Seagrass Samples Research Articles

Accumulation of metals by the seagrass, Z. Capricorni in Lake Illawarra

The concentrations of arsenic, cadmium, copper, lead, manganese, nickel and zinc in Zostera capricorni leaves and rhizomes were analyzed in order to document the accumulation of metals in Lake Illawarra seagrass tissues and to evaluate the potential role of Z. capricorni in the cycling of metals within the lake. Metal concentrations in seagrass tissues were compared with porewater metal concentrations and previously documented sediment concentrations to determine if the seagrass tissues reflect ambient metal concentrations. Zostera leaves and/or rhizomes reflected ambient concentrations of arsenic, cadmium, copper, manganese and zinc. Lead and nickel were not accumulated to high concentrations in most tissue samples from Lake Illawarra, although differences in ambient lead concentrations were reflected in some groups of leaf samples. Metal concentrations in seagrass tissues collected near to the Port Kembla industrial complex, and adjacent to the former Tallawarra power station, were significantly higher than concentrations in seagrass samples collected from the lake entrance. The majority of metals was accumulated to higher concentrations in leaves than in rhizomes; however, arsenic concentrations were highest in rhizomes. Z. capricorni in Lake Illawarra is likely to play a significant role in the cycling of copper, manganese, and possibly lead, via uptake from sediments, acropetal transferrance to leaves, and the release of metals from leaves into the water column or into the detrital food chain via leaf litter.

Research Article: Quality of Halodule wrightii growing near marinas

Researchers are just beginning to discover the importance of seagrasses, such as Halodule wrightii, to coastal ecosystems, but unfortunately seagrasses are being eliminated because of human manipulations. In the current study three locations of seagrass beds in Tampa Bay were studied: seagrass beds next to Tampa Bayside Marina, outside the marina, and a control group from Ft. DeSoto. The marina sites are disturbed by boating activities, which do not occur at Ft. DeSoto. It is hypothesized that the seagrasses next to the marina will have lower chlorophyll a, b, and carotenoid pigment concentrations as well as lower seagrass densities than at Ft. DeSoto because of boating disturbance and possible gasoline in the water. Although water analysis did not detect the presence of gasoline compounds in the water, seagrass density was significantly greater at Ft. DeSoto than the other two sites. Seagrass samples from each site were dissolved in Dimethylformamide to determine their photosynthetic qualities. From spectrophotometer readings at 480, 510, 646, and 664 nm the total chlorophyll a, b, and carotenoid concentrations were determined. All tests supported the hypothesis that the seagrass beds had greater amounts of chlorophyll a, b, and seagrass density, but carotenoids did not have significant difference among the three sites. This research is the first step to a project monitoring the health of H. wrightii at Tampa Bayside Marina that is being transplanted.

Role of physical disturbance in structuring fish assemblages in seagrass beds in Port Phillip Bay, Australia

Disturbance in seagrass habitats may cause variation in the structure of fish assem- blages and individual taxa. One important form of disturbance is wave action associated with strong winds. Total fish abundance and species richness from seagrass beds at 2 sites in Port Phillip Bay, Australia, were sampled during low and high wave disturbance. During high wave action (> 0.25 m) in seagrass beds, abundance of fish at one site decreased significantly, but species richness was unaf- fected at both sites. Plankton sampling conducted at the same time as seagrass sampling (directly 300 m offshore from the seagrass sites) found that species richness significantly increased during high wave conditions at both sites. Total fish abundance similarly increased in the plankton during high wave conditions at one site. We conclude that variation in assemblage structure during increased physical disturbance is related to variation in a small number of numerically dominant spe- cies within the assemblage. At the individual taxon level, numerically dominant species in the sea- grass and plankton showed considerable variation in response to disturbance. In the seagrass assem- blage, post-larval King George whiting Sillaginodes punctata (Cuvier and Valenciennes), adult weedfish Heteroclinus perspicillatus (Cuvier and Valenciennes), and pipefish juveniles and adults from the genus Stigmatopora decreased in abundance at either one or both sites during high wave conditions. Conversely, in the plankton, adult pipefish Hypelognathus rostratus (Waite and Hale), juvenile Stigmatopora and larval Gymnapistes marmoratus (Cuvier and Valenciennes) significantly increased in abundance during these same physical conditions. It appears that for some taxa physical disturbance may facilitate secondary planktonic dispersal.

