Fish Community Metrics Research Articles

Three-dimensional conservation planning of fish biodiversity metrics to achieve the deep-sea 30×30 conservation target.

Accelerating rate of human impact and environmental change severely affects marine biodiversity and increases the urgency to implement the Convention on Biological Diversity (CBD) 30×30 plan for conserving 30% of sea areas by 2030. However, area-based conservation targets are complex to identify in a 3-dimensional (3D) ocean where deep-sea features such as seamounts have been seldom studied mostly due to challenging methodologies to implement at great depths. Yet, the use of emerging technologies, such as environmental DNA combined with modern modeling frameworks, could help address the problem. We collected environmental DNA, echosounder acoustic, and video data at 15 seamounts and deep island slopes across the Coral Sea. We modeled 7 fish community metrics and the abundances of 45 individual species and molecular operational taxonomic units (MOTUs) in benthic and pelagic waters (down to 600-m deep) with boosted regression trees and generalized joint attribute models to describe biodiversity on seamounts and deep slopes and identify 3D protection solutions for achieving the CBD area target in New Caledonia (1.4millionkm2). We prioritized the identified conservation units in a 3D space, based on various biodiversity targets, to meet the goal of protecting at least 30% of the spatial domain, with a focus on areas with high biodiversity. The relationship between biodiversity protection targets and the spatial area protected by the solution was linear. The scenario protecting 30% of each biodiversity metric preserved almost 30% of the considered spatial domain and accounted for the 3D distribution of biodiversity. Our study paves the way for the use of combined data collection methodologies to improve biodiversity estimates in 3D structured marine environments for the selection of conservation areas and for the use of biodiversity targets to achieve area-based international targets.

The influence of spatial processes on fish community structure: using a metacommunity framework for freshwater bioassessment.

The use of biological indicators in a bioassessment approach is important for inferences of anthropogenic stress in routine monitoring programs. One of the primary assumptions of bioassessment is that biological indicators observed at specific sampling sites will allow for inferences of local environmental quality; however, this assumption requires a reliable understanding of dispersal processes, which is particularly relevant in river systems due to their dendritic network. Inter-stream dispersal between different points of the river network could bias bioassessment, especially for highly mobile organisms like fish. Here, we examine standard biological metrics used in routine biomonitoring to determine how spatial variables, including dispersal, influence inferences between fish populations and environmental gradients. Using redundancy analysis (RDA) and variation partitioning, we tested the relative influence of both environmental and spatial variables on fish community structure and related community metrics. Fish were collected from 99 sampling sites distributed across 44 rivers and streams of the Great Morava River Basin, Serbia. Electroconductivity, the percentage of agricultural areas, dissolved oxygen, ammonia, and nitrate-nitrogen were found to be significant environmental variables, while ten spatial predictors from broad- to small-scales were found to influence fish community structure and community metrics. Our results suggest that contemporary dispersal among streams influences fish community composition, but that trait-based metrics are less sensitive than basic measures of diversity to spatial processes. Our results highlight the need for spatially independent sampling, as well as the need to consider dispersal-based processes in routine biomonitoring.

Direct and indirect effects of a fishing ban on lacustrine fish community do not result in a full recovery

Abstract Protected areas are increasingly being promoted as an important means of protecting freshwater biological diversity and ecological processes. A robust assessment of ecological changes in protected areas is fundamental to optimize conservation policies and adaptive management. China's efforts to establish aquatic reserves have attracted worldwide attention, especially the “10‐year fishing ban” implemented in the Yangtze River basin. We focused on Liangzi Lake, a freshwater protected area in the Yangtze River basin, to understand the effect of a fishing ban occurring after a short period of overfishing. In this aim, the time series of fish community taxonomic and functional structure encompassing the overfishing period and a post‐ban period have been analysed. Fish community metrics with direct, indirect and no responses to fishing bans were identified. The results indicate that in the early period of the fishing ban, the trophic level and body size structure of the fish community were in the way of recovery. However, species that prefer benthic habitats did not recover after fishing‐induced habitat degradation. Functional traits were more sensitive than taxonomic indices and revealed subtle community changes, such as the recovery of some ecological functions, despite a non‐recovering species richness. Synthesis and applications. This study provides a rare case of a freshwater protected area in which the effects of conservation measures are studied with a temporal survey. The effectiveness of the functional trait approach in the application of protected area assessment was demonstrated by revealing the recovery of trophic level and body size structure of fish communities after the implementation of fishing ban, and the inadequacy of habitat restoration efforts. We suggest that in freshwater protected areas, insistence on fishing ban is necessary but not sufficient for full biodiversity recovery, and other measures are needed, such as habitat restoration and species‐focused stocking.

