Subtidal Seagrass Beds Research Articles

Shallow estuarine reef as nursery habitat for Australasian snapper (Chrysophrys auratus)

ABSTRACT Estuaries are important recruitment sites for many fish species, with structurally-complex habitats such as subtidal seagrass beds on soft sediments particularly valuable due to their provision of food and shelter. Soft sediments dominate most estuaries, but where hard-bottom reefs are present they have the potential to act as nursery habitats for juvenile fish. We document recruitment of juvenile Australasian snapper (Chrysophrys auratus) to a shallow linear sandstone reef in Whangateau Harbour, a small estuary in north-eastern New Zealand. Up to several hundred 0 + juveniles (∼20–70 mm fork length) were present on the reef during early summer to mid-late autumn each year from 2018 to 2021. Numbers were consistently highest at the seaward end of the reef, facing into incoming tidal currents, and lowest in the deeper central part of the reef, where larger, potentially cannibalistic, snapper were common. Juveniles disappeared from the reef fairly abruptly at the end of each season, with departure in at least two of the years appearing to follow a sudden decrease in water temperature rather than being associated with body size or absolute temperature. Although relatively small in area, estuarine reefs may be increasingly important nursery habitats in the future given the widespread loss of subtidal seagrass beds.

Understanding ecosystem services for climate change resilience in coastal environments: a case study of low-canopy sub-tidal seagrass beds in Fiji

The Pacific Island Countries (PICs) are exposed to extreme wave conditions which are projected to be exacerbated by rising sea levels due to climate change, prompting the need for strategic planning of coastal communities and assets. Nature-based protection has been proposed as a sustainable solution to promote the resilience of coastal areas from physical impacts such as wave-induced erosion. In this study, we investigate the potential coastal protection service of shallow sub-tidal low-canopy seagrass beds, dominated by Halodule uninervis, on the rate of wave height and wave energy reduction on a barrier and fringing reefs. The data was collected using bottom-mounted pressure sensors to measure wave height and energy reduction as waves moved toward the shoreline across the seagrass beds. The results show that on average, the seagrass beds were able to reduce wave height by 30% and energy by 47% in both reef environments. These reduction rates are strongly influenced by water depth, seagrass characteristics and local reef conditions. Based on these results, seagrasses can strengthen the resilience of coastal shorelines to wave erosion, thus conserving healthy low-canopy seagrass habitats has measurable benefits for shoreline protection in Fiji and other PICs.

The Contribution of Subtidal Seagrass Meadows to the Total Carbon Stocks of Gazi Bay, Kenya

Seagrass beds occur globally in both intertidal and subtidal zones within shallow marine environments, such as bays and estuaries. These important ecosystems support fisheries production, attenuate strong wave energies, support human livelihoods and sequester large amounts of CO2 that may help mitigate the effects of climate change. At present, there is increased global interest in understanding how these ecosystems could help alleviate the challenges likely to face humanity and the environment into the future. Unlike other blue carbon ecosystems, i.e., mangroves and saltmarshes, seagrasses are less understood, especially regarding their contribution to the carbon dynamics. This is particularly true in regions with less attention and limited resources. Paucity of information is even more relevant for the subtidal meadows that are less accessible. In Kenya, much of the available information on seagrasses comes from Gazi Bay, where the focus has been on the extensive intertidal meadows. As is the case with other regions, there remains a paucity of information on subtidal meadows. This limits our understanding of the overall contribution of seagrasses in carbon capture and storage. This study provides the first assessment of the species composition and variation in carbon storage capacity of subtidal seagrass meadows within Gazi Bay. Nine seagrass species, comprising of Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule uninervis, Halophila ovalis, Halophila stipulacea, Syringodium isoetifolium, Thalassia hemprichii, and Thalassodendron ciliatum, were found. Organic carbon stocks varied between species and pools, with the mean below ground vegetation carbon (bgc) stocks (5.1 ± 0.7 Mg C ha−1) being more than three times greater than above ground carbon (agc) stocks (0.5 ± 0.1 Mg C ha−1). Mean sediment organic carbon stock (sed Corg) of the subtidal seagrass beds was 113 ± 8 Mg C ha−1. Combining this new knowledge with existing data from the intertidal and mangrove fringed areas, we estimate the total seagrass ecosystem organic carbon stocks in the bay to be 196,721 Mg C, with the intertidal seagrasses storing about 119,790 Mg C (61%), followed by the subtidal seagrasses 55,742 Mg C (28%) and seagrasses in the mangrove fringed creeks storing 21,189 Mg C (11%). These findings are important in highlighting the need to protect subtidal seagrass meadows and for building a national and global data base on seagrass contribution to global carbon dynamics.

