Non-vegetated Habitats Research Articles

Extracellular Enzyme Activity and Stoichiometry Across Vegetated and Non-Vegetated Coastal Ecosystems

The conversion of organic matter by extracellular enzymes can reveal important insights into carbon and nutrient cycling. The activity and stoichiometry of hydrolytic extracellular enzymes were investigated to assess the effects of vegetation cover and sediment characteristics on microbial-enzyme-mediated decomposition in coastal ecosystems. Extracellular enzyme activity (EEA) was quantified across transects extending from mangrove to tidal flat habitats in two New Zealand coastal ecosystems that differ in mud content (sandy: Hobson Bay, muddy: Snells Beach). We determined the activity of five key hydrolyzing enzymes: β-glucosidase (hydrolyzes cellulose to glucose); β-N-acetylglucosaminidase (catalyzes the terminal reaction in chitin degradation); alkaline phosphatase (releases soluble inorganic phosphate groups from organophosphates); β-D-cellobiohydrolase (hydrolyzes cellulose to generate cellobiose); and β-xylosidase (catalyzes hemicellulose). All enzymes involved in C acquisition and in N and P cycling had higher activity at the muddy site. No habitat differences in EEA were observed at the sandy site, whereas EEA was lower in the non-vegetated habitats for some enzymes at the muddy site. Models of microbial metabolic limitations highlighted that most habitats at both muddy and sandy sites were predominately C and P limited. The EEA in these coastal wetlands was generally lower than has been reported for other terrestrial, freshwater, and estuarine ecosystems, with values often one to two orders of magnitude lower than other wetland studies. These results can be used to advance our understanding of the biogeochemical processes underpinning the response of coastal ecosystems to land-derived nutrient and sediment inputs.

Methane dynamics in vegetated habitats in inland waters: quantification, regulation, and global significance

Freshwater ecosystems, including lakes, wetlands, and running waters, are estimated to contribute over half the natural emissions of methane (CH4) globally, yet large uncertainties remain in the inland water CH4 budget. These are related to the highly heterogeneous nature and the complex regulation of the CH4 emission pathways, which involve diffusion, ebullition, and plant-associated transport. The latter, in particular, represents a major source of uncertainty in our understanding of inland water CH4 dynamics. Many freshwater ecosystems harbor habitats colonized by submerged and emergent plants, which transport highly variable amounts of CH4 to the atmosphere but whose presence may also profoundly influence local CH4 dynamics. Yet, CH4 dynamics of vegetated habitats and their potential contribution to emission budgets of inland waters remain understudied and poorly quantified. Here we present a synthesis of literature pertaining CH4 dynamics in vegetated habitats, and we (i) provide an overview of the different ways the presence of aquatic vegetation can influence CH4 dynamics (i.e., production, oxidation, and transport) in freshwater ecosystems, (ii) summarize the methods applied to study CH4 fluxes from vegetated habitats, and (iii) summarize the existing data on CH4 fluxes associated to different types of aquatic vegetation and vegetated habitats in inland waters. Finally, we discuss the implications of CH4 fluxes associated with aquatic vegetated habitats for current estimates of aquatic CH4 emissions at the global scale. The fluxes associated to different plant types and from vegetated areas varied widely, ranging from−8.6 to over 2835.8 mg CH4 m−2 d−1, but were on average high relative to fluxes in non-vegetated habitats. We conclude that, based on average vegetation coverage and average flux intensities of plant-associated fluxes, the exclusion of these habitats in lake CH4 balances may lead to a major underestimation of global lake CH4 emissions. This synthesis highlights the need to incorporate vegetated habitats into CH4 emission budgets from natural freshwater ecosystems and further identifies understudied research aspects and relevant future research directions.

