Does estuarine health relate to catchment land-cover in the East Kleinemonde system,South Africa?

Temporarily open/closed estuaries in South Africa are being subjected to varying degrees of catchment land-cover transformation. Natural landscapes and hydrological functions are integral to the functioning of estuaries. The relationship between catchment land-cover and the health of the East Kleinemonde Estuary was investigated between 2011 and 2013, using geographic information system (GIS) techniques to delineate and quantify land-cover in the whole catchment, in the lower section of the catchment, and in the 1 km and 100 m buffer zones surrounding the estuary. Human activities, as outlined by the Department of Water Affairs resource directed measures (RDM) studies, and their associated land-cover classes are described. Possible links between catchment and buffer zone land-cover class composition and the health of the East Kleinemonde Estuary were explored. There was a relationship between catchment land-cover and estuarine health within all assessed catchment delineations. Natural land-cover was determined to be the best predictor of estuarine health for the East Kleinemonde system. The methods employed in this study can be applied to other temporarily open/closed estuaries in South Africa to prioritise these systems for rehabilitation and/or conservation.     

Iron limitation of phytoplankton in an urbanized vs. forested southeastern U.S. salt marsh estuary

Over the last two decades, escalating rates of coastal development have altered macro- and micronutrient loading patterns to many southeastern U.S. estuaries. This study addresses a potential consequence of urbanization-associated coastal deforestation that may have important implications for estuarine ecosystem productivity: a reduction in bioavailable Fe. We compared the potential for Fe limitation at representative sites in two neighboring South Carolina salt marsh estuaries, one (“Parsonage Creek” site in Murrells Inlet estuary) impacted by urbanization-associated clear-cutting, and the other (“Oyster Landing” site in North Inlet estuary) undeveloped and surrounded by forests. The urbanized estuarine site was marked by lower dissolved Fe concentrations compared to the forested estuarine site. In bioassay experiments conducted from 1996 to 1999, the addition of chelated Fe to natural phytoplankton populations stimulated chlorophyll a concentrations in water from Parsonage Creek on 6 of 11 sampling dates. Chlorophyll responses in Oyster Landing water also were observed on two of those sampling times, dates that followed periods of relatively low rainfall. In one experiment, the addition of Fe+NO₃⁻ to Parsonage Creek water led to significantly higher chlorophyll concentrations than when NO₃⁻ was added alone, but Fe+NH₄⁺ addition did not result in higher chlorophyll than NH₄⁺ addition alone. It was hypothesized that the difference in NO₃⁻ and NH₄⁺ responses was related to a greater tendency towards Si depletion in Fe-stressed NO₃⁻-grown samples, or alternatively, to the higher Fe requirement for NO₃⁻ assimilation relative to that needed for NH₄⁺ assimilation. In bioassay experiments using Fe-deplete semi-continuous cultures of Synechococcus WH8101, Fe addition did not affect the net growth rate of cultures transferred to water from either estuary, but increased the chlorophyll a content of cells transferred to Parsonage Creek water. Finally, photosynthesis vs. irradiance parameters (α, P_max) obtained from Oyster Landing samples (<2 μm size fraction) were similar to those measured in Fe-replete Synechococcus continuous cultures, while the same parameters derived from Parsonage Creek samples were much lower and comparable to those from Fe-deplete cultures. The results indicate that phytoplankton population growth from high salinity salt marsh estuaries can be Fe-limited. Also, the potential for Fe limitation was more prevalent in a urbanized deforested estuary than in an undeveloped forested estuary, consistent with the hypothesis that organically bound Fe from coastal forests plays an important role in supplying Fe for the growth of estuarine phytoplankton.     

