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Subtidal Zones (subtidal + zone)
Selected AbstractsWave and sediment dynamics along a shallow subtidal sandy beach inhabited by modern stromatolitesGEOBIOLOGY, Issue 1 2008J. E. ECKMAN ABSTRACT To help define the habitat of modern marine stromatolites, wave-dominated flow and sediment transport were studied in the shallow subtidal region (1,2 m depth) along the slightly concave, windward face of Highborne Cay, Exuma, Bahamas , the only face of the cay that includes a population of stromatolites concentrated near the region of highest curvature of the beach. Wave energy impacting this island's most exposed beach was driven by local wind forcing which increases largely in response to the passage of atmospheric disturbances that typically affect the region for periods of a few days. Although some wave energy is almost always noted (maximum horizontal orbital speeds at the bottom are rarely <10 cm s,1), wave conditions remain comparatively calm until local winds increase above speeds of ,3,4 m s,1 at which point maximum wave speeds rapidly increase to 50,80 cm s,1. Stromatolites, which are largely restricted to the shoreward side of a shallow platform reef, are sheltered by the reef beyond which wave speeds are one to four times higher (depending on tidal stage). Moreover, stromatolite populations are predominantly found along a region of this wave-exposed beach that experiences comparatively reduced wave energy because of the curved morphology of the island's face. Maximum wave speeds are 1.4 to 2 times higher along more northern sections of the beach just beyond the locus of stromatolite populations. A quantitative model of sediment transport was developed that accurately predicted accumulation of suspended sediment in sediment traps deployed in the shallow subtidal zone along this beach. This model, coupled with in situ wave records, indicates that gross rates of suspended sediment deposition should be two to three times higher northward of the main stromatolite populations. Regions of the beach containing stromatolites nevertheless should experience significant rates of gross suspended sediment deposition averaging 7,10 g cm,2 day,1 (,4,6 cm day,1). Results suggest that one axis of the habitat of modern marine stromatolites may be defined by a comparatively narrow range of flow energy and sediment transport conditions. [source] RAMET DYNAMICS FOR THE CLONAL SEAWEED PTEROCLADIELLA CAPILLACEA (RHODOPHYTA): A COMPARISON WITH CHONDRUS CRISPUS AND WITH MAZZAELLA CORNUCOPIAE (GIGARTINALES)JOURNAL OF PHYCOLOGY, Issue 6 2000Ricardo Scrosati Little is known about the dynamics and the ecological interactions among ramets (fronds) from populations of clonal red seaweeds. Small ramets are very difficult to tag, so their growth cannot be monitored directly. The temporal variation of the relationship between stand biomass and ramet density offers information on ramet performance. We calculated this relationship for an intertidal population of Pterocladiella capillacea (Gmelin) Santelices et Hommersand (Gelidiales) from Baja California, Mexico. Biomass and density were positively correlated on an annual basis, indicating that biomass accumulated without involving self-thinning among ramets. This contrasts with nonclonal seaweeds, for which self-thinning among individuals occurs during growth, but agrees with other clonal red seaweeds, such as Chondrus crispus Stackhouse and Mazzaella cornucopiae (Postels et Ruprecht) Hommersand (both Gigartinales). The growth pattern for these members of the Gelidiales and of the Gigartinales holds despite differences in holdfast morphology and ramet branching degree and despite differences in the capacity of coalescence during early stages, known only for the Gigartinales. The positive slope for the dynamic biomass,density relationship, on a bilogarithmic scale, was statistically steeper for M. cornucopiae than for P. capillacea and for C. crispus. This suggests that the addition of new ramets during the growth season may be relatively more beneficial for biomass accumulation rates for M. cornucopiae. This would be expected for high-intertidal species subjected to strong abiotic stress, for which ramet crowding constitutes a key protection. Pterocladiella capillacea occurs at the mid-intertidal zone and C. crispus at the subtidal zone, so ramets would be relatively less important in that respect. [source] Marine biogeographical structure in two highly dispersive gastropods: implications for trans-Tasman dispersalJOURNAL OF BIOGEOGRAPHY, Issue 4 2007Jonathan M. Waters Abstract Aim, Recent genetic and ecological studies of marine invertebrate species with planktotrophic larvae have inferred high rates of gene flow across wide oceanic barriers. We therefore aim to test for the genetic signature of long-distance dispersal in two widespread and abundant marine gastropod taxa. Location, The intertidal and shallow subtidal zones of southern Australia and New Zealand (NZ), which house similar marine invertebrate assemblages despite being separated by the 2000-km-wide Tasman Sea. Methods, We used mtDNA cytochrome oxidase I gene sequence analysis of two gastropod genera exhibiting trans-Tasman distributions, namely Austrolittorina (Littorinidae) (139 specimens; 28 localities) and Scutus (Fissurellidae) (154 specimens; 32 localities). The cool-temperate Australian (A. unifasciata; S. antipodes) and NZ (A. antipodum; S. breviculus) taxa within each genus are morphologically similar but of uncertain taxonomic status. Results, The mtDNA analyses indicate major trans-Tasman genetic discontinuities for both gastropod genera, with no evidence of recent or ongoing intercontinental gene flow. Although both Scutus and Austrolittorina show significant east,west structure within southern Australia , consistent with recent studies of regional marine phylogeography , neither taxon