Tropical intertidal seagrass beds as fish habitat: Similarities between fish assemblages of intertidal and subtidal seagrass beds in the Philippines

Tropical intertidal seagrass beds have recently been identified as foraging grounds for multiple fish species, although the possible drivers of fish migration to such beds remain unknown. Investigations of fishes occurring in intertidal and subtidal seagrass beds, and comparison of food resources of the dominant trophic groups in the intertidal and subtidal beds, and surrounding bare-sand areas, were conducted at two sites in northern Mindanao, Philippines. Fish species collected in the intertidal and subtidal seagrass beds overlapped by 65%, with species richness and abundance of both residents and visitors between the two habitats not differing substantially (although significantly higher than in intertidal and subtidal bare-sand areas), as many site-attached residents appeared to remain in the intertidal beds during low tide. Benthic-invertebrate feeders, including juveniles of commercially important species, dominated intertidal seagrass beds, comprising >70% of species richness and abundance. Four of them (Halichoeres argus, H. papilionaceous, Lethrinus harak, and Parupeneus barberinus) fed primarily on small crustaceans, such as harpacticoid copepods and amphipods, the densities of such food resources being significantly higher in the intertidal and subtidal seagrass beds than in the surrounding bare-sand areas. The results demonstrated that intertidal seagrass beds function as foraging grounds for many visiting fishes, in addition to providing a permanent habitat for resident species. Recognition of the importance of tropical intertidal seagrass beds as fish habitat has significant implications for the management and protection of coastal fish biodiversity and fishery resources.

Winter Nutrient Pulse and Seagrass Epiphyte Bloom: Evidence of Anthropogenic Enrichment or Natural Fluctuations in the Lower Florida Keys?

Nutrient enrichment continues to disrupt marine ecosystem function worldwide. Assessing eutrophication in seagrass ecosystems such as the Great White Heron National Wildlife Refuge (GWHNWR), Florida Keys is critical for protecting the diverse community that depends on the intertidal and subtidal seagrass beds. We quantified water column nutrients, chlorophyll a, tissue nutrients in macroalgae and Thalassia testudinum, and epiphyte percent cover on seagrasses on tidal flats seasonally over 1 year at three sites: Howe Key, Water Keys, and Upper Harbor Key. Water column nutrients (total nitrogen, total phosphorus, nitrate–nitrite, ammonium, dissolved inorganic nitrogen, dissolved organic nitrogen, soluble reactive phosphorus, dissolved organic phosphorus) increased from fall to winter at Water Keys. These increased nutrients coincided with a bloom of the epiphyte Spyridia filamentosa on seagrasses that exceeded 40 % cover at Water Keys and Upper Harbor Key in two consecutive seasons. Seagrasses at all sites had chronic percent cover of small epiphytes exceeding 60 %. Additionally, low δ13C in T. testudinum tissues at Upper Harbor Key compared to the other sites suggested variations in carbon sources across the study area. Spatial patterns in macrophyte nitrogen-to-phosphorus (N:P) ratios point to sources of nutrients from the inhabited islands of the Keys and from the Gulf of Mexico. Water column total nitrogen and total phosphorus concentrations exceeded the numeric nutrient criteria for the study area suggesting that the area should be monitored closely.

