Glenn A. Hyndes

Differences in recreationally targeted fishes between protected and fished areas of a coral reef marine park

Many comparisons have been made between sanctuary (no-fishing) and fished areas, where fishing pressure is exerted by artisanal or commercial fishers, but few have examined the effect of recreational fishing on fish assemblages in coral reef habitats. In this study, we compared assemblages of targeted fish from coral reef habitats in sanctuary (no-fishing) and recreationally fished zones of a marine protected area (MPA). Surface visual census (SVC) transects were conducted two times, at three regions, to compare the composition of predatory fish assemblages and the abundance, biomass, and size of the most commonly targeted fish. Baited remote underwater video (BRUV) was used to make relative counts of fish between zones. We also measured benthic cover and rugosity, which may influence fish assemblages. Analysis of similarity (ANOSIM) revealed significant differences in the composition of fish families/genera targeted by fishers (Lethrinidae, Lutjanidae, Haemulidae, Serranidae, and the genus Choerodon of the family Labridae) in terms of biomass (P<0.01) and abundance (P<0.05). The most consistent trends were recorded for biomass and this was supported by clustering of replicates in nonmetric multidimensional scaling (nMDS) ordinations. Similarity percentages (SIMPER) analysis indicated that the family Lethrinidae accounted for 73% (as abundance), and up to 69% (as biomass), of the dissimilarity between zones. Three-factor ANOVA highlighted significantly greater biomass, size, and abundance of legal-sized lethrinids (the most targeted family in the region) in sanctuary zones, but no differences in other families/genera. Results of BRUV supported SVC with greater relative counts of lethrinids (P<0.01) in sanctuaries, but no significant differences for other families. Cover of Acropora coral and hard substrate differed between zones at some regions but differences were inconsistent. There were no significant differences in algal cover or rugosity between zones. Given the inconsistency in benthic cover, the similarity of rugosity between zones, the consistently greater biomass of lethrinids in sanctuaries, and the abundance of large lethrinids in sanctuaries, the cessation of fishing in sanctuary zones appears responsible for observed differences in the populations of these fish. These results demonstrate that recreational

Surf-zone fish assemblages in south-western Australia: do adjacent nearshore habitats and the warm Leeuwin Current influence the characteristics of the fish fauna?

Nearshore fish faunas from 32 sites along 1500 km coastline of temperate south-western Australia were sampled by seine net between 1991 and 1992 to examine the species composition in sandy surf zones along this region, and to determine whether it is influenced by adjacent nearshore habitats and the warm southward flowing Leeuwin Current. Although the ichthyofauna was diverse, with 95 species from 47 families recorded, it was numerically dominated by only a few species. Species of Atherinidae, Mugilidae, Tetraodontidae, Clupeidae and Pomatomidae, such as Atherinomorus ogilbyi, Leptatherina presbyteroides, Mugil cephalus, Aldrichetta forsteri, Torquigener pleurogramma, Hyperlophus vittatus, Spratelloides robustus and Pomatomus saltatrix, were often common to these surf zones. When the species composition of the surf zones was compared with that found in adjacent nearshore habitats, 38 and 42% of the species were shared with reefs and seagrass beds, respectively, and 22% were present in all three habitats. Classification and ordination demonstrated that the faunal composition on the west coast was distinct from that on the south coast, and within each of these regions there were discrete assemblages. There was a marked decline in the number of species on the south coast, with 20 to 66 species reported from the six west-coast assemblages and 11 to 16 species collected from the four south-coast assemblages. A high proportion of resident species was found in the surf zones on both coasts; however, there was a smaller contribution of transient species on the south coast than on the west coast. This decline in transient species was associated with the absence of tropical species on the latter coast. Benthic invertevores were dominant on both coasts, while trophic diversity decreased and the proportion of zooplanktivores increased on the south coast. These differences in the characteristics of the fish fauna between the two coasts can be related to the presence of seagrass beds and limestone patch reef adjacent to sandy surf-zone areas on the west coast which provide more microhabitats for fish. The presence of inshore limestone reefs along the west coast moderates wave energy, producing more sheltered and temporally stable surf zones. The lower number of species on the south coast can also be attributed to the reduced influence of the Leeuwin Current. This southward flowing current acts as a mechanism for the dispersal of tropical species which display no regular association with the surf zones on the lower west coast.

