Presence Of Seagrass Research Articles

Analysis of Water and Seagrass Quality in Estimating Possibility of Fish Cultivation around Mallusetation Beach, Barru Regency, Indonesia

This r esearch aims to determine the possibility of fish farming on the coast of Mallusetasi, Barru Regency, Indonesia based on water quality analysis and the presence of seagrass. The data obtained were then processed and analyzed by descriptive analysis. The results showed that the water quality such as the current velocity of 0.14-2.4 m/s was still suitable for seagrass growth, the brightness value was 2.4-5.4 m and the water temperature during the study was in the range of 27.27 o C -28.47 o C.and this is still in accordance with the needs of seagrass to carry out photosynthesis and grow. Likewise, the pH of the water during the study was in the range of 7.86-8.22 which was still in accordance with the needs of seagrass. The average dissolved oxygen during the study was in the range of 3.51-5.11 ppm,the salinity of seawater during the study at the research site was in the range of 33.3-34 ppt which was still within the tolerance limit. Likewise, the presence of seagrass plants is still found on the coast of Mallusetasi Beach. Based on the results of the analysis of water quality and the condition of the seagrass beds, it can be stated that Mallusetasi Beach has the possibility or potential to develop fish farming.

Seagrass seed bank spatial structure and function following a large-scale decline

We examined the spatial structure (distribution, density) and function (viability) of the seagrass sediment seed bank, the storage of viable propagules (e.g. seeds, tubers, diaspores) in the sediment over time,in the northern Great Barrier Reef World Heritage Area in Cairns, Queensland, following a large-scale decline in seagrass area. A spatially explicit seagrass seed bank analysis was paired with a long-term annual assessment of seagrass distribution to assess seed bank spatial patterns and their relationship with the recovery and presence of seagrass, and water depth. Four years post-decline, the seed bank contained Zostera muelleri, Halodule uninervis, Halophila ovalis and Cymodocea serrulata seeds. Seed banks reflected adjacent meadow community composition; however, the density of seeds for all recorded species was significantly lower than analogous seagrass populations, indicating a reduction in the capacity for recovery from the seed bank. A spatial structure existed in both the total (viable + non-viable) and viable seed bank, and distance between seed clusters ranged from 50-550 m depending on species and seed type. Observed patterns in clustering may be explained by variation in water depth and the past distribution of seagrass in these meadows. These results demonstrate that the distribution of seagrass seeds within the seed bank, which directly influences the natural recovery of seagrass communities, is not uniform across species and may result in patchy recovery of the meadows. Therefore, the resilience provided by the seed bank in seagrass communities should not be viewed as a static level of insurance for the entire meadow, but rather as dynamic and species-specific, with variability over both space and time.

Estimated footprint of shellfishing activities in Zostera noltei meadows in a northern Spain estuary: Lessons for management

Intertidal seagrasses often occupy areas of high ecological importance that are also targeted for human activities, such as shellfishing and leisure walking. These activities could affect the growth or survival of seagrass. The society at large lacks knowledge of the ecological relevance of seagrasses and their vulnerability, presenting an obstacle for their conservation. Here, the Oka estuary (Basque Country, N. Spain) is used as a case study to analyse the spatial extent of shellfishing activities in seagrass (Zostera noltei). This estuary holds 84% of the intertidal seagrass meadows present in the Basque Country and is visited during the year by professional and recreational shellfishers. Bait digging is legal year-round, and clam digging (by professionals only) from October to February. Human presence over 11 years averaged 17 people on the tidal flat in each daylight hours from August to October. Each professional shellfishing daily trip affected 7.4–21.6 m2 by fishing and 110–188 m2 by trampling in seagrass, but was substantially different between clam and bait (crustacean, worm) fishing. Scaling up this area to estimated annual number of shellfishers, 8–69% of the total seagrass area is trampled and 1–9% is dug per year. In comparison to a habitat suitability map for seagrass, 98% of trampling occurred within a very highly suitable area for seagrass presence (i.e., >90%). This pressure could adversely affect seagrass density and prevent the expansion of meadows into areas suitable for seagrass. Management of public impacts to seagrass in this estuary could occur through prohibition of some activities in seagrass and awareness campaigns among shellfishers and walkers.

