Distribution patterns of macrobenthic biodiversity in the intertidal seagrass beds of an estuarine system, and their conservation significance

Intertidal stands of seagrass are important elements in the ecology of many estuaries yet the manner in which their associated macrobenthic biodiversity is distributed throughout any single estuary has never been determined. This has now been attempted for the Knysna estuarine bay in the Garden Route National Park, South Africa, an important site for one vulnerable and declining seagrass, Cape dwarf-eelgrass (Nanozostera capensis), and for several associated animals. Although spanning a salinity range of <5–35, the seagrass beds of this estuary contained a unitary fauna with local variation in frequency and abundance of the various species. Faunal biodiversity was highest along the main estuarine channel in the marine-influenced region and declined both upstream and into the sheltered peripheral zones, overall faunal abundance being inversely correlated with species diversity (though not with species richness). This pattern results in the beds around the 4 km shoreline of a single island near the mouth supporting 91 % of the total macrobenthic invertebrate species present in the system. This situation is discussed in relation to such data as are available from other comparable systems and to the conservation of estuarine seagrass faunal biodiversity. It is concluded that in general and with caveats for some individual species of concern where conservation resources are limited attention would most profitably be focused on the seagrass meadows of downstream estuarine areas.     

Long-term studies of the benthic biology of Tees bay and the Tees estuary

Tees bay on the north-east coast of England receives the waters from the highly industrialised Tees estuary. Since 1970 there have been considerable reductions in both the industrial and domestic sewage discharges to the estuary.The benthic populations of Tees bay have been routinely monitored since 1971, grabbing surveys have been completed at six areas in the spring, summer and autumn of each year. In 1979 the survey was extended to include stations within the Tees estuary itself.Tees bay appears to have a stable benthic fauna. Though the simple analysis of faunal statistics has demonstrated fluctuations within the benthos, neither this analysis nor classification analysis has indicated that there were any long-term changes in abundance or diversity.Classification analysis has also failed to differentiate between the fauna of the different areas within Tees bay. However, studies of biomass and T. fabula growth rate did indicate a difference between the areas close to the mouth of the Tees and those remote from it.The studies of the Tees estuary benthos indicated an improvement in both the abundance and the diversity of the fauna. However, the monitoring took place over a limited period and further work is necessary to ensure that this improvement does not simply represent natural fluctuations within the estuarine benthic population.     

The Benthic Macrofauna Associated with the Oyster Reefs of the James River Estuary,Virginia, U.S.A.

Productive, natural oyster reefs within the James River estuary, were quantitatively sampled for associated macrofauna for a year. The 192 samples yielded 142 taxa. Mean faunal density on these reefs ranged from 5,757 to 57,857 m⁻². Over 770/0 of the individuals collected belonged to 11 taxa. The number of species and informational diversity (H') decreased up the estuarine gradient. The quality of available shell surface was deemed important in determining density. The spatial heterogeneity provided by the shell surface allowed development of a densely populated, diverse faunal assemblage which differs from soft-bottom assemblages principally in quantitative aspects. The assemblage is not spatially or temporally homogeneous and undergoes significant changes in community structure both seasonally and along the estuarine gradient.     

Rapid development of a restored oyster reef facilitates habitat provision for estuarine fauna

Oyster reef restoration has become a principal strategy for ameliorating the loss of natural Crassostrea virginica populations and increasing habitat provision. In 2014, a large‐scale, high‐relief, 23‐ha subtidal C. virginica reef was restored at the historically productive Half Moon Reef in Matagorda Bay, TX, using concrete and limestone substrates. Encrusting and motile fauna were sampled seasonally until 17 months postrestoration at the restored reef and at adjacent unrestored sites. Restored oysters developed rapidly and were most abundant 3 months postrestoration, with subsequent declines possibly due to interacting effects of larval settlement success on new substrate versus post‐settlement mortality due to competitors and predators. Oyster densities were 2× higher than in a restored oyster population in Chesapeake Bay that was reported to be the largest reestablished metapopulation of native oysters in the world. Resident fauna on the restored reef were 62% more diverse, had 433% greater biomass, and comprised a distinct faunal community compared to unrestored sites. The presence of three‐dimensional habitat was the most important factor determining resident faunal community composition, indicating that substrate limitation is a major hindrance for oyster reef community success in Texas and other parts of the Gulf of Mexico. There were only minor differences in density, biomass, and diversity of associated fauna located adjacent (13 m) versus distant (150 m) to the restored reef. The two substrate types compared had little influence on oyster recruitment or faunal habitat provision. Results support the use of reef restoration as a productive means to rebuild habitat and facilitate faunal enhancement.     