Fish fauna of the Severn Estuary. Are there long-term changes in abundance and species composition and are the recruitment patterns of the main marine species correlated?

Fish were collected from the intake screens of the Oldbury Power Station in the Severn Estuary in each week between early July 1972 and late June 1977 and at least twice monthly between early January 1996 and late June 1999. The annual catches, after adjustment to a common sampling effort, demonstrate that the abundance of fish at Oldbury was far greater in the 1990s than 1970s, mainly due to marked increases in the numbers of certain marine species, such as sand goby, whiting, bass, thin-lipped grey mullet, herring, sprat and Norway pout. These increases may reflect the great improvement that occurred in the water quality of the Severn Estuary between these decades. The only species that declined markedly in abundance was poor cod. Modest declines in flounder and River lamprey paralleled those occurring elsewhere in the UK. The species composition in the two decades also differed, reflecting changes not only in the relative abundances of the various marine estuarine-opportunistic species, which dominated the ichthyofauna, but also in those of the suite of less abundant species in the estuary. The cyclical changes undergone each year by the species composition of the fish fauna of the Severn Estuary reflect sequential intra-annual changes in the relative abundances of species representing each of the marine, diadromous and freshwater categories. New approaches have been developed to test whether or not large sets of correlations between patterns of recruitment amongst abundant marine species (internal correlations), and between those patterns and salinity and water temperature within the estuary (cross-correlations), were significant. The correlation profile analyses found no evidence that the annual recruitment strengths of these species were either intercorrelated, or correlated with either one or a combination of both of the above environmental variables. Yet, the timings of the recruitment of these species into the estuary were intercorrelated, i.e. a slightly earlier or later than normal immigration by one species in a given year was paralleled by the same trend in other species. However, this association in recruitment times could be linked neither to salinity nor water temperature within the estuary, nor to a combination of these two variables. These results indicate that, while the factors that influence the annual recruitment strengths of the juveniles of different marine species vary, inter-annual differences in the phasing of events that regulate spawning times and/or larval dispersal influence, in the same direction, the times when marine species are recruited into the estuary.

Mechanisms and ecological role of carbon transfer within coastal seascapes

Worldwide, coastal systems provide some of the most productive habitats, which potentially influence a range of marine and terrestrial ecosystems through the transfer of nutrients and energy. Several reviews have examined aspects of connectivity within coastal seascapes, but the scope of those reviews has been limited to single systems or single vectors. We use the transfer of carbon to examine the processes of connectivity through multiple vectors in multiple ecosystems using four coastal seascapes as case studies. We discuss and compare the main vectors of carbon connecting different ecosystems, and then the natural and human‐induced factors that influence the magnitude of effect for those vectors on recipient systems. Vectors of carbon transfer can be grouped into two main categories: detrital particulate organic carbon (POC) and its associated dissolved organic and inorganic carbon (DOC/DIC) that are transported passively; and mobile consumers that transport carbon actively. High proportions of net primary production can be exported over meters to hundreds of kilometers from seagrass beds, algal reefs and mangroves as POC, with its export dependent on wind‐generated currents in the first two of these systems and tidal currents for the last. By contrast, saltmarshes export large quantities of DOC through tidal movement, while land run‐off plays a critical role in the transport of terrestrial POC and DOC into temperate fjords. Nekton actively transfers carbon across ecosystem boundaries through foraging movements, ontogenetic migrations, or ‘trophic relays’, into and out of seagrass beds, mangroves or saltmarshes. The magnitude of these vectors is influenced by: the hydrodynamics and geomorphology of the region; the characteristics of the carbon vector, such as their particle size and buoyancy; and for nekton, the extent and frequency of migrations between ecosystems. Through a risk‐assessment process, we have identified the most significant human disturbances that affect the integrity of connectivity among ecosystems. Loss of habitat, net primary production (NPP) and overfishing pose the greatest risks to carbon transfer in temperate saltmarsh and tropical estuaries, particularly through their effects on nekton abundance and movement. In comparison, habitat/NPP loss and climate change are likely to be the major risks to carbon transfer in temperate fjords and temperate open coasts through alteration in the amount of POC and/or DOC/DIC being transported. While we have highlighted the importance of these vectors in coastal seascapes, there is limited quantitative data on the effects of these vectors on recipient systems. It is only through quantifying those subsidies that we can effectively incorporate complex interactions into the management of the marine environment and its resources.