Kinorynchs from sea-grass beds in south eastern Australia - with notes on a new collecting method

Kinorhynchs are usually collected from soft bottom and sandy sediments, whereas their occurrence in sea-grass beds rarely has been explored. In the present study we developed two new collecting methods that can recover specimens from amongst sub-tidal sea-grass beds and mangrove mud. Several species of kinorhynchs were found and one could be identified as Echinoderes teretis Brown, 1985. The species was originally found in silty mud and described from localities in Sydney Harbour and Broken Bay. We recorded the species in the Clyde River Estuary and Candlagan Creek, some 250 km further south, and in sub-tidal mud and tidal mud, also in Lake Wellington in the Gippsland Lakes, Victoria. The presence of E. teretis and several unidentifiable kinorhynch species in sea-grass beds and mangrove vegetation indicates that the provided collecting methods can reveal new information about kinorhynch diversity in such habitats.

Early post-settlement habitat and diet shifts and the nursery function of tidepools during Sillago spp. recruitment in Moreton Bay, Australia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 384:207-219 (2009) - DOI: https://doi.org/10.3354/meps07992 Early post-settlement habitat and diet shifts and the nursery function of tidepools during Sillago spp. recruitment in Moreton Bay, Australia Nils C. Krück1,*, Craig A. Chargulaf1, Ulrich Saint-Paul2, Ian R. Tibbetts1 1Centre for Marine Studies (CMS), University of Queensland, Brisbane, Queensland 4072, Australia 2Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany *Email: krueck@uni-bremen.de ABSTRACT: Knowledge of settlement and recruitment processes is crucial for the conservation and sustainable management of commercial fish stocks, yet for some species such information is limited. We investigated the length-frequency distribution and feeding activity of 0-group Sillago whiting on mudflats in Moreton Bay, Australia, and evaluated whether permanent intertidal residence is (1) an integral component of recruitment and (2) related to the suitability of temporary microhabitats (tidepools) as primary nursery refuges. A total of 399 whiting, comprising the 3 commercially and/or recreationally important species S. analis, S. ciliata and S. maculata, were collected from intertidal pools and adjacent subtidal waters during low tide. Newly settled metamorphic larvae dominated whiting assemblages in tidepools (>80%) and fed almost exclusively on meiofaunal copepods and nematodes. It was only once metamorphosis was complete that new settlers joined the main juvenile population—i.e. they commenced tidal migrations, or they took up permanent residence in subtidal seagrass beds (>90% juveniles), and shifted their diet towards macrofaunal decapods and polychaetes. During the critical first weeks after settlement, occupation of intertidal pools seemed likely to increase fitness of whiting. Specifically, the pools may provide shelter from predation, temperature-induced increases in growth and temporally extended access to intertidal meiofauna. The latter, however, appeared to vary depending on whether copepods or nematodes were the preferred prey, and whether occupied pools were isolated or interconnected. Resource and conservation managers should consider largely structureless mud- and sandflats as primary nursery zones for Sillago populations throughout their range in the Indo-Pacific. KEY WORDS: Whiting · Nursery · Tidepool · Ontogenetic shift · Diet · Settlement · Metamorphosis · Fullness index Full text in pdf format PreviousNextCite this article as: Krück NC, Chargulaf CA, Saint-Paul U, Tibbetts IR (2009) Early post-settlement habitat and diet shifts and the nursery function of tidepools during Sillago spp. recruitment in Moreton Bay, Australia. Mar Ecol Prog Ser 384:207-219. https://doi.org/10.3354/meps07992 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 384. Online publication date: May 29, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Molluscan assemblages of seagrass-covered and bare intertidal flats on the Banc d'Arguin, Mauritania, in relation to characteristics of sediment and organic matter

The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass ( Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km 2 of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m − 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m − 2 ) than seagrass meadows (30.0 g AFDM m − 2 ). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m − 2 and seagrass meadows 6.9 g AFDM m − 2 . As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.

Habitat characteristics and spatial arrangement affecting the diversity of fish and decapod assemblages of seagrass ( Zostera marina) beds around the coast of Jersey (English Channel)

Recent research and management plans for seagrass habitats have called for landscape level approaches. The present study examines the spatial utilisation of subtidal seagrass beds by fish and decapods around the coast of Jersey (49°N 02° W). A hierarchical scale of landscape configuration and the plant characteristics of eight seagrass beds were measured and the contributions of these variables as predictors of the properties of the fish and decapod assemblages were evaluated using multiple linear regression models. The results indicated that total diversity had a negative relationship with transect heterogeneity and total species number had a weak negative association with increasing fragmentation. Both total diversity and total species number showed a positive relationship with depth. In fact, in all models of species number and densities, values were higher in deeper seagrass beds. Total decapod density increased with aggregation of seagrass patches within a landscape. In addition to landscape configuration, smaller-scale structural changes in both canopy height and epiphyte load appeared to influence densities of decapod crustaceans. At night, fewer patterns could be explained by the independent variables in the model.

