Subtidal Bottoms Research Articles

Potential impacts of marine urbanization on benthic macrofaunal diversity

Urbanization and associated human activities have caused numerous changes to natural environments, including the loss of natural habitats and replacement with artificial structures. How these changes impact coastal marine biodiversity and ecosystem functioning is not well known. In this study, we examined the potential impacts of habitat changes by comparing species commonality and community structure (i.e., species richness, abundance, and functional composition) among artificial (a breakwater wall) and natural habitats (eelgrass bed, intertidal flat, and subtidal bottom) within a semi-enclosed coastal sea impacted by marine urbanization. We found considerable species overlap (i.e., high species sharing) among the eelgrass bed, intertidal flat, and subtidal bottom habitats. By contrast, the breakwater wall was a distinctive habitat with little overlap in species and functional groups with the other habitats, and was therefore a poor substitute for natural habitats. Our study suggests that marine urbanization degrades redundancy and inhibits the maintenance of biodiversity in coastal marine zones.

Living on a trophic subsidy: Algal quality drives an upper-shore herbivore's consumption, preference and absorption but not growth rates.

The transfer of seaweeds from subtidal bottoms to nearby intertidal rocky shores is a common but often overlooked phenomenon. Freshly detached seaweeds often represent critical trophic subsidies for herbivores living in upper-shore rocky intertidal areas, such as the marine snail Diloma nigerrima. This species relies on three species of seaweeds for food and displays feeding strategies to deal with a resource that is scarce and at times unpredictable. This study focused on the nutritional quality of freshly detached algae (Durvillaea antarctica, Lessonia spicata and Lessonia trabeculata) and measured Diloma nigerrima’s algal consumption rates in trials with and without choice. Absorption efficiency and growth of individual snails fed on each alga were also measured. Durvillaea antarctica had the highest nutritional quality and was the most consumed algae in both single and multiple-choice trials. Absorption efficiency was also highest for D. antarctica but growth rates of snails fed with this species were similar to those fed with the other algae. Combined, these results suggest that D. nigerrima has the ability to discriminate among seaweeds based on their nutritional quality. A potential increase in oxygen uptake when D. nigerrima is consuming the preferred food item is also proposed as a plausible hypothesis to explain the mismatch between snails’ preference and growth rate. These results aim to guide further studies on trophic subsidies and their role in coastal systems.

An approach based on the total-species accumulation curve and higher taxon richness to estimate realistic upper limits in regional species richness.

Most of accumulation curves tend to underestimate species richness, as they do not consider spatial heterogeneity in species distribution, or are structured to provide lower bound estimates and limited extrapolations. The total‐species (T–S) curve allows extrapolations over large areas while taking into account spatial heterogeneity, making this estimator more prone to attempt upper bound estimates of regional species richness. However, the T–S curve may overestimate species richness due to (1) the mismatch among the spatial units used in the accumulation model and the actual units of variation in β‐diversity across the region, (2) small‐scale patchiness, and/or (3) patterns of rarity of species. We propose a new framework allowing the T–S curve to limit overestimation and give an application to a large dataset of marine mollusks spanning over 11 km2 of subtidal bottom (W Mediterranean). As accumulation patterns are closely related across the taxonomic hierarchy up to family level, improvements of the T–S curve leading to more realistic estimates of family richness, that is, not exceeding the maximum number of known families potentially present in the area, can be considered as conducive to more realistic estimates of species richness. Results on real data showed that improvements of the T–S curve to accounts for true variations in β‐diversity within the sampled areas, small‐scale patchiness, and rarity of families led to the most plausible richness when all aspects were considered in the model. Data on simulated communities indicated that in the presence of high heterogeneity, and when the proportion of rare species was not excessive (>2/3), the procedure led to almost unbiased estimates. Our findings highlighted the central role of variations in β‐diversity within the region when attempting to estimate species richness, providing a general framework exploiting the properties of the T–S curve and known family richness to estimate plausible upper bounds in γ‐diversity.

