Performance of tropical fish recruiting to temperate habitats: role of ambient temperature and implications of climate change

The warming of coastal oceans due to climate change is increasing the overwinter survival of tropical fishes transported to temperate latitudes by ocean currents. However, the processes governing early post-arrival mortality are complex and can result in minimum threshold temperatures for overwinter survival, which are greater than those predicted based upon physiological temperature tolerances alone. This 3.5 mo laboratory study monitored the early performance of a tropical damselfish Abudefduf vaigiensis that occurs commonly during austral summer along the SE Australian coast, under nominal summer and winter water temperatures, and compares results with a co-occurring year-round resident of the same family, Parma microlepis. Survivorship, feeding rate, growth and burst swimming ability (as a measure of predator escape ability) were all reduced for the tropical species at winter water temperatures compared to those in summer, whereas the temperate species experienced no mortality and only feeding rate was reduced at colder temperatures. These results suggest that observed minimum threshold survival temperatures may be greater than predicted by physiology alone, due to lowered food intake combined with increased predation risk (a longer time at vulnerable sizes and reduced escape ability). Overwinter survival is a significant hurdle in pole-ward range expansions of tropical fishes, and a better understanding of its complex processes will allow for more accurate predictions of changes in biodiversity as coastal ocean temperatures continue to increase due to climate change.

Trophic responses to nutrient enrichment in a temperate seagrass food chain

Simple ecological models that predict trophic responses to bottom-up forcing are valuable tools for ecosystem managers. Traditionally, theoretical ecologists have used resource-dependent functional responses to explain the modification of food chains exposed to bottom-up perturbations. These models predict alternating positive, negative and zero responses at each trophic level. More recently, ratio-dependent functional response models that predict proportional increases at each level have challenged this paradigm. The present study tested the predictions of the 2 hypotheses empirically by comparing the relative biomasses of 4 trophic levels of an estuarine seagrass food chain in relatively undisturbed, low-nutrient catchments and ‘developed’ catchments subjected to a prolonged period of nutrient enrichment. We found that nutrient-enriched sites had significantly greater biomass of both epiphytic algae and grazing invertebrates; however, the bottom-up forcing of nutrients was attenuated at higher trophic levels (occupied by juvenile and piscivorous fish), with no significant effect of catchment development. This disconnect in the upward cascade of energy may be due to a number of possible reasons including high levels of diversity and omnivory, trophic subsidy within the system or the strength or nature of perturbations. Although the predictions of both hypotheses failed to hold across all trophic groups, ratio dependence was prevalent at the lower levels of the food chain, which has implications for catchment management.

Towards more integrated and participatory coastal management : insights from Victoria’s Estuary Entrance Management Support System.

Participation and integration are core elements of coastal management. A key argument is that involving stakeholders from the broader community in collaborative coastal management allows for a more reflexive approach to consideration of ecological science outputs. However the role of stakeholder participation is still problematic especially when the involvement is short term and limited in its knowledge co-production. We argue for the development of a participatory logic that includes five key elements: the institutionalization of the processes that derive from stakeholder co-production and co-management; the ability and capacity to make meaningful decisions about issues of importance in an on-going way; the inclusion of all stakeholders in the process; the flexibility of central policies that enable participation by stakeholders at local level; the allowance for pathways for the uptake of all knowledge systems. Using this approach we report in this paper on the Estuary Entrance Management Support System (EEMSS) and ask whether this is a model system for answering the following questions as part of participatory logic: What types of collaborative activities can be used to improve the management of coastal zones? Are these activities a sufficient pathway for integrating different knowledge forms including science into coastal management? How important is stakeholder participation to science uptake? How can stakeholder participation be institutionalized in coastal management?

Stakeholder participation in estuary management: the development of Victoria's Estuary Entrance Management Support System

Stakeholder involvement in the management of estuaries is a necessary element of good environmental governance. In Victoria, Australia, a key challenge for estuary managers is whether or not estuaries should be artificially opened since many river mouths close ‘naturally’ from time to time. Estuary closure resulting in raised estuarine water levels leads to economic and social impacts on local communities. In the past these effects have been addressed by artificial river mouth openings, often without reference to associated environmental impacts. This article discusses the development and features of an Estuary Entrance Management Support System and considers its performance against principles of effective environmental management. It concludes that, in bringing together technical information with stakeholder input through a structured process, such a system makes a useful contribution to improving estuary entrance management.