Modelling the distribution and growth of ‘problem’ green seaweed in the Medway estuary,UK

The results of a modelling study to investigate the mechanisms controlling macroalgal growth within the Medway estuary, UK, are presented. Intertidal zone bathymetry, tidal dynamics and turbidity control the time available for nutrient uptake and photosynthesis, and were used as a basis for predicting areas where macroalgae will grow. Tidal bed stress was also considered as a controlling factor for the presence of the less robust green macroalgae species. Two approaches to predicting macroalgal distributions were applied: (1) a simple ‘suitability index’ method based on tidal flooding and drying, taking account of the conflict between time available for nutrient uptake and for photosynthesis; and (2) a biological macroalgal growth model that includes a detailed treatment of nutrient uptake and plant growth. The former approach assigns a value between zero and one for the suitability of a location for macroalgal occurrence, while the latter predicts the full macroalgal growth dynamics over an annual cycle. Tidal bed stress was included in both approaches as an independent modifier of macroalgal occurrence/growth. Results were compared with aerial survey maps of observed vegetation cover and time series of measured biomass density. Both approaches gave good predictions of non-species-specific vegetation cover in the intertidal zone of the Medway. Tidal bed stress was found to be a strong predictor of the specific occurrence of Enteromorpha spp. and Ulva spp., with these species favouring areas of low tidal energy. It was concluded that light and a lack of suitable regions with low tidal bed stress, rather than nutrients, were the main factors limiting excessive growth of Enteromorpha spp. and Ulva spp. in the estuary. Although this study was focussed on the Medway, the results are likely to be applicable to a broad range of relatively turbid, meso- and macro-tidal estuaries. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Changes in the sublittoral hard substrate communities in the Oosterschelde estuary (SW Netherlands), caused by changes in the environmental parameters

In order to assess the effects of the execution of the Delta Project, the sessile sublittoral communities on hard substrates in the Oosterschelde estuary and the environmental parameters were quantitatively investigated from 1985 till 1990. During the construction period of the barrier, three communities were sampled in the photic zone and four in the aphotic zone. The distribution of the communities in the photic zone seemed to be determined by the exposition to water movement and depth, while the communities in the aphotic zone were restricted to geographic areas, with differences in tidal current velocities: the mouth of the estuary, the Hammen, the central part and the Zijpe. Two years after the completion of the enclosure works, the community structure changed rapidly, caused by decreases of tidal current velocities, increases of the amounts of sedimentation, especially of fine sediments, and an increase of the transparency of the water. Changes within the associated vagile animals showed the same tendency as the sessile communities: under less exposed conditions the number of organisms remained the same or increased, while at some locations this increase was nullified by increasing amounts of sedimentation.     

General Patterns in Invasion Ecology Tested in the Dutch Wadden Sea: The Case of a Brackish-Marine Polychaetous Worm

The success of invasive aquatic species is determined by a variety of attributes such as wide environmental tolerance, high genetic variability, short generation time, early sexual maturity, high reproductive capacity, and a broad diet. Usually, introduced species, after some time lag since inoculation, show an exponential population increase and expansion. Maintenance of the immigrant species at a high population level will be dependent on interspecific competition with native species and availability of habitat and food. Eventually, the immigrant population may decline, for instance due to increased predation pressure, parasite infestation or loss of genetic vigour. These characteristic patterns in invasive species are reviewed for the case of the North American spionid polychaete Marenzelleria cf. wireni in the Dutch Wadden Sea. This species was first recorded in estuaries and coastal waters of the European continent in the Ems estuary (eastern Dutch Wadden Sea) in 1983. In the western part of the Dutch Wadden Sea the first specimens were found in 1989. The Ems estuary population showed the typical lag-phase, explosive increase, stabilisation, and eventual decline. In the western part of the Dutch Wadden Sea the latter two phases have not yet developed. The strong development and stabilisation of the population in the Ems estuary may have been caused by the availability of a yet not utilised food source. The species' final decline remains largely unexplained.     

Floristic Development Patterns in a Restored Elk River Estuarine Marsh, Grays Harbor, Washington

