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Status of coral reefs, southwest Puerto Rico

¹Department of Marine Sciences University of Puerto Rico at Mayagüez, P.O. Box 908, Lajas, PR 00667-0908 morelock@coqui.net
²Geology Department University of Puerto Rico at Mayagüez, P.O. Box 9017, Mayagüez, PR 00861-9017 ramirezw@coqui.net
³National Oceanographic and Atmospheric Administration Fisheries Service Office of Protected Resources, Silver Springs, MD 20910 andy.bruckner@noaa.gov

Like most of the world's reefs, the Puerto Rican reefs have shown marked loss of living coral during the past thirty years ^{pers. observ.} from natural and anthropogenic causes. Rapid rates of human population growth and density in Puerto Rico has led to increased coastal development, dredging and sand extraction in nearshore environments, deforestation for agriculture, and increased discharge of sewage and industrial waste. Some of the consequences associated with increased human pressure include high terrigenous sediment influx, increased nutrient levels, overfishing and habitat modification. In addition, natural threats such as the island-wide mortality of the herbivorous sea urchin, Diadema antillarum in the 1980s, coral disease epizootics, bleaching and storm damage have contributed to an overall reduction in coral abundance and cover and increases in fleshy macroalgae.

Puerto Rico has a variety of reef types located on the west, south, and east insular shelf and slope of the Island. These include fringing reefs, bank-barrier reefs and patch reefs. Very general and descriptive surveys were done by Goenaga and Cintron ¹⁹⁹⁰ and a comprehensive survey of the physical parameters and reefs for much of the island was presented in Morelock, et al. 2000 and in Garcia, et al. ^{in press}

For this study, we have surveyed more than 60 sites on the southwestern Puerto Rico shelf during the last 20 years. The present condition of the reefs range from good (more than 20 percent living coral cover, a low incidence of recent mortality, and a high abundance of new recruits) to near total loss (less than one percent living coral).

One factor confounding appropriate management actions is a limited knowledge of the functions and processes controlling reef environments, a paucity of information on the condition of Puerto Rico's reefs, and a general inaccessibility of data sources. A gap analysis needs to be conducted for reefs of Puerto Rico in order to identify what information is available and what types of surveys need to be conducted in order to answer questions that would address management needs. Managers and researchers have the daunting task of compiling and organizing available data and of initiating and completing comprehensive surveys of these reefs. These tasks must be undertaken to identify the most pressing needs in order to protect remaining reefs and restore degraded areas so that future generations may benefit from the environmental and economic services these reefs can provide.

Photoquadrats were used to determine coral abundance and condition and to estimate coral cover. In each location, 30 m transects are extended parallel to depth contours (Figure 1) . A total of 10 quadrats are placed along each transect at 3 m intervals, with each quadrat (70 x 100 cm; 0.7 m² area) positioned such that the narrow (70 cm length) side is parallel to the line. Numbered tags are placed next to each coral within the quadrat to assist in identification of the corals (Figure 2) . For each quadrat, one diver records the coral species associated with each number, and notes the condition of the coral. A second diver photographs the quadrat. All quadrats are photographed from a planar perspective at a vertical distance of 1.2 m above the quadrat. This distance is maintained by using a 1.2 m stick. Although variation from true vertical to the surface may introduce cover errors, these are slight. Cover is underestimated because the photo is a planar projection of three-dimensional coral.

Coral cover is determined for each quadrat using Deneba Canvas that has an area measuring function. Initially, individual corals are identified on the photograph and the perimeter of the coral is marked with a pen. The photograph is then scanned and individual corals are traced on the photograph and measured to determine the area in cm² relative to the area of the print . All data are entered into a spreadsheet in order to calculate percent cover by species and total cover for each quadrat and for the total transect, average colony size, and number of colonies.

In this study, "coral cover" is defined as the amount of the total bottom area occupied by living coral colonies within an entire area that includes sand channels and bare areas.

Whenever possible, corals identified within quadrats were recorded to species level. Although the Montastraea annularis group (species complex) have been subdivided into three species as proposed by Knowleton, ¹⁹⁹² many of the surveys used in this paper were made before the introduction of new species. Therefore, the cover is designated the Montastraea annularis group and the individual species are not distinguished. Forms or morphotypes of Agaricia agaricites, Porites porites and Meandrina meandrites were not differentiated. In addition, encrusting colonies of Madracis were recorded as Madracis decactis. In this study, we only recognized one species of Stephanocoenia (Stephanocoenia intersepta) and one species of Dichocoenia (Dichocoenia stokesii). The percent cover by all Mycetophyllia species and Diploria species was so low that both are recorded only to genera.

