Prec. Indian Acad. Sci. (Anim. Sci.), Vol. 89, Number 5, September 1980, pp. 407-414. (~ Printed in India.

Ecology of Heteromastus similis Southern 1921 (Polychaeta : Capitellidae) in the Vasishta Godavari estuary

D SRINIVASA RAO Department of Zoology, Andhra University, Waltair 530 003, India

MS received 19 September 1979 ; revised 20 March 1980

AbslraeL Ecology of Heteromastus similis, capiteUid, inhabiting the intertidal area of the Vasishta Godavari estuary has been studied for a period of 15 months. Its abundance and distribution in relation to the distance from the river mouth, tidal level, temperature, interstitial salinity, dissolved oxygen, sediment composition and organic matter in the sediment is discussed.

Keywords. Heteromastus similis; fixed level transect sampling ; high annum floods; organic pollution indicator.

L Introduction

Capitellids received considerable attention all over the world because of tlzeir cosmopolitan distribution and their capacity to tolerate wide range of fluctuations in physical factors. They are known to inhabit widely diverse substrata ; Capi- tella capitata lives in black muds, Notomastus and Heteromastus in cleaner sands. While Dasybranchus inhabits sandy mud substratum. C. capitata survives even under anoxic conditions and is reckoned as an indicator of organic pollution (Reish 1959; Gilet 1959). Except the description of C. capitata as a pollution indicator in Visakhapatnam harbour (Ganapati and Raman 1976) there is no other published account on other eapitellids of common occurrence on the Indian coast and marginal coastal bodies of water.

Heteromastus similis, the dominant capiteUid in the estuary, has elongate reddish body which is rounded in cross-section. It is a sluggish animal burrowing various grades of sandy mud. The unarmed nature of its proboscis suggests that it swallows mud containing detritus.

2. Area of investigation

Vasishta Godavari, the southern most branch of the river Godavari, opens into Bay of Bengal at Antervedi Oat. 16 ° 18' N, long. 81 ° 42' E). The area investi- gated is the 16 km stretch of the lower reaches of the Vasishta Godavari estuary extending between the confluence at Antervedi and about 2 km beyond Narsapur town (figure 1). Six stations were fixed against permanent landmarks along the bank o f the estuary.

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Figure 1. Vasishta Godavari estuary--Location of the stations (inset showing the three tidal levels from where collections were made).

3. Material and methods

At each station a transect was fixed and three locations were selected along the transect following the fixed level transect sampling (FLTS) method suggested by Bloom et al (1972). The three locations selected on the transect were mean high

Ecology of Heteromastus similis 409

water mark (MHWM), mean mid water mark (MMWM) and mean low water mark (MLWM) (inset of figure 1).

Collections were made systematically at monthly intervals at each station from October 1976 to January 1978 except in August 1977 when sampling became physi- cally impossible as the area remained flooded with a continuous flow of fresh water in the seaward direction and tidal action from the sea was suppressed.

Temperature of the sediment was measured directly using 0.2 ° C sensitive mer- cury thermometer. The interstitial water for salinity and dissolved oxygen was collected by digging a hole and collecting the water that seeped in. Salinity and oxygen were estimated following the time-tested Knudsen's and Winkler's methods respectively. Sediment was collected by pushing a PVC corer of 8 cm diameter and sand, silt and clay fractions were determined by separating them in a sus- pended condition taking into consideration differences in the settlement velocities of sediment particles. Organic carbon was estimated following the procedure suggested by Gaudette et al (1974).

Quantitative sampling was made at all the three tidal levels using a metal frame of 20 x 20 x 15 cm dimensions. The frame is pushed to a depth of 15 cm and the sediment inside the frame is dug out and transferred to a bucket. The sediment was initially sieved in the field itself by using a 0.5 mm sieve. The animals retained in the sieve were transferred to a container and preserved in 5700 neutral formalin.

4. Results

The maximum and minimum temperatures recorded during the period of study were 40.2°C and 22-0°C respectively. Along the transect the temperature is always high at MI-IWM and low at MLWM. The temperature generally followed the trend of the atmosphere.

