Temperate Reef Fish Assemblages Research Articles

A Comparison of Methods of Visual Census and Cryptobenthic Fish Collecting, an Integrative Approach to the Qualitative and Quantitative Composition of the Mediterranean Temperate Reef Fish Assemblages

The present research quantitatively compared the fish composition among two methods for non-cryptic benthic fish species and one method for cryptobenthic fish species for the first time for the Mediterranean temperate reef fish assemblage. A visual census of fishes was performed within a cylinder of 4 m radius and within a cylinder of 2 m radius, while the cryptobenthic fishes were collected using a square of 1 m2 with anesthetic. The data and material were collected at fifty sampling points. The visual census methods together recorded 31 species, and the square with anesthetic method recorded 18 species. The quantitative comparison of methods of visual census and cryptobenthic fish collecting showed significantly different species richness, total fish abundance, and fish assemblage structure among methods. The applied methods were highly complementary. The cylinder of 2 m radius is well suited for epibenthic fishes and the cylinder of 4 m radius is reliable for hyperbenthic and benthopelagic fishes. Therefore, each of the methods well covered one of three components of ichthyobenthos (hyperbenthic, epibenthic, and cryptobenthic fishes), and all three methods together provided a far more complete assessment of fish species composition than any individual census method for the Mediterranean littoral benthic fishes.

Temperate zone coastal seascapes: seascape patterning and adjacent seagrass habitat shape the distribution of rocky reef fish assemblages

Whilst the composition and arrangement of habitats within landscape mosaics are known to be important determinants of biodiversity patterns, the influence of seascape patterning and connectivity on temperate reef fish assemblages remains largely unknown. We examined how habitat patterns at multiple spatial scales (100–1000 m) explained the abundance and diversity of temperate reef fish in a reef-seagrass dominated seascape. Fish assemblages were surveyed using remote underwater videos deployed on 22 reefs in Jervis Bay, NSW, Australia. Using full-subset GAMMs, we investigated if habitat area, edge, structural connectivity and a metric for habitat diversity (Shannon’s diversity index) of reef and seagrass can predict variations in a temperate reef fish assemblage. A key finding of the study was that temperate reefs close ( 6.25 ha) seagrass meadows contained greater abundance and diversity of fish. A consistent negative correlation was also found between reef area (> 0.01 ha) and the fish assemblage. The influence of seascape metrics on the abundance of fishes varied with functional traits (trophic groups, mobility and habitat associations). Fish-seascape relationships occurred at a range of spatial scales with no single scale being solely important for structuring the fish assemblage. We demonstrate that it is important not to view reef habitats in isolation, rather consider a reefs context to adjacent seagrass when predicting the distribution of temperate reef fish. This finding improves current understanding of the multi-scale factors structuring temperate reef fish assemblages and highlights the importance of reef-seagrass connectivty for the management of temperate marine ecosystems.

Remote drifted and diver operated stereo–video systems: A comparison from tropical and temperate reef fish assemblages

Underwater visual census methods for sampling reef fish that use scientific divers are common and can be effective in shallow water habitats. There is an ongoing need to develop methods that can sample reef fish assemblages in a similar manner, but at depths that are unsafe or inefficient for scientific divers using conventional SCUBA equipment. This study aimed to assess the limitations and biases associated with a drifted stereo–video system (Drifter) by comparing data collected with a diver operated stereo–video system (stereo–DOVs) at the same locations. The composition, number of species, total abundance and the abundances of dominant reef fishes were compared across the two sampling techniques at three temperate and three tropical reefs. There were no significant differences between the compositions of the assemblage sampled by each technique at either the temperate or tropical reefs. There was significantly higher dispersion in the data collected by the Drifter. This higher dispersion was most likely caused by the combined effects of low vehicle stability, the positioning of the drifter higher in the water column in comparison to the stereo DOVs and the challenges associated with navigating the drifter along narrow and fragmented reefs. The stereo–DOVs sampled more species of fish and more individuals than the Drifter. No significant differences were detected in the abundance of any of the dominant species. The Drifter provides a comparable technique to stereo–DOVs, without the depth and time limitations inherent to that system. The high dispersion of the data, low number of species and lower number of individuals sampled by the Drifter result in a slightly lower statistical power from an equivalent sampling effort when compared to stereo–DOVs. Future developments which will help overcome these differences are discussed.