We divided the insular shelf of southwest Puerto Rico six major reef areas that are unique in reef character and geographic features:

• La Parguera reefs & Playa Santa
• West Coast Carbonate Platform
• Añasco-Mayagüez Bay
• Guánica reefs
• Guayanilla reefs
• West Ponce reefs

La Parguera reefs & Playa Santa

Coral reefs are located along a broad carbonate platform that extends up to 15 km offshore (Figure 7) , with examples of emergent fringing reefs, bank-barrier reefs and submerged patch reefs. The coastline is fringed by mangroves, with extensive grass beds found in shallow (less than 10 m depth) water, especially around inner reefs.

The coral reefs at La Parguera have a higher diversity, abundance and cover of living coral than all other sites included in this survey, although these reefs are being degraded from a host of human and natural threats. There is no river discharge and the local sewage discharge is into a mangrove channel which traps most of the effluent close to shore (Figure 8) . ^{Corredor, et al., 1999} Sediment composition on the reef tract shows less than ten percent terrigenous sediments (Figure 9) . ^{Morelock, et al. 1994} However, clear cutting of the hillsides surrounding Parguera and rapid urbanization has contributed to increased sheet run-off of sediments during rainy periods (Figure 10) . In addition, nutrient loading may be an increasing problem, due to the rapid population growth and discharge of untreated sewage, especially from upstream sources (i.e.., Guayanilla, Guanica and Ponce). Other factors contributing to an overall decline in reef health include an increased dominance by mmacroalgae and boring sponges, ^{Vicente, 1985} possibly associated with nutrient loading, overfishing, a loss of herbivorous urchins, bleaching ^{Williams and Williams, 1988; Williams, et al., 1987} and coral disease outbreaks. ^{Bruckner and Bruckner, 1998}

These reefs have been investigated since 1963. ^{Almy & Torres} The results from earlier studies were published in Morelock, et al., ¹⁹⁷⁷ Rogers, ¹⁹⁷⁷ Boulon, ¹⁹⁸⁰ Ramirez, ¹⁹⁹² Morelock, et al., ¹⁹⁹⁴ and Torres ¹⁹⁹⁸ Early surveys of general areas of the reef from 1973 ^{Glynn, 1973} were compared to surveys in 1999 by Firman, et al. ¹⁹⁹⁹ Vicente ¹⁹⁹⁴ discussed changes at Enrique Reef over 20 years. Data and comments presented in this section draw from these sources. We surveyed these reefs between 1985 and 1999. These data are presented in this paper. The reefs are mapped (Figure 11) as either emergent or submerged as defined earlier.

Emergent reefs on the La Parguera platform had three distinct fore reef zones similar to those observed at Yucatan, ^{Logan, 1969} Jamaica, ^{Goreau and Goreau, 1973; Liddell & Ohlhorst, 1987} and Belize. ^{James and Ginsburg, 1979}

In shallow exposed environments (0-5 m depth), reef communities were formerly dominated by extensive thickets of Acropora palmata (Figure 12) . This coral was recorded on the fore reef of all outer reefs (Pinnacles, Turrumote, Media Luna, Laurel, San Cristobal, Margarita) and on inner reefs (Enrique, La Gata, Mario), and occasionally occurred in back reef habitats of these reefs, but was rare or absent on turbid, nearshore reefs (Collado, La Conserva, Atravasada).

Since 1975, the abundance and cover of this coral has been in decline, primarily from hurricane damage, white-band disease and corallivorous mollusks. In most locations, the density has been reduced to less than one colony every 2-5 m, although small patches of 5-10 colonies can still be found. Extensive thickets were still documented on Laurel as recently as August, 1998; ^{pers. observ} but a near total loss was documented after Hurricane Georges. The only area identified in the La Parguera reef system where this coral still flourishes is between the east end of Margarita and San Cristobal and on Atrevesado Reef. Both Margarita Reef and San Cristobal reef are being repopulated with Acropora palmata. ^{pers. observ}

In reef environments formerly dominated by Acropora palmata, few corals now exist; these include small brain corals (Diploria spp.), Porites astreoides, and Millepora spp., as well as soft corals (i.e., Gorgonia spp. and Psuedoterigorgia spp.). the coral cover at five meters is mainly species of massive coral (Figure 13) although Acropora palmata were abundant on the shelf reefs 25 years ago. Acropora palmata was present on the shelf edge reefs 6,000 yBP, but coral growth could not keep up with rising sea level.