Structural impoverishment of the subtidal vegetation of southeastern Bay of Biscay from 1991 to 2013 in the context of climate change

This study assesses changes in the taxonomic and functional structure and in the diversity of the shallow (3–9m) subtidal vegetation off the southeastern coast of the Bay of Biscay by studying 19 locations between 1991 and 2013. Results provide evidence that the three-dimensional assemblages of shallow subtidal bottoms in the study area may be shifting towards less structurally complex communities. Canopy-forming algae are declining whereas simple thallus turfs composed of a combination of filamentous, polysiphonated and foliose non-corticated algae are becoming abundant along with articulated corallines and crustose species. Moreover, a significant increase in taxa richness and diversity was found, mainly due to the development of opportunistic and morphologically simple forms with warm-water affinity. The potential ecological consequences of canopy loss for coastal ecosystems are discussed. Given that changes in climate conditions are predicted to intensify, the prevalence of the new turfing space occupiers in the study area here considered seems to be realistic on the basis of their ability to compete for space and resist disturbance. Consequently, major implications for the functioning and diversity of the ecosystem and for ecosystem services may be expected.

New species ofMonticellinaandChaetozone(Polychaeta: Cirratulidae) in the SW Atlantic, and a review ofMonticellinaspecies

During quantitative surveys two new species of Cirratulidae from subtidal bottoms of the Atlantic coast of Argentina were collected. They belong to the generaMonticellinaandChaetozone. Monticellina moraesp. nov. is characterized by the presence of a long peristomium of smooth appearance, but triannulated at SEM, bearing the dorsal tentacles in the posterior part, with the first pair of branchiae posterolateral to the dorsal tentacles in chaetiger 1. The body is divided into three parts, an anterior region laterally expanded and with crowded segments, a middle region with beadlike chaetigers and an inflated and crowded posterior region.Chaetozone laraesp. nov. is characterized by an inflated dorsally and laterally expanded anterior crowded region. Peristomium biannulated laterally, with a dorsal crest on the first and second annuli that occupy the entire width, and then a narrow crest in the following annulus (interpreted as an achaetous segment). Capillaries are lanceolate, short and long, with acicular spines curved, forming partial cinctures. In addition, a comparative table of all described species ofMonticellinais included and the distinctive characters are discussed.

Spatial variability of the infauna adjacent to intertidal rocky shores in a subtropical estuary

Negative responses of infauna close to rocky substrates are well known to subtidal bottoms, but there are few studies addressing similar intertidal habitats. We tested the hypothesis that the proximity to rocky shores negatively affects the density and richness of intertidal infauna of tidal flats by assessing infaunal variation across the increasing distances from rocky shores in two tidal flats (Pasto and Limoeiro) of a subtropical estuary in southern Brazil. Total density decreased significantly with the proximity to rocks only in Pasto due to density variations in the two numerically dominant species, the bivalve Anomalocardia flexuosa and the polychaete Armandia hossfeldi. Richness decreased significantly with the proximity to the rocky shores only in Limoeiro. Multivariate analyses revealed significant differences in species and functional groups composition between assemblages near and far from the rocky shores. Assemblage variability patterns were mostly explained by sediment variables. Our hypothesis was partially refuted because negative effects on the infauna were spatially inconsistent, due to differences in species composition between tidal flats, and to distinct responses of individual taxa. Even with the absence of consistent response patterns, the proximity to the rocky shores emerged as a relevant structuring factor of the surrounding intertidal infauna.

Contrasting recruitment seasonality of sea urchin species in Gran Canaria, Canary Islands (eastern Atlantic)

Despite sea-urchins can play an important role affecting the community structure of subtidal bottoms, factors controlling the dynamics of sea-urchin populations are still poorly understood. We assessed the seasonal variation in recruitment of three sea-urchin species (Diadema africanum, Paracentrotus lividus and Arbacia lixula) at Gran Canaria Island (eastern Atlantic) via monthly deployment of artificial collectors throughout an entire annual cycle on each of four adjacent habitat patches (seagrasses, sandy patches, ‘urchin-grazed’ barrens and macroalgal-dominated beds) within a shallow coastal landscape. Paracentrotus lividus and A. lixula had exclusively one main recruitment peak in late winter-spring. Diadema africanum recruitment was also seasonal, but recruits appeared in late summer-autumn, particularly on ‘urchin-grazed’ barrens with large abundances of adult conspecifics. In conclusion, this study has demonstrated non-overlapping seasonal recruitment patterns of the less abundant species (P. lividus and A. lixula) with the most conspicuous species (D. africanum) in the study area.

