Distribution of Mysids (Crustacea: Mysidacea) in Auckland Region, New Zealand

N.N. Punchihewa, S.R. Krishnarajah

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Distribution of Mysids (Crustacea: Mysidacea) in Auckland Region, New Zealand

N.N. Punchihewa1,, S.R. Krishnarajah1

1Department of Zoology, The Open University of Sri Lanka, Nawala, Nugegoda, Sri Lanka

Abstract

Given the ecological significance of mysids in brackish and freshwater food chains and the potential importance in toxicity testing in estuarine systems, it is important to understand the distribution of these animals. However, to date, few studies have been undertaken on mysids in the Auckland region. DThe main focus of this study was to find out the distribution of estuarine mysids in this region. Reconnaissance surveys took place to locate mysid habitats in the estuarine waters entering the Manukau Harbour and the East Coast estuarine environments from May of 2006 to January 2009. The samples were taken using a hand held dip net with 500 µm mesh size along an eighty meter transect at the edge of the stream during day time at low tide. At each site four replicate surveys were undertaken (transects of 10 m length, 10 m apart). Five species of mysids have been identified from and are described for estuarine environments in the Manukau Harbour and along the Auckland East Coast: the sometimes sympatric Tenagomysis chiltoni and T. novaezealandiae, and the non-sympatric and patchily distributed Gastrosaccus australis, T. macropsis and a potentially new Tenagomysis sp.. The present distributional studies in the North Island reflects that the native mysid T. novaezealandiae is the dominant mysid species along the east coast, and the most geographically widespread species on both east and the west coasts, while T. chiltoni was equally dominant with T. novaezealandiae in the Manukau Harbour. G. australis and T. macropsis reported from North Island estuarine waters for the first time. The salinity ranges where species occurred were different: T. chiltoni 0-18‰, T. novaezealandiae 0-26‰ and G. australis 1.5-12.6‰. T. chiltoni, Tenagomysis sp. and T. novaezealandiae shows that the higher percentages of females than males.

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Cite this article:

  • Punchihewa, N.N., and S.R. Krishnarajah. "Distribution of Mysids (Crustacea: Mysidacea) in Auckland Region, New Zealand." American Journal of Marine Science 1.1 (2013): 16-21.
  • Punchihewa, N. , & Krishnarajah, S. (2013). Distribution of Mysids (Crustacea: Mysidacea) in Auckland Region, New Zealand. American Journal of Marine Science, 1(1), 16-21.
  • Punchihewa, N.N., and S.R. Krishnarajah. "Distribution of Mysids (Crustacea: Mysidacea) in Auckland Region, New Zealand." American Journal of Marine Science 1, no. 1 (2013): 16-21.

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1. Introduction

Mysids have a worldwide distribution and occupy a wide variety of aquatic environments, from fresh and brackish to fully saline oceanic waters. Given the internationally recognised ecological significance of mysids in brackish and freshwater food chains [1], it is important to understand the distribution of native estuarine mysid species. Mysids are not only an important food source or a main food link in estuarine ecosystem but also make use of them worldwide as most important bioindicators for toxicity testing in aquatic systems.

Since the establishment of the genus Tenagomysis to accommodate specimens as a new species, Tenagomysis novaezealandiae [3], from different locations, near Dunedin, in most of the New Zealand waters, the recorded mysids belong to the genus Tenagomysis (10 species). Twelve species reported during the “Terra Nova” expedition [2], and other shore collections in New Zealand waters. Sixteen mysid species have been so far described from New Zealand waters, presently accommodated within five genera. Among them, only few species are estuarine. Therefore, several of these species have not been reported subsequent to original descriptions, but other species have proven to be more widespread in distribution, and more regularly reported (T. chiltoni, T. macropsis, and T. novaezealandiae) in estuarine waters. However, the most of the studies on mysids in New Zealand has been carried out in South Island waters whereas there were very few studies from the North Island.

