title: Niche partitioning of intertidal seagrasses: evidence of the influence of substrate temperature

authors: Campbell, Marnie L.

subjects: Science & Technology

abstract: • The influence of soil temperature on rhizome depths of four intertidal seagrass species was investigated in central Queensland, Australia. We postulated that certain intertidal seagrass species are soil temperature‐sensitive and vertically stratify rhizome depths.
• Below‐ground vertical stratification of intertidal seagrass rhizome depths was analysed based upon microclimate (soil temperature) and microhabitat (soil type).
• Soil temperature profiles exhibited heat transfer from surface layers to depth that varied by microhabitat, with vertical stratification of rhizome depths between species. Halodule uninervis rhizomes maintain a narrow median soil temperature envelope; compensating for high surface temperatures by occupying deeper, cooler soil substrates. Halophila decipiens, Halophila ovalis and Zostera muelleri rhizomes are shallow‐rooted and exposed to fluctuating temperatures, with broader median temperature envelopes. Halodule uninervis appears to be a niche specialist, with the two Halophila species considered as generalist niche usage species.
• The implications of niche use based upon soil temperature profiles and rhizome rooting depths are discussed in the context of species’ thermal tolerances and below‐ground biomass O₂ demand associated with respiration and maintenance of oxic microshields. This preliminary evidence suggests that soil temperature interaction with rhizome rooting depths may be a factor that influences the distribution of intertidal seagrasses.

text: Niche partitioning of intertidal seagrasses: evidence of the influence of substrate temperature • The influence of soil temperature on rhizome depths of four intertidal seagrass species was investigated in central Queensland, Australia. We postulated that certain intertidal seagrass species are soil temperature‐sensitive and vertically stratify rhizome depths.
• Below‐ground vertical stratification of intertidal seagrass rhizome depths was analysed based upon microclimate (soil temperature) and microhabitat (soil type).
• Soil temperature profiles exhibited heat transfer from surface layers to depth that varied by microhabitat, with vertical stratification of rhizome depths between species. Halodule uninervis rhizomes maintain a narrow median soil temperature envelope; compensating for high surface temperatures by occupying deeper, cooler soil substrates. Halophila decipiens, Halophila ovalis and Zostera muelleri rhizomes are shallow‐rooted and exposed to fluctuating temperatures, with broader median temperature envelopes. Halodule uninervis appears to be a niche specialist, with the two Halophila species considered as generalist niche usage species.
• The implications of niche use based upon soil temperature profiles and rhizome rooting depths are discussed in the context of species’ thermal tolerances and below‐ground biomass O₂ demand associated with respiration and maintenance of oxic microshields. This preliminary evidence suggests that soil temperature interaction with rhizome rooting depths may be a factor that influences the distribution of intertidal seagrasses.

year: 2018

title: An integrated biostratigraphy and seismic stratigraphy for the late Neogene continental margin succession in northern Taranaki Basin, New Zealand

authors: Hansen, Rochelle J.

subjects: Ariki Formation

abstract: Our aim has been to develop an integrated biostratigraphy and seismic stratigraphy for the Pliocene and Pleistocene formations (Ariki, Mangaa, Giant Foresets) in northern Taranaki Basin to better understand the evolution of the modern continental margin offshore central-western North Island, New Zealand. Detailed mapping of seismic reflectors in part of the basin, when compared with correlations of late Neogene stage boundaries between 11 well sections, has highlighted crossover between the datasets. To help resolve this issue, the biostratigraphy of the Pliocene-Pleistocene parts of each of four well sections (Arawa-1, Ariki-1, Kora-1, and Wainui-1) has been re-examined using a dense suite of samples. In addition, the biostratigraphy of seven other well sections (Awatea-1, Kahawai-1, Mangaa-1, Taimana-1, Tangaroa-1, Te Kumi-1, and Turi-1) has been re-evaluated. The crossover is partly attributed to a combination of sampling resolution inherent in exploration well sections, the mixed nature of cuttings samples, and the general scarcity of age-diagnostic planktic foraminifera in the late Neogene formations. The achievement of seismic closure suggests that error in the mapping of the seismic reflectors is not a significant source of the uncertainty (crossover). We have developed a workable time-stratigraphic framework by qualitatively weighting the biostratigraphic data in each of the well sections, thereby identifying the parts of particular well sections with the highest resolution microfossil data and the optimal stratigraphic position of stage boundaries with respect to the mapped seismic horizons/seismic units. Hence, it is possible to assign the known numerical ages for these stage boundaries to reflection horizons/seismic units mapped within the basin. We have applied this information to produce a series of isopach maps for successive stage boundaries that help show the sedimentary evolution of the continental margin succession west of central North Island.