Solar radiation (PAR and UVA) and water temperature in relation to biochemical performance of Gelidium corneum (Gelidiales, Rhodophyta) in subtidal bottoms off the Basque coast

Gelidium corneum (Hudson) J.V. Lamouroux is a very important primary producer in the Cantabrian coastal ecosystem. Some local declines in their populations have been recently detected in the Basque coast. Occurrences of yellowing and an unusual branch breakdown pattern have also been reported for some G. corneum populations. In order to gain further insight into those environmental stressors operating at a local scale, here we investigate if shallow subtidal populations of G. corneum living under potentially different conditions of irradiance (PAR and UVA) and water temperature exhibit differences in some biochemical indicators of stress, namely C:N, antioxidant activity (radical cation of 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate); ABTS+ assay) and mycosporine-like amino acids (MAAs) (Asterine 330 and Palythine). We hypothesised that G. corneum subjected to higher ambient levels of irradiance and water temperature would show higher C:N ratios, lower antioxidant activity and higher MAA concentrations. Our results partially support this hypothesis. We found that G. corneum exposed to increased levels of irradiance (PAR, UVA) exhibited greater C:N ratios and lower antioxidant activity (higher IC50), whereas no relationship was found regarding MAAs. No differences in biochemical performance in relation to temperature were detected among G. corneum exposed to comparable high light. Similarly, G. corneum growing under lower UVA radiation levels showed no differences in any of the measured biochemical variables with regard to PAR and water temperature. These findings suggest that, among the environmental factors examined, UVA radiation may be an important driver in regulating the along-shore variation in G. corneum biochemical performance. Therefore, the role of irradiance, especially UV radiation, in potential future alterations in Cantabrian G. corneum populations cannot be ruled out as a potential underlying factor.

A New Species of the Ghost Shrimp Family Ctenochelidae (Crustacea: Decapoda: Axiidea) from Japan

A new species of the ghost shrimp genus Ctenocheloides (Decapoda: Axiidea: Ctenochelidae), C. nomurai, is described on the basis of two male specimens from the shallow subtidal bottom of Arita Bay, Kushimoto, Wakayama Prefecture, Japan. The new species differs from its sole known congener, C. attenborougi Anker, 2010, in the structure of the carapace, the well developed crista dentata of the third maxilliped, the strongly asymmetrical chelipeds, and the chelate fifth pereopod. The two type specimens were found under a rock on soft bottom, suggesting that the new species is a burrower like other callianassoid species.

Molluscan assemblages in littoral soft bottoms of the Alboran Sea (Western Mediterranean Sea)

The structure of the molluscan assemblages inhabiting the subtidal bottoms off the west coast of Malaga province (southern Spain) and their relation to sediment characteristics were analysed with both univariate and multivariate parameters. Five significantly different molluscan assemblages were identified and assigned to ‘sables fins bien calibrés’ (SFBC, well sorted fine sands); ‘détritique côtier’ (DC, coastal bioclastic sands); ‘détritique envasé’ (DE, muddy bioclastic sands); and ‘coralligène’ (CO, coralligenous) biocoenoses of Pérès and Picard classification. A total of 234 molluscan species were identified, with gastropods as the dominant group (135 species). An increase of diversity and evenness with depth has been observed, with the highest values for both indexes on a rocky outcrop, and the lowest in the shallower fine sand assemblage dominated by few species. The different molluscan assemblages inhabiting these sublittoral bottoms were conditioned by depth, percentage of gravel and percentage of clay. A large proportion of tropical West African species is found in the area, some of them reaching their distributional limit towards the Mediterranean Sea. The southern Iberian coasts, in the confluence of Atlantic and Mediterranean waters and between Africa and Europe, are therefore highlighted as one of the areas with highest molluscan species richness in Europe, and require a conservation policy in order to preserve this unique European biodiversity heritage.