Macrobenthos ofPotamogeton andMyriophyllum beds in the upper reaches of Canal de Mira (Ria de Aveiro,NW Portugal): Community structure and environmental factors

The community structure of the macrobenthic fauna (>0.5 mm) ofPotamogeton andMyriophyllum beds of the upper reaches of Canal de Mira (0.5–2) and of macrofauna density (369, 240 ind m^–2).Potamopyrgus jenkinsi, Corophium multisetosum andLimnodrilus hoffmeisteri are dominant species in the study area. The community of station 1 includes an important set of taxa usually associated to freshwater habitats (oligochaetes, leeches and insect larvae) whilst in station 3 typically estuarine species (Cyathura carinata, Leptocheirus pilosus, Nereis diversicolor, Streblospio shrubsolii) occur. A succession of peak densities of different taxonomic groups during the year indicates seasonal variation in the community structure. The faunal assemblage of the study area is compared with similar ones in NE Atlantic and Mediterranean coastal systems.     

Seasonal and interannual variation in distribution and population abundance of the shrimp Crangon franciscorum in San Francisco Bay

Shrimp are an important component of the San Francisco Bay biota, both as predators on benthic fauna, and as a food source for predatory fish. Of three common species in the bay, Crangon franciscorum is the most abundant. The bay is predominantly a nursery area for maturing shrimp of this species. During the main reproductive period in the early spring, ovigerous females and planktonic larvae are in most years centered outside the bay in the nearshore ocean, although both are also present in the bay. Juveniles move into both the southern reach and the northern reach shortly after settling, and landward-flowing bottom currents are possibly instrumental in this migration. The seasonal cycle of shrimp abundance in the bay, dominated by this spring immigration of newly settled juveniles, is characterized by a progressive migration of the growing shrimp up the estuary coincident with upstream penetration of higher salinity water during summer. Differences in abundance and distribution between the years 1980, 1981, and 1982 suggest that the level of river discharge and accompanying salinity regime are important controlling factors in the distribution, recruitment levels, and subsequent survival and growth of C. franciscorum in the San Francisco Bay.     

Spatial Patterns of Benthic Macroinvertebrates in Intertidal Areas of a Southern European Estuary: The Tagus, Portugal

This study characterizes the composition and spatial distribution patterns of the benthic macrofauna in the intertidal mudflats of the Tagus estuary, western Portugal. A total of 68 species, more than 226,000 specimens with a total wet weight biomass of approximately 1170 g were identified in 380 sites. The species Streblospio shrubsolii, Cyathura carinata, Tharyx sp., Hydrobia ulvae and Tubificids were the most common and abundant. Scrobicularia plana strongly dominated the biomass. The invertebrate macrofauna of the Tagus estuary shows similarities to what is known from other temperate mudflats. The diversity of species, their overall abundance and the ratio of Molluscs plus Crustaceans to Polychaete species corroborate the distinctiveness between temperate and tropical mudflats and sandflats. The spatial distribution of the fauna reflects the sediment characteristics but the relationship between the environmental and the biological data is not as strong as obtained for sublittoral areas. This relationship diminishes from the sublittoral shelf to sublittoral estuarine areas, showing minimum values in this study, suggesting that such a relationship is less straightforward as natural disturbance increases. Nevertheless, a mixture of grain-size, elevation (inundation time) and particular habitats (relic oyster beds) form the best explanatory factors for the spatial distribution patterns of the intertidal benthic macrofauna of the Tagus estuary.     