exhibits significant differentiation within NZ. Main conclusions, Morphologically conserved but biogeographically disjunct gastropod populations may exhibit striking phylogeographic discontinuities, even when dispersal abilities appear to be high. On the basis of these data we reject recent calls for the synonymy of NZ and Australian lineages. [source] Marine biogeography of southern Australia: phylogeographical structure in a temperate sea-starJOURNAL OF BIOGEOGRAPHY, Issue 12 2003Jonathan M. Waters Abstract Aim, To test whether marine biogeographical patterns observed at the community level are also important within species. It is postulated that historical hydrogeographic barriers have driven in situ diversification. Location, The intertidal and shallow subtidal zones of southern Australia, New Zealand and nearby islands. Australia's temperate marine communities are characterized by a high degree of endemism and show strong biogeographical structure along an east,west axis. Methods, Phylogeographical analysis of the widespread asteriid sea-star Coscinasterias muricata Verrill across southern Australia and New Zealand. Forty-two samples from 27 locations were included in phylogenetic analyses of mitochondrial (CO1; control region) and nuclear (ITS2) DNA sequences. Results, Analysis of mtDNA revealed a deep phylogenetic split within Australian C. muricata, strongly correlated with latitude. ,Northern' haplotypes (latitude , 37.6° S, nine sites, 15 samples) were 7.3,9.4% divergent from ,southern' haplotypes (latitude , 37.6° S, 19 sites, 27 samples), consistent with late Pliocene separation. Eastern and western representatives of the ,northern' clade were 0.5,1.0% divergent, probably reflecting Pleistocene isolation. The ,southern' clade of Australia is also represented in New Zealand, indicating Pleistocene oceanic dispersal. Nuclear DNA (ITS2) sequences yielded relatively little phylogenetic resolution, but were generally congruent with mtDNA-based groupings. Main conclusions, The phylogeographical pattern detected within Australian C. muricata closely resembles marine biogeographical groupings proposed on the basis of community and species distributions. Recurring evolutionary patterns may have been driven by the hydrographic history of southern Australia. Specifically, we suggest that Plio-Pleistocene temperature change and the repeated opening and closure of Bass Strait promoted allopatric divergence and perhaps cryptic speciation in C. muricata. [source] MARINE ALGAE ASSOCIATED WITH CARIBBEAN ROCKY SHORES, QUINTANA ROO, MEXICOJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Albert, E. M. & Lehman, R. L. Center for Coastal Studies, Texas A&M University-Corpus Christi, Corpus Christi, TX 78412 USA Rocky shores located on the east coast of the Yucatan Peninsula are typically high-energy habitats associated with fringing or barrier reef systems. They are phytokarstic (iron-shore) consisting of fossiliferous limestone that is composed of stony coral skeletons. This study compares the macroalgae from three rocky shores located on the east coast of the Yucatan Peninsula, Quintana Roo, Mexico. Fifteen 0.25m2 quadrates were randomly placed in the intertidal and subtidal zones and evaluated for dominant algal cover. In addition, fifteen 0.25 m2 quadrates of standing stock material was randomly collected and used to characterize algal composition, species richness, abundance, and biomass. A voucher collection including herbarium mounts and preserved specimens were prepared for all species encountered. Thirty-five species were identified representing three divisions: Rhodophyta, Chlorophyta, and Phaeophyta. Rhodophyta had the highest species richness with a total of fifteen taxa identified. Phaeophyta had the lowest species richness with seven taxa but dominated algal coverage at two of the three sites. Chlorophyta was represented by thirteen species. Species common to all points were represented by Digenia simplex, Laurencia poiteaui, Laurencia sp., Polysiphonia sp., Microdictyon marinum, Halimeda opuntia, Dictyosphaeria cavernosa, Padina sanctae-crucis, and Turbinaria tricostata. [source] Ecological contrasts across an Antarctic land,sea interfaceAUSTRAL ECOLOGY, Issue 5 2006CATHERINE L. WALLER Abstract We report the composition of terrestrial, intertidal and shallow sublittoral faunal communities at sites around Rothera Research Station, Adelaide Island, Antarctic Peninsula. We examined primary hypotheses that the marine environment will have considerably higher species richness, biomass and abundance than the terrestrial, and that both will be greater than that found in the intertidal. We also compared ages and sizes of individuals of selected marine taxa between intertidal and subtidal zones to test the hypothesis that animals in a more stressed environment (intertidal) would be smaller and shorter lived. Species richness of intertidal and subtidal communities was found to be similar, with considerable overlap in composition. However, terrestrial communities showed no overlap with the intertidal, differing from previous reports, particularly from further north on the Antarctic Peninsula and Scotia Arc. Faunal biomass was variable but highest in the sublittoral. While terrestrial communities were depauperate with low biomass they displayed the highest overall abundance, with a mean of over 3 × 105 individuals per square metre. No significant differences in ages of intertidal and subtidal individuals of the same species were found, with bryozoan colonies of up to 4 years of age being present in the intertidal. In contrast with expectation and the limited existing literature we conclude that, while the Antarctic intertidal zone is clearly a suboptimal and highly stressful habitat, its faunal community can be well established and relatively diverse, and is not limited to short-term opportunists or waifs and strays. [source] | ||||||||||