N. S. Jones

Aspects of the Biology of Laminaria Hyperborea III. Survival and Growth of Gametophytes

The lower limit of the Laminaria hyperborea (Gunn.) Foslie zone is probably not always determined only by lack of sufficient light, even when a suitable substratum is present (Kain, 1962). It also appears that the establishment stage is critical although growth conditions deteriorate with depth (Kain, 1963). It therefore seemed desirable to determine exactly what the light requirements of the various different early stages were, and relate these to what could be found out about the light penetration in the natural habitat. The effect of temperature on these stages is also of interest, in relation to the seasonal cycle as well as to the geographical distribution of the species. In this study two different techniques were used: culturing the gametophytes on cover-slips and also studying changes in oxygen concentration as measured by the Winkler method. The gametophytes of the different members of the Laminariales show a similar general course of development. A zoospore from a fertile frond of a Laminaria plant loses its motility, rounds off, swells and produces a tube with another sphere at the end into which all the cell contents pass (Killian, 1911). This process can be carried through in the dark but further development depends on light (Schreiber, 1930). In this genus the gametophytes are dioecious (Sauvageau, 1918; Williams, 1921) and equal numbers of male and female plants are produced (Schreiber, 1930). The female gametophyte may become fertile before dividing further (Sauvageau, 1918), resulting in a single egg, or may form a luxuriant filamentous structure which may produce many oogonia over a period of time (Ikari, 1921; Myers, 1925; Schreiber, 1930).

Aspects of the Biology of Laminaria Hyperborea : II. Age, Weight and Length

A method of determining the age of Laminaria hyperborea by examination of a longitudinal median section of the lower stipe and holdfast was found to be reliable for at least the first 4 years.

Subtidal algal colonization following the removal ofEchinus

KurzfassungAn der Sesseite des Port Erin Wellenbrecherdammes kommen keine größeren Algen im Bereich der unteren 3 m vor. Hier herrscht eine große Besiedlungsdichte des SeeigelsEchinus esculentus (3,6 Individuen pro m2). Über eine Zeitspanne von 3 Jahren wurden nun sämtlicheE. esculentus von einem 10 m breiten und 12 m langen Felsstreifen allmonatlich entfernt; insgesamt wurden dabei etwa 3000 Individuen abgesammelt. Ein Jahr nach Beginn des Absammelns betrug die mittlere Siedlungsdichte der jungenLaminaria hyperborea auf dem von Seeigeln freigehaltenen Felsstreifen 22,7/m2. In den folgenden Jahren wurden zwei- und dreijährigeL. hyperborea nur auf diesem Felsstreifen oder in der Nähe seiner Begrenzungen gefunden. Andere Algenarten reagierten in ähnlicher Weise. Aus den Befunden wird gefolgert, daß die untere Verbreitungsgrenze vonL. hyperborea zumindest zum Teil durch Seeigelfraß bestimmt wird, und daßE. esculentus die Siedlungsdichte der anderen Algenarten beeinflußt.Summary1. On the seaward face of Port Erin breakwater large algae do not occur on the lowest three metres. Here the density ofEchinus esculentus is high.2. Over a three year period allEchinus were removed from a 10 m wide strip at about monthly intervals. The total number of individuals removed approached 3000.3. One year after initial clearance the mean density ofLaminaria hyperborea sporelings on the strip was 22.7/m2 and 5.1/m2 to one side of it. By the winter these had almost disappeared outside the strip and in the succeeding years second and third year plants were found only on the strip or close to its edge. Other algae were similarly affected.4. It is concluded that the lower limit ofL. hyperborea is determined at least in part by the grazing pressure ofEchinus and that the urchins exercise some control over the numbers of other algae.

The Biology of Laminaria hyperborea. V. Comparison with early stages of competitors

The responses to light and temperature variations of the gametophytes and early sporophytes of Laminaria hyperborean were compared in culture with those of its main competitors in Britain, namely L. digitata, L. saccharina and Saccorhiza polyschides . Some undeveloped gametophytes of all species are able to survive in the dark for at least 80 days.

