MATERIALS AND METHODS

Study area: The two sites were located on the northeastern coast of Trinidad (located between 10°-11°N, 61°-62°W), close to the two largest South American rivers (Amazon and Orinoco). These rivers heavily influence the study reefs through contributions of freshwater, nutrients and sediments. The Caribbean Sea surrounds the study areas. Both sites in the Toco region are on the north coast, within ~4.0 km from Galeota Point which is the extreme northeastern point of Trinidad (Fig. 1).

Both study sites were investigated between two periods in time, (1) August 2008 and (2) January 2012. Toco Bay (TB) and Baptist Bay (BB) (10°50.107`N to 10°50.266`N) are adjacent to each other, located towards the eastern end of the island next to the Toco Fishing Depot. Transect points were previously marked and served as points where coral cover data were collected (Belford and Phillip, 2011).

Field survey: The line and point transect method was used to estimate intertidal benthos distribution and abundance. Transect lines were made from brightly colored yellow polypropylene line (40 m) with colored surveyors tape at 1 m intervals.

Fig. 1:	Map of the Caribbean (inset) showing the study sites surveyed in August 2008 and January 2012 along the northeastern coast of Trinidad

The line was stretched perpendicular to the shore towards the reef and each reef component (biota and non-biota) were tallied under 1 m intervals along the transect line (Belford and Phillip, 2011). A total of 8 transect points, 50 m apart were measured from the west to east at both TB and BB. Transect points were set at 50 m intervals and were marked by spray painting an entry point on terrestrial substrate (trees and walls). A hand-held Global Positioning System (GPS) and photographs were also used to record the position of each transect point to provide location confirmation during subsequent visits.

Four intertidal zones were used to represent distances from the maximum tide imprint left on the shore (hereafter shoreline) during low tide. Zone 1 was 0-10 m from the shoreline and zone 2 (11-20 m), 3 (21-30 m) and 4 (31-40 m) were respectively designated. Coral abundances were determined as percentage coral cover of 4 zones on transect lines. Scleractinian coverage of reef-building Porites porites and Siderastrea radians were calculated for each zone and compared to total zoanthid (P. caribaeorum and Z. sociatus) cover for 2008 and 2012.

Statistical analysis: Data were collected during daytime falling tides (mean low tide depth 0.30-0.35 m) and water surface temperature was also measured using a hand-held digital thermometer. Local tide tables were used to determine the lowest tides of the month. These low tides provided easy access to collect data on benthic reef components using the line and point transect method.

RESULTS

P. caribaeorum forms brown mat-like colonies but can appear as solitary polyps (Fig. 2a, b). Polyps are separated by a thin coenenchyme (P. caribaeorum). Zoanthid species were observed in both solitary and colony forms and in particular P. caribaeorum was seen growing as mats throughout the reef benthos at Toco Bay (TB) and Baptist Bay (BB) and also at a fringing reef located at Salybia Bay approximately 2 km from TB. Although, Z. sociatus often include a diverse array of colors including gray, blue, purple and orange (Fig. 2c, d), they mostly appear as green mats throughout various sites of the northeastern Toco region of Trinidad (Fig. 2e, f).

Percentage cover of reef-building corals such as Porites porites and Siderastrea radians have not changed as much for a period of approximately 3.5 years. There were slight increase in coral cover in zones 2 and 3, compared to similar decreases in zones 1 and 4 (Fig. 3a). Surprisingly, the average hard coral cover for zones 1-4 in August 2008 was 16.8% compared to 17.2% in January 2012.

Zoanthid sp. showed increased coverage in all zones for the 3.5 year time period. However, the most noticeable increase occurred in zones 2 and 4 (17.5% and 14.5% respectively, Fig. 3b). These values were the result of an 11.3% increase in coverage for Z. sociatus in zone 2 (Fig. 3c) and a 16.7% increase for P. caribaeorum in zone 4 (Fig. 3d). Interestingly, there wasn’t that much change in cover for Z. sociatus in all zones, except zone 2, compared to a similar pattern for P. caribaeorum in all zones except zone 4.

Overall, although reef-building corals showed increase in coverage only for zones 2 and 3, zoanthids showed a steady increase in all zones, with higher coverage in zones 2 and 4 compared to their reef-building scleractinian counterparts. Consequently, zoanthid percentage cover was greater than twice that of reef-builders in all zones examined in January 2012, compared to similar examination in August 2008 (Fig. 3a, b).

Fig. 2(a-f):

The two common zoanthid species were visibly growing in either solitary polyps or forming extensive mats in all zones as shown in, (a) P. caribaeorum growing as solitary polyps at Toco Bay, (b) Salybia Bay and displayed various color morphotypes, (c) Orange color morphotype of Z. sociatus, (d) Brown morph, (e) In various shades of green at Toco Bay and (f) In the reef within the immediate vicinity of the Toco Lighthouse

Fig. 3(a-d):	Intertidal coral cover in zones 1-4 for combined Toco and Baptist Bays during August 2008 and January 2012, (a) Reef-builders, (b) Zoanthids, (c) Z. sociatus and (d) P. caribaeorum

DISCUSSION

The results of this study showed favorable growth for zoanthids in all 4 intertidal zones compared to their scleractinian counterparts over a short period of time (3.5 years). The noticeable increased cover in zones 2 and 4 correlated with either a decrease or only a slight increase in scleractinian cover in these zones. Interestingly, although the only indication of decreased coverage was reported for Z. sociatus in zone 4, its counterpart, P. caribaeorum had a noticeable increase in this zone and favorable growth in all zones. Past research by Belford and Phillip (2011) has shown initial scleractinian cover at 13.3% and more recently 17.2% (this study) with an overall 6 year increase in coral cover of just 3.9%. Consequently, zoanthid growth is more favorable as shown from its steady increase in cover and it will be interesting to see if this pattern continues in the wake of dynamic climate change.