The interstitial salinity ranged from near zero to 35~oo. The maximum and mini- mum salinity values differed from station to station. Generally lowest salinity coincided with the annual flood season (July:September) and the salinity gradually increased to reach the maximum in summer (March-June). Generally, in each transect a decreasing trend in salinity was noticed in the direction of MLWM.

During the period of study a maximum value of 10-4 ml/L in the dissolved oxygen concentration was recorded at MHWM at station III in October and a minimum value of 2.2 ml/L at MLWM at station II in September.

The sediment was predominantly sandy near the river mouth (stations I and II) as the confluence area was influenced by the adjoining neretic waters. The silt- clay fraction increased with increasing distance (stations III-VI) under the influence of the river. The pattern of sediment distribution at each transect showed that the sand fraction was relatively high at MHWM. Organic matter in the sediment was generally high with a maximum observed value of 4"370 at MHWM at station VI in May. It varied with the sand, silt and clay percentages in the sediment.

The quantitative distribution of H. similis in the estuary is presented in table 1. It is abundant at stations II to VI and in summer months. A very high density of 2167/m 2 was recorded in June at MI-IWM at station IV. The density decreased with the onset of floods and gradually increased afterwards. The distribution of 1t. similis in relation to the distance from the river mouth and tidal level is shown in figure 2,

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Ecology o f Heteromastus similis 411

Stotions I II I I I IV V Vl

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Figure 2. Station-wise and tidal-wise distribution of //. similb in the ©stuary

5. Discussion

Salinity does not appear to limit the distribution of 1t. similis as it is found in a wide range of salinities ranging almost from that of fresh water (July-September) to that of sea water of normal salinity (April-June). Dean and Haskin (1964) and Tenore (1972) found similar tolerant capacities for closely related H. filiformis in Raritan Bay and Pamlieo river estuary respectively. However, it was less com- mon in high saline areas, i.e., at the river mouth which may be due to its inability to compete with other organisms living there as suggested by Warren (1977). The high abundance of H. similis in summer months and reduction during floods is in concurrence with the observations of Tenore (1972) made in Pamlico river estuary for H. filiformis. Though capitellids are known to tolerate low oxygen tension and even anoxic conditions (Reish 1959) such conditions were not encountered in the area of study.

H. similis occurred in 90~ of the samples collected at MMWM and in 70~o and 55Yo of the samples at MHWM and MLWM respectively. Though it preferred MMWM, it appears that the tidal levels and subsequent exposure to environmental factors do not influence the distribution.

Variations in the sediment composition do not appear to be a barrier to the existence of this species (figure 3). The absence of H. similis at MHWM at sta- tion I may be attributed to the occurrence of coarse sand and high temperature. While it occurred in any type of substrata in the study area, H.filiformis was found in sandy substrata (Tenore 1972) and C. capitata in sand (Southward 1957) and mud (Barnard and Reish 1959).

One major environmental factor which apparently affects the distribution of H. similis is the organic matter content of the sediment (figure 4). Substrata with high organic matter content are known to attract capitellids (Augustin and Auger 1974). However, assimiable fragment of the organic matter content seems to be an equally important factor (George 1964; Warren 1977).

In the area of study a major portion of the organic matter is of terrestrial origin comprising of rotting vegetation, especially at MMWM. This may also be of some importance as noticed by Bagge (1969) and Pearson (1972) for C. capitata. The

412 D Srinivasa Rao

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Figure 3. Abundance of H, similis in rolation to the sediment composition.

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Figure 4. Monthly variation in the organic matter content in the sediment and d e n s i t y o f 1t. sirnilis a t M M W M a t s t a t i o n I V .

increased number of microorganisms associated with the plant material probably serves as food as capitellids are not known to have such of the enzymes that can deal directly with the substrata (Warren 1977). Stephens (1975) however believes that the process of nutrition is by direct absorption as he found very little consump- tion of bacteria in case of C. capitata. But Warren (1977) found the presence of enzymes in the gut of C. capitata which makes us to conclude that the information available on hand is insufficient.