A break in slope may separate the Acropora palmata Zone and the Massive Coral Zone. Coral species in the massive zone (Figure 14) grow on a relatively steep slope and are dominated by Montastraea, Agaricia, and Porites species (Figure 15) . The upper part of the zone terminates at 12 to 14 m on the emergent reefs where the lower part of the reef front is covered by a sand and gravel fore-reef talus zone on Enrique and Turrumote reefs. The lower part of the massive zone was measured at the submerged reef southeast of Turrumote reef (Figure 16) and at the submerged shelf-edge reef (Figure 17) . The cover at 20 m (Figure 18) was measured at the submerged reef southeast of Turrumote and at the shelf edge.

The Buoy site and Playa Santa are similar with dominance by Montastraea annularis and high cover by Agaricia; but at Turrumote southeast (on the shelf), Montastraea cavernosa is dominant with Agaricia and Montastraea annularis secondary. The cover by species pattern at Margarita west shelf edge is similar to the Buoy and Playa Santa sites, but less total cover. There is a pattern of reduced coral cover from Playa Santa to the shelf south of Cabo Rojo lighthouse.

Colony morphology changes from the massive rounded heads found in the shallower zones to platy forms (Figure 19) at 22 to 24 m. The composition of the reef community on the insular slope changes and the Montastraea-Agaricia coral zone can be distinguished. Agaricia species and Montastraea annularis dominate the zone as measured at 25 and 30 m ( Figure 20 and Figure 21).

The total cover of coral (Figure 22) differs between the nearshore reefs and the shelf edge reefs. The lower cover inshore probably reflects different environmental conditions. The map view of percent coral cover (Figure 23) on these reefs shows higher cover than at any of the other sites in this report.

Figure 23. Percent total coral cover La Parguera Reefs

A series of cores drilled into the outer and mid shelf reefs ^{Hubbard, et al., 1996} allow reconstruction of the Holocene reef development history. The outer reef complex is comprised of roughly parallel but discontinuous ridges which are cut by distributaries from the deeper landward trough of the Turrumote Basin. The Holocene shelf edge reefs began 8,000 to 9,000 yBP as Acropora palmata growth (Figure 24) on the newly submerged Pleistocene surface. Based on the regional sea-level curve of Lighty, et al. ¹⁹⁸² and the local Acropora palmata curve (Figure 25) , water depths over the reefs were near 6 m, which is beyond the optimum range for branching acroporids but was observed at Los Roques, Venezuela. ^{Morelock, pers. obv.} The dominantly Acropora palmata reefs accreted at rates up to one centimeter per year, maintaining a constant depth below rising sea level.

These coral died off 6,000 yBP and the surface was barren until massive coral began to grow a few hundred years ago. The modern massive coral are a single coral layer dominated by head corals that cover up to 50 percent of the bottom over the relict Acropora palmata reef. From the maximum size of massive corals on the La Parguera shelf edge, we assume that this modern "coral carpet" is only one to two hundred years old.

These data are valid only for the La Parguera shelf edge reefs, but if we assume a similar history for the rest of the southwestern Puerto Rico shelf reefs, the modern coral cover is only a thin reef layer lying over a 6,000 year old Acropora palmata reef (Figure 26) . Coring at Lang Bank off St. Croix, USVI has a similar history ^{Hubbard, pers. observ.} which makes the assumption reasonable.

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West Coast Carbonate Platform

As at La Parguera, we see two types of reef on this platform (Figure 27)

• the shelf edge reefs at the shelf margin break and
• shelf/patch reefs on the top of this broad platform.

