Recruitment and the structure of assemblages of fish on coral reefs

Much recent research has focused on the question of the high species richness and population densities of fish inhabiting coral reefs. Both density-dependent (post-recruitment) and density-independent (pre-recruitment) processes have been implicated in the regulation of these assemblages. These processes may operate at a variety of spatial and temporal scales. Here we review recent progress and point to some of the key questions for future research.     

Decadal changes in parrotfish assemblages around reefs of Guam,Micronesia

Coral Reefs - Modern coral reefs face substantial threats that endanger their capacity to function and provide resources for human populations. Chronic human pressure through exploitation and...     

Oceanographic and lunar forcing affects nearshore larval fish assemblages from temperate rocky reefs

The influence of oceanographic features and moon phases on ichthyoplankton assemblages in a temperate nearshore rocky reef off El Quisco Bay, central Chile, was assessed during austral spring–summer 2015–2016 using Bongo nets. Wind direction was predominantly south-west, and ocean temperature increased gradually during the study period, fluctuating between 11.6°C and 17.7°C. A relatively cold period (from late September to early December, 12.42?±?0.64°C) was distinguished from a relatively warmer phase (from mid-December to February, 13.56?±?1.08°C). Nearshore ichthyoplankton was composed of 13,700 individuals, belonging to 43 taxa. Larval Strangomera bentincki (Clupeidae) were collected in high numbers between late September and late October with peaks during full moon and first quarter (maximum?=?734 ind. 100?m^?3); larval Engraulis ringens (Engraulidae) was most abundant between late October and late December 2015, with peaks during the third quarter and full moon. Principal Component Analysis of ichthyoplankton data explained more than 44% of total variance and showed the influence of cold/warm periods in the structuring of larval fish assemblages. Water temperature had more influence than lunar phase in the structure and composition of nearshore fish larvae off central Chile. We conclude that larval fish assemblages found in nearshore waters change on a seasonal scale by differences in the reproductive activity among species, and that lunar phase exerts a low, but significant effect on the abundance of fish larvae, but this variability is species-specific.     

A preliminary examination of depth associated spatial variation in fish assemblages on small artificial reefs

Small concrete artificial reef modules (hemisphere-shaped, approximately 1.3 m diameter, 1 m high) were placed at two sites, eight modules per site. The sites were in 7 m and 21 m of water, 1.6 km apart, off the coast of southeast Florida, USA. The reefs were censused monthly for fish over a 19-month period. Species, number of fish, and estimated total length of each individual were recorded by divers using SCUBA. After the monthly census, all fish were removed from the reefs with a piscicide. A total of 88 species were recorded in the study, with significantly greater diversity on the deep reefs (monthly mean of 7.6 versus 3.0 shallow, P < 0.001, anova ). There were also significantly more biomass (calculated from length), and more large fish (>5 cm) on the reefs at 21 m than at 7 m (P < 0.001). There were more small fish at the shallow site (P < 0.05). Although it is not clear what variable(s) associated with the two depths is responsible for the differences, these results highlight the potential differences in artificial reef and ambient environment interactions within a localized area.     

Precision and accuracy of visual census technique for fish assemblages on coral patch reefs

Synopsis A visual census technique is described in which the results of three separate enumerations of fish at a site are combined to produce a best estimate of the fish fauna present. Its precision and accuracy are examined, and compared to those of censuses obtained by modifications of the technique. Visual censuses can display high repeatability, but they seldom (if ever) completely sample the fish present at a site. Accuracy varies with technique used. In our tests, the preferred method yielded 82% of species and 75% of individuals known to be present and potentially censurable at the time the observations were made. Visual censuses are of comparable accuracy to ichthyocide collections of unenclosed sites, but the two methods sample different components of the total fish fauna. It is important when using visual censuses to remember that their accuracy is not 100%.     

