Relationships between faunal assemblages and habitat types in Broke Inlet, Western Australia

The work for this thesis was undertaken in Broke Inlet, a seasonally-open estuary on the south coast of Western Australia and the only estuary in that region which is regarded as “near-pristine” (Commonwealth of Australia, 2002). The only previous seasonal studies of the environmental and biotic characteristics of this estuary involved broad-based descriptions of the trends in salinity, temperature and ichthyofaunal characteristics at a limited number of sites. Furthermore, no attempt has been made to identify statistically the range of habitats present in the nearshore and offshore waters of this system, and the extents to which the characteristics of the fish and benthic invertebrate faunas are related to habitat type. These types of data provide not only reliable inventories of the habitat and faunal characteristics of Broke Inlet, but also a potential basis for predicting the likely impact of anthropogenic and climatic changes in Broke Inlet in the future. The main aims of this thesis were as follows. (1) To use the method of Valesini et al. (2010), which employs enduring environmental characteristics, to identify quantitatively the range of habitats present throughout the nearshore and offshore waters of Broke Inlet. The enduring environmental characteristics represent three broad categories, i.e. the location of any site in terms of its proximity to marine and freshwater sources, the degree of exposure to wave activity and the type of substrate and/or submerged vegetation. (2) To test the hypothesis that the species richness, density, diversity and species compositions of the fish and benthic macroinvertebrate faunas differ among habitat types, seasons and, in the case of the fish fauna, also years. (3) To test the hypothesis that the pattern of relative differences among habitat types, as exhibited by their faunal compositions, is correlated with that defined by their (i) enduring environmental characteristics and (ii) non-enduring environmental characteristics (water physico-chemical variables and sediment characteristics). A high resolution satellite image and a digital elevation model of Broke Inlet were used to measure the enduring environmental characteristics at 104 and 36 widely-distributed sites in nearshore and offshore waters, respectively. These data were used to construct separate Manhattan distance matrices for nearshore and offshore waters, which were then subjected to the CLUSTER and SIMPROF routines in PRIMER v6 to identify the various groups of sites that did not differ significantly in their environmental characteristics and which were thus considered to represent habitat types. Twelve and four distinct habitat types were identified in nearshore and offshore waters, respectively. The ichthyofaunas at sites representing 11 nearshore (A-K) and three offshore (A-C) habitat types were sampled seasonally for two consecutive years using seine and gill nets, respectively. A total of 83,047 fish was collected from nearshore waters, representing 27 species from 19 families, with 99.6% of those fish belonging to six species which represent the Atherinidae (Atherinosoma elongata, Leptatherina wallacei and Leptatherina presbyteroides) or Gobiidae (Afurcagobius suppositus, Pseudogobius olorum and Favonigobius lateralis) and complete their life cycles within the estuary. Each of these species were found at each nearshore habitat type, except for P. olorum, which was not caught at habitat A. The species richness, density and diversity of the nearshore fish fauna differed significantly among habitats, seasons and years, with habitat being the most influential factor. Generally, mean species richness and density were greatest at habitat types located in the entrance channel (B, G and H) and/or on the southern shore of the basin (C and G), while the fish assemblages were most depauperate at habitats near freshwater sources (A and J). The nearshore ichthyofaunal composition of Broke Inlet differed significantly among habitats, seasons and years, with the first again being the most influential. However, the extents of the overall differences in composition during each sampling occasion were moderate. The lack of very pronounced ichthyofaunal differences among the various habitat types reflects the widespread distributions and high abundances of the above atherinid and gobiid species, and particularly of A. elongata and L. wallacei, which typified the fish fauna of each habitat type on almost all sampling occasions. The most distinctive of the faunas were those at habitat types in the entrance channel, where L. presbyteroides and F. lateralis, which are typically found in higher salinities, were in their greatest densities, and where several marine straggler species, such as the labrids Notolabrus parilus and Achoerodus gouldii, were occasionally caught. Seasonal and inter-annual changes in ichthyofaunal composition were small and often not consistent across habitats. The pattern of relative differences among nearshore habitats in terms of their ichthyofaunal composition was correlated at a moderate level with that defined by their enduring environmental characteristics in all but one of the eight seasons. Such indicate that the ichthyofaunal composition likely to be found at any site in the nearshore waters of Broke Inlet at any time of year can be predicted, simply by assigning that site to its most appropriate habitat type on the basis of its enduring environmental characteristics. Differences in ichthyofaunal composition among habitat types were also correlated, but to a slightly greater extent, with those among the suite of non-enduring water physico-chemical variables, with salinity and the biomass of macrophytes being particularly relevant. Gill netting in the three offshore habitats yielded 1,050 fish representing 31 species. Species richness, catch rates and diversity all varied significantly among habitats, with the values for each of these biotic characteristics always being greatest at habitat A in the entrance channel and lowest at habitat B near the Shannon River mouth. These biotic variables did not always vary, however, among seasons and/or years. In contrast to the situation in nearshore waters, the offshore ichthyofauna comprised mainly marine estuarine-opportunists and marine stragglers, which contributed 84% to the number of species and 80% to the total number of fishes. The contribution of individuals belonging to the marine straggler guild was only 5% and no estuarine resident species were caught. Ichthyofaunal composition in offshore waters differed significantly among habitats, seasons and years, with habitat being the most influential factor. Faunal composition only differed among habitats in spring and autumn, and even then the extent of those differences was low. During those seasons, habitat B contained the most distinct and depauperate fauna, which was typified mainly by Mugil cephalus and Aldrichetta forsteri. In contrast, the fish assemblages at habitats A and C were also typified by Arripis georgianus, Arripis truttaceus, Rhabdosargus sarba, Pagrus auratus, Pseudocaranx dentex and Engraulis australis. The pattern of relative differences among offshore sites in terms of their ichthyofaunal composition was significantly correlated with that defined by their enduring environmental characteristics only in autumn, but was moderately correlated with that exhibited by the suite of non-enduring water physico-chemical variables in each season except summer. Seasonal sampling of benthic macroinvertebrates at six of the nearshore habitat types (A, C, D, F, H and K) for a year yielded 7,485 individuals representing 28 species and seven phyla and, at the three offshore habitat types (A-C), 2,459 individuals representing 26 species and eight phyla. Polychaetes (64 and 57%) and crustaceans (24 and 34%) were the most abundant taxa in nearshore and offshore waters, respectively. The mean density of invertebrates in the nearshore waters did not differ significantly among habitats, but did vary significantly among seasons, and was greatest in summer. The mean densities of invertebrates in offshore waters did not differ significantly, however, among habitats or seasons. The compositions of nearshore benthic macroinvertebrate assemblages differed significantly among habitats and, less conspicuously, seasons. Comparisons between the faunal compositions in each pair of habitats in spring and summer were almost invariably significantly different and to a moderate extent. However, such pairwise comparisons were rarely significant in autumn and winter. Habitats A and K contained the most distinct and depauperate invertebrate fauna, comprising mainly the polychaete Capitella capitata and amphipod Corophium minor, whereas the other habitats also contained large numbers of the polychaete Ceratonereis aequisetis. In offshore waters, the composition of the benthic macroinvertebrate assemblages differed to a low to moderate degree among habitats, with habitat B containing the most distinct fauna due to large densities of C. minor. The extent of seasonal differences in these faunal compositions was small. The pattern of relative differences among nearshore habitats in terms of their benthic macroinvertebrate composition was highly correlated with that defined by both their (i) enduring environmental characteristics and (ii) non-enduring water physico-chemical and sediment characteristics in spring and/or summer. Although the faunal and enduring environmental data were not correlated at offshore sites, the fauna and non-enduring environmental variables at those sites were correlated to a moderate extent. In summary, the composition of the nearshore fish fauna at any site in Broke Inlet at any time of year can now be predicted by allocating that site to a particular habitat type on the basis of its enduring environmental characteristics. The less consistent spatial correlations between the compositions of the offshore fish fauna and benthic macroinvertebrate faunas and the enduring environmental variables largely reflected the ubiquitous nature of the majority of the abundant species representing those faunas, i.e. they are typically at least moderately abundant in all habitats and thus have no strong preferences for a particular habitat type