Annual changes in water quality and sportfish community structure following commercial harvest of common carp and bigmouth buffalo

Martin A. Simonson, Michael J. Weber, Grace M. Wilkinson and Andrew R. Annear. 2023. Annual changes in water quality and sportfish community structure following commercial harvest of common carp and bigmouth buffalo. Lake Reserv Manage. XX:XXX–XXX. Commercial harvest of common carp (Cyprinus carpio; hereafter carp) and bigmouth buffalo (Ictiobus cyprinellus; hereafter buffalo) populations had little detectable effect on shallow lake ecosystems. We tested whether carp and buffalo biomass removal affects limnological variables and fish community metrics across 6 shallow, natural lakes of northwestern Iowa using mixed effects models. Annual commercial harvest of carp ranged from 0 to 71 kg/ha; annual harvest of buffalo ranged from 0 to 356 kg/ha. Biomanipulation (i.e., commercial harvest) of carp was associated with decreases in soluble phosphorus and nitrogen concentrations, but not total phosphorus or nitrogen. Buffalo harvest was unrelated to annual changes in nutrient concentrations but was associated with reductions in chlorophyll a and phycocyanin concentrations. Secchi disk transparency and total suspended solids were unrelated to carp and buffalo harvest. Carp harvest was associated with reduced biomass of large cladocerans but no other zooplankton biomass densities; buffalo harvest was unrelated to zooplankton biomass. Species richness and rake density of aquatic macrophytes were unrelated to carp and buffalo harvest. Carp and buffalo harvest was unrelated to changes in most indices of sportfish abundance, condition, and size distribution. Our results suggest harvest of carp and buffalo <71 kg/ha has little effect on abiotic and biotic ecosystem components on short time scales and highlights the challenges associated with shallow lake restoration.

Stream restoration produces transitory, not permanent, changes to fish assemblages at compensatory mitigation sites

There is inconsistent evidence that stream restoration projects lead to recovery of ecosystem attributes, especially stream biota. While some assessments have documented desired changes in fish community metrics in the first years following restoration, longer‐term studies have not always corroborated these findings. In this study, we used data and monitoring reports submitted to federal regulators by stream mitigation consultants to examine whether in‐stream restoration activities led to changes in fish community attributes at 23 compensatory mitigation projects representing 53 sampling sites in Georgia, United States over 7 years of post‐restoration monitoring. Modeling results indicated that abundance and species richness of fishes generally increased in the first years after restoration before decreasing to baseline levels by the seventh year. This pattern was consistent for models considering sensitive fish taxa, as well as at sites across a range of agricultural and forested land cover percentages. However, the effect of restoration on species richness was dampened in larger streams and at more urbanized locations. A community trajectory analysis supported the findings that fish community change was transitory at most sites. Remote estimation of canopy cover change at restoration sites suggested that the hump‐shaped response may be driven by increased light availability during the immediate‐post restoration period, followed by subsequent re‐shading of stream channels by riparian plantings. Our analysis indicates that reach‐level manipulation of streams should not be expected to induce long‐term changes in fish communities, and that publicly available monitoring reports may be leveraged to address questions of stream restoration efficacy.

Eutrophication induces functional homogenization and traits filtering in Chinese lacustrine fish communities