Day and night mesopelagic fish assemblages off the Kerguelen Islands (Southern Ocean)

Mesopelagic fish assemblages were investigated in the Polar Frontal Zone off the Kerguelen Islands during summer 1995, in parallel with a king penguin tracking study. During the day, the upper offshore water layers (0–200 m) have low potential prey diversity and abundance with only three fish species: a lanternfish, Krefftichthys anderssoni, a member of the Muraenolepididae, Muraenolepis marmoratus, and the early stages of the nototheniid, Lepidonotothen squamifrons. The mesopelagic fish community, including the typical myctophids, first appears in the deeper layer (300 m). At night, the surface layer (50 m) is invaded by the mesopelagic Myctophidae Electrona antarctica, Gymnoscopelus braueri, G. piabilis, G. fraseri, G. nicholsi, Protomyctophum bolini and P. tenisoni. Deeper (>100 m), a cline of species assemblages from the coast to offshore is observed. Accepted: 4 August 1999     

The influence of prey communities on fish species assemblages on artificial reefs in Puget Sound,Washington

Synopsis Research on eleven artificial reefs in Puget Sound, Washington examined the relative importance of reef-produced prey items to recreationally important reef fish species assemblages. The colonization of potential prey items, and fish species assemblages to ten artificial reefs were examined for the reefs first two to five years, and observations were conducted on an eleventh reef during its forty-ninth productive year. Fish species became more abundant, or were seen more frequently on reef habitats whose substrates had successionally developed from barnalces to algal mats. Fish species most affected by this successional change foraged heavily on organisms which were associated with reef algae. Starfish and nudibranchs. who preyed on the barnacles, were identified as the ‘keystone’ predators of these subtidal reef habitats.     

Analysis of temporal changes in fish assemblages in Serpentine Creek,Queensland

Synopsis From November 1975 to April 1977 nocturnal dermersal fish were sampled fortnightly at ten sites in Serpentine Creek using a three meter beam trawl with a 3.2 cm mesh net. Forty-five species from thirty-four families were obtained totalling 14 518 individuals with the six most abundant species comprising approximately 72% of the catch. Using multiple regression techniques with Fourier transformations, the mean number of species (S) and abundance (N) of all fish were found to conform to a regular annual cyclical pattern with maxima in April and May. A trend toward declining abundances of individuals and species was present. Shannon (H′) and Gleason (G) diversity indices showed no regular seasonal trends and are considered poor indicators of pollution. In comparison with other estuarine studies at different latitudes Serpentine Creek conforms to the theory that more tropical waters have the greatest faunal diversity. Seventeen of the 22 most abundant species demonstrated a regular annual cycle of abundance. The number of species, abundance and diversity measures were greatest about 1 km from the mouth of the creek and gradually declined upstream. This was the region with highest macrobenthos diversity and with the most stable abiotic values. Temperature and/or salinity were positively correlated with the abundance of eleven species. The species were placed in five groups according to their periodic characteristics. The proportion of ‘resident’ species was low and this is consistent with Tyler's (1971) theory of temperature stabilized fish assemblages. The known biology of six species is related to their occurrence. Salinity and temperature values in the creek exhibit an annual cycle which preceeds that of Bramble Bay by approximately one month. Rainfall in the watershed was correlated with observed salinity values. It is postulated that salinity is the common feature between temperate and tropical estuaries in the maintenance of community cycles.     

River of the dammed: longitudinal changes in fish assemblages in response to dams

Although dams are a common feature on rivers throughout the world, their effects on diversity, composition, and structure of fish assemblages are often unclear. We used electrified benthic trawls and stable isotope analysis of δ¹³C and δ¹⁵N to determine the complex relationships between taxonomic diversity and food web structure of fish assemblages among sites in the free-flowing and impounded reaches of the Allegheny River, Pennsylvania, USA. We found higher gamma and beta fish diversity in the free-flowing section, where Brillouin diversity increased in a downstream direction; however, in the impounded section, we found decreasing diversity downstream. Analysis of similarity and non-metric multi-dimensional scaling revealed longitudinal differences in Bray–Curtis similarity between assemblages from impounded and those from free-flowing sites. Finally, using stable isotope analysis, we showed that fishes in the free-flowing section derived nutrients primarily from benthic sources while fishes in the impounded section had a stronger reliance on pelagic nutrients. Our findings reveal that dams can reduce fish taxonomic diversity, driven primarily by decreases in lotic taxa, while shifting resource use from benthic toward pelagic nutrients. A multi-faceted approach to assess the cumulative effects of dams on aquatic communities is, therefore, recommended.     

