Life at the margins of the continents: an examination of the intertidal marine life of the south Western Cape

Imagine surviving in an environment that is neither truly marine nor truly terrestrial. That area just beyond the low-water mark of neap tides along the seashore is an example of just such an environment. The organisms living here have to cope with the combined extremes of both land and sea environments: salt spray, immersion in salt water, emersion in air, drenching by heavy rainfall, heating by the sun, freezing winter temperatures, unstable substrates (such as sand, gravel or boulders), and exposure to strong winds. Just how do they cope? Animals generally find it easier coping in this harsh environment because among other ways, they can simply get up and move when the going gets too tough. Plants (both terrestrial and marine) on the other hand, have to either tolerate, or succumb to it. The following is an account of some of the astonishing ways in which both plants and animals from a typical southwestern Cape shore have evolved to adapt and cope in the harsh environment of the intertidal zone.Web of Scienc

You use seaweeds for that?

Introduction: The word seaweed is commonly used, yet to refer to these marine algae as 'weeds' is very far from the truth. Together with microscopic algae called phytoplankton and other photosynthetic organisms, seaweeds are responsible for all primary production in the oceans and therefore form the basis of the food chain in the sea. Although we often cannot smell or taste them, many ingredients in our foods and household products come from the sea and from seaweeds. They are therefore both directly and indirectly valuable to humans. Seaweeds assimilate minerals directly from the sea and are thought to be the single most nutritious foods that you can eat. Rich in trace elements and vitamins, many of them may frequently contain more protein than meat and more calcium than milk

West Coast plants for a waterwise garden

The new gardening mantra is 'grow indigenous'. Besides their aesthetic value, most indigenous plants are less costly to maintain, largely because they have long adapted to the local climate and thus to the local rainfall. For this reason, many indigenous plants, particularly those adapted to low rainfall environments, are more cost effective in their water consumption and many have subsequently been termed waterwise plants. But, why encourage waterwise gardens? First and foremost, it is important to mention that South Africa is a relatively dry country; most parts of the country receive less than 500 mm of rain per annum. With an ever-increasing population, the demand for this precious resource will grow. In response to both of these factors, we have already become accustomed to municipal water restrictions in the Western Cape during summer, as well as legislation pertaining to its conservative use. Despite this, the most alarming fact is that gardens, particularly those with large lawns, are still singled out as the main water-wasting culprits, often consuming up to 50% of all domestic water used in suburban areas. So, it makes perfect sense to convert to a waterwise garden - if you do not already have one - because they cut down on this waste

Kelp forests: forests of a different kind

The United Nations (UN) Food and Agriculture Organization (FAO) defines a forest as being 'more than 0.5 ha with trees higher than 5 m and a canopy cover of more than 10%, or trees able to reach these thresholds in situ', ... and that this 'does not include land that is primarily under agricultural or urban land use'. According to this definition, a forest is 'determined by the presence of trees'. Critical to the interpretation of the term forest, is the capacity of the structural components (trees) to attain the minimum thresholds in their natural environment, unaided by direct human intervention

Chromista

As a group, the chromists show a diverse range of forms from tiny unicellular, flagellates to the large brown algae known as kelp. Molecular studies have confirmed the inclusion of certain organisms once considered Fungi, as well as some heterotrophic flagellates. Despite their diversity of form and feeding modes, a few unique characters group these organisms.Web of Scienc

Of purple laver, tongue weed and hedgehog seaweed: common red seaweeds of the Cape Peninsula

The fourth part of our series on the common intertidal seaweeds of the Cape Peninsula looks at the red seaweeds, which form by far the largest group of seaweeds on the Peninsula and dominate the mid to lower intertidal area to a large extent. Like the brown seaweeds many of the reds are fleshy and bulky and generally occur lower down the shore because they are less tolerant of salinity and temperature extremes than some of the common green seaweeds

Don't cut that 'grass'

Introduction: Have you ever noticed the abundance of wildflowers on public open spaces during spring in Cape Town? I suppose some Capetonians would be aware of Rondebosch Common and the astonishing botanical diversity it contains, including many threatened species. However, it appears that very few people are aware of the many other public open spaces that may be just as precious and put on a spectacular spring flower show. But for how much longer

Two new melobesioid algae (Corallinales, Rhodophyta), Synarthrophyton robbenense sp. nov. and S. munimentum sp. nov., in South Africa and Namibia

