II/E-1
BENTHIC ORGANISMS OF FERTILIZED AND UNFERTILIZED PONDS IN WINTER¹

by

JIUM-KUO LIANG
Tainan Fish Culture Station
Taiwan Fisheries Research Institute
Tainan, Taiwan

BENTHIC ORGANISMS OF FERTILIZED AND UNFERTILIZED PONDS IN WINTER

Abstract

Populations of benthic organisms in ponds at Auburn, Alabama, U.S.A. were sampled from December, 1963 through February, 1964. The twelve 0.1-hectare ponds used had been fertilized with either (N-P-K) 8-8-2 or 0-8-2, with necessary controls.

Multiple-plate samplers were used for obtaining samples.

Dry weights of organisms and counts of individual animals were obtained. The dominant groups of animals are listed and their average numbers per square meter given.

The rate of increase of biomass in the samples from ponds that had received 8-8-2 and those that had received 0-8-2 fertilization were significantly greater than those from the ponds that had received no fertilization, but the rates from the 8-8-2 and 0-8-2 ponds were not significantly different from each other. The variations in populations due to depth were not significant.

A comparison of dry weights obtained in winter with previous records of dry weights from samples in summer indicated that the productive capacity in summer was significantly higher than that in winter.

ORGANISMES BENTHIQUES DES ETANGS FERTILISES ET NON FERTILISES EN HIVER

Résumé

Des échantillons de peuplements d'organismes benthiques ont été prélevés dans des étangs à Auburn, Alabama (Etats-Unis), de décembre 1963 à février 1964. Les douze étangs, d'une superficie de 0,1 hectare chacun avaient été fumés soit avec (N-P-K) 8-8-2, soit avec 0-8-2 et avaient fait l'objet des contrôles requis.

Des échantillonneurs à plaques multiples ont été utilisés pour les prélèvements.

Le benthos a été pesé à sec et des décomptes d'organismes individuels effectués. L'auteur donne la liste des principaux groupes d'organismes repérés et le nombre moyen d'individus par mètre carré.

Dans les échantillons provenant des étangs fertilisés avec 8-8-2 et de ceux fertilisés avec 0-8-2, le taux d'accroissement de la biomass était sensiblement égal, mais nettement supérieur à celui des étangs non fertilisés. Les variations de population en profondeur sont insignifiantes.

La comparaison du poids sec des échantillons prélevés en hiver avec des données relatives au poids sec en été indique que la capacité de production est sensiblement plus élevée en été qu'en hiver.

ORGANISMOS BENTONICOS EN LOS ESTANQUES FERTILIZADOS Y NO FERTILIZADOS EN INVIERNO

Extracto

De diciembre de 1963 a febrero de 1964, se tomaron muestras de las poblaciones de organismos bentónicos en los estanques de Auburn, Alabama, (E.U.A.). Los doce estanques de 0,1 Ha utilizados habían sido fertilizados con (N-P-K) 8-8-2 o 0-8-2, con los controles necesarios.

Para obtener las muestras, se emplearon toma muestras de placas múltiples.

Se obtuvieron el peso en seco de los organismos y los recuentos de los distintos ejemplares de animales. Se da la relación de los grupos de animales dominantes y el número medio de los mismos por m².

La tasa de incremento de la biomasa en las muestras correspondientes a los estanques con una fertilización de 8-8-2 y de los que habían recibido 0-8-2 fueron notablemente mayores que la de los estanques que no habían recibido ninguna fertilización. Pero en cambio, no difirieron mucho una de otra la de los estanques con 8-8-2 y 0-8-2. Las variaciones en las poblaciones debido a la profundidad no fueron notables.

La comparación de los pesos en seco obtenidos en invierno con los anteriores datos de peso en seco correspondientes a muestras obtenidas en verano, indicaron que la capacidad productiva en esta estación del año era sensiblemente más elevada que en invierno.