Rapid anthropogenic nutrient enrichment has caused widespread ecological problems in aquatic ecosystems and the resulting eutrophication has dramatically changed fish communities throughout the world. However, few studies addressed how fish communities responded to eutrophication in terms of multidimensional functional and taxonomic structure, especially how eutrophication acted as an environment filter on functional traits. The aim of the present study was to investigate the effects of eutrophication on fish species composition, community metrics and species functional traits in 26 shallow lakes from the middle reaches of Yangtze River basin, China. This study validated that eutrophication is an important factor shaping the fish community structure. Regression analyses showed that eutrophication favored higher total biomass and lower functional diversity of fish communities but had little effect on species richness. Despite the fact that some pelagic zooplanktivorous species were more abundant in the most eutrophic lakes, multivariate analyses of the relationships between species traits and environmental variables revealed weak relationships between feeding traits and eutrophication. In contrast, species with a benthic life stage were negatively associated with eutrophication while those with a large body size and high absolute fecundity showed the opposite trend. Due to demersal habitat degradation, and to a lesser degree, to changes in trophic resources availability, eutrophication caused functional simplification of fish communities by increasing functional traits homogeneity among the most tolerant species. Some relationships between functional traits and eutrophication well established in the western palearctic have not been observed in this study, emphasizing the importance of biases resulting from specific evolutionary histories. This work will provide useful insights on on-going restoration and management of shallow lakes in the Yangtze River basin.

Oxbow Restorations for Topeka Shiner (Notropis topeka) Recovery: Defining Success

Within the Great Plains region of North America, oxbow wetlands were lost as streams were channelized and straightened to allow for agricultural use of the landscape. Topeka Shiner, which rely on these oxbow wetlands, have declined in abundance, currently occupy 20% of their historical geographic range, and are now an endangered species. A large emphasis has been placed on restoring oxbow wetlands to recover Topeka Shiner populations. As the number of oxbow restorations has increased, so has the number of monitoring projects focused on these habitats. Currently, conservation practitioners rely on the presence of Topeka Shiner to determine the success of an oxbow restoration. Given the rarity of the species, this method is likely ineffective. Within this study we attempt to create a model that can be used to determine the success of an oxbow restoration that will benefit the Topeka Shiner without relying on the presence of the species in the wetland. We used multiple fish community metrics and modelling strategies to determine the best model for predicting Topeka Shiner CPUE and presence/absence within oxbows. We determined that the top models were ineffective at predicting Topeka Shiner CPUE and presence/absence. Our findings illustrate the random nature by which fish communities become established within oxbows, and the island-like nature of oxbows in terms of how fish communities may become established and change over time. These findings indicate that the success of oxbow restoration for Topeka Shiner needs to be defined at a larger scale than for individual oxbows. Furthermore, our findings corroborate the inability of previous studies to determine reproducible associations of Topeka Shiner with various fish community metrics.

Reef fish community structure along the southeastern US Atlantic continental shelf break and upper slope appears resistant to increasing lionfish (Pterois volitans/miles) density

Temperate reefs host diverse fish communities along the southeast United States Atlantic coast (SEUS), yet the sustainable management of reef fishes faces myriad challenges. One challenge has been the introduction of Indo-Pacific lionfish (Pterois volitans/miles; hereafter "lionfish"), which have spread quickly throughout the SEUS since their introduction in the late 1900s. We analyzed long- term (2001–2019) video data along the continental shelf break and upper slope (45–125 m deep) of the SEUS to assess changes in lionfish densities over time, characterize reef fish community structure, and determine if native reef fish community structure has changed due to lionfish. Lionfish densities increased substantially during the study, from zero individuals observed in 2001 to approximately 1.2 individuals observed per 100 m 3 (and present in all included transects) by 2019, yet no fish community metrics were negatively related to lionfish density. Demersal habitat influenced fish community structure more than any other variable examined, with more individuals and different fish communities occurring on high-relief compared to low-relief hardbottom habitats. The effects of latitude, depth, and bottom temperature on reef fish community structure were generally weak or nonexistent. Although previous empirical work has found that lionfish negatively affect native fishes at small scales (&lt;30 km2), it is unclear why we did not find similar results in our larger- scale study. It may be related to vagaries of the spatial scale of observation, lionfish effects being primarily limited to high- relief habitats, time lags, or lionfish densities not being high enough yet to cause observable ecological effects.

