High Fish Biomass Research Articles

Genomics of a novel ecological phase shift: the case of a ‘weedy’ Montipora coral in Ulithi, Micronesia

Local and global ecological stressors are leading to increased documentation of phase shifts in coral reefs from healthy stony corals to macrophytes. In more rare cases, phase shifts result in sponge, zoantharian or other dominant species. In Ulithi Atoll, Federated States of Micronesia, we have documented an unusual phase shift from reefs with a diverse stony coral assemblage to reefs dominated by a single species of stony coral: Montipora sp.—a coral-to-coral phase shift. This monospecific type of reef lowers fish diversity and biomass, impacting both ecological integrity, and livelihoods of reef-dependent human communities. In this study, we used a genomic approach to characterize such a reef. We assembled a de-novo reference genome and used RAD seq data with thousands of SNPs to determine if different reefs result from sexual or asexual reproduction, if weedy Montipora fragments are transported between islands by human activities, and if there is evidence of natural selection on specific genotypes, thus favoring spreading success. We found that sexual reproduction is predominant in the focal species, that there is no evidence of human-mediated spread, and that some genomic regions might be under selection. While such results eliminate a number of spreading hypotheses, more precise dispersal maps will be important to determine the tempo and mode of ‘invasion’ of Montipora in Ulithi Atoll. This study shows that selection and adaptation may be contributing to the success of a stony coral (e.g., Phase shift). While a stony coral may be successful in a disturbed environment, it does not necessarily provide the type of habitat that is conducive to high fish biomass and coral diversity. These results serve as a cautionary tale for restoration efforts that focus on single species coral resilience rather than ecosystem function.

Estimation of The Potential of Large Pelagic Fish Fisheries Using Satellite Data in The Banda and Arafura Seas

The Banda and Arafura Sea possesses significant potential for the fisheries and fishing industry in the country. The large pelagic fish production data studied were derived from satellite imagery data in the Banda and Arafura Seas (2002-2022). The data of chlorophyll-a content, sea surface temperature and Photosynthetically Available Radiation (PAR) derived from AQUA MODIS satellite images were used to estimate the value of primary productivity with the Vertically Generalised Production Model (VGPM). The results showed that the biomass of large pelagic fish fluctuated seasonally, with the Banda Sea and Arafura Sea having high average fish biomass values in the eastern season. With the highest fish biomass peak in August and the lowest in December. The high value of fish biomass in the Banda Sea and Arafura Sea is caused by upwelling events where sea surface temperatures are low but chlorophyll is high. in the Arafura Sea the value of fish biomass is higher than the Banda Sea, this is due to the large amount of nutrient input from large rivers in the area.

Stocking density optimisation of pangasius (Pangasianodon hypophthalmus) fingerlings with basil (Ocimum basilicum L.) in nutrient film technique (NFT) based aquaponics

An experiment for 90 days was performed to optimise the stocking density of pangasius(Pangasianodon hypophthalmus) with basil (Ocimum basilicum L.) in a nutrient film technique(NFT) based aquaponics. The experiment had four treatments with different stockingdensities of pangasius as T1 (2.5 kg m-3), T2 (2.75 kg m-3), T3 (3.0 kg m-3) and T4 (3.25 kg m-3)with a constant plant density of 24 plants m-2 and control viz., C (2.5 kg m-3 withoutplants). Significant (p<0.05) difference in final body weight of fish was found among thetreatments and control. The highest fish biomass was recorded in T3 (10.29±4.41 kg m-3)followed by T4, T2, T1 and C. The highest plant yield was found in T4 (510.90±6.25 g);however, no significant difference was found between T4 and T3. No significant (p>0.05)difference in macro and micronutrient content of basil leaves was recorded in T4 and T3.The physiological parameters (hematological, serum biochemical and anti-oxidant stressenzymes) were found to be within the acceptable range. Considering the water qualityparameters, fish growth, total biomass of fish, fish physiological responses, basil yield andnutrient content, the stocking density of 3.00 kg m-3 (pangasius) with 24 plants m-2 of basilcould be recommended for basil-pangasius aquaponics. Keywords:Aquaponics, Aquaculture wastewater, Basil,Nutrient film technique, Pangasius

