Seagrass Condition Research Articles

Assessing the potential for satellite image monitoring of seagrass thermal dynamics: for inter- and shallow sub-tidal seagrasses in the inshore Great Barrier Reef World Heritage Area, Australia

ABSTRACTSeagrass meadows are at increasing risk of thermal stress and recent work has shown that water temperature around seagrass meadows could be used as an indicator for seagrass condition. Satellite thermal data have not been linked to the thermal properties of seagrass meadows. This work assessed the covariation between 20 in situ average daily temperature logger measurement sites in tropical seagrass meadows and satellite derived daytime SST (sea surface temperature) from the daytime MODIS and Landsat sensors along the Great Barrier Reef coast in Australia. Statistically significant (R2 = 0.787–0.939) positive covariations were found between in situ seagrass logger temperatures and MODIS SST temperature and Landsat sensor temperatures at all sites along the reef. The MODIS SST were consistently higher than in situ temperature at the majority of the sites, possibly due to the sensor’s larger pixel size and location offset from field sites. Landsat thermal data were lower than field-measured SST, due to differences in measurement scales and times. When refined significantly and tested over larger areas, this approach could be used to monitor seagrass health over large (106 km2) areas in a similar manner to using satellite SST for predicting thermal stress for corals.

The enhancement in comprehension for the younger generation of school age in conserving coastal biodiversity in Kepulauan Seribu, Indonesia

Handayani T, Widiarti R, Soepardjo AH, Afriyani F, Burhanuddin E. 2017. The enhancement in comprehension for the younger generation of school age in conserving coastal biodiversity in Kepulauan Seribu, Indonesia. Ocean Life 1: 20-25. The exploration and exploitation can lead to the ecosystem and natural resources degradation. Kepulauan Seribu of Special Area of Jakarta has been extensively utilized and developed for tourism area, which could lead to the decreasing of environmental conditions. The awareness for keeping the ecosystem and marine life should be developed since early age. The objective of this research is to determine the level of understanding and ability in conserving the marine environment in their neighborhood for school-age generation. The method used in this study was quantitative with descriptive analysis. Two groups of the Junior High School students of Pulau Tidung and Pulau Harapan of the Kepulauan Seribu were provided training on conservation on coastal ecosystems. The education and training encompass the observation activity for coral reef using the Coral Health Chart method, seagrass condition observation through SeagrassWatch method, and introduction in the mangrove ecosystem. Based on the study, it can be inferred that the resulting activity indicated the level of understanding of cognitive abilities of two groups of the Junior High School in those two locations has increased. In addition, they affective ability increased sharply toward the students from Pulau Tidung whereas in Pulau Harapan an occurred a large increase in psychomotor abilities. The conclusion of this program is managed to improve the understanding and ability to act for the younger generation in conserving marine and coastal environments.

Land use is a better predictor of tropical seagrass condition than marine protection

Effective coastal conservation requires a better understanding of how human activities on land may directly and indirectly affect adjacent marine communities. However, the relationship between terrestrial and marine systems has rarely been considered in terrestrial and marine reserve design. Seagrasses are affected by land-based activities due to their proximity to terrestrial systems and sensitivity to fluxes of terrestrially-derived organic and inorganic material. Our study examines how land use patterns adjacent to seagrass meadows influence the ecological integrity of seagrass using a suite of seagrass condition metrics on a landscape level across the Philippine archipelago. Using canonical correlation analysis, we measured the association between environmental variables (land use and seagrass abiotic conditions) with biotic variables (seagrass species richness and abundance). Terrestrial protection adjacent to seagrass meadows, defined as the absence of various anthropogenic land use perturbations, had significant positive effects on seagrass condition. The watershed area, and area of farmland and human development, had the most negative effect on seagrass condition. Using analysis of covariance and regression, we examined how marine protected area (MPA) establishment, size, and age, affected seagrass biotic conditions while holding environmental conditions constant. The relationship between biological and environmental canonical factors did not vary as a function of an MPA. This study provides evidence that land use is more important than marine protection for tropical seagrass condition. Our results demonstrate the complementary connection between land and sea, justifying the ‘ridge-to-reef’ approach in coastal conservation. Proper management of seagrasses should account for stewardship of the adjacent watersheds.

