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The effect of biological and physical factors on the early life history and settlement of the Tasmanian blenny Parablennius tasmanianus tasmanianus in the Derwent estuary, Tasmania

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Chamchang, Chongkolnee (1997) The effect of biological and physical factors on the early life history and settlement of the Tasmanian blenny Parablennius tasmanianus tasmanianus in the Derwent estuary, Tasmania. PhD thesis, University of Tasmania.

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Abstract

The effect of pulses in phytoplankton production (chlorophyll-a
concentration) and physical factors on recruitment of the Tasmanian
Blenny Parablennius tasmanianus tasmanianus was examined in the
Derwent Estuary, Storm Bay, south-east Tasmania. The species is the
only Tasmanian representative of the Family Blenniidae and is abundant
in shallow reef habitats around Tasmania. Although the larvae are
abundant around Tasmania and readily distinguished from those of other
fish in plankton samples, it has been the subject of few scientific studies.
Pulses in chlorophyll-a concentration regularly occur in spring within the
region, although the exact timing and magnitude vary interannually. To
test the hypothesis that short-duration pulses in phytoplankton production
translate into periods of high rates of larval survival and subsequent
juvenile settlement, larval fish were sampled weekly from mid spring to late
summer in 1992-93 and 1993-94, and newly settled blennies were
collected biweekly from tide pools in a rock reef platform from mid spring to
late summer in 1992-93, 1993-94, and 1994-95. Otolith analysis was used
to determine larval durations and to back-calculate settlement patterns and
hatching dates.
Blennies spent an average of 46 days in the plankton, and were on
average 17.3 mm at settlement which did not appear to vary interannually
(F> 0.05). Both larval abundance and settlement patterns differed
markedly between years, with the highest settlement in 1994-95.
However, there was no consistent relationship between the timing or
magnitude of spring pulses in phytoplankton production and larval
abundance, hatching times, or subsequent settlement.
An alternative hypothesis, that larval abundance and settlement were
determined by physical factors, was examined by seeking correlation with
surface water temperature, salinity, river discharge, rainfall, wind, tidal
range and lunar phase. Water column data on these variables were
collected during larval and phytoplankton sampling. No clear relationship emerged between any environmental factor and hatching times or
subsequent settlement, but peaks in larval abundance consistently
correlated with high water temperatures and low salinities. Intensive
sampling in different water masses confirmed that larvae were primarily
distributed in water characterised by low or intermediate salinity (26 - 30%0)
and were mostly found in warmer water (16.3°C - 17.9 0C). The
observations suggested that newly settled blennies were likely to be most
abundant in the area with low salinity. To test this, surface water
temperatures and salinities were measured every other day and newly
settled blennies were collected biweekly from three sites characterised by
different mean salinities. In contrast to expectations, the highest settlement
occurred at the site with the highest mean salinity (P <0.05). This
suggests that the salinity preferences of newly settled blennies differ from
those sampled in plankton tows, or that settlement at the site with the
highest salinity was an artifact of other conditions that differed in tide pools
between the three areas.
The results of this study suggest that hatching times, larval abundance,
and settlement of the Tasmanian blenny were not strongly influenced by
phytoplankton production pulses or most of the physical factors assessed.
Salinity and temperature appeared to affect the abundance of planktonic
larvae. This relationship became less clear at settlement. It is suggested
that hatching time of the Tasmanian blenny is regulated by simple
environmental cues such as photoperiod, and subsequent recruitment is
mainly influenced by factors not examined in this study such as predators,
prey items, habitat availability, or post-settlement mortality. The broad
range of physical environmental factors tolerated by Tasmanian blennies,
and the suggested importance of biological factors, are discussed in
relation to recruitment of estuarine rocky reef fish in general.

Item Type: Thesis (PhD)
Keywords: Blenniidae
Copyright Holders: The Author
Copyright Information:

Copyright 1997 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

The results of this study suggest that hatching times, larval abundance, and settlement of the Tasmanian blenny were not strongly influenced by Phytoplankton production pulses. Salinity and temperature appeared to affect the abundance of planktonic larvae. It is suggested that hatching time of the Tasmanian blenny is regulated by simple environmental cues such as photoperiod, and subsequent recruitment is mainly influenced by factors such as predators, prey items, habitat availability, or post-settlement mortality. Thesis (Ph.D)--University of Tasmania, 1998. Includes bibliographical references. The results of this study suggest that hatching times, larval abundance, and settlement of the Tasmanian blenny were not strongly influenced by Phytoplankton production pulses. Salinity and temperature appeared to affect the abundance of planktonic larvae. It is suggested that hatching time of the Tasmanian blenny is regulated by simple environmental cues such as photoperiod, and subsequent recruitment is mainly influenced by factors such as predators, prey items, habitat availability, or post-settlement mortality

Date Deposited: 25 Nov 2014 00:48
Last Modified: 28 Jun 2016 04:00
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