Strong hydrodynamic drivers of coral reef fish biodiversity on submerged pinnacle coral reefs

AbstractHydrodynamic processes are important in all marine environments and on coral reefs drive patterns of habitat zonation, community structure, and biodiversity. Abrupt geomorphological features like pinnacles and seamounts often possess distinct localized currents and these habitats are also often characterized by high abundance and biomass of fishes. However, differences in fish community structure between pinnacles and emergent reefs, and their key drivers are poorly understood. In this study, we compared fish communities among emergent fringing and offshore coral reefs, and submerged pinnacle reefs in Papua New Guinea. Submerged pinnacles possessed higher fish biomass, abundance, and species richness than both fringing and offshore emergent reefs. We collected in‐situ current speed and temperature data over a full year at each reef and used random forest analysis to investigate the relative influence of hydrodynamics compared to other well‐established drivers of reef fish biodiversity, including habitat and biogeographic factors. Environmental variables explained 70%, 52%, and 5% of variability in models for species richness, abundance and biomass respectively. In all models, average current speed, current speed variability, and reef area were consistently among the most influential variables. Models examining relationships between fish biodiversity metrics and current speed did not yield conclusive results but did highlight the association of distinct hydrodynamic regimes on pinnacles with high fish richness, abundance, and biomass. Our study highlights the strong influence of reef‐scale hydrodynamics on fish biodiversity and demonstrates the ecological value of small, submerged coral reefs, which are globally numerous yet remain understudied in coral reef ecology.

Quantifying endolithic bioerosion rates on remote coral reefs in the Central Indian Ocean

Bioerosion of calcium carbonate is a fundamental process that impacts net coral reef accretion. Besides large grazers, endolithic organisms play a major role in carbonate removal. Here we provide the first rate data for both macro- and microendolithic bioerosion in the remote Chagos Archipelago, Indian Ocean. Based on analysis of experimental blocks using computer tomography, we show similar macrobioerosion rates at 5 m (0.086 ± 0.026 kg m−2 yr−1) compared to at 10 m depth (0.066 ± 0.016 kg m−2 yr−1) after three years of exposure, with a succession from worm to sponge bioeroders over time. Microbioerosion rates analysed with scanning electron microscopy were 2–5 × higher than macrobioerosion rates at 5 m (0.187 ± 0.028 kg m−2 yr−1) and 10 m depth (0.313 ± 0.049 kg m−2 yr−1), but the microborer community was dominated by cyanobacteria in all samples. Total endolithic erosion was small compared to external erosion by parrotfishes, which increased over time, but did not show significant differences between 5 m (0.74 ± 0.11) and 10 m depth (1.12 ± 0.16 kg m−2 yr−1) after three years of exposure. These erosion rates are indicative of the oligotrophic and remote reef setting in the Chagos Archipelago (clear water, low nutrients, high fish biomass). The data will help to improve local carbonate budget estimates and provide a context for wider regional and environmental comparisons.

Defining multi-scale surface roughness of a coral reef using a high-resolution LiDAR digital elevation model

