Temperate Fish Assemblages Research Articles

Fine-scale variation in the proximity of baited remote underwater video stations (BRUVS) to rocky reefs reveals changes in the structure of temperate fish assemblages

We investigated changes in the structure of coastal fish assemblages in Northern Patagonia, Southwestern Atlantic, by using baited remote underwater video stations (BRUVS) deployed at increasing distances from rocky reefs: 0–5 m, 15–20 m and 50–60 m. We estimated species richness and abundance (total and by preferred habitat type) and searched for diagnostic species in each distance range. We recorded 14 taxa across 11 families in 19 areas surveyed. Species richness and abundance were higher on reef ledges and decreased with distance from them, at a finer spatial scale than previously reported. Acanthistius patachonicus and Sebastes oculatus were indicative of reef ledges; they were less abundant at 15–20 m and disappeared at 50–60 m. Callorinchus callorynchus and Odontesthes spp. occurred only at distances >15–20 m from the reefs, while Galeorhinus galeus was distributed homogeneously throughout the surveyed area. Our findings have practical implications for monitoring ecotone demersal habitats with BRUVS.

Macroalgal physical structure predicts variation in some attributes of temperate fish assemblages better than macroalgal species composition

The importance of vegetative habitat in influencing distribution patterns, species interactions, and biodiversity is well documented in marine ecosystems, yet most previous studies on macroalgal–fish relationships have focused on influences of density and identity of macroalgae, often ignoring how the unique physical structure provided by each alga contributes to patterns. We tested whether the distribution, abundance, and biomass of rocky reef fishes could be predicted as well or better by measures of physical structure of macroalgae than by species identity and abundance. Divers visually sampled fishes and macroalgae at seven sites spread over several km at Santa Catalina Island, California, over a 1-year period, to examine how the distribution patterns of fishes related to spatiotemporal differences in the macroalgal assemblage. We found that variation in the composition, density, and diversity of the fish assemblage was equally or better explained by macroalgal structure (total surface area and height) than by macroalgal species density. In contrast, biomass and vertical distribution of fishes were better predicted by macroalgal species identity and density than by macroalgal physical structure. Of the macroalgal attributes, surface area was the best predictor of fish abundance and multivariate assemblage structure (species and their densities). However, much of the spatiotemporal variation in the fish assemblage was not explained by macroalgae, indicating that even in habitats visually dominated by macroalgae, macrophytes are only one of many factors that drive spatiotemporal variation in community structure. Our results suggest that quantifying the physical structure provided by marine macroalgae can be more useful than macroalgal species identity in predicting some aspects of fish assemblage structure.

Macroalgal physical structure predicts variation in some attributes of temperate fish assemblages better than macroalgal species composition

Macroalgal physical structure predicts variation in some attributes of temperate fish assemblages better than macroalgal species composition

No detrimental effects of desalination waste on temperate fish assemblages

Abstract Water resources are becoming increasingly scarce due to population growth and global changes in weather patterns. Desalination plants that extract freshwater from brackish or seawater are already being used worldwide, with many new plants being developed and built. The waste product from the extraction processes has an elevated salt concentration and can potentially cause substantial impacts to local marine flora and fauna. The present study assesses the impact of saline waste from a 100 GL/year desalination plant on southern Australian temperate fish assemblages, using baited remote underwater video. The study compared four reference sites to the impact site (desalination outfall) and found no evidence that the saline waste was having a detrimental effect on fish assemblages in proximity to the outfall, with species diversity and abundance comparable to those observed at reference sites. However, species diversity and abundance varied across geographical location, protection from fishing pressure, and reef type. Our study is one of the few assessing the ecological impacts of saline waste discharged from a large desalination plant and shows no decrease in fish diversity or abundance, which is the response typically associated with the negative impacts of anthropogenic activities on fish assemblages.

Underwater Visual Census of Deeper Vertical Rocky Reefs

Diver-based underwater visual census (UVC), particularly transect-based survey, is a widely used method for the study of tropical and temperate fish assemblages. However, due to logistical constraints associated with conventional SCUBA diving, deeper habitats, such as vertical rocky reefs, are rarely studied and poorly known. This paper describes the Deep Vertical Transect (DVT) method as a safe and effective method for assessing fish in waters up to 50 m of depth. It is based on sampling of vertical transects browsing within it (S-type transect) by divers using Full HD video cameras. The diving profile includes the use of deep decompression stops and Nitrox 50 as a decompression gas. Hence, the study yields information on fish assemblages associated with deeper vertical coralligenous reefs. The results of 51 recorded species, yielded 41 considered as reef-associated and 10 as occasional. This suggests that underwater steep coralligenous reefs are marine biodiversity hotspots. They may be considered to represent a distinctive marine subecosystem, possessing its own food chain, with the depth, in relation to temperature, as the most important factor responsible for the diversity of fish assemblages within this habitat.

