L. 1996. An Introduction to the Biology of Marine Life, sixth edition. Dubuque, IA: Wm. C. Brown. pp. 255-269.

Turgeon, D.D. and R.G. Asch. In Press. The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States. Washington D.C.; NOAA.

Veron, JEN. 2000. Corals of the World. Vol 3. Australia: Australian Institute of Marine Sciences and CRR Qld Pty Ltd.

The following information on La parguera, Puerto Rico is abridged from  La Parguera, Puerto Rico, USA, Jeorge R. Garcia, Christoph Schmitt, Craig Herbere, and Amos Winter; United Nations Educational,  Scientific and Cultural Organization;  available from : http://www.unesco.org/csi/pub/papers/garciab.htm, [Accessed: November 23, 2010].

La Parguera, Puerto Rico, USA

Jorge R. García, Christoph Schmitt, Craig Heberer, and Amos Winter

Department of Marine Sciences, University of Puerto Rico, Isla Magüeyes Laboratories, La Parguera, PO Box 908, Lajas PR 00667 USA

The insular shelf of La Parguera, on the southwest coast of Puerto Rico, is characterized by an extensive development of coral reefs, seagrass beds, and mangrove forests. The dry, warm, and relatively stable climate, low wave energy, high water transparency, relatively wide shelf, oligotrophic offshore waters, and low urban coastal development are some of the factors that contribute to the conditions of the marine ecosystem of La Parguera. Interactions among coral reef, seagrass, and mangrove communities provide for a highly productive, structurally complex, and biologically diverse ecosystem. Coastal development and associated anthropogenic impact, technologically advanced exploitation of fisheries, global climatic change, and natural events all have potentially detrimental effects on marine ecosystems and need to be analyzed from a regional perspective. We review and summarize information leading to a baseline characterization of the ecosystem of La Parguera.

Introduction                                                                                             

La Parguera is a coastal village within the township of Lajas on the southwestern coast of Puerto Rico. Its insular shelf boundaries extend from Punta Montalva in the east (66°59'W) to Punta Tocón in the west (67°06'W) and from the coastline (18°01'N) to the shelf edge (18°07'N) (Fig. 1). The southwestern coast is a generally dry and warm region, classified as a subtropical dry forest life zone (Ewel and Whitmore, 1973). A chain of low hills, known as Sierra Bermeja, separates the coastal plain from the Lajas Valley. Sierra Bermeja acts as an important hydrographic boundary that confines the watershed of La Parguera to the southern slopes of the Sierra and to the relatively narrow coastal plain. The shelf is composed mainly of carbonates deposited during the Cretaceous (Almy, 1965) and flooded some 5,000 to 9,000 years ago due to eustatic sea level rise (Goenaga, 1988), thereby forming the neritic zone of La Parguera.

La Parguera is recognized for the exceptional value of its marine resources, which include two bioluminiscent bays (Bahía Fosforescente and Monsio José), a coastal mangrove fringe with several small lagoons, mangrove islands associated with coral reefs, seagrass beds, and perhaps the best developed, most extensive coral reef ecosystem of the island. Such attributes, and the significant improvement in transportation and infrastructure across the island, have transformed La Parguera from a mostly undeveloped and quiet fishing village to a center of tourism. Resorts, guest houses, and private vacation homes have proliferated over the past ten years, and the transient population has increased at least three-fold — from approximately 35,000 visitors per year (NOAA/DNR,

Fig. 1.   Location map of La Paraguera, Puerto Rico, and its marine ecosystems.

1984) to more than 100,000. In order to halt chaotic deforestation of the natural semi-arid forest and mangrove coastline, the Puerto Rico Planning Board classified La Parguera as a Zone of Special Planning. In further recognition of the ecological value of its marine resources, La Parguera has also been designed as a Natural Reserve by the Department of Natural Resources. At present, there is a proposal for the establishment of a Marine Fishery Reserve at Turrumote Reef (Plan Development Team, 1990; García, 1990); a previous effort to establish a Marine Sanctuary Program (NOAA/DNR, 1984) was not accepted by the local community (Fiske, 1992). Field and laboratory research facilities of the Department of Marine Sciences, University of Puerto Rico Mayaguez Campus, are based on Magüeyes Island off La Parguera.