Seagrass complexity hierarchies: Influence on fish groups around the coast of Jersey (English Channel)

Recent research has identified a need for seagrass habitat management plans to be based on landscape-level approaches as they offer a more appropriate scale for large mobile fauna than smaller scales. Also, conservation decisions are more likely to be a choice between different seagrass beds rather than parts of individual beds. The present study examined the spatial utilisation of subtidal seagrass beds by fish around the coast of Jersey, English Channel (49°N 02°W) with the aim of identifying influential scales of complexity. A hierarchical-scale of landscape configuration and habitat characteristics was measured for eight seagrass beds using aerial photographic analysis (e.g. core area, contiguity and other landscape metrics), digital echo-sounder data (e.g. depth, canopy height) and diver surveys (e.g. epiphyte load). The contributions of these variables as predictors of functional fish groups were explored using multiple linear regression models. Results indicated that more fragmented seagrass beds supported lower numbers of fish species than more homogenous seagrass landscapes (squared semi-partial correlation coefficient, sr 2 = − 0.3). Densities of juveniles of larger fish species showed a negative relationship with increased fragmentation of the seagrass (sr 2 = − 0.34). At smaller scales of structural complexity the densities of cryptic fish were related positively to canopy height (sr 2 = 0.46). At night, fewer patterns could be explained by the independent variables in the model, which was attributed to the greater movement of fish between the seagrass and adjacent habitats to forage, and a breakdown in the association with seagrass habitat as a refuge from predation.

Influence of seagrass beds ( Zostera noltii) on the species composition of juvenile fishes temporarily visiting the intertidal zone of the Wadden Sea

It is generally accepted that the presence of seagrass habitats significantly contributes to faunal diversity and density in coastal ecosystems. Most scientific research has been conducted in subtidal seagrass beds. Especially for highly motile fauna such as fishes, the relevance of intertidal seagrass stocks has scarcely been documented, and the studies that exist are limited to tropic coastal areas and to the temperate zone of the southern hemisphere. Therefore, no information is available on the impact of intertidal Zostera noltii (Hornemann) beds on shallow-water fish communities in the Wadden Sea (North Sea), although such meadows survived the major seagrass loss in the 1930s. We compared species composition and abundances of juvenile tidally migrating fishes in vegetated and unvegetated parts of the intertidal zone of a shallow tidal basin in the northern Wadden Sea near the Island of Sylt (Germany). During the seagrass growth period, the occurrence of juvenile fishes varied considerably. Ten fish species visiting the intertidal zone showed no significant difference between numerical densities in Z. noltii beds and adjacent bare sand flats. However, based on their distribution in the intertidal zone at high tide, three groups of fishes could be identified by cluster analysis: (i) five species found exclusively in Z. noltii beds, (ii) two species found predominantly in Z. noltii beds but also on bare sand in lower numbers, and (iii) three species found exclusively on bare sand flats. On tidal flats, Groups (i) and (ii) appeared simultaneously with the main growth period of Z. noltii in August and September, whereas the seasonal distribution of Group (iii) did not correspond with the period of maximum seagrass coverage. The results indicate an – up to now unknown- qualitative impact of Z. noltii beds on the species composition of 0-group common North Sea fishes temporarily visiting the intertidal zone, asking for further research.

