Alan D. Ansell

Biology of Living Brachiopods

Publisher Summary This chapter describes the biology of living brachiopods. The Brachiopoda are significant components of the early Cambrian marine Faunas and are therefore one of the few phyla to be represented of the Phanerozoic era, which extends from the first widespread appearance of organisms with mineralized skeletons until modern times. The objective of chapter review is to chronicle some of the important biological work conducted over the past 25 years and to present an overview of current trends in brachiopod biology. Moreover, many of the recent studies of living brachiopods owe their motivation to a desire to improve palaeontological interpretation of the group. The scaling patterns of brachiopod tissue and other components in relation to total size and their morphological architecture show significant differences from the bivalves and may impose important constraints. Moreover, a general impression of many living articulate brachiopods is of a relatively small organism, in terms of organic tissues, inhabiting a relatively large space, defined by the shell. Brachiopods approximate spherical shapes, as much as their growth patterns and articulation systems allow. This chapter concludes that the brachiopod biomineralization system is ideally suited for the investigation of the interaction between the organic and the inorganic phases during shell growth.

Studies on Tellina tenuis da costa I. Seasonal growth and biochemical cycle

The seasonal changes in the body weight and composition of Tellina tenuis from Kames Bay, Millport, and Firemore Bay, Loch Ewe, have been studied during 1965–1966. The composition of an animal of standard size was calculated for each sampling date to give information on seasonal changes independent of shell growth. Increase in body weight took place rapidly in both localities in early summer as the gonad developed and reserves were built up. Spawning resulted in a fall in body weight in June in both localities, and this was followed in Kames Bay by fluctuations in body weight and in Firemore Bay by a steady rise in body weight. Glycogen forms the major reserve in the body, accounting for about 90% of the total carbohydrate, and this is partially utilized during the winter months, resulting in a fall in body weight in both localities at this time. The changes in body weight for animals of the 5 + year group during one-years growth have been calculated and estimates made of the contribution to total production represented by growth, gonadal development and storage of reserves.

Distribution, growth and seasonal changes in biochemical composition for the bivalve Donax vittatus (da Costa) from Kames Bay, Millport

Abstract The bivalve Donax vittatus (da Costa) occurs in Kames Bay, Millport, Scotland,only intermittantly. Successful settlements may occur with a frequency of no more than two in twenty years. There was one such settlement in the summer of 1962. The distribution in 1967 of survivors from this settlement was mainly just below L.W.S.T. Shell ring measurements indicated that the maximum mean size was reached in 5–6 years. Seasonal changes in body weight and biochemical composition are associated with the processes of reproduction, growth, and storage and utilization of reserves. The main period of increase in reserves and of gametogenesis corresponded with the spring peak of diatom abundance. The autumn peak of phytoplankton abundance is apparently less well utilized, although there is some increase in carbohydrate reserves. Spawning, which occurs in the early summer, produces a marked fall in the mean body weight, and a slower fall during the winter months is the result of elimination of reserves to meet the metabolic demands of the animal when food is scarce.

Behavioural adaptations of intertidal molluscs from a tropical sandy beach

Abstract Observations were made on the movements of the bivalves Mactra olorina and Donax incarnatus , and of the gastropod Bullia melanoides , collected from an exposed sandy beach near Shertallai in southwest India. The burrowing movements were remarkable for the speed at which they occurred. In Mactra olorina , the foot probed with a frequency of at first 8–9 probes per sec, later reduced to 5 probes per sec. The events associated with the establishment of the pedal anchorage and of active downward movement occupied 0.35 sec only and those of establishment of the shell anchorage and of probing occupied 1.15 sec. The complete digging cycle occupied 1.5 sec. These movements are compared with those of M. corallina from the Mediterranean and from the Clyde. The movements responsible for recovery from deep burial were also examined. Rapid burrowing and active upward movement through the sand, as appropriate, enable the animal to maintain its position in disturbed sediments. Similar observations were made on Donax incarnatus , which was compared with the north temperate species D. vittatus . In D. incarnatus rapid burrowing and active emergence form part of a complex of movements which lead to tidal migration of the population on the beach. Tidal migration was also a feature of the behaviour of Bullia melanoides , and in this species too, rapid burrowing and active emergence from the substratum at appropriate times are elements in the complex of movements by which this tidal migration is performed.

Alternative predation tactics of a tropical naticid gastropod

Abstract Aquarium observations of naticid gastropods from Hong Kong show that different species attack their bivalve prey in different ways. Natica gualteriana and Glossaulax didyma appeared always to use conventional modes of boring, i.e., through one shell valve, before consuming the prey, but some larger prey of C. didyma with incomplete borings were consumed after having apparently suffocated before boring was complete. In contrast, Polinices tumidus prey may be side-bored, edge-bored (i.e., through the commisure of the valves) or suffocated and consumed without boring. The frequency of each of these modes of attack vary with different prey species. Non-boring predation, in aquarium experiments, accounted for 14.7–54.9% of attacks with different species of prey. Suffocated prey were found to be enwrapped in a thick, viscous coat of mucus, which in partially consumed prey showed a round hole overlying the ventral shell gape marking the entrance hole made by the proboscis. The observations reveal considerable flexibility in predation behaviour in this tropical naticid and have important implications in the interpretation of naticid predation rates in recent and fossil dead shell assemblages.