Synarthrophyton robbenense sp. nov. and S. munimentum sp. nov., the fourth and fifth species in this apparently southern hemisphere genus, are described from southern Africa. Synarhrophyton robbenense occurs on rock and shells in the subtidal zone. Its thalli are minutely warty, with the surface covered by short, narrow protuberances that are fused into elongate, scrolled structures. The surface [scanning electron microscopy (SEM)] is of the Leptophytum type. Mature tetraibisporangial conceptacles have raised rims and sunken pore plates. The pore plates are composed of filaments made up of two or three cells plus an enlarged epithallial cell. The pore canal is lined by filaments with cells that do not differ in size or shape from those of the other filaments making up the pore plate. Cells of filaments within the tetrasporangial and bisporangial conceptacle rim are narrower and more elongate than cells of the pore plate and surrounding vegetative filaments. Tetralbisporangial pores are surrounded by five to eight rosette cells that tilt somewhat toward the pore in surface SEM view. Tetraibisporangial conceptacles do not become buried in the thallus, but are shed on senescence, often leaving shallow craters on the surface. Synarthrophylon munimenlum occurs on rocks and shells in low-shore tide pools, and on rock, shells, and kelp holdfasts in the subtidal zone. Thalli are usually smooth, occasionally warty, but never show protuberances that are fused into scrol l-like structures. The thallus surface (SEM) is made up of Leptophytum-type epithallial cells. Tetral bisporangial conceptacle roofs are volcano-shaped with a raised peripheral rim and sunken pore plate. The pore plates are composed of filaments made up of five to seven cells plus an epithallial cell. The rosette cells that surround the tetral bisporangial pore are distinct from surrounding roof cells (SEM, surface view) in being narrower and sunken below the level of the surrounding pore plate. The pore canal is lined by filaments with cells that do not differ in size or shape from those of the other filaments making up the pore plate. Cells of filaments within the tetrasporangial and bisporangial conceptacle rim are more or less similar in size and shape to cells of the pore plate and surrounding vegetative filaments.Web of Scienc

Effects of herbivore grazing on the physiognomy of the coralline alga Spongites yendoi and on associated competitive interactions

The territorial gardening limpet Scutellastra cochlear occurs along the south and southern west coasts of South Africa, while one of its primary food items, the encrusting coralline alga Spongites yendoi, extends much further north along the west coast. A combined analysis of geographic variation in limpet grazing frequency and a limpet-manipulation experiment was used to study the interaction between the limpet and its coralline food. The coralline comprised most (c. 85 %) of the limpet’s diet while fleshy algae from the limpet’s garden comprised c. 7 %. Grazing caused the thallus of the coralline to be thin and smooth; in the absence of herbivory, or under low grazing frequencies, the crust became thick and highly protuberant. Grazing weakened the coralline’s interference (overgrowth) competitive ability and also reduced its fecundity. In spite of these two apparently negative impacts, the intimate herbivore-coralline association between S. cochlear and S. yendoi showed characteristics of a facultative mutualism. Grazing by S. cochlear reduces the coralline’s thallus thickness and consequently increased its lateral margin extension rate. Thinner forms of the coralline grew 5X faster than thicker forms. An increased lateral growth results in the thinner form of the coralline being very abundant on south and southern west coasts, occupying as much as 79 % of the substratum in the lower eulittoral zone. Thinner forms of S. yendoi were also less burrowed by boring organisms and more strongly attached than thicker forms of the coralline. Grazing by S. cochlear has thus conferred the advantages of faster lateral growth (i.e. success at exploitation competition) and stronger attachment. The coralline and fleshy algae from the limpet’s garden were equally high in organic content on a volume basis. This suggests that the crude food value per bite in the coralline and fleshy algae is comparable. This study has shown that incompletely overlapping distributions between strongly interacting species along a broad geographical gradient is not just a significant feature of the ecology of terrestrial, but also of marine ecosystems.Web of Scienc

Of sea bamboo, split fan kelp and bladder kelp: three common kelp species of the Cape Peninsula and West Coast

The third part in our series on the common intertidal seaweeds of the Cape Peninsula looks at the kelps, the giant brown seaweeds that occur in the subtidal and intertidal gullies of the Cape Peninsula and the west coast. Like trees an ancient forest, kelp dominate the canopy of the subtidal zone in the cool, nutrient-rich waters of the South African west coast. Kelp is the largest and fastest growing of the seaweeds, growing as much as 13 mm in a day. Some of these seaweeds as the giant kelp (Macrocystis pyrifera) of central and southern California are known to grow to over 30 m in length