Lake Habitats Research Articles

Nutrients limiting the growth of planktonic and benthic-littoral primary producers in Patagonian Andean Lakes

In this work, we assess differences in nutrient limitation (nitrogen and phosphorus) between benthic-littoral (in the littoral habitat) and planktonic (in the epi-pelagic habitat) primary producers of seven Patagonian Andean lakes in southern South America. We conducted nutrient enrichment experiments using nitrate, ammonium, and phosphate to identify which nutrient(s) restrict primary producers’ growth in each lake habitat. Also, we determined the concentration of dissolved inorganic nitrogen (DIN), soluble reactive phosphorous (SRP), and the nitrogen to phosphorous ratio (DIN:SRP) at the littoral and epi-pelagic habitats of each lake. For all the lakes, benthic-littoral primary producers were limited by nitrogen, while planktonic primary producers in the epi-pelagic habitat were colimited by nitrogen and phosphorus. Our study is the first to show that different nutrients limit the growth of benthic-littoral and planktonic primary producers in Patagonian Andean lakes. This contributes to our understanding of lake ecology in a region where there is limited information on benthic-littoral habitats. This is important because globally, there is an increase in periphyton blooms in the benthic-littoral habitats of oligotrophic lakes, while the pelagic habitats remain unchanged. Additionally, we found nutrient concentrations in the lakes are up to 7.4 times higher than those described in previous studies, which may be related to anthropogenic impact and natural events. If nutrient levels continue to increase, algal blooms in Patagonian Andean lakes may become a regional issue, especially in the benthic-littoral habitats.

Atmospheric CO2 absorption and counteraction by CH4 emission across contrasting habitats in a large eutrophic lake

Lakes are a crucial component of global carbon cycling and play a key role in the global CO2 and CH4 budgets. Intensified anthropogenic activity contributes to eutrophication, and reduces macrophytes while increasing phytoplankton in shallow lakes. However, the information on how the CO2 and CH4 fluxes at water–air interface temporally varies across habitats dominated by various primary producers in lakes and how CH4 emission counteracts CO2 adsorption is limited. In this study, in situ fluxes of CO2 and CH4 were measured monthly for one year at four sites in Lake Taihu, China. These sites had contrasting habitats dominated by high-density phytoplankton, low-density phytoplankton, floating-leaved macrophytes, and submerged macrophytes. We found that the CO2 fluxes ranged from − 439 ± 385 to − 106 ± 348μmol m−2h−1 and the CH4 fluxes ranged from 1.96 ± 3.79 to 10.7 ± 14.8μmol m−2h−1. The fluxes of CO2 and CH4 were mainly regulated by water pH, phosphorus levels, and sediment organic carbon. All four habitats acted as sinks of atmospheric CO2 and sources of atmospheric CH4, and the habitats with high-density phytoplankton showed the highest CO2 absorption and strongest CH4 emission. Generally, the CH4 emission counteracted 7–69 % of the atmospheric CO2 absorption in the four sites. These results collectively revealed that in a large, shallow eutrophic lake, habitats dominated by various primary producers consistently adsorb atmospheric CO2, even being counteracted by CH4 emission. These findings provide valuable insights for understanding carbon cycling and CO2 and CH4 dynamics across the water–air interface in shallow lakes.

Lake Trout (Salvelinus namaycush) origin, behavior, and habitat residency in Sherbrooke Lake, Nova Scotia, Canada

Lake Trout (Salvelinus namaycush) origin, behavior, and habitat residency in Sherbrooke Lake, Nova Scotia, Canada

Comparing seasonal heterogeneity of phytoplankton habitat and community in northern lakes with low to moderate but historically variable DOC concentrations

Comparing seasonal heterogeneity of phytoplankton habitat and community in northern lakes with low to moderate but historically variable DOC concentrations

Analysis of bacterial community structure, functional variation, and assembly mechanisms in multi-media habitats of lakes during the frozen period