¹ From a thesis submitted in partial fulfillment of the requirements for the M. S. degree at Auburn University, Auburn, Alabama, U. S. A.

1 INTRODUCTION

Benthic organisms are of great importance in nutrition cycles in fish ponds and their quality and quantity have been used as indications of productivity.

When studying benthos, different kinds of dredges, artificial substrata, and other devices have been employed to collect samples from various types of bottom. The quantities of organisms sampled by these devices provide a measure of the “standing crop”. This measurement has usually been considered a poor index of productivity without some indications of the time factors involved in its formation (Ryther, 1956).

To investigate the formation and growth of populations of benthic organisms, Hester and Dendy (1962) developed the multiple-plate sampler. For the organisms that attach themselves to the samplers, this provides protection from fish predation. It thus measures the biomass on the substrata between the plates of sampler, rather than standing crop after predation by fish.

When samplers were hung at a certain depth in the water, the artificial substrata were populated by free-swimming stages of various animals. The bottom-dwelling organisms which burrow in mud and live in or on the bottom deposits at all stages of their life histories could not be sampled by such hanging samplers. To sample this part of the benthos with multiple-plate samplers, a method was needed to place the samplers in contact with the bottom and yet not allow them to sink into the soft mud.

Previous work using multiple-plate samplers for studies on the benthic organisms of experimental ponds in the Auburn University Agricultural Experiment Station, Alabama, had been conducted in summer. The effectiveness of these samplers for study of winter populations and seasonal variations was not known. Information was needed on the composition of winter populations and on the seasonal variation of populations under different conditions of fertility.

Fertilization of pond water to increase fish-food organisms has been practised in many countries, but much still needs to be learned about its effects. In America, Howell (1942) and Gross et al. (1946) observed that complete fertilization of pond water could increase the production of bottom organisms. Ball (1949; 1951) found that the volume of fish-food organisms could often be greatly increased by the addition of fertilizer. Neess (1949) discussed the function of bottom soils and the usefulness of fertilizing substances in increasing fish yields. In the brackish-water ponds of Taiwan, Tang and Chen (1957) reported that chemical fertilizer could be used to promote the growth of benthic algae which serve as the main food of the milkfish, Chanos chanos.

The effects of summer fertilization on benthic populations in winter have not been studied.

The bottom deposits have important effects on the distribution and abundance of benthic invertebrates. These deposits usually vary according to depth. In Auburn, Alabama, Howell (1942) found that during the drought in November 1940, the numbers of organisms per square metre at depths of 0.15, 0.46 and 0.92 metre were 17,493, 16,707, and 23,528 respectively in fertilized ponds and were 1,173, 5,583 and 2,033 in unfertilized ponds. Curry (1954) concluded that one of the principlal factors affecting distribution of benthic fauna appeared to be bottom type. McIntire and Bond (1962) observed that the benthic organisms in fertilized ponds became abundant initially in very shallow water (0.3 m or less); and built up populations in deeper water more slowly. Nevertheless, very little was known about the effect of depth on winter populations.

Table I

Total amount of fertilizers applied to ponds from 1959 through 1963, Auburn, Alabama¹

¹ Data from Annual Reports of Auburn University Agricultural Experiment Station, Auburn, Alabama

Table II

Invertebrates present in the samples from multiple-plate sampler in contact with the bottoms of ponds. Auburn, Alabama, December 1963 to February 1964

2 MATERIALS AND METHODS

2.1 Ponds

The samples in this study were taken from twelve 0.1 ha earthen ponds, known as F16 to F27, at the Auburn University Agricultural Experiment Station, Alabama. All these ponds had a common water supply from a canal.

During the period of this experiment the water was 0.6 m at the shallow ends of the ponds and gradually increased to a maximum depth of 2.4 m near the drain pipes. The bottoms of these ponds were generally alike, ranging from slightly stiff sandy clay in the shallow edges to soft muddy ooze in the deep waters.