A decline in coral reef surface roughness may indicate that a coral reef ecosystem is approaching functional collapse. This is because surface roughness underpins many critical ecosystem metrics, such as, live coral cover and high fish biomass. Yet, we understand very little about how surface roughness changes at ecosystem scales due to the limited spatial extents of coral reef ecological surveys. Here, we investigate the surface roughness of a coral reef across multiple spatial scales on a high-resolution Light Detection and Ranging (LiDAR) derived digital elevation model (DEM, 0.25 m cells). We found that complex features dominated regions with high roughness (e.g., spur and groove systems on the reef slope) and increased the average roughness of geomorphic zones that are otherwise flat and featureless (e.g., lagoonal patch reefs in the sandy deep lagoon). Each geomorphic zone had a unique signature with high values of roughness usually expressed over finer spatial scales and, conversely, lower values of roughness observed over broader spatial scales. We allocated each geomorphic zone into one of four roughness equivalent habitats (REHs 1–4) that share similar surface roughness properties but are not necessarily geographically contiguous regions. These results identify fine scale features and geomorphic zones that are important for providing roughness to coral reef systems, such as spur and groove systems and the fore-reef slope respectively. They also suggest that morphodynamic processes operating at broader spatial scales influence the physical structure of coral reef ecosystems. The quantification of coral reef surface roughness is becoming increasingly important due to the wider availability of high (<1 m) and hyper (<0.1 m) resolution DEMs. Our approach and findings here can be used to provide greater surface textural information for common coral reef geomorphic zones and aid future management and research efforts, such as, monitoring of coral reef ecosystem response to environmental change and reef restoration and adaptation programs.

Unusual high fish biomass suggests healthy conditions in a Mexican reef on the southern Gulf of Mexico

Reef health can be assessed from the fish biomass (roving herbivorous and predatory commercial species). In this preliminary note, the biomass of fish indicators of a healthy reef of Blake Reef, Veracruz, is estimated and compared with that recorded in other systems in the southern Gulf of Mexico. The size and abundance of fish observed in Blake Reef determine a remarkable biomass that exceeds the estimates of other reefs. The health of this reef makes it an important reservoir of regional diversity.

Viral predation pressure on coral reefs

BackgroundPredation pressure and herbivory exert cascading effects on coral reef health and stability. However, the extent of these cascading effects can vary considerably across space and time. This variability is likely a result of the complex interactions between coral reefs’ biotic and abiotic dimensions. A major biological component that has been poorly integrated into the reefs' trophic studies is the microbial community, despite its role in coral death and bleaching susceptibility. Viruses that infect bacteria can control microbial densities and may positively affect coral health by controlling microbialization. We hypothesize that viral predation of bacteria has analogous effects to the top-down pressure of macroorganisms on the trophic structure and reef health.ResultsHere, we investigated the relationships between live coral cover and viruses, bacteria, benthic algae, fish biomass, and water chemistry in 110 reefs spanning inhabited and uninhabited islands and atolls across the Pacific Ocean. Statistical learning showed that the abundance of turf algae, viruses, and bacteria, in that order, were the variables best predicting the variance in coral cover. While fish biomass was not a strong predictor of coral cover, the relationship between fish and corals became apparent when analyzed in the context of viral predation: high coral cover (> 50%) occurred on reefs with a combination of high predator fish biomass (sum of sharks and piscivores > 200 g m−2) and high virus-to-bacteria ratios (> 10), an indicator of viral predation pressure. However, these relationships were non-linear, with reefs at the higher and lower ends of the coral cover continuum displaying a narrow combination of abiotic and biotic variables, while reefs at intermediate coral cover showed a wider range of parameter combinations.ConclusionsThe results presented here support the hypothesis that viral predation of bacteria is associated with high coral cover and, thus, coral health and stability. We propose that combined predation pressures from fishes and viruses control energy fluxes, inhibiting the detrimental accumulation of ecosystem energy in the microbial food web.

Homogenisation of water and sediment bacterial communities in a shallow lake (lake Balihe, China)