The coexistence and interdependence of coral reef, seagrass, and mangrove communities within the insular shelf of La Parguera result in a highly productive and structurally complex ecosystem with very high biodiversity. Coral reefs act as barriers to wave action and permit the establishment of seagrasses and fringing mangroves (Goenaga and Cintrón, 1979). In turn, seagrasses and mangroves contribute organic matter for coral nutrition and serve as important foraging and nursery habitats for coral reef fishes and other organisms. Each of these communities can be regarded as highly productive and taxonomically diverse. For example, mangrove lagoons function as nurseries for many juvenile coral reef fishes (Austin, 1971; Yáñez-Arancibia and Nugent, 1977; Gonzalez-Sansón, 1983), many of which are commercially important as adults (e.g., snappers, jacks, barracudas, and others). The lagoons are also the natural habitat of resident populations of, for example, snook, tarpon, ladyfish, mojarra, and sole that add to the structural complexity and diversity of the ichthyofauna in La Parguera. Likewise, seagrasses are particularly important foraging (transient) areas for coral reef fishes and endangered species such as manatees and green sea turtles (Gonzalez-Liboy, 1979) and, as well, provide a permanent niche for a highly diverse and abundant flora (Glynn, 1964; Matthews, 1967) and fauna (Gonzalez-Liboy, 1979; Vicente, 1992).

Coral reefs extend throughout a wide range of depths and distances from the coast in La Parguera and consequently are exposed to gradients of physical, chemical, and biologically interacting forces (e.g., wave energy, light penetration, temperature, salinity, nutrient availability, suspended sediments). These gradients affect the structure of the biological community within reefs (e.g., vertical coral zonation patterns) and between reefs (Morelock et al., 1977; Acevedo and Morelock, 1988). This variability in community structure within and between reefs promotes the biological diversity of coral reef-associated organisms. These changes in coral reef community structure introduce variable patterns of sedimentation adjacent to the reefs (Morelock et al., 1977), potentially influencing variability in benthic communities associated with different sediment types. The submerged shelf-edge reef of La Parguera is an important spawning site for coral reef fishes (Colin and Clavijo, 1988) and serves as a foraging area for pelagic (oceanic) predators. Such neritic-pelagic interaction contributes to ichthyofaunal biodiversity and local fisheries production.

The insular shelf of La Parguera extends 8-10 km offshore; a well developed coral reef formation exists at the border of the shelf (Morelock et al., 1977) and serves as a first barrier against wave action. Two other lines of barrier reefs provide further protection for the mangrove coastline and submerged seagrass beds of La Parguera. Nevertheless, storm-generated waves may play an important role in the distribution, structural complexity, and biodiversity of local coral reefs and associated communities (Yoshioka and Yoshioka, 1989).

Climate and Oceanography                                                                      

La Parguera is located on the southwestern coast of Puerto Rico in the subtropical climate belt influenced by easterly trade winds during 90% of the year. However, by the time the moisture-laden trade winds have crossed the island and reached La Parguera, most of the moisture has been lost. Therefore, La Parguera is one of the driest and hottest areas along the coast of Puerto Rico; the average annual rainfall 1961-1990 was 74.52 cm (Table 1), compared to 132.74 cm at San Juan. The "rainy season" occurs during the fall (average 35.61 cm), the "dry season" occurs in winter (average 9.12 cm). The highest one-day rainfall 1961-1990 was 35.31 cm on September 17, 1975 (Table 1). Most of the high rainfall amounts are caused by tropical storms that stall in the northeastern Caribbean. Occasional cold fronts in winter, which may sometimes be associated with large amounts of rain in Puerto Rico, seem not to affect the southwestern corner of the island. Total precipitation amounts vary from year to year. The lowest annual rainfall 1960-1991 was 40.94 cm in 1977, the highest was 123.57 cm in 1960.

Coral Reefs                                                                                         

According to Almy (1969), coral reefs in La Parguera originated from erosion and deformation of Upper Cretaceous limestones (with interbedded mudstones and volcanic rocks) into a WNW-ESE trending syncline. The northern limb of the syncline is the Sierra Bermeja, and the southern limb is a platform of lower relief represented by the coral reefs on the shelf. The rise in sea level associated with the last Pleistocene glaciation (Wisconsin) flooded the lower limestone ridges on the shelf, providing appropriate sites for coral growth and subsequent reef development (Glynn, 1973; Goenaga and Cintrón, 1979 Substrate, depth, and water transparency conditions in La Parguera allowed for extensive development of coral reefs during the mid-Holocene (Vicente, 1993).

Two distinct lines of emergent reefs align east-west, parallel to the coastline, and divide the insular shelf of La Parguera into inner, middle, and outer shelf zones (Morelock et al., 1977). There are many other smaller submerged patch reefs dispersed throughout the shelf, as well as a large submerged reef at the shelf edge. Altogether, it has been estimated that coral reefs occupy about 20% of the La Parguera insular shelf (Morelock et al., 1977). Margarita Reef, the westernmost in the second line of emergent reefs, is the largest of the "island reefs," with a maximum underwater extension of 4.2 km. The shelf-edge reef is located at 20 m and has a "buttressed" appearance, with channels cut into the slope down to 30 m (Morelock et al., 1977).