2.2 Previous treatments of ponds

The ponds were constructed in 1940–1941 and were fertilized at an average rate of N-P-K 100-46-36 kg/ha per year from 1942 to 1959. From 1959 through 1963, these ponds were used for fertilization experiments with four replications of three different levels of fertilization: (i) no fertilization, (N-P-K) 0-0-0; (ii) non-nitrogenous fertilization, (N-P-K) 0-8-2; and (iii) “complete” fertilization, (N-P-K) 8-8-2. All ponds were drained in October or November each year and then were refilled. The total amounts of fertilizer applied to these ponds from 1959 to 1963 are listed in Table 1. In 1963, the ponds were not drained. Eight applications of fertilizer were made between 12 March and 17 September, but no further fertilizer was added throughout the period of the study from 7 December 1963 to 28 February 1964.

2.3 Fishes

Each pond was stocked with 250 fathead minnows, Pimephales promelas, (0.63 kg) on 1 March 1963; 375 bluegill, Lepomis macrochirus, fingerlings (0.68 kg) on 4 March; and 25 largemouth bass, Micropterus salmoides, fingerlings on 30 April 1963.

2.4 Sampling and analysis

A total of 288 samples were collected between 7 December 1963 and 28 February 1964. Sampling for the organisms was carried out with two types of multiple-plate sampler.

Multiple-plate samplers supported by frames to ensure contact with the bottom (Fig 1) were used for sampling the organisms in or on bottom deposits. They consisted of two plates of tempered hardboard (masonite), 0.23 cm thick and 7.62 cm² separated by a 2.54 cm² plate of the same material. The sampler was attached in a vertical position to the frame with a rubber band, and by a nylon cord to a stake driven into the pond bottom.

In each experimental pond, stations at depths of 0.6 m, 1.2 m, and 2.4 m were marked with wooden stakes inserted into the bottom. The samplers were set and raised from a boat. At each station, two samplers were placed on the bottom near the stake.

All samplers were exposed for three weeks. In recovering the samplers, each was pulled up gently, and carefully enclosed in a plastic bag before bringing it out of the water. They were transported to the laboratory where the contents were sorted into pans. The organisms on the edges and the protected inner surfaces of the plates were scraped off with a spatula. The two samples from the same station were combined and concentrated in the “bucket” of a Wisconsin type plankton net equipped with No. 20 standard silk bolting cloth. Concentrates were examined under a binocular microscope. The sample was preserved in 10 percent formalin.

Fig. 1 Multiple-plate sampler supported by a frame to allow contact with the bottom

The analyses of samples from this type of sampler were carried out by a numerical method. The large chironomid larvae and other large aquatic insects were separated from other organisms and debris by the technique described by Lyman (1943). The remainder of the sample was then made up to either 20 or 40 ml depending on the abundance of animals present, and stirred with a magnetic stirrer. Three 1-ml sub-samples were taken and the kinds and numbers of animals present were recorded. Total numbers of different groups were then calculated. The identification of the animals was carried out by using the keys in Edmondson (1959), Johannsen (1936; 1937), Ross (1944) and Pennak (1953).

The multiple-plate sampler described by Hester and Dendy (1962) was used in sampling organisms for determining quantities by the dry weight method.

Two of these samplers were hung on a T-shaped iron stake. In each pond one stake with two samplers was set midway between the two ends of the pond and 0.9 m to 1.5 m from the shore, so that the samplers were kept 0.3 m above bottom and 0.3 m below water surface. All samplers were left in the water for three weeks. At the end of this period, each sampler was enclosed in a small plastic bag before removal from the water, to prevent loss of organisms. The samples were taken to the laboratory to be sorted.

The animals, cases, algae, silt, and other materials on the edges and the inner surface were scraped off with a spatula. After concentration with a Foerst electric plankton centrifuge, the samples were preserved in 70 percent alcohol. A few days later, they were concentrated again and the accumulated organisms and debris were transferred into weighed crucibles, and dried at 60°C in an electric oven for 48 hours. The crucibles with the samples were then kept in desiccators for 24 hours. They were then reweighed and net weights were obtained and recorded.