Fine‐scale patterns in the day, night and crepuscular composition of a temperate reef fish assemblage

AbstractThe distribution, abundance and composition of marine fish assemblages are influenced by changes in behaviour and movement associated with the diel cycle. The majority of studies exploring day–night differences have demonstrated that there is a greater abundance and diversity of fishes during diurnal compared with nocturnal hours, and that fish assemblage composition varies with time of day or night. We investigated fine‐scale (hourly) diel cycles in the composition and relative abundance of temperate reef fishes using unbaited remote underwater video systems. We observed short crepuscular changeover periods with the hours around dawn and dusk sharing many species, some of which are nocturnal and others diurnal. Diurnal surveys recorded a greater number of individuals (16,990) and species (70) than nocturnal surveys (1053 individuals and 19 species). There was a clear difference between the diurnal assemblage, which was characterized by benthic invertivores, and the nocturnal assemblage composition, which contained zooplanktivores and generalist feeders. Within the diurnal period the hourly temporal variation was relatively homogenous, indicating that standardization of diurnal sampling to a particular time of day may not be necessary.

Appropriate set times to represent patterns of rocky reef fishes using baited video

Baited Remote Underwater Video (BRUV) has become a popular technique to survey fish assemblages for a wide range of purposes. BRUV methodology has, however, also varied greatly for a range of reasons. A major dichotomy occurs, in particular, in the time used to sample the fish assemblages i.e. the BRUV set time. The aim of this study was to determine whether differences in set time were likely to affect the conclusions reached by studies using different set times, and what might be the most appropriate and cost-effective set time to use to sample temperate reef fish assemblages. In this study, we test whether there were significant differences between the two main set times used (i.e. 30 and 60min) in BRUV sampling for assemblage patterns, species diversity, and relative abundance of rocky reef fishes. In particular, we sampled fished and unfished rocky reefs to assess whether the different set times would lead to differences in the patterns or the interpretation of the subsequent data. We sampled fish assemblages on six rocky reefs (20–35m) across two marine parks on the east coast of Australia. At each location replicate BRUVs were deployed for 30 and 60min in a ‘no take’ area (marine sanctuary) and a fished area. The interpretations of the data across the fished and unfished zones were consistent with both set times indicating that the conclusions from both set time were comparable. Furthermore, there were no differences in fish assemblages or species richness between the set times. The relative abundances of the recreationally and commercially important snapper (Chrysophrys auratus) were greater in the longer set times, but the actual spatial patterns between zones and amongst locations were consistent. Piecewise regression analysis of the breakpoint times for species accumulation found that there were no significant differences between locations or between fished and unfished areas. Mean breakpoint, the time when species accumulation changes, occurred at 12min±1.04S.E. for all sites combined whilst the shorter set time was found to be less costly and require less field and laboratory times. This study quantifies that either 30 or 60min will provide a reasonable estimate of rocky reef fish diversity and relative abundance for comparative purposes, on these shallow rocky reefs.

Topographic complexity and the power to detect structural and functional changes in temperate reef fish assemblages: The need for habitat-independent sample sizes

Functional approaches have shown promising results to detect degradation in marine fish assemblages. However, background variability significantly affects the amplitude of change that is detectable by a monitoring plan, and failing to detect such changes can have devastating consequences and carry aggravated recovery costs due to unnoticed degradation. The present study aimed to understand the relationship between topographic complexity in temperate reefs and the power to detect variations in fish-based metrics. Underwater visual census of fish assemblages was performed using strip transects and a Monte Carlo simulation approach was used to generate a large number of replicates and simulate three alternative hypotheses representing different magnitudes of change. Statistical power to detect differences between null and alternative hypotheses was estimated through 10,000 Mann–Whitney tests for numbers of replicates ranging from 2 to 15. Power tended to vary with topographic complexity particularly with small and medium changes in metric values and when using small sample sizes. While power increased with complexity for most metrics, some showed decreasing trends. With a large effect, 5–15 transects were needed, depending on the metric, to stabilise power above 0.80 independently of habitat features. A power of 0.95, however, could not be achieved for most metrics in all sites, even when using 15 transects. The observation that the power to detect degradation and recovery in temperate reef fish seems to vary with habitat features means that a monitoring programme that is correctly planned for a particular area may not be directly applicable in a nearby reef. Adding to the need to maximise power in monitoring, this study highlights the need to take into account habitat variability in these calculations and estimate habitat-independent sample sizes that are appropriate for the scale and location of interest.