Habitat and seascape patterns drive spatial variability in temperate fish assemblages: implications for marine protected areas

We thank Marie-Claire Demers, Rhiannon Kiggins, Mark Fackerell and Simon Rees for assistance with fieldwork. We acknowledge support from JBMP and Booderee National Park staff. We thank Geoff Hurt for assistance and construction of the BRUV units. We thank the 3 anonymous reviewers for their constructive comments. We also thank the Ecological Society of Australia and The Nature Conservancy, Australia, for project support.

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.

Temporal variability of a temperate fish assemblage in Africa's oldest marine protected area

A standardised research-based, shore-angling survey was conducted in the 47-year-old Tsitsikamma National Park Marine Protected Area (MPA) between 1998 and 2005. The aim of this study was to examine variability in community structure, relative abundance (catch per unit effort, CPUE) and size frequency of the shore-angling fish assemblage in this no-take MPA. A total effort of 8 141 angler hours yielded 8 236 fish of at least 54 species from 19 families. The overall CPUE showed no significant trend over time (r 2 = 0.015, p = 0.1). The interannual variation in CPUE indicated relatively stable populations for some species (e.g. blacktail Diplodus capensis) and patterns of recruitment failure for others (e.g. galjoen Dichistius capensis). However, the lack of a significant trend in taxonomic distinctness (r 2 =0.008, p = 0.8), the stable rank order of species abundance (χ2, r = 361, p < 0.05) and the high coefficient of concordance (W = 0.84) indicated a relatively stable fish assemblage. This was attributed to the extended length of protection afforded by this MPA. One noticeable trend was an increase in the abundance of species with an affinity for warm water and whereas this correlated to an annual increase in water temperature of 0.024 °C between 1998 and 2005, a longer time-series is necessary to identify rise in sea temperature (climate change) as a driver of change in this warm-temperate fish assemblage.

Assessing the impact of spear fishing by using competitions records and underwater visual censuses

Recreational fishers are increasingly competing for space and resources with commercial fishers worldwide, but have been poorly studied. In particular, the impacts of spearfishing competitions on the temperate fish assemblages have seldom been analysed. In Galicia (NW Spain), there are currently 5000 spear fishers, and 500 of them participate in spearfishing competitions. An historic archive of spearfishing competitions was used to assess their influence on the subsequent competitions in the area and to analyse their effect on the fish abundances estimated by underwater visual censuses. The annual recreational catch of the spear fishers was also estimated and comparisons with the commercial landings were performed. The spear fishers targeted 29 species, although six accounted for 95% of the catch. Most of the species show low vulnerabilities to fishing pressure and only Dicentrarchus labrax, among frequently caught species, can be considered as moderately vulnerable. The overall impact of spearfishing competitions on fish populations was limited, although some competitions temporarily reduced the abundances of Labrus bergylta, the main target species, by up to 83%. Spear fishers caught a large proportion of the total catch of common species, with recreational catches of some species (e.g. L. bergylta) matching or exceeding the commercial catch. The inclusion of this fishery in the management models of the coastal ecosystems is strongly recommended

Spatial pattern of coastal fish assemblages in different habitats in North‐western Mediterranean

AbstractVariability of fish assemblages across habitat structures can depend on spatial scales. A hierarchical sampling design was used to assess the spatial variability of temperate fish assemblages in different habitats and at multiple scales. Underwater visual censuses were carried out along the coasts of Elba Island (NW Mediterranean) on Posidonia oceanica beds, rocky algal reefs and sandy habitat at three spatial scales, namely tens of metres (individual replicates), hundreds of metres (sites) and tens of kilometres (locations). At the assemblage level, there was a clear relationship between fish and habitat type and the observed habitat‐related differences were largely dependent on species identity. Fish assemblages on P. oceanica beds and rocky reefs shared a high number of species, whereas overlap with sandy assemblages was negligible. Multivariate analyses revealed significant differences in fish assemblages among habitats, although there was also a significant habitat × site interaction. These differences relied mainly upon assemblage composition and species richness. Assemblages on rocky reefs and P. oceanica meadows usually harboured a higher number of species and individuals compared with sandy assemblages. Nevertheless, the patterns of habitat‐related differences in species richness and, especially, in the total number of fish, changed significantly from site to site. Eight species showed significant differences over habitats, but they were not consistent due to the interaction of habitat with site. Predictability of fish at both assemblage and population levels decreased with the scale of observation, and the spatial pattern of fish observed at the smallest scale was likely dependent on factors other than habitat type.