Effect of El Nĩno on demographic, morphological, and chemical parameters in turtle-grass (Thalassia testudinum): an unexpected test of indicators.

We examined the response of demographic, morphological, and chemical parameters of turtle grass (Thalassia testudinum), to much-higher-than-normal rainfall associated with an El Niño event in the winter of 1997-1998. Up to 20 inches of added rain fell between December 1997 and March 1998. triggering widespread and persistent phytoplankton blooms along the west coast of Florida. Water-column chlorophyll concentrations estimated from serial Sea WiFS imagery were much higher during the El Niño event than in the previous or following years, although the timing and magnitude of phytoplankton blooms varied among sites. Seagrass samples collected in 1997, 1998, and 1999 provided an excellent opportunity to test the responsiveness of Thalassia to decline and subsequent improvement of water quality and clarity in four estuaries. Using a scoring technique based on temporal responsiveness, spatial consistency, and statistical strength of indicators, we found that several morphological parameters (Thalassia shoot density, blade width, blade number, and shoot-specific leaf area) were responsive and consistent measures of light stress. Some morphological parameters, such as rhizome apex density, responded to declines and subsequent improvement in water clarity, but lacked the statistical discriminating power necessary to be useful indicators. However, rhizome sugar, starch, and total carbohydrate concentrations also exhibited spatially and temporally consistent variation as well as statistical strength. Because changes in shoot density, as well as water clarity, affect rhizome carbohydrate levels, a composite metric based on Thalassia shoot density and rhizome carbohydrate levels together is probably more useful than either parameter alone as an indicator of seagrass health.

Spatial variability in the epiphytic algal assemblages of Zostera marina seagrass beds

Within-bed variation of epiphytic algal assemblages was studied in 3 Zostera marina beds around Plymouth Sound (Devon, United Kingdom) in order to determine if distance from edge of bed affected the assemblage composition. Replicate seagrass samples were taken at 0, 1, 3 and 6 m along a transect running from the edge of each bed. Individual epiphytes were enumerated and placed into 6 'functional' groups: filamentous, foliose, corticated filamentous, corticated foliose, sac- cate and coralline. The abundance of each functional group did not vary with distance into each bed, nor was it related to measures of seagrass architecture or potential grazing pressure from gastropods. A positive relationship between amphipod abundance and total epiphytes suggest these crustaceans are influenced by epiphytes as an available substrate rather than exerting a grazing effect. Differ- ences amongst beds, however, were evident for filamentous, corticated filamentous and coralline functional groups. These groups comprised 99% of all epiphytes, resulting in the total algal abun- dance being different amongst beds. Similarly, the assemblage composition of the epiphytes was con- sistent within each bed, but differed amongst all 3 beds. Overall, therefore, epiphytic abundance and composition was not affected by distance from the edge of the bed, seagrass architecture or grazing pressure within the bed, but existence of within-bed variation cannot be completely ruled out due to the comparatively low power of the analysis. The only significant variation occurred at the amongst- bed level, probably due to variations in large-scale factors.

Mortality estimates from age distributions: Critique of a method used to study seagrass dynamics

Age structure of seagrass samples has been used to estimate survival and recruitment and then used to estimate population growth rate. Survival rate can be estimated from age structure only if the population is neither growing nor declining (r = 0), so the age distribution is both stable and has stationary structure. If survival is estimated from age structure, it must be assumed that r = 0 or additional information about the population must be known. If a decaying exponential model is used for number (N) in each age class, ln N versus age has a slope of −(M + r), and so an incorrect survival rate, exp (−M), would be estimated if r ≠ 0. Simulations show that when r > 0, the slope of the regression of ln N versus age is too steep and hence mortality rate would be overestimated, and the reverse when r < 0. Ignoring the assumption of r = 0 is a fundamental flaw in many seagrass studies and calls into question the mortality and population growth rates that have been published.

