Various hypothesis have been proposed to explain why floating artificial habitats are successful in attracting fishes. Food may be a stimulus for aggregating some species around Fish Aggregating Devices (FADs). This study attempts to discover if sessile marine organisms which readily encrust traditional FADs, are important food organisms for fish. A new group of FADs was installed in a rich fishing ground. Different parts of the FADs were sampled every 2 weeks for identification of encrusted organisms, and ten species were identified. The density of the organisms fluctuated with time of immersion. Plankton collected from the water at the FAD sites was also identified. Stomach contents of 90 fishes caught around these FADs were analyzed and the organisms found in the stomachs were compared with those on the FADs. This study suggests that the attraction of fishes to FADs is due to mechanisms other than feeding on organisms encrusting the FADs.
The epiphytic algae on surfaces of the macrophyte Ranunculus penicillatus (Dumort .) Bab . var. calcareus (R . W. Butcher) C . D . K. Cook and on Cladophora glomerata (L .) Kiitz growing in the River Itchen at Otterbourne near Southampton were studied between February 1984 and June 1985 . The river at this site has a mean flow rate of 0 .33 m s -1 , and is about 16 m wide and on average 20 cm deep, with a discharge ranging through the year between 0.34 and 2 .46 m 3 s -1 . The pH of the river varies little around 8 .2, with a mean alkalinity of 236 mg HCO3 1 -', because of its origin from chalk springs . Ranunculus grows throughout the year, with peaks of biomass in spring and autumn . It forms a very large surface for attachment of epiphytes, and covers on average 40% of the stream bed . Numbers of epiphyte cells removed from Ranunculus ranged through the year between 52 x 103 and 271 x 103 cells mm -2 stream floor, with maximum numbers in April, and a secondary peak in October. This pattern partly reflects fluctuations in the biomass of Ranunculus ; the number of cells per unit area of plant surface showed a broader spring peak and lower fluctuations in other seasons . Diatoms formed 65 to 98% of these epiphyte cells, with chlorophytes reaching their peak (10%) in summer and cyanophytes (25%) in autumn . Estimates of biomass of these epiphytic forms, derived from measurements of chlorophyll c, indicate a range between 30 and 100 g dry weight m -2 of weed bed .Colonisation studies showed that the algae grow and reproduce throughout the year, with a mean generation time of about 5 days, suggesting an annual production of about 3 kg dry weight m -2 of weed bed, which makes epiphytic algae the principal primary producers in the stream . The numbers and biomass of epiphytic algae on Cladophora are considerably less .The species of epiphytic algae found on Ranunculus were generally similar to those growing on Cladophora, and to epilithic algae on pebbles of the stream bed, but different species were dominant on the different substrata . Algal cells in the water column were all derived from benthic habitats, although their relative abundance was very different .
Microscopic epilithic algae in the River Itchen at Otterbourne near Southampton and in the Ober Water in the New Forest were studied during 1984 and 1985. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO, 1-I ; at the study site the river is about 16 m wide and 20 cm deep, with a mean flow rate of 0.33 m s -' and a discharge ranging through the year between 0.34 and 2.46 m3 s -'. The Ober Water, which drains sands and gravels, has a pH between 6.9 and 7.2 and a mean alkalinity of about 50 mg HCO, 1 I ; at the study site it is about 6 m wide, with a mean flow rate of 0.27 m s ' and a discharge ranging through the year between 0.08 and 1.0 m3 s l .Epilithic algae removed from the pebbles that form the major part of the beds of both streams show seasonal changes in abundance and composition. Diatoms peaked in AprilIMay and dominate the epilithic flora in both streams, comprising 70-95" of all algal cells; highest numbers of chlorophytes occurred in summer and cyanophytes increased in autumn. The species composition of the epilithic flora in the two streams was different, as was the population density; algal cell numbers ranged between 500 and 7000 cells mm -of stream floor in the River Itchen and between 8 and 320 cells mm -* of stream floor in the Ober Water. The chlorophyll a content of epilithic algae in the River Itchen ranged between 1 15 and 4 15 mg m * of stream floor, representing an annual mean biomass of about 8 g m -2, whereas in the Ober Water a chlorophyll a content of 2.2 to 44 mg m -2 of stream floor was found, representing an annual mean biomass of about 1 g m p 2 . Cautious estimates of the annual production of epilithic algae in these streams suggest a value of about 600 g organic dry weight m in the River Itchen and about 75 g m in the Ober Water.
Periphytic algal assemblages, comprising bacillariophytes, cyanophytes and chlorophytes of standing dead trees in Lake Kenyir, a tropical drowned forest reservoir, were studied during 1995. A total of 317 algal taxa were identified in this study. The monthly floral mean species richness and cell count data demonstrated significant temporal differences between the months, in one-way ANOVA (P < 0.05). Both redundancy analysis and cluster analysis on monthly blue-green abundance and diatom assemblages exhibited conspicuous groupings among the months, with underpinning seasonal differences. The responses were not similar, however, between the upstream and downstream ends of the lake. The grouping or clustering of months can be generalized as: (i) November, December and January as the monsoonal months; (ii) February, March, April and May as the transitional months; and (iii) June to October as the dry months. Based on stepwise multiple regression with forward selection, alkalinity and dissolved oxygen concentration were significant environmental predictors at the downstream dam sampling site, and reactive silica, electrical conductivity, Secchi depth transparency and sunshine hours were significant predicators at the upstream riverine sampling site, based on Monte Carlo tests. Being a ploymictic, mesotrophic lake, the limnology and temporal changes for Lake Kenyir appears to be complex and driven by monsoons, as evidenced from the temporal changes in its periphytic algae communities, particularly the diatom assemblages. The downstream sampling site (site 1) at the dam, in the main basin and deeper zone of the lake, the seasonal amplitude was likely complex because of thermocline formation and stratification processes. In contrast, the upstream sampling site in the Petang River (site 2) exhibited a clearer distinction between the dry and monsoon months, based on its cyanophyte and diatom floral assemblages. These study results are pertinent for lake management, especially for developing biomonitoring programmes or lake productivity studies, as well as for climate change studies, within the context of tropical lake ecology.
Red tide of dinoflagellate was observed in brackish water fish ponds of Terengganu along the coast of the South China Sea during the study period between January 1992 to December 1992. The nearby coastal moat water facing the South China Sea is the source of water for fish pond culture activities of sea bass during the study period. An examination of water quality in fish ponds during the study period indicated that both the organic nutrients were high during the pre-wet monsoon period. The source of the nutrients in coastal water was believed to be derived from the agro-based industrial effluents, fertilizers from paddy fields and untreated animal wastes. This coincided with the peak production of dinoflagellate in the water column in October 1992. The cell count ranges from 8.3 to 60.4×10.4×10(4)/l during the bloom peak period and the bloom species were compared entirely of non-toxic dinoflagellates with Protoperidinium quinquecorne occurring >90% of the total cell count. However, both cultured and indigenous fish species were seen to suffer from oxygen asphyxiation (suffocation due to lack of oxygen). The bloom lasted for a short period (4-5 days) with a massive cell collapse from subsurface to bottom water on the sixth day. The productivity values ranged from 5-25 C g/ l / h with a subsurface maximum value in October 1992. Two species of Ciliophora, Tintinnopsis and Favella, were observed to graze on these dinoflagellates at the end of the bloom period.
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