Ecology of Heteromastus similis 413

Many workers consider that the capitellids serve as biological indicators of pollution (Reish 1959; Ganapati and Raman 1976) but some doubt their direct relationship to pollution (Henriksson 1968 ; Rosenberg 1973) while Muus (1967) Wolff (1973) are against counting it as a pollution indicator. C. capitata and H. filiformis are generally associated with pollutants of organic nature resulting from domestic wastes, paper production, etc., and are seldom found with other forms of pollutants (Warren 1977). Grassle and Grassle (1974) conclude that capitellids are typical opportunistic species indicative of unpredictable environ- ments rather than polluted habitats.

Waters in the lower reaches of the Vasishta Godavari estuary are relatively free from pollution. The high abundance may be related to the prevailing high tempo- ratures as they can reproduce rapidly at such high temperatures and build up into a large population in localities with high organic matter content (Grassle and Grassle 1974). Similar observations were made by Tenore (1972) for the high order of abundance of H. filiformis in the Pamlico river estuary.

Acknowledgements

Thanks are due to Dr D V Rama Sarma under whose direction this work was carried out, to the management of Sri Y N College, Narsapur, and to Prof. K H Rao for providing necessary facilities, and to the Council of Scientific and Industrial Research, New Delhi, for a fellowship.

Rderences

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Baggo P 1969 Effects of pollution in ostuarino ecosystems. 1. Effects of effluents on the hydro- graphy, bottom and fauna Saltkallcfjord (W. Swod(m); Merentutkimusleitoksen Julk. Havsforskningsinst. Skr. 228 3-118

Barnard J L and Roish D J 1959 Ecology of Amphipoda and Polyehaota of Newport Bay, California; Occ. Pap. Allan Hancock Fdn. 21 1-106

Bloom S A, Simon J L and Hunter V D 1972 Animal sediment relationship and community analysis of a Florida estuary ; Mar. Biol. 13 43-56

Dean D and Haskin H H 1964 Benthic populations of the Raritan river estuary following pollution abatement ; Limnol. Oceanogr. 9 551-563

Ganapati P N and Raman A V 1976 Capitella capitata (Fabricius, 1780) (Polychaota: Capitol- lidao) : An indicator of pollution in Visakhapatnam Haxbour ; Indian J. Mar. Sci. 5 251

Gaudotto H E, Wilson R F, Toner R and David W F 1974 An inexpensive titration method for the detcxmination of organic carbon in recur sodinmnts ; J. Sed. Pet. 44 249-253

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Gilet R 1959 Water pollution in Marseilles and its relation with flora and fauna ; in Waste disposal in the marine environment ; Ed. E A Pearson (New York : Pergamon Press) p. 39

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H~iksson R 1968 The bottom fauna in polluted areas of the Sound ; Oikos. 19 111-115 Muus B J 1967 The fauna of Danish estuaries and lagoons, distribution and ecology of domi-

nating speci~ in the shallow water of mssohalino zone ;Medd. Dann. Fisk. Havanders 5 147-174

Pearson T H 1972 The effect of industrial effluent from pulp and paper mills on the marine benthic environment ; Prec. R. Soc. (London) B180 469-485

414 D Srinivasa Rao

Roish D J 1959 An ecological study of poUution ia Los Angeles, Long Bo~ch Harbour, California ; Occ. Pap. Allen. Hancock. Fdn. 20 119

Rosonberg R 1973 Benthic faunal recovery in a Swedish fjord subsequortt to the closure of a sulphito pulp mill ; Oikos 24 244-248

Southward E C 1957 The distribution of polychaota in off-shore deposits in the Irish sea ; J. Mar. Biol. Assn. U.K. 36 49-75

Stophons G C 1975 Uptake of naturally occurring primary amines by marine anaelids ; Biol. Bull. Mar. Biol. Lab. Woods Hols. Mas. 149 397-407

Tonoro K R 1972 Macrobenthos of the Pamlico river estuary, North Carolina ; Ecol. Monogr. 42 51-59.

Warren L M 1977 The ecoIogy of Capitella capitata in British waters ; J. Mar. Biol. Assn. U.K. 57 151-159.

Wolff W J 1973 The estuary as habitat, an analysis of data on the soft bottom macrofauna of the ¢stuadno area of the rivers Rhino, Meuse and Schddt; Zool. Verhandelingen 126 1-242