Effects of the Zostera noltei meadows on benthic macrofauna in North Atlantic coastal ecosystems of Morocco: spatial and seasonal patterns

The influence of seagrass on benthic macroinvertebrates was investigated in four semi-enclosed coastal systems in Morocco. Biological and environmental variables were examined in vegetated and bare habitats at four selected sites in two seasons (winter and summer). A total of 28,687 individuals were reported as belonging to 69 taxa. Species richness increased significantly with latitudinal gradient. Macrofaunal biomass varied significantly across sites and had a significant positive relationship with the presence of seagrass in both summer and winter. The DIMO model indicated that the variations in macrobenthic faunal structure were mainly due to the existence of the Zostera noltei; PERMANOVA analysis detected that faunal assemblages shifted within the site and that their variation was enhanced with latitude, in both seasons. A seasonal cause for the spread of macrofauna at all the study sites may be the type of habitat. Distance-based linear models (DistLM) revealed that sediment characteristics (carbon and calcium carbonate concentrations and clay percentage) are the main predictor variables that explain the composition of the macrobenthic faunal assemblage. This study proposes a general model for evaluating spatial distribution patterns at various levels within seagrass-dominated coastal lagoons.

The suitability of seagrass ecological function for the survival of the bivalvia on the East Coast of Lombok, Indonesia

The presence of seagrass in coastal waters has an ecological contribution to marine life’s sustainability, such as bivalves. This study aims to assess the structurer bivalves communities associated with seagrass and the relationship between seagrass communities’ structure and the environment against an abundance of bivalves—the Collected data using transect lines and squares. The data analysis used descriptive statistical analysis. Besides, a regression analysis was carried out between the seagrass community’s structure and its environment with the abundance of bivalves. This study found 40 species of bivalves that include 11 families (Veneroidae, Arcidae, Mytilidae, Cardidae, Pinnadae, Pteriidae, Mactridae, Donacidae, Pectinidae, Tellinidae, and Lucinidae). The next, Anadara antiquata has an abundance of top 1.43 ind/m2, and Atrina vexillum, chlamys luculenta, and Fragum unedo are the lowest of 0.003 ind/ m2. Simultaneously, the analysis results showed that the value of R 2 = 0.42 between the abundance of bivalves with the substrate’s depth. Values are different between seagrass closing with a lot of bivalves, wherein R 2 = 0.80. However, R 2 = 0.36’s value between the abundance of bivalves with a density of seagrass. Of the three parameters, the closure of seagrass is a parameter that can be used to identify the wealth of bivalves’ wealth in the location of the study.

Characterizing Fish–Habitat Associations through Paired Fisheries‐Independent and In Situ Habitat Assessments

AbstractEstuarine habitat has a significant influence on the growth, recruitment, and survival of fish and invertebrate species, and understanding habitat dynamics can improve fisheries management. However, the cost and effort associated with habitat monitoring can be limiting, and many large‐scale fisheries‐independent monitoring programs do not capture habitat and biological data concurrently. Consequently, fisheries and their associated habitats are often managed separately. We designed a pilot study to assess the utility and effectiveness of incorporating rapid in situ habitat characterization into a statewide fisheries management program. The occurrence of six focal species (Red Drum Sciaenops ocellatus, Spotted Seatrout Cynoscion nebulosus, blue crab Callinectes sapidus, Atlantic Croaker Micropogonias undulatus, brown shrimp Farfantepenaeus aztecus, and white shrimp Litopenaeus setiferus) and the overall faunal community composition were compared across estuarine habitats to assess the ability of this method to accurately depict fish–habitat associations. Focal species’ occurrence and community composition was significantly correlated with shoreline vegetation, seagrass presence, presence of mangroves, substrate type, and heterogeneity in vegetated habitat. This study demonstrates an effective approach to integrating habitat into fisheries‐independent monitoring in pursuit of an ecosystem‐based approach to fisheries management.