Abstract Planktonic and benthic bacterial communities hold central roles in the functioning of freshwater ecosystems and mediate key ecosystem services such as primary production and nutrient remineralisation. Although it is clear that such communities vary in composition both within and between lakes, the environmental factors and processes shaping the diversity and composition of freshwater bacteria are still not fully understood. In order to assess seasonal and spatial variability in lake bacterial communities and identify environmental factors underpinning biogeographical patterns, we performed a large‐scale sampling campaign with paired water and sediment sample collection at 18 locations during four seasons in Lake Balihe, a subtropical shallow fish‐farming lake in mid‐eastern China. Pelagic and benthic bacterial communities were distinctly different in terms of diversity, taxonomic composition and community structure, with Actinobacteria, Bacteroidetes, Cyanobacteria and Alphaproteobacteria dominating lake water, and Acidobacteria, Bacteroidetes, Chloroflexi, Gammaproteobacteria and Deltaproteobacteria dominating sediment. Nevertheless, these two communities had stronger spatial concordance and overlap in taxa during spring and autumn seasons. Together, the main drivers of both the spatial and temporal variations in Lake Balihe bacterial communities were identified as water temperature, turbidity, nitrogen and phosphorus availability, and thermal stratification controlled by wind‐mixing and activity of the dense farmed fish populations. Notably, populations affiliated with Firmicutes, known to be abundant in fish gut microbiome, were especially abundant in the summer season and locations where high fish biomass was found, suggesting a potential link between fish gut microbiome and the pelagic bacterial communities. Our findings demonstrated seasonal homogenisation of pelagic and benthic bacterial communities linked to marked shifts in a set of seasonally‐driven environmental variables including water temperature and nutrient availability.

The coastal design of the Sumur Tiga beach as a coastal tourism destination

The East Coast of Weh Island, Aceh has good ecological conditions with high coral fish biomass. The coastal tourism activities spread over the east coast of Weh Island, especially at Sumur Tiga Beach. The tourism activities in Weh Island especially Sumur Tiga Beach can certainly contribute to the development and economic sectors and also have an impact on the surrounding environment. Thus, an alternative landscape design is needed for structuring the site to create environmental preservation, and sustainable tourism. This study aims to identify the elements and characteristics of the site, analyze-synthesize the potential and constraints of its coastal landscape, and create the concept and design of the landscape. The study was located in Sumur Tiga Beach, Sabang City, Ie Maulee District, Sukajaya Village, Weh Island, Aceh. The method includes several aspects, such as physical and biophysical, tourism, social, and hydro oceanography which is using both qualitative and quantitative descriptive and spatial analysis. The basic concept is “Adat ngon hukom lagee dzat ngon sifeuet” which is implemented into three concepts, such as hablumminallah, hablumminannas, and hablumminalalam. This concept is used to determine the design concept. then the development concept and block plan are determined then used as a reference in developing alternative designs for the site. And from these alternatives, the final design for the site is concluded. The design concept is a metaphor of “Ragam Hias” refer to the Acehnese motifs, such as pucuk reubong, awan si on, awan meucanek, putra taloe dua, and sulur. Such as gazebo, main gate, main hall, main signage by a form that comes from a pucuk reubong motif with the additional pattern of acehnese culture, also plantation and circulation patterns using a combination of pucuk reubong, awan si on, awan meucanek, putra taloe dua, and sulur motifs. There are also seawalls on the shoreline to avoid abrasion due to high sea waves and wind speeds that blow quite fast during the east season.

Effect of density and mixed culture of largemouth bass (Micropterus salmoides) and pikeperch (Sander lucioperca) on growth, survival and feed conversion rate in intensive culture

