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Previous extensive studies of zooplankton distribution in the eutrophic Kingston Harbour established that it was being continuously contaminated. We assessed the community in 2011, 17 years after a previous study and five years after the introduction of a tertiary waste water system. Sampling was conducted for four weeks at eight stations identical to those sampled in a previous study. We used horizontal surface tows with a 200µm net. A total of 73 zooplankton taxa were identified and copepods dominated with 20 species. Mean total abundances were high, ranging from a ]]>
m-3 in the southern region of Hunts Bay to 194 166 animals m-3at the Inner Harbour. Five zooplankton taxa (Acartia tonsa, Paracalanus spp., Temora turbinata, Penilia avirostris and Lucifer faxoni) that were ]]>
Key words: Kingston Harbour, ]]>
Resumen
Extensos estudios previos de la distribución de zooplancton en el Puerto de Kingston ]]>
m-3 en la zona sur de Bahía Hunts a 194 166 animales m-3 en lo interior del puerto. Cinco taxones de zooplancton (Acartia tonsa, Paracalanus spp., T. turbinata, Penilia avirostris y Lucifer faxoni) identificados previamente como indicadores, fueron importantes de nuevo en la Bahía. La ]]>
Previous extensive studies of zooplankton distribution in the eutrophic Kingston Harbour established that the harbor was being continuously contaminated (Grahame, 1974; Dunbar, 1997). Based on the different zooplankton communities, the harbor was zoned with the Upper Basin and Hunts Bay being the most eutrophic, the Inner Harbour, showing less contamination and the Outer ]]>
Approximately 17 years have passed since the 1990’s study and with the changes as described above; a rapid ]]>
The objectives of the study were therefore to determine zooplankton abundance and species composition in ]]>
Materials and Methods
Station selection: Eight stations ]]>
Fig. 1, Table 1) to those sampled by Dunbar (1997) and Ranston (1998) and represented each of the zones identified by Dunbar & Webber (2003). Sampling was conducted for four weeks between May 21, 2011 and June 9, 2011.
Zooplankton collections:Outer, Upper and Inner Harbour- Zooplankton collections were made with a SCOR, WP2 pattern 20µm plankton net with a hoop diameter of 0.5m (United Nations Educational, Scientific and Cultural Organization [UNESCO], 1968). Horizontal surface tows were conducted in a circular path at approximately 1knot (0.5ms-1). Each tow lasted for two minutes with the net kept just below the surface of the water. Flow meter readings were taken before and after each tow using a calibrated (one revolution= 0.048m) General Oceanics flow meter which hung in the mouth of the net. This replicated the sampling method employed by the previous baseline study (Dunbar & Webber, 2003).
Hunts Bay-Replicate zooplankton samples were collected at each station using a 100µm mesh aperture net with a 12.5cm hoop diameter. Replicate oblique or vertical hauls were done at each station through the water column. The net with attached weight and rope (marked at 1m intervals) was hand-thrown as far as possible from the boat. It was allowed to sink far enough below the surface then an oblique/vertical haul was done at a steady pace at approximately 2ms-1 at the total distance hauled with this net was at least 8m. With this deployment the net sampled both the upper fresh water and lower more saline layers of the water column without disturbing the soft sediment at the bottom of the bay. This replicated the sampling method employed during the previous sampling of Hunts Bay by Ranston (1998).
Samples at each station were immediately fixed in the field using 10ml of full strength formalin (37% formaldehyde) and later preserved in 10% formalin. The volume of sea water filtered was calculated using the formula πr2h, where ‘r’ is the radius of the hoop of the plankton net and ‘h’ is distance towed; determined by the number of revolutions of the calibrated flow meter. The filtering efficiency (FE) of each net was applied to the volume calculations based on FE values generated from studies done by Dunbar (1997).
Identification and counting of the zooplankton were conducted on preserved sub-samples obtained using the beaker split method (Van Guelphen, Markle, & Duggan, 1982; Webber, Roff, Chisholm, & Clarke, 1996; Dunbar, 1997). Each sub-sample was transferred to a Bogorov tray and counted using a Wild M5/M7 Binocular Microscope. The taxonomic guides employed to identify the animals included: Davis (1955), Gonzales and Bowman (1965), Wickstead (1965), Owre and Foyo (1967), Newell and Newell (1977), Ramirez and Zamponi (1981), Michel (1984), Campos–Hernández and Suárez-Morales (1994), Todd, Laverack and Boxshall (1996) and Webber (2004). The numbers of each species were converted to numbers per m3 using the formula and the relevant dilution factors. All samples were pseudo-replicated.
Physico-chemical data were collected at each station on each sampling occasion using a Hydrolab® Surveyor DS5. These included depth (±0.08m); Temperature (±0.15°C); Salinity (±0.1ppt); pH (±0.2 units); dissolved oxygen (±0.2mgl-1).
Statistical analysis: Two tailed t-tests were applied to normally distributed physiochemical and biological data to determine if there were significant differences between the present and previous studies.
Results
Variation in physico-chemical parameters: Temperature, Salinity and Dissolved Oxygen were the primary physico-chemical parameters which varied significantly across the Harbour. The variations in temperature were minimal with values ranging from 28°C at Outer Harbour to 31ºC at Hunts Bay. The greatest temperature was recorded at the Hunts Bay stations 5 to 7. Temperatures recorded in 2011were not significantly different from those recorded in 1994.