text: An integrated biostratigraphy and seismic stratigraphy for the late Neogene continental margin succession in northern Taranaki Basin, New Zealand Our aim has been to develop an integrated biostratigraphy and seismic stratigraphy for the Pliocene and Pleistocene formations (Ariki, Mangaa, Giant Foresets) in northern Taranaki Basin to better understand the evolution of the modern continental margin offshore central-western North Island, New Zealand. Detailed mapping of seismic reflectors in part of the basin, when compared with correlations of late Neogene stage boundaries between 11 well sections, has highlighted crossover between the datasets. To help resolve this issue, the biostratigraphy of the Pliocene-Pleistocene parts of each of four well sections (Arawa-1, Ariki-1, Kora-1, and Wainui-1) has been re-examined using a dense suite of samples. In addition, the biostratigraphy of seven other well sections (Awatea-1, Kahawai-1, Mangaa-1, Taimana-1, Tangaroa-1, Te Kumi-1, and Turi-1) has been re-evaluated. The crossover is partly attributed to a combination of sampling resolution inherent in exploration well sections, the mixed nature of cuttings samples, and the general scarcity of age-diagnostic planktic foraminifera in the late Neogene formations. The achievement of seismic closure suggests that error in the mapping of the seismic reflectors is not a significant source of the uncertainty (crossover). We have developed a workable time-stratigraphic framework by qualitatively weighting the biostratigraphic data in each of the well sections, thereby identifying the parts of particular well sections with the highest resolution microfossil data and the optimal stratigraphic position of stage boundaries with respect to the mapped seismic horizons/seismic units. Hence, it is possible to assign the known numerical ages for these stage boundaries to reflection horizons/seismic units mapped within the basin. We have applied this information to produce a series of isopach maps for successive stage boundaries that help show the sedimentary evolution of the continental margin succession west of central North Island.

year: 2006

title: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2014

authors: Hicks, Brendan J.

abstract: The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (eels, goldfish, and koura). In the current study, we present the findings from the eighth year of sampling (2014) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 642 fish (11.3 kg) 11 sites on 9 December 2014, which comprised 2,914 lineal m and 11,656 m² in area. Koura and 4 fish species were present, with common bully most abundant (up to 27 fish 100 m⁻² at the site 5, edge habitat). Goldfish (up to 5.92 g m⁻²) was the next most abundant species, and was most abundant in sites 8-11 the lower channel, especially at site 11, the excavated side channel. Rainbow trout were next the most abundant species (up to 0.25 fish 100 m⁻² ). Mean bully biomass (5.25 g m⁻²) was much higher than for smelt (0.07 g m⁻²). Koura had a patchy distribution; 5 individuals were caught.
Comparing catches over the 8 years of sampling, the abundance of common bullies in 2014 (4.81 fish 100 m⁻²) was consistent with catch rates in most post-wall years (after 2007; range 0.81-5.72 fish 100 m⁻²), but lower than in 2013. The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, suggesting that bully density estimates might decrease with decreasing BDD. However, common bully densities in 2012 and 2011 were inversely related BDD. In 2014, catches of smelt, a similar sized fish to bullies, were extremely low.
Goldfish biomass increased initially 2009 and 2010 because of targeted fishing in the excavated side channel (site 11), which has dense macrophyte beds that provide good habitat for goldfish. The continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers has occurred. Eels were scarce in the Ohau Channel and catches were very variable. Longfin eels were caught in most years, and in 2012 and 2013 shortfin eels were also caught, but in 2014 no eels were caught.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 7 years of post-wall data, and comparison of means and standard deviations suggest that the number of bullies has decreased.
An intriguing trend of decreasing rainbow trout densities with increasing BDD, which is a measure of both water clarity and phytoplankton abundance, has occurred following wall construction (Figure 3). The trend is opposite to the usual decline of catch rate by boat electrofishing with reduced water clarity. The explanation for this is not immediately clear, and could be increased avoidance of the electrofishing boat by trout in clearer water. It is also possible that reduced BDD indicates high algal productivity in Lake Rotorua, which in turn could increase trout abundance in the Ohau Channel. This remains to be tested

text: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2014 The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (eels, goldfish, and koura). In the current study, we present the findings from the eighth year of sampling (2014) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 642 fish (11.3 kg) 11 sites on 9 December 2014, which comprised 2,914 lineal m and 11,656 m² in area. Koura and 4 fish species were present, with common bully most abundant (up to 27 fish 100 m⁻² at the site 5, edge habitat). Goldfish (up to 5.92 g m⁻²) was the next most abundant species, and was most abundant in sites 8-11 the lower channel, especially at site 11, the excavated side channel. Rainbow trout were next the most abundant species (up to 0.25 fish 100 m⁻² ). Mean bully biomass (5.25 g m⁻²) was much higher than for smelt (0.07 g m⁻²). Koura had a patchy distribution; 5 individuals were caught.
Comparing catches over the 8 years of sampling, the abundance of common bullies in 2014 (4.81 fish 100 m⁻²) was consistent with catch rates in most post-wall years (after 2007; range 0.81-5.72 fish 100 m⁻²), but lower than in 2013. The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, suggesting that bully density estimates might decrease with decreasing BDD. However, common bully densities in 2012 and 2011 were inversely related BDD. In 2014, catches of smelt, a similar sized fish to bullies, were extremely low.
Goldfish biomass increased initially 2009 and 2010 because of targeted fishing in the excavated side channel (site 11), which has dense macrophyte beds that provide good habitat for goldfish. The continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers has occurred. Eels were scarce in the Ohau Channel and catches were very variable. Longfin eels were caught in most years, and in 2012 and 2013 shortfin eels were also caught, but in 2014 no eels were caught.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 7 years of post-wall data, and comparison of means and standard deviations suggest that the number of bullies has decreased.
An intriguing trend of decreasing rainbow trout densities with increasing BDD, which is a measure of both water clarity and phytoplankton abundance, has occurred following wall construction (Figure 3). The trend is opposite to the usual decline of catch rate by boat electrofishing with reduced water clarity. The explanation for this is not immediately clear, and could be increased avoidance of the electrofishing boat by trout in clearer water. It is also possible that reduced BDD indicates high algal productivity in Lake Rotorua, which in turn could increase trout abundance in the Ohau Channel. This remains to be tested

year: 2015