The coral cover by species at five meters was measured at Cayo Ron east and Escollo Rodriguez, two reefs stressed by sediment influx and resuspension of fine grained sediments (Figure 29) . Montastraea annularis was dominant on Cayo Ron east. Escollo Rodriguez had about the same about of cover by Colpophyllia natans, Meandrina meandrites, Siderastrea siderea and Porites asteroides - the only coral present at five meters.

The Montastraea annularis group dominates the ten meter level (Figure 30) on the shelf and platform reefs on the northern part of the platform. The 15 m level (Figure 31) has less than ten percent cover by any species and total coral cover is reduced. The most common species were Montastraea annularis and Montastraea cavernosa.

The 20 meter level, measured on the shelf slope (Figure 32) , had very low coral cover with no coral of the fourteen species present dominating. If we assume the same history as at La Parguera for the shelf edge reefs off Boquerón and Punta Cabo Rojo, something has prevented the colonization of these areas and they are presently hard grounds. Both shelf edge sites (Boquerón west R4 and Punta Cabo Rojo shelf edge) are in clear water far from shore and show no effects of increased nutrient or sediment load. Some other factor such as strong currents causing a lack of larval recruitment must be acting in what is still a natural environment. The shelf edge of this platform has consistently higher currents than any other part of Puerto Rico. ^{pers. obv.} Both areas had almost no coral larval recruits (juvenile).

The mapped view of coral cover on the reefs (Figure 33) shows that the status (cover on the reefs and density of reefs on the platform) of these reefs is much less than at La Parguera, even though the environmental stresses (sediments, nutrients, storm waves) should be low.

Figure 33. Percent total coral cover Boqueron Carbonate Platform

Some of the shelf reefs had thick accumulations of Acropora palmata with almost total canopy cover by the overlapping fronds of the coral in 1995. Observations in 2001 showed a loss of more than half of the Acropora palmata.

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Añasco-Mayagüez Bay

The shelf between Punta Jigüero and Punta Cadena has no sediment influx from rivers and is clear of the plume of sediments from the Añasco River. Despite having a more favorable environment than the Añasco reefs, coral is almost absent from this part of the shelf. No shelf edge reefs were found during our investigation, and in discussions with local divers, no one has found coral reefs on the shelf break.

As sea level rose, the higher topography of the shelf on either side of the Añasco, Yagüez and Guanajibo river channels was colonized by reef corals along with several inshore highs which were probably remnants or former beach lines. These areas were flooded less than 10,000 years ago, and sea level approached its present position about 5,000 yBP. This was a fairly rapid rise of sea level that must have been accompanied by relatively high erosion and turbidity as the shoreline eroded creating conditions in which coral growth and reef accretion were restricted.

Grab samples have been collected in several studies of this area ^{Morelock, et al., 1983; Webb, et al., 1994} and the results of the grain size analyses (Figure 36) show that the coarsest sediments are associated with the shelf edge reefs and patch reefs. These are carbonate sediments, and shell material in the gravel size makes up as much as half of some of these sediments. The carbonate sources are the reefs, which are present as bathymetric highs.

The sediment facies mapped by Morelock, et al. ¹⁹⁸³ shows a large area of fine-grained terrigenous sediments in both bays (Figure 37) . Additional sediments are added from discharge of the three local rivers and during periods of high rainfall, the bays are very turbid. Sediment resuspension is a common occurrence.

The reefs at Añasco-Mayagüez have been studied in more detail than the rest of the western shelf area. The results from earlier studies of this shelf were published in Morelock, et al. ¹⁹⁸³ and Webb, et al. ¹⁹⁹⁴ More recent investigations (1996-1997) are presented in this paper, including detailed studies at Manchas North, Manchas Exteriores, Manchas Interiores, Algarrobo, Manchas Grande and Escollo Rodriguez. All of the reefs are submerged except at Algarrobo and Escollo Rodriguez Figure 38).

Coral reef condition is described in terms of coral community, abundance and coral cover (Figure 39).

Figure 39. Percent total coral cover Añasco-Mayagüez Reefs

Even though the shelf is narrow at Añasco, the shelf edge reef at Manchas Interiores 7 has relatively high coral cover (Figure 40) . The other parts of the shelf edge reef have less than 10 percent coral cover.