In order to offer mathematical support of the results obtained, analysis of variance was made with a computer. The results and interpretation are given in the following sections.

The author wishes to express his gratitude to Dr. John S. Dendy for directing this investigation and for criticizing the manuscript.

3 RESULTS

3.1 Samplers in contact with pond bottom

The animals sampled with multiple-plate samplers in contact with the bottom were identified. They are listed in Table II.

The average numbers of the four dominant groups, Chaetogaster, copepods, other entomostraca, and chironomid larvae, under different fertilizer treatments are given in Table III; the distributions of these groups with depth are given in Table IV; and the variations in their numbers in different months are given in Table V.

The analysis of variance suggested that there were no significant differences (P<0.05) in numbers of invertebrates with the month or depth of sampling in fertilized or unfertilized ponds. The numbers of the invertebrates from 0-8-2 and 8-8-2 ponds were significantly greater (P<0.05) than those from 0-0-0 ponds, but the effects of 0-8-2 fertilizer treatments upon the invertebrates were not significantly different from those of 8-8-2 treatment.

3.2 Hanging samplers

The monthly variation of dry weights of organisms plus debris on samplers from ponds which received different levels of fertilizer treatment are presented in Table VI.

The analysis of variance indicated that the dry weights sampled in February were significantly greater (P<0.05) than those sampled in December and January. However, there were no differences in dry weights between those sampled in December and those sampled in January. The dry weights from 0-8-2 and 8-8-2 ponds were significantly greater (P<0.05) than those from 0-0-0 ponds, but the weights from 0-8-2 ponds were not significantly different from those from 8-8-2 ponds.

Table III

The average numbers of four dominant groups per square metre of surface of multiple-plate sampler in contact with pond bottoms, Auburn, Alabama, December 1963 to February 1964

Table IV

The average numbers of four dominant groups, g/m² of surface of multiple-plate sampler in contact with the bottoms at different depths in ponds, Auburn, Alabama, December 1963 to February 1964

Table V

The average numbers of four dominant groups, g/m² of surface of multiple-plate sampler sampling in different months

Table VI

The average dry weights, g/m², of organisms plus debris on multiple-plate samplers by months, from ponds which had previously received different levels of fertilizer treatment

Table VII

The comparison of average dry weights, g/m², of organisms plus debris in winter samples with those in previous summer, Auburn, Alabama, August 1963 to February 1964

¹ Data by courtesy of Dr. J. S. Dendy

The comparison of dry weight of organisms plus debris in winter samples with those from the previous summer samples are given in Table VII. The summer data were obtained from Dr. J.S. Dendy's records. Samples for his study were taken with the same type of samplers exposed in ponds from 21 August to 11 September 1963.

By analysis of variance the dry weights from samples in summer were shown to be significantly greater (P<0.05) than those from the samples in winter. The dry weights from samples of 0-8-2 and 8-8-2 ponds were significantly greater than those from samples of 0-0-0 ponds. There were no significant differences between the dry weights from samples of 0-8-2 ponds and those from samples of 8-8-2 ponds.

4 DISCUSSION

4.1 Evaluation of the multiple-plate sampler in contact with the bottom in sampling of benthic organisms

The results proved that the multiple-plate sampler in contact with the bottom is an effective device for sampling benthos. The samples obtained (i) included seven phyla including at least 31 genera of benthic fauna (Table II); (ii) were adequate for qualitative and quantitative studies; (iii) gave an estimate of the rate of increase of biomass resulting from different levels of fertilization. The fact that there was little or no damage to organisms sampled by this method helped the qualitative and quantitative studies.

The most important benefit of this method is that it shows the numbers of organisms that the water can produce in the absence of fish predation. The space between two plates provides a shelter for those invertebrates which are attracted by the surface of the plates. This shelter was also a desirable place for growth of periphyton.