In this study, two experiments were performed with the aim to optimize intensive aquaculture of largemouth bass (Micropterus salmoides). In the first 140-day experiment the effect of the initial fish density was assessed at three levels: low density (LD) 23 kg/m&lt;sup&gt;3&lt;/sup&gt;, medium density (MD) 35 kg/m&lt;sup&gt;3&lt;/sup&gt; and high density (HD) 46 kg/m&lt;sup&gt;3&lt;/sup&gt;. All three densities provided the same final Fulton’s condition coefficient (FC = 1.24–1.28), specific growth rate (SGR = 0.22–0.24%/day) and survival rate (97–100%). No cannibalism was observed at all tested densities. Feed conversion ratio (FCR = 1.39 ± 0.21 g/g) was the lowest for LD and the highest (1.61 ± 0.08 g/g) for MD. The highest fish biomass (25.7 ± 2.7 kg/m&lt;sup&gt;3&lt;/sup&gt;) was obtained at HD and this density was considered as the most effective density of all tested ones during the intensive culture of largemouth bass. The second 60-day experiment tested the effect of largemouth bass and pikeperch (Sander lucioperca) monoculture and biculture of both species on production efficiency. Higher size heterogeneity was obtained in both (mono- and bicultural) groups of pikeperch (308.91–314.56‰/day) compared to the groups of largemouth bass (279.26–284.05 ‰/day). The higher FC (1.09) was found in both types of culture in largemouth bass compared to both methods of culture in pikeperch (0.74–0.78). The lowest SGR was evident in both types of largemouth bass cultures (1.20–1.28%/day). In contrast, the highest SGR was achieved in the bicultural pikeperch (1.88%/day). Similar results like for SGR were also assessed for FCR, where the highest value of FCR was in both cultures of largemouth bass (1.44–1.48 g/g) compared to the lowest FCR in the bicultural of pikeperch (0.73 g/g). Largemouth bass in both tested types of culture had higher survival rates (99.95–99.99%) compared to pikeperch (98.61–98.63%).

Application of an unsupervised clustering algorithm on in situ broadband acoustic data to identify different mesopelagic target types

Abstract The mesopelagic zone (200–1000 m depth) contains high fish species diversity but biomass and abundances are uncertain yet essential to understand ecosystem functioning. Hull-mounted acoustic systems (usually 38 kHz) often make assumptions on average target strength (TS) of mesopelagic fish assemblages when estimating biomass/abundance. Here, an unsupervised clustering algorithm was applied on broadband acoustic data (54–78 kHz), collected by a towed instrumented platform in the central Northeast Atlantic, to identify different mesopelagic target types based on similarity of individual TS spectra. Numerical density estimates from echo-counting showed spatial differences in vertical distribution patterns of the different target types and TS spectra data suggested that &amp;gt;30% of the gas-bearing targets had high resonance frequencies (&amp;gt;60 kHz) with low scattering strength at 38 kHz. This conceptual study highlights the importance of separating targets into different target groups to obtain correct backscatter information and to account for all relevant scatterers when estimating average TS at 38 kHz, in order to achieve more accurate biomass/abundance estimates. It furthermore demonstrates the use of a towed broadband acoustic platform for fine-scale numerical density estimates as a complementary method to hull-mounted acoustic data to increase knowledge on mesopelagic ecosystem structure.

Filter-feeding fish (Hypophthalmichthys molitrix) mediated phosphorus recycling versus grazing pressure as drivers of the trophic cascade in large enclosures subsidized by allochthonous detritus

Stocking of filter-feeding fish is a common tool used in (sub)tropical Chinese reservoirs to control phytoplankton. However, field investigations have showed that such stocking would enhance instead of controlling phytoplankton in these reservoirs. Reservoirs generally receive a considerable amount of detritus from their catchments which may constitute an important carbon source to filter-feeding fish. Whether direct consumption of detritus increases the availability of dissolved inorganic phosphorus (P) to phytoplankton and thereby provides resilience against the control of phytoplankton biomass is debated. We conducted an enclosure experiment in a (sub)tropical Chinese reservoir (Liuxihe Reservoir) to assess how a gradient of filter-feeding fish (Silver Carp Hypophthalmichthys molitrix) biomass affected P dynamics and fish grazing and predation when subsidized by allochthonous detritus. Fish had strong effects on the dynamics and fluxes of P. TP concentration in the water column increased over time in all enclosures, but the presence of fish slowed its increase. Thus, TP decreased with increasing fish biomass. Fish were a net sink of P to the water column, because they gained mass during the experiment. Moreover, P sequestered by fish could largely account for the lower TP concentrations observed in enclosures with fish compared to fishless enclosures. Fish presence at high biomass strongly reduced the abundance of large zooplankton species and P excretion by zooplankton. However, the negative effect of fish predation on zooplankton was negligible when fish was present at low biomass. Increasing fish biomass increased the relative role of fish in P cycling but decreased the overall P excretion by fish and zooplankton. Compared to enclosures with high fish biomass, both zooplankton grazing effect on phytoplankton (zooplankton: phytoplankton biomass ratio as a proxy) and the overall P excretion were much higher, whereas fish grazing effect on phytoplankton (fish: phytoplankton biomass ratio as a proxy), chlorophyll a and the yield of chlorophyll a per TP were much lower in enclosures with low fish biomass. This suggested that phytoplankton limitation might shift from one of zooplankton control to one of limitation by P availability with increasing fish biomass. Relative to fish mediated P recycling and fish grazing, zooplankton grazing appeared to be more important as a driver of trophic cascades in systems subsidized by allochthonous detritus. Silver Carp stocked at high biomass would strongly reduce zooplankton grazing pressure and increase the yield of phytoplankton per TP.