SEASONAL, ANNUAL AND REGIONAL VARIATIONS IN ICHTHYOFAUNAL COMPOSITION IN THE INNER SEVERN ESTUARY AND INNER BRISTOL CHANNEL

Monthly samples of fish from the intake screens of power stations at Oldbury and Berkeley in the inner Severn Estuary and Hinkley Point in the inner Bristol Channel, were used to analyse the community structures of the ichthyofauna in these regions. Marine species that use the estuary as a nursery area (marine estuarine-opportunists) were very abundant in the shallow inshore waters at Oldbury. Diadromous species were more abundant in the offshore and deeper waters at Berkeley than at Oldbury. Only one of the two species that complete their life cycles in the estuary was even moderately abundant in the inner estuary and the 15 freshwater species were relatively rare. Bass and particularly the sand goby complex were more numerous in the protected, inshore waters than the more offshore waters of the estuary. With the yellow and silver stages of the European eel, the reverse situation pertained. Seasonal changes in faunal composition were more pronounced in the inshore shallow than in more offshore deeper waters of the estuary. This largely reflected the sequential immigration of large numbers of the juveniles of marine estuarine-opportunist species into the former area for relatively short periods. Although the ichthyofaunal composition in the shallows at Oldbury underwent the same pattern of cyclical variation in each of five consecutive years, the degree of intra-annual variability differed, reflecting interannual differences in the recruitment strengths of the 0+ age classes of the different marine estuarine-opportunists. These cyclical changes were not correlated strongly with either salinity or water temperature. The faunal composition of the protected inshore, more marine waters of the inner Bristol Channel differed from those in both inshore and offshore regions of the inner estuary. The species which typified the fauna of the Channel were bib, poor cod, five-bearded rockling, sole and conger eel. Although the first four of these species were relatively more abundant in these waters than in the estuary, their juveniles often made extensive use of the shallows at Oldbury. This study emphasizes that, for some marine species, the protected inshore, and more marine, waters in the Bristol Channel can act as alternative nursery areas to those provided by the inshore shallows of the Severn Estuary.

Composition of the fish fauna of a permanently open estuary on the southern coast of Australia, and comparisons with a nearby seasonally closed estuary

The fish faunas of the outer basin (Nornalup Inlet), inner basin (Walpole Inlet) and saline region of the main tributary (Frankland River) of the permanently open Nornalup-Walpole Estuary on the southern coast of Western Australia, were sampled bimonthly for a year using seine and gill nets, and also during a further two months by the former method. Although the Nornalup-Walpole Estuary is permanently open, the catches of fish in its shallows were dominated (98.4%) by estuarine-spawning species, thereby paralleling the situation in the nearby and seasonally closed Wilson Inlet. In contrast, larger representatives of several marine species were present in appreciable numbers in the offshore, deeper waters of both of these estuaries. The delayed recruitment of marine species into these estuaries apparently reflects the distance that the juveniles of these species have to travel from the areas where they are believed predominantly to spawn. The larger representatives of marine species made a greater contribution to the fish faunas of the offshore, deeper waters in the Nornalup-Walpole Estuary than in Wilson Inlet (64.5 vs 36.9%) and, unlike the situation in the latter estuary, they included five species of elasmobranchs, two of which (Mustelus antarcticus and Myliobatis australis) were relatively abundant. Classification and ordination of the combined data for both estuaries demonstrated that the composition of the fish fauna in the offshore, deeper waters of the outer basin of the Nornalup-Walpole Estuary was particularly distinct, with some marine species being restricted to these waters. This is presumably related both to the presence of a permanently open entrance channel and the relatively deep waters found in Nornalup Inlet, which allow the ready exchange of water between the sea and estuary and the maintenance of high salinities in the deeper regions of the outer basin for much of the year. The fish faunas in Walpole Inlet and the tributaries of both the Nornalup-Walpole Estuary and Wilson Inlet were more similar to each other than they were to those in the more seawards end of either estuary. This similarity reflects the apparent preference of certain teleosts, such as the estuarine species Acanthopagrus butcheri and the marine species Mugil cephalus and Aldrichetta forsteri for reduced salinities and/or features associated with riverine environments.