Reef building corals were found on all reefs investigated. Live coral occurred to 27 m depth on shelf edge reefs south of Añasco Canyon and to 14 m on the Manchas North reef. The highest cover was observed on the shallowest part of the shelf edge reefs (Figure 41) . The total coral cover shows a rapid decrease with depth. The reefs varied in live coral cover from less than 1 percent to over 17 percent at Manchas Interiores 7, with the best developed reefs on shelf edge sites farthest from the Añasco River and the ship channel.

Colpophyllia natans, Diploria strigosa, Montastraea cavernosa and the Montastraea annularis group are the most conspicuous corals on the shelf edge buttresses. Coral masses are separated by narrow sand channels that serve as conduits for the transport of sediments downslope.

The shelf edge reef north of Añasco Canyon has been severely impacted by chronic (virtually continuous) sedimentation (Figure 42) . Visibility was poor (2 m) and a layer of fine silt covered the reef substrate. No live coral was found below 14 m, and only 4.7 percent cover was measured at 10 m. The community was dominantly the Montastraea annularis group, Montastraea cavernosa and Agaricia species with the size of an individual coral colony typically less than 10 cm (Figure 43).

Although sediment influx has been low, the Punta Jigüero to Punta Cadena shelf had only two coral reefs. Both reefs had low coral cover by flattened colonies. Many of these are one meter across (Figure 44) . Almost no Montastraea annularis were present. Dominant corals on both reefs were Porites asteroides, Colpophyllia natans and Diploria species (Figure 45) . Meandrina meandrites were common on the eight meter deep Punta Jigüero reef, but absent on the five meter deep las Brisas reef. On the shelf edge reefs of Manchas Exteriores and Manchas Interiores, maximum coral development was at 10 m (Figure 46) . Montastraea cavernosa was the dominant coral in the 10 m community in terms of abundance and cover. Montastraea annularis (morphotype Montastraea faveolata), Agaricia agaricites, Porities astreoides and Colpophyllia natans were significant members of the community.

The shallow reef platforms on Manchas Exteriores and Manchas Interiores had fewer coral species and a more dense gorgonian assemblage when compared with the shelf edge reefs. On these reefs, the major coral groups included plating corals (Agaricia and Leptoseris) and massive species (Montastraea cavernosa, Diploria strigosa and Porites astreoides) which are all species tolerant of sediment influx and turbid low light conditions. Acevedo, ^{et al., 1989} These reefs are all relatively low in coral cover, but at Manchas Interiores 8 which is the closest reef to the Mayagüez sewer outfall, the coral colonies show less cover by species.

Sites in Añasco Bay (Figure 47) are influenced by Añasco River water (nutrients from agriculture and sewage), the Mayagüez outfall (nutrients from sewage) and the Mayagüez tuna canneries (nutrients from tuna waste). These nutrient sources appear to have affected local reef areas for a long time. Algal turf was prevalent at all shallow sites; deep reefs were covered with a fine layer of silt, which may prevent settlement of algal spores.

The impact of nutrient loading was most pronounced on Algarrobo Reef (Figure 48) . Surveys performed during previous years (while tuna plant effluent was still being discharged into the Bay) demonstrated a high cover of Bryopsis algae. Although Bryopsis was less prevalent after 1997, this algae may have out-competed corals through shading, competition for space with adults and by preventing sexual coral recruits from becoming established. While this reef is shallow and currently lacks a major canopy, recolonization by reef-building corals may be prevented by distance from other reefs and the high abundance of turf algae limiting settlement sites.

The diversity and abundance of invertebrates on Algarrobo was low. Coral species included Porites astreoides, Diploria clivosa, Meandrina, Siderastrea and Scolymia. Because few coral were present, a visual examination of the bottom for 60 m was made observing two meters to each side of a guide line. This resulted in finding 15 coral colonies which were measured. The calculated cover for the 240 m² area was 0.012 percent. Observations showed about one coral every four meters. All were less than 10 cm diameter, and many were riddled with worm tubes. Many dead Acropora palmata fragments were lying on the bottom but no live Acropora palmata were present.

Escollo Rodriguez reef has been heavily impacted by sediments from the Guanajibo River and sediment resuspension on the reef (Figure 49) . The reef ends before the ten meter level with very low coral cover at 8.5 m (Figure 50) . Cover at four meters is surprisingly high, with cover primarily by Montastraea cavernosa Figure 51) . Although no Montastraea annularis are present at four meters, this species is more than half the total coral cover at two meters.