A little bait goes a long way: The influence of bait quantity on a temperate fish assemblage sampled using stereo-BRUVs

Baited remote underwater video systems are becoming a widely adopted tool for sampling fish assemblages. One of the outstanding knowledge gaps associated with this technique is the effect of different quantities of bait on the fish assemblages sampled. We investigated how different quantities of bait (0g, 200g, 1000g or 2000g of crushed pilchards, Sardinops sagax) influenced the relative abundance and species richness of a temperate, Western Australian reef fish assemblage sampled with baited remote underwater stereo-video systems (stereo-BRUVs). The presence of bait significantly increased the relative abundance and numbers of fish species sampled, with few differences between the three quantities of bait. Trends in fork length were identified between bait quantities for some species. For example, juvenile stage Coris auricularis (a protogynous labrid) were significantly larger in the unbaited treatment, whereas males of the same species were significantly smaller at unbaited treatments. This pattern was interpreted as being the result of intraspecific competition and the dominance of larger males in the presence of bait. When bait was present, fish were significantly closer to the stereo-BRUVs. However, there was again no difference between the three baited treatments.At this location in temperate Western Australia, stereo-BRUVs with 200g of bait are as effective at sampling the temperate reef fish assemblage as stereo-BRUVs set with greater quantities of bait. In our study, the numbers of high trophic level species recorded were low. In areas with abundant high trophic level fishes, such as tropical reef systems, greater quantities of bait may be required to prevent it being quickly depleted by intense feeding.