PCDDs in the water/sediment–seagrass–dugong ( Dugong dugon) food chain on the Great Barrier Reef (Australia)

Polychlorinated dibenzo- p-dioxin (PCDD) and dibenzofuran (PCDF) concentrations were measured in sediment and seagrass from five locations in or adjacent to the Great Barrier Reef Marine Park. A full spectrum of Cl 5–8DDs were present in all samples and, in particular, elevated levels of Cl 8DD were found. PCDFs could not be quantified in any samples. The PCDD concentrations ranged over two orders of magnitude between sites, and there was a good correlation between sediment and seagrass levels. There were large quantities of sediment present on the seagrass (20–62% on a dry wt. basis), and it was concluded that this was a primary source of the PCDDs in the seagrass samples. The PCDD levels in the seagrass samples were compared with the levels in the tissue of three dugongs stranded in the same region. The relative accumulation of the 2,3,7,8-substituted PCDD congeners in the dugongs decreased by over two orders of magnitude with increasing degree of chlorination. This was attributed to the reduced absorption of the higher chlorinated congeners in the digestive tract, a behaviour that has been observed in other mammals such as domestic cows.

Alpha and beta diversity of harpacticoid copepods in a tropical seagrass bed: the relation between diversity and species' range size distribution

Alpha and beta diversity of harpacticoid copepods was studied in a Kenyan seagrass bed (Gazi Bay, Kenya) with a clear zonation of different seagrass species. The application of an appropriate sampling strategy made the interpretation of different spatial diversity levels possible. Alpha diversity was defined as the diversity of harpacticoid copepods associated with 1 seagrass spe- cies or 1 subhabitat (roots or leaves). Beta diversity was interpreted as changes in diversity between both subhabitats of 1 seagrass species and between different seagrass species along the tidal gradi- ent. A total of 115 harpacticoid copepod species were recorded in the seagrass samples. Of these, 36 species (31.3%) were restricted to the root subhabitat and 12 (10.4%) were only recovered from leaf samples. Higher diversity was recorded for the deeper seagrass species (Syringodium isoetifolium, Halophila stipulacea). Copepod communities associated with Halophila ovalis and H. stipulacea (both pioneer seagrass species) were clearly different from one another in terms of diversity. A trend towards more specialized habitat preference (i.e. a lower ecological range size) was found with increasing diversity. The left-skewed species' range size distribution for the more diverse samples was clearly different from the typical right-skewed curves reported in most terrestrial studies. This may provide evidence for fundamental differences between marine species and terrestrial ones in their range size distribution.

SPATIAL VARIABILITY IN EPIPHYTIC FORAMINIFERA FROM MICRO- TO REGIONAL SCALE

Density of epiphytic foraminifera varies spatially from sub-leaf to regional scales within Posidonia australis meadows of south Western Australia. Foraminiferal populations on individual seagrass leaves show compositional zoning and aggregation around algae and serpulid worm tubes. Such microscale spatial heterogeneity could reflect microhabitat, leaf growth history, food source and recruitment patterns. Most foraminifera have homogeneous densities on individual plants, and are distributed evenly throughout seagrass samples from meadows at a given geographic site. Only species associated with patchy epiphytic algae within the meadows show spatial heterogeneity at the local scale. Spatial homogeneity within the seagrass meadow reflects repetition of seagrass leaf substrate and microhabitats, and the uniformity of ambient environmental variables at scales larger than the seagrass leaves. Spatial homogeneity in this environment permits characterization of a given geographic site based on three samples. At regional scales, foraminifera may have homogeneous and heterogeneous distributions. Abundance of individual species is uniform, sporadic, or shows a gradient pattern along the coast. Patterns of variation in foraminiferal populations regionally, partly reflect the climate gradient, but also factors operating at micro- and local scales. Regionally distinct assemblages could be defined for different climatic regions along the coast. Thus, populations of the various foraminiferal species are regulated by environmental or biotic variables at different scales. This study shows how sample composition at each site reflects spatial variation of species at micro-, local and regional scales and how these differences can be used to define assemblages which characterize microhabitats, localities and regions.