Ice, water, and sediment represent three interconnected habitats in lake ecosystems, and bacteria are crucial for maintaining ecosystem equilibrium and elemental cycling across these habitats. However, the differential characteristics and driving mechanisms of bacterial community structures in the ice, water, and sediments of seasonally frozen lakes remain unclear. In this study, high-throughput sequencing technology was used to analyze and compare the structure, function, network characteristics, and assembly mechanisms of bacterial communities in the ice, water, and sediment of Wuliangsuhai, a typical cold region in Inner Mongolia. The results showed that the bacterial communities in the ice and water phases had similar diversity and composition, with Proteobacteria, Bacteroidota, Actinobacteria, Campilobacterota, and Cyanobacteria as dominant phyla. The bacterial communities in sediments displayed significant differences from ice and water, with Chloroflexi, Proteobacteria, Firmicutes, Desulfobacterota, and Acidobacteriota being the dominant phyla. Notably, the bacterial communities in water exhibited higher spatial variability in their distribution than those in ice and sediment. This study also revealed that during the frozen period, the bacterial community species in the ice, water, and sediment media were dominated by cooperative relationships. Community assembly was primarily influenced by stochastic processes, with dispersal limitation and drift identified as the two most significant factors within this process. However, heterogeneous selection also played a significant role in the community composition. Furthermore, functions related to nitrogen, phosphorus, sulfur, carbon, and hydrogen cycling vary among bacterial communities in ice, water, and sediment. These findings elucidate the intrinsic mechanisms driving variability in bacterial community structure and changes in water quality across different media phases (ice, water, and sediment) in cold-zone lakes during the freezing period, offering new insights for water environmental protection and ecological restoration efforts in such environments.

Biodiversity Assessment of a Mississippi River Backwater Complex Using eDNA Metabarcoding

The backwater lowland habitats of large rivers, like the Mississippi River in North America, present complex and often inaccessible environments for traditional capture-based fish biodiversity sampling. Our knowledge of the assemblages of the fishes that occupy such habitats is often incomplete, and this can compromise management efforts. We employed environmental DNA (eDNA) metabarcoding methods to sample a Mississippi River bottom wetland system to assess the ichthyofaunal diversity and the assemblage structure across habitat types, and we compared our results with capture-based survey records for the same habitats. We collected water samples in the spring and fall of 2022 from slough, ditch, shallow lake, and bayou habitats that varied in depth, vegetation, seasonal variability, and connectivity to the Mississippi River channel. We detected a diverse array of fish species that included 51 taxa. Nearly all the species previously documented in the habitats were detected using eDNA metabarcoding, and we increased the number of documented species by more than a third. Most of the species were ubiquitous across the range of habitats, but there was also a substantial assemblage structure, with some species exhibiting clear habitat specificity. Fall sampling was limited to the deeper bayou habitats where seasonal variation between the spring and fall was minimal. eDNA metabarcode sampling was demonstrated to be effective at detecting invasive species as well as uncommon species, which included several species of conservation concern.

Water temperature and salt ions respectively drive the community assembly of bacterial generalists and specialists in diverse plateau lakes

Plateau lakes (e.g., freshwater and saltwater lakes) are formed through intricate processes and harbor diverse microorganisms that mediate aquatic ecosystem functions. The adaptive mechanisms of lake microbiota to environmental changes and the ecological impacts of such changes on microbial community assembly are still poorly understood in plateau regions. This study investigated the structure and assembly of planktonic bacterial communities in 24 lakes across the Qinghai-Tibetan and Inner Mongolia Plateaus, with particular focus on habitat generalists, opportunists, and specialists. High-throughput sequencing of the 16S ribosomal RNA genes revealed that bacterial generalists had a lower species number (2196) but higher alpha diversity than the specialist and opportunist counterparts. Taxonomic dissimilarity and phylogenetic diversity analyses unraveled less pronounced difference in the community composition of bacterial generalists compared to the specialist and opportunist counterparts. Geographical scale (14.4 %) and water quality (12.6 %) emerged as major ecological variables structuring bacterial communities. Selection by water temperature and related variables, including mean annual temperature, elevation, longitude, and latitude, mainly shaped the assembly of bacterial generalists. Ecological drift coupled with selection by salt ions and related variables, including total phosphorus, chlorophyll a, and salinity, predominantly drove the assembly of bacterial specialists and opportunists. This study uncovers distinct bacterial responses to interacting ecological variables in diverse plateau lakes and the ecological processes structuring bacterial communities across various lake habitats under anthropogenic disturbance or climate change.