HABITAT PREFERENCES OF SURFACE-DIVING WATERBIRDS AND AMERICAN WHITE PELICANS WINTERING IN REDFISH BAY, TEXAS

Habitat preferences were determined for a guild of surface-diving waterbirds wintering in Redfish Bay, Texas: common loon (Gavia immer), eared grebe (Podiceps nigricollis), pied-billed grebe (Podilymbus podiceps), double-crested cormorant (Phalacrocorax auritus), red-breasted merganser (Mergus serrator), and American coot (Fulica americana). American white pelican (Pelecanus erythrorhynchos) also was included because it occupies habitats similar to those of the surface divers. Between November 2001 and April 2002, the locations of 4,232 surface divers and American white pelicans using aquatic habitats in Redfish Bay were recorded and entered into a GIS that included a National Wetlands Inventory layer. Bird habitat preferences-avoidances were determined using a test based on Bonferroni's inequality. American coots, American white pelicans, and pied-billed grebes preferred shallower estuarine subtidal seagrass beds, whereas common loons, double-crested cormorants, and eared grebes preferred deeper estuarine subtidal unconsolidated bay bottom. Red-breasted mergansers showed no habitat preferences.

Biology and functional morphology of Kendrickiana gen. nov. veitchi (Bivalvia: Anomalodesmata: Clavagelloidea) from southern Australia

Abstract. The largest extant species of the adventitious tube‐building Clavagelloidea has hitherto been placed in the genus Foegia (itself formerly a subgenus of Brechites), the type species of which is the Western Australian F. novaezelandiae (Bruguiére 1792). Following examinations of and comparison with F. novaezelandiae and the southern Australian F. veitchi, the latter is herein placed in its own new genus Kendrickiana.Individuals of both F. novaezelandiae and K. veitchi are essentially amyarian in terms of adductor and pedal retractor muscles, but in the latter species the connection to the adventitious tube is located dorsally by an unique horseshoe‐shaped array of muscular papillae, which are inserted into holes in the tube. K. veitchi is different from other clavagelloids too in that the siphons are capable of only limited retraction into the tube. Their extension in K. veitchi is almost exclusively by hydraulic means because the complex internal siphonal muscles seen in other species of the Clavagelloidea, and which act antagonistically with extensive blood‐filled haemocoels, are vestigial. Kendrickiana can also be separated from Foegia in other anatomical respects. For example, members of the former have paired anterior suspensory muscles, and vestigial posterior pedal retractor muscles with pericardial proprioreceptors associated with them (as in Humphreyia and Dianadema), whereas the latter does not. Similarly, in Foegia there is a muscularized pedal disc, not found in Kendrickiana. Members of F. novaezelandiae are inhabitants of intertidal hypoxic muds, whereas those of K. veitchi apparently live exclusively in subtidal sea grass beds.

A comparison of fish communities of subtidal seagrass beds and sandy seabeds in 13 marine embayments of a Caribbean island, based on species, families, size distribution and functional groups

Differences in fish community structure between different estuaries, lagoons and bays can be very large, and generalisations are complicated by the use of a wide variety of sampling methods. In the present study, fish communities of subtidal seagrass beds and sandy seabeds in 13 marine embayments of a single Caribbean island were therefore sampled using a uniform method. The objective of the study was to determine whether the seagrass and sandy seabed habitats of various embayments are characterised by typical fish assemblages which differ in terms of taxa (species, families), size classes (life stages) and functional groups (ecological species groups, feeding time and diet). This was linked to the hypothesis that differences in fish assemblages between habitats in different embayments are larger at taxonomic levels than at the level of functional groups. A second objective was to determine the most useful discriminating features between the two habitat types. The above hypothesis was rejected, since differences in fish assemblages from different seagrass and sandy seabed sites did not increase from functional to taxonomic level, but from size class to diet/species to family/feeding time to ecological species group. However, the seagrass and sandy seabed habitats could each be characterised by typical fish assemblages which differed in taxonomical and functional group composition, irrespective of differences in environmental and biotic variables between the embayments in which these habitats were situated. The two habitat types could be best characterised on the basis of fish family, ecological species group, feeding time and size distribution. Seagrass beds mainly harboured nocturnally active nursery species (Haemulidae, Lutjanidae, etc.), whose relative abundance was related to vegetation (mainly seagrass) cover. Sandy seabeds mainly harboured diurnally active bay species (Gerreidae, etc.) whose relative abundance was related to cover of bare sand. Similarities in taxonomical and functional traits of fish species predicted whether they occurred more abundantly in seagrass beds or in sandy seabeds.

