Tane 35: 195 - 205 (1995)

BENTHIC FORAMINIFERA AND OTHER MICROBIOTIC REMAINS IN WAIMAMAKU RIVER ESTUARY, WEST COAST, NORTHLAND

Chris Hollis' , Emily Jenns, Michael Begbie and Annette Pullin

Department of Geology, University of Auckland, Private Bag 92019, Auckland

SUMMARY Four associations of brackish foraminifera occur in the Waimamaku River

estuary. In the upper reaches at the extreme limits of marine influence, Trochamminita salsa is dominant with common Haplophragmoides wilberti (Trochamminita association). H. wilberti is dominant, and Trochammina inflata and Miliammina fusca common, above low water in the middle reaches (Haplophragmoides association). Ammonia beccarii is dominant and M. fusca abundant subtidally in middle and lower reaches (Ammonia-Miliammina association), apart from two stations where A. beccarii comprises 90% of the total fauna (Ammonia association).

Faunas of the lower estuary include numerous normal marine benthic and planktic species probably carried in at high tide by prevailing on-shore winds and seas. Reworked foraminifera and radiolarians of Late Cretaceous, Early Tertiary and Miocene age occur throughout the estuary. Centric diatoms also occur throughout the estuary and small pennate diatoms were found attached to microbiotic remains at two stations. Sponge spicules and ostracods are restricted to the lower reaches.

INTRODUCTION

The Waimamaku River estuary lies on the west coast of Northland, 8km south of the entrance to Hokianga Harbour and 5km north of the Auckland University Field Club's field station at Kawerua (Fig. 1). The estuary is at the mouth of the 20km Waimamaku River which drains the largely pastoral Waimamaku Valley.

A full description of bathymetry, sediments and vegetation was included in an earlier study of the macrofaunal ecology of the estuary (Hayward & Hollis 1993).

Current address: Institute of Geological and Nuclear Sciences, P O Box 30368, Lower Hutt

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Kaikai

Beach

Waimamaku River estuary v^ ( V

1 / . 500 m V ^ - V /* i\ 1 1

Fig. 1. Location of sampling stations in Waimamaku River estuary, west coast, Northland (after Hayward & Hollis 1993).

M E T H O D S

The estuary was sampled in April 1992 as part of an Auckland Museum study (Hayward & Hollis 1993). 20 sediment samples of about 200cc were collected by hand from intertidal stations and by hand-hauled bucket dredge from subtidal stations. 16 of these were selected for foraminiferal study as a Stage III Paleontology laboratory exercise in Geology Department, University of Auckland. Each sample was washed with water through 75/xm and 1mm mesh sieves to remove mud and large pebbles and shells. The remaining sediment was oven dried at 80°C and split into two portions. One portion was put aside for later study. The other portion was dry sieved through 150 .̂m and 300^im sieves. The 3 resulting size fractions were examined for foraminifera and a representative pick of at least 100 specimens was made, either by picking 30-50 specimens from each size fraction or, where foraminifera were only rich in one size fraction, by picking an equal number of trays for each fraction. In the case of sparse samples, the entire foraminiferal fauna was picked (Stations 1,2,7 and 8). A l l benthic foraminifera were identified and the relative abundance of each species determined; the relative abundance of planktic foraminifera was determined; the occurrence and general abundance of other microbiotic remains

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(ostracod valves, diatom frustules, sponge spicules, reworked foraminiferal and radiolarian tests) were also recorded (Appendix I). Washed sediment residues and sample splits, picked faunas and figured specimens (Figs. 3,4; prefix "AK") are held in the marine collections of the Auckland Institute and Museum.

RESULTS

Benthic foraminiferal associations Four benthic foraminiferal associations are recognised in the estuary (Fig. 2).

Characterising species are illustrated in Fig. 3a-m.

1. Trochamminita association (Ts). Consists of dominant Trochamminita salsa with abundant Haplophragmoides wilberti. No other species are present. Occurs in the upper reaches of the estuary at the extreme range of marine influence. Sediment is sand or sandy mud.

An equivalent association is found throughout New Zealand in estuaries at the extreme limit of marine influence (Hayward & Hollis 1994). Diversity is typically low, although elsewhere Miliammina fusca is often present.

2. Haplophragmoides association (Hw). Consists of dominant Haplophragmoides wilberti, with localised occurrences of Miliammina fusca, M. cf. obliqua, Trochammina inflata and Trochamminita salsa. No other species are present. Occurs above low tide level in middle reaches (Stations 8, 9, 10 and 14). Sediment is muddy sand or soil (i.e. organic-rich sediment within rushes).