A fourteen-year overview of the fish assemblages and yield of the two oldest Algarve artificial reefs (southern Portugal)

Artificial reefs have been deployed worldwide for the last three decades in response to problems concerning coastal resources, ecosystems and fisheries. In many countries they have became important elements of integrated fisheries management plans. In Portugal two artificial reef systems (ARSs) were deployed by the Portuguese Institute of Marine Research (IPIMAR) in 1990, in the southern coast (Algarve). They were located off Faro and Olhão, over different sea-bottom types and located at different distances from the coastline. To analyse the effect of ARSs deployment on local fish assemblages and to evaluate their effectiveness in terms of mean fishing yields and mean number of species caught, fishing surveys have been conducted over 14 years (256 net sets) using a gillnet to sample the ARS of Faro and Olhão and respective control sites. The fishing yields from the ARs continually exceeded those from the control sites, in both the mean number of species caught and the mean CPUE in weight (1.8–2.6 times); both were higher at Faro. Moreover, the comparison between fish assemblages from the ARS and respective control sites showed that the deployment of the man-made structures did not change the composition of the fish assemblages caught by the gill nets, or the equilibrium of the community, since the relative proportion of the different functional groups of fish remained stable. The ARSs are a useful management tool on the Algarve coast, enhancing and diversifying the catches, thus contributing to improved local artisanal fisheries, which play a major role in this region.     

Free-living scleractinian corals on reefs of the Seychelles Islands

Thirty-nine species of unattached scleractinian corals that belong to 22 genera of 9 families were found on the Seychelles reefs. Variations of the colony form of corals living on soft sediments under continuous wave action are described. Irrespective of their initial growth form and taxonomic position, corals assume a form close to spherical. Because of the worldwide deterioration of coral reefs, the adaptation to changing ecological conditions by reef-building corals needs to be studied.     

Baselines and degradation of coral reefs in the Northern Line Islands

Effective conservation requires rigorous baselines of pristine conditions to assess the impacts of human activities and to evaluate the efficacy of management. Most coral reefs are moderately to severely degraded by local human activities such as fishing and pollution as well as global change, hence it is difficult to separate local from global effects. To this end, we surveyed coral reefs on uninhabited atolls in the northern Line Islands to provide a baseline of reef community structure, and on increasingly populated atolls to document changes associated with human activities. We found that top predators and reef-building organisms dominated unpopulated Kingman and Palmyra, while small planktivorous fishes and fleshy algae dominated the populated atolls of Tabuaeran and Kiritimati. Sharks and other top predators overwhelmed the fish assemblages on Kingman and Palmyra so that the biomass pyramid was inverted (top-heavy). In contrast, the biomass pyramid at Tabuaeran and Kiritimati exhibited the typical bottom-heavy pattern. Reefs without people exhibited less coral disease and greater coral recruitment relative to more inhabited reefs. Thus, protection from overfishing and pollution appears to increase the resilience of reef ecosystems to the effects of global warming.     

Stony coral diseases observed in southwestern Caribbean reefs

Thirteen reef areas of Colombian territories in the Southwestern Caribbean were surveyed during the last 10 years. Coral diseases have been recorded in all these areas since 1990 and some of them have increased progressively. Six types were differentiated in the region, of which black band disease (BBD), dark spots disease (DSD), white band disease (WBD) and white plague disease (WPD) are widespread and common. Yellow band disease (YBD) was observed only since April 1998 but has been found now in seven reef areas and eight coral species (most of them recorded here as new hosts). In total, 25 species of hard corals were observed with diseases in the region, of which Colpophyllia natans, Diploria labyrinthiformis, Montastraea annularis, M. faveolata, M. franksi and Acropora spp. appear to be highly susceptible.     

Distribution of introduced and native fish in Patagonia (Argentina): patterns and changes in fish assemblages

