Changes to the Marine Biota of the Auckland Harbour, by F. I

TANE 29, 1983 CHANGES TO THE MARINE BIOTA OF THE AUCKLAND HARBOUR by F. I. Dromgoole* and B. A. Fostert * Department of Botany, University of Auckland, Private Bag, Auckland t Department of Zoology, University of Auckland, Private Bag, Auckland SUMMARY The history of study of the marine biota of Auckland Harbour is briefly reviewed, and it is concluded that there is insufficient documented information to make quantitative assessment of changes that have resulted from reclamation, sedimentation and pollution that have occurred with the development of the Port of Auckland. Losses of mangrove and saltmarsh communities are indisputable, but causes of declines in populations of Zostera, Pomatoceros and Perna are not so clear. On the other hand, a number of species have been introduced, and circumstantial evidence suggests these adventives have arrived as ship- fouling. Cases discussed are Codium fragile tomentosoides, Colpomenia bullosa, Limaria orientalis and Sagartia luciae. The most conspicuous newcomer, the oyster Crassostrea gigas, may have been deliberately introduced. INTRODUCTION Regular use of the Auckland Harbour by European ships stems from the early 1800s, so there has been ample opportunity for the introduction of adventive fouling species. Maritime reclamation in Auckland Harbour dates back to about 1860 when shores near the commercial centre were filled and extended as wharves and breakwaters. Modification of habitats and inhabitants of the harbour has now been going on for more than 120 years, but scientific study of them has been of much shorter duration. In this paper we wish to document some additions and alterations to the marine biology. Auckland Harbour has three parts (see Fig. 1). The lower harbour includes southern shores of Rangitoto and Motutapu Islands, and also Motuihe and Browns Islands. The middle harbour is clearly defined; it contains the Port of Auckland and is the most modified. In the middle harbour 45% of the shoreline has been modified by reclamation and 24% of the harbour bed has been claimed for wharves, breakwaters, embankments, causeways and other uses. The upper harbour contains expansive intertidal flats, and is under increasing pressure from surrounding urbanisation. Further local changes are inevitable with the spread of coastal industries and the construction of harbour works, 79 leading to more widespread changes in sedimentation resulting from reclamation and dredging. Fig. 1. Auckland Harbour (=Waitemata Harbour), subdivisions and localities mentioned in the text. Shoreline modification is shown blacked. (1) Rangitoto Island, (2) Narrow Neck Beach, (3) Cheltenham Beach, (4) North Head, (5) Torpedo Bay, (6) Stanley Bay, (7) Birkenhead, (8) Westmere Reef, (9) Port of Auckland, (10) Container Terminal, (11) Hobson Bay, (12) Orakei Basin, (13) Okahu Bay, (14) Orakei Point, (15) Mission Bay. HISTORICAL REVIEW Many early writers of taxonomic accounts of the New Zealand biota probably used specimens collected at Auckland, but the locality identified was not always specified. Among early Auckland records are those of Hooker (1867) who lists some algae from Auckland, and Hutton (1878) who identified Auckland as a locality for two species of barnacles. The first ecological description of the intertidal biota was that of Oliver (1923). He identified and figured shores at Takapuna and Westmere Reef as examples in his wider account of such communities for all New Zealand shores. Powell's (1937) account of the benthic communities stands as a notable contribution to a part of the harbour's biota that has received very little subsequent study. Studies on the algal flora subsequent to those of Oliver were stimulated with the arrival in 1945 of the first Professor of Botany at 80 the University of Auckland. Professor V. J. Chapman's enthusiasm led to papers on saltmarsh vegetation (Chapman and Ronaldson 1958), intertidal algae (Dellow 1948, 1950, 1953, 1955, Cooper 1951, Carnachan 1952) and subtidal algae (Bergquist 1957, Dromgoole 1965). Work on the marine angiosperm Zostera by Armiger (1965) examined the causes of decline of this species first noted by Hounsell (1935) and Powell (1937). Further interest in the marine biology of the region was rekindled with the arrival of the first Professor of Zoology in 1960. Professor J. E. Morton's book "The New Zealand Sea Shore" (Morton and Miller 1968) contains a number of shore descriptions based on localities in the harbour and makes reference to subsequently published thesis studies concerned with shore ecology (Wood 1962, 1968, Luckens 1976). Fouling species in the harbour were examined by Skerman (1959, 1960b). The pelagic biota of the Hauraki Gulf has been studied by Kramer (1894), and Fuller (1950, 1953), and the relation between gulf