Identification of Priority Sites to Support Management of Commercially Important Sea Cucumber Species by Applying Infomap and Habitat Filters to Larval Dispersal Data

Stocks of commercially valuable sea cucumber species have declined in most tropical countries, which supply majority of the global demand. This work aimed to locate priority sites for the management ofHolothuria scabraandStichopus horrensin the western central Philippines. A passive larval dispersal model was run under four monsoonal regimes (Northeast monsoon, dry-transition, Southwest monsoon, and early Northeast monsoon), and the results subjected to theInfomapnetwork detection algorithm. Three clusters of closely related geographical nodes were identified [southeastern Palawan (Group I), western Panay and eastern Mindoro (Group II), and northern and western Palawan with western Mindoro (Group III)]. Remotely sensed habitat data were used to parameterize the degree of connectivity observed among sites (H. scabraspawning and settlement requires the presence of seagrass and mangrove, whileS. horrensrequires corals and seagrass). Local retention, self-recruitment, settlement success and sink diversity were then calculated for each node with suitable habitat. The locations were ranked according to each metric and those with higher larval export rates, a higher diversity of larval sources and a high degree of successful larval contribution to other sites were deemed crucial for the management of wild populations. Sixteen high-priority sites were identified, distributed mainly along northern Palawan and western Panay. Six sites were common for both species at different seasons, and no single location fulfilled all stated criteria across the four seasons and both sea cucumber species considered. The priority sites for management could serve as broodstock selection and juvenile restocking areas for aquaculture production clusters, which when properly implemented, could lead to an increase in sea cucumber production and contribute to natural populations. On a broader scale, the designation of closely related clusters and incorporation of habitat requirements to dispersal data provided critical input for the delineation of ecologically meaningful management units for sea cucumbers within the region.

Palaeoenvironmental significance of sponge spicules in pre-Messinian crisis sediments, Northern Italy

The Messinian Salinity Crisis (MSC) created a substantial negative impact on the Mediterranean marine fauna and flora because hypersaline conditions were established in many marginal basins. At the northern margin of the Tertiary Piedmont Basin, Northern Italy, the Messinian successions exposed at Banengo and Moncalvo recorded the transition into and through the MSC with well-preserved nanno-, micro- and macrofossils. Siliceous sponge spicules present in these pre-MSC sediments reflect the sponge population in this area with twenty different morphological types of spicule identified, twelve of them attributable to sponge genera of the modern Mediterranean sponge fauna. The most common genera were Stelletta, Geodia and Dercitus, with fewer records of Tethya, Chondrilla, Alectona and Samus. Only two types of spicule belong to species not currently present in the Mediterranean sponge fauna and are putatively attributed to the tropical species Stelletta purpurea and Diplastrella megastellata. The sponge assemblage thriving before the onset of the MSC provided new information on the sponge diversity and palaeoenvironment of this northern sector of the palaeo-Mediterranean basin over this crucial period. These data, integrated with information derived from the associated fossils (nannofossils, benthic and planktic foraminifers, and bryozoans), indicate that the considered sites were coastal localities, with sediments rich in an organic matter likely derived from phytoplankton blooms. At both sites, the presence of patchy rocky substrates on the seafloor is testified by a diversified group of sponges typical of hard substrata. These rocks were, very likely, carbonate as suggested by the presence of spicules of typical boring sponges. In the studied sites, common epiphytic foraminifers and bryozoan segments indicate the presence of Posidonia seagrass or algal meadows.

Variasi Fluks CO2 Udara-Laut di Perairan Pesisir Pulau Bintan

<strong>Variation of Air-Sea CO<sub>2</sub> Fluxes in Bintan Island Coastal Water. </strong>Eastern part of Bintan coastal water plays a major role as CO<sub>2</sub> sink. However, flux and partial pressure of CO<sub>2</sub> (<em>p</em>CO<sub>2</sub>) dynamically follows spatio-temporal variability. Spatio-temporal variability of CO<sub>2</sub> flux may shows the whole condition of Bintan Island coastal water, especially in correlation with the primary production. Systematic study on variability of CO<sub>2</sub> flux from or to the watern column is essential to understand the whole conditions of Bintan Island coastal water. This study aims to understand the spatio-temporal variation of CO<sub>2</sub> fluxes in Bintan Island coastal water, and the factors influencing it. This study was conducted in the eastern part of Bintan coastal water in April and August 2014. In addition, this study was also conducted in the southern and northern parts in April 2016. CO<sub>2</sub> fluxes dynamics were calculated from <em>p</em>CO<sub>2</sub> (surface water and atmosphere), temperature, salinity, and wind speed. The result showed that almost all parts of the Bintan coastal water were carbon sources during first transition season. The largest CO<sub>2</sub> emission was observed in the northern part (4.02 ± 1.92 mmol/m<sup>2</sup>/d) followed by the southern part (2.28 ± 0.80 mmol/m<sup>2</sup>/d) and then the eastern part (0.46 ± 0.28 mmol/m<sup>2</sup>/d). The eastern part temporally turned into CO<sub>2</sub> sink in the southwest monsoon season (-0.27 ± 0.10 mmol/m<sup>2</sup>/d). Temperature was the main factor causing spatial and temporal variability of air-sea CO<sub>2</sub> fluxes in the Bintan coastal water. Spatially, the presence of seagrass and coral reef ecosystems causes the partial pressure of surface water CO<sub>2</sub> in the eastern part of waters of Bintan is much lower compared to the waters of north and south Bintan, thus emitting less CO<sub>2</sub> to the atmosphere