Multi-habitat carbon stock assessments to inform nature-based solutions for coastal seascapes in arid regions

Coastal ecosystems are integral to global carbon cycling and are increasingly recognised for their role in mitigating climate change. Within these ecosystems, the dynamics of carbon storage are diverse, varying significantly across different habitats. However, existing management strategies often focus predominantly on vegetated habitats neglecting the contributions of non-vegetated areas. We address this knowledge gap by providing a quantitative spatial assessment of carbon storage across coastal seascapes varying in plant biomass. Our comprehensive multi-habitat inventory of carbon stocks in the United Arab Emirates confirmed that mangroves are the largest carbon-storing habitat per hectare (94.3 t/ha), followed by saltmarshes (63.6 t/ha), microbial mats (51.6 t/ha), mudflats (46.8 t/ha), seagrass (32.5 t/ha), and coastal sabkha (31.0 t/ha).Mean carbon content in the top 50 cm of mangrove soils (53.9 t/ha) was similar to saltmarshes (52.7 t/ha), microbial mats (51.6 t/ha), and mudflats (46.8 t/ha). We highlight the importance of including non-vegetated habitats in carbon accounting and management strategies. Our findings suggest that a more context-specific whole-system approach is essential for guiding effective ecosystem management and designing ecologically meaningful Nature-based Solutions (NbS). Adopting this broader perspective in NbS can ensure more comprehensive conservation and restoration outcomes, which not only protect and enhance blue carbon ecosystems but also contribute to broader ecological and social benefits. This approach is pivotal for advancing our understanding of interconnected coastal ecosystems and their role in climate change mitigation.

Effect of Linear Infrastructure on Protected Areas: A Study Relating to the Giritale Nature Reserve and Angamedilla National Park, Sri Lanka

Rapid urbanization in the dry zone of Sri Lanka has resulted in considerable losses in its original forest cover. Urban expansion, which typically includes expansion of human settlements and commercial establishments, and the construction of linear infrastructural facilities (roads, railways, and transmission lines) have led to many adverse impacts on natural landscapes. Linear infrastructure would be particularly detrimental when natural habitats are fragmented. Here we report on the changes in green cover along a stretch of the Elahera-Giritale B112 road where reconstruction took place during 2017-2019. The road traverses through the Giritale Nature Reserve block II and Angamedilla National Park, in the North Central Province of Sri Lanka. The study area covered a 3.8 km section of the road, 80% of which runs through the protected areas, and a 1 km buffer on either side of this road. We monitored changes in forest cover over the two decades i.e., from 2000 to 2020, using differences in the Normalized Difference Vegetation Index (NDVI), calculated based on the images in Landsat 5,7 and 8 thematic mapper using the ArcGIS platform. The accuracy of the classified habitats was verified using Google Earth images and ground-truthing. Accordingly, non[1]vegetated areas and four types of vegetated areas were identified. The range of NDVI recorded were non-vegetated (0.14-0.39), grasslands (0.39-0.41), shrublands (0.41-0.48), open forests (0.48-0.54) and dense forests (0.54-0.74). The study revealed that there were considerable losses in the forest cover over the 20 years. The non-vegetated habitats within the buffer zone of 200 m on either side of the road accounted for 8.6% of the total non-vegetated areas in the year 2000 whereas this had increased to 15.4% in the year 2020. Similarly, losses were noted for dense and open forests. Scrublands, grasslands, and built-up areas on the other hand have increased, replacing the forest habitats. The findings highlight the need to monitor forest cover losses arising from such linear infrastructure facilities, particularly when they are within or adjacent to protected habitats, and for remedial measures to be taken to strengthen the protection of these vital ecosystems.
 Keywords: Forest cover, Fragmentation, NDVI, Roads

Saltmarsh vegetation and social environment influence flexible seasonal vigilance strategies for two sympatric migratory curlew species in adjacent coastal habitats

BackgroundAnimals need to adjust their vigilance strategies when foraging between physically contrasting vegetated and non-vegetated habitats. Vegetated habitats may pose a greater risk for some if vegetation characteristics function as a visual obstruction but benefit others if they serve as protective shelter. Variation in group size, presence of similar species, along with variation in environmental conditions and anthropogenic disturbance can also influence vigilance investment.MethodsIn this study, we quantified the vigilance behaviour of two large-bodied, sympatric migratory curlew species—Far Eastern Curlew (Numenius madagascariensis) and Eurasian Curlew (N. arquata)—in vegetated Suaeda salsa saltmarsh and non-vegetated mudflat habitat in Liaohekou National Nature Reserve, China. We used linear mixed models to examine the effects of habitat type, season, tide time, flock size (conspecific and heterospecific), and human disturbance on curlew vigilance investment.ResultsBoth species spent a higher percentage of time under visual obstruction in S. salsa habitat compared to mudflat habitat but in response, only Far Eastern Curlew increased their percentage of vigilance time, indicating that visual obstruction in this habitat is only a concern for this species. There was no evidence that S. salsa vegetation served as a form of cryptic background colouration since neither species decreased their vigilance effect in S. salsa habitat in spring compared to the autumn migration season. The effect of curlew social environment (i.e. flock size) was habitat dependent since percentage of vigilance time by curlews in saltmarsh increased with both the number of individual curlews and number of other birds present, but not in mudflat habitat.ConclusionsWe conclude that both migratory curlew species exhibit a flexible vigilance adjustment strategy to cope with the different environmental and social conditions of adjacent and sharply contrasting coastal habitats, and that the trade-off between the risks of foraging and the abundance of prey may be a relatively common phenomenon in these and other shorebird populations.