Estimating basal area coverage of subtidal seagrass beds using underwater videography

Although seagrasses have been identified as vital living marine resources, their distribution has not been rigorously quantified at many locations. This fact is often due to the high cost of sampling seagrass habitats, especially those with deep-water plants that cannot be sensed from aerial platforms. We present a cost-effective method of estimating basal area coverage of submersed vegetation that uses differential global positioning system data linked to underwater video images of the bottom. Our sampling design and statistical procedures are identical to estimating proportions using cluster sampling with unequal cluster sizes. This method has several advantages over other techniques: (1) confidence intervals around basal area coverage estimates permit hypothesis testing of changes over time; (2) sampling efficiency is better than simple random sampling with quadrats; (3) deep-water zones out of the range of aerial platforms can be sampled; (4) video images provide positive identification of plants which is not possible with acoustic techniques; and (5) the techniques provide a permanent archive of visual images that can be analyzed for other bottom attributes, such as other vegetation, macro-invertebrates, and gross sediment types. This method has some limitations: (1) it is not possible to sample extremely shallow or turbid waters and under some physical structures; (2) it is impractical to sample very large regions; (3) errors in differential global positioning system data must be accounted for; and (4) seagrass density must be measured subjectively. We illustrate our sampling methods and data analysis with an example from Puget Sound, Washington, USA.

Habitat linkages: the effect of intertidal saltmarshes and adjacent subtidal habitats on abundance, movement, and growth of an estuarine fish.

In this study we used pinfish (Lagodon rhomboides) in field experiments to examine linkages between intertidal saltmarsh and adjacent subtidal habitats. Pinfish are more than twice as abundant in intertidal marshes adjacent to seagrass beds than in those adjacent to the unvegetated subtidal bottom. Movement of pinfish between the marsh edge and the adjacent subtidal habitat was greater for fish captured in areas with both intertidal and subtidal vegetation than in those with intertidal vegetation and adjacent unvegetated mudflats. This movement provides an important link between habitats, allowing transfer of marsh-derived secondary production to subtidal seagrass beds and vice versa. Pinfish held in enclosures with both intertidal and subtidal vegetation were, on average, approximately 90% heavier than fish held in enclosures with intertidal vegetation and unvegetated subtidal bottom. Because saltmarshes and seagrass beds contribute to the production of living marine resources, active measures are being taken to preserve and restore these habitats. The results from this study have direct application to decisions concerning site selection and optimal spatial proximity of saltmarsh and seagrass habitats in the planning of restoration and mitigation projects. To maximize secondary production and utilization of intertidal marshes, managers may opt to restore and/or preserve marshes adjacent to subtidal seagrass beds.

Effects of trace metals on infaunal species composition in polluted intertidal and subtidal marine sediments near a lead smelter, Spencer Gulf, South Australia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 135:123-135 (1996) - doi:10.3354/meps135123 Effects of trace metals on infaunal species composition in polluted intertidal and subtidal marine sediments near a lead smelter, Spencer Gulf, South Australia Ward TJ, Hutchings PA The infauna of intertidal and subtidal marine sediments at 18 sites near a large lead-zinc smelter in Spencer Gulf, South Australia, was sampled twice about 6 mo apart. The sampled habitats were bare intertidal mudflats, intertidal seagrass (Zostera sp.) beds, subtidal seagrass (Posidonia spp.) beds, and unvegetated sediments at 5 to 10 m depth. The infauna consisted of 372 identifiable taxa, mainly polychaetes, molluscs and crustaceans. The number of taxa at each site and time showed no simple relationship with the concentrations of trace metals in sediments, habitat type or time of sampling. However, the patterns of distribution, analysed using frequencies of occurrence of taxa derived from multivariate classification and ordination techniques, were related to the sediment concentrations of As, Cu, Mn, Pb, Sb and Zn. The extremely high concentrations of these trace elements (probably mainly Pb and Zn) appeared to affect both the abundances and distribution of many infaunal species. The multivariate techniques could detect which species were affected in the most metal-polluted sites (the intertidal sites). However, in the less-polluted subtidal sites, patterns in species composition were detected but only a few individual species could be unambiguously correlated to the presence of the metals. The polluted intertidal sediments, which had some of the highest metal concentrations ever recorded in marine sediments (Pb up to 5270 ug g-1 and Zn up to 16700 ug g-1), supported 42 taxa. The polychaetes Heteromastus filiformis, Capitella 'capitata' and Glycera americana, and the crustacean Tanais dulongii were very abundant in these sites; they apparently can selectively exploit the metal-contaminated conditions. C. 'capitata' and T. dulongii were found almost exclusively in these sites. In contrast, 15 species of polychaetes, 5 crustaceans and 4 molluscs found elsewhere in the study area, representing 26, 20, and 17% of these intertidal taxa respectively, were not found in the metal-polluted sites. No taxonomic selectivity in the effects of the metals was detected amongst the 3 major groups-polychaetes, molluscs and crustaceans. Future studies may, therefore, be able to sample indicator species from only one of these major groups to determine the spatial extent of ecological effects or to monitor metal effects in this area. Metals . Infauna . Species composition . Biological effects . Monitoring . Smelter Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 135. Publication date: May 17, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Experimental Studies of Caribbean Seagrass Bed Development