Long-term annual and monthly changes in mysids and caridean decapods in a macrotidal estuarine environment in relation to climate change and pollution

© 2018 Elsevier B.V. A 26-year time series of monthly samples from the water intake of a power station has been used to analyse the trends exhibited by number of species, total abundance, and composition of the mysids and caridean decapods in the inner Bristol Channel. During this period, annual water temperatures, salinities and the North Atlantic Oscillation Index (NAOI) in winter did not change significantly, whereas annual NAOI declined. Annual mean monthly values for the number of species and total abundance both increased over the 26 years, but these changes were not correlated with any of the measured physico-chemical/climatic factors. As previous studies demonstrated that, during a similar period, metal concentrations in the Severn Estuary and Bristol Channel (into which that estuary discharges) declined and water quality increased, it is proposed that the above changes are due to an improved environment. The fauna was dominated by the mysids Mesopodopsis slabberi and Schistomysis spiritus, which collectively contributed 94% to total abundance. Both species, which were represented by juveniles, males, non-brooding females and brooding females, underwent statistically-indistinguishable patterns of change in abundance over the 26 years. When analysis was based on the abundances of the various species, the overall species composition differed significantly among years and changed serially with year. When abundances were converted to percentage compositions, this pattern of seriation broke down, demonstrating that changes in abundance and not percentage composition were responsible for the seriation. As with the number and abundance of species, changes in composition over the 26 years were not related to any of the physico-chemical/climatic factors tested. Species composition changed monthly in a pronounced cyclical manner throughout the year, due to statistically different time-staggered changes in the abundance of each species. This cyclicity was related most strongly to salinity