Spatial and temporal variation in fish community structure of a marine embayment in Zanzibar,Tanzania

Spatial and temporal variation in the fish community structure were studied in a tropical non-estuarine embayment in Chwaka Bay, Zanzibar (Tanzania). Fish samples were collected bi-monthly (at each spring low tide) for 1 year (November 2001–October 2002) from a range of bay habitats ranging from mangroves deep inside the bay to seagrass beds close to the mouth of the bay. Additionally, environmental variables were examined to determine their relationship with the fish community structure. Being a non-estuarine embayment, the environmental variables as well as the fish community structure in each habitat remained relatively constant for most part of the year; however, a marked decline was observed during the rainy period (April–May). Significant variations in fish community variables (density, biomass and species richness) and in water temperature and salinity were observed during the rainy season in all habitats, with larger changes in the mangrove and mud/sand flats habitats than in the seagrass beds. Seasonal variations in water clarity and dissolved oxygen were not significant, though. Many species disappeared from the mangrove and mud/sand flats habitats during the rainy season and those which persisted showed a remarkable decrease in density. Moreover, the results indicate that mangroves were the preferred settling habitats for Gerres filamentosus, Gerres oyena, Lethrinus lentjan and Monodactylus argenteus, especially during the dry period (December–February) before the rainy season. This observation is contrary to what has been reported from some other tropical regions where greater abundance and species richness was observed during the rainy season. A significant relationship was found between density of fish and temperature, salinity and turbidity. Since salinity was the most conspicuously changing environmental variable with seasons, we propose that salinity, alone or in combination with low visibility and temperature, was probably the most important environmental factor structuring the fish assemblage in the mangrove and mud/sand flats habitats, particularly during the rainy season. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. A. Cambray     

Macrobenthos of the subtidal Wadden Sea: revisited after 55 years

During the years 1923–1926 Hagmeier & Kändler (1927) sampled the macrofauna of subtidal shallows and channels of the Wadden Sea close to the Island of Sylt (German Bight, North Sea). Reinvestigating this study area in 1980, a substantially altered faunal composition was recorded. An approach is made to quantify the comparison in terms of abundance, species richness and diversity of invertebrate taxa. Human interference is assumed to be responsible for the major changes. Natural oyster beds have been overexploited and the local population ofOstrea edulis has been driven to extinction. Subsequently, mussels(Mytilus edulis) spread in the entire region, promoted by shell fishery. Particularly barnacles and many polychaetes took advantage of the expansion of mussel banks which is substantiated by correlation analysis. Reefs of the colonial polychaeteSabellaria spinulosa stood in the way of shrimp trawling and became destroyed together with the associated fauna. A subtidalZostera marina bed was wiped out in 1934 by a natural epidemic disease but never succeeded in reestablishing itself. The associated fauna disappeared. Large epibenthic predators and scavengers (crabs, snails and starfish) survived all these changes. The total number of species remained approximately at the same level but molluscs experienced losses and polychaetes diversified. Overall abundance increased with a disproportionately large share of a few species(Mytilus edulis, Balanus crenatus, Cerastoderma edule, Scoloplos armiger). The subtidal fauna of the Wadden Sea proved to be vulnerable to human disturbance; thus, the present community can no longer be viewed as the outcome of entirely natural processes.     

Distributional patterns of mobile fauna associated with Halimeda on the Tiahura coral-reef complex (Moorea,French Polynesia)