Precision mapping of snail habitat in lake and marshland areas: Integrating environmental and textural indicators using Random Forest modeling

Schistosomiasis japonica continues to pose a significant public health challenge in China, primarily due to the widespread distribution of Oncomelania hupensis, the sole intermediate host of Schistosoma. This study aims to address the constraints of existing remote sensing analyses for identifying snail habitats, which frequently neglect spatial scale and seasonal variations. To this end, we adopt a multi-source data-driven Random Forest approach that integrates bottomland and ground-surface texture data with traditional environmental variables, enhancing the accuracy of snail habitat assessments. We developed four distinct models for the lake and marshland areas of Guichi, China: a baseline model incorporating ground-surface texture, bottomland variables, and environmental variables; Model 1 with only environmental variables; Model 2 adding ground-surface texture and environmental variables; and Model 3 integrating bottomland with environmental variables. The baseline model outperformed the others, achieving a true skill statistic of 0.93, an accuracy of 0.97, a kappa statistic of 0.94, and an area under the curve of 0.99. Our analysis pinpointed critical high-risk snail habitats distributed in a belt-like pattern along major water bodies, near the Yangtze River, QiuPu River, and around Shengjin Lake, Jiuhua River, and Qingtong River. These insights can aid local health authorities in more efficiently allocating limited resources, developing effective snail surveillance and control strategies to combat schistosomiasis. Additionally, this approach can be adapted to localize other endemic hosts with similar ecological characteristics.

Documentation of a probable spawning run of cisco Coregonus artedi in the Spanish River, Ontario, Canada

Coregonines were historically diverse and abundant in the Laurentian Great Lakes but declined throughout the 19th and 20th centuries due to multiple factors, including overfishing, habitat degradation, and interactions with invasive species. Great Lakes fishery managers are now working to restore coregonines across the basin. An important aspect of restoration efforts is the identification of key habitats, such as spawning habitats. Our understanding of the extent and diversity of coregonine spawning habitats in the Great Lakes is limited. Historical accounts suggest some cisco Coregonus artedi migrated to tributaries to spawn, but contemporary runs have not been reported. Moreover, cisco display considerable phenotypic variation, with different “forms” often occupying specific habitats or regions. We provide evidence for a previously undocumented spawning run of cisco in the Spanish River, a tributary to the North Channel of Lake Huron. We captured 31 mature and ripe fish (25 males, 6 females) approximately 52 km upstream of the river mouth on 15–16 November 2022. The fish ranged in age from 3-9 yr and total length from 287-394 mm. Of these 31 individuals, 27 were morphologically similar to C. artedi manitoulinus, a subspecies of cisco found in the North Channel; however, four individuals more closely resembled cisco captured in other areas of Lake Huron. These findings represent the best evidence of tributary spawning by cisco since the 1880s, and they have important implications for coregonine conservation and restoration efforts. Ongoing work aims to augment our understanding of the ecological and evolutionary importance of this population.

Significant diurnal variations in nitrous oxide (N2O) emissions from two contrasting habitats in a large eutrophic lake (Lake Taihu, China)

Algae and macrophytes in lake ecosystems regulate nitrous oxide (N2O) emissions from eutrophic lakes. However, knowledge of diurnal N2O emission patterns from different habitats remains limited. To understand the diurnal patterns and driving mechanisms of N2O emissions from contrasting habitats, continuous in situ observations (72 h) of N2O fluxes from an algae-dominated zone (ADZ) and reed-dominated zone (RDZ) in Lake Taihu were conducted using the Floating Chamber method. The results showed average N2O emission fluxes of 0.15 ± 0.06 and 0.02 ± 0.04 μmol m−2 h−1 in the ADZ and RDZ in autumn, respectively. The significantly higher (p < 0.05) N2O fluxes in the ADZ were mainly attributed to differences in nitrogen (N) levels. The results also showed significant diurnal differences (p < 0.05) in the N2O emission fluxes within the ADZ and RDZ, and daytime fluxes were significantly higher (p < 0.05) than nighttime fluxes. The statistical results indicated that N2O emissions from the ADZ were mainly driven by diurnal variations in N loading and the dissolved oxygen (DO) concentration, and those from the RDZ were more influenced by DO, redox potential, and pH. Finally, we determined the proper time for routine monitoring of N2O flux in the two habitats. Our results highlight the importance of considering diverse habitats and diurnal variations when estimating N2O budgets at a whole-lake scale.

Comparing Sediment Bacterial Communities of Volcanic Lakes and Surrounding Rivers in Inner Mongolia Autonomous Region, Northeastern China.