The Effect of the Invasive Alga Sargassum muticum (Yendo) Fensholt on the Seagrass Zostera marina L. and its Associated Fauna

The first reports of attached Sargassum muticum occurring in British waters coincided with a warning that this invasive alga may replace the seagrass Zostera marina. While many subsequent studies have investigated the biology of the alga and the effects of the introduction of the indigenous algal and the associated faunal community, few have responded to the original warning. Presented here are three studies into the interactions between the two species and any effects on the associated fauna of Z. marina. I show that contrary to previous thoughts, S. muticum can inhabitat soft substratum and successfully attach and grow within a Z. marina bed, although the size of the plant is reduced. Moreover, it may be the presence of the Zostera itself which enhances S. muticum settlement. Growth and photosynthetic responses to inter and intra-specific competition in each species were also recorded. Although the growth measures were shown to be unaffected by the presence of the other species, a reduction in photosynthetic efficiency was demonstrated in both species when involved in inter-specific competition. The mobile epifauna and mobile epibenthos occurring in a range of vegetation types containing both Z. marina and S. muticum was sampled using FBA and seine nets over a four month period, to assess the effect of S. muticum on faunal assemblage structure within two Zostera beds in South-West England. S. muticum stands and mixed areas of Z. marina and S. muticum were found to contain a richer, more abundant, and faunally distinct community compared to Zostera beds. The implications of the S. muticum invasion on Z. marina and the associated fauna are discussed with relation to the original warning that S. muticum may replace Z. marina beds.Faculty of Scienc

Baseline survey of the fish fauna of a highly eutrophic estuary and evidence for its colonisation by Goldfish (Carassius auratus)

Abstract This study represents the first quantitative survey of the fish fauna of the highly eutrophic Vasse and Wonnerup estuaries, part of the Ramsar-listed Vasse-Wonnerup Wetland System in south-western Australia. Sampling at five sites in each of these estuaries occurred in January 2012 (austral summer) to provide a species inventory and determine whether the number of species, total density and fish community composition differed between the two water bodies. A total of 18,148 fish were recorded, representing six species across four families. Three species that can complete their life cycle within estuaries, i.e. the atherinids Lepthatherina wallacei and Atherinosoma elongata and the gobiid Pseudogobius olorum, dominated the fish fauna, accounting for >99% of all fish collected. No significant inter-estuary differences were observed in the mean number of species, mean total density or fish community composition. Although the fish community was depauperate in terms of the number of species, total density was high, reflecting the presence of permanent and seasonal barriers to the immigration of marine species into these estuaries and the highly productive nature of this system, respectively. Two introduced freshwater species, i.e. the Eastern Gambusia Gambusia holbrooki and the Goldfish, Carassius auratus, were recorded in the Vasse Estuary. As C. auratus was found in mesohaline conditions, individuals may be able to use the estuary as a ‘saltbridge’ to gain access to other tributaries and/or the Wonnerup Estuary, and thus expand their distribution. These findings are of concern given the potential deleterious biological and ecological effects of these alien species

Partitioning of food resources among three sympatric scorpionfish (Scorpaeniformes) in coastal waters of the northern Yellow Sea

International audienceThe partitioning of food resources among three abundant co-occurring reef-associated scorpionfish, Hexagrammos agrammus, Hexagrammos otakii and Sebastes schlegelii, was determined on an artificial reef zone in nearshore and offshore coastal waters of northern China, using stomach content and stable isotope analyses (δ13C and δ15N). The three species consumed similar prey items, mainly a variety of crustaceans, teleosts, polychaetes and macroalgae, but the proportions of the items differed among species. The dietary composition of all three scorpionfish differed significantly in nearshore waters, but not between H. otakii and S. schlegelii in offshore waters, where both species fed predominantly on carideans, penaeids and brachyurans. The δ13C values varied significantly among the three scorpionfish in nearshore waters, and tended towards significance (P = 0.053) between H. otakii and S. schlegelii in offshore waters, suggesting that they partition food resources. Bayesian mixing models further confirmed that all scorpionfish were generalist carnivorous and that the main food sources were assimilated in different proportions. In the nearshore waters, resource partitioning occurs among the three scorpionfish, reducing the potential for competition and the feeding ecology implies that they have dietary plasticity, which facilitates their coexistence and maintains local benthic fish community stability