Food sources of benthic animals on intertidal and subtidal bottoms in inner Ariake Sound, southern Japan, determined by stable isotopes

To evaluate the relative importance of possible food sources, including riverine particulate organic matter, reeds, benthic microalgae, seaweeds, cultured laver ( Porphyra) and coastal phytoplankton, for commercial bivalves and co-occurring benthic animals, 73 macrofaunal species were collected from intertidal and subtidal soft bottoms in the inner part of Ariake Sound, Kyushu, southern Japan, and their isotopic compositions were analyzed. The results revealed that (1) both intertidal and subtidal food webs were constituted of 3 trophic levels, (2) suspension-feeding bivalves utilize a mixture of benthic microalgae and coastal phytoplankton, and omnivores and carnivores incorporate benthic microalgae and phytoplankton through their intermediate prey, and (3) 3 bivalves ( Scapharca kagoshimensis, Modiolus metcalfei and Atrina lischkeana) inhabiting both intertidal and subtidal bottoms showed similar seasonal fluctuations, suggesting no difference in the diet composition among the species and between the 2 habitats. We conclude that a large biomass of benthic microalgae which was approximately equal to that of phytoplankton and the strong tidal currents that would resuspend benthic microalgae and transport them to subtidal bottom areas account for the benthic microalgal and phytoplankton based trophic structure in the inner part of Ariake Sound.

A new gastrotrich species of the genus ptychostomella (macrodasyida, thaumastodermatidae) from South Korea

A new marine gastrotrich species, Ptychostomella jejuensis n. sp. belonging to the family Thaumastodermatidae, is described on the basis of the specimens from subtidal sand bottom at about 6–7 m depth of Jeju Island, South Korea. Ptychostomella jejuensis n. sp. is distinguished from its congeneric species with smooth cuticular armature by the character combination: (1) small body up to about 160 μm in length; (2) presence of knob‐like cephalic tentacles; (3) absence of dorsal and ventral adhesive tubes; (4) bifid pedicles; (5) pyriform copulatory organ. Under scanning electron microscopy, numerous epidermal gland openings were observed in the new species, characteristically flanking a bristle. Taxonomic accounts on the affinities, some brief remarks on the epidermal gland openings and the cooccurrence with P. orientalis Lee and Chang, 2003 are also presented with detailed illustrations and scanning electron photomicrographs.

Distribution of Polychaeta in soft-bottoms of a Galician Ria (NW Spain)

Macrobenthic polychaete distributions were studied along the soft-bottoms of the Ensenada de San Simon (Galicia, NW Spain). Results suggest that the distribution and abundance of polychaetes in the inlet were highly dependent on depth, sediment characteristics (grain size, organic matter and calcium carbonate content) and bottom water temperature. In the inner area of the inlet, intertidal bottoms colonised by the seagrasses Zostera marina and Z. noltii were dominated by spionids and capitellids, and showed low species number and diversity. Shallow muddy bottoms of central areas were mostly dominated by ampharetids, terebellids and cirratullids. These families along with paraonids, maldanids and syllids were the most abundant families in the deeper subtidal muddy bottoms at the mouth of the inlet. These sediments also showed the highest number of species, diversity and density of individuals.