This study deals with the mobile fauna living associated with the turfs of three Halimeda species [H. incrassata, H. opuntia (three forms) and H. macroloba] from the Tiahura Reef complex. Ten 0.05 m² test areas of each Halimeda form have been randomly sampled from each geomorphological reef unit in order to obtain the specific abundance and biomass of different faunistic groups and species living within Halimeda populations. Then the raw data have been classified using the correspondence factor analysis to highlight the relationships between faunistic groups, or species, and the different Halimeda forms studied. The distributional patterns of the faunal communities seems to be controlled by the morphological features of the host-alga. The complex arborescent structure of the rhyzophytic H. incrassata species shelters fauna three times higher in abundance than other Halimeda heads. This fauna is mostly composed of a highly rich community of microcrustaceans and a very diversified community of Syllidae polychaetes. H. macroloba living on the outer reef flat retains a lot of small Nereidae polychaetes and a rich microgastropod assemblage. Dense H. opuntia tussocks (type A) on the fringing-reef and isolated H. opuntia fronds of pendulous chains (type B) on the barrier reef as well as beds of scattered H. opuntia (type C) on the outer reef flat provide environment for larger animals, and according to their zone of life, they retain very different faunal associations. Some ophiuroids, and some fish, collected in H. opuntia A and C, are newly reported from the Society Islands, French Polynesia, and the Pacific province. One Brachyurid species is presumably undescribed.     

Recent increase of filamentous algae in shallow Swedish bays: Effects on the community structure of epibenthic fauna and fish

A summary is presented of estimates of distribution and growth of filamentous algae and its effect on the structure and functioning of epibenthic fauna and fish communities in shallow bays on the Swedish west coast. As a consequence of coastal eutrophication vegetation cover has gradually increased during the last decade, and during 1990's most bays in the Skagerrak-Kattegat area were variously covered with filamentous algae during spring and summer (May–July). In some areas filamentous algae (mainlyCladophora andEnteromorpha) completely covered the bottom. In field studies it was demonstrated that increased cover and dominance of filamentous algae result in structural changes of the epibenthic fauna community. Field studies showed that species richness and biomass of epibenthic fauna increased in a sandy bay with a moderate increase (30 to 50%) of filamentous algae cover. At higher cover (90%), biomass of epibenthic fauna was reduced, however, to the same level as for the sandy habitat, although the dominant epibenthic species were different. Heavy growth of epiphytic filamentous algae on eelgrass resulted in reduced biomass and a shift in the species composition of the epibenthic fauna community. Fish assemblage structure was also related to changes in vegetation. In eelgrass beds, fish species numbers were reduced with increasing cover of epiphytic filamentous algae, and at rocky bottoms with kelp algae (dominated byFucus), fish biomass decreased with increasing cover of attached filamentous algae. Further, foraging efficiency of juvenile cod and settling success of plaice were reduced as a response to increasing dominance of filamentous algae.     

Associations of planktonic and periphytic rotifers in a Malaysian estuary and two nearby ponds

Samples were taken from a Malaysian estuary along a salinity gradient from full strength sea water down to a conductivity of 27 µS cm^–1. In a region where the conductivity fluctuated between 6500 and 14000 µS only empty loricas of Keratella cochlearis and Lecane bulla were found. Where the salinity reached a maximum of 3800 µS Lecane bulla was the dominant rotifer, and 17 other species were found. Where the conductivity remained below 1000 µS at all stages of the tidal cycle there were more species of rotifers, up to 33 at one station.The rotifer fauna of the estuary was compared to the assemblage found in two local ponds. Of the 63 species found in the estuary only 29 were also found in the ponds. Compared to the total known rotifer fauna of Malaysia the estuary has a higher proportion of Lecane species (40%), and the genera Brachionus and Trichocerca are under-represented.Species associated with inland saline waters, such as Brachionus plicatilis, B. dimidiatus and Hexarthra jenkinae were not found in the estuary.     

Macrobenthic Distribution within the Sediment along an Estuarine Salinity Gradient

The distribution of the macrobenthic infaunal community within the upper 25 cm of the sediment was studied at 16 stations in the lower Chesapeake Bay. Stations were located from the tidal freshwater to the polyhaline zone of major tributaries (James, York and Rappahannock Rivers) and in the polyhaline portion of the lower bay mainstem. Profiles for total number of individuals, total ash-free dry weight biomass and species encountered with depth were calculated. Except for the deep dwelling bivalve, Macoma balthica, tributary macrobenthic communities had a shallow depth distribution compared to the mainstem sites which were found in generally coarser sediments in the higher salinity region of the estuary.     