After the earlier studies [2, 3], there have been only a few occasions that mysids recorded from the North Island and the Greater Auckland region: T. novaezealandiae from Raglan Harbour and the mouth of the Waikato River [4]; T. chiltoni from a fresh water coastal lake, near Waverley [5] and from the Waikato River ([6, 7]) and both T. novaezealandiae and T. chiltoni together from stream at Piha [8]. Some studies on T. novaezealandiae also reported: T. novaezealandiae for toxicity testing [4, 6] studied the biology of T. chiltoni of the lower Waikato River. However, no comprehensive study on mysids has otherwise been undertaken throughout the North Island of New Zealand, and also few studies of any nature have been undertaken within the Auckland region. The insufficiency of the knowledge on distribution of New Zealand mysids specially in greater Auckland region requires a geographical survey to establish their estuarine habitats.

The objective of this study is to investigate the current distribution of mysids throughout the greater Auckland region in order to extend this knowledge in a comparative manner in other geographical regions as well.

Figure 1. Locations of 59 survey sites throughout the greater Auckland region

2. Methodology

Reconnaissance surveys for mysids in estuarine habitat were conducted at 59 sites extending from Mathesons Bay, north of Auckland, to Miranda in the Firth of Thames, along the east coast of the Auckland region, and from Bethells Beach, north of Manukau Heads, to Waiuku, Manukau Harbour, on the west coast of the Auckland region (Figure 1). For logistical reasons, most sites could be surveyed on a single occasion only; reconnaissance surveys commenced in May of 2006 and concluded in January of 2009. At each site reconnaissance surveys took place during day time at low tide. The samples were collected using a hand held dip net along an eighty meter transect at the edge of the stream. At each site four replicate surveys were undertaken (transects of 10 m length, 10 m apart). All mysids retained in the net along each transect were immediately collected into separate, appropriately labeled bottles containing 70% ethyl alcohol. On each sampling event, the environmental variables salinity, pH, dissolved oxygen (DO), temperature and turbidity were measured. Mysid samples collected from each transect were separated into species, sexed, and counted.

3. Results

Mysids were located at 26 of these survey sites (Figure 2, Table 1). Sites at which mysids were not recorded were surveyed only once. Among the sites from where mysids were collected, 12 were on the east and 14 on the west coast of Auckland (Table 1).

Five species were identified: the sometimes sympatric Tenagomysis novaezealandiae and Tenagomysis chiltoni (at 11 sites), patchily distributed Gastrosaccus australis (at four sites), and Tenagomysis macropsis (at one site) and a potentially new Tenagomysis sp. nov (at one site). Four taxa occurred on both west and east coasts; the most frequently encountered and most common species, T. novaezealandiae, occurred at 21 sites and T. chiltoni at 15 sites (Table 1 and Figure 2); T. novaezealandiae was the most geographically widespread species in both east and the west coasts while T. chiltoni occurred at a comparable number of sites as T. novaezealandiae within west coast (12 sites each). In west coast both T. novaezealandiae and T. chiltoni were equally distributed (Table 1 and Figure 3). In east coast T. novaezealandiae had a wider distribution (nine sites) than west coast (three sites). G.australis occurred at more sites in east coast (three sites) than west coast (one site) (Figure 3). However, in east coast G. australis and T. chiltoni had similar occurrences (Figure 3). Makatane, Huia Bay and Waitangi falls T. chiltoni occurred as a single species. In nine sites T. novaezealandiae occurred as a single species (Table 1). Mysid occurrences in all 26 sites indicated that the native mysid T. novaezealandiae is the most geographically widespread species (Figure 3).

Table 1. Incidence of mysid taxa throughout the greater Auckland estuarine environments (P denotes Presence)

Figure 2. Recognised distribution of mysid taxa throughout survey region
Figure 3. Number of occurrences of mysid species at west and east coast of Auckland
Figure 4. Mean number of individuals of all species in the entire survey

Figure 4 shows the mean number of individuals in each species. For each species mean values are different from each other. However, T. chiltoni G. australis and T. novaezelandiae values are overlapping. There is no significant difference between mysid species. T. novaezelandiae shows the highest number of individuals with a mean of 24.87, T. chiltoni shows the second highest number of individuals with a mean of 20.67 and G. australis with a mean of 5.8. Tenagomysis sp. and T. macropsis recorded only once with 21 and 52 individuals respectively.