An equivalent association occurs throughout New Zealand in moderately brackish intertidal situations (Hayward & Hollis 1994). It is usually more diverse (5-6 species, including abundant Miliammina and rare Ammotium and Pseudothurammina) than observed at Waimamaku. Miliammina cf. obliqua is a characteristic member of this association, within its known range of Northland and Nelson (Hayward & Hollis 1994). The species has not been reported previously from the west coast.

3. Ammonia - Miliammina association (AM). Consists of dominant Ammonia beccarii, abundant Miliammina fusca and common Haplophragmoides wilberti. Occurs subtidally from middle reaches to near estuary mouth (Stations 7, 1, 13, 16, 18, 20, 22). Sediment varies from mud through sandy mud to muddy sand.

The ratio of M. fusca to H. wilberti increases towards the estuary mouth (Fig. 2). Diversity increases from 5 species in the middle reaches to 20 species near the mouth. Although diversity is moderate in the lower reaches, few additional species occur regularly in the association (e.g. Cassidulina carinata, Florilus

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AM, A , A M , A , AM , Ts subtidal associations-^

- 40% >v - 40% >v ^ * i l i P ^ Trochamminita salsa

marginal marine benthics

20 19 18 16 15 13 stations

Fig. 2. Location of foraminiferal associations and trends in relative abundance of common benthic foraminiferal species, planktic foraminifera and benthic foraminiferal diversity in subtidal stations. Ammonia beccarii and most "marginal marine" benthic species have calcareous perforate tests; Trochamminata salsa, Haplophragoides wilberti and Miliammina fusca have agglutinated tests.

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Fig. 3. Common foraminifera of Waimamaku River estuary. Scale bar = 100/un. a. Trochamminita salsa, Stn 2, AK87509. b. T. salsa, Stn 2, AK87508. c. Trochammina inflata, Stn 10, AK87504. d. T. inflata, Stn 10, AK87505. e. Haplophragmoides wilberti, Stn 10, AK87501. f. H. wilberti, Stn 10, AK87502. g. H. wilberti, Stn 10, AK87503. h. Miliammina cf. obliqua, Stn 10, AK87506. i. M. fusca, Stn 7, AK87516. j . M. fusca, Stn 7, AK87515. k. Ammonia beccarii, Stn 7, AK87519. 1. A. beccarii, Stn 7, AK87520. m. Elphidium excavatum forma excavatum, Stn 20, AK87526. n. Globigerina falconensis, Stn 22, AK87530. o. Globigerina quinqueloba, Stn 22, AK87531. p. G. quinqueloba, Stn 22, AK87532.

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Fig. 4. Reworked microfossils and other microbiotic remains from Waimamaku River estuary. Scale bar = 100/i/ra, unless noted otherwise. a. Globigerina sp., Stn 20, AK87523. b. Globigerina woodi, Stn 2, AK87511. c. Matanzia varians, Stn 9, AK87541. d. Glomospira charoides, Stn 2, AK87510. e. Bolivinopsis spectabilis, Stn 8, AK87542. f. Spherical radiolarian (actinommid), Stn 15, AK87539. g. Discoidal radiolarian (phacodiscid), Stn 15, AK87538. h. Phormocyrtis striata striata, Stn 20, AK87522. i. Dictyomitra multicostata, Stn 9, AK87540. j . Florilus parri, with pennate diatoms on apertural face, Stn 20, AK88100. k. Enlargement of apertural face in Fig. 4j. 1. Amphipyndax stocki, with scattered pennate diatoms, Stn 15, AK875536. m. Enlargement of surface of Fig. 41; scale bar = 10/x/w. n. Centric diatom, Stn 22, AK87527. o. Centric diatom, Stn 7, AK87512. p. Ostracod, Stn 20, AK87521.

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parri and Hanzawaia bertheloti). An equivalent association occurs in moderately brackish low intertidal and

subtidal areas throughout New Zealand (Hayward & Hollis 1994). Usually it contains a greater abundance of infaunal agglutinated taxa {Ammobaculites, Reophax, Textularia) and fewer calcareous taxa.