‘Reserve effect’ within a temperate marine protected area in the north-eastern Atlantic (Arrábida Marine Park, Portugal)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 481:11-24 (2013) - DOI: https://doi.org/10.3354/meps10204 ‘Reserve effect’ within a temperate marine protected area in the north-eastern Atlantic (Arrábida Marine Park, Portugal) Bárbara Horta e Costa1,2, Karim Erzini2, Jennifer E. Caselle3, Henrique Folhas1, Emanuel J. Gonçalves1,* 1Eco-Ethology Research Unit, ISPA - Instituto Universitário, R. Jardim do Tabaco 34, 1149-041 Lisboa, Portugal 2Centre of Marine Sciences, CCMAR, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal 3Marine Science Institute, University of California, Santa Barbara, Santa Barbara, California 93106, USA *Corresponding author. Email: emanuel@ispa.pt ABSTRACT: Benefits of marine protected areas depend on local ecological and socio-cultural aspects which are critical to the success of the protection measures. In particular, before-after comparisons are indispensable to disentangle the effects of protection from those of different physical and ecological characteristics among areas. Using underwater visual surveys, we assessed whether biomass and abundance of temperate reef fish assemblages and target invertebrates increased inside a no-take area in the Arrábida Marine Park (Portugal) 3 to 4 yr after its establishment. Data were compared to a previous study, conducted 10 yr before protection was effective. Control-effect comparisons after reserve establishment showed a positive response of legal-size demersal fish and below legal-size target invertebrates. The first evidence of protection was found in biomass but not in numbers. Non-target groups and below legal-size demersal fish had a significant interaction among reserve and habitat complexity indices for either density or biomass, suggesting a lack of a reserve effect. Before-after comparisons revealed non-significant patterns of increase in numbers of target species compared to non-target ones. The most important commercial species showed the largest increase in density after protection was established. Significantly higher abundances and proportionally heavier individuals of these species were also found inside the reserve in the control-effect comparisons. These findings are reinforced by an increasing trend in landings which are consistent with the early detection of a reserve effect. KEY WORDS: Marine protected area · Before-after data · Temperate reef fishes · Target species · Habitat · Artisanal fisheries Full text in pdf format PreviousNextCite this article as: Horta e Costa B, Erzini K, Caselle JE, Folhas H, Gonçalves EJ (2013) ‘Reserve effect’ within a temperate marine protected area in the north-eastern Atlantic (Arrábida Marine Park, Portugal). Mar Ecol Prog Ser 481:11-24. https://doi.org/10.3354/meps10204 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 481. Online publication date: May 07, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Bait type affects fish assemblages and feeding guilds observed at baited remote underwater video stations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 477:189-199 (2013) - DOI: https://doi.org/10.3354/meps10137 Bait type affects fish assemblages and feeding guilds observed at baited remote underwater video stations James Wraith1,3, Tim Lynch2, Todd E. Minchinton1, Allison Broad1, Andrew R. Davis1,* 1Institue for Conservation Biology and Environmental Management, School of Biological Sciences, University of Wollongong, New South Wales 2522, Australia 2CSIRO Marine and Atmospheric Research Hobart, Castray Esplanade, Hobart, Tasmania 7000, Australia 3NOAA Fisheries, Southwest Fisheries Science Center, 8604 La Jolla Shores Dr., La Jolla, California 92037-1508, USA *Corresponding author. Email: adavis@uow.edu.au ABSTRACT: Baited remote underwater video stations (BRUVS) are increasingly being used to examine assemblages of fishes, yet critical methodological questions related to sampling limitations and bias, such as the influence of bait type, remain poorly understood. At multiple locations, we examined the hypothesis that diversity and abundance in temperate reef fish assemblages were independent of bait type. We used 3 bait types (abalone viscera, pilchards and crushed urchin) and quantified commonly used metrics for the fish assemblage, including species richness, time of first arrival and relative abundance on 3 shallow rocky reefs in southeastern Australia over 2 yr. We distinguished the following 6 feeding guilds: herbivore, zooplanktivore, alga/invertebrate consumers, invertebrate carnivore, macroinvertebrate carnivore and generalist carnivore. The response of fishes was dependent on bait type, with urchin bait performing particularly poorly. Although we did not detect statistical differences between the performance of pilchards and abalone viscera as bait, pilchards produced more consistent outcomes. Importantly, we also observed strong spatial effects. In general, bait type had a marked effect on species richness, but little influence on relative abundance. Overall we conclude that oily bait such as pilchards, which have been widely used in most studies, yield the most consistent outcomes. Consequently, bait type and spatial variation in fish assemblages needs to be considered in sampling designs to assess the limitations of BRUVS. KEY WORDS: Subtidal fish assemblages · BRUVS · Temperate rocky reefs · Feeding guilds · Jervis Bay Marine Park Full text in pdf format PreviousNextCite this article as: Wraith J, Lynch T, Minchinton TE, Broad A, Davis AR (2013) Bait type affects fish assemblages and feeding guilds observed at baited remote underwater video stations. Mar Ecol Prog Ser 477:189-199. https://doi.org/10.3354/meps10137 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 477. Online publication date: March 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Response of fish-based metrics to anthropogenic pressures in temperate rocky reefs

The increasing degradation of marine ecosystems as a result of increasing impact caused by anthropogenic pressures, urges for well-founded knowledge to develop efficient tools to appraise the quality status of fish assemblages, as required by the “Marine Strategy Framework Directive”. This study analyzed the structural and functional response of rocky fish assemblages to several pressures on the Portuguese coast, i.e. fishing, sewage discharges, port activities and thermal effluent, by selecting fish-based metrics that best distinguished disturbed from control areas. One of the novel aspects of this research is the integrated assessment made through the analysis of several metrics representing numerous attributes of fish assemblages (namely diversity, abundance, trophic structure, mobility, resilience, habitat association, nursery function), which contrasts with the most commonly used approaches that in general focus on fish species/families. PERMANOVA results showed significant differences on metrics composition for all pressures with the exception of the thermal effluent. Moreover, two major patterns of stress were identified: (1) selective pressure, which affects differentially the fish assemblages (fishing); (2) broad-range pressure, which affects the entire fish assemblage with metrics of several attributes (e.g. structure, resilience, trophic guilds, nursery function) responding to its presence (sewage discharges, port activities). Taking into account the sensitivity results (discriminant analysis and Mann–Whitney test), biological meaning and redundancy with other metrics (Spearman correlations), the following metrics were selected as the most suitable to detect changes on temperate reef fish assemblages: “density of generalist individuals”, “density of territorial individuals”, “density of large individuals with medium to high commercial value (>20cm)”, “density of juveniles” and metrics relative to trophic guild (except zooplanktivores). Since metrics grouped species that have some degree of functional overlap, the present approach was useful to understand human-induced changes at the assemblage level, contributing for the future use of marine fishes as biological indicators.