Meandrina meandrites was common at 15 m depth on the Manchas Exteriores and Manchas Interiores shelf edge reefs (Figure 52) . This coral had wide depth distribution with small colonies, including new recruits, occurring to 25 m. The Montastraea annularis group, Montastraea cavernosa, Porites astreoides and Agaricia agaricites were the dominant corals at this depth.

Below 15 m, species composition at the shelf edge shifts to a community consisting primarily of plating species. Dominant corals at 20 m included Montastraea cavernosa, Agaricia, Madracis, Stephanocoenia, Leptoseris, Meandrina meandrites and Meandrina. Stephanocoenia was the most abundant coral on horizontal surfaces from 15 to 25 m as a small (3-5 cm) flattened crust (Figure 53).

At and below 25 m Figure 54) , the bottom was muddy but large isolated boulders were found. The plating corals Agaricia and Mycetophyllia were observed on vertical surfaces of these boulders to a depth of 27 m. Although both species are patchy in their distribution, their large size contributes significantly to total cover. Montastraea cavernosa and Siderastrea siderea were the other common coral.

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Guánica reefs

Both shelf and shelf edge reefs are present at Guaníca (Figure 56) . The number of species, and diversity have declined over the last ten years and the total coral cover shows relatively low coral cover at all sites (Figure 57).

Figure 57. Percent total coral cover Guanica Reefs

The total coral cover on the reefs was less than 10 percent for the shelf reefs and about 20 percent on the shelf edge reefs (Figure 58) . The lowest coral cover on a shelf reef was at the Caña Gorda reef and the highest total coral cover was at the g3-buoy which is the site closest to the terrigenous mud source.

The total number of species at 10 m at each shelf site was low with a different species being dominant at each site (Figure 59) . Montastraea cavernosa was the dominant species at the g3-buoy, the dominant coral at the Canyon North site was Montastrea annularis, and at the Caña Gorda, Porites astreoides was dominant.

The Canyon North site showed a marked decrease in total coral cover from 1988 to 1999 from 14.2 percent to 8.4 percent. A significant decrease in the percentage of Porites astreoides, Siderastrea siderea, Meandrina meandrites, Colpophyllia natans, and Diplora strigosa was found. The number of species found in each area remained the same.

The pattern of cover on the shelf edge reefs was less than at La Parguera (Figure 60) , but still a reasonable amount of cover and species diversity.

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Guayanilla reefs

The three sedimentary environments on the insular shelf of the Guayanilla and Tallaboa canyons (Figure 61) are the relatively bare rock and reefs (Figure 62) on the shelf platform and the muddy sediment-floored submarine canyon floors. Sediments in the mud facies are resuspended by ship traffic in the Guayanilla and Tallaboa canyons. The present Guayanilla and Tallaboa bays are turbid-water areas with Secchi visibilities of less than three meters.

Modern reef growth is limited to areas of hard bottom with bathymetric relief. Larges areas of dead coral heads (Figure 63) suggests that until very recent time, coral growth was far more vigorous than in the present environment. Rock surfaces of dead coral colonies show that development of the reefs probably followed the same pattern as at La Parguera. Reefs are now restricted to shallow-water areas at the open shelf edge. Little of this reef growth is thriving, and the community ecology of the reef resembles a much deeper-water assemblage. Patch reefs that were present in the bay areas are now shoal mounds of rubble covered with grass beds.

The surveys show the reduced living coral cover that occurs with increased sediment stress beyond the normal condition ( Figure 64 and Figure 65).

Figure 65. Percent total coral cover Guayanilla Reefs

The eastern wall of Punta Ventaña canyon shows a total coverage of five percent living coral at 15 m and only 2.5 percent at 20 m. All depths for these reefs have less than six percent living coral cover. At several of the sites, there is no living coral below 10-12 m.

The five meter (Figure 66) sites in Guayanilla and Tallaboa bays have very low coral cover and a very limited number of species. Relict reefs in the inner bays are now covered with Thalassia.

At 10 m (Figure 67) , the shelf reefs showed a marked increase in the dominance of Montastraea cavernosa, compared to the same depth zone at Turrumote Reef (La Parguera); it is three to six percent cover or more than half of the living coral present. The number of species has been reduced, with only five species having more than one percent cover on the transects. The Montastraea annularis group are present but comprise only a small part of the coral cover.

