Gerry P. Quinn

Aquatic Ecosystems: Flood plains: critically threatened ecosystems

Riparian zones, river-marginal wetland environments and flood plains are key landscape elements with a high diversity of natural functions and services. They are dynamic systems that are shaped by repeated erosion

Effects of secondarily treated sewage effluent on intertidal macroalgal recruitment processes

Effluent is discharged below the low-water mark at Boags Rocks, Victoria, Australia, at an average rate of 437 × 106 L day–1. Three study sites following a gradient of pollution from high (at Boags Rocks) to intermediate (Cape Schanck) to unpolluted (Cheviot Beach) were chosen for the main experiments. Surveys of the algal assemblages were conducted in spring and summer and showed the absence of the pre-discharge dominant Hormosira banksii at Boags Rocks and an abundance of turf-forming and ephemeral species at the two polluted sites. There was no evidence that the treated sewage detrimentally affected either the availability of propagules (asexual spores, gametes, zygotes or fragments) or macroalgal recruitment to artificial or natural substrata. Opportunistic genera such as UIva and Enteromorpha showed very high recruitment and propagule densities in the water column at polluted sites, apparently benefiting from the increased nutrient loads. Investigation of the number of H. banksii zygotes in water samples from various habitats showed very limited dispersibility for this species. The small dispersal shadow of H. banksii, combined with the environmental pressures placed on establishing zygotes, would severely limit the re-establishment of this species at polluted sites, even if given suitable conditions.

LEGISLATIVE VS. PRACTICAL PROTECTION OF AN INTERTIDAL SHORELINE IN SOUTHEASTERN AUSTRALIA

Harvesting of intertidal biota is a concern in many areas of the world. While the published literature is focused on reports of strong impacts of subsistence harvesting, recreational collection of biota can also have a strong effect. In either case, the management of these impacts is a major concern and is most often done by complete or partial closures of sections of coastline. This management method may require ongoing intervention, in the form of policing, education, or construction of barriers, and it is important to identify the effectiveness of these actions. We have previously shown that physical closure of a section of rocky coastline in southeastern Australia resulted in increased mean sizes of a range of intertidal molluscs collected for food and bait. The shoreline in question had legislative protection and mechanical barriers, and we present data that demonstrate that the mechanical barrier was a critical component. Removal of barriers resulted in changes in mean sizes and abundance of some gastropods over a period of 5 yr. The two most heavily harvested species, Turbo undulatus and Cellana tramoserica, showed reductions in mean size of ∼15%, relative to nearby areas that had been exploited for many years, while two less harvested species, Austrocochlea constricta and Nerita atramentosa, showed no changes following opening of the former protected areas. Three control (i.e., nonharvested) species, Bembicium nanum, Lepsiella vinosa, and Cominella eburnea, continued to show no differences between harvesting categories. Abundance of these gastropods, measured by catch per unit effort (CPUE), declined for the two harvested species over the 5 yr following opening of the protected shores. For Cellana, CPUE fell at sites in the reserve from 36% above exploited areas to similar values; for Turbo, CPUE values at the time of opening were 200–300% higher in the protected areas, but then fell to match values for exploited shores. These results show that legislative protection, which applied to the entire coastline, is ineffective in this section of the Australian coast, and effective protection requires physical barriers to exclude humans, or greatly increased enforcement.

Geographical range, heat tolerance and invasion success in aquatic species

Species with broader geographical ranges are expected to be ecological generalists, while species with higher heat tolerances may be relatively competitive at more extreme and increasing temperatures. Thus, both traits are expected to relate to increased survival during transport to new regions of the globe, and once there, establishment and spread. Here, we explore these expectations using datasets of latitudinal range breadth and heat tolerance in freshwater and marine invertebrates and fishes. After accounting for the latitude and hemisphere of each species’ native range, we find that species introduced to freshwater systems have broader geographical ranges in comparison to native species. Moreover, introduced species are more heat tolerant than related native species collected from the same habitats. We further test for differences in range breadth and heat tolerance in relation to invasion success by comparing species that have established geographically restricted versus extensive introduced distributions. We find that geographical range size is positively related to invasion success in freshwater species only. However, heat tolerance is implicated as a trait correlated to widespread occurrence of introduced populations in both freshwater and marine systems. Our results emphasize the importance of formal risk assessments before moving heat tolerant species to novel locations.