However, the effectiveness of the device is limited by the selectivity of the substratum by the organisms. Further study will be needed to determine the most desirable length of time for exposing the samplers in water, so that the rate of increase of biomass per unit time most accurately estimates the productive capacity of the environment during the sampling period.

4.2 Estimate of winter populations

There were four dominant groups of invertebrates present in samples in winter. They were Chaetogaster, Copepoda, and “other Entomostraca” including Cladocera and Ostracoda, and chironomid larvae. The counts of these groups showed that the “other Entomostraca” was numerically the most abundant group (Table III). Regardless of the fertilizer treatments, the average numbers per square metre of surface of plates in three-week exposure were Chaetogaster 2,227, Copepoda 1,786, other Entomostraca 41,945, and chironomid larvae 1,702. In the “other Entomostraca” group, the Cladocera appeared more abundant than the Ostracoda, especially in 0-8-2 and 8-8-2 ponds. There were considerable numbers of Nais and Trichoptera, but very few Mollusca, Ephemeroptera, Zygoptera, and Turbellaria were present in samples.

4.3 The effects of previous fertilizer treatment upon the benthic organisms

The results from both the counting method and dry weight method showed that the rate of increase of benthos on samplers in the 0-8-2 and 8-8-2 fertilized ponds were significantly greater than those in 0-0-0 unfertilized ponds, but no significant difference (P<0.05) was demonstrated between rates of increase in 0-8-2 and in 8-8-2 ponds. Both types of multiple-plate samplers gave quite satisfactory results in sampling benthic organisms. Studies in the same ponds by Rabanal (1960) indicated that higher production of benthic invertebrates resulted when fertilizers were applied. The results of this experiment were in agreement with the findings of Rabanal, and those of Ball (1948; 1949; 1951) in Michigan ponds and lakes.

With the exception of the chironomid larvae, the data in Table III and Table V indicate that the rates of growth of benthos in winter responded to the effects of fertilizer applied in the previous spring and summer.

It was observed in this study that Ostracoda from samplers in fertilized ponds differed from those in unfertilized ponds. There were large numbers of young individuals in fertilized ponds, while only a few large ones in unfertilized ponds. This indicated that a large and expanding population occurred in the fertilized ponds.

4.4 Variation due to depth

The average counts of four groups of dominant benthic invertebrates show a variation due to depth in 0-8-2 and 8-8-2 ponds (Table IV). In 8-8-2 ponds, the average numbers in shallow water were considerably higher than those in deeper waters. However, the depth variation was not great enough to show a significant difference by statistical analysis. The results of the analysis, therefore, did not correspond with the findings of other investigators (Howell, 1942; Curry, 1954; McIntire and Bond, 1962). Since these were relatively shallow ponds, no stratification of water occurred during the period of this study, and therefore a uniform growth of populations at all depths could be expected.

4.5 Comparison of the benthic organisms in winter with those in summer

As mentioned in the Introduction, “standing crop” has been considered a poor index of productivity. It is a measure of the quantities of organisms which are left after predation by fish or other predators. Therefore, the standing crop means little unless the populations of predators are known.

Regarding fish predation, Ball and Hayne (1953) observed that the average level of invertebrate fauna for the year following the removal of fish was 2.6 times the average for the two previous years. Dendy (1956) warned that the use of bottom fauna data for assessing productivity should be applied with caution since interpretation is difficult where different species and numbers of fish affect the result through their predation.

The multiple-plate sampler sampled the organisms that were attracted by the artificial substrata and were being protected from predation by fish.

The rate of increase of biomass per unit area of the surface of sampler for a given length of time could be measured by dividing the total biomass by the length of time of exposure and by the area on which the biomass accumulates. This measurement gives a new approach to evaluating the capacity of an aquatic environment in producing biomass. The results showed that the rate of increase of biomass per unit area of protected surface of sampler was greater in summer than in winter.

5 REFERENCES

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