There are distinct changes in the ecology of the submarine canyon and shelf edge reefs at 15 m, 20 m and 25 m ( Figure 68, Figure 69 and Figure 70 ). The coral community shows elements of both the massive coral zone and the deeper-water platy zone. The dominant coral was now Montastraea cavernosa, with Montastraea annularis and Agaricia agaricites lower in abundance. There was an increase in Siderastrea siderea abundance, and the shape and growth of Agaricia was modified to a platy form attached to vertical surfaces. These changes reflect sediment stress and lowered light level adaptations of the community. The coral system is now living close to the limits of tolerance.

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West Ponce reefs

The carbonate platform is separated from the shoreline by the Ponce Basin which extends west of Ponce Harbor and grades northward into the nearshore zone. Sediments in the Ponce Basin (Figure 72) are poorly sorted terrigenous silts and clays with small amounts of carbonate mud and sand that have been carried in from surrounding areas and have accumulated in low-energy, deeper-water conditions. Similar sediments floor the Ponce Submarine Canyon. The fine-grained sediments are resuspended by wave action and ship traffic causing underwater visibility of less than one meter. ^{pers. obs.} The resuspension develops a sediment plume that is transported by currents, carrying fine sediments over the West Ponce reefs. ^{Acevedo, et al., 1989}

The platform is an area of hard carbonate pavement with thin carbonate sands and small reefs. The water is generally turbid with Secchi disc readings of less than 5 m. The shallow shelf reefs had very low coral cover and the least sediment-tolerant specie, Acropora palmata, is not present (Figure 73).

Below five meters, the reefs had large amounts of fine-grained terrigenous sediments. The coral cover and diversity on the reefs has been severely modified by chronic sediment stress. The total coral cover is drastically reduced at depth in relation to the other reefs. A striking effect of terrigenous sediment influx is increased turbidity and loss of light, which results in shifting of the zonation and an upward migration of zone depths (Figure 74) . ^{Hallock and Schlager, 1986} Loss of light is critical to the deeper coral assemblages, and a chronic increase in turbidity will move the lower limit of coral growth to shallower depths. This is reflected by a marked change in the reef-front zonation with depth (Figure 75) . A compression of the depth zonation is accompanied by changes in coral species domination, which is directly related to individual species tolerances for sediment stress. Both loss in total coral cover and a shift to slower growing coral species were seen in the reefs between the Ponce Canyon and Cayo Ratones Reef.

Coral cover was reduced near the source of terrigenous sediment influx. As we move westward from the source of the sediment plume, the effect on the coral cover is reduced (Figure 76) . Past Cayo Ratones Reef, the reefs at Peñuelas are much less affected, and coral cover at all depths is more like the reefs at La Parguera (Figure 77).

Figure 77. Percent total coral cover West Ponce Reefs

A maximum of 18 species of corals were recorded at 10 m depth (Figure 78) . Of these, only seven species were more than 0.5 percent cover (by species) on the eastern reefs. Montastraea cavernosa was dominant at 10 m. This coral is one of the most sediment-resistant species of the scleractinian corals. ^{Lasker, 1980; Loya, 1976} The total cover of Montastraea cavernosa is not significantly different from values at La Parguera, but the reduction or absence of other coral species changes the relative abundance and reinforces the conclusion that Montastraea cavernosa is highly tolerant to a long-term sediment stress condition. No living corals were found below 12 m at Cayo Cardona.

A deep-water coral, Agaricia lamarcki, was found at 15 m on Bajo Tasmanian and Ratones (Figure 79) , suggesting that the light levels were greatly reduced. The deeper reefs all have low coral cover and rapid attenuation of cover with depth. The values for Montastraea annularis and Agaricia agaricites decreased significantly with increased sediment conditions. The main loss in total cover was reduction in cover by Montastraeas annularis. The cover by Montastraea cavernosa, Siderastrea siderea, Porites astreoides, Colpophyllia natans, and Meandrina meandrites was not significantly different between sites. Cayo Ratones showed changes in coral cover related to sediment stress, but less than at Cardona. Montastraea cavernosa dominates the coral cover except at Peñuelas where the zonation is more normal.