Predation selects for smaller eye size in a vertebrate: effects of environmental conditions and sex.

Increased eye size in animals results in a larger retinal image and thus improves visual acuity. Thus, larger eyes should aid both in finding food as well as detecting predators. On the other hand, eyes are usually very conspicuous and several studies have suggested that eye size is associated with predation risk. However, experimental evidence is scant. In this study, we address how predation affects variation in eye size by performing two experiments using Eurasian perch juveniles as prey and either larger perch or pike as predators. First, we used large outdoor tanks to compare selection due to predators on relative eye size in open and artificial vegetated habitats. Second, we studied the effects of both predation risk and resource levels on phenotypic plasticity in relative eye size in indoor aquaria experiments. In the first experiment, we found that habitat altered selection due to predators, since predators selected for smaller eye size in a non-vegetated habitat, but not in a vegetated habitat. In the plasticity experiment, we found that fish predators induced smaller eye size in males, but not in females, while resource levels had no effect on eye size plasticity. Our experiments provide evidence that predation risk could be one of the driving factors behind variation in eye size within species.

A decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the Holocene sedimentary record of the Gulf of Trieste.

Carbonate sediments in non‐vegetated habitats on the north‐east Adriatic shelf are dominated by shells of molluscs. However, the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because: (i) monitoring of ecosystems prior to the 20th century was scarce; and (ii) ecosystem history inferred from cores is masked by condensation and mixing. Here, based on geochronological dating of four bivalve species, carbonate production during the Holocene is assessed in the Gulf of Trieste, where algal and seagrass habitats underwent a major decline during the 20th century. Assemblages of sand‐dwelling Gouldia minima and opportunistic Corbula gibba are time‐averaged to >1000 years and Corbula gibba shells are older by >2000 years than shells of co‐occurring Gouldia minima. This age difference is driven by temporally disjunct production of two species coupled with decimetre‐scale mixing. Stratigraphic unmixing shows that Corbula gibba declined in abundance during the highstand phase and increased again during the 20th century. In contrast, one of the major contributors to carbonate sands – Gouldia minima – increased in abundance during the highstand phase, but declined to almost zero abundance over the past two centuries. Gouldia minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top‐core increments but are rarely alive. Although Gouldia minima is not limited to vegetated habitats, it is abundant in such habitats elsewhere in the Mediterranean Sea. This live–dead mismatch reflects the difference between highstand baseline communities (with soft‐bottom vegetated zones and hard‐bottom Arca beds) and present‐day oligophotic communities with organic‐loving species. Therefore, the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century. More than 50% of the shells on the sea floor in the Gulf of Trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats.

Seasonal and environmental influences on recruitment patterns and habitat usage among resident and transient fishes in a World Heritage Site subtropical estuary.

This study investigated whether the fish communities inhabiting shallow non-vegetated habitats in two divergent bays in a subtropical World Heritage Site estuarine system differed according to wet (spring-summer) and dry (autumn-winter) seasons or polyhaline and mesohaline zones, within the broader objective of facilitating spatio-temporal management. Species richness (total of 74 taxa; total length, LT = 11-552 mm) and abundance (51 109 individuals) were mostly greater in the wet than dry season and in polyhaline than mesohaline areas. There was a major effect of rainfall on recruitment, particularly among transient fishes, which could be the result of enhanced survival of young via greater productivity (food resources) and protection from predators (via turbidity reducing visual cues). Salinity had strong interactive effects with rainfall and temperature in one bay, with greater species richness and overall abundances as well as large abundances of four key species [Anchoa januaria and Atherinella brasiliensis (pelagic residents), Cetengraulis edentulus (pelagic transient) and Diapterus rhombeus (demersal transient)] during the wet season in polyhaline areas; possibly reflecting a biodiversity hotspot that might be affected by distance to the estuary mouth and convergence hydrology. Regionally, the results support enforcing spatio-temporal restrictions to minimize anthropogenic activities within statutory (but not always enforced) protected areas. Globally, the data reiterate the need to identify and understand biotic and abiotic effects on estuarine ichthyofaunal distributions and abundances as a precursor to their management.