Temporal scope influences ecosystem driver-response relationships: A case study of Lake Erie with implications for ecosystem-based management

Understanding environmental driver-response relationships is critical to the implementation of effective ecosystem-based management. Ecosystems are often influenced by multiple drivers that operate on different timescales and may be nonstationary. In turn, contrasting views of ecosystem state and structure could arise depending on the temporal perspective of analysis. Further, assessment of multiple ecosystem components (e.g., biological indicators) may serve to identify different key drivers and connections. To explore how the timescale of analysis and data richness can influence the identification of driver-response relationships within a large, dynamic ecosystem, this study analyzed long-term (1969–2018) data from Lake Erie (USA–Canada). Data were compiled on multiple biological, physical, chemical, and socioeconomic components of the ecosystem to quantify trends and identify potential key drivers during multiple time intervals (20 to 50 years duration), using zooplankton, bird, and fish community metrics as indicators of ecosystem change. Concurrent temporal shifts of many variables occurred during the 1980s, but asynchronous dynamics were evident among indicator taxa. The strengths and rank orders of predictive drivers shifted among intervals and were sometimes taxon-specific. Drivers related to nutrient loading and lake trophic status were consistently strong predictors of temporal patterns for all indicators; however, within the longer intervals, measures of agricultural land use were the strongest predictors, whereas within shorter intervals, the stronger predictors were measures of tributary or in-lake nutrient concentrations. Physical drivers also tended to increase in predictive ability within shorter intervals. The results highlight how the time interval examined can filter influences of lower-frequency, slower drivers and higher-frequency, faster drivers. Understanding ecosystem change in support of ecosystem-based management requires consideration of both the temporal perspective of analysis and the chosen indicators, as both can influence which drivers are identified as most predictive of ecosystem trends at that timescale.

Correction to: Fish composition, but not richness or abundance, differ among Phragmites, Typha, and Schoenoplectus zones during a high-water year

Phragmites australis (ssp australis) is an aggressive colony-forming species that displaces emergent vegetation in North America, including native bulrushes (Schoenoplectus sp.) and both native and invasive cattails (Typha sp.). Phragmites expansion can alter habitat and negatively affect reptiles, amphibians, and birds; less is known about Phragmites’ utility as fish habitat and its impact on fish communities in freshwater coastal wetlands. To assess fish use of Phragmites in summer, we compared habitat characteristics, water quality, and fish community composition, diversity, and abundance among stands of flooded Phragmites, Typha, and Schoenoplectus at 16 sites across four regions of the Laurentian Great Lakes. Despite marked differences in water quality (higher pH and morning dissolved oxygen in Schoenoplectus) and habitat characteristics (higher stem density in Phragmites), there were no significant differences in fish species richness or catch per unit effort among vegetation types; there was a distinct fish assemblage in Schoenoplectus (more Cyprinids) compared to both Phragmites and Typha (more Centrarchids). This suggests that expansion of Phragmites or Typha at the expense of Schoenoplectus may alter wetland fish assemblages; however, with no clear differences in other fish community metrics, flooded Phragmites may provide habitat for some fishes during the summer, in the study wetlands.

How Surface Water Management Can Benefit Fish Conservation in Urban Streams

Abstract We analyzed 33 y of fish community data collected from a low-order, urban stream in central Illinois, USA, to determine the effects of municipal wastewater management projects and urbanization on fish communities. From 1985 to 2017, species richness, number of pollution-intolerant species, and alternative index of biotic integrity significantly increased at sites across this system. Species diversity likewise increased, but was mostly significant only at sites downstream of the effluent outflow. Ceasing the chlorination of wastewater in 1990 resulted in significant increases in fish community metrics both upstream and downstream of effluent outflow, although effects varied from site to site. Completing a combined sewer overflow abatement project in 2008 resulted in some significant increases in species richness, diversity, and number of pollution-intolerant species at sites downstream of effluent outflow. From 2001 to 2016, the change in the number of pollution-intolerant species correlated inversely with the increased percentage of impervious cover in the study system. There was no significant correlation of other metrics with the change in percent impervious surfaces. These results suggest that urbanization at upstream sites limited to some extent the benefits of water management interventions that improved fish community metrics at downstream sites.

Understanding shifts in estuarine fish communities following disturbances using an ensemble modeling framework

