Jodie Peers

Osua7b

 

Physical factors and nutrient availability the influence the distribution of Dinoflagellates.

Introduction

 

The dinoflagellates form an exceedingly important part of the ocean, the source of primitive food supply in the sea, both in the number of the individuals and in the total mass of living substances produced.

As synthetic producers of carbohydrates, proteins and fats they hold high rank among the protists of the sea and of fresh water. In abundance they are second only to the diatoms in the marine plankton, while locally and in midsummer they may far outnumber even those abundant organisms. At their periodic maxima they may surpass the diatoms in the total mass of their substance produced and in the rapidity of their development.

The dinoflagellates are one of the most important members of the phytoplankton in our marine and freshwater ecosystems and represent a major constituent of food webs.

Members of the division Pyrrophyta are generally characterised by having chlorophylls a and c, ß-carotene, and one or more of the xanthophylls. The primary storage products are starch and oil. Total lipids make up from 5-28% of the dry weight of dinoflagellates. Hydrocarbons account for 0.5-20% of the dinoflagellate lipid fraction.

Ecology and distribution.

Perhaps the largest number of species is planktonic, swimming freely, or floating, in the sea or in large bodies of water.

They are found in all latitudes from the Arctic and Antarctic seas to the tropics.

Many dinoflagellates occur in marginal habitats. Some are confined to near-shore or neritic waters which are probably more nutritious and of lower salinity than the open oceans waters.

 

Methods

 

Plankton was collected from 5 sites around Anglesey. The five sites were as follows; Menai Bridge pier, Puffin Island, Llandudno, Llandonna and at an offshore site. Plankton trawls were taken on 5 different days throughout the month of October 2003. Plankton nets were trawled for approximately six minutes at each station. Enumeration and separation techniques were specialised to the size of plankton that was intended to be collected. The size class of organisms that were being sampled were 250um-500um.

For nutrient analyses to be carried out a CTD was deployed daily at each of the sites. The nutrients that were collected were filtered through GF/F filters and then were frozen until they could be analysed at a later date.

 

 

 

 

 

 

Results.

 

Figure 1

Abundance of dinoflagellates throughout the month of October.

Colours correspond to the different species and can be referred to in the key.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Only four dates are shown on the graph, this is due to no dionflagellate organisms being found on the 5th date.

The graph shows that the species that is found in the greatest biomass over the length of the research trip is C. fusus, as can be seen, this species is present in relatively high abundances.

Throughout the month of October, the species that has the highest abundance is C. longpipes, this species reaches an abundance high of 18.5 individuals per m-3.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

figure 2

Abundance of dinoflagellates at the 5 sites sampled during the field course.

 

 

This graph also indicates that C. fusus is the most distributed species over the 5 sites. C. longpipes has the highest abundance than all the other species found at the sites.

The dinoflagellates was the lowest of all phytoplankton at less than 20 cells per dm-3 found at the sites.

 

Table 1.

Physical properties of the water around the 5 sites sampled.

 

 

Site

Mean temperature (oC)

Mean

depth (m)

Mean salinity

Pier

13.9

9.6

33.3

Puffin

14.7

22.0

33.3

Llandonna

11.8

14.5

33.4

Llandudno

15.3

13.7

33

Offshore

34.4

15.1

33.8

Temperature values were similar for all of the sites varying between 13.7-15.1˚C, the lowest temperature was seen at Llandudno and the highest at the offshore site. The salinity showed little variation at all sites. The depth was the lowest at Menai Bridge Pier and the greatest Offshore.

 

 

 

 

 

 

Nutrient analyses that were carried out at each of the five sites found that:

The phosphate concentration was similar for all of the sites values range between 0.59-0.76 mg/l. The silicate concentration varies the most with values ranging from 3.25-5.28 mg/l, the greatest value being at Llandudno and the lowest being at Puffin Island. The nitrite values were similar between 0.11-0.49 mg/l, and these were similar but slightly lower than the nitrate values (0.13-0.85mg/l). The ammonium values showed little variation (0.15-0.46mg/l).