Five years on: monitoring of Long Island Point’s Western Port wastewater discharge

The Esso Long Island Point facility is situated on the edge of Western Port, an important Ramsar designated wetland for migratory birds in Victoria, Australia. The gas fractionation and crude oil storage facility has operated for over 40 years and has discharged treated wastewater to Western Port for most of these years in accordance with its environmental regulatory licence. The 2003 State Environment Protection Policy for Waters of Western Port is the Victorian Environment Protection Authority’s regulatory framework for licensing wastewater discharges to the wetland, and among other items, requires that discharges must cause no ‘detrimental change in the environmental quality of the receiving waters’ or ‘chronic impacts outside any declared mixing zone’. A major upgrade to the water treatment facility in 2010 included a risk-based marine ecosystem program to monitor key environmental indicators including water quality, jetty pile invertebrate communities and seagrass condition. The program’s longer-term monitoring record has allowed assessment of potential chronic effects on invertebrates and seagrass by comparing temporal changes at monitoring sites over the period from pre-operations (2010) to present (2016) and spatial changes between near-field to far-field sites, kilometres from the discharge point. The program has shown that management of the discharge maintains beneficial uses and environmental objectives at the boundary of the mixing zone, and the marine ecosystem is protected from potentially slower and longer-term adverse effects in the far-field. The program demonstrates that the treated wastewater discharge has had no adverse impact on key environmental indicators in Western Port over the longer-term study period.

What lies beneath: Why knowledge of belowground biomass dynamics is crucial to effective seagrass management

Conservation of seagrasses meadows is important, because these habitats are ecologically important and under threat. Monitoring and modelling are essential tools for assessing seagrass condition and potential threats, however there are many seagrass indicators to choose from, and differentiating between natural variability and declining conditions poses a serious challenge. Tropical seagrass meadows in the Indo-Pacific, in contrast to most temperate meadows, are characterized by a multi-species composition and a year-round growth. Differences in characteristics between species growing within one meadow could induce uncertainty in the assessment of the dynamics of these meadows if variation in productivity and related biomass turnover timescales are not taken into consideration. We present data on biomass distribution, production and turnover timescales of above- and belowground tissues for three key tropical seagrass species (Thalassia hemprichii, Cymodocea rotundata and Halodule uninervis) in two mixed-species meadows in the Spermonde Archipelago, Indonesia. Seagrass leaf turnover time scales were comparable for the three studied seagrass species and varied between 25 and 30 days. Variation in leaf and rhizome turnover timescales were small (or insignificant) between the two meadows. In contrast, rhizome turnover time scales were around ten times longer than leaf turnover timescales, and large differences in rhizome turnover time scales (200–500 days) were observed between the species. The late-successional species T. hemprichii had much slower rhizome turnover compared to the two early successional species. Furthermore, since rhizome biomass has a much longer turnover time compared to leaf biomass, changes in rhizome biomass reflect effects on seagrass meadows on a much longer timescale compared to changes in leaf biomass for these tropical meadows. We conclude that belowground biomass dynamics are an important proxy to assess long-term effects of environmental stressors on seagrass ecosystems and should be included in tropical seagrass management programmes.

Unravelling complexity in seagrass systems for management: Australia as a microcosm

Environmental decision-making applies transdisciplinary knowledge to deliver optimal outcomes. Here we synthesise various aspects of seagrass ecology to aid environmental decision-making, management and policy. Managers often mediate conflicting values and opinions held by different stakeholders. Critical to this role is understanding the drivers for change, effects of management actions and societal benefits. We use the diversity of seagrass habitats in Australia to demonstrate that knowledge from numerous fields is required to understand seagrass condition and resilience. Managers are often time poor and need access to synthesised assessments, commonly referred to as narratives. However, there is no single narrative for management of seagrass habitats in Australia, due to the diversity of seagrass meadows and dominant pressures. To assist the manager, we developed a classification structure based on attributes of seagrass life history, habitat and meadow form. Seagrass communities are formed from species whose life history strategies can be described as colonising, opportunistic or persistent. They occupy habitats defined by the range and variability of their abiotic environment. This results in seagrass meadows that are either transitory or enduring. Transitory meadows may come and go and able to re-establish from complete loss through sexual reproduction. Enduring meadows may fluctuate in biomass but maintain a presence by resisting pressures across multiple scales. This contrast reflects the interaction between the spatial and temporal aspects of species life history and habitat variability. Most management and monitoring strategies in place today favour enduring seagrasses. We adopt a functional classification of seagrass habitats based on modes of resilience to inform management for all seagrass communities. These concepts have world-wide relevance as the Australian case-studies have many analogues throughout the world. Additionally, the approach used to classify primary scientific knowledge into synthesised categories to aid management has value for many other disciplines interfacing with environmental decision-making.