Ecological disturbances may result in mortality events that alter biotic communities and ecosystems. In many coastal zones disturbances are increasing, including algal blooms and fish kills. These two disturbances are often related, with blooms releasing toxins or depleting oxygen, ultimately killing fish. Depending on the intensity, duration, and geographic extent of an algal bloom, the fish community can take days to years to recover from disturbances. To explore the relationship among environmental disturbances, sport fish, and forage fish communities, this study examines a non-toxic brown algal bloom (Aureoumbra lagunensis) occurring from December 2015 through March 2016. Using an ensemble modelling framework combining generalized linear models (GLM), Bayesian modelling, and Bayesian structural equation modeling (SEM), this complementary framework helped elucidate complex relationships among environmental variables and the fish community following a disturbance. The algal bloom crashed over a three-day period in March 2016 and resulted in a fish kill when dissolved oxygen concentrations dropped below hypoxic levels (DO < 2 mg/L). The bloom and subsequent fish kill led to shifts in both forage and sport fish communities, and their relationships, when compared to non-disturbed years. Both sport fish and forage fish abundances decreased following the bloom, but the response of the forage fish community was more rapid. When looking at direct correlations between individual sport fish and forage fish community metrics during the bloom, a large amount of variation in sport fish abundance was explained by forage fish abundance (R2 = 0.34). Also, the variation in forage fish abundance was explained well by pH (R2 = 0.72). Forage fish community dynamics were more closely related to water quality metrics than sport fish communities during non-disturbed periods. However, during this algal bloom, sport fish community dynamics were more closely associated with water quality metrics than forage fish community dynamics. Furthermore, sport fish community dynamics were strongly related to bloom dynamics during the three months prior to the fish kill. In the three months following the kill, the forage and sport fish communities were less strongly linked than in non-disturbed years. These large shifts in community dynamics and relationships following a disturbance suggest both forage and sport fish communities, food webs, and trophic dynamics may be at increasing risk of crossing ecological thresholds as algal blooms become more common in coastal ecosystems.

Wood Removals from Lakes May Not Necessarily Elicit Fish Population Responses

AbstractCoarse woody habitat (CWH) in aquatic ecosystems provides structural complexity and a surface for food production for fish. Depending on abundance and complexity of CWH, it is usually associated with influencing predator–prey dynamics, fostering greater localized fish abundance, increasing fish growth, and contributing to fish production, but some conflicting evidence exists about its importance as fish habitat. Our experiment was designed to test for direct linkages between whole‐lake CWH availability and fish community abundance, biomass, and production. We removed ~50% of CWH from three lakes while concurrently sampling them and two other unaffected lakes as controls in a before‐after–control‐impact (BACI) design. Due to the loss of quality foraging habitat, structure, and cover for small fish, we hypothesized that the CWH removal would cause a measurable decline in fish abundance, biomass, and/or production. Despite CWH being a preferred habitat type for fish, our hypothesis was not supported because observed changes in measured fish community metrics could not be attributed to the CWH removal. The inability to directly link the wood removal to changes in the fish metrics we examined may have been due to a number of factors including the composition of the fish community, the high availability of alternate habitat structure (rocks, macrophytes), large quantities of wood remaining in the lakes, the relative lack of littoral habitat use by piscivores, or low statistical power (small sample size, high variance). However, we still urge resource managers to be cautious when considering authorizing removal of CWH from lakes because it does provide temporally stable year‐round structure and high‐quality foraging habitat with unique microbial, fungal, and invertebrate communities. Coarse woody habitat was a preferred habitat for fish and may have a greater relative importance in lakes with minimal alternative cover for fishes or in lakes containing different fish assemblages.

High diversity, abundance and distinct fish assemblages on submerged coral reef pinnacles compared to shallow emergent 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 of fundamental processes driving these patterns is largely derived from studies of shallow, emergent and nearshore reefs. Although research efforts are expanding to deeper mesophotic coral reef ecology, distinct and isolated reef morphologies like submerged pinnacles or seamounts have received scant attention. Despite being potentially important for connectivity and as refugia, the extent to which established patterns and processes in coral reef ecology apply to these systems is unknown. Here we examine the fish and benthic communities associated with coral reefs found on submerged pinnacles in Kimbe Bay, Papua New Guinea. Community structure and diversity metrics are compared with emergent reefs at the same depth in both near and offshore settings. We then explicitly test whether benthic complexity variables known to influence reef fish communities exhibit similar patterns at each reef type. Pinnacles were characterised by 3.70 times the mean fish abundance and 1.98 times the species richness recorded at the same depths on emergent reefs. Fish community structure showed distinct separation across reef morphologies, with pinnacles most similar to offshore reefs. Benthic habitat complexity did not vary across reef types while fish assemblages were weakly related to benthic habitat variables, with reef morphology the most consistent predictor of fish community metrics. The pinnacles in our study support high coral reef fish biodiversity despite their small habitat area and relative isolation by depth and offshore setting. Our results suggest that habitat-specific environmental conditions are generated by the distinct geomorphology of pinnacles. As coastal reefs become more increasingly disturbed, understanding ecological patterns on deep patch reef habitats like pinnacles will be useful to provide a more holistic understanding of coral reef seascapes and their resilience.