Pesticide and Herbicide Residues in Sediments and Seagrasses from the Great Barrier Reef World Heritage Area and Queensland Coast

Pesticides and herbicides including organochlorine compounds have had extensive current and past application by Queensland's intensive coastal agriculture industry as well as for a wide range of domestic, public health and agricultural purposes in urban areas. The persistent nature of these types of compounds together with possible continued illegal use of banned organochlorine compounds raises the potential for continued long-term chronic exposure to plants and animals of the Great Barrier Reef. Sediment and seagrass samples were collected from 16 intertidal and 25 subtidal sampling sites between Torres Strait and Townsville, near Mackay and Gladstone, and in Hervey and Moreton Bays in 1997 and 1998 and analysed for pesticide and herbicide residues. Low levels of atrazine (0.1–0.3 μg kg −1), diuron (0.2–10.1 μg kg −1), lindane (0.08–0.19 μg kg −1), dieldrin (0.05–0.37 μg kg −1), DDT (0.05–0.26 μg kg −1), and DDE (0.05–0.26 μg kg −1) were detected in sediments and/or seagrasses. Contaminants were mainly detected in samples collected along the high rainfall, tropical coast between Townsville and Port Douglas and in Moreton Bay. Of the contaminants detected, the herbicide diuron is of most concern as the concentrations detected have some potential to impact local seagrass communities.

Settlement and recruitment of the abalone Haliotis cyclobates Péron, 1816

The settlement preference, distribution and juvenile recruitment distribution of Haliotis cyclobates were investigated in a seagrass meadow in Gulf St Vincent, South Australia, in 1993 and 1994. Samples of hard substratum and seagrass were collected from seagrass patches and open areas and examined for newly settled and 0+ recruits. Hard substrata consisted of small rocks, large bivalve shells and bottles. Twelve newly settled recruits (<3 mm) were found: 11 on seagrass and one on hard substratum. Settlement onto seagrass blades is the first field example of an abalone species settling naturally onto soft substratum. 0+ recruits (4–9 mm) were found from March to October, indicating a single spawning and settlement season. 0+ recruits were found on small isolated patches of hard substratum in open and seagrass areas, suggesting that post-settlement migration may have some influence on recruitment patterns. The results indicate that the early life history of Haliotis cyclobates is adapted for enhancing recruitment into seagrass areas. Settlement onto seagrass blades is different from that observed for other species of abalone, and clarification of the specific settlement cue may contribute to the understanding of abalone settlement behaviour.

The Effects of Anthropogenic Nutrient Enrichment on Turtle Grass (Thalassia testudinum) in Sarasota Bay, Florida

Four meadows of turtle grass (Thalassia testudinum Banks ex Konig) in Sarasota Bay, Florida were sampled on a bimonthly basis from June 1992 to July 1993 to determine spatial and temporal variation in short shoot density, biomass, productivity, and epiphyte loads. Concurrent with the seagrass sampling, quarterly water-quality monitoring was undertaken at ≥3 sites in the vicinity of each studied seagrass meadow. Three months after termination of the seagrass sampling effort, a biweekly water-quality monitoring program was instituted at two of the seagrass sampling sites. In addition, a nitrogen loading model was calibrated for the various watersheds influencing the seagrass meadows. Substantial spatial and temporal differences in turtle grass parameters but smaller spatial variation in water quality parameters are indicated by data from both the concurrent quarterly monitoring program and the biweekly monitoring program instituted after termination of the seagrass study. Turtle grass biomass and productivity were negatively correlated with watershed nitrogen loads, while water quality parameters did not clearly reflect differences in watershed nutrient inputs. We suggest that traditional water-quality monitoring programs can fail to detect the onset or continuance of nutrient-induced declines in seagrass health. Consequently, seagrass meadows should be monitored directly as a part of any effort to determine status and/or trends in the health of estuarine environments. *** DIRECT SUPPORT *** A01BY074 00029

Radioactivity levels in fish, shellfish, algae and seagrass collected from the Eastern Black Sea coast of Turkey, 1992

Radioactive pollution of fish, shellfish, algae and seagrass samples collected in the Trabzon littoral region of the Eastern Black Sea coast of Turkey was investigated. Radioactivity was detected in all samples and varied with species and location. The highest concentrations of Cs 137 were found in U.lactuca and Z.marina while the lowest activity was detected in T.medditerraneus and A.fallax. The findings of 1992 were compared with those of our earlier study. It appears from our data that Chernobyl‐derived radiocesium has diminished considerably in Turkish coastal waters during the period 1900–1992.