The interaction between native fishes and salmonids introduced in Patagonia at the beginning of the 20th Century, developed at the same time as the environmental change. The phenomenon of global warming has led to the formulation of predictions in relation to changes in the distribution of species, in the latitudinal dimension, both at intralacustrine, or small streams levels. The aim of the present work includes three main objectives: a) to compose a general and updated picture of the latitudinal distribution range of native and alien fishes, b) to analyze the historical changes in the relative abundance of Percichthys trucha, Odontesthes sp., and salmonids in lakes and reservoirs, and c) to relate the diversity and relative abundance of native and salmonid fishes to the environmental variables of lakes and reservoirs. We analysed previous records and an ensemble of data about new locations along the northern border of the Patagonian Province. We compared current data about the relative abundance of native fishes and salmonids in lakes and reservoirs, with previous databases (1984–1987). All samplings considered were performed during spring-summer surveys and include relative abundance, as proportions of salmonids, P. trucha, and Odontesthes sp. For the first time, we found changes in fish assemblages from twenty years back up to the present: a significant decline in the relative abundances of salmonids and an increase of P. trucha. We studied the association between the diversity and relative abundance of native and salmonid fishes and the environmental variables of lakes and reservoirs using Canonical Correspondence Analysis. Relative abundance showed mainly geographical cues and the diversity relied largely on morphometric characteristics. Relative abundance and diversity seem to have a common point in the lake area, included into the PAR concept. Native abundance and alien diversity were negatively related with latitude. Greater native diversity was observed in lakes with high PAR compared with salmonids. Historical changes such as southward dispersion, relative abundance changes, and geographical patterns for relative abundance and diversity are basic concepts needed not only in future research but also in management design for Patagonian fish populations.     

Temporal changes in replicated experimental stream fish assemblages: predictable or not?

Summary 1. Natural aquatic communities or habitats cannot be fully replicated in the wild, so little is known about how initially identical communities might change over time, or the extent to which observed changes in community structure are caused by internal factors (such as interspecific interactions or traits of individual species) versus factors external to the local community (such as abiotic disturbances or invasions of new species).
2. We quantified changes in seven initially identical fish assemblages, in habitats that were as similar as possible, in seminatural artificial streams in a 388-day trial (May 1998 to May 1999), and compared the change to that in fish assemblages in small pools of a natural stream during a year. The experimental design excluded floods, droughts, immigration or emigration. The experimental fish communities diverged significantly in composition and exhibited dissimilar trajectories in multivariate species space. Divergence among the assemblages increased from May through August, but not thereafter.
3. Differences among the experimental assemblages were influenced by differences that developed during the year in algae cover and in potential predation (due to differential survival of sunfish among units).
4. In the natural stream, fish assemblages in small pools changed more than those in the experimental units, suggesting that in natural assemblages external factors exacerbated temporal variation.
5. Our finding that initially identical assemblages, isolated from most external factors, would diverge in the structure of fish assemblages over time suggests a lack of strong internal, deterministic controls in the assemblages, and that idiosyncratic or stochastic components (chance encounters among species; vagaries in changes in the local habitat) even within habitat patches can play an important role in assemblage structure in natural systems.     

High diversity,abundance and distinct fish assemblages on submerged coral reef pinnacles compared to shallow emergent reefs

Coral Reefs - Coral reefs exhibit consistent patterns in biodiversity across multiple spatial scales, from local to global clines in species richness, abundance and community structure. Knowledge...     

Late Pleistocene molluscan assemblages from the coral reefs of the Kenya coast

Since the Last Interglacial, there have been profound changes in the nature of the fringing reef along the Kenya coast. These are most apparent in the back-reef region where a marked decline in habitat diversity has led to a significant reduction in the variety of molluscan assemblages. Despite dramatic changes in the composition of these assemblages, very few species have become extinct. The four late Pleistocene species apparently missing from the Recent fauna of the Kenya coast still occur further east in the Indonesia-West Pacific region. There is evidence to suggest that range retractions from the periphery to the core region occurred at the same time in other parts of the Indo-Pacific province too. The province's margins may well have been more susceptible to fluctuations in certain environmental parameters, such as temperature, during the Pleistocene climatic cycles.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

Short-term effects of recent land-use changes in Eastern Austria on farmland bird assemblages in a human-dominated landscape

To study effects of short-term land-use changes on birds in a predominantly agriculturally used landscape in Northeastern Austria, birds were surveyed in 22 circular study areas with a diameter of 1 km in 2005 and 2009. Because of the abolition to obligate set-aside land from 2008, it was suspected that the amount of set-aside land would be reduced dramatically. Consequently, a loss of farmland birds was expected. Results show that the amount of set-aside land indeed decreased significantly between 2005 and 2009 from 15.05% to 9.69% (mean proportion of set-aside land per study area). Farmland birds were represented by 20 species in both years. Neither richness and abundance nor species composition of farmland birds were affected by changes of set-aside land. The amount of set-aside land in these landscapes was already high (compared to other areas in Austria) before the amendment of the law and still relatively high after it. Therefore, perhaps changes in the extent of set-aside land were below the threshold to find detectable effects on farmland birds.