3.1. Sex Ratio

The sex ratio of all mysid species in the entire survey was determined on the basis of examination of all individuals captured during the entire survey during 2006-2009 is presented in Table 2. The sex ratio of all mysid species in the entire survey was determined on the basis of examination of all individuals captured during the entire survey during 2006-2009 is presented in Table 2. Sex ratios (male to female ratio) of T. chiltoni (2.13), Tenagomysis sp. (3) and T. novaezealandiae (2.86) varied, more or less higher percentages of females (68%, 74% and 75% respectively). However, G. australis and T. macropsis 23 and 52 females with broods were found respectively and none of the males were recorded (Table 2).

Table 2. Sex ratio of mysids from the entire survey

3.2. Salinity Preference

The error bar plotted for salinity verses mysid species is shown in Figure 5. T. novaezelandiae occurred within varying ranges of the salinity indicating the wider salinity tolerance, (0-25‰) and mean occurrence of this species show under the lower salinity. Similarly, the occurrence of the majority of T. chiltoni were also confined to the lower salinity range and two extreme conditions also noted (12.6‰ and 17.9‰). G. australis occurrences show nearly symmetric distributions within lower salinities. Tenagomysis sp. and T. macropsis, were only found in higher and lower salinity ranges respectively. However, the occurrence of these two species shows oppositely different salinity.

Figure 5. Salinity variation of mysid species recorded from entire survey

Considering the occurances of these mysids, 80% of T. chiltoni, 47.6% of T. novaezealandiae and 25% of G. australis were recorded between the salinity range of 0-5‰. Overall the salinity ranges which species occurred were different: T. chiltoni 0-18‰, T. novaezealandiae, 0-26‰ and G. australis 1.5-12.6‰ (Figure 5). T. macropsis recorded only once at the 0‰ salinity.

4. Discussion

However, mysids are recognized to be widely but sporadically distributed throughout the Auckland region, present at less than half, 26, of those 59 sites surveyed during the reconnaissance of mysid habitat reported herein. The apparent absence of mysids at 33 sites could be a cause for concern, although sites could be assessed once only for the purposes of the reconnaissance survey; reconnaissance surveys were conducted over 31 months over three years, and during certain months mysid abundance is known to be relatively low (and thus they might have been missed); mysids may have been present at low numbers or in aggregated populations; and some mysid taxa (ex: G. australis) are known to be more active at night (and no reconnaissance surveys were undertaken during night). Additionally, without historical data on the presence, abundance and diversity of mysid taxa throughout the Auckland region, it cannot be determined whether any change in their distributions and population dynamics have occurred. As an aside, similar studies in the South Island, around Otago, encountered mysids at 27 of 30 surveyed estuarine sites [9].

Only five species of mysid are recognised at those surveyed estuarine sites throughout Manukau Harbour and the east coast of the Auckland region: T. novaezealandiae, T. chiltoni, patchily distributed G. australis, T. macropsis and a potentially new species of Tenagomysis. With the exception of the potentially new Tenagomysis species, these same taxa occured within the Avon-Heathcote Estuary, Christchurch ([10, 11]), Taieri River [12] and the Otago coastline [9]. However, another species, T. robusta reported [13] from the mouth of Taieri River, sympatric with T. macropsis, T. novaezealandiae, and a species of Gastrosaccus. Those surveyed New Zealand estuarine environments appear to be dominated by a limited number of widely distributed species of Tenagomysis and Gastrosaccus, although the combination of species present in any estuarine aquatic body can differ.

Earlier studies have reported only two species of mysid from North Island aquatic environments: T. chiltoni from, Lake Oturi near Waverley [5] T. novaezealandiae from Raglan Harbour [4] and at the mouth of the Waikato River; T. chiltoni in the Waikato River ([6, 7]), T. novaezealandiae and T. chiltoni at Piha [8], west coast, Auckland. During this present study, T. chiltoni and T. novaezealandiae were found to be sympatric at 10 locations on the west coast and one location at the east coast of the Auckland region, including five streams at Piha. This overall mysid distribution supports the finding that T. novaezealandiae and T. chiltoni are the common species present in estuarine environments in the North Island.