Seasonal Dynamics Are the Major Driver of Microbial Diversity and Composition in Intensive Freshwater Aquaculture.

Aquaculture facilities such as fishponds are one of the most anthropogenically impacted freshwater ecosystems. The high fish biomass reared in aquaculture is associated with an intensive input into the water of fish-feed and fish excrements. This nutrients load may affect the microbial community in the water, which in turn can impact the fish health. To determine to what extent aquaculture practices and natural seasonal cycles affect the microbial populations, we characterized the microbiome of an inter-connected aquaculture system at monthly resolution, over 3 years. The system comprised two fishponds, where fish are grown, and an operational water reservoir in which fish are not actively stocked. Clear natural seasonal cycles of temperature and inorganic nutrients concentration, as well as recurring cyanobacterial blooms during summer, were observed in both the fishponds and the reservoir. The structure of the aquatic bacterial communities in the system, characterized using 16S rRNA sequencing, was explained primarily by the natural seasonality, whereas aquaculture-related parameters had only a minor explanatory power. However, the cyanobacterial blooms were characterized by different cyanobacterial clades dominating at each fishpond, possibly in response to distinct nitrogen and phosphate ratios. In turn, nutrient ratios may have been affected by the magnitude of fish feed input. Taken together, our results show that, even in strongly anthropogenically impacted aquatic ecosystems, the structure of bacterial communities is mainly driven by the natural seasonality, with more subtle effects of aquaculture-related factors.

Diversity pattern and juvenile fish assemblage in the nearshore habitats of the Sumbawa Island, Indonesia

The coastal ecosystem plays a vital role as essential habitat for juvenile and small marine fishes. This study aimed to analyze juvenile and small-sized fish assemblage in the nearshore habitats of Sumbawa Island. Sampling was carried out in the morning at low tide when new and full moon from November 2020 to January 2021. Five sampling sites were selected based on habitats their adjacency to the river mouth. During the study period, 6349 individuals belonging to 74 species and 37 families were recorded. The number ofAmbassis vachelliiwas the most significant, followed byHypoatherina temminckii, andEubleekeria splendens. The highest fish biomass was occupied by E. splendens, followed by Plotosus lineatus, andPlaniliza macrolepis. Physico-chemical parameters were not varied between sampling sites, except salinity. Estuaries with vegetated areas have a higher species richness, diversity, and evenness index than the unvegetated area. Juvenile and small-sized fishes varied between sites but not varied between moon phases. Research findings confirm that the nearshore habitat of Sumbawa Island has a significant capacity to support the early life stage of many marine fish species.