The biology of Laminaria hyperborea VII. Reproduction of the sporophyte

There are two critical stages in the life history of Laminaria hyperborea (Gunn.) Fosl. The first is the attachment of the zoospores (meiospores) to suitable rock surfaces and the second is the successful fusion of gametes. The second clearly partly depends on the first which is in turn affected by the efficiency of zoospore production by the sporophyte and the time of year that this takes place. Because of lack of information on these aspects the present study of reproduction in the sporophyte was undertaken.

The movement of sand waves on Warts Bank, Isle of Man

Abstract Warts Bank, near the Isle of Man, Irish Sea, was surveyed by echo sounder and the sand waves on its surface were observed by diving. Their rate of travel averaged 5–10 cm/day during 2 summer months while one crest moved 74 cm during a single flood tide. Bottom samples and near-bed current data made it possible to compare observed and theoretical values of volume transport.

The biology of Laminaria hyperborea X. The effect of depth on some populations

Some understanding of the mechanisms involved in the development and maintenance of forests of Laminaria hyperborea (Gunn.) Fosl. can be gained from the analysis of populations under different conditions. The main variable is depth and unfortunately the available depth range of suitable substrata in the Isle of Man is limited. For this reason two visits were made to western Scotland and the Outer Hebrides, in 1970 and 1976. This paper, which is intended as the last in this series, reports on results obtained rom there and from certain sites in the Isle of Man.

The Biology of Laminaria Hyperborea . VIII. Growth on Cleared Areas

INTRODUCTION Studies of established populations of Laminaria hyperborea (Gunn.) Fosl. have indicated that there is often less change of growth rate with depth than might be expected to result from the decrease in irradiance (Kain, 1967; Luming, 1969; Jupp & Drew, 1974). This has been attributed to self-limitation by the canopy of Laminaria fronds (Luning, 1969; Kain et al. 1976). The removal of this canopy can result in fast growth in shallow water (Kitching, 1941; Svendsen, 1972) and a marked differential in growth rate over a small depth range (Svendsen, personal communication). A series of rocky subtidal areas at two depths off the Isle of Man was cleared of vegetation at various times (Kain, 1975 a ). This provided an opportunity to make growth measurements on individuals of known age in the absence of a canopy formed by older plants.

Aspects of the biology of Laminarja hyperborea IV. Growth of early sporophytes

Sporophytes of Laminaria hyperborea have been grown under various conditions in the laboratory up to the stage of 1000 cells. Some larger plants have been observed after exposure in the sea. Growth was not increased by artificial aeration of the normally stagnant cultures, nor by introducing a dark period each day. The cell number per sporophyte was found to increase exponentially with time. In from 10- to 1000-celled plants the logarithm of the cell number was proportional to the logarithm of the plant length; the relationship corresponded to two-dimensional growth in the presence of increase in cell length. In this size range, when the plants were mainly monostromatic, the growth rate in the laboratory was 0.5 cell divisions/day and 22% increase in length/day. The growth rate of larger sporophytes, partly polystromatic, in the sea, was 10% increase in length/day. A sporophyte would take at least 54 days from the release of the parent zoospores to reach a length of 1 cm. The minimum continuous irradiance necessary for growth was 2 μg.cal/cm 2 sec (20 lux) at 10° C and 4–5μg.cal/cm 2 sec (40–50 lux) at 17° C. The saturating continuous irradiance was at about 100 μg.cal/cm 2 sec (1000 lux) at 10° C and about 150 μg.cal/cm 2 sec (1500 lux) at 17° C. Up to 360 μg.cal/cm 2 sec (3600 lux) from fluorescent lamps was not inhibitory. Growth at 15–20° C was approximately the same as at io° C.

The biology Of Laminaria hyperborea IX. Growth pattern of fronds

INTRODUCTION In the genus Laminaria the origin of the growth of the frond (blade, lamina) is known to be the meristematic transition zone between frond and stipe. Parke (1948) showed, by observing holes punched in the frond, that the fastest rate of growth in length in L. saccharina (L.) Lamour. was in the proximal 25 mm. However, during measurements of the rate of growth of fronds of plants of known age on previously cleared areas (Kain, 1976), it was noted that in L. hyperborea (Gunn.) Fosl. the maximum rate of elongation occurred at some distance from the transition zone. This led to an investigation of the whole pattern of growth, in terms of elongation, increase in area, decrease in thickness and change in cell size and numbers over the surface of the frond at different stages.