Within and between day variability in temperate reef fish assemblages: Learned response to baited video

Many studies that test for spatial patterns in fish assemblages do not have temporal replication, and where they do, the scale of this replication is in the order of seasons or years. Rarely are patterns tested at the scale of days or time of day. As a result, any descriptions of spatial patterns are potentially confounded by within or between day variations, with differences between locations possibly due to the differences between times sampled. This study aimed to determine whether significant short-term temporal variability existed within and between days in a temperate, shallow-water reef fish assemblage in south-western Australia. Three sites were sampled at morning, midday and afternoon for five consecutive days using baited remote underwater stereo–video systems. Significant differences were detected in the fish assemblage at different times of the day with morning and midday assemblages different from afternoon assemblages. Differences were detected between days with a significant shift in the assemblage after day two. The use of bait in this study was thought to influence the behaviour of Pseudocaranx spp. which furthermore influenced sampling of the entire fish assemblage between days. This study shows that large scale monitoring and sampling programmes using baited cameras need to consider the possible influence of within and between day variability in their experimental designs and must carefully design sampling to test for spatial and temporal structures in fish assemblages.

The Fish Assemblages Inside and Outside of a Temperate Marine Reserve in Southern California

Abstract The purpose of this investigation was to evaluate the effect of a small marine reserve (established 1988) on a temperate rocky reef fish assemblage at Santa Catalina Island, California. Fish surveys on SCUBA were conducted at two reserve and two non-reserve sites from October 2002 to January 2004. Sites were similar in fish density, species richness and biomass of the entire fish assemblage. However, the adult densities of two important fishery species, California sheep-head (Semicossyphus pulcher; 7.6 ±0.5 and 5.5 ±0.4/100 m2 inside versus outside) and kelp bass (Paralabrax clathratus; 3.6 ±0.4 and 2.9 ±0.4 inside versus outside), were significantly higher within the reserve. The reserve appears to be effective in increasing density and biomass of two impacted species that were readily observed and surveyed on SCUBA.

Erratum to: A comparison of temperate reef fish assemblages recorded by three underwater stereo-video techniques

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A comparison of temperate reef fish assemblages recorded by three underwater stereo-video techniques

Three underwater stereo-video techniques were used to sample the relative densities and species richness of temperate reef fish assemblages at three reef locations and two habitats (high- and low-relief reef) within Hamelin Bay, south-western Australia. The three techniques compared were diver-operated stereo-video strip transects, baited remote stereo-video and unbaited remote stereo-video. While unbaited remote stereo-video and diver-operated stereo-video transects recorded greater species richness at high compared to low-relief reefs, baited remote stereo-video recorded similar species richness at the two habitat types. The diver-operated stereo-video system was manoeuvred through caves and under overhangs recording small, cryptic, cave-dwelling species that were not recorded by either remote video techniques (Trachinops noarlungae, Trachinops brauni, Chromis klunzingeri, Trachichthys australis). Both remote video techniques recorded greater species richness and relative density of the most common species of Labridae, Ophthalmolepsis lineolatus. Baited remote video recorded the rarer, large predatory fish species (e.g. Seriola hippos, Glaucosoma hebraicum, Heterodontus portusjacksoni). None of the techniques sampled small cryptic fish families such as Gobiidae or Blenniidae. A combination of survey techniques is recommended for comprehensive fishery-independent studies that aim to sample broad components of fish assemblages.