Staying out of the heat: how habitat use is determined by local temperature.

Atlantic cod (Gadus morhua) and the Tvedestrand fjord on the Norwegian Skagerrak coast studied by Freitas etal. (). Photographs by Øystein Paulsen (left), and Institute of Marine Research, Norway (right). In Focus: Freitas, C., Olsen, E. M., Knutsen, H., Albretsen, J. & Moland, E. (2016) Temperature-associated habitat selection in a cold-water marine fish. Journal of Animal Ecology, 85, 611-613. In the marine environment, species distributions are closely linked to temperature gradients, but how individual behaviour is affected by local temperatures is less well understood. Freitas etal. () tracked Atlantic cod within a Norwegian fjord using electronic acoustic tags. They showed that when surface waters were warm, cod occupied the cold deep non-vegetated habitats. However, when surface waters cooled, fish moved into shallow seagrass and macroalgae beds that were previously out-of-bounds. The study provides a clear example of how thermal regimes determine habitat use over fine spatial and temporal scales, with potential implications for population dynamics under climate warming.

Spatial Biodiversity Patterns of Fish within the Aransas Bay Complex, Texas

The goal of this study was to consider the effects of habitat type and environmental conditions on the biodiversity of fishes within the Aransas Bay Complex, Texas and provide a management framework and an ecosystem examination of Essential Fish Habitat (EFH). A stratified, randomized experimental design was used to collect fishes from seagrass, oyster, and non-vegetated habitats within the Aransas Bay Complex from February through May 2010 over large spatial scales at the “bay-complex” level. We developed a biodiversity habitat model using Boosted Regression Trees (BRT). Fitted functions from the “best” fit BRT habitat model indicated that fish biodiversity was greatest in seagrass areas closest to the inlet (< 80 cost-distance units) during early spring, with temperatures < 18°C and dissolved oxygen levels between 7-8 mg O2/L in shallow depths (< 0.5 m). Results from community assemblage analyses showed significant differences among habitats with highest abundance of fishes found in seagrass, followed by non-vegetated substrate, and oyster reef. The relatively high abundance of fishes at non-vegetated bottom compared to the low abundance found at the oyster reef was most likely due to the spatial location of the habitats sampled. Our results indicate that future conservation measures should focus along the eastern and southern areas of Aransas Bay to protect EFH with highest levels of biodiversity. The modeling approach developed in this study provides a framework for natural resource managers to identify habitats supporting the greatest biodiversity of juvenile fishes.

The role of annual macroalgal morphology in driving its epifaunal assemblages

Coastal vegetated habitats harbour higher epifaunal abundance and diversity compared with non-vegetated habitats. In this study, intertidal annual macroalgae were used as model organisms to test the role of macroalgal morphology in driving the structure of their associated epifaunal assemblages. For this aim, 6 macroalgal species, apparently different in morphology, were sampled from two intertidal rocky shores to examine the effects of habitat morphology on the number of individuals, taxa richness and the structure of its associated epifaunal assemblages by means of univariate and multivariate techniques. To provide a complete overview of macroalgal morphology, biomass was used as a proxy of habitat quantity and fractal measures as proxies of habitat complexity. Results showed that almost all the studied pairs of macroalgae showed significant differences at least for one of the morphological measures used. Moreover, epifaunal assemblages showed significant differences between macroalgae mainly due to the different identities and relative abundance of epifaunal species. However, differences in the abundance and structure of assemblages were shore dependent, possibly due to the surrounding landscape heterogeneity. Finally, the quantity of habitat was a better predictor variable than fractal measures but fractal area was also important particularly for the abundance of the total assemblage and crustaceans.