Production and energy flow in the macrobenthos of two sandy beaches in South West India

Estimates of the rates of secondary production by the individual macrofaunal invertebrates of two Indian beaches are presented and these are combined to give an estimate of the energy flow through the macrobenthos of the two beaches. The production by individual species and by the macrofauna as a whole is compared with that of other tropical, and of temperate beaches, and it is concluded that a similar biomass in the tropical beaches produces a rate of turnover of biomass some ten times that of the temperate beaches. Values of production to biomass ratios ( P/ B ) and of elimination to biomass ratios ( E/ B ) for the invertebrates of sandy substrata in various geographical areas are reviewed and the use of these ratios in comparisons of productivity, and their relationship to mortality and longevity are discussed.

Oxygen consumption by the bivalve Donax vittatus (da Costa)

Abstract The acute oxygen consumption of Donax vittatus (da Costa) freshly collected at different times from a beach at Barrassie, Ayrshire, Scotland, has been measured at different temperatures. The logarithmic relationship between oxygen consumption and body weight showed a significant difference on only one occasion, and a common regression coefficient ( b ) of 0.865 could be used for regressions of oxygen consumption on weight. Over the temperature range 2.9–20 °C oxygen consumption rose with temperature. There was a linear decline of Q 10 with temperature in the range 2.9 –20 °C. Differences in values of the constant ( a ) in the regression equation suggest that there is some acclimation to temperature, resulting in rotation of the rate/temperature curve counterclockwise for warm-acclimated animals, and a reduction of Q 10 in cold-acclimated animals. The differences in oxygen consumption which result are small and appear to have little practical significance. High levels of metabolically-inactive materials such as stored glycogen reserves lead to a reduction in the weight-specific oxygen consumption. Spawning animals show an increased oxygen consumption.

Genetics of indigenous and transplanted populations of Pecten maximus: no evidence for the existence of separate stocks

Abstract Genetic variation at eight polymorphic enzyme loci was investigated in 13 populations of the scallop Pecten maximus (L.) from a number of sites in Scotland, UK and Brittany, France. Two of the populations had initially been transplanted, as spat, to Brittany from Scottish and Irish collection sites. In common with other studies of marine bivalves, an overall deficiency of heterozygotes was observed, but genotype frequencies of transplanted populations were generally in agreement with the Hardy-Weinberg model indicating little post-transplant selection. There was high genetic similarity among all the populations surveyed and no overall differences between the Scottish and Brittany samples. The results are discussed in relation to contrasting evidence, derived from studies on the reproductive cycle of P. maximus and the genetics of Aequipecten (Chlamys) opercularis (L.), which suggests that the Scottish and Brittany scallop populations are, nevertheless, genetically distinct.

Oxygen consumption by Bullia (Dorsanum) Melanoides (Deshayes) and Bullia digitalis meuschen (Gastropoda, Nassaridae)—an example of non-acclimation

Abstract 1. 1. Relationships between size and oxygen consumption in two species of Butlia, one from temperate South Africa, the other from tropical India, do not differ significantly from one another. 2. 2. The regression coefficients defining this relationship do not differ significantly from the generally accepted value of 0.75. 3. 3. The oxygen consumption of Bullia melanoides at 30°C is about an order of magnitude higher than that of Bullia digitalis of the same size at 15°C, despite the fact that these temperatures are consistent with field conditions. 4. 4. It is suggested that this difference in metabolic rate may be explained in terms of differences in activity and life span.

Movements and burrowing activity in the Antarctic bivalve molluscs Laternula elliptica and Yoldia eightsi

Burrowing was investigated in two Antarctic infaunal bivalve molluscs, Laternula elliptica and Yoldia eightsi, representing amongst the least and most active members of the class Bivalvia in the Southern Ocean. Burrowing rate was expressed via the Burrowing Rate Index (BRI=[3√wet weight/time to bury]×104), and produced values of 0.1–10.6 for L. elliptica and 8.8–49.8 for Y. eightsi. These compare with values ranging from 3 to 2,000 for N. American bivalves (mean=222, SE=42.6, n=81), and 200 to 2,200 for Hong Kong bivalves (mean=1,140, SE=346, n=6). Values for the Antarctic species are, therefore, low compared to warmer-water bivalves, and the values below 1 for large L. elliptica are the lowest on record by around ×5. There is no compensation of burrowing activity for low temperature in these species. The relative BRI values for L. elliptica and Y. eightsi reflect the differences in their mode of life, with the former being large, sedentary and suspension-feeding, and the latter being smaller, mobile, ploughing through the sediment and feeding on sediment-surface organic matter. Burrowing in L. elliptica is unexpected, because other members of the Laternulidae do not burrow. This ability is most probably a response to the regular disturbance of sediments in Antarctica by ice, and the strong selective advantage to being able to resume a protected position after disturbance. The burrowing cycle in L. elliptica is composed of three main phases: (1) foot extension and sediment penetration; (2) foot dilation to form an anchor; (3) the drawing down of the shell by contraction of the pedal retractor muscles. Burrowing in Y. eightsi also has three phases: (1) foot extension and penetration of the sediment (digging); (2) rocking movements in the upright position; (3) shell anchorage. In excess of burrowing activity, L. elliptica exhibits a unique suite of movements when exposed at the surface. These comprise levering, where the tips of the siphons are pressed against the sediment to lift the shell from the substratum, looping, where the siphons are extended and rotated and, in the process, translocate the whole animal across the sediment, and jetting, where water is ejected forcibly through the siphons while their tips are directed towards the sediment, lifting part or all of the animal clear of the substratum. In the field, following exhumation by icebergs, these activities serve to place the animal in a favourable position for reburial, which is a clear advantage in disturbed polar environments where predatory nemerteans and asteroids are abundant.