Spatial distribution of soft-bottom molluscs in the Ensenada de San Simón (NW Spain)

Distribution and abundance of the molluscan fauna was studied in the intertidal and subtidal soft-bottoms of the Ensenada de San Simón (NW Spain). Depth, grain size, and total organic matter were the most important factors in determining distribution patterns of molluscs in this inlet. Three major malacological assemblages have been determined in the Ensenada de San Simón, two of them subdivided in two facies. In the intertidal area of the inlet, one facies (A1) was located in areas associated with seagrass meadows of Zostera spp. and was dominated by Hydrobia ulvae (Pennant, 1777) whereas the second facies (A2) had a high dominance of H. ulvae, Cerastoderma edule (Linnaeus, 1758), and Tapes decussatus (Linnaeus, 1758). An impoverished facies of this community was present in reduced, muddy bottoms (Group C). In the subtidal bottoms, one group (B1) was located in the central part of the inlet with H. ulvae, Rissoa labiosa (Montagu, 1803), Turboella radiata (Philippi, 1836), Parvicardium exiguum (Gmelin in Linnaeus, 1791), Loripes lacteus (Linnaeus, 1758), and Abra nitida (Müller, 1789) as characteristic species. A second facies (B2) was found in outer areas of the inlet, characterized by Thyasira flexuosa (Montagu, 1803), Mysella bidentata (Montagu, 1803), Abra alba (Wood, 1802), and Nucula nitidosa Winckworth, 1930.

Macrobenthic fauna in the Ensenada de San Simón (Galicia, north-western Spain)

Distribution and abundance of the macrobenthic fauna was studied in the intertidal and subtidal soft-bottoms of the Ensenada de San Simón (north-western Spain). Depth and grain size were the most important factors in determining patterns of distribution of the macrozoobenthos. A reduced Macoma community was present in the inner area of the inlet structured in two facies subdivision in the community that does not affect its qualitative composition: the first one was in intertidal areas associated with meadows of the sea grasses Zostera noltii and Z. marina and defined by the dominance of Hydrobia ulvae; the second facies in intertidal sediments was characterized by the dominance of Tubificidae and nematodes and Pseudopolydora paucibranchiata. The poverty of these bottoms in number of species can be due to salinity fluctuations and human activities developed in the area. Subtidal bottoms were characterized by a Syndosmya(=Abra)alba community. Two facies were detected: one facies located in shallow subtidal bottoms with H. ulvae and Thyasira flexuosa as characteristic species, and a second facies in deeper areas, characterized by the polychaetes Ampharete finmarchica, P. paucibranchiata, Aphelochaeta marioni, Melinna palmata and Paradoneis lyra.

Nekton use ofVallisneria americana Michx. (Wild celery) beds and adjacent habitats in Coastal Louisiana

We compared nekton use ofVallisneria americana Michx. (submerged aquatic vegetation, SAV) with marsh shoreline vegetation and subtidal nonvegetated bottom (SNB) using a 1-m2 drop sampler in the oligohaline area of Barataria Bay, Louisiana. Mean densities of most abundant species were significantly different among six habitat types. Harris mud crabRhithropanopeus harrisii, Ohio shrimpMacrobrachium ohione, blue crabCallinectes sapidus, daggerblade, grass shrimpPalaemonetes pugio, white shrimpLitopenaeus setiferus (fall), rainwater, killifishLucania parva, naked gobyGobiosoma bosc, code gobyGobiosoma robustum (fall), speckled worm eelMyrophis punctatus (fall), and gulf pipefishSyngnathus scovelli (spring), were much more abundant, and species richness also was greater, inVallisneria than over SNB.Vallisneria supported densities of most species that were similar to those in marsh vegetation, although naked goby and gulf pipefish were more abundant inVallisneria, and speckled worm eel and saltmarsh topminnowFundulus jenkinsi were more abundant in marsh. Within theVallisneria bed, densities of Harris mud crab, rainwater killifish, and speckled worm eel were higher at sites near the marsh (SAV Inside Edge) than at sites more distant from the marsh (SAV Outside Edge), and Ohio shrimp (fall) densities were higher in the interior of the bed than along the edges. The mean size of blue crab was larger in marsh thanVallisneria and large inVallisneria than SNB. White shrimp did not differ in size among habitat types.Vallisneria beds may provide an important nursery habitat for young blue crab and white shrimp that use oligohaline estuarine areas. These SAV beds can provide an alternative structural habitat to emergent vegetation during periods of low water, becauseVallisneria occurs in the subtidal and generally persists throughout the year on the Gulf coast. Species whose young thrive in low-salinity waters and also depend on structure would benefit most fromVallisneria habitat in estuaries.