Rotifers of the Kalahari Gemsbok National Park,South Africa

The Kalahari Gemsbok National Park in the Northern Cape Province, South Africa, is bounded by two dry river beds in which 39 artificial water sources have been provided for the use of the wild animals. The water in these sources varies from fresh to highly saline and an opportunity is thus provided to determine, not only which rotifer species are able to colonise such sources, but what their salinity tolerances are. The rotifer fauna, studied in summer and winter, is dominated by mixed populations of Brachionus calyciflorus, B. plicatilis and Hexarthra jenkinae, with only a few other monogononts and bdelloids. The most striking feature of the rotifer fauna in these troughs is the very low species diversity encountered.     

Edge effects influence the composition and density of reef residents on subtidal restored oyster reefs

Within estuarine and coastal ecosystems globally, extensive habitat degradation and loss threaten critical ecosystem functions and necessitate widescale restoration efforts. There is abundant evidence that ecological processes and species interactions can vary with habitat characteristics, which has important implications for the design and implementation of restoration efforts aimed at enhancing specific ecosystem functions and services. We conducted an experiment examining how habitat characteristics (presence; edge vs. interior) influence the communities of resident fish and mobile invertebrates on restored oyster (Crassostrea virginica) reefs. Similar to previous studies, we found that restored reefs altered community composition and augmented total abundance and biomass relative to unstructured sand habitat. Community composition and biomass also differed between the edge and interior of individual reefs as a result of species-specific patterns over small spatial scales. These patterns were only weakly linked to oyster density, suggesting that other factors that vary between edge and interior (e.g. predator access or species interactions) are likely more important for community structure on oyster reefs. Fine-scale information on resident species' use of oyster reefs will help facilitate restoration by allowing decision makers to optimize the amount of edge versus interior habitat. To improve the prediction of faunal use and benefits from habitat restoration, we recommend investigations into the mechanisms shaping edge and interior preferences on oyster reefs.     

Environmental influences on benthic fauna associations of the Kara Sea (Arctic Russia)

Macrobenthic faunal associations, hydrography and sediment structure were examined at 14 stations in the Kara Sea. The stations were located in an area influenced by huge runoff from the Ob and Yenisei Rivers and in areas influenced by Barents Sea water. Sampling depths varied from 17 to 43 m, with one station at 195 m. The sediments were predominantly muddy but some stations were sandy. Three hundred and eighty-seven taxa were identified and Polychaeta, Crustacea and Mollusca were the most conspicuous. Species number, abundance and biomass varied widely among stations, and were generally higher in the more marine waters. Boreal-arctic species predominated, but an increase of arctic species from marine to the estuarine areas was evident. Five faunal associations were delineated by cluster analysis and suggested quite heterogeneous sampling areas. The most conspicuous species of each faunal association were Spiochaetopterus typicus, Tridonta borealis, Serripes groenlandicus, Portlandia arctica, and Marenzelleria arctia, respectively. The sedimentation rate, as well as depth, sediment structure and salinity, apparently influenced the main differences in the fauna. Accepted: 29 June 1999     

Seasonal composition and spatial distribution of hyperbenthic communities along estuarine gradients in the Westerschelde

The hyperbenthic fauna of the Westerschelde estuary was sampled in spring, summer and winter of 1990 at 14 stations along the salinity gradient. Mysids dominated the hyperbenthos in each season. Other important species, either permanently (e.g. amphipods and isopods) or temporarily (e.g. fish larvae and decapod larvae) hyperbenthic, belong to a variety of faunistic groups. Spatial structure was stable through time: the estuary could be divided in the same geographically defined zones in each season. Each zone had a characteristic fauna. Gradients in salinity, dissolved oxygen and turbidity correlated strongly with the observed variation in community structure. The spatial patterns dominated over the temporal patterns, especially in the brackish part of the estuary. In the marine part, seasonal differences in the communities were more pronounced due to the occurrence of a series of temporary hyperbenthic species in spring and summer. In each season, the upstream (brackish) communities were characterized by few species occurring in very high numbers, whereas the downstream (marine) communities were composed of many species but at lower densities.     