Spatial variation and effects of habitat on temperate reef fish assemblages in northeastern New Zealand

Reef-associated fishes can respond to changes in habitat structure and the nature of their response can change with different spatial scales of observation. A structured hierarchical mensurative sampling design was used to sample temperate reef fish assemblages in northeastern New Zealand at several spatial scales over 2 years. The three spatial scales examined were tens of meters (transects), hundreds to thousands of meters (sites) and hundreds of kilometers (locations). We tested the hypothesis that fish assemblages differed between kelp forest habitat (relatively dense stands of the kelp, Ecklonia radiata (C. Agardh) J. Agardh, median depth=13.5 m) and barrens habitat (rocky reef dominated by turfing and encrusting red algae and the grazing urchin, Evechinus chloroticus (Valenciennes), median depth=6.7 m). Recently developed multivariate techniques were used to test for and quantify multivariate variation at different spatial scales. There were significant effects of habitat on the spatial distribution of fish assemblages, characterised by greater abundances or frequencies of Parika scaber, Chromis dispilus, Trachurus novaezelandiae, Nemadactylus douglasii, Bodianus unimaculatus, Odax pullus and Pseudolabrus miles in kelp forest habitat, and greater abundances or frequencies of Notolabrus celidotus, Notolabrus fucicola, Girella tricuspidata, Coris sandageri, Chironemus marmoratus, Parma alboscapularis, Scorpis violaceus and Kyphosus sydneyanus in barrens habitat. Some of the more common species, including Upeneichthys lineatus, Scorpis lineolatus and Cheilodactylus spectabilis showed no strong consistent effects of these two differing habitats on their distributions. There was, however, a significant Habitat×Locations interaction: effects of habitat did not occur at all locations. Variability was highest at the scale of individual transects and variability from site to site and from location to location was comparable. Spatial variation was large compared to inter-annual variation, which was minimal, and spatial patterns were consistent in the 2 years examined. Further experiments, including manipulations, are required to understand what mechanisms and processes might be driving these patterns. This study, coupled with results from previous studies, suggests that there may be a dynamic inter-play between effects of habitat on fish and effects of fish on biogenic habitat, such as kelp forests.

Wave exposure, swimming performance, and the structure of tropical and temperate reef fish assemblages

We examined the relationship between swimming performance, wave exposure, and the distribution patterns of labrids on temperate rocky reefs, in comparison with previous functional analyses of a tropical assemblage. Visual censuses of the distribution and abundance of labrids across two major gradients of wave exposure (depth and aspect to prevailing winds) were made at two offshore islands near Port Stephens, New South Wales, Australia. Distinct shifts in species composition and abundance were evident between high and low wave exposure habitats on temperate rocky reefs, particularly between deep and shallow habitats on exposed reef fronts. The swimming performances of temperate labrids were assessed through examination of pectoral fin shape (aspect ratio) and in situ swimming speeds. A diversity of pectoral fin morphologies was exhibited within this temperate assemblage, ranging from rounded to tapered fins (aspect ratios of 0.52 and 1.43, respectively). Fin shape was strongly correlated (Pearson’s correlation 0.884, P<0.001) with swimming speed (ranging from 1.05 and 3.06 body lengths s−1), in a relationship comparable to that observed in tropical labrids. Inter-specific differences in swimming ability provided some explanation for differences in the distribution and abundance of temperate labrids in relation to wave exposure. However, our findings suggest that although coral reef labrids appear to predominantly use high aspect-ratio fins to successfully occupy wave-exposed habitats, temperate labrids appear to be using an enhanced swimming ability through increased body size.

Spatial and habitat-related patterns of temperate reef fish assemblages: implications for the design of Marine Protected Areas

Patterns of rocky reef fish assemblages (composition and relative abundance of species) were examined to provide data on the design of Marine Protected Areas (MPAs), which aim to protect these organisms. A hierarchical design was used to investigate changes in fish assemblages at scales of metres to kilometres along-shore, and among reef habitat types within two 10-km areas on the central coast of New South Wales, Australia. Influences of physical and biological attributes of a reef on assemblages of fish were also examined. The greatest variation in fish assemblages occurred at scales of 2–6 km along-shore. Eighty percent of species recorded were found within a 6-km section of coastline. The most predictable differences in assemblages were found between reef habitats (urchin-grazed barrens, Ecklonia forest and sponge habitat), and between depths. Marine Protected Areas should ideally incorporate all available habitats over the entire depth range at which they occur. This may require MPAs larger than 2–6 km, or multiple MPAs that have been specifically located to include these features, as representation of habitats was found to vary at scales of kilometres to tens of kilometres along shore.