Volcanic lakes originate from a volcanic crater or caldera, and were a crucial component of aquatic ecosystems. Sediment bacteria play an important role in the nutrient cycling of aquatic ecosystems; however, their patterns distribution in volcanic lakes and the surrounding river habitats are unknown. In this study, we compare the sediment bacterial communities and their co-occurrence networks between these two habitats in the Inner Mongolia Autonomous Region, Northeastern China (the Arxan UNESCO Global Geopark), using 16S rRNA gene amplicon sequencing. The results revealed that there were significant variations in the physicochemical parameters of the sediment between these two habitats. The bacterial α-diversity, β-diversity, and community composition of the sediment also significantly differed between these two habitats. Network analysis showed that the co-occurrence patterns and keystone taxa in the sediment differed between these two habitats. The sediment bacterial communities in the river habitats were more stable than those in the lake habitats in the face of environmental change. Canonical correspondence analysis demonstrated that both physical (pH and MC) and nutrition-related factors (TN, TP, LOI, and TOC) were the most important environmental factors shaping the variations of bacterial community composition (BCC) in the sediment between these two habitats. This work could greatly improve our understanding of the sediment BCC of the sediment from aquatic ecosystems in the UNESCO Global Geopark.

Lebertia litoralis sp. nov. a new water mite described on morphological and molecular characters (Acariformes, Hydrachnidia, Lebertiidae)

An integrative taxonomic approach, combining new morphological data with the analysis of partial COI sequences (DNA-barcodes) is used to describe Lebertia litoralis Zawal & Szenejko sp. nov. from lake habitats in Poland and Norway. The obtained DNA-barcodes of Polish and Norwegian specimens differ only slightly (k = 4.142, Π = 0.006). Morphologically, the new species is most similar to Lebertia porosa Thor, 1900 and L. obscura Thor, 1900, from which it differs by a slenderer shape of the first leg and the position of the distoventral setae of p-4, inserted rather far away from the distal segment edge. http://zoobank.org/urn:lsid:zoobank.org:pub:27F6FFD0-CA98-4FAD-BC16-58FA654E36ED

Breeding Common Scoters Melanitta nigra in Scotland’s Flow Country: a population in decline despite productivity being stable

ABSTRACT Capsule The breeding productivity of the Common Scoter population in Scotland’s Flow Country remained relatively stable during a 44% population decline in Britain and Ireland. Aim To investigate breeding productivity changes in the eastern Flow Country’s Common Scoter population over 22 years and identify possible threats and causes of change during a period of national population decline. Methods Common Scoters from 32 breeding sites were surveyed annually between 2002 and 2023. Each site was visited two to three times in May (pre-nesting period) and two to three times in July and August (post-hatching period) to record the numbers of adult and juvenile Common Scoters. Results Between 2002 and 2023, whilst the Common Scoter population declined (approximately 44% from 27 to 15 breeding pairs) across the study area, breeding productivity (defined as large ducklings per female) remained stable, averaging 0.44 (range of annual means 0.00–1.06) large ducklings per female. The number of small ducklings per female also remained relatively stable. A year of higher breeding productivity did not result in an increase in the number of breeding females in the following years, suggesting that the cause of the population decline lies away from the breeding region. Conclusion Breeding productivity needs to increase, and poor breeding seasons need to be prevented to help maintain this population. The causes of the Common Scoter’s decline away from the breeding area need to be resolved to prevent local extinction. This could be assisted with the removal of non-native forestry plantations in the area, which has been observed to benefit other ground-nesting species by alleviating predation pressure, and by maintaining lake habitat quality, as reflected in shallow water and abundant large invertebrates.

Populations of the stygobiotic amphipod Palearcticarellus pusillus (Martynov, 1930) maintain genetic connectivity between the mountain springs and the deep bottom habitats of Lake Teletskoye (Altai Mountains, Russia)

The diversity of underground fauna is often associated with the presence of karst areas, which have extensive underground cavities and connecting channels. Non-karst areas, however, make up a larger portion of the planet’ surface, and our understanding of the distribution and dispersal abilities of underground fauna in these areas currently remains limited. During a recent study of the diversity of stygobiotic crustaceans in the mountain streams of the Kurai Mountain Range (Altai, Russia), a small-sized species of crangonyctid amphipod, Palearcticarellus pusillus (Crustacea, Amphipoda, Crangonyctidae) was found in high-altitude springs. This species has been previously known only from deep-water habitats in Lake Teletskoye, and molecular genetic analysis revealed that these amphipods maintain genetic connections between the springs and bottom lake habitats. We assume that individuals of this certainly stygobiotic species fall to the bottom of the lake as a result of leaching from tectonic faults connecting these habitats and are not permanent inhabitants of the lake bottom. This hypothesis also suggests that the very small body size of these animals may be related to the narrow crevices and pores of the tectonic faults, rather than neoteny, as it has been previously suggested. The estimated divergence time calculation has also revealed that P. pusillus obviously diverged from its sister species, Palearcticarellus mikhaili from valley springs in Kurai Steppe, ~5 Ma, at the beginning of the Pliocene, possibly due to the uplifting of the Kurai Mountain Range. Subsequent speciation occurred as a result of secondary tectonic activity and changes in groundwater flow, likely during the Pleistocene, approximately 2.7–0.7 Ma. Populations that were isolated for a long time continue to live near mountain springs in the study area.

