Alan Logan

Geochemistry of modern brachiopods: applications and implications for oceanography and paleoceanography

Abstract Modern Rhynchonellida, Terebratulida, Thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2–3940 m, from the equator to high latitudes covering the Atlantic, Pacific, Indian, Caribbean and Mediterranean Oceans/Seas. Well-preserved fibers of the secondary layer combined with Sr (450–1928 mg/kg), Mn (1–199 mg/kg) and Fe (1–610 mg/kg) contents confirm, with few exceptions, the excellent preservation of the modern brachiopod material. Evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations. It revealed that oxygen isotope incorporation into shell calcite (secondary layer) of modern articulated brachiopods, in most cases, occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions. Thecideida as a group (shallow water and low latitude) incorporate oxygen isotopes (−3.04‰ to +0.35‰) into shell calcite in equilibrium with their ambient water. A large majority of genera and species of the Terebratulida (shallow water and low-mid latitude) also incorporate oxygen (−2.30‰ to +3.48‰) into shell calcite in isotopic equilibrium with their surrounding water. In contrast, equilibrium incorporation of oxygen isotopes into shell calcite by the Rhynchonellida is uncertain, but a vital effect probably applies to the Craniida. The question of equilibrium/disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time. Isotope compositions range up to 4.5‰, 5.6‰ and 1.5‰ for δ 13 C, and up to 5.5‰, 5.9‰ and 0.3‰ for δ 18 O, for shallow-water low, mid, and high latitude brachiopods, respectively. Strontium isotopes of modern brachiopods, as expected, show no significant variation with location, latitude, water depth, temperature, salinity and general water conditions. Once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered, their isotopic/elemental values should be valuable diagenetic indicators and important oceanographic/chemostratigraphic proxies.

Elevated temperatures and bleaching on a high latitude coral reef: the 1988 Bermuda event

Sea temperatures were normal in Bermuda during 1987, when Bermuda escaped the episodes of coral bleaching which were prevalent throughout the Caribbean region. Survey transecs in 1988 on 4–6 m reefs located on the rim margin and on a lagoonal patch reef revealed bleaching only of zoanthids between May and July. Transect and tow surveys in August and September revealed bleaching of several coral species;Millepora alcicornis on rim reefs was the most extensively affected. The frequency of bleaching in this species,Montastrea annularis and perhapsDiploria labyrinthiformis was significantly higher on outer reefs than on inshore reefs. This bleaching period coincided with the longest period of elevated sea temperatures in Bermuda in 38 years (28.9–30.9°C inshore, >28° offshore). By December, when temperatures had returned to normal, bleaching of seleractinians continued, but bleaching ofM. alcicornis on the outer reefs was greatly reduced. Our observations suggest that corals which normally experience wide temperature ranges are less sensitive to thermal stress, and that high-latitude reef corals are sensitive to elevated temperatures which are within the normal thermal range of corals at lower latitudes.

Interspecific aggression in hermatypic corals from Bermuda

Interspecific aggression between hermatypic corals on Bermudian reefs has been investigated by aquarium and field studies, the latter involving induced interactions, observations from 30 m-2 transects and random SCUBA traverses. Resultant hierarchies, constructed by ranking the abilities of species to damage competitors, show close similarities with each other and with the Jamaican hierarchy at the family level, notwithstanding some differences in the ranking of some species. Only 11% of natural-occurring interactions depart from the aquarium-derived results; in terms of species-pair combinations, 30% show partial or complete inversions from aquarium to field, with most changes involving species close together in the field hierarchy. Circular (intransitive) interactions occur mostly within a network of weakly-aggressive species in both aquarium- and fieldderived hierarchies. While number of potential interactions m-2 varies directly with density, frequency of aggression is positively correlated with coral diversity (species richness), while frequency of “no reactions” and conspecific fusion (combined) shows a correspondingly negative correlation with diversity. Frequency of aggression does not appear to be depth related. Comparison of aquarium and field hierarchies suggest that digestion by mesenterial filaments is the most important mechanism of aggression under natural conditions. Sweeper tentacle activity is the most likely cause of field reversals involving Madracis mirabilis and Montastrea cavernosa. Other factors, such as stress caused by seasonal environmental extremes, may be responsible for reversals or inconsistent behaviour in other species.

Extension growth rates in two coral species from high-latitude reefs of Bermuda

Mean annual growth rates (skeletal linear extension) in the hermatypic coralsPorites astreoides Lamarck andDiploria labyrinthiformis (L.) were investigated mainly by X-radiography from a variety of localities at various depths on the high-latitude coral reefs of Bermuda. Growth rates of both species show an inverse curvilinear relationship with depth, with highest growth rates in the shallow inshore waters of Castle Harbour and lowest at the edge of the Bermuda platform and on the adjacent fore-reef slope. Annual density bands form seasonal couplets, with narrow, high density bands appearing to form in the spring-summer months and wider, low density bands over the rest of the year in both species. Comparison of the growth rates ofP. astreoides from Bermuda with those from lower latitude West Indian localities, particularly Jamaica, indicates an inverse relationship with latitude and a similar inverse curvilinear relationship with depth at both geographic locations. Growth rate-locality differences in Bermuda for both species are suggested to be controlled mainly by local differences in wave energy and food supply and possibly seasonal water temperature fluctuations; growth rate-depth differences by decreasing illumination with depth; and growth rate-latitudinal differences by reduction in winter water temperatures and light levels with increasing latitude.