We describe the changes in the floral assemblage in a salt marsh after reconnection to estuarine tidal inundation. The Elk River marsh in Grays Harbor, Washington was opened to tidal flushing in 1987 after being diked for approximately 70 years. The freshwater pasture assemblage dominated by Phalarais arundinacea (reed canary grass) converted to low salt marsh vegetation within 5 years, with the major flux in species occurring between years 1 and 4. The system continued to develop through the 11‐year post‐breach monitoring period, although change after year 6 was slower than in previous years. The assemblage resembles a low salt marsh community dominated by Distichlis spicata (salt grass) and Salicornia virginica (pickleweed). Because of subsidence of the system during the period of breaching, the restored system remains substantially different from the Deschamsia cespitosa (tufted hairgrass)‐dominated reference marsh. Use of a similarity index to compare between years and also between reference and restored marshes in the same year revealed that similarity in floral composition between year 0 and subsequent years decreased with time. However, there was a period of dramatic dissimilarity during years 1 to 3 when the system was rapidly changing from a freshwater to estuarine condition. Similarity values between the reference and restored system generally increased with time. Somewhat surprisingly the reference marsh showed considerable between‐year variation in similarity, which indicated substantial year‐to‐year variability in species composition. Based on accretion rate data from previous studies we predict that full recovery of the system would take between 75 and 150 years.     

Effect of lowered salinity on the survival,condition and reburial of Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae)

Abstract Mass mortalities of fauna are known to occur in estuarine environments during flood events. Specific factors associated with these mortalities have rarely been examined. Therefore, the effect of exposing, to lowered salinities, an infaunal bivalve that is susceptible to mass mortalities during winter flooding in a southern Australian estuary was tested in the present study. In a laboratory experiment, low salinities (≤6 parts per thousand [ppt]), which mimicked those expected during flood events in the Hopkins River estuary, were shown to affect Soletellina alba, both lethally and sublethally. All bivalves died at 1 ppt, while those at 6 ppt took longer to burrow and exhibited a poorer condition than those at 14 and 27 ppt. The limited salinity tolerance of S. alba suggests that lowered salinities are a likely cause of mass mortality for this species during winter flooding.     

Microfossils in surface sediments of brackish waters on the west coast of South Africa and their palaeoecological implications

A faunistic survey covering 25 sites in estuaries, coastal lakes and ponds along the west coast of South Africa between the Cape of Good Hope in the south and the Olifants River in the north was carried out in May 2014. The study aimed to establish a dataset with ecological and distribution data of ostracods and foraminifers for later palaeoenvironmental reconstructions. Canonical correspondence analysis showed that the distribution of the 19 foraminifer and 32 ostracod taxa was controlled mainly by habitat structure, but that specific conductivity (salinity) was best and solely described by the second axis, highlighting the usefulness of the two microfossil groups for salinity reconstructions. Habitat structure was demonstrated by the foraminifer species Trochamminita irregularis’ preference for stillwater areas of lakes. Sarscypridopsis aculeata and Sarscypridopsis glabrata were the dominant ostracod species in coastal ponds and lakes. However, their living distributions excluded each other, with S. aculeata preferring areas of lower salinity and S. glabrata dominating areas of higher salinity up to hyperhaline conditions in small, closed water bodies.     

MACROALGAL RECRUITMENT IN A HIGH MARSH CREEK OF NORTH INLET ESTUARY,SOUTH CAROLINA1

The temporal and spatial variability in recruitment patterns of macroalgae were stuided by evaluating the appearace of propagules on marble tiles set over a depth gradient in a high marsh tidal creek in North Inlet Estuary, South Carolina. Ulvoids and Porphyra occurred over a wide range of depths in the intertidal zone unlike Ectocarpus and members of the Florideophycease, which grew over a more restricted zone. Ulvoid propagules were the most abundant, attaining maximum densities at 0 and -15 cm mean low water (MLW) at all seasons except winter. In summer, coincident with high tubbidity, ulvoid densities decreased at -15 cm MLW but not in other seasons. Ulvoid densities at 0 MLW were depressed in January, February was preceded with the lowest recoreded temperatures and salinities during the study period, while the decrease in July was preceded by the highest recorded temperature. The number of taxa was highest in April and September, representing winter-spring and summer-fall transition periods, respecitively. The biomass of adult forms was higher on the tiles than on naturally occurring substrala, perhaps due to lack of stable suitable substrata in the field. Inhibition of subsequent recruitment by initial recreuitment was evident only on tiles submerged in October. The initial recruitment pattern of Porphyra rosengurtii coll et Cox and Ectocarpus siliculosus (Dillwyn) Lyngbye seem to determine the biomass distribution of adult forms, while that of ulvoids may be altered later by other factors. The considerable decrease in the number of adult forms compared to the initial denisties of propagules indicales high juvenile mortalities.