Opisthobranch molluscs from the subtidal trawling grounds off Blanes (Girona, north-east Spain)

Studies on the opisthobranch molluscs inhabiting the continental platform in areas not accessible by SCUBA diving are rare in the subtidal bottoms of the Iberian Peninsula. Data obtained from trawls are not adequate for quantitative analysis, due to the indirect method used and the high number of variables which affect the capture of the samples. However, with the aim of obtaining qualitative information on the opisthobranch molluscs inhabiting the subtidal trawling grounds off Blanes, we took more than 500 samples over a two-year period, on the non-commercial fraction of the trawling fisheries, finding opisthobranchs in 306 samples. We analysed samples from 16 trawling sites, at depths between 50 and 300 m, by using ten fishing boats of the ‘Confraria de Pescadors del Port de Blanes’. We obtained 4.295 specimens of opisthobranchs belonging to 29 species. From these, 4 are Cephalaspidea s.s., 1 Anaspidea, 1 Umbraculacea, 3 Pleurobranchacea and 20 Nudibranchia (3 Arminina, 3 Dendronotina and 14 Doridina). The most abundant species were Gastropteron rubrum and Scaphander lignarius, both cephalaspideans present during all seasons, and the dendronotacean Tethys fimbria. For Scaphander lignarius it was possible to distinguish three size-groups, from which the smallest one was usually found in summer. Other interesting species found were, among others, Armina tigrina, Baptodoris cinnabarina, Thordisa filix and Kaloplocamus ramosus. The richest trawling grounds in species numbers and abundances were La Planassa and Els Capets. The total number of opisthobranch species reported for the trawling grounds off Blanes is now 48.

Nekton use of subtidal oyster shell habitat in a Southeastern U.S. estuary

Subtidal accumulations of oyster shell have been largely overlooked as essential habitat for estuarine nekton. In southeastern U.S. estuaries, where oyster reef development is mostly confined to the intertidal zone, eastern oyster (Crassostrea virginica) shell covered bottoms are often the only significant source of hard subtidal structure. We characterized and quantified nekton use of submerged shell rubble bottoms, and compared it to use of intertidal reefs and other subtidal bottoms in the North Inlet estuary, South Carolina. Replicate trays (0.8 m2) filled with shell rubble were deployed in shallow salt marsh creeks, and were retrieved after soak times of 1 to 25 days from May 1998 to March 2000. Thirty six species of fishes, representing 21 families, were identified from the 455 tray collections. Water temperature, salinity, soak time and the presence of a shell substrate all affected the catch of fishes in the trays. Catches during the warmer months were two to five times greater than those during the winter. Fishes were present in 98% of the trays with an overall average of 5.7 fish m−2. The assemblage was numerically dominated by small resident species including naked goby (Gobiosoma bose), oyster toadfish (Opsanus tau), and crested blenny (Hypleurochilus geminatus). Transient species accounted for 23% of all individuals and 62% of the total biomass due to the presence of relatively large sheepshead (Archosargus probatocephalus) and black sea bass (Centropristis striata). Both the transient and resident species displayed distinct periods of recruitment and rapid growth from April to October. Lower abundances of juvenile gobies and blennies during 1998 were attributed to long periods of depressed salinity caused by high rainfall associated with El Nino conditions in spring. Crabs and shrimps, which were often more abundant than the fishes, accounted for comparable biomass in the tray collections. In comparisons of subtidal tray and trawl catches, trays yielded 10 to 1,000 fold higher densities of some demersal fish groups. Comparisons of intertidal and subtidal gear catches indicated that many species remain in the subtidal shell bottom at all stages of the tide. This study suggests that subtidal shell bottom may be essential fish habitat for juvenile seabass, groupers, and snappers and that it may be the primary habitat for a diverse assemblage of ecologically important resident fishes and crustaceans. Given the high levels of nekton use and the areal extent of oyster shell bottoms in eastern U.S. and Gulf estuaries, increased attention to protection and restoration of these areas appears justified.