Traceability and discrimination among differently farmed fish: a case study on Australian Murray cod.

The development of traceability methods to distinguish between farmed and wild-caught fish and seafood is becoming increasingly important. However, very little is known about how to distinguish fish originating from different farms. The present study addresses this issue by attempting to discriminate among intensively farmed freshwater Murray cod originating from different farms (indoor recirculating, outdoor floating cage, and flow through systems) in different geographical areas, using a combination of morphological, chemical, and isotopic analyses. The results show that stable isotopes are the most informative variables. In particular, delta(13)C and/or delta(15)N clearly linked fish to a specific commercial diet, while delta(18)O linked fish to a specific water source. Thus, the combination of these isotopes can distinguish among fish originating from different farms. On the contrary, fatty acid and tissue proximate compositions and morphological parameters, which are useful in distinguishing between farmed and wild fish, are less informative in discriminating among fish originating from different farms.

Association of reduced riparian vegetation cover in agricultural landscapes with coarse detritus dynamics in lowland streams

Studies were conducted on streams flowing through agricultural floodplains in south-eastern Australia to quantify whether reductions in riparian canopy cover were associated with alterations to the input and benthic standing stocks of coarse allochthonous detritus. Comparisons were made among three farmland reaches and three reaches within reserves with intact cover of remnant overstorey trees. Detritus inputs to these reaches were measured monthly over 2 years using litter traps. Direct inputs to streams within the reserves were relatively high (550–617 g ash free dry weight (AFDW) m–2 year–1), but were lower at farmland reaches with the lowest canopy covers (83–117 gAFDW m–2 year–1). Only a minor fraction of the total allochthonous input (<10%) entered any of the study reaches laterally. The mean amounts of benthic detritus were lowest in the most open farmland reaches. Standing stocks of benthic detritus were found to be highly patchy across a large number of agricultural streams, but were consistently very low where the streamside canopy cover was below ~35%. Canopy cover should be restored along cleared agricultural streams because allochthonous detritus is a major source of food and habitat for aquatic ecosystems. Given the absence of pristine lowland streams in south-eastern Australia, those reaches with the most intact remnant overstorey canopies should be used to guide restoration.

Synchronized group association in little penguins, Eudyptula minor

Most seabirds form groups on land and at sea, but there is little information whether seabird groups are formed deliberately or randomly. We investigated whether little penguins formed groups composed of the same individuals when they crossed the beach each day over four breeding seasons (2001–2004) using an automated penguin monitoring system (APMS). We used an association matrix to determine the number of times any two birds crossed the APMS in the same group. The number of these group associations or ‘synchronized parade’ behaviour was determined for every possible pair of individuals, giving a total association value for each pair of birds during the postguard stage of the reproductive cycle. We concluded that a penguin group was composed of 5–10 individuals within 40-s intervals. Penguin groups were formed nonrandomly in years of high breeding success (2002 and 2003), but not in years of low breeding success (2001 and 2004). Age of birds was a significant factor in composition of groups. Little penguins with higher association values shared similar characteristics or ‘quality’, which in turn may increase the functional efficiency of their groups, especially if they are also foraging together. However, low association indices indicated that seeking the same associates was not a priority. It is costly for any animal to synchronize their attendance with the same individuals, so it could be beneficial to display synchronized parade behaviour in good breeding years but it could result in intraspecific competition for food during poor breeding years.