Applying a Social–Ecological Systems Approach to Understanding Local Marine Management Trajectories in Northern Mozambique

This study applied the social–ecological systems framework (SESF) to six fishing communities in northern Mozambique where marine resource management is being implemented through the Our Sea Our Life project. Data on 11 variables and 27 indicators were organised using the SESF to represent the key system dimensions (Governance system, Actors, Resource units and Resource system). Variables within each dimension were weighed to a cumulative score of one. High scores (&gt; 0.50) for Governance system occurred where communities had fisheries management rules and good knowledge of fishing gear regulations. High scores for Actors were evident in communities with few migrant fishers and high participation in village savings and loans associations. Elevated scores of the Resource units occurred where fishers targeted a variety of fish taxa. A healthy Resource system was found in communities neighbouring highly productive and resilient reefs, characterised by high fish biomass and diversity. The status of social and ecological conditions coupled with initial levels of project support and quality of technical support were linked with project achievements. Application of the SESF is therefore valuable in understanding interdependent linkages between social and environmental conditions to inform the design of localised management interventions for social–ecological sustainability.

Reduced abundance but increased diversity of chironomid larvae under higher trophic pressure from fish in semi-permanent ponds

Fish may affect macrobenthic communities through trophic interactions and modification of habitat conditions. We compared the density, diversity and taxonomic composition of larval chironomids under low vs high fish impact, created by stocking semi-natural ponds with either young/small common carp Cyprinus carpio at low biomass densities or with high biomass densities of older/large common carp, supplemented by other cyprinids and predatory fish species.Over the study season, May–August, total chironomid abundance was considerably lower in ponds with high fish biomass than in low fish biomass ponds. In July–August larval densities declined significantly, irrespective of the fish status of the ponds. The composition of larval communities diverged between ponds with different fish status. Chironomus riparius and C. plumosus accounted for most of the observed dissimilarity. C. plumosus densities were not affected by the fish status of the pond, constituting on average >38 % of chironomid specimens in both types of ponds. C. riparius was abundant in ponds with low fish biomass (on average 30 %), but rare in ponds with high fish biomass (4 %). Other common taxa were Glyptotendipes pallens (15 % and 13 %, respectively) and Procladius sp. (14 % in ponds with low fish impact). Canonical correspondence analysis showed that fish biomass was more important in determining chironomid community composition than environmental variables indicative of pond eutrophication (total N, P, chlorophyll a and conductivity).Despite adverse effects on total abundance, chironomid diversity was higher under apparently stronger trophic pressure by fish. Fish may have relieved some chironomid species from invertebrate predation and competition with dominant Chironomus larvae. Other important drivers of chironomid assemblage and diversity patterns may include species-specific feeding modes and prey size selectivity of fish, the ability of chironomid larvae to attain size- and depth-refuge from small fish but not larger fish, and differential vulnerability of free-living and tube-dwelling larvae relative to ontogenetic niche shifts of fish.

Influence of Local Habitat and Climatic Factors on the Distribution of Fish Species in the Tonle Sap Lake

Tonle Sap Lake (TSL) is a highly productive system and hosts a high fish diversity and is of paramount importance for sustaining protein supply for over 15 million Cambodians. Nevertheless, the ecology and factors influencing the spatial distribution of many fishes within the lake remain poorly understood. Using commercial fishing lot catch data from 1994/1995 to 1999/2000, fishing seasons and environmental data (land cover and bioclimatic variables), we describe spatial distribution of the eight most commercially important fish species, and investigate the effects of environmental factors on their distributions in the TSL. We found a strong variability in fish biomass across areas and between species. Specifically, Channa micropeltes was most abundant in the southern and northern sections of the TSL. Channa striata and Trichopodus microlepis were more common in the northern part of the TSL. Cyclocheilos enoplos, Barbonymus gonionotus, Pangasianodon hypophthalmus, and Gymnostomus spp. were abundant in the southern areas of the TSL while Phalacronotus spp. were abundant in few areas in both the north and the south. Flooded forest positively explained the variation in the biomass of P. hypophthalmus, C. striata, C. enopolos, and Phalacronotus spp. Likewise, the lake’s open water positively affects the biomass of P. hypophthalmus, C. enopolos, and Phalacronotus spp., while the agricultural field negatively impacts Gymnostomus spp. biomass distribution. We also found that some areas consistently hosted high fish biomass (e.g., lot 2, Kampong Thom; lot 6, Pursat; lot 2, Battambang, etc.). We, therefore, suggest that fisheries management and conservation planning focus on those areas, considering those areas significance as core fish habitat and important for catching fish.