Impact of mangrove vegetation on seasonal carbon burial and other sediment characteristics in the Vellar-Coleroon estuary, India

This work quantified the total carbon and 12 other sediment characteristics at 10 soil depths, in planted and or natural mangrove forests in comparison with non-vegetated soil for four seasons of the year 2009–2010 in the Vellar-Coleroon estuarine complex, India. The sediment characteristics varied significantly between mangrove-vegetated and non-vegetated habitats or seasons of analysis, but not between soil depths. The mangrove sediments were rich in total carbon and total organic carbon as compared to non-mangrove sediments (p <0.01). Total carbon was 98.2% higher in mature mangroves and 41.8% in planted mangroves than that in non-mangrove soil. Total organic carbon was as much as 2.5 times greater in mature mangroves and 2 times greater in planted mangroves than that in unvegetated soil. Carbon contents also varied many fold by season. Total carbon content was 8.6 times greater during pre-monsoon, 4.1 times greater during post-monsoon and 2.5 times greater during monsoon than during summer (p<0.01 in all cases). Similarly, total organic carbon was 5.9 times greater during pre-monsoon, 3.1 times greater during post-monsoon and 69% greater during monsoon than during summer. In general, higher levels of sediment carbon were recorded during pre and post-monsoon seasons than during other seasons. Total carbon concentration was correlated negatively to temperature, sand and phosphorus (p <0.01); positively correlated with redox potential, silt, clay, C/N ratio, potassium (p <0.01) and nitrogen (p <0.05); but not correlated with soil depth, pH or salinity. This work revealed that the carbon burial was rapid at the annual rate of 2.8% for total carbon, and 6.7% for total organic carbon in mangrove-planted sediment. Clearing of mangroves can result in significantly and rapidly reduced carbon stores. Our study highlights the importance of natural and plantation mangrove stands for conserving sediment carbon in the tropical coastal domain.

Spatial and Habitat-Mediated Food Web Dynamics in An Oyster-Dominated Estuary

ABSTRACT Understanding spatial dynamics and creating spatial boundaries of marine food webs is an important topic that resource managers are beginning to understand. Food web structure, mediated by spatial and habitat differences, was examined in a subtropical estuary using stomach content and stable isotope analyses. The goal of this study was to characterize the trophic structure in subtidal oyster reef, intertidal marsh edge, and nonvegetated bottom habitats. Fish and macroinvertebrates were sampled seasonally from July 2006 to April 2007. Spatially, the lower region of the bay supported a more robust food web, with more species and links (72 and 130, respectively) than the upper bay (63 and 87, respectively). Trophic levels (determined by 15N) and carbon sources (determined by 13C) were combined with dietary links (determined by stomach contents), relative population levels, and linkage strength (determined by food volume) to construct 5 dimensional food web diagrams for the 2 regions and 3 habitats s...

Critical Habitats and Stock Assessment: Age‐Specific Bias in the Chesapeake Bay Blue Crab Population Survey

AbstractPopulation surveys used in stock assessments often ignore habitats that are difficult to sample under the assumption that these habitats harbor an inconsequential fraction of the population. We tested this assumption for the Chesapeake Bay population of blue crab Callinectes sapidus, which numbers in the hundreds of millions, supports one of the world's most productive crustacean fisheries, and is managed based on a rigorous stock assessment. The stock assessments rely on a baywide winter dredge survey (WDS), which produces an absolute estimate of abundance for age‐1 and older crabs. Although the WDS does not sample waters shallower than 1.5 m deep, where some age‐0 crabs overwinter, it has been assumed that abundance in these shallow habitats is not substantial. We sampled vegetated and nonvegetated shallow‐water habitats not sampled by the WDS at four locations in lower Chesapeake Bay in February‐April 2011. Age‐0 density in shallow vegetated habitats was about two orders of magnitude higher than in deeper vegetated habitats sampled by the WDS; density in shallow nonvegetated habitats was about 40 times that of deep nonvegetated habitats. Even after excluding juvenile crabs that would not be retained by WDS gear, juvenile density was still 50 times higher in shallow vegetated and 32 times higher in nonvegetated habitats than in deep nonvegetated habitats. Extrapolating these densities baywide, we estimated approximately 850‐1,500 million age‐0 crabs in Chesapeake Bay, in contrast to the 2011 WDS estimate of about 205 million age‐0 crabs. Thus, the WDS only sampled 14‐24% of age‐0 crabs. If the fraction of age‐0 crabs sampled by the WDS differs interannually, then empirical estimates of abundance and exploitation rate will be biased and potentially lead to risk‐prone management actions. Our findings provide an empirical example whereby inattention to habitat utilization as a function of age or ontogeny may introduce significant error into fishery management.Received May 17, 2013; accepted February 18, 2014