Variations in the dietary compositions of morphologically diverse syngnathid fishes

SynopsisWe examined the diets of 12 morphologically diverse syngnathid species in shallow seagrass-dominated marine waters of south-western Australia to determine whether they differed among species that varied in body form, size and snout morphology, and in particular whether species with long snouts ingested more mobile prey. Although all species consume mainly small crustaceans, the dietary compositions of these species often vary markedly. We suggest that these differences are related to factors that influence both their foraging capabilities and/or locations. Those species with long snouts (e.g. the common seadragon Phyllopteryx taeniolatus and long-snouted pipefish Vanacampus poecilolaemus) consume far more relatively mobile prey than species with short snouts. Species with short snouts (e.g. the pug-nosed pipefish Pugnaso curtirostris and Macleay’s crested pipefish Histiogamphelus cristatus) mainly consume slow moving prey. Spotted pipefish, Stigmatopora argus, and wide-bodied pipefish, Stigmatopora nigra, restrict their diets to planktonic copepods, probably because their small gape size limits their ability to feed on alternative larger prey. Both the short-snouted seahorse, Hippocampus breviceps, and West Australian seahorse, Hippocampus subelongatus, ingest mainly slow-moving prey, even though the latter species possesses a moderately long snout. This may reflect the fact that seahorses are weak swimmers that anchor themselves to vegetation or the substrate with a strongly prehensile tail and rarely venture into open water to pursue mobile prey. In contrast, the relatively large P. taeniolatus, which resides above, rather than within, the macrophyte canopy, consumes mysids, which aggregate in open water above the seabed. Those pipefishes with characters that imply relatively enhanced mobility, such as well developed caudal fins and non-prehensile tails, are trophically diverse, suggesting that they are able to feed either on the sediment or phytal surfaces or in the water column.

The fish fauna of a seasonally closed Australian estuary. Is the prevalence of estuarine-spawning species high?

The fish at sites located throughout the large, seasonally closed Wilson Inlet, on the southern coast of Western Australia, were sampled bimonthly between September 1987 and April 1989. Seine nets were used to sample nearshore shallow waters, while gill nets were employed in slightly more offshore and deeper waters. Twenty species were recorded in the shallows, of which the three species of atherinid and the three species of goby comprised >97% of the total catch. In terms of number of individuals, the 27 species recorded in gill nets in the deeper waters were dominated by Cnidoglanis macrocephalus and Platycephalus speculator, and to a lesser extent Engraulis australis, Aldrichetta forsteri, Sillaginodes punctata and Arripis georgianus. Fifty-five percent of the species recorded in the nearshore shallow waters and 18% of those in offshore deeper waters spawn within Wilson Inlet; these species contributed 98.5 and 63.0%, respectively, to the total catches in those waters. Classification and ordination showed that the composition of the fauna in the shallows was similar at all sites throughout the large basin and did not change conspicuously with season. However, the composition of catches taken in offshore waters differed between the lower part of the basin and the middle and upper regions of the basin, which in turn differed from those in the saline reaches of a tributary river. The four diagnostic species of the lower estuary were all marine species, while the three diagnostic species in the river included a marine species (Mugil cephalus) that often penetrates far upstream in other systems, and a species which was confined to the rivers (Acanthopagrus butcheri). The composition of the fish fauna in the offshore waters of the lower estuary between the middle of spring and middle of autumn was different in 1987/1988 (when the estuary mouth was open for only the first two months of that period) from that in 1988/1989 (when the mouth was open for the whole of that period). This difference is related to the greater number of marine species that were retained in the first of these years, when the estuary was open to the ocean for only a short period. The greater retention of marine species in 1987/1988 than in 1988/1989 probably reflects a far lower level of freshwater flusing and/or a less marked decline in salinity.

