Midlittoral Zone Research Articles

INTERTIDAL ZONATION OF MACROFAUNA AND STRATIFICATION OF MEIOFAUNA ON HIGH ENERGY SANDY BEACHES IN THE EASTERN CAPE, SOUTH AFRICA

Summary Intertidal macrofauna on high energy beaches in the East Cape occurs in two zones: a lower zone dominated by Bullia rhodostoma, Donax sordidus and Gastrosaccus psammodytes; a midlit-toral zone starting about 0,9 m above extreme low water of spring tides and extending to about 1,9 m above ELWS is wetted on every tide and is dominated by Donax serra, with isopods also present. There is no upper zone or subterrestrial fringe, probably due to the absence of a distinct drift line. Meiofaunal distribution has been divided into four strata in the sediment: a dry sand stratum in the upper sediment near the top of the shore is wetted only at high tide and its meiofauna is predominantly nematodes; a moist sand stratum underlies the dry sand down to the permanent water table and here a rich and diverse meiofauna, usually dominated by crustaceans, occurs; a water table stratum at and below the permanent water table has lowered oxygen tensions and moderate meiofauna numbers dominated by nematodes and crustacea...

Analysis of Marine Hybridization between Two Species of the Genus Cyclograpsus (Crustacea : Brachyura) in South-eastern Australia

The structure, extent and maintenance of two zones of overlap, with hybridization, between the grapsid crab species Cyclograpsus audouini and C. granulosus were determined. A modified hybrid index technique was used for analysis. The hybrids were found to be the most abundant group in the central regions of sympatry. In these areas hybrids were found in the central midlittoral zone with C. audouini above them in the supralittoral fringe and C. granulosus in the central and lower midlittoral. The number of hybrids present on shores north and south of the centre of sympatry decreased markedly. The observations led to the conclusions that the interaction was ecologically controlled and that the two interacting taxa were separate species. The geographic distribution of C. audouini and the hybrids was limited by the effect of seawater temperatures on the survival of their planktonic larval stage (a pre-settling factor). Conversely the geographic distribution of C. granulosus was limited by the action of air temperature on the adult crabs (a post-settling factor).

Zonación y estructura de la comunidad macrofaunística en playas de arena del Sur de Chile (Mehuín, Valdivia)

Summary Zonation and Structure of the Macrofaunistic Community in Sandy Beaches of Southern Chile (Mehuin, Valdivia) Two beaches of Mehuin (Valdivia) were studied with the purpose of finding out the zonation and structure of the macrofaunistic community in sandy beaches of Southern Chile. Some variability is present between the species composition of the two beaches studied. Notwithstanding, a general scheme for the zonation of the beaches at Mehuin is proposed. The upper level of the midlittoral zone is occupied by talitrid amphipods (O. tuberculata) and cirolanid isopods (E. braziliensis). The intermediate level by cirolanids (E. braziliensis, E. hirsuticauda and E. monodi), theinferior level by anomuran decapods (E. analoga), polychaetes (N. impressa) and bivalves (M. donacium) and the upper level of the infralittoral zone by idotheid isopods (C. paucidens, M. mehuinensis, M. setifer and M. aff. lilianae), haustorid amphipods (two species), anomuran decapods (L. chilensis and B. spinimana) and brachyur...

Spatial structure of an intertidal molluscan assemblage on a sheltered sandy beach

The intertidal molluscan fauna on a sandy-mud beach in Newport Bay, California, USA, is divisible into two vertically distinct species assemblages which correspond to the midlittoral zone and sublittoral fringe observed on rocky coastlines and exposed sandy beaches. The species assemblage comprising the midlittoral zone is unusual, however, in that the numerically dominant species are not confined to this zone but range downward through the sublittoral fringe. The two species assemblages are vertically separated at +0.5 to +1.0 ft (+0.15 to +0.30 m; relative to 0.0 tidal datum at mean lower low water), which is higher than previously observed for the separation between the midlittoral zone and sublittoral fringe on rocky shores and exposed sandy beaches. The species composition of some of the samples at +0.5 and +1.0 ft (+0.15 and +0.30 m) was intermediate between samples higher and lower on the beach, while several samples were devoid of molluscs altogether. Additionally, the surface sedimentary environment changes in terms of an increased percent silt-clay fraction and higher sorting coefficients below +0.5 ft (+0.15 m). Since infaunal zonation is correlated with tidal height at the substrate surface, environmental factors operative at the surface are probably most important in influencing the zonation on this beach.