Structure and composition of the macrobenthic community associated to shallow mangrove-seagrass habitat along the southern Red Sea coast, Saudi Arabia

Macrobenthic communities in shallow mangrove-seagrass habitat at the southern portion of Saudi Arabia, Red Sea were explored to (i) characterize their diversity and abundance; (ii) examine the variability among outer, middle and inner stations; and (iii) evaluate the catch performance of scoop (bulldozer) and Van Veen grab. Fifteen sampling collections (9 scoop and 6 grab) captured 4,491 individuals encompassing 18 taxonomic groups. Polychaetes predominated the samples, followed by pelecypods, gammarids, gastropods, and isopods. The species richness did not differ among stations. The density of macrobenthos was significantly (ANOVA, F = 5.51, p = 0.020) higher in the outer and middle stations than the inner station. Moreover, the difference of macrobenthos abundance was seemingly associated with the sediment type and the presence and absence of seagrass. The proportion of non-shared groups over the total number of groups increases from the outer to the inner stations (30.7 to 57.1%), which revealed a degree of difference in the community. The exclusive presence of stomatopods in the inner station suggests their territorial behavior. As well, Van Veen grab captured higher taxonomic groups than scoop; the difference in abundance was not significant. Grab was more pragmatic with ease to operate and thus higher catch efficiency.

A Fuzzy Inference System for Seagrass Distribution Modeling in the Mediterranean Sea: A First Approach

A Mamdani-type fuzzy-logic model was developed to link Mediterranean seagrass presence to the prevailing environmental conditions. UNEP-WCMC (seagrass presence), CMEMS, and EMODnet (oceanographic/environmental) datasets, along with human-impact parameters were utilized for this expert system. The model structure and input parameters were tested according to their capacity to accurately predict the presence of seagrass families at specific locations. The optimum Fuzzy Inference System (FIS) comprised four input variables: water depth, sea surface temperature, nitrates, and bottom chlorophyll-a concentration, exhibiting reasonable precision (76%). Results illustrated that Posidoniaceae prefers cooler water (16–18 °C) with low chlorophyll-a levels (<0.2 mg/m3); Zosteraceae favors similarly cooler (16–18 °C) and mesotrophic waters (Chl-a > 0.2 mg/m3), but also slightly warmer (18–19.5 °C) with lower Chl-a levels (<0.2 mg/m3); Cymodoceaceae lives in warm, oligotrophic (19.5–21.0 °C, Chl-a < 0.3 mg/m3) to moderately warm mesotrophic sites (18–21.3 °C, 0.3–0.4 mg/m3 Chl-a). Finally, Hydrocharitaceae thrives in the warm Mediterranean waters (21–23 °C) of low chlorophyll-a content (<0.25 mg/m3). Climate change scenarios show that Posidoniaceae and Zosteraceae tolerate bathymetric changes, and Posidoniaceae and Zosteraceae are mostly affected by sea temperature rise, while Hydrocharitaceae exhibits tolerance at higher sea temperatures. This FIS could aid the protection of vulnerable seagrass ecosystems by national and regional policy-makers and public authorities.