Identification of fish behaviours in littoral habitats of Lake Buyo (south-west Ivory Coast) using video surveillance

Video surveillance is a non-extractive and less disruptive method of observing fish in their natural environment. Increasingly used, this technique makes it possible to describe the behaviour of fish in their habitat. In Côte d'Ivoire, the use of waterproof cameras for ichthyological purposes is still not widespread. This study proposes to use video surveillance to identify the different behaviours performed by fish in the littoral habitats of the Buyo dam lake. The objective is to know the mode how fish use the littoral habitats of Lake Buyo in order to provide managers with important data for developing programmes to preserve and manage these environments. Four unbaited camera systems were deployed at each station between 7 am and 6 pm. In the laboratory, various criteria were used to identify the behaviour of the fish. The results show that 8 species of fish frequented the littoral habitats of Lake Buyo to feed, reproduce and protect themselves from predators. Feeding (62.70%) was the most frequently observed activity, followed by reproduction (32.32%). The Dera and Pk15 stations recorded the highest number of species and behaviours. These behaviours varied according to species; Coptodon zillii stood out by displaying the highest average frequency (32.12 activities/day) of all types of behaviour observed in fish. The data from this study are essential for developing strategies to effectively conserve coastal areas in order to ensure the long-term survival of the species.

Importance of a Lake-Wetland Complex for a Resilient Walleye Fishery

Wetlands serve as unique habitats that can support high biodiversity. Large-scale loss of wetland habitats can threaten important linkages between lake and wetland habitats that could affect diversity and growth of aquatic organisms. In this study, we compare prey diversity and abundance as well as Walleye (Sander vitreus) diets and condition in a large glacial lake (Lake Kampeska, South Dakota) with a connected wetland to better understand seasonal changes in the benefits provided by each habitat. We examined seasonal differences (spring, summer, and fall) through two years (summer 2021 through fall 2022) between the habitats using prey fish catch per unit effort, richness, Shannon diversity, and Bray–Curtis dissimilarity as well as Walleye relative weight, percent of empty stomachs, diet weight, stomach fullness, diet energy, and diet taxa importance. The prey fish community was more diverse and abundant in the wetland, and Walleye consumed more prey (by weight) in the wetland during all seasons except spring. Wetland reconnection can be a tool for managers to improve water quality while providing seasonal habitat needs for fish. Additionally, the diversity of prey resources provided by wetlands, many of which are unique, support resilience in the face of ecological change. Protection of wetlands may be critical for maintaining healthy and resilient fisheries into the future.

Distribution of toxigenic cyanobacteria in Alpine lakes and rivers as revealed by molecular screening

The increasing frequency of cyanobacteria blooms in waterbodies caused by ecosystem eutrophication could endanger human health. This risk can be mitigated by effective monitoring incorporating molecular methods. To date, most molecular studies on toxigenic cyanobacteria have been limited to microcystins (MCs), disregarding other cyanotoxins, to freshwater planktic habitats while ignoring benthic habitats, and to limited geographic areas (usually one or a few specific waterbodies). In this study, we used PCR-based methods including PCR product sequencing and chemical-analytical methods (LC-MS/MS) to screen many plankton (n = 123) and biofilm samples (n = 113) originating from 29 Alpine lakes and 18 rivers for their cyanotoxin production potential. Both mcyE (indicating MC synthesis) and anaC (indicating anatoxin (ATX) synthesis) gene fragments were able to qualitatively predict MC or ATX occurrence. The abundance of mcyE gene fragments was significantly related to MC concentrations in plankton samples (R2 = 0.61). mcyE gene fragments indicative of MC synthesis were most abundant in planktic samples (65 %) and were assigned to the genera Planktothrix and Microcystis. However, mcyE rarely occurred in biofilms of lakes and rivers, i.e., 4 % and 5 %, respectively, and were assigned to Microcystis, Planktothrix, and Nostoc. In contrast, anaC gene fragments occurred frequently in planktic samples (14 % assigned to Tychonema, Phormidium (Microcoleus), and Oscillatoria), but also in biofilms of lakes (49 %) and rivers (18 %) and were assigned to the genera Phormidium, Oscillatoria, and Nostocales. The cyrJ gene fragment indicating cylindrospermopsin synthesis occurred only once in plankton (assigned to Dolichospermum), while saxitoxin synthesis potential was not detected. For plankton samples, monomictic and less eutrophic conditions were positively related to mcyE/MC occurrence frequency, while oligomictic conditions were related to anaC/ATX frequency. The anaC/ATX frequency in biofilm was related to the lake habitats generally showing higher biodiversity as revealed from metabarcoding in a parallel study.