Below 15 m, wave action does not remove all the fine sediments. The combination of depth and turbidity causes light reduction with consequent cover reduction. A platy coral assemblage was dominant at 20 m and deeper (Figure 80) . A hummocky topography was formed by dead coral heads covered with a sediment-algae mat.

At 25 m (Figure 81) , few coral species were present in the eastern reefs, with only Agaricia lamarcki common. The number of colonies was low, but the size of each colony was large with some approaching one meter diameter. These grew on vertical surfaces of the boulders easing sediment removal. The Peñuelas reefs had higher cover but dominance was skewed to Agaricia species at the Tallaboa east site and Montastraea cavernosa at the Peñuelas shelf edge site.

Only two species (Agaricia lamarcki and Madracis decactis) were found at 30 m on Ratones (Figure 82) which had total coral cover of only 0.2 percent. The MPI site had six species but only 0.8 percent total cover. To the west, the reef at Peñuelas had 8.0 percent total cover at 30 m from eight species, but most of the cover (7.2 percent) was Agaricia species. If we compare this to the cover at La Parguera where total cover is 41 percent, we see the dramatic effect that sedimentation has produced. The La Parguera 30 m level is definitely in the Montastraea-Agaricites zone with dominance by these two species, and cover is high. The hummocky topography continues to more than 40 m at Ratones showing that there was once good coral development - probably similar to La Parguera on this reef.

These reefs showed an absence of many species that normally extend to depths of 25 or 30 m. The reduced light levels resulted in domination of the community by deeper fore-reef coral. Tolerance of individual species to sediment particles is probably another factor in the final coral species assemblage. Continued stress has reduced the total cover and the number of species. The reefs with high sediment input showed decreased coral species diversity and percent cover. Sediment-resistant species tolerated this adverse environment and their percent cover remained relatively constant.

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High sediment influx, resuspension and turbid water conditions at Añasco-Mayagüez and Guánica-Guayanilla-West Ponce have resulted in low coral cover on the reefs (Figure 83) . At the surveyed sites, the bottom is hard dead coral rock which indicates that these once had cover comparable to that on the platforms of Boquerón, La Parguera and Peñuelas. It is therefore a reasonable assumption that much of the insular shelf and slope of southwest Puerto Rico has turned from coral reef to "hard ground" condition with a loss of more than 35 percent of the original Modern coral cover. This is especially evident if we compare the total cover by species at the 20 m level for sites (see figure 55) discussed in this paper. The La Parguera and Peñuelas platforms are the only areas of "normal" coral cover at 20 m. The western platform insular slope has low coral cover due to some natural process. The Añasco-Mayagüez and Guayanilla-west Ponce reefs have very low total coral cover at 20 m compared to the La Parguera and Penuelas reefs at this depth (Figure 84) . The shelf edge reef at Guánica still has a moderate cover of living coral at 20 m.

Individual reefs on the carbonate platforms show loss of coral cover by areas of dead coral rock. Continued rapid urbanization and development has contributed to sheet runoff and influx of terrigenous sediments even into areas without river discharge. The development of the coastal area has also increased discharge from the sewer outfalls at Ponce, La Parguera, Boquerón and Añasco. This untreated sewage has raised nutrient levels and promoted the growth of algae on the reef.

And finally, overfishing and drastic reduction of the biodiversity around the reefs is leading to rapid loss of coral to a shift in competition balance favoring algae and destroyers of coral such as corallavore, fire worms, echinodermatra and damsel fish. Along with this we are finding increased coral disease and invasion by sponge.

Specific members of the reef-building coral community have suffered higher loss under present conditions. The two major reef building species - Acropora palmata and Montastraea annularis have been drastically reduced in percent of cover on the stressed reefs. At depths greater than 12 to 15 meters, dead coral is all that remains of reefs that must have once had a cover comparable to the magnificant shelf edge reefs at La Parguera.

Because of different techinques of measurement, no data from Carlos Goenaga or Jorge Garcia were used in this paper, but their information about reef locations was gratefully accepted. Matt Kendal supplied spot check information on bottom type on the west carbonate platform and La Parguera. A seed money grant from the Sea Grant College Program in 2000 and a research grant in 2001 has allowed us to complete the work for this paper.

Thanks also go to Jose Mari Mutt for sponsoring the concept of electronic publication which is a new and important tool for reporting scientific research.

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