Effects of small-scale trawling on benthic communities of estuarine vegetated and non-vegetated habitats

The pink prawn Farfantepenaeus paulensis is one of the most valuable fishery resources in the southwest Atlantic. It is exploited along the inner shelf and inside estuarine nursery grounds. Inside the nursery grounds, mainly artisanal fisheries are responsible for the capture of pink prawn juveniles. In this study, we experimentally assessed the impact of a light mini trawl, a gear extensively used for the capture of estuarine prawn along the southeast and south coast of Brazil. We simulated a single impact (represented by three consecutive trawling runs) on vegetated and non-vegetated bottom. Then we monitored changes in sediment properties and the response of the benthic fauna at the trawling and control sites at a logarithmic temporal scale in order to determine the initial impact and the recovery rates. Meiofauna and macrofauna, both numerically dominated by the ostracod Cyprideis multidentata, were significantly more diverse and abundant inside the submerged algal beds than in non-vegetated areas. In the vegetated areas, the only change caused by the mini trawl was a significant decrease in the percentages of fine sediments (silt+clay). By contrast, in the non-vegetated areas, the mini trawl caused a significant decrease of the total meiofauna, mainly due to lower nematode and C. multidentata abundances. Our results show that the mini trawl does not produce a loss of benthic diversity and causes minimal damage to the estuarine benthos. The absence of a general faunal response, as well as the absence of significant changes in sediment properties of the non-vegetated areas suggests that meiofauna may be resuspended rather than killed during trawling. The present study highlights the need for basic studies on gear impact and environmental health of nursery grounds. Otherwise, management of small-scale fisheries will continue to be based on evidence from large-scale fisheries.

Nematode assemblage response to fish-farm impact in vegetated (Posidonia oceanica) and non‑vegetated habitats

We investigated the impact of fish farming on the benthic biota of 2 habitats (sea- grass meadows of Posidonia oceanica and non-vegetated soft bottoms), by examining in detail the nematode assemblages, and the effects of organic enrichment on their abundance, diversity (spe- cies richness and trophic diversity), community structure and individual size. All investigated faunal variables differed significantly between impact and control sediments, except for indi - vidual nematode biomass. Nematodes displayed reduced biodiversity beneath the investigated fish farms in both vegetated and non-vegetated habitats. The nematode genera Richtersia, Desmoscolex and Halalaimus were highly sensitive to biodeposition and disappeared almost com- pletely in farm sediments, whereas other genera such as Daptonema and Prochromadorella largely increased their relative abundance. The impact of biodeposition was investigated also in terms of K-dominance curves and functional variables (life strategies as maturity index, and func- tional (i.e. trophic) diversity) which showed that nematodes are very sensitive to this kind of envi- ronmental disturbance. Our results indicate that the analysis of nematode assemblage composi- tion, the life traits of the dominant species and the presence/disappearance of certain nematode species represent a reliable tool for monitoring the quality state of marine sediments exposed to fish-farm organic wastes.

Spatial, diel, and seasonal changes in the fish community structure of a Mexican tropical estuary