Processes important in the development of subtidal seagrass beds composed of Thalassia testudinum, Syringodium filiforme, Halodule wrightii, and many rhizophytic algal species were examined in situ for 52 mo in a coral reef lagoon on St. Croix, United States Virgin Islands. The study emphasized the early stages of development of the seagrass beds and the role played by colonizing rhizophytic algae. I tested the hypotheses that nutrient accumulation in the sediments limits seagrass recolonization, and that rhizophytic algae facilitate sediment nutrient accumulation by stabilizing the sediments and adding organic matter from rapidly decomposing thalli. Vegetation was removed from 0.25— and 1—m2 plots in 3 m of water. Plot treatments consisted of: (1) no further manipulation, (2) adding nitrogen plus phosphorus fertilizer to the sediments, (3) removing colonizing rhizophytic algae to minimize algal effects (e.g., sediment stabilization, organic input), and (4) removing colonizing algae and adding "plastic algae" to stabilize sediments without organic input. Plant densities, sediment grain size, redox potential, inorganic nitrogen concentrations in porewaters, and ammonium production rates were measured over time in all plots, including undisturbed controls. All recolonization occurred through vegetative propagation. The sequence of plant recolonization was unaffected by the treatments, corresponding instead to life history characteristics and nutrient requirements of the species involved. Rhizophytic algae invaded the plots within a few months, followed by the seagrass Syringodium, then Thalassia. The seagrass Halodule was insignificant in the recolonization. Densities of rhizophytic algae and Syringodium declined when the density of Thalassia reached 200 leaf shoots/m2. The rates of increase in seagrass leaf shoot densities and biomass were greatest in the fertilized plots, supporting the nutrient limitation hypothesis. Rhizophytic algae facilitated seagrass recolonization; seagrass densities, biomass, and porewater ammonium concentrations were lowest in plots where algae were removed. Sediment ammonium concentrations decreased when Thalassia became dominant. Ammonium production in the sediments increased as the plant community developed. The nitrogen required for Syringodium productivity was met easily by ammonium production, assuming no competition from Thalassia. In contrast, Thalassia accounted for >93% of the nitrogen required for total seagrass productivity, and ammonium production could supply up to 45% of this requirement. At the end of the experiment (52 mo), Thalassia density and ammonium production rates in the sediments were lower than in the surrounding undisturbed seagrass bed. The experiment provides evidence for a resource—ratio model where the rate of succession is controlled by a sediment nutrient supply that increases over time. The sequence of colonization is determined by relative rates of vegetative propagation by stolons and rhizomes across the sediment surface, which are inversely correlated with whole plant productivity and thus with requirements for nutrients. Algal colonizers tolerate low nutrients by having low productivities. The climax species Thalassia is a competitive species effective at exploiting the sediment nutrient resource. Co—existence, rather than replacement, of species occurs, despite a relatively benign disturbance regime.