Stony Corals and Their Associated Fauna Residing in Marine Lakes under Extreme Environmental Conditions

Tropical marine lakes are small land-locked marine waterbodies occurring in karstic coastal areas. During biodiversity surveys in 12 marine lakes in Raja Ampat, Southwest Papua province, Indonesia, we recorded at least 37 species belonging to 29 genera of hard corals. Their observed associated symbiont fauna consisted of bivalve molluscs and polychaete worms. Marine lake temperature ranged from 30.0 to 32.5 °C, acidity from pH 7.6 to 8.1, and salinity from 26.4 to 33.2 ppt. This study provides the first inventory of the marginal coral communities in the extreme habitat of marine lakes, under chronic extreme environmental conditions of higher temperatures, land-based nutrient loads, and sedimentation.

A multi-metric approach to characterize variability in Yellow Perch (Perca flavescens) use of Lake Ontario and two barrier-protected coastal wetlands

Yellow Perch (Perca flavescens) inhabit both nearshore and coastal wetland habitats of the Laurentian Great Lakes throughout their lifetime and are known to exhibit different movement life histories. However, uncertainty persists in the spatial extent of this variation and in the duration of habitat use. To explore these uncertainties, we used a multi-metric approach that included water and otolith microchemistry and tissue stable isotope ratios (δ13C, δ15N). The ratio of manganese to calcium in otoliths was used to identify transitional movements between nearshore Lake Ontario and wetland habitats while carbon and nitrogen tissue isotope ratios revealed variable duration of wetland inhabitance. Our research suggests that the multi-metric approach was useful for addressing questions that could not be answered by one method alone. Our results demonstrate individual differences in duration of coastal wetland habitat residence among Yellow Perch, which may influence their susceptibility to recreational harvest. As Yellow Perch are an important species of consideration for management agencies such as the Great Lakes Fishery Commission, exposing such diversity is important when considering the potential for differential contributions of individuals with variable movement life histories to overall population stability and resilience over time.

Shifts in dominance of benthic communities along a gradient of water temperature and turbidity in tropical coastal ecosystems.

Tropical coastal benthic communities will change in species composition and relative dominance due to global (e.g., increasing water temperature) and local (e.g., increasing terrestrial influence due to land-based activity) stressors. This study aimed to gain insight into possible trajectories of coastal benthic assemblages in Raja Ampat, Indonesia, by studying coral reefs at varying distances from human activities and marine lakes with high turbidity in three temperature categories (<31°C, 31-32°C, and >32°C). The benthic community diversity and relative coverage of major benthic groups were quantified via replicate photo transects. The composition of benthic assemblages varied significantly among the reef and marine lake habitats. The marine lakes <31°C contained hard coral, crustose coralline algae (CCA), and turf algae with coverages similar to those found in the coral reefs (17.4-18.8% hard coral, 3.5-26.3% CCA, and 15-15.5% turf algae, respectively), while the higher temperature marine lakes (31-32°C and >32°C) did not harbor hard coral or CCA. Benthic composition in the reefs was significantly influenced by geographic distance among sites but not by human activity or depth. Benthic composition in the marine lakes appeared to be structured by temperature, salinity, and degree of connection to the adjacent sea. Our results suggest that beyond a certain temperature (>31°C), benthic communities shift away from coral dominance, but new outcomes of assemblages can be highly distinct, with a possible varied dominance of macroalgae, benthic cyanobacterial mats, or filter feeders such as bivalves and tubeworms. This study illustrates the possible use of marine lake model systems to gain insight into shifts in the benthic community structure of tropical coastal ecosystems if hard corals are no longer dominant.