Seagrass species communities around Trinidad and Tobago

Study Extent

In Trinidad, surveys were conducted along the Gulf of Paria coastline from Scotland Bay to Mosquito Creek, around the offshore islands, the northeast coastline, and in Guayaguayare Bay. In Tobago, the entire coastline was surveyed. Surveys were conducted by boat. In Tobago, they were conducted in March 2001, while in Trinidad they were conducted from April – September 2001. Each site was surveyed at least once during the study period.

Sampling

Seagrass beds were mapped using information obtained form GPS (Global Positioning System) readings, aerial photographs (taken by Survair International Limited in 1994, at elevation 1,800m above sea level, at scale 1:12500; FS160, f/4.0), as well as visual surveys. Maps showing the location and extent of seagrass communities were produced using Arc Info Software.

Method steps

1. Temperature, salinity, dissolved oxygen, and pH were measured at 1 m depth using a Sonde. Visibility of the water was determined by taking secchi disc readings. Total suspended solids concentration (TSS) was measured at 1 m depth at sites on the west coast of Trinidad. TSS was determined according to the gravimetric (difference) method outlined in APHA/ AWWA/ WEF, 1995. A known quantity of seawater was filtered through a pre-weighed Whatman glass fibre filter paper. The residue was dried for two hours at 105oC and re-weighed. Detection limit is 1mg l-1 Water nutrient concentrations {total nitrogen (TN) and total phosphates (TP)}, as well as Chlorophyl-a concentrations were measured at sites on the Northwestern Peninsula of Trinidad. Measurements were made once in the dry season and once in the wet season. TN and TP were determined according to methods outlined in APHA/ AWWA/ WPCF, 1995. Complexing agents were added to produce coloured complexes of each anion. Quantification of these anions was performed using UV/ fluorescence spectrometric analysis. Quantification of ammonia was performed using the method outlined in Grasshoff et al. (1983). Chlorophyll-a was measured using a method outlined by Strickland and Parson, 1972. Two-litre water samples were collected and the phytoplankton species were filtered onto a Millipore AA glass filter, using a vacuum pump system. Pigments were extracted from the algal cells by soaking in acetone over night, and then measured using a Perkin-Elmer 552A UV/VIS Spectrophotometer. Active chlorophyll-a concentrations (C) were calculated using Lorenson’s (1967) Equation.
2. Seagrass beds were visually surveyed and observations were made of seagrass and algal species composition, dominant seagrass species, and status of the seagrass beds using the following key: dense (> 10 shoots per 0.1 m2); sparse / sparingly (< 10 shoots per 0.1 m2); patchy (<5 shoots per 0.1 m2). The macrofaunal compositions of the seagrass beds were determined using a methodology adapted from English et al. (1994). A beam trawl (1.3 m wide, 0.5 m high, mesh size-2 inches) was towed behind a small boat over the seagrass beds. Tows were carried out for two minutes at two knots, parallel to the shore and opposite the flow of the surface current. The faunal species collected were counted, measured and identified as far as possible using identification keys. Plant species collected in the trawls were also identified using taxonomic text.

The biodiversity found in these events consist of Plante: Seagrass, Algae and Mangrove and Animalia: Arthropoda, Chordata, Echinodermata and Mollusca The phylum of Arthropoda, Chlorophyta, Chordata, Chorophyta, Cnidaria, Echinodermata, Mollusca, Mollusca, Rhodophyta, and Tracheophyta

1. Thalassia testudinum
   rank: genus
2. Haloudle Wrightii
   rank: genus
3. Syringodium Filiforme
   rank: genus

Coastal areas around Trinidad and Tobago