First record of Synidotea laevidorsalis (Miers, 1881) (Crustacea: Isopoda) in Europe (Gironde estuary,France)

This note reports on the presence of a well established population of the isopod Synidotea laevidorsalis (Miers) in the Gironde estuary (southwestern France). This species is new for the European fauna. S. laevidorsalis is a nonendemic cool-temperate to subtropical, shallow-water species which was probably introduced into the study area from Asia. In the salinity range of 1 to 10 g 1^-1 of the Gironde the species constitutes an important component of the brackish-water hyperbenthic community. The population was already present in 1975 when it was misidentified as the native species Idotea emarginata (Fabricius).     

Benthic macrofauna in Tasmanian estuaries: scales of distribution and relationships with environmental variables

Information on the distribution of species richness, faunal density, biomass and estimated productivity of benthic invertebrates in Tasmanian estuaries was quantified at a variety of spatial and temporal scales to assess general hypothesis relating community metrics to such environmental variables as salinity, seagrass biomass and sediment particle size. An associated aim was to assess appropriate scales of investigation for soft-sediment biota distributed in estuaries, including whether patterns identified at individual sites, estuaries, tidal levels or times are likely to have more general relevance. Faunal biomass and productivity varied principally at between-estuary (10 to 1000 km) and replicate-sample (1 m) scales, indicating that these two community metrics were largely responding to estuary-wide effects, such as nutrient loading, and to microhabitat features, rather than to locality characteristics at intermediate scales such as salinity, anoxia or sediment particle size. By contrast, faunal density showed greater response to tidal height (1 to 100 m) and to factors distributed at the locality scale within estuary (10 km) than to factors between estuary. Both faunal density and species richness in estuaries declined over three- and fivefold ranges down the shore from high water mark to the shallow sublittoral, while estimated productivity and biomass showed highest overall levels at low water mark. The greatest component of variance in species richness was associated with tidal height, with variance then distributed approximately evenly between other spatial scales examined. At the low-tide and shallow subtidal levels, species richness, faunal biomass and estimated productivity were all highly correlated with salinity and biomass of macrophytes, whereas faunal density was highly correlated with biomass of macrophytes only. Relationships between environmental and biological variables examined were poorly defined at high tidal levels. Seasonal plus interannual variance was much lower than spatial variance—a clear indication that sampling effort in studies would generally be better directed across a range of localities than for a single locality to be repeatedly investigated over time.     

Macrozoobenthic community structure in a poikilohaline Mediterranean lagoon (Laki Lagoon, northern Aegean)

The community structure of the macrobenthic fauna was studied in the overall area of Laki Lagoon in September 1997 (salinity 32–35 psu) and monthly from February 1998 to February 1999 in the innermost part of the lagoon (salinity 0.1–6.8 psu). Community structure was analyzed by means of uni- and multivariate methods. In September 1997, the macrofauna in the outer part of the lagoon was characterized by a higher diversity and the occurrence of both lagoonal and marine species, and in the innermost part by a higher total abundance and the occurrence of a few lagoonal species. The combination of distance from the sea, depth, salinity and sediment organic matter correlated best with the spatial distribution pattern of the macrobenthic fauna. Community structure in the innermost part of the lagoon showed a seasonal periodicity. Species composition during spring 1998, at 0.1–2.0 psu, was similar to that in September 1997. During summer the macrobenthic fauna became impoverished, but recovered from late summer onwards. The salinity increase during summer (up to 5–7 psu) was followed by the appearance of marine species in the innermost part of the lagoon. Total abundance displayed a peak in late spring and a lower one in mid-autumn. The seasonal dynamics of the faunal assemblage was mainly governed by water temperature. Predation pressure by Atherina boyeri may have contributed to quantitative community changes during autumn.