Of 26 sites at which mysids occurred throughout the greater Auckland region, T. chiltoni occurred at 15 of them and T. novaezealandiae at 21 of them. Thus, T. novaezealandiae is the most geographically widespread of regionally occurring estuarine mysid taxa, followed by T. chiltoni, although the former species is prevalent on the east coast and the latter in Manukau Harbour (occurring at 12 sites). Tenagomysis novaezelandiae is also the most regularly encountered species in both open and closed estuarine systems around Otago [9]. Both the North Island and South Island distributions reflect that T. novaezealandiae is the most geographically widespread estuarine mysid species in New Zealand.

G. australis is reported from North Island estuarine waters for the first time since 1923[2] in estuarine waters at four sites, during daylight hours. They were collected from the stream floor in low water covered with sand. Therefore, it becomes difficult to collect them during daylight. However, the same species was recorded in South Island localities to be abundant species at night ([2, 9, 11]) in addition to an undescribed Gastrosaccus sp. [13]. As the previous studies reveal G. australis to be largely nocturnal, its apparent absence from 55 of 59 daylight-surveyed sites in the present study might not be particularly remarkable.

T. macropsis was collected during both day and night sampling in the surface waters and deep waters of North Cape, and Bay of Islands in the North Island [2]. This species has not been previously reported from North Island estuarine waters. Herein, it is recorded from Orewa-Nukumea Stream, but only on one occasion, when 52 brooding females were encountered within a small channel in the mid estuary (0‰ salinity). The distribution of this species in estuarine waters around Auckland is limited. However, it appears [2] that the habitat of this species extends into fully saline and offshore waters that were not surveyed over the course of this research programme. Perhaps and somewhat unusually, this species is both abundant and widespread in South Island estuarine waters ([9, 10, 11, 13, 15]). However, T. macropsis has wide salinity tolerance limits (optimum salinity 18.5‰), as determined from its distribution in the Avon-Heathcote Estuary [15].

5. Conclusion

During this investigation, mysids were abundant and widely distributed on a variety of streams from smaller channels to larger streams throughout the west and the east coast of the Auckland region.

This is the first study to incorporate comprehensive spatial survey throughout the this region for discovery of mysid habitats. From these surveys including 59 streams, 26 mysid habitats were detected. There has been no mysid distributional data provided previously for the estuarine environments in the Auckland region except an observation at Piha, Auckland west coast [8]. Since the Terra Nova expedition, surveying the north of the North Island [2], until the present study there have been no extensive mysid distributional studies in the North Island, only studies of a few individual sites [4, 5, 6, 8]. Therefore this work contributes novel information on the spatial distribution of mysid taxa throughout the greater Auckland region.

The number of mysid taxa detected in this present study was five, from the estuarine environments in the Manukau Harbour and along the Auckland east coast: T. novaezealandiae (in 21 sites), T. chiltoni (in 15 sites), G. australis (in four sites), T. macropsis (in one site) and a new Tenagomysis sp (in one site), demonstrating their distribution in the Auckland region. Earlier studies have reported only two species. T. novaezealandiae and T. chiltoni, at Piha [8], west coast, Auckland. Therefore, the diversity of mysid taxa occuring throughout this region has been significantly increased.

The present distributional studies in the North Island reflects that the native mysid T. novaezealandiae is the dominant mysid species along the east coast, and the most geographically widespread species on both east and the west coasts, while T. chiltoni was equally dominant with T. novaezealandiae in the Manukau Harbour. It is also important to consider that this is the first time G. australis and T. macropsis have been recorded in the Auckland region, and also anywhere in the North Island, after the historical studies [2]. Although the number of occurances were highest for T. novaezealandiae for the entire survey, T. chiltoni recorded the highest number of individuals.

T. novaezealandiae occurred within varying ranges of the salinity (0-25‰) than the other species. This smay be the reason that the number of occurrences was highest for T. novaezealandiae for the entire survey.

Acknowledgement

This project was funded by the Auckland University Of Technology, Auckland, New Zealand.

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