Cost-efficient sampling of fish assemblages: comparison of baited video stations and diver video transects

Baited remote underwater stereo-video (stereo-BRUV) stations and diver operated stereo-video (stereo-DOV) transects are increasingly used to sample both tropical and temperate fish assemblages. Compared to in situ visual census methods, the use of stereo-video reduces inter- observer variability, improves definition of the sample unit area, increases accuracy of fish length estimates and provides a permanent record of the assemblage that can be validated where required or independently reanalysed. Previous studies have suggested that stereo-BRUV collects representa- tive data on both carnivorous and herbivorous species and can be more cost-efficient than diver- based survey methods. This study compares estimates of common fish assemblage metrics obtained with stereo-BRUV stations and stereo-DOV transects across 3 biogeographic regions, and uses a cost- optimization procedure to compare the efficiency of these 2 methods. Stereo-BRUV stations were found to sample greater species richness and obtain greater estimates of relative biomass of general- ist carnivores, but no differences occurred in the biomass of herbivores sampled by the 2 techniques. Stereo-BRUV stations generally obtained estimates of assemblage metrics with less variance, result- ing in greater power to detect spatial and temporal changes in the fish assemblage metrics. Cost-benefit analyses found that stereo-BRUV was generally more time efficient than stereo-DOV transects in terms of smaller standard error around the mean of the various metrics considered. How- ever, across the 3 biogeographic regions sampled there was considerable variation in the magnitude of these differences. Results suggest that stereo-BRUV stations are, in general, a more cost-effective method for monitoring fish assemblages than stereo-DOV transects.

Habitat connectivity as a factor affecting fish assemblages in temperate reefs

Habitat connectivity exerts a significant effect on the structure of biological communi- ties. However, it is generally difficult to study such an effect while controlling for other specific com- ponents of habitat structure. Here, temperate fish assemblages were studied in artificial reefs in localities differing chiefly in connectivity among complex habitat patches. Total fish abundance and biomass were higher in localities with high habitat connectivity, while species evenness followed the opposite trend. In most cases, the assemblages can also be distinguished by composition and relative abundance of species, as well as multispecies variability. Species responses were related to specific ecological profiles. Small species and those with restricted mobility were associated with high habi- tat connectivity. By contrast, medium-sized, off-reef foragers and vagile species were associated with reef isolation. The abundance ratio between 2 representative families of both groups of species, labrids and sparids, confirmed this finding. The temporal consistency of the observed patterns was also studied. The assemblages differed between periods of the year in terms of species composition and relative abundances. Total fish abundance, number of species and evenness were higher during the cold period than the warm, due to the presence of transient species. The results highlight the importance of habitat connectivity for the conservation and management of Mediterranean reef fishes.

Effects of high-relief structures on cold temperate fish assemblages: A field experiment

High-relief structures may influence the abundance and diversity of reef-associated fish. We conducted a field experiment to investigate whether the presence of vertical structures (PVC pipes) affects fish communities on artificial reefs. The effect of the height of the structures (1 and 3 m) was also tested. Furthermore, the effects on fish of placing artificial reefs on otherwise featureless bottoms were quantified. Algal and macro-invertebrate colonization of the reefs was also recorded. The experiment was carried out on the west coast of Sweden over a period of 1 year. The vertical structures had a positive effect on fish abundance but not on diversity. The height of the structures did not, however, influence the fish communities. Natural as well as urban vertical structures on the seafloor could have a positive effect on local fish abundance. The positive effects of artificial reefs on total fish abundance and diversity were immediate. Of the 10 species recorded, two, the black goby Gobius niger and the goldsinny wrasse Ctenolabrus rupestris, dominated over the whole survey period. There were significant temporal differences in fish abundance, and diversity increased with time.

The effects of disturbance and severe seasonal fluctuations in environmental conditions on north temperate shallow-water fish assemblages

The shallow-water fish populations at one disturbed and one undisturbed site in the Oslofjord, Norway were sampled with a beach seine from September 1981 to September 1982. The inner site (inner fjord; Hvervenbukta) is in the most polluted part of the fjord and has a heavy recreational usage during the summer months, the outer site (Ellingstad) is in a least polluted part of the fjord and has only sporadic recreational usage. Physical conditions at the two sites differ primarily in seasonal changes of dissolved oxygen levels (Hvervenbukta 3·3–11·1 ml O 2 1 −1 and Ellingstad 5·3–7·1 ml O 2 1 −1). Thirty-three fish species were caught at Ellingstad compared with only 23 at Hvervenbukta, with 0·61 similarity in species lists. Both sites had approximately equal numbers of resident and non-resident species. The mean density of individuals was much greater at Hvervenbukta (0·36 m −2) than at Ellingstad (0·04 m −2). Both sites showed a high dominance factor with a few species comprising the majority of the abundance. Overall species diversity ( H′), evenness ( F′) and species richness ( D) were greater at Ellingstad, consistent with the reduced disturbance. The overall range in seasonal similarity was relatively high for both sites as a function of the severe seasonal cycle in temperature (ice cover to approximately 20 °C). These relatively high variations are to be expected for north temperate fish assemblages. The range in the seasonal similarity index was greater at Hvervenbukta reflecting increased disturbance. There were dissimilar patterns in the seasonal cycles of community parameters at the two sites. Changes in population structure were largest during the period of recruitment of new year classes.