Seagrass vegetation affect the vertical organization of microbial communities in sediment

Seagrasses represent high primary productivity and provide important ecosystem services to the marine environment. Seagrass-associated microbial communities are playing essential ecological functional roles in biogeochemical cycles. However, little is known about the effect of seagrass vegetation on microbial communities in sediment. In the present study, the sediment cores of seagrass bed (dominated by Zostera japonica and Zostera marine) and degradation area in Swan Lake (China) were sampled; then, biogeochemical parameters were analyzed, and microbial community composition was investigated by using high-throughput sequencing of the 16S rRNA gene.The results showed that the presence of seagrass could lead to a decrease in the richness and diversity of the microbial community. In the vertical direction, a pronounced shift from Proteobacteria-dominated upper layers to Chloroflexi and Crenarchaeota-dominated deep layers in all sediment cores were observed. Besides, Bathyarchaeia is more abundant at degradation area, while Vibrionaceae, Sulfurovum and Lokiarchaeial overrepresent at the seagrass bed area. Vibrionaceae was abundant in the rhizosphere of Z. marina and Z. japonica, and the proportions reached 84.45% and 63.89%, respectively. This enrichment of Vibrio spp. may be caused by the macrobenthic species near the seagrass rhizosphere, and these Vibrio spp. reduced the diversity and stability of microbial community, which may lead to the degradation of seagrass.This study would provide clues for the distribution patterns and niche preferences of seagrass microbiome. The conservation strategy of seagrass would be further elucidated from the perspective of the microbiome.

The potential of coastal ecosystems to mitigate the impact of sea-level rise in shallow tropical bays

Shallow tropical bays in the Caribbean, like Orient Bay and Galion Bay in Saint Martin, are often sheltered by coral reefs. In the relatively calm environment behind the reefs, seagrass meadows grow. Together, these ecosystems provide valuable ecosystem services like coastal protection, biodiversity hotspots, nursery grounds for animals and enhancing tourism and fisheries. However, sea-level rise imperils these ecosystems and the services they provide because of changing hydrodynamic conditions, with potential effects on the interdependencies between these ecosystems. By means of a hydrodynamic model that accounts for the interaction with vegetation (Delft3D Flexible Mesh), the impact of sea-level rise (0.87 m in 2100) is investigated for three scenarios of future reef development (i.e. keep-up, give-up and catch-up). If coral reefs cannot keep up with sea-level rise, the wave height and flow velocity increase significantly within associated bays, with the wave height doubling locally in case of eroding reefs in our model simulations. Since the presence of seagrass strongly depends on the hydrodynamic conditions, the response of seagrass to the future hydrodynamic conditions is projected using a habitat suitability model that is based on a logistic regression. The spatial character of the bays determines the response of seagrass. In Orient Bay, which is deeper and partly exposed to higher waves, the seagrass will likely migrate from the deeper parts to shallow areas that become suitable for seagrass because of the surf zone moving landward. In contrast, the conditions for seagrass worsen in Galion Bay for the catch-up and give-up scenario; due to the shallowness of this bay, the seagrass cannot escape to more suitable areas, resulting in significant seagrass loss. It is shown that healthy coastal ecosystems are able to limit the change in hydrodynamic conditions due to sea-level rise. Therefore, preserving these ecosystems is key for ensuring the resilience of shallow tropical bays to sea-level rise and maintaining their ecosystem services.

Change-mapping of estuarine intertidal seagrass (Zostera muelleri) using multispectral imagery flown by remotely piloted aircraft (RPA) at Wharekawa Harbour, New Zealand

This research assesses a survey method for measuring the change in density of intertidal estuarine seagrass (Zostera muelleri) at Wharekawa Harbour, New Zealand, using an autonomous remotely piloted aircraft fitted with a narrowband multispectral camera. Image classification was modelled using the random forest classifier trained with ground observation data sourced from 63 photographed quadrat stations upon three parallel transect lines. Seagrass coverage in the georeferenced and rectified ground photography was estimated by visual interpretation on a three-tier (low, medium and high) density scale, then exact leaf area additionally calculated from digitised seagrass leaf coverage visible in rectified ground photography. Three replicate aerial surveys across four months were conducted to compare predicted change in seagrass density with actual measured change, during austral summer growth and autumn decline. Classification of the resulting image mosaic (2.5 cm pixel size) achieved up to 90–93% overall accuracy across multiple surveys when attributing density class, 93–96% accuracy for prediction of seagrass presence, and 81–91% in terms of detection of seagrass on the ground. Change-maps allow regions of growth and decline to be visualised. Correlation (r) between actual and predicted change for 48 independent test grid squares was 0.89 and 0.61 for the summer and autumn change periods respectively. Rapid visual interpretation of classification end-member classes yielded change measurement equivalent to that of accurately measured seagrass leaf area. The research demonstrates that RPA survey using a multispectral camera is viable for monitoring change in seagrass condition.