Comparison of remotely-sensed surveys vs. in situ plot-based assessments of sea grass condition in Barnegat Bay-Little Egg Harbor, New Jersey USA

With the increasing appreciation that sea grass habitats are in global decline, there is a great need to be able to efficiently and effectively assess and characterize the status and trends of sea grass in our coastal ecosystems. This paper examines the utility of remotely sensed vs. in situ plot-based monitoring using the Barnegat Bay-Little Egg Harbor (BB-LEH), New Jersey, USA estuarine system as a case study. Eelgrass (Zostera marina) is the dominant species, while widgeon grass (Ruppia maritima) is also common in lower salinity regions of the BB-LEH. Aerial imagery collected during the months of July and August 2009 was interpreted and mapped using object based image analysis techniques, similar to techniques used in the 2003 mapping survey of this system. Boat-based in situ monitoring data were collected concurrently with the aerial photography to assist the image interpretation and for an independent accuracy assessment. We compared the remotely-sensed mapping of sea grass cover change (in 2003 vs. 2009) vs. in situ plot-based monitoring conducted from 2004 through 2009. Comparison of the remotely-sensed vs. the in situ plot-change analysis suggests that the two methodologies had broadly similarly results, with the percent area showing declines in sea grass cover greater than those that exhibited increases. In conclusion, the two studies provide corroborating evidence that sea grass has declined in percent cover in the BB-LEH system during the decade of the 2000’s. While remotely-sensed surveys provide synoptic information for a “big picture” view on sea grass distribution, site specific in situ sampling is required to determine other aspects of sea grass status, e.g. above vs. below-ground biomass, blade length, shoot density, epiphytic loading, etc. Either method alone gives an incomplete picture. As demonstrated in this study, to fully characterize the spatial extent, health, and density of sea grass meadows across the entire estuary, combining remote sensing surveys concomitantly with comprehensive in situ assessment provides the most robust approach.

Watershed discharge patterns, secondary consumer abundances, and seagrass habitat condition in Yap, Micronesia

Watershed discharge, water quality, and seagrass assemblages were examined along the western coast of Yap Proper, Micronesia. Submarine groundwater discharge (SGD) during low tides associated with new and full moons contributed disproportionally to freshwater delivery where compromised Thalassia habitats existed. Despite SGD influence, nutrient sampling indicated that one characteristic regime may be a net import of new nitrogen and phosphorous (NO3 and PO4) from offshore to inshore waters, agreeing with sparse watershed development. Biologically recycled nitrogen (NH4), however, was highest where SGD contribution was largest. Time-and-tide-limited sampling likely precluded generalized relationships between SGD and NH4 across the entire study area, however, spatial profiling of SGD during low-tide events (i.e., a proxy to nutrient input) was strongly associated with seagrass habitat condition (defined within). Concomitantly, sea cucumber densities were over a magnitude of order lower than in regionally comparable Thalassia habitats, and negatively correlated with seagrass condition. Both top-down and bottom-up considerations are discussed.

Komunitas Lamun di Pulau Barranglompo Makassar: Kondisi dan Karakteristik Habitat

Indication on seagrass decline has been observed in many places including Barranglompo Island of Makassar. Condition of damaged seagrass has significant impacts to the roles of seagrass as habitat, spawning ground, and feeding ground for various marine organisms and also role of seagrass as carbon absorbent and stocks. In order to provide a reference for appropriate seagrass management and conservation, it is required data on seagrass habitat. A research was done in Barranglompo Island, Makassar from December 2010 to November 2011. Seagrass condition was observed based on McKenzie et al . (2001) and Balestri et al . (2003). This research showed that large seagrass coverage was dispersed in southern, western and northern sides of the island. Meanwhile, seagrass spesies with wider distribution were E. acoroides, T. hemprichii and C.rotundata .

Integrating Scales of Seagrass Monitoring to Meet Conservation Needs

We evaluated a hierarchical framework for seagrass monitoring in two estuaries in the northeastern USA: Little Pleasant Bay, Massachusetts, and Great South Bay/Moriches Bay, New York. This approach includes three tiers of monitoring that are integrated across spatial scales and sampling intensities. We identified monitoring attributes for determining attainment of conservation objectives to protect seagrass ecosystems from estuarine nutrient enrichment. Existing mapping programs provided large-scale information on seagrass distribution and bed sizes (tier 1 monitoring). We supplemented this with bay-wide, quadrat-based assessments of seagrass percent cover and canopy height at permanent sampling stations following a spatially distributed random design (tier 2 monitoring). Resampling simulations showed that four observations per station were sufficient to minimize bias in estimating mean percent cover on a bay-wide scale, and sample sizes of 55 stations in a 624-ha system and 198 stations in a 9,220-ha system were sufficient to detect absolute temporal increases in seagrass abundance from 25% to 49% cover and from 4% to 12% cover, respectively. We made high-resolution measurements of seagrass condition (percent cover, canopy height, total and reproductive shoot density, biomass, and seagrass depth limit) at a representative index site in each system (tier 3 monitoring). Tier 3 data helped explain system-wide changes. Our results suggest tiered monitoring as an efficient and feasible way to detect and predict changes in seagrass systems relative to multi-scale conservation objectives.