In both studies, Hunts Bay stations 5 to 8 had the lowest salinity values (Fig. 2B), while Outer Harbour, Inner Harbour and Upper Basin stations (1 to 4) had greatest salinity values. Low salinity is indicative of fresh water inputs from the Rio Cobre, Duhaney River and Sandy Gully. The salinity values in 2011 were shown to be significantly higher than those of the previous study.
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Higher Dissolved Oxygen (D.O.) readings were recorded in the 1994 study at all except stations 7 and 8 (Hunts Bay) where the 2011 study had slightly higher dissolved oxygen readings. The lowest DO reading for 2011 was recorded at station 5/3 in Hunts Bay. This is the opposite to the findings of the previous study where that station recorded the highest DO value. The two t-test revealed no significant difference in dissolved oxygen between the studies.
Variation in zooplankton parameters: A total of 73 zooplankton taxa were identified from the eight stations sampled during the present study which is the same amount (73 species) found in the 1994 study of the harbor. Again the copepods were the most dominant group, however only 20 species were recorded, 18 species less than previously (Dunbar, 1997; Dunbar & Webber, 2003). In the present study, eight copepod species were from the order Calanoida, one more than Cyclopoida (seven species) while the Harpacticioda had five species. The second most dominant group after copepods was the group comprised of larvae with 19 species. The average number of species varied significantly (p=0.01, Table 2) between the two studies (Fig. 3). Station 1/21 had the highest average number of species 28 and 35 for the 2011 and 1994 studies respectively. The lowest number of species were found at the Hunts Bay stations with station 6 having the lowest (7 species) for the 2011 study and station 3 (10 species) for the 1994 study.
Mean zooplankton abundances ranged from 2 383 animals m-3 at Station 7 Hunts Bay- South to 194 166 animals m-3 at station 4 in the Inner Harbour near the Shipping Channel (SC) for the 2011 study (Fig. 4). In 1994, a minimum value of 381 animals m-3 were found at station 4 (middle of Hunts Bay) and maximum of 81 742 at station 8 (near the Port Royal Mangroves). The two-tailed test revealed significantly higher abundances for the 2011 study over the 1994 study (p=0.03), with higher abundances at the Inner Harbour stations (2 and 4) and lower abundances at the Hunts Bay stations (5 to 7). During the present study five indicator species were identified, Acartia spp., Paracalanusspp., Penilia avirostris, Temora turbinata and Lucifer faxoni. These species had a similar distribution to the mean total zooplankton numbers, with maximum numbers at the airport-mangrove station and minimum numbers at the Hunts Bay stations (Fig. 5). T. turbinata was the only species with maximum numbers at the shipping channel station. The 1994 study had T. turbinata, Paracalanusspp. and P. avirostris showing dominance at the airport-mangrove station while Acartia spp. and Lucifer faxoni were dominant at the shipping channel station. T. turbinata, Paracalanusspp. and P. avirostris were found to be significantly different between the two studies with T. turbinata and Paracalanus spp. having higher abundances during 2011 and P. avirostris being more abundant in 1994.
Discussion
Although the results showed ]]>
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This and other studies (Webber et al. 1996; Dunbar & Webber, 2003) have shown Outer Harbour to be the least eutrophic due to its influence by mesotrophic waters and the introduction of species from the shelf area. The diversity (number of species) found in the Outer Harbour in this present study, though higher than the other sections of the harbor, was lower than that obtained by Dunbar (1997). This was accompanied by increased zooplankton abundances, which are indices of increased eutrophication (McArthur, 1955; Clutter, 1972).
In the 1974 study of the Harbour, Grahame found the plankton community of the Upper basin to be the “most diverse and biologically accommodating, offering the largest number of niches available to the zooplankton in the Harbour”. It was therefore expected that the zooplankton community observed in this area would be different from the other areas of the Harbour. The mean abundance for the Upper Basin was higher than what was observed by Dunbar (1997), but ]]>
Like the previous ]]>
The maximum abundance (193 287 animals
m-3) found at station 2 (Airport runway/ mangroves) is similar to the maximum of 194 248 animals/m3 reported by Dunbar (1997) for the 1994 study. These values were significantly higher than the mean number recorded by Grahame (1976) of 25 248 animals m-3. The mangrove area is said to be “one of the most productive areas in the Harbour” (Dunbar, ]]>
Conditions within the harbour have not changed significantly since the last baseline conducted 17 years ago by Dunbar (1997) and the implementation of the Soapberry treatment facility five years ago. The most eutrophic area remains within the Hunts Bay as indicated by minimal species diversity and zooplankton ]]>
It therefore can be concluded that while changes (slight improvements) have taken place in areas like ]]>
Acknowledgments
We thank our research partners Sheree Broomfield, Anya Duncan, Helen Liu, Leon Grant and the staff of the Port Royal Marine Laboratory, University of the West Indies (UWI) for their assistance with fieldwork collection. Department of Life Sciences, UWI provided funding for this research.
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1. Department of Life Sciences, The University of the West Indies (UWI), Mona, Kingston 7, Jamaica; patrice.francis06@uwimona.edu.jm, stacymax1@hotmail.com, mona.webber@uwimona.edu.jm
Received 01-IX-2013 Corrected 31-III-2014 Accepted 01-IV-2014
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