Dugong (Dugong dugon) movements and habitat use in a coral reef lagoonal ecosystem

Little is known about how the Vulnerable dugong Dugong dugon uses coral reef lagoons despite the importance of these habitats throughout much of its vast range. We used GPS satellite tracking systems to explore the space use of 12 dugongs at 3 locations in the coral reef lagoons of the main island of New Caledonia in the southwest Pacific: Cap Goulvain, Ouano and Nouméa. The movements of the tracked dugongs varied among individuals and all except one animal undertook large-scale movements (>15 km; mean [±SE] 37.7 ± 5.2 km) from their capture location (maximum waterway distance range: 13.8 to 72.9 km). The straight-line distances between the furthest GPS locations during each animal’s tracking period ranged from 21.3 to 74.5 km. We identified areas used intensively by dugongs in all 3 study areas, some of which were areas where seagrass presence has not been verified, or where dugongs have not been observed during past aerial surveys. Dugongs spent most of their tracking time within the lagoons, with 99.4% of GPS locations found inside the barrier reef. Nonetheless, where the lagoon was narrow and confined, 3 tracked dugongs used the fore reef shelf outside the barrier reef in the open ocean to commute between bays. Our findings can inform conservation and management initiatives in New Caledonia as well as other countries within the dugong’s range which have similar habitat geomorphology but where dugongs occur in numbers too low to be tracked and are considered Critically Endangered.

Effects of Fine Sediment on Seagrass Meadows: A Case Study of Zostera muelleri in Pāuatahanui Inlet, New Zealand

Seagrass meadows are vulnerable to fine sediment (mud) pollution, with impacts usually attributed to reduction in submerged light. Here we tested two non-exclusive hypotheses, that mud particles (<63 µm) impact seagrasses through both (1) the light climate and (2) changes in substrate physico-chemistry. We tested these hypotheses in Pāuatahanui Inlet, New Zealand, by comparing seagrass presence, abundance, and health, together with light climate and substrate physico-chemistry at contrasting habitats where (1) seagrass used to thrive but no longer grows (historical seagrass), (2) seagrass still persists (existing seagrass) and (3) seagrass has been present recently, but not currently (potential seagrass). Historical seagrass substrate had significantly higher mud (35% average), bulk density (1.5 g cm−3), porewater ammonium concentration (65 µM), and a more reduced redox profile (negative redox at only 2 cm soil depth) as well as a lower light availability when submerged compared to other habitats, while total daily light exposure differed little between habitats. This suggests that failure of seagrass to recolonize historical seagrass habitat reflects substrate muddiness and consequent unfavorable rhizosphere conditions. Our results provide evidence for the multi-stressor effects of fine sediment on seagrasses, with substrate suitability for seagrass being detrimentally affected even where light exposure seems sufficient.

Seagrass characterization on the southern Pacific coast of Costa Rica: history, vegetation, and environment

Abstract Seagrass conservation and management requires scientific understanding of spatial and temporal variability, information that is currently limited for the Eastern Tropical Pacific (ETP). Here, we analysed seagrass presence based on previous reports, herbarium collections and stakeholder knowledge, combined with field characterization in Golfo Dulce, southern Pacific coast of Costa Rica. Seagrasses were found at multiple locations along a narrow border close to shore and in up to 6 m depth within Golfo Dulce, dating back to 1969. Two seagrass species were found, Halophila baillonii and Halodule beaudettei. Seagrass biomass values for Golfo Dulce (12.0 ± 8.5 g DW m−2) were lower and water nutrient concentrations were higher than previously reported in the gulf. Shoot density (1513 ± 767 shoots m−2) was similar to previous reports. Stable isotope values in seagrass were −11.3 ± 1.0‰ δ13C and 1.2 ± 0.9‰ δ15N; while those in sediments were −26.1 ± 1.3 and 2.5 ± 0.9‰. In Golfo Dulce, isotopic values of both seagrass species do not overlap with other known primary producers. Management strategies should aim to minimize known seagrass stressors, protect potential seagrass habitat, and take into account the dynamic life strategies of the two seagrass species found.

