HABs have been reported in every U. HABs are known to be a national concern because they affect not only the health of people and marine ecosystems but also the 'health' of local and regional economies.
Let's look for the source of the red tide. Algae bloom frequently turn the water red, as the name implies. In its most basic form, a red tide is a phytoplankton bloom. Phytoplankton is microscopic and single-celled plants that live in our coastal waters. Phytoplankton species do not all produce visible blooms. Red tides are caused by a type of phytoplankton known as dinoflagellates, which appear to prefer warmer and calmer waters. The phytoplankton cells that cause a red tide contain pigments that allow them to capture sunlight, which is required for cell nourishment, growth , and reproduction.
When millions of cells are concentrated in each gallon of seawater along our coast, these pigments can emit a reddish colour. If you looked at just one of these cells under a microscope, you might notice that it has a golden-brown colour.
In some parts of the world, red tides can appear in a variety of colours, ranging from brown to burgundy, to bright red, and even yellow. The colour of a bloom is determined by the phytoplankton species that are blooming, as well as other factors such as light intensity and the angle at which the sun shines on the water. The maximum particulate carbon levels during this red-tide were 2. The increase in paniculate carbon in the bloom from 25 to 30 July, and the subsequent decrease, were consistent with the variation of paniculate nitrogen Figure 2A and B.
These increases and decreases corresponded to the development and decline of the D. The C:N ratio in the fractionated phytoplankton assemblages was relatively steady during July August 1. However, the ratio increased drastically from 8. Photosynthesis of D. A Photosynthesis as a function of cell number; B photosynthetic rates of D. An increase in C:N ratio is a feature of stressed algae.
For example, Goldman et al. The ranges of a B and 4 in general are comparable with those of the dinoflagellates Ceratium spp. Rivkin and Voytek, and the diatom Nitzschia delicatissima Erga, Assimilation rates P B m of the present red- tide phytoplankton dominated by D. Summary of photosynthetic rates of selected algae Taxon Growth conditions u.
Autumn blooms essentially comprising of Ceratium sp. Assimilation numbers of D. It is extremely low compared to the diatoms Thalassiosira rotula and Ditylum brightwelli, and larger dinoflagellates, such as Pyrocystis spp. Whether toxigenic species show similar photosynthetic characteristics that differ from non-toxigenic species can only be established by a comparative study on cultures of these algae grown under identical conditions.
The variation in carbon uptake rates of D. There was a correspond- ence in the low values, for example on 25 July Carbon uptake rates normalized to chlorophyll a 0. Primary production during D. The contribution of D. Based on the similarities in the photosynthetic characteristics between the red-tide of D. Acknowledgements We are grateful to Drs J.
Stewart, K. Mann, W. Harrison and D. Gordon Jr and Mr G. Wohlgeschaffen for constructive criticism of the manuscript. Comments of two anonymous reviewers were most helpful in improving the text. Pan has been supported by a research grant to Dr K. References Amadi,I.
In Soumia. II Environmental control of photosynthesis. Plankton Res. C, McCarthy,J. Nature, , — In Sournia. Pan Marquardt. Nature, , Toxicon, 13, In Anderson,D. Elsevier, New York, pp. Vertical profiles of the area show a vertically homongeneous zone and a stratified sector with simple and double thermoc1ines. This discontinuity indicates the existence of a frontal system between well-mixed and stratified waters, where physico-chemical properties exhibit sharp gradients.
The satellite image Figure 2 c1early shows the position and extent ofthis structure during the summer season, when its maximum development is reached.
Nevertheless, during the study period the structure of this system presented latitudi- nal differences related to the depth of the mixed zone Pingree et al. In Section A, the homogeneous side presents a lower temperature than the super- ficiallayer of the stratified zone between stations 3 and 4, decreasing again towards the shelf-break. The lowest temperatures occur at the deepest layers of the station far- thest from the coast Figure 3a.
Section B for a temperature, b nitrate and e chlorophyll a. The highest values occur at the deepest layers of station 2. In Section B, the superficial temperature gradient between the homogeneous zone and the stratified one disappears Figure 4a ; the latter presents a higher nitrate con- centration than Section A, although lower than that ofthe homogeneous zone Figure 4b. Section e shows a more complex picture.
The homogeneous zone presents higher temperatures and lower nitrate concentrations than the superficiallayers of the stratified area; it is noteworthy that in the well-developed transitional zone there is an upwelling suggested by nitrate distribution Figure 5a and b. Differences observed in the structure of the analyzed sections may be considered in terms of the model of Pingree et al. After this model, the studied system must be considered as the transition between a deep front Section A and an intermediate one in conditions of a developing stability Section D , or upwelling Section C.
Section e for a temperature, b nitrate and e chlorophyll a. Distribution and abundance of phytoplankton species Distribution and abundance of phytoplankton species in the front sections also show marked differences. In Section A, the highest concentrations of cWorophylla Figure 3c and phytoplankton cells Table 1 occur at the frontal zone in the superficiallayers of the stratified side, where dinoflagellates are almost exclusively observed.
In contrast, diatoms are domi- nant on the homogeneous side. The dominant organism on the stratified side was the toxic dinoflagellate G. Another dinoflagellate found in the area was the phagotrophic Polykrikos schwartzii Table 1. Microscopic observation shows it to be an active predator of G.
In the contents of P. The distribution of this predator is closely related to the presence of G. The highest concentrations of P. Section O for a temperature, b nitrate and e chlorophyll a. The correlation predator-prey is very high in the northern edges of the path station 7, 1: 10 , being lower in the centre and in the homogeneous zone Figure 7a and b where G. It may be assumed that distribution of G.
The importance of the vertical mixture in this area is c1early pointed out by the presence in the plankton of typically benthic species P. The highest concentrations of resting cysts Table 1 occur at intermediate depths of the homogeneous side 30 m: cysts , being absent in the stratified side of the front. The phytoplankton composition on both sides of the front is similar to that observed in the tidal fronts ofthe North Sea Pingree et al. Cal'reto el al. Vertical distribution of a Gonyaulax excavata and b Polykrikos schwertzii in section A.
In that year concen- trations of G. In , although concentrations of G. It may be assumed that the bloom was in its maintenance stage, which agrees with the presence of sexual forms of G. The distribution and abundance of phytop1ankton species of this section is notab1y different from the other sections of this same front. In Section B, the same distribution of species is observed and the highest concen- trations of ch10rphyIl a correspond to the abundance of G. In Section C, the maximum chlorophyIl a is on the homogeneous side of the front, corresponding to high concentrations of diatoms Chaetoceros sp.
Vegetative cells of G. In Section D, chlorophyll a restricted to the superficial area is associated with high concentrations of mucilaginous colonies of Phaeocystis and some re1ated diatoms of the genus Thalassiosira spp.
Discussion Dinoflagellate blooms have been associated with different hydrographic conditions river runoff, tidal or other oceanic fronts whose common feature supposes an appropriate combination between the stability of the water column and the continuous flow of nutrients Margalef et al.
In addition, different mechanisms like current inter- actions, Langmuir circulation, and convergence areas, have been pointed out as the causes for the concentration of organisms in patches or streaks Steidinger and Had- dad, These physical mechanisms can also transport bloom s and in some cases act as dispersion agents.
Blooms of G. The initiation of a G. Neither toxic red-tides nor the presence of G.
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