Quantifying the Potential Water Filtration Capacity of a Constructed Shellfish Reef in a Temperate Hypereutrophic Estuary

Shellfish reefs have been lost from bays and estuaries globally, including in the Swan-Canning Estuary in Western Australia. As part of a national program to restore the ecosystem services that such reefs once provided and return this habitat from near extinction, the mussel Mytilus galloprovincialis was selected for a large-scale shellfish reef construction project in this estuary. To assess the potential filtration capacity of the reef, estuary seston quality, mussel feeding behavior, and valve gape activity were quantified in the laboratory and field during winter and summer. In general, estuary water contained high total particulate concentrations (7.9–8.7 mg L−1). Standard clearance rates were greater in winter (1.9 L h−1; 17 °C) than in summer (1.3 L h−1; 25 °C), the latter producing extremely low absorption efficiencies (37%). Mussel valves remained open ~97% and ~50% of the time in winter and summer, respectively. They often displayed erratic behavior in summer, possibly due to elevated temperatures and the toxic microalgae Alexandrium spp. Despite numerous stressors, the reef, at capacity, was estimated to filter 35% of the total volume of the estuary over winter, incorporating 42.7 t of organic matter into mussel tissue. The reefs would thus make a substantial contribution to improving estuary water quality

Differences in Recreational Fishers’ Motivations for Utilising Two Estuarine Fisheries

Effective fisheries management requires an understanding of human dimensions. This study elicited the salient motivations for recreational blue swimmer crab and black bream fishing in Western Australia and whether these views differed depending on the fishing location and/or the characteristics of the fisher. Crab fishers were strongly consumption-orientated and aimed to “catch big crabs” and “catch enough crabs to eat”. Furthermore, 91% consumed their catch, with only 2% practicing catch-and-release fishing. In contrast, 81% of black bream fishers did so for the sport/challenge, with the strongest motivation being to catch a bream considerably above legal size and with food only selected by 15% of respondents; most fishers released caught fish. The marked differences between the fisheries for the two species, which co-occur in the same estuaries, are likely driven by the accessible nature of the crab fishery, ease of catching crabs, the low cost of fishing equipment, and their taste. Fishing for black bream, however, requires more expensive equipment, patience, and a greater skill level. Fishers considered crabbing to be as important as other fishing and outdoor activities, whereas bream fishers considered bream fishing considerably more important, reflecting the trophy nature of this fishery

Selecting from the Fisheries Managers’ Tool-Box: Recreational Fishers’ Views of Stock Enhancement and Other Management Options

As recreational fishers act relatively autonomously, management relies heavily on voluntary compliance. Therefore, understanding fishers’ views on management options can be beneficial. This study used a two-phase approach of face-to-face interviews and subsequent online questionnaires to evaluate recreational fishers’ salient views on issues affecting the Blue Swimmer Crab (Portunus armatus) and Black Bream (Acanthopagrus butcheri) fisheries in Western Australia as well as current and potential management arrangements, including stock enhancement. The strength and heterogeneity of views were also determined. Minimum size limits were mainly considered acceptable or very acceptable, with restricting recreational fishing and spatial closures the least supported management options for both species, in addition to maximum size limits for crabs. These views were not always consistent across fishing locations for each species and among types of crab fishers, indicating heterogeneity in views. Stocking was the most acceptable of the management measures not already utilised for crabs and among the most popular for bream fisheries. Recreational fishers of both species believed stock enhancement could have strong positive outcomes for the abundance of their target species and increase their subsequent catches. They also recognized that some negative outcomes, e.g., increased fishing pressure and environmental issues, might occur but considered them unlikely

Figure 14. Metapenaeus dalli Post larvae I in Larval development of the western school prawn Metapenaeus dalli Racek, 1957 (Crustacea: Decapoda: Penaeidae) reared in the laboratory

Figure 14. Metapenaeus dalli Post larvae I (a) lateral view; (b) first antenna; (c) second antenna; (d) mandible; (e) first maxilla; (f) second maxilla; (g) first maxilliped; (h) second maxilliped; (i) third maxilliped; (j) third pereiopod; (k) fifth pereiopod; (l) pleopods; (m) telson and uropods. Scale bars: a–c, g–m = 0.1 mm; d–f = 0.05 mm.Published as part of Crisp, Jason A., Tweedley, James R., D, Frances M. L., Souza, Partridge, Gavin J. & Moheimani, Navid R., 2016, Larval development of the western school prawn Metapenaeus dalli Racek, 1957 (Crustacea: Decapoda: Penaeidae) reared in the laboratory, pp. 1699-1724 in Journal of Natural History 50 on page 1719, DOI: 10.1080/00222933.2016.1155669, http://zenodo.org/record/399214