 

Table 2.

Spearmans rank correllation coefficient of chlorophyll and dinoflagellates.

 

Analysis was performed ate the 5% significance level.

 

 

P value

R value

C. longpipes

0.279

-0.149

C. fusus

0.132

0.204

C. furca

0.037

0.280

C. macroceros

0.716

-0.050

C. triops

0.336

0.131

C. arcticum

0.336

0.131

 

The data was tested for normality, but non was shown even after it was transformed, hence a Spearmans rank corellation was carried out instead.

All the values except for C. furca, show that data to be > 0.05, which means that there is no significant relationship between chlorphyll concentration and dinoflagellate numbers. C. furca value <0.05 which indicates that for this species there is a significant linear relationship between chlorophyll and the species abundance.

 

It would be expected that where there is more chlorophyll, there should be a higher abundance of phytoplankton present, which would indicate that there was a higher level of nutrients to allow the phytoplankton to photosynthesis and produce chlorophyll.

 

Discussion.

 

The dinoflagellates are the second most abundant phytoplankton group (Lalli & Parsons, 1997). In this study the dinoflagellates were found to be the least abundant phytoplankton group. Dinoflagellate blooms usually occur in the summer, after the blooms of other phytoplankton have occurred, this is due to the dinoflagellates having a preference for less turbulent water and warmer. Due to this it is possible that the dinoflagellate numbers were relatively low because they had already reached the bloom peak earlier in the year and had the number had begun to reduce due to the weather being colder and the water currents being more turbulent.

The offshore site had the lowest abundance of dinoflagellates, this is because coastal waters are considerably richer in phytoplankton than offshore oceanic waters.

In the month of October nutrients should be in high amount due to degradation of the thermocline and the strong mixing of the water column. This could contribute to why there are still numbers of dinoflagellates left in the water column after their bloom has ceased, while there is still a nutrient availabilty, then the phytoplankton can still thrive.

Llandudno was the site that had the highest values for all five nutrients

Silicate is the nutrient that is present in the highest concentrations.

The concentration of the phosphate is lower than that of silicate.

Observing the physical facotrs that effect the water masses at the five sites, I noticed there was some variation in the depths. Menai Bridge Pier had the lowest depth, while the offshore site had the greatest depth as it was the site that was the furthest away from the shore. Temperature variations were noticeable. The offshore site was the warmest. This would provide an explanation as to why the greatest diversity in dinoflagellates was seen at the sites furthest away from the shore.

The salinity did not differ by much between the sites. It is the amalgamation of these physical factors that also contribute to the distribution and abundance of dinoflagellates, for they determine the surrounding environment that these organisms need to live in.

 

The investigation that took place in the October of 2003, could be extended so that a more accurate picture of the factors that control dinoflagellate distribution could be drawn up. The experiments could be carried out throughout the year which will provide a larger understanding not only of dinoflagellate distribution but on the larger scale of phytoplankton and zooplankton distributions. It would also allow for a closer examination of the temporal and spatial variations of the plankton. A year round study would also allow comparisons to be made of the different blooms that occur throughout the year.

 

 

References

 

Lalli, C. M. & Parsons, T. R. 1997. Biological Oceanography an Introduction, 2nd edition, Butterworth-Heinemann, Oxford.

 

Sykes, J. B. 1981. An illustrated guide to the diatoms of British coastal plankton. Field Studies 5, Field Studies Council.

 

Harris, G. P. 1978. Photosynthesis, productivity and growth: the physiological ecology of phytoplankton. E. Schweizerbart’ sche Verlagsbuchhandlung.

 

Spector, D. L, 1984. Dinoflagellates. Accademic Press Inc.

 

Dodge, J. D, 1985. Atlas of Dinoflagellates. Blackwell Scientific Publications.