Short-term changes in reef fish community metrics correlate with variability in large shark occurrence

Large predators exert control on lower trophic levels, often influencing long-term changes in community structure. Many large predators are highly mobile and occur in habitats along a continuum of presence and absence. In many natural systems, the movement of large predators through an area has been shown to lead to rapid changes in prey distribution through trait-mediated behavioral responses. To test whether a similar interaction also occurs for artificial habitats, we examined how reef fish community metrics (abundance, species richness, community composition) varied with the presence of a large coastal shark (sand tiger shark, Carcharias taurus). Remotely-operated vehicle surveys of large sharks and reef fishes on shipwrecks along the North Carolina, USA, continental shelf revealed that short-term shark presence correlated with changes in reef fish community metrics. Specifically, when sharks were present, fish species abundance and richness did not differ compared to when sharks were absent. Finer-scale analyses near sharks revealed similar abundance but elevated species richness proximate to sharks. We confirmed that this fine-scale pattern of similar abundance but higher richness near sharks held when the ROV was not in the water by repeating analyses using time-lapse videos from nearby shipwrecks. The detected differences in fish community metrics in the presence of sharks correlated with higher numbers of water-column associated species, such as jacks and barracuda, but lower numbers of benthic-associated species, including seabass and grouper. These findings suggest that the presence of large predators on artificial structures, as in natural systems, can drive short-term changes in community structure.

Meta-Analysis Reveals Artificial Reefs Can Be Effective Tools for Fish Community Enhancement but Are Not One-Size-Fits-All

Approaches towards habitat conservation and restoration often include supplementing or enhancing existing, degraded, or lost natural habitats. In aquatic environments, a popular approach towards habitat enhancement is the introduction of underwater human-made structures or artificial reefs. Despite the nearly global prevalence of artificial reefs deployed to enhance habitat, it remains debated whether these structures function similarly to comparable natural reefs. To help resolve this question, we conducted a literature review and accompanying meta-analysis of fish community metrics on artificial reefs within the coastal ocean and made comparisons with naturally-occurring reference reefs (rocky reefs and coral reefs). Our findings from a synthesis of 39 relevant studies revealed that, across reef ecosystems, artificial reefs support comparable levels of fish density, biomass, species richness, and diversity to natural reefs. Additional analyses demonstrated that nuances in these patterns were associated with the geographic setting (ocean basin, latitude zone) and artificial reef material. These findings suggest that, while artificial reefs can mimic natural reefs in terms of the fish assemblages they support, artificial reefs are not one-size-fits-all tools for habitat enhancement. Instead, artificial reefs should be considered strategically based on location-specific scientific assessments and resource needs to maximize benefits of habitat enhancement.

The no-take zone network of the Mexican Caribbean: assessing design and management for the protection of coral reef fish communities

Understanding the effects and benefits provided by the design and management of Marine Protected Areas (MPAs) is crucial for developing cost‐effective management actions. We characterized the management and design of no-take zone (NTZ) networks of eight Mexican Caribbean MPAs. To determine protection effectiveness, we followed a two-step approach. First, we evaluated the effect of the level of protection (NTZ, partial and unprotected areas), habitat structure and local human threats on four fish community metrics: total biomass, commercial fish biomass, mean trophic level and commercial fish mean size. If the protection afforded by the NTZ was significant, a second model was developed to evaluate design and management effectiveness. Total biomass, commercial fish biomass and mean trophic level were correlated significantly and positively with no-take protection; and, partially protected areas showed a significant and positive correlation with commercial fish biomass and mean trophic level. MPA age was the only significant and positive design and management characteristic that explained the variation in commercial fish biomass. This might be in part due to the suboptimal design of the MPA network that has mostly resulted from economic and social opportunities with little consideration for ecological guidelines and management capacities. Our findings suggest that to increase reef fish protection it would be necessary to include reef habitats with high coral cover and structural complexity inside NTZs. However, the effectiveness of an MPA network not only requires ecological considerations but also factors that include compliance, enforcement and true community participation to achieve greater benefits. Policymakers must ensure adequate design and management of MPAs in order to improve the effectiveness of marine resource protection, promoting both sustainable use and long-term biodiversity conservation.