Description of a Tetraclita stalactifera panamensis community on a rocky intertidal Pacific shore of Panama

The midlittoral zone at Paitilla Beach, Panama, Is occupied by a group of organisms closely associated with Tetraclita stalactifera panamensis. Upon death, this cirripede provides housing for a number of species bound by common substrata and interacting with each other due to their close physical proximity; the faunistic group associated with each barnacle qualifies then, as a small, well-defined community which represents a subsample of the more comprehensive midlittoral community dominated by T. stalactifera panamensis. In patches where it is abundant, T. stalactifera panamensis occupies 28% of the surface area available. It has a relative abundance of only 1% of the specimens found in the zone, but all the other 95 species (with an average of 26, 810 individuals/m2) identified from the area are associated either with the parietal canals, or the external or internal surfaces of T. stalactifera panamensis tests. Each one of these structures represents a habitat which provides surface for attachment, shelter, or both, to 37 species of polychaetes, 32 of mollusks, 20 of crustaceans, 3 of actiniarians, 2 of pycogonids, 2 of sipunculans and an unknown number of tanaid, nemertean and turbellarian species. The single most diverse space-niche is represented by the parietal canals (H=0.783), occupied mostly by polychaetes. dead barnacles harbor an average of 131 individuals per test, which compose a fauna of higher diversity (H=0.678) than that associated with live barnacles (H=0.163). The latter contain 53 specimens per test on the average. Although there is considerable overlapping of species associated with the different T. stalactifera panamensis space-niches, mollusks are clearly more abundant on internal surfaces, polychaetes in parietal, canals; Balanus spp. on external surfaces, and anemones at the base of the parapet on the external surfaces of the tests. Over 220 species of macro-invertebrates were identified from the rocky intertidal at Paitilla. Most of the species are concentrated in the lower (157 species, 1824 specimens/m2) and midlittoral (96 species, 26, 810 specimens/m2) intertidal zones. Splash zone is depauperate (6 species, 1578 specimens/m2). Of the entire fauna identified from the intertidal, 73 species (33%) occur in more than one zone and 147 (67%) are restricted to a particular belt. This last category of zone-restricted species breaks down into 42% for the lower intertidal, 17% for the midlittoral, 6% for the intermediate zone, and 2% for the splash zone.

Succession of invertebrates in vacant tests of Tetraclita stafactifera panamensis

The colonization of vacant Tetraclita stalactifera panamensis tests over a period of 15 months by a varied fauna of invertebrates is described. Vancant spaces are used first by the crab Pachygrapsus transversus. Within 1 month, a group of 6 species of mollusks and polychaetes and species of Balanus appear in the collections. Eventually 50 different species of invertebrates are found associated with T. stalactifera panamensis. The colonization curve typically shows a higher rate of species incorporation in the initial stages and a more or less stable plateau after a few months. New species colonizing the tests reach a maximum of 12 after 5 months and soon decrease to 3 or 4/month. Diversity (H) increases gradually for 8 months and then fluctuates around 0.77 to 1.21. Animals colonizing barnacle tests settle on external or internal surfaces or in parietal canals. Polychaetes are more diverse in parietal canals, mollusks on the internal surface and species other than mollusks or polychaetes, on the external surface. Over a period of 15 months (March 12, 1971 to June 13, 1972) as many as 62% of the T. stalactifera panamensis tests present in the study area disappeared through causes other than collection. Settlements of new T. stalactifera panamensis in the study area occurred throughout the observation period, and many of the young barnacles matured and produced cypris larvae when they reached a size about one fifth that of the old vacant tests where they had settled. After 6 months of colonization, the community of invertebrates associated with the barnacles reached a composition, diversity, biomass and spatial arrangement comparable to communities found on barnacles of adjacent areas in the midlittoral zone of Paitilla Beach (Panama). Within 1 year of the initiation of colonization some signs of “aging” emerge in the community, mainly through the appearance of some burrowing organisms, particularly the bivalve Lithophaga aristata, which weaken the structure of the barnacles leaving them prone to removal by wave shock.

Haemoglobin function inTerebella lapidariaL., an intertidal terebellid polychaete

Terebella lapidariaL. is a small terebellid common in crevices in the mid-littoral zone of rocky shores in the Plymouth area. The coelom contains abundant coelomocytes charged with haemoglobin in sufficient quantity to give the worm a brick-red colour.T. lapidariaalso has a discrete vascular system with haemoglobin dissolved in the plasma. When covered by the tide the worm irrigates its burrow intermittently. When revealed by the tide it cannot do so, and is then left in a thin film of water or in moist air for 3–4 h. We thought it was of some interest therefore to determine the oxygen equilibrium characteristics of these pigments.

El modelo de zonación en la orilla rocosa del departamento de Lima

Durante el año 1972 y parte de 1973 se estudió la zonación biocenológica en la orilla rocosa maciza del Departamento de Lima, entre los 10°45'38"S y los 12°57'39"S, con la finalidad de establecer el esquema de zonación aplicable, entre los diversos esquemas empleados en otros lugares del mundo. En siete lugares guía, se delimitaron los niveles de pleamar y bajamar de sicigias y cuadraturas, para determinar la distribución vertical de los organismos, asociaciones y comunidades que integran la biocenosis de este tipo de orilla, caracterizando los diversos niveles de la zona entre mareas. Se encontró aplicable el siguiente esquema zonacional, modificado de Stephenson y Stephenson (1949): La ZONA LITORAL se extiende desde el nivel superior de Littorina peruviana, hasta el nivel promedio de las bajamares de sicigias ordinarias (MLWS = 0 m), y comprende: a) Franja supralitoral, extendida entre el nivel superior de Littarina peruviana y el límite superior de Chthamalus cirratus. b) Zona mediolitoral, extendida desde el límite inferior de la franja supralitoral hasta el nivel superior de Megabalanus psittacus; y la Franja infralitorol, comprendida desde el nivel inferior de la zona mediolitoral hasta la línea de bajamares medias de sicigias ordinarias.