Changes in organic-matter dynamics and physicochemistry, associated with riparian vegetation loss and river regulation in floodplain wetlands of the Murray River, Australia

Extensive clearing of floodplain forests potentially reduces organic matter available to floodplain wetlands. Furthermore, on rivers regulated to provide irrigation water in summer, floodplain wetlands that were previously inundated in spring, now flood in summer/autumn. In the Murray–Darling Basin, Australia, this has changed the timing of organic matter entering the aquatic phase, since leaf fall peaks in summer. Field surveys and mesocosm experiments on floodplain wetlands on the River Murray revealed faster processing rates of leaves in summer/autumn than spring, and no difference between cleared and forested wetlands. Temperature and leaf carbon : nitrogen ratio could not explain these differences, and instead, changes to leaf chemistry associated with ‘terrestrial ageing’ between peak leaf fall in summer and inundation in spring is more likely. The results indicated that the reduction of input of organic matter through riparian tree clearing and changing the timing of inundation interact to alter organic-matter standing stocks and rates of decomposition in floodplain wetlands. Restoring both natural timing of high flows and riparian vegetation might be required for recovery of these wetlands.

Zooplankton dynamics from inundation to drying in a complex ephemeral floodplain-wetland

Abstract.Ecological responses to wetting and drying in dryland river floodplain systems are often described in terms of “boom” and “bust”. We suggest that patterns in floodplain species abundances and assemblage structures will be closely linked to the changes in spatial habitat heterogeneity that accompany flooding and drying phases. This study examined the responses of zooplankton through a wetting and drying cycle in a complex floodplain-wetland system in semi-arid Australia, the Narran Lakes. We illustrate the complexity of the zooplankton “boom” and “bust” response. Total densities of zooplankton varied considerably over time and patterns were very dissimilar between sites with abundances varying from <30 animals/L to over 4000 animals/L. We detected different patterns in the proportion of variance in abundances of the broad taxonomic groups (rotifers, cladocerans, ostracods, calanoid copepods, cyclopoid copepods and nauplii) explained by time and space. Site explained the highest proportion of variation in cladoceran and ostracod abundances,whereas variance in calanoid abundances was explained predominantly by time since inundation. Variation in the abundances of the remaining groups was explained largely by the site by time interaction. Zooplankton assemblages were observed to diverge during drying with highest between-site dissimilarities in assemblage structure occurring during the later stages of drying. Such high spatial and temporal variability in zooplankton abundances and community composition could have important consequences for consumers such as fish and some wetland birds that utilize these ephemeral systems for feeding and breeding while they are inundated.

Influences of agricultural landuse and seasonal changes in abiotic conditions on invertebrate colonisation of riparian leaf detritus in intermittent streams

The structure and function of agricultural stream reaches with sparse riparian and floodplain vegetation differ from those of forested reaches, but may be ‘reset’ as these streams flow through reaches with forested riparian zones. We investigated whether invertebrate colonisation of River Red Gum (Eucalyptus camaldulensis) leaf packs in lowland intermittent streams was influenced by the adjacent reach-scale landuse (cleared farmland or forested reserve) within an agricultural catchment in Victoria, Australia. Further, we examined the influence of seasonal changes in hydrology and associated changes in abiotic conditions on the colonisation of leaves by repeating experiments over two summers and one spring. Across these experiments, there were no consistent differences in the structure of communities that colonised leaves in farmland and reserve reaches. In both seasons, most leaf colonists were collectors and few were shredders in both farmland and reserve reaches. Relative abundances of gastropod grazers were much higher in summer than in spring. The structure of invertebrate communities colonising leaves in the different reaches converged over time when streams flowed in spring, but diverged over time as the streams dried and abiotic conditions within disconnected pools became increasingly harsh in summer. Thus, patterns of leaf pack colonisation were influenced by the regional climate causing large seasonal changes in hydrology, but not by reach-scale landuse. The large-scale disturbances of agricultural landuse across the catchment and a supra-seasonal drought probably contributed to low diversities of invertebrate communities in the streams.