Remote influence of off-shore fish farm waste on Mediterranean seagrass (Posidonia oceanica) meadows

The aim of this study was estimating the remote influence of waste dispersed from a large off-shore fish farm complex (6197 ton year(-1)) on the near-shore Posidonia oceanica meadow (26-27 m deep) located at a distance of 3 km. Measurements of isotopic nitrogen content in epiphytes and seagrass leaf tissues, epiphyte biomass, shoot size, herbivory pressure, shoot density and seagrass meadow cover, performed in this meadow (FA area) were compared with those obtained in an undisturbed control meadow (CA area) to evaluate: (1) the remote influence of waste and (2) the impact of such influence on seagrass condition. In addition, delta(15)N measurements in particulate organic matter of natural and anthropogenic origin were used in a single-isotope mixing model to elucidate the relative contributions of these sources to the isotopic N signal measured in epiphytes and leaf tissues. Total tissue N content was similar between meadow areas, but delta(15)N signatures were significantly higher in the FA area than in the CA area both in epiphytes and seagrass leaf tissues. Results from the mixing model, together with available information on local currents and previous studies, support the conclusion that the dispersion of farm wastes over large areas (spanning kilometres) are responsible for the elevated delta(15)N signatures found in the FA meadow area. Despite this, no changes in meadow structure were detected and only some changes at the level of seagrass community (epiphytes abundances and herbivores activity) could be interpreted at the light of nutrient-induced effects in the FA area. Results from this study indicate that concentrating aquaculture facilities in off-shore areas is a strategy not totally exempt of environmental risk on near-shore sensitive habitats such as seagrass meadows.

Rapid monitoring of extent and condition of Seagrass habitats with aerial photography “mega‐Quadrats”

Monitoring seagrass habitats is required by many agencies and jurisdictions including Natural Resource Management (NRM) regions in Australia. Baseline mapping of seagrass habitats is proceeding in Tasmania, Australia and the next stage will be to conduct regular monitoring of extent and condition. This paper presents a summary of the results of recent research that addressed outstanding issues in reliable measurement of seagrass condition with optical remote sensing. The results enable the proposal of a new monitoring methodology based on sampling habitats with “mega‐quadrats” (around 200 m x 200 m) extracted from “low tech” imagery and present a prototype image visualisation comparison matrix (IVCM).

Effects of drift macroalgae and light attenuation on chlorophyll fluorescence and sediment sulfides in the seagrass Thalassia testudinum

We examined fluorescence parameters, chlorophyll indices, and sediment sulfides in the leaves of the subtropical seagrass Thalassia testudinum in relation to shading by drift macroalgae and artificial light reduction in a shallow meadow near Port Aransas, Texas, USA. Experiments conducted during a 5-week period in autumn 2003 included three cages in 0.7 m water depths covered with neutral density screening to achieve four light treatments: a control at full insolation ( I o) and at 10%, 33%, and 50% I o. Seagrasses in six remaining cages were covered with a 50% cover of drift macroalgae similar to that observed in situ. Effective quantum yield ( Y), non-photochemical quenching (NPQ), and minimal fluorescence ( F o) at the apex and base portions of six leaves were measured under the four different light regimes and under the drift algal treatment once a week for four weeks. Values of fluorescence quantum yield in older distal segments were lower than in proximal younger segments in all treatments, likely reflecting differences in tissue age. Y decreased at the leaf apex in both the light reduction and drift macroalgae treatments following the first week of the study. At the end of two weeks Y had also decreased at the leaf base and continued to decrease in both leaf areas over the course of the experiment in all treatments relative to the control. Shading by drift algae and artificial light reduction also induced increases in NPQ. The increase was highest at the 10% I o treatment. F o values were stable beneath the drift macroalgae treatment but increased in plants subjected to artificial light reduction. Leaf chlorophyll (chl) a content, measured in each treatment at the end of the study, ranged from 4 to 5.2 mg chl g dry weight − 1 . Chl a increased at 50% and 33% I o, showed no change in the drift macroalgal treatment, but decreased significantly at 10% I o. Chl a : b ratios at 10% I o (1.3) were also significantly lower than all other treatments (range 1.9 to 2.2), including the control. The changes in pigment concentrations under various regimes of light reduction suggest various degrees of photoacclimation relative to controls and plants shaded by macroalgae. Coincident with the changes in Y and NPQ, sediment porewater sulfide concentrations increased in drift macroalgal and artificial light reduction treatments, and were inversely correlated to light. Highest sulfide values were measured in the 10% I o treatment but were significantly different at each experimental light level. These preliminary results suggest that chlorophyll fluorescence is a useful and non-destructive indicator of seagrass condition that has potential as a monitoring tool for management of an important but threatened coastal resource.