Linear skeletal extension rates in two species of Diploria from high-latitude reefs in Bermuda

X-radiography was used to study annual linear skeletal extension rates of the reef-building scleractinian corals Diploria strigosa and Diploria labyrinthiformis from the high-latitude reefs of Bermuda. Coral samples for X-radiography were collected from seven localities of varying biotopes and depths around the Bermuda platform and band couplets were measured. Mean extension rates of both species were highest on inshore and nearshore reefs, gradually decreasing towards the edge of the Bermuda platform and onto the fore-reef slope. Extension rates of D. labyrinthiformis were statistically higher than those of D. strigosa at three localities, while at the other four, the rates of both species were not statistically separable. extension rates of d. labyrinthiformis were statistically higher than D. strigosa within depths of 20 m and 32 m but not statistically separable at 3 m and 6 m depths. Extension rates of both species decreased significantly with increasing depth (r2=0.92, P<0.03 for D. labyrinthiformis and r2=0.95, P<0.02 for D. strigosa). Each species showed an inverse curvilinear relationship between extension rate and depth, the rate of change (i.e. slope) being the same for each species. Comparison of extension rates of each species from Berumuda with published rates of these species from lower latitudes showed an inverse relationship between extension rate and latitude.

Sessile invertebrate coelobite communities from reefs of Bermuda: Species composition and distribution

Sessile invertebrate coelobite communities attached to the walls and roof of cavities in coralgal reefs on the annular rim of the Bermuda platform near North Rock (4 sites) and in the algal cup reef tract on the south shore (3 sites) have been studied by belt photo-transects and direct sampling. Irradiance measurements reveal a light gradient which appears to exert a strong influence on the composition, relative coverage and zonation of the attached biotic communities. Two main communities are recognised from cluster analysis and relative areal coverage data. Near the cavity entrances is a community dominated by crustose coralline algae, with subsidiary ascidians, demosponges, bryozoans and Foraminifera. Species richness is high and there is total biotic coverage of walls and roof. This community grades laterally into an exclusively animal community characterised by encrusting sponges and Foraminifera, with subsidiary bryozoans and unidentified branching organisms. Coverage varies from 100% to 30%, the substrate often exhibiting high micro-relief from the branching growth forms of the Foraminifera. Species richness is high at North Rock sites, less so on the south shore. The distribution of coelobite species is compared with that described from previous studies in Bermuda, Grand Cayman and Madagascar.

Size-frequency distributions and taphonomy of brachiopods: A recent model

Abstract Comparison of size-frequency distributions and other population characteristics of life and associated death assemblages of the Recent North Atlantic brachiopod Terebratulina septentrionalis in the natural environment sheds considerable light on the processes of fossilization of brachiopod populations. The factors of population dynamics are the most important in shaping the size-frequency distribution of the dead (fossil) population. Taphonomic factors are relatively unimportant even in high-energy environments where the degree of fragmentation and disarticulation of valves is relatively high. Predation is of minor importance. Differences in size-frequency distributions of fossil and Recent dead populations are probably due in many cases mainly to differences in recruitment mode and especially to the more extensive brooding behaviour of Recent brachiopods.

Depth zonation of epibenthos on sublittoral hard substrates off Deer Island, Bay of Fundy, Canada

Abstract Three locations were selected for detailed study of the epibenthos of sublittoral hard substrates in the Deer Island region of the Bay of Fundy. A total of 10 transects, using photographic and quadrat methods, yielded data on percentage coverage, density and diversity of biota in relation to depth. A cluster analysis, using the Jaccard Coefficient of Association, produced five major clusters, representing three depth zones. The shallow and mid-depth zones lie within the infralittoral, the deep zone within the circalittoral. The shallow zone extends from mean low water (MLW) to a mean depth of 5 m below MLW and consists of two clusters representing minor biological differences. It is characterized by crustose coralline algae and Petrocelis middendorfii which together cover over 70% of the primary substrate. Other macro-algae are rare, as are bryozoans, while sponges are absent. The sea urchin Stronglyocentrotus droebachiensis, the limpet Acmaea testudinalis and chitons belonging to Tonicella are very common and may exert a significant influence on the community structure in terms of grazing pressure. The mid-depth zone has a mean depth of 10 m and consists of two clusters, one representing well-illuminated upward-facing surfaces, the other representing shaded steeply-inclined cliff faces. The zone is characterized by higher species richness (relative to the shallow zone); greater coverage of sponges, bryozoans and hydroids; lower densities of sea urchins and limpets; and less areal coverage by encrusting algae. The cliff-face cluster is characterized by enrichment of bryozoans, anemones, sponges and brachiopods. The deep zone has a mean depth of 18 m, and is animal-dominated, supporting the greatest species richness, with sponges, hydroids, anemones, brachiopods and tunicates common, but algal coverage much reduced. Organisms colonizing the upward-facing surfaces in the shallow and mid-depth zones are here regarded as belonging to the encrusting algae-urchin community, while biota of the shaded cliff faces of the mid-depth zone, together with the biota of the deep zone, are regarded as belonging to the Terebratulina septentrionalis community of previous authors.