4. Ammonia association (A). Consists of dominant A. beccarii (89% and 92%), with relatively high diversity but all other species are rare. Occurs at two stations (15 and 19) in mid channel in lower reaches of the estuary. Sediment is muddy sand. This association differs from the Ammonia-Miliammina association only by the much reduced abundance of M. fusca and absence of H. wilberti. The lower station also contains the single miliolin specimen encountered in the study.

A similar "Ammonia" association, widely distributed around New Zealand in marginal marine subtidal areas (Hayward & Hollis 1994), differs by having a greater abundance of elphidiids {Elphidium excavatum, E. advenum, Haynesina depressula) and common infaunal agglutinated species (as above).

Trends The dominant factor controlling the distribution of foraminiferal associations

is salinity. Trends observed in subtidal stations (Fig. 2) which are related to a seaward increase in salinity are: • Agglutinated species decrease from 100% to 30%; • Calcareous perforate species increase from 0 to 70%; • Diversity increases from 2 species to 20; • Planktonic foraminifera increase from 0 to 10%.

The second factor controlling foraminiferal distribution is tidal level. Trends from high tidal to subtidal stations, as evident from a transect from Station 10 to 7 and also from Station 14 to 15 (see Appendix I), are: • Agglutinated species Trochammina inflata and Haplophragmoides wilberti

decrease in abundance; • Other agglutinated species (Miliammina fusca, Textularia earlandi) tend to increase; • Ammonia beccarii and other calcareous species increase; • Diversity increases from 2-4 species to 5-12 species.

Planktic foraminifera Planktic foraminifera are present in all subtidal stations in the lower estuary

(Stations 15-22) and comprise 10% and 14% of the total foraminiferal fauna in Stations 22 and 19 (Fig. 3n-p). Planktics are usually absent in brackish waters

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and rarely greater than 15% on the inner shelf (Hayward 1986). However, high numbers (up to 40%) have been reported previously from intertidal sediments at Kawerua to the south (Hayward 1979, 1986). As at Kawerua, it seems likely that the planktic tests have been concentrated and carried into the estuary by prevailing on-shore winds and seas. The abundance of planktics in Station 22 suggests that high seas may cross the beach and empty into the backwater at high tide. It is very likely that many of the normal marine benthic foraminifera present in the estuary have also been carried in by strong seas or winds, particularly small taxa such as Cassidulina, Hanzawaia, Gavelinopsis, Nonionella, Bulimina and Virgulopsis.

Reworked foraminifera and radiolarians Samples from the upper reaches of the estuary contain high numbers of

reworked foraminifera (Fig. 4a-e), either Late Cretaceous to Paleocene benthic taxa (Ammodiscus, Bolivinopsis spectabilis, Glomospira charoides, Matanzia varians) or Miocene planktic species (Globigerina woodi). Reworked radiolarians occur throughout the estuary (Fig. 4f-i, 1). These are mainly spherical or discoidal spumellarians of indeterminate age but rare specimens of Late-Cretaceous-to-Early-Paleocene (Amphipyndax stocki, Dictyomitra multicostata) and Eocene species (Buryella tetradica, Phormocyrtis striata striata) were encountered. Late Cretaceous and Early Tertiary microfossils have probably been derived from argillaceous limestones and mudstones of Motatau and Mangakahia Complexes (Northland Allochthon) which outcrop throughout the Waimamaku Valley from about 2km upstream of the estuary mouth. Miocene planktic foraminifera probably come from sandstones of the Otaua Formation which outcrops 1.5km upstream of the mouth (adjacent to station 2).

Diatoms, sponge spicules and ostracods Large centric diatoms occur throughout the estuary (Fig. 4n, o), while sponge

spicules and ostracods (Fig. 4p) are restricted to the lower reaches (below Station 14).

Because all samples were sieved through a 15pm sieve, isolated smaller diatoms were not retrieved. However, S E M examination of foraminiferal and radiolarian tests turned up two interesting occurrences of small pennate diatoms. A cluster of diatoms was observed on the apertural face of a specimen of Florilus parri (Fig. 4j, k). The final chamber was broken and it appeared that the diatom frustules adhering to the apertural face may represent the foraminifer's last meal. In most foraminifera digestion takes place in food vacuoles situated in the final chamber. If the diatoms had attached after the foraminifer had died, the frustules would not be restricted to the apertural face.