Macroinvertebrate and Fish Community Metrics: Confounding Effects and Consistency over Time

Macroinvertebrate and fish metrics are an essential tool in freshwater biomonitoring. Yet, many well-known stream metrics do not perform well as indicators of anthropogenic stress in lakes and wetlands, and there is a need to better understand the role of potential confounding factors such as latitude or environmental variables acting at regional scales. We attempt to untangle the relationships among metrics and watershed stressors while accounting for potential confounding factors using hierarchical partitioning, and test metric consistency across time, focusing on the Laurentian Great Lakes wetland monitoring programs conducted 10 years apart. Our results show that many frequently used metrics have high temporal variability and are significantly affected by spatial factors, most notably richness-type metrics used in numerous regional monitoring studies. Only a few metrics (invasive fish species richness and relative abundance, mayfly family richness and the relative abundance of Ephemeroptera, Trichoptera, Sphaeriidae and Odonata) had slightly better and more consistent correlations with watershed land use. We suggest that explicit consideration of confounding factors is essential in the context of large-scale monitoring programs, and focus on the less general (such as habitat-specific) metrics may be a more promising approach.

Diel patterns in spatial distribution of fish assemblages in lentic and lotic habitat in a regulated river

AbstractFish assemblages in large rivers are governed by spatio‐temporal changes in habitat conditions, which must be accounted for when designing effective monitoring programmes. Using boat electrofishing surveys, this study contrasts species richness, catch per unit effort (CPUE), total biomass, and spatial distribution of fish species in the Saint John River, New Brunswick, Canada, sampled during different diel periods (day and night) and macrohabitats (hydropower regulated river and its reservoir) in the vicinity of the Mactaquac (hydropower) Generating Station. Taxa richness, total CPUE, and total biomass were significantly higher during night surveys, resulting in marked differences in community composition between the two diel periods. Furthermore, the magnitude of diel differences in catch rate was more pronounced in lentic than in lotic macrohabitats. The required sampling effort (i.e., number of sites) to increase accuracy and precision of CPUE estimates varied widely between fish species, diel periods, and macrohabitats and ranged from 15 to 185 electrofishing sites. Determining a correction factor to contrast accuracy and precision of day‐ with night‐time surveys provide useful insights to improve the design of long‐term monitoring programmes for fish communities in large rivers. The study also shows the importance of multihabitat surveys to detect differences in the magnitude of diel changes in fish community metrics.

Flat and complex temperate reefs provide similar support for fish: Evidence for a unimodal species-habitat relationship.

Structural complexity, a form of habitat heterogeneity, influences the structure and function of ecological communities, generally supporting increased species density, richness, and diversity. Recent research, however, suggests the most complex habitats may not harbor the highest density of individuals and number of species, especially in areas with elevated human influence. Understanding nuances in relationships between habitat heterogeneity and ecological communities is warranted to guide habitat-focused conservation and management efforts. We conducted fish and structural habitat surveys of thirty warm-temperate reefs on the southeastern US continental shelf to quantify how structural complexity influences fish communities. We found that intermediate complexity maximizes fish abundance on natural and artificial reefs, as well as species richness on natural reefs, challenging the current paradigm that abundance and other fish community metrics increase with increasing complexity. Naturally occurring rocky reefs of flat and complex morphologies supported equivalent abundance, biomass, species richness, and community composition of fishes. For flat and complex morphologies of rocky reefs to receive equal consideration as essential fish habitat (EFH), special attention should be given to detecting pavement type rocky reefs because their ephemeral nature makes them difficult to detect with typical seafloor mapping methods. Artificial reefs of intermediate complexity also maximized fish abundance, but human-made structures composed of low-lying concrete and metal ships differed in community types, with less complex, concrete structures supporting lower numbers of fishes classified largely as demersal species and metal ships protruding into the water column harboring higher numbers of fishes, including more pelagic species. Results of this study are essential to the process of evaluating habitat function provided by different types and shapes of reefs on the seafloor so that all EFH across a wide range of habitat complexity may be accurately identified and properly managed.