The Use of Imagery and GIS Techniques to Evaluate and Compare Seagrass Dynamics across Multiple Spatial and Temporal Scales

Using aerial imagery and GIS techniques, a retrospective study conducted fine-scale (1.0 m2 resolution) seagrass mapping to document the spatial heterogeneity within seagrass habitats previously mapped at a broad scale (0.202 ha resolution). Thirty randomly selected estuarine habitats in Tampa Bay, Florida, were manually interpreted and digitized using 0.3 m resolution imagery from 2004, 2006, and 2008. Seagrass patches and patterns of seagrass change were quantified at multiple levels of spatial organization and multiple temporal scales. Habitats classified as patchy seagrass were found to contain, on average, 52.7% less seagrass when mapped using the patch-based, fine-scale approach compared to broad-scale map data. In higher-resolution mapping, seagrass was increasingly differentiated from bare sediment and the amount of seagrass quantified within the study’s extent was reduced compared to broad-scale mapping, which included some bare area in estimates of seagrass cover. Additionally, fine-scale mapping detected the presence of seagrass on tidal flat habitat that was previously considered “unvegetated” in broad-scale mapping. These findings can be used to improve the definitions of broad-scale mapping classes and suggest the selection of smaller ratio digitizing scales when mapping complex or sparsely covered seagrass habitats. Overall, fine-scale mapping at a large spatial extent provided insights into the patterning and rate of seagrass gap formation and fragmentation, appears to be a reasonable method for local studies or resource disturbance assessments, and has potential applications as a training tool for further advancement of semi-automated classification techniques.

Seasonal occurrence patterns of seagrass should influence resource assessment and management decisions: A case study in the Indian River Lagoon and Loxahatchee River Estuary, Florida

Seagrasses provide and maintain critical ecosystem functions and support rich biodiversity, yet they are highly susceptible to anthropogenic impacts. From 2002 to 2016 seagrasses were surveyed monthly or bimonthly for presence in the Indian River Lagoon (IRL) and Loxahatchee River Estuary (LRE) along the east coast of Florida. These data were used to assess seasonal seagrass presence patterns (i.e., annual maxima) and their relevance to management initiatives. Three species were examined (Halodule wrightii, Syringodium filiforme, and Halophila johnsonii) at 37 sites spanning 200 km of the IRL and 5.3 km of the LRE. Seagrass annual maxima, defined as bimonthly maximum annual percent presence of visible above-ground blades, exhibited clear seasonal trends: 61% of H. wrightii annual maxima (across years) occurred between May and August, 71% of S. filiforme annual maxima occurred between May and October, and 65% of H. johnsonii annual maxima occurred between March and June. Surveys intended to document and protect the spatial extent of seagrasses should, therefore, be scheduled during periods of expected annual maxima to capture the full extent of seagrass presence. These findings stress that any conservation-based seagrass monitoring program should conduct sampling efforts that account for the considerable seagrass seasonality. At a minimum, the survey period for H. johnsonii, a federally listed “threatened” species, should be revised to include March through June as an addendum to the current state and federal guidelines of June through September to provide better protection for this species. The results of this study suggest seagrass surveys for dredge and fill projects, dock permits, or other activities potentially damaging to seagrasses, should be conducted during periods when the annual maxima are most likely. Doing so will afford a more appropriate level of protection for these valuable ecosystem components.

Stable isotopes reveal the importance of saltmarsh-derived nutrition for two exploited penaeid prawn species in a seagrass dominated system

Estuaries represent highly important nursery habitats for a range of species, with refuge and nutrition being two key benefits derived from estuaries. Quantifying these benefits provides us with a means for enhancing fisheries productivity. Metapenaeus macleayi (School Prawn) and Penaeus plebejus (Eastern King Prawn) are two commercially and recreationally important species in New South Wales that utilise estuarine nurseries throughout their life history. In this study, stable isotopes of carbon, nitrogen and sulfur were used to determine the proportional contribution of primary producers to prawn nutrition in Brisbane Water (NSW). Both the saltmarsh grass Sporobolus virginicus and seagrass Zostera muelleri were found to support a high trophic contribution to prawns (up to 53% and 40%, respectively). The contributions of other primary producers such as mangroves, fine benthic organic matter (FBOM) and C3 saltmarsh plants were generally found to be much lower (0.7–15%). Such findings are generally consistent with patterns observed in other south-east Australian estuaries, however such a dominant role of saltmarsh in the presence of seagrass is a novel finding. These results highlight linkages between habitats of conservation concern and highly valuable fisheries species, and the benefit of using sulfur as an additional marker in Bayesian mixing models examining estuarine food webs.