La fauna de caprélidos (Crustacea: Amphipoda: Caprellidea) de la costa de Coquimbo, centro-norte de Chile, con una clave taxonómica para la identificación de las especies

Caprellids are abundant in many littoral habitats ofthe marine environment. Nevertheless, this group of amphipods has been scarcely studied along the coast of Chile. The study ofthe Caprellidea is particular! y difficult dueto the high degree of intra-specific morphological variability and the fact that literature and specimens from Museums are not easily located. The objective of the present study was to pro vide the taxonomical tools to identify the most common caprellid species from northem-central Chile. Severa! habitats were examined (buoys, boulders, algal/seagrass beds) and six caprellid species were found: Caprellina longicollis (Nicolet, 1849), Cap re/la equilibra S ay, 1818, C. scaura Templeton, 1836, C. verrucosa Boeck, 1871; Deutella venenosa Mayer, 1890 and Paracaprella pusilla Mayer, 1890. Cap re/la scaura, C. verrucosa and D. venenosa were most abundant among algae, hydrozoans and bryozoans growing on buoys. Cap re/la equilibra, al so present on buoys, was most abundant undemeath boulders in exposedrocky intertidal zones, where additionally D. venenosa and P. pusilla were found. Caprella scaura was dominant in plant beds above sandy subtidal bottom, especially among the alga Gracilaria chilensis and the seagrass Heterozostera tasmanica, where it occurred together with Caprellina longicollis. Paracaprella pusilla represents a new citation for the pacific coasts of S-America, being a new record for Chile. The species D. venenosa, which was recorded for the first time since the original description by Mayer in the year 1890, is considered an endemic species from the central coast of Chile.

Marsh terracing as a wetland restoration tool for creating fishery habitat

Terracing is a relatively new wetland-restoration technique used to convert shallow subtidal bottom to marsh. This method uses existing bottom sediments to form terraces or ridges at marsh elevation. A terrace field is constructed by arranging these ridges in some pattern that maximizes intertidal edge and minimizes fetch between ridges; the intertidal area is planted with marsh vegetation. We examined the habitat value of terracing for fishery species at Sabine National Wildlife Refuge, Louisiana (USA) in spring and fall 1999 by quantifying and comparing nekton densities in a 9-yr-old terrace field and nearby reference area using a 1-m2 drop sampler. Decapod crustaceans were more abundant than fishes, composing 62% and 95% of all organisms we collected in spring and fall, respectively. White shrimp Litopenaeus setiferus, daggerblade grass shrimp Palaemonetes pugio, blue crab Callinectes sapidus, and brown shrimp Farfantepenaeus aztecus accounted for 94% of all crustaceans, whereas 60% of all fishes were gulf menhaden Brevoortia patronus. Mean densities of white shrimp (fall), daggerblade grass shrimp, blue crab, and brown shrimp (spring) were significantly greater in terrace marsh than on non-vegetated bottom in the reference pond. Densities of most nekton on non-vegetated bottom were similar in the terrace field and the reference pond, but gulf menhaden and white shrimp had higher densities at terrace pond sites and brown shrimp (spring) were more abundant at reference pond sites. The pattern for biomass was similar to that for density in that the mean biomass of most species was significantly greater at terrace marsh sites than reference pond sites and similar at terrace and reference pond sites. Terrace marsh, however, was not functionally equivalent to natural marsh, as mean densities of daggerblade grass shrimp (fall), brown shrimp (spring), and blue crab and mean biomass of white shrimp (fall), striped mullet Mugil cephalus (spring), and spotted seatrout Cynoscion nebulosus (fall) were greater at reference marsh sites than terrace marsh sites. Using these density and biomass patterns and the percentage of marsh and pond area in the terrace field, we concluded that terrace fields support higher standing crops of most fishery species compared with shallow marsh ponds of similar size. Future restoration projects could include design changes to increase the proportion of marsh in a terrace field and enhance the habitat value of marsh terraces for fishery species.