An efficient method for estimating seagrass biomass

Seagrass biomass was estimated in a 37.649 km 2 area in Moreton Bay, Queensland. The study area was stratified by hand-digitising seven strata that were identified by photo-interpretation of a colour aerial photograph. A pilot study was undertaken to calculate how many samples should be taken at each site and how best to allocate sampling effort to the seven strata. Seagrass samples taken with a modified ‘orange-peel’ grab and by coring were the same ( P 0.5). As the grab is easier to use, quicker, can be operated by one person from a small dinghy, and does not call for diving or wading, we used it for the main study. Four seagrasses were found in the study area. The dominant seagrass was Zostera capricorni Aschers., with smaller quantities of Halophila ovalis (R.Br.) Hook.f., Halophila spinulosa (R.Br.) Aschers. and Halodule uninervis (Forssk.) Aschers. The total seagrass biomass in the study area was estimated at 2145±568 t (95% confidence interval). Stratification improved the precision of the simple random sampling estimate by 68%. The use of a Geographic Information Systemm (GIS) and Computer Aided Drafting (CAD) for sample design, a Global Positioning System (GPS) for locating sample sites in the field and the grab for taking samples substantially enhanced research productivity and accuracy. The experimental design is statistically robust and provides large samples for cost-effective and reliable estimates of seagrass biomass.

Regional geochemistry of metal-contaminated surficial sediments and seagrasses in upper Spencer Gulf, South Australia

Surficial sediments, shallow sediment cores and seagrass samples were collected over an area of about 600 km 2 of upper Spencer Gulf, South Australia, adjacent to a major lead-zinc smelter. Regional variation in heavy metal contents was studied in relation to different pathways of contamination from the smelter complex, and geochemical association with natural constituents of the sediments. About 300 km 2 were contaminated to some extent. Areas of appreciable contamination (10 × background) were greatest for Cd and least for As, with Pb and Zn intermediate. Regional trends of heavy metals in the sediment reflected inputs of pollutants from both liquid effluents and atmospheric fallout, modified by tidal currents. Total accessions to Germein Bay were estimated to be at least 25 000 tonnes each of Pb and Zn and 500 tonnes of Cd and As. Arsenic differed both in its distribution with sediment depth and in its geochemical associations when compared to Pb, Zn and Cd. Correlation of Cd with the fine fraction (< 20 μm) permitted a normalization of data which accounted for marked regional variations in sediment grain size and provided a better basis of assessing the regional impact of pollution. Metal concentrations in Posidonia leaves were highly correlated with total and EDTA extractable metal concentrations in the sediments, and may provide a more sensitive indicator of metal dispersion. Background levels of metals in Posidonia were not found in our study area.

Evidence for the occurrence of specific iron (III)-binding compounds in near-shore marine ecosystems.

Aqueous extracts of samples from representtive types of near-shore marine ecosystems were examined for growth-promoting activity for the siderochrome auxotroph, Arthrobacter JG-9. Blue-green algal mat and sea grass samples gave strongly positive responses. Relative to Desferal (Ciba Pharmaceutical Co., Summit, N.J.), concentrations up to 110 ng/g (wet weight) of sample were found. In contrast, extracts of anaerobic muds or macroalgae gave no detectable activity. The hydroxamate type of iron chelator may be important in providing a form of iron in sea water readily utilized by the microalgae and marine higher plants.

Evidence for the Occurrence of Specific Iron (III)-Binding Compounds in Near-Shore Marine Ecosystems

Aqueous extracts of samples from representtive types of near-shore marine ecosystems were examined for growth-promoting activity for the siderochrome auxotroph, Arthrobacter JG-9. Blue-green algal mat and sea grass samples gave strongly positive responses. Relative to Desferal (Ciba Pharmaceutical Co., Summit, N.J.), concentrations up to 110 ng/g (wet weight) of sample were found. In contrast, extracts of anaerobic muds or macroalgae gave no detectable activity. The hydroxamate type of iron chelator may be important in providing a form of iron in sea water readily utilized by the microalgae and marine higher plants.