Structure and trophic organization of subtidal fish assemblages on the northern Chilean coast: the effect of habitat complexity

A series of local factors such as substrate structure, presence or absence of kelp forests and environmental variables play an important role in determining both the diversity and abundance of temperate reef fish assemblages. The presence of kelp forests has been shown to increase struc- tural complexity, available shelter, and prey availability in the reef environment. This, in turn, may affect the structural organization of the fish assemblage. In this study, the diversity, abundance and trophic patterns of subtidal fish assemblages at 2 localities off the northern Chilean coast were ana- lyzed. These localities differ markedly in their spatial structure: the subtidal substratum at Caleta Errazuriz is characterized by a sloping bedrock with large rocks and boulders and a kelp forest, while at Carrizal Bajo it consists of a sharply declining bedrock with few boulders and isolated kelp stands. We hypothesized that structurally highly complex habitats would exhibit higher diversity, abundance and a more complex trophic organization in terms of more functional groups and guilds of reef fish assemblages than less structured environments. Contrary to our hypothesis, we found similar species diversity and fish abundance at both localities. However, there were clear differences in species dom- inance, number of functional groups and trophic guilds. There were also marked differences in the trophic webs between localities. In the presence of kelp forest, both carnivores and omnivores con- sumed mainly benthic prey inhabiting the understory canopy, while in its absence carnivores fed on pelagic prey in the water column. Therefore, a more complex spatial structure would seem to support a more complex trophic organization with a greater degree of connectivity, as well as interaction between the species in a reef fish assemblage.

Biogenic habitat structure and characteristics of temperate reef fish assemblages

AbstractAssemblages of non‐cryptic, substrate‐oriented species of fish were compared on a series of reefs in Southern California, USA. Reefs were grouped according to algal cover: dense beds of giant kelp (Macrocystis pyrifera) with turf understorey; sparse beds of giant kelp with foliose algae understorey: foliose algae &lt; 1 m in height; and open barrens. Despite affinities to particular algal substrates by many individual species, we detected no differences in fish species richness and only weak differences in species composition among reefs of different habitat types. Planktivores and species that consume macro‐invertebrates were less likely to occur on reefs that supported giant kelp; the frequencies of occurrence of three other trophic groups (piscivores, herbivores and micro‐carnivores) were unaffected by giant kelp.Algal composition on reefs in Southern California is temporally highly dynamic. Changes in macro‐algal composition of reefs influenced population dynamics of two fish species (black surfperch and striped surfperch) examined. Overall, the weak spatial variation in fish assemblages on reefs in Southern California appears to result from relatively unspecialized ecological requirements of many species combined with temporal changes in algal structure on reefs that are rapid relative to generation times of the fish. We hypothesize that the degree of spatial differentiation in assemblages of substrate‐associated species of fish may be inversely related to the temporal constancy of biogenic reef structure.

Improving multispecies rocky reef fish censuses by counting different groups of species using different procedures

A number of factors can influence the accuracy and precision of underwater visual transect techniques. Among these are observer swimming speed and, during multispecies surveys, the effect of counting all fishes on estimates of particular species. This paper examines the effect of these factors on population estimates of inconspicuous fishes (defined as Type 1) in a temperate reef fish assemblage near Sydney, Australia. Counting Type 1 fishes with all others yielded significantly lower estimates of species richness and abundance than when counted alone. This suggests that multispecies surveys should be split into 2 or more counts, using a census procedure that is appropriate to the group of species cencused. Further, the effect of counting all other fishes on estimates of Type 1 fishes varied according to the relative abundance of the former: their effect was lowest when abundance of other fishes was lowest. There was a negative relationship between observer speed and estimated abundance for Type 1 fishes. Survey precision of Type 1 fishes was generally improved by surveying at slower observer speeds.