Regional environmental variation and local species interactions influence biogeographic structure on oyster reefs.

Although species interactions are often assumed to be strongest at small spatial scales, they can interact with regional environmental factors to modify food web dynamics across biogeographic scales. The eastern oyster (Crassostrea virginica) is a widespread foundational species of both ecological and economic importance. The oyster and its associated assemblage of fish and macroinvertebrates is an ideal system to investigate how regional differences in environmental variables influence trophic interactions and food web structure. We quantified multiple environmental factors, oyster reef properties, associated species, and trophic guilds on intertidal oyster reefs within 10 estuaries along 900km of the southeastern United States. Geographical gradients in fall water temperature and mean water depth likely influenced regional (i.e., thenorthern, central and southern sections of the SAB)variation in oyster reef food web structure. Variation in the biomass of mud crabs, an intermediate predator, was mostly (84.1%) explained by reefs within each site, and did not differ substantially among regions; however, regional variation in the biomass of top predators and of juvenile oysters also contributed to biogeographic variation in food web structure. In particular, region explained almost half (40.2%) of the variation in biomass of predators of blue crab, a top predator that was prevalent only in the central region where water depth was greater. Field experiments revealed that oyster mortality due to predation was greatest in the central region, suggesting spatial variation in the importance of trophic cascades. However, high oyster recruitment in the middle region probably compensates for this enhanced predation, potentially explaining why relatively less variation (17.9%) in oyster cluster biomass was explained by region. Region also explained over half of the variation in biomass of mud crab predators (55.2%), with the southern region containing almost an order of magnitude more biomass than the other two regions. In this region, higher water temperatures in the fall corresponded with higher biomass of fish that consume mud crabs and of fish that consumejuvenile and forage fish, whereas biomas oftheir prey (mud crabs and juvenile and forage fish, respectively)was generally low in the southern region. Collectively, these results show how environmental gradients interact with trophic cascades to structure food webs associated with foundation species across biogeographic regions.

Harmful Cyanobacteria in Three Oregon Lakes: Comments on Hall et al. Beyond Water Quality Advisories and Total Maximum Daily Loads (TMDLs). Water 2019, 11, 1125

The article “An Ecological Function Approach to Managing Harmful Cyanobacteria in Three Oregon Lakes: Beyond Water Quality Advisories and Total Maximum Daily Loads (TMDLs), Water 11:1125” by Hall et al. critiques the current approach used by the state of Oregon with regard to managing cyanobacterial blooms and offers the proper functioning condition (PVC) as a superior method of managing cyanobacterial blooms in lakes derived from nonpoint sources of pollution. They evaluated three lakes in Oregon as examples of how this approach could be applied to support water quality improvement. Two of the three lakes, Lemolo and Diamond, experienced cyanobacterial blooms, not as a function of nonpoint source loadings from the watershed, but rather because of internal nutrient cycling associated with high fish biomass. The third lake, Tenmile Lakes, in additional to having a greatly altered fish community, also experiences cyanobacterial blooms (CyanoHABs) issues because of timber harvest on steep slopes, loss of wetlands, altered watershed hydrology and nutrient input from septic systems. The authors’ attempts to use satellite images and PVC methodology on the stream networks is incomplete with respect to Tenmile Lakes and is totally misdirected regarding Lemolo and Diamond Lakes. Although I don’t support the current system employed by the state of Oregon to manage lakes experiencing CyanoHABs issues, the proposed approach offered by staff with the U.S. Environmental Protection Agency will yield little water quality benefit for the lakes in question.