Scenarios involving future climate and water extraction: ecosystem states in the estuary of Australia's largest river

 

Estuary environmental flows assessment methodology for Victoria

This report sets out a method to determine the environmental water requirements of estuaries in Victoria. The estuary environmental flows assessment method (EEFAM) is a standard methodology which can be applied consistently across Victorian estuaries.
The primary objective of EEFAM is to define a flow regime to maintain or enhance the ecological health of an estuary. The method is used to inform Victorian water resource planning processes.
The output of EEFAM is a recommended flow regime for estuaries. This recommendation is developed from the known dependence of the estuary’s flora, fauna, biogeochemical and geomorphological features on the flow regime. EEFAM is an evidence-based methodology. This bottom-up or ‘building block’ approach conforms to the asset-based approach of the Victorian River Health Strategy and regional river health strategies.
EEFAM is based on and expands on FLOWS, the Victorian method for determining environmental water requirements in rivers. The list of tasks has been modified and re-ordered in EEFAM to reflect environmental and management issues specific to estuaries. EEFAM and FLOWS can be applied
simultaneously to a river and its estuary as part of a whole-of-system approach to environmental flow requirements. Like the FLOWS method, EEFAM is modular, and additional components can be readily incorporated.

Diel vertical migration behaviour of Calanus hyperboreus at temperate latitudes

Samples historically collected and analysed by the Continuous Plankton Recorder survey in the North Atlantic and adjacent seas were used to examine temporal patterns in the near-surface abundance of copepodite stages V and VI Calanus hyperboreus (n = a total of 32836 samples; mean latitude of samples = 54* N, SD = 6.7*). The occurrence of CV and VI C. hyperboreus was largely restricted to samples collected in April, May and June. During this period there was a diel cycle in near-surface abundance which was consistent with a normal pattern of diel vertical migration. For example, CV-VI C. hyperboreus were 1.9 times more abundant at night than during the day, a difference which was highly significant (t-test, t5072 = 3.9, p < 0.001). The ratio of night:day abundance was similar in CV-VI C. finmarchicus (night:day abundance = 1.4), but markedly higher in CV-VI Metridia lucens (night:day abundance = 12.3) and CV-VI M. longa (night:day abundance = 15.0).

The broad-scale distribution of five jellyfish species across a temperate coastal environment

Jellyfish (medusae) are sometimes the most noticeable and abundant members of coastal planktonic communities, yet ironically, this high conspicuousness is not reflected in our overall understanding of their spatial distributions across large expanses of water. Here, we set out to elucidate the spatial (and temporal) patterns for five jellyfish species (Phylum Cnidaria, Orders Rhizostomeae and Semaeostomeae) across the Irish & Celtic Seas, an extensive shelf-sea area at Europe’s northwesterly margin encompassing several thousand square kilometers. Data were gathered using two independent methods: (1) surface-counts of jellyfish from ships of opportunity, and (2) regular shoreline surveys for stranding events over three consecutive years. Jellyfish species displayed distinct species-specific distributions, with an apparent segregation of some species. Furthermore, a different species composition was noticeable between the northern and southern parts of the study area. Most importantly, our data suggests that jellyfish distributions broadly reflect the major hydrographic regimes (and associated physical discontinuities) of the study area, with mixed water masses possibly acting as a trophic barrier or non-favourable environment for the successful growth and reproduction of jellyfish species.

Jellyfish aggregations and leatherback turtle foraging patterns in a temperate coastal environment

Leatherback turtles (Dermochelys coriacea) are obligate predators of gelatinous zooplankton. However, the spatial relationship between predator and prey remains poorly understood beyond sporadic and localized reports. To examine how jellyfish (Phylum Cnidaria: Orders Semaeostomeae and Rhizostomeae) might drive the broad-scale distribution of this wide ranging species, we employed aerial surveys to map jellyfish throughout a temperate coastal shelf area bordering the northeast Atlantic. Previously unknown, consistent aggregations of Rhizostoma octopus extending over tens of square kilometers were identified in distinct coastal “hotspots” during consecutive years (2003–2005). Examination of retrospective sightings data (>50 yr) suggested that 22.5% of leatherback distribution could be explained by these hotspots, with the inference that these coastal features may be sufficiently consistent in space and time to drive long-term foraging associations.

Variation with depth in temperate seagrass-associated fish assemblages in Southern Victoria, Australia

Variability in the abundance and distribution of seagrass-associated fish assemblages was examined at different depths in a temperate bay in southern Australia. Depth differences in seagrass-associated fish assemblages are poorly known but this information is critical given that seagrass loss can occur at specific depths depending on the cause. Overall, 69 species of fish from 26 families were recorded, with higher species richness in shallow than deep beds, with 12 species found only in deep beds and 22 species found only in shallow beds. While the total fish abundance (i.e. abundance of all species recorded) varied between years and seasons, and to some extent between sites, it was significantly higher in shallow than deep seagrass beds in the majority of cases. Although there was some variation between sites, seagrass tended to be longer and have a higher biomass in shallow than deep beds during both spring and autumn throughout the study. A positive relationship between seagrass biomass/length and total fish abundance/species richness was apparent. Assemblage structure tended to be distinct at each depth, with the largest species recorded in shallow seagrass. Large numbers of small schooling fish, such as atherinids, dominated in shallow seagrass but were not found in deep seagrass. Loss of seagrass could therefore have varying implications for distinct assemblages found at different depths.