and harbour plankton explored by Jillett (1971). In recent years a number of reports have been prepared in association with a variety of environmental proposals, most notable of these is the Ecology Report for the Waitemata Harbour Survey (Chapman and Larcombe 1973). BIOLOGICAL CHANGES Despite the numerous publications and reports on marine biology that can be identified, replicable quantitative data are rare, and it is difficult to find the exact location of most ecological observations. Only the more extreme biological changes can be deduced, for example, the decline of the Zostera beds (cf. data in Wood 1962) and the now rarity of the green- lipped mussel (Perna canaliculus) on accessible harbour shores. Another example is the decrease in the physiognomic dominance of the tubeworm Pomatoceros cariniferus at Westmere (see Fig. 2, 3). The causes in decline in populations, and resultant community alterations, may or may not be associated with long-term, man-induced causes. Decline of mussels is almost certainly so, because of their edibility and use as fish bait. The causes of changes in populations of eel-grass and tubeworms may be more subtle. The mangrove and saltmarsh flats of Auckland Harbour have been materially modified by reclamation and the construction of roads across them. An example of the associated effects on flora is seen in the changes in Hobson Bay where, prior to 1921, large areas were dominated by the eel-grass Zostera but this has now completely disappeared. Hounsell (1935) suggests that this was due to rapid silting following the construction of the waterfront drive and the railway embankments; Powell (1937) on the other hand states that the bay 81 Fig. 2. Westmere Reef, from Oliver (1922), showing hummocks of the tubeworm Pomatoceros cariniferus. bottom became hard and that shell deposits may have completed the destruction. Armiger (1965) questions whether sedimentation was the only factor involved as epidemic losses of Zostera have been linked to disease. The disappearance of Zostera from the harbour is perhaps the best documented change in the flora of soft-bottom communities apart from the loss of mangroves through reclamation. Hounsell (1935) records the loss of Zostera from Stanley Bay attributing it to an undermining of the formation by the tidal stream following construction of tide deflectors in the harbour. Zostera beds recorded by Armiger (1965) in the Tamaki estuary, Howick Beach, Okahu Bay, Torpedo Bay and Cheltenham have now also disappeared and whilst this can be largely attributed to a disease by the Labyrinthula slime mould (Armiger 1964) it is conceivable that pathogenic susceptibility is enhanced by unfavourable conditions for growth such as increased sediment load, reduced salinity or pollutants. Decline in Zostera abundance is not unique to Auckland Harbour, similar epidemic losses were recorded in the Avon-Heathcote estuary during 1929-1953 and in many Northern Hemisphere locations in the 1930s. Because Zostera beds normally support a rich and varied biota the disappearance may have significant effects on other foodchain linked organisms. Faunal elements associated with the Auckland Zostera beds are listed by Oliver (1923) and Wood (1962) and it seems reasonable to assume that these have also declined drastically in numbers since 1921. Alterations in substrate can also have a marked effect on the local abundance of plants. For example, increased sedimentation reduces the area available for colonisation by the larger perennial brown algae (Carpophyllum spp. ) and the small turf forms (Corallina officinalis) and these may disappear to be replaced by soft shore flora of seasonal species such as Codium fragile subsp. tomentosoides and Gracilaria secundata var. pseudoflagellifera. Pollution effects are not well documented although the discharge of raw sewage was once severe, and still continues on a reduced scale. Wallace and Newman (1953a, b) in a bacteriological survey of beaches to the east of the Orakei outfall, reported serious pollution at Mission Bay with MPN Coliform mounts of 51 per 100 ml and mean diatom counts of 21 per 10 ml. Diatom counts increased with distance from the outfall reaching 286 per 100 ml at Karaka Bay where MPN Coliforms had fallen to 11. They concluded that the southern and perhaps eastern shores of Rangitoto Island were in a semi-permanent state of pollution from the diluted sewage fields. However, Carnachan's (1952) study of benthic algal zonation at Rangitoto Island does not reveal any characteristics that can be attributed to the detrimental effects of this type of pollution. Discharge of sewage at Orakei ceased in 1963—5 but continued on a small scale at North Head and Birkenhead (Jillett 1971) and isolated accidental discharges sometimes together

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