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In the second occurrence the same types of pennate diatoms were observed to be randomly scattered over the reworked tests of Cretaceous-Paleocene microfossils — the radiolarian Amphipyndax stocki (Fig. 41, m) and the agglutinated foraminifer Bolivinopsis spectabilis (Fig. 4e). In this case, the diatoms may have attached themselves during life or they may have become cemented during early stages of diagenesis within the sediment. Diagenetic cementation seems likely because the frustules do not appear restricted to one side of the radiolarian test and it also appears that some of the frustules are losing detail because of etching or overgrowth of silica.

C O N C L U D I N G R E M A R K S

Two features distinguish these brackish foraminiferal associations from similar ones reported elsewhere in New Zealand and overseas (Hayward & Hollis 1994).

1. Only 5 species are common in the estuary: Trochamminita salsa, Trochammina inflata, Haplophragmoides wilberti, Miliammina fusca and Ammonia beccarii. Other species characteristic of brackish environments were not recorded and are therefore very rare or absent, i.e. Ammotium fragile, Ammobaculites exiguus, Jadammina macrescens. Three other characteristic species are unusually rare: Reophax moniliforme, Elphidium excavatum and E. gunteri.

2. Normal marine species are more common than usual in brackish associations, i.e. Cassidulina carinata, Florilus parri, Hanzawaia bertheloti. It is likely that these species and other normal marine foraminifera do not usually live in the estuary but are carried in by strong westerly swells. Flori/^-dominated faunas, with common Ammonia, Cassidulina and Hanzawaia, have been reported living in intertidal pools at Kawerua (Hayward 1979).

ACKNOWLEDGEMENTS

We are grateful to the Auckland Institute and Museum for supplying the samples used in this study. We thank members of the 1994 paleontology class who assisted in preparing and picking samples and identifying the faunas; Louise Cotterall for drafting Fig. 1 and part of Fig. 2; Sue Courtney and Barry O'Connor for assistance with SEM photography. We also thank Jack Grant-Mackie, Hugh Grenfell and Bruce Hayward for reading the manuscript and suggesting improvements.

REFERENCES

Hayward, B.W. 1979: An intertidal Zostera pool community at Kawerua, Northland and its foraminiferal microfauna. Tane 25: 173-186.

Hayward, B.W. 1986: Abundant planktic foraminifera in intertidal sediments, Kawerua, Northland. Tane 31: 1-12.

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Hayward, B.W. & Hollis, C.J. 1993: Ecology of Waimamaku River estuary, north of Kawerua, North Auckland. Tane 34: 69-78.

Hayward, B.W. & Hollis, C.J. 1994: Brackish foraminifera in New Zealand: A taxonomic and ecologic review. Micropaleontology 40: 1K5-222.

APPENDIX I. Relative abundance (%) of benthic foraminifera in representative picks (x = < 0.5%), percentage of planktic foraminifera and approximate abundance of other microbiotic remains in Waimamaku estuary stations. Abbreviations - depth: HT = high tide, M T = mid tide, L T = low tide, otherwise in metres below low tide; sediment: S = sand, mS = muddy sand, M = mud, sM = sandy mud, pM = pebbly mud; approximate abundance: C = common, F = few, R = rare.

BENTHIC FORAMINIFERA

Cribrostomoides jeffreysii

Haplophragmoides wilberti

Miliammina fusca

Miliammina cf. obliqua

Reophax moniliforme

Textularia earlandi

Trochammina bartrami

Trochammina inflata

Trochammina sorosa

Trochamminita salsa

Ammonia beccarii

Bolivina pseudoplicata

Bolivina spathulata

Bulimina submarginata

Cassidulina carinata

Cibicides marlboroughensis

Elphidium advenum

Elphidium charlottensis

Elphidium excavatum

Elphidium gunteri

Evolvocassidulina orientalis

Florilus parri

Fursenkoina fusiformis

Gavelinopsis spp.

Gyroidina neosoldanii

Hanzawaia bertheloti

Haynesina depressula

Lagena sulcata

Nonionella turgida

Oolina tasmanica

Quinqueloculina sp.

Virgulopsis turris

T o t a l C o u n t

PLANKTIC FORAMINIFERA

OSTRACODS

DIATOMS

SPONGE SPICULES

REWORKED FORAMINIFERA

Ammodiscus sp.

Bolivinopsis spectabilis

Glomospira charoides

Matanzia varians

Planktics

REWORKED RADIOLARIANS

undet. spumellarians

Amphipyndax stocki

Dictyomitra multicostata

Buryella tetradica

Lychnocanium sp.

Phormocyrtis striata striata