The zonation of Tetrachthamalus oblitteratus Newman, and Tetraclita squamosa rufotincta Pilsbry in the Gulf of Elat, Red Sea

The zonation of barnacles on rocky shores along the northern 40 km of the eastern shore of the Gulf of Elat is described. Tetrachthamalus oblitteratus Newman, forms a wide belt in the midlittoral zone; Tetraclita squamosa rufotincta Pilsbry, forms a second barnacle zone which dissects the Tetrachthamalus belt and nearly obliterates it in its central portion. On south-facing slopes the Tetrachthamalus belt is more developed while the Tetraclita belt is reduced and found lower than on other slopes. On beachrock Tetraclita is found on rough surfaces or forms a rim on the margins of crevices and ledges. It is concluded that Tetraclita is favoured by turbulence and wave action. It is suggested that Tetraclita and Tetrachthamalus compete in the main part of the midlittoral and that Tetrachthamalus is more tolerant to heat and desiccation than Tetraclita.

Adaptations of the intertidal midge Clunio to arctic conditions.

1. The arctic population of Clunio marinus in Tromsö (Norway) (69°39'N) shows a tidal periodicity of emergence (period: 12.4 hours). Emergence occurs between the times of high and low tide. 2. A semilunar periodicity of pupation could not be detected. 3. In accordance with the tidal periodicity of emergence and reproduction, the habitat is situated in the midlittoral zone (area between the high and low water levels of neap tides). High densities of pupation are found in a sandy mud flat. 4. The Tromsö population is compared with European populations in temperate latitudes, which are characterized by a semilunar periodicity of emergence, and a habitat around the infralittoral fringe of the midlittoral zone. The different adaptations of the populations in biological rhythms and preferred habitat are discussed with regard to the geographic differences in photoperiodic conditions.

Succession of a wharf‐pile fauna at Lyttelton, New Zealand

Summary A 31/2‐year succession of wharf‐pile fauna is described from communities of different known ages on piles at Lyttelton, New Zealand. Intertidal regions of the piles were initially colonised by the barnacle Elminius modestus; these populations developed to form a subclimax community which was subsequently replaced by a climax community of the mussel Modiolus neozelanicus after 21/2 years. The stability of this climax is discussed. In the infratidal region initial settlement of the tubicolous amphipod Corophium acherusicum and an erect bryozoan Bugula sp. was followed after 5 months by colonisation by solitary tunicates. These tunicates became dominant only after H years and provided numerous niches for superficial foulers, crevice dwellers, and motile organisms. This succession is compared and contrasted with a terrestrial succession of plants. Four vertical zones were recognised: supralittoral zone, midlittoral zone, in‐fralittoral fringe, and infralittoral zone. Species additional to those record...

Arctic and Subarctic Examples of Intertidal Zonation

Analysis based on extensive observations of shores on Baffin Island, at Coppermine, and other localities on the north mainland coast and arctic islands of Canada. Populations on rocky shores were found to exist only where shore ice was thinner than tidal amplitude; in the Arctic proper, they are rare and limited to low levels as exemplified from Coronation Gulf - Boothia Peninsula, Admiralty Inlet, etc. In the sub-Arctic they have a mid-littoral zone dominated by Balanus balanoides and fucoids, bordered by infralittoral and supralittoral fringes. Sedimentary shores in the subarctic localities showed dense populations only near low-water level; in the Arctic they are almost barren.

Note on the Temperature Tolerances of some Intertidal animals in Relation to Environmental Temperatures and Geographical Distribution

In experiments on four species of barnacles and four species of top-shells, the barnacles were found to be more resistant to high or low temperatures than the top-shells. Among each group of animals the degree of tolerance was related to the geographical distribution of the species and their zonation on the shore. Thus most tolerance of high temperature was shown by species of southern distribution, especially by those occurring at the upper limit of the midlittoral zone, and most tolerance of low temperature by species of northern distribution. Least tolerance of high and low temperatures was shown by species found only in the infralittoral fringe or below low water.Field measurements of the body temperatures of barnacles and limpets while exposed to the air were made with thermocouples. Under many weather conditions the body temperatures were higher than would be expected from local meteorological values of air temperature. This difference was due to retention of sea temperature by the animals and the rocks and to the heating effects of sunlight.The results of the laboratory experiments and of the field measurements are discussed together in relation to weather and geographical distribution. It is clear that the temperatures experienced on the shore are well within the tolerance limits of most of the animals, and even exceptional extremes of temperature may have little direct influence on the distribution of adult intertidal animals. Evidence for a causal relation between temperature and distribution must be sought in non-lethal terms such as debilitating effects, or indirectly through competition between species, or in combination with other factors.