Habitat partitioning by whiting species (Sillaginidae) in coastal waters

SynopsisThe ways in which the distributions of six species of whiting (Sillaginidae) in the coastal marine waters of south-western Australia are related to the type of substrate (bare sand vs. seagrass), degree of exposure of habitat, water depth and body size have been investigated. Whiting in near shore waters (< 1.5 m) were sampled using a fine-meshed seine net, while those in ‘shallow’ (5–15 m) and ‘deep’ (20–35 m) waters of the inner continental shelf were sampled with a trawl net. Shallow nearshore waters are shown to provide nursery habitats for five of the six whiting species. In these waters, Sillaginodes punctata, Sillago burrus, Sillago schomburgkii and Sillago vittata mainly occur in protected areas, while Sillago bassensis predominantly occupies areas that are more exposed to wave and swell activity. The first three of these species also use estuaries as nursery areas. In nearshore waters, whiting were captured almost exclusively over bare sand, rather than in interpersed beds of the seagrass Posidonia spp., presumably reflecting the fact that the dense canopies produced by the wide blades of Posidonia spp. must inhibit penetration by the benthic whiting species. As 0 + S. punctata increase in size, they tend to move offshore during the day and inshore at night. Many mature representatives of S. schomburgkii are present in nearshore areas, whereas the other four species move offshore into inner-shelf waters as they increase in length. Sillago burrus and S. vittata remain in shallow inner-shelf waters, whereas the larger S. bassensis subsequently migrate into deeper inner-shelf waters. Large Sillago bassensis thus co-occurs with Sillago robusta, which is mainly found in those deeper waters, but does not reach as large a size. The larger S. punctata occupy areas near reefs which could not be sampled by trawl netting. There are thus interspecific differences in (i) the times of recruitment of the 0 + age class into nearshore areas, (ii) the types of habitat occupied during juvenile and adult life, and (iii) the degree to which fish move into more offshore waters as they increase in length, and one species is restricted to deeper waters. The resultant partial segregation among habitats of the coastal waters of south-western Australia by different size groups of these relatively abundant whiting species presumably reduces the potential for intra- and interspecific competition amongst these species.

Spatial patterns in herbivory on a coral reef are influenced by structural complexity but not by algal traits.

Background Patterns of herbivory can alter the spatial structure of ecosystems, with important consequences for ecosystem functions and biodiversity. While the factors that drive spatial patterns in herbivory in terrestrial systems are well established, comparatively less is known about what influences the distribution of herbivory in coral reefs. Methodology and Principal Findings We quantified spatial patterns of macroalgal consumption in a cross-section of Ningaloo Reef (Western Australia). We used a combination of descriptive and experimental approaches to assess the influence of multiple macroalgal traits and structural complexity in establishing the observed spatial patterns in macroalgal herbivory, and to identify potential feedback mechanisms between herbivory and macroalgal nutritional quality. Spatial patterns in macroalgal consumption were best explained by differences in structural complexity among habitats. The biomass of herbivorous fish, and rates of herbivory were always greater in the structurally-complex coral-dominated outer reef and reef flat habitats, which were also characterised by high biomass of herbivorous fish, low cover and biomass of macroalgae and the presence of unpalatable algae species. Macroalgal consumption decreased to undetectable levels within 75 m of structurally-complex reef habitat, and algae were most abundant in the structurally-simple lagoon habitats, which were also characterised by the presence of the most palatable algae species. In contrast to terrestrial ecosystems, herbivory patterns were not influenced by the distribution, productivity or nutritional quality of resources (macroalgae), and we found no evidence of a positive feedback between macroalgal consumption and the nitrogen content of algae. Significance This study highlights the importance of seascape-scale patterns in structural complexity in determining spatial patterns of macroalgal consumption by fish. Given the importance of herbivory in maintaining the ability of coral reefs to reorganise and retain ecosystem functions following disturbance, structural complexity emerges as a critical feature that is essential for the healthy functioning of these ecosystems.