A new lacazelline species (Brachiopoda, Recent) from the Maldive Islands, Indian Ocean

Abstract A new lacazelline brachiopod species is described from reef caves in the outer reef slope zone off Addu and South Male atolls in the Maldive Islands, Indian Ocean. Based on anatomical features of the soft parts, shell morphology and shell microstructure the new taxon is assigned to the genus Ospreyella Lüter and Wörheide 2003 in the subfamily Lacazellinae of the family Thecideidae. This new species, here named O. maldiviana and representing the first occurrence of the genus in the Indian Ocean, is compared with the type species O. depressa Luter from Osprey Reef, Coral Sea, Australia. Comparisons are made between Ospreyella (now two species) and the other extant lacazelline genera Lacazella Munier‐Chalmas (three species) and Pajaudina Logan (one species).

Endoscopic Investigations of Feeding Structures and Mechanisms in Two Plectolophous Brachiopods

The feeding structures and mechanisms of the brachiopod species Terebratulina septentrionalis from the Bay of Fundy, eastern Canada and Terebratalia transversa from the west coast of Canada were examined, in vivo, with an endoscope linked to a video recording system. A diet consisting of various-sized, light-reflective particles and natural seston was given to both species. Our observations demonstrate that the lateral arms are the sites where most particle rejection occurs and the median coil is the site where particle acceptance occurs. Low particle retention may be attributed to the way particles move on the outer filaments. The combined effect of localized currents produces the large-scale flow through the lophophore. The lophophores delicate hydrodynamics are easily disturbed by attempts to observe them. Only by relatively non-invasive techniques such as endoscopy can we accurately record normal feeding behaviour. Additional key words: lophophorate, Terebratulina septentrionalis, Terebratalia transversa The lophophore, the main organ of feeding and respiration in brachiopods, is a ciliated tentacular organ that acts as a ciliary pump, producing currents that flow through the mantle cavity. The two articulate species investigated in this study have plectolophous lophophores (Fig. 1), a complex type consisting of two lateral arms that lie on either side of a median coil. Two series of ciliated filaments fringe both the lateral arms and the median coil. At the base of these filaments is a ciliated food groove (brachial groove) covered by the flexible brachial lip. Particles captured on the ciliated filaments enter the brachial groove and are transported to the mouth for ingestion (Rudwick 1970). In plectolophous species, water enters through the lateral commissure and exits through the anterior part of the gape (Atkins 1959; Rudwick 1962; Savage 1972; James et al. 1992). One aspect of brachiopod physiology that has generated increasing interest is the mechanism of feeding, especially particle acceptance and rejection (Strathmann 1973, 1982; Gilmour 1978, 1981; Jorgensen 1981; Rhodes & Thompson 1992, 1993). Although many studies have addressed feeding processes (reviewed by James et al. 1992), there is still disagreement on the role of ciliary action on the inner and outer filaments (Strathmann 1973; Gilmour 1978; a Author for correspondence. E-mail: bmacdon@unbsj.ca LaBarbera 1981), as well as on the selectivity of brachiopod feeding (McCammon 1969; Rudwick 1970; Gilmour 1981; Thayer 1986). Previous studies have described the function of the lophophore from dissected structures, or surgically altered and narcotized animals, or from observations on intact animals yielding limited views (summarized in James et al. 1992). These invasive techniques could have altered the hydrodynamics within the lophophore and mantle cavity. Also, stress associated with surgery could have stimulated excess mucus production and caused the lophophore to function abnormally. In contrast, our study, using recently developed techniques in video endoscopy (Ward et al. 1991), allowed direct in vivo observations of feeding structures and mechanisms with minimal disturbance to the animals. No surgery was performed so that the animals remained intact. Our technique enabled us to observe, at a magnification of 150X, areas such as the inside of the median coil, that are impossible to view using conventional methods. The resulting video recordings allowed for post-observational analysis of events. The aim of this study was to investigate and describe lophophore activity in the articulate brachiopods Terebratulina septentrionalis (COUTHOUY 1838) and Terebratalia transversa (SOWERBY 1846) with respect to feeding, and to clarify some of the ways these brachiopods accept and reject particles. We report on parThis content downloaded from 157.55.39.231 on Wed, 05 Oct 2016 04:36:24 UTC All use subject to http://about.jstor.org/terms Endoscopy of feeding in plectolophous brachiopods < current inside coil < current outside coil