To extend our knowledge about spatial and temporal variations in the structure of estuarine fish communities, diel samplings (collections every 2 h) were carried out every two months over a one-year period in two different habitats (vegetated and nonvegetated). We collected a total of 34,766 individuals, corresponding to 72 species, most of them with marine and tropical affinities. Species richness was significantly higher in the vegetated habitat, whereas abundance (number of fish) was higher in the nonvegetated habitat. The diel pattern of abundance showed peaks at dusk and dawn, whereas richness was higher at night. Seasonally, fish abundance and species richness showed peaks during January, March, and July–September, and these peaks were related to the entry of temperate species, production processes in the system, and rainfall pattern. Fish assemblages showed significant differences among habitats, day/night, and months. In the vegetated habitat, Lagodon rhomboides, Menidia beryllina, and Orthopristis chrysoptera were the predominant species. Microphagus species such as Brevoortia gunteri, Brevoortia patronus, and Mugil curema were predominant during the warm, dry season (March–May) and they were more abundant during the day. In contrast, predatory species such as Citharichthys spilopterus and Opsanus beta were more abundant during the rainy season and their capture was higher at night. The two most numerically abundant species, Anchoa mitchilli and Membras martinica, showed a twilight pattern, with abundance peaks at dusk and dawn, respectively. Hence, in Pueblo Viejo Lagoon (Mexico), the spatiotemporal changes in species composition are in part related to predator avoidance and feeding strategies, through a coupling of life histories with the diel and seasonal variation in the availability of resources, the presence of submerged vegetation playing an important role in this dynamic.

Decapod Utilization of Adjacent Oyster, Vegetated Marsh, and Non-Vegetated Bottom Habitats In A Gulf of Mexico Estuary

Abstract Few studies have compared oyster habitat use with adjacent vegetated and non-vegetated habitats. We investigated habitat use by six common, estuarine, invertebrate species. In order to better understand the species-specific use of oyster and adjacent habitats within the salt marshes of Grand Bay NERR, MS, we examined the abundance patterns and size distributions among oyster, vegetated marsh edge (VME), and non-vegetated bottom (NVB) for three seasons (Fall 2003, Spring 2004, Summer 2004) for the following species: blue crab Callinectes sapidus, brown shrimp Farfantopenaeus aztecus, white shrimp Litopenaeus setiferus, daggerblade grass shrimp Palaemonetes pugio, flatback mud crab Eurypanopeus depressus, and oystershell mud crab Panopeus simpsoni. Three main trends emerged concerning habitat use: 1) the three crab species (juvenile C. sapidus, E. depressus, P. simpsoni) occupied oyster and VME habitats in higher abundances relative to NVB with minor to moderate fluctuations in seasonal abundance. ...

Quantitative Assessment of Yield, Precision, and Cost-Effectiveness of Three Wetland Invertebrate Sampling Techniques

Macroinvertebrates are increasingly used as indicators of wetland integrity and productivity. However, accurate interpretation of biological information depends on effective sampling methods, which are also preferably cost-effective. We compared sampling yield, precision, and cost-effectiveness of two traditional wetland sampling methods (dipnet, stove pipe corer) to a dipnet combined with a dropframe in wetlands in the Platte River Valley, USA. The dropframe method was designed to be more quantitative than standard dipnet techniques and to maximize capture of mobile taxa. We compared measures of macroinvertebrate community structure (e.g., abundance, richness, diversity) and function (functional structure, habitat associations), as well as processing time for each sampling technique in vegetated and non-vegetated habitats. Vegetated habitats harbored higher richness, diversity, abundance, and biomass of most invertebrates. The dipnet consistently yielded the lowest values in vegetated and non-vegetated habitats, suggesting that sampling with a dipnet alone can greatly underestimate macroinvertebrate populations and diversity. The corer and the dropframe yielded similar results, but the dropframe produced significantly higher richness values. While the dropframe appeared to be a good choice for sampling in these wetlands, sample processing times for this method were more than two times longer than the other methods. Results provide a basis for informed decisions regarding quantitative sampling of wetland macroinvertebrates.

Trade-offs Between Gear Selectivity and Logistics when Sampling Nekton from Shallow Open Water Habitats: A Gear Comparison Study

We compared logistical issues and the catch composition, density, and size structure of nekton samples collected with a drop sampler, benthic sled, and a fine mesh cast net in shallow non-vegetated habitats of Galveston Bay, Texas. Approximately 16 cast net replicates were collected and sorted for every one drop or benthic sled sample. The drop sampler collected the greatest number of species and provided the highest density estimates for the majority of crustaceans and small demersal fishes; the sled provided comparable density estimates for penaeids and small demersal nekton, while under-representing more mobile fishes. Densities of small benthic nekton were underestimated by the cast net, but it provided the highest density estimates for larger and mobile fishes. Within the selectivity constraints of each gear, the sled and cast net provide viable alternatives to the drop sampler for sampling particular nekton from shallow open water habitats.