Additionally, the results of this study add the first quantitative comparison of benthos cover for zoanthid species and reef-building corals growing at Toco and Baptist Bays, on the northeast coast of Trinidad, in the southern Caribbean. Currently, there is a need for long-term data due to the inexistence of an official reef-monitoring program in the area. Both sites are ~2.5 km away from Salybia Bay (the best developed fringing reef in Trinidad) and long-term effects of climate change and human influence may affect all coral ecosystems on the northeastern coast of Trinidad. Ultimately, quantitative baseline data in this study can be used to encourage the implementation of a reef-monitoring program to follow annual patterns in cnidarian abundance and distribution.

The rocky intertidal nature at TB partly restricted the growth of reef-builders in 2008 and 2012. The combination of high energy and turbidity in conjunction with the closeness of the upper surface of the rocks at low tide levels is a limiting growth factor of scleractinians. Ultimately, high energy and shallowness favors zoanthid growth because they are better adapted to strong wave action and exposure. Scleractinian coral cover maintained consistent coverage in all zones, compared to noticeable zoanthid increases in a few zones for the 3.5 year period of time. An increase in P. caribaeorum growth in zone 4 and approximately consistent growth of Z. sociatus in zone 2 provided an illustration of the dynamic nature of zoanthid cover on the coral reef. P. caribaeorum cover in zone 4 correlated with a decrease in scleractinian cover as noted for the time period.

P. caribaeorum was the most abundant cnidarian species at the outer intertidal zone close to the reef crest at all sites including Salybia Reef (Belford and Phillip, 2011), whereas Z. sociatus was more abundant nearer the shoreline in zones 1 and 2. In Venezuela, Bastidas and Bone (1996) found similar high abundances of P. caribaeorum in shallow fore reef zones where this species formed massive brown slippery mats while Z. sociatus dominated nearest to the shore. Bastidas and Bone (1996) further suspected that P. caribaeorum can over-grow Z. sociatus, since P. caribaeorum exhibited faster initial growth after cover removal, which did not favor Z. sociatus. Karlson (1983) noticed a decrease in Z. sociatus cover when he investigated the effects of storm, due to the overturning of rocks and shading. Shading occurs in certain parts of the reef near to the shore at Toco and Baptist Bays, thus may be one reason why many types of Z. sociatus color morphotypes can be seen closer to the shoreline (Belford and Phillip, 2011).

Unlike many corals, zoanthids are common on shallow reef flats in the Caribbean and Bahamas (Wood and Wood, 2000). Intertidal sections of reef flats on the northeastern coast of Trinidad show similar zoanthid distributions, but abundances are different within the intertidal zone. At TB and BB, Z. sociatus mean cover was higher closer to the shore (0-15 m), compared to higher coverage of P. caribaeorum in zones 3 and 4, that is, further away from the shore. Cnidarians such as beaded anemones, Epicystis crucifer, lesser starlet coral, Siderastrea radians, finger coral, Porites porites, fire coral, Millepora alcicornis and algae were less common than Z. sociatus 0-15 m from the shore. Zoanthids at both sites covered rocks, boulders and coral rubble. Both zoanthid species are exposed to the atmosphere at spring tides for at least 3.5 hours for three days each month. This exposure may contribute to the “hardiness” of zoanthid species in this region, due to inconsistent fluctuations in surface and water temperatures but this is entirely speculative.

The low percentage scleractinian cover at the sites in this study is representative of reef benthos seen throughout the Caribbean. Scleractinian (reef-building) corals are the fundamental unit of reef ecosystems (Souter and Linden, 2000). Major Caribbean reef-builders such as Acropora palmata, Acropora cervicornis and Montastraea annularis have declined in abundance over the last two decades (Mumby and Steneck, 2008). Such declines have been attributed to changing climate, disease (Hoegh-Guldberg, 1999; Hughes et al., 2003; Mumby and Steneck, 2008) and anthropogenic factors such as coastal development, which has affected 30% of the world’s reefs (Bryant et al., 1998).

The impact of using reefs to educate local high school, undergraduate students and communities living in close proximity to reefs extends towards being better stewards of our environment. This study can be used to present data to government authorities, as well as local stakeholders to illustrate the need to implement long-term reef monitoring initiatives in the area. Furthermore, knowledge of coral species distribution can be used to determine long-term changes, which may be on the horizon as climate change becomes more apparent.

ACKNOWLEDGMENTS

We thank Dr. James Reimer for valuable comments throughout the development of this paper. We also thank Dr. A. Ramsubhag and Grace Surju-Charran (UWI) for their support. We acknowledge Mr. Winston Montano for geological advice about the study sites and Dr. Dennis Mullen at Middle Tennessee State University (MTSU) for his advice on this project. This project was funded by a J. Gerald Parchment Biological Field Station scholarship (MTSU), Wayne Price Biological Research fund and Martin Methodist College.