Derek Keats

Gradients of intertidal primary productivity around the coast of South Africa and their relationships with consumer biomass

The structure of rocky intertidal communities may be influenced by large-scale patterns of productivity. In this study we examine the in situ rates of production by intertidal epilithic microalgae (chlorophyll a production per unit area per month), intertidal nutrient concentrations (nitrates, nitrites, phosphates and silicates), and standing stocks of different functional-form groups of macroalgae around the South African coast, and their relationships to consumer biomass. Clear gradients of in situ intertidal primary production and nutrient concentrations were recorded around the South African coast, values being highest on the west coast, intermediate on the south and lowest on the east coast. Primary production by intertidal epilithic microalgae was correlated with nutrient availability and could also be related to nearshore phytoplankton production. The dominance patterns of different functional forms of macroalgae changed around the coast, with foliose algae prevalent on the west coast and coralline algae on the east coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, being equally high on the east and west coasts, and low in the south. Positive relationships existed between the average biomass of intertidal intertebrate consumers (grazers and filter-feeders) and intertidal productivity, although only the grazers were directly “connected” to in situ production by epilithic intertidal microalgae. The maximum body size of a widely distributed limpet, Patella granularis, was also positively correlated with level of in situ primary production. The maximal values of biomass attained by intertidal filter-feeders were not related to intertidal primary production, and were relatively constant around the coast. At a local scale, filter-feeder biomass is known to be strongly influenced by wave action. This implies that the local-scale water movements over-ride any effects that large-scale gradients of primary production may have on filter-feeders. The large-scale gradient in intertidal productivity around the coast is thus strongly linked with grazer biomass and individual body size, but any effect it has on filter-feeder biomass seems subsidiary to the local effects of wave action.

Antifouling effects of epithallial shedding in three crustose coralline algae (Rhodophyta, Coralinales) on a coral reef

Abstract Crustose coralline algae cover a substantial fraction of surfaces on the shallow parts of coral reefs. The shedding of surface layers of cells by three common species was studied using light and electron microscopy. All three species examined shed epithallial cells in one of two ways: synchronous epithallial shedding involving the simultaneous shedding of a sheet of cells across a large area of the thallus surface (Sporolithon ptychoides and Neogoniolithon fosliei), or non-synchronous epithallial shedding which occurs when epithiallial cells degenerate individually (Hydrolithon onkodes). Experiments were done to determine whether these types of epithallial shedding could produce an anti-fouling effect. Recruitment onto the surfaces of live and bleach-killed coralline fragments was compared for two synchronous and one non-synchronous shedding species. In all cases, the killed corallines became overgrown within a few weeks. Live corallines remained largely free of other organisms for the duration of the experiment. The results thus demonstrate that both types of epithallial shedding can influence recruitment in the reef ecosystem.

Ecological significance of deep-layer sloughing in the eulittoral zone coralline alga, Spongites yendoi (Foslie) Chamberlain (Corallinaceae, Rhodophyta) in South Africa

Abstract The crustose coralline alga Spongites yendoi (Foslie) Chamberlain (Corallinaceae, Rhodophyta) dominates the lower eulittoral zone along the South Coast of South Africa, together with the limpet Patella cochlear Born. This coralline alga was previously shown to undergo a deep-layer sloughing twice a year, as well as continuous epithallial sloughing. The hypothesis that deep-layer sloughing could perform an antifouling function was tested by determining the percentage cover of fleshy algae developing in a limpet exclusion experiment on live and killed coralline. Substantial fleshy algal cover developed in both limpet removal treatments, negating any possible antifouling function of deep-layer sloughing. A measurable decrease in the mean thickness of the coralline population was noted during periods of sloughing. A thicker crustose coralline, Leptophytum ferox (Foslie) Chamberlain & Keats, grew more slowly and was much more heavily burrowed and more weakly attached than S. yendoi . These results are consistent with a hypothesis that deep-layer sloughing contributes to the algas relatively thin thallus, thereby conferring the advantages of faster growth and stronger attachment. However, further studies are still needed to evaluate these hypotheses further.

PNEOPHYLLUM CONICUM (DAWSON) COMB. NOV. (RHODOPHYTA, CORALLINACEAE), A WIDESPREAD INDO-PACIFIC NON-GENICULATE CORALLINE ALGA THAT OVERGROWS AND KILLS LIVE CORAL

A common Indo-Pacific non-geniculate coralline alga was studied in Fiji, French Polynesia, Ryukyu Islands (Japan) and South Africa, and compared with an isotype of Hydrolithon concium. The isotype contains only bisporangial material, but it is concordant with the material studied in the tropical IndoPacific. The species is transferred to Pneophyllum on the basis of its agreement with the characters of that genus. Pneophyllum conicum is characterised by a monomerous thallus with a predominantly coaxial medulla, the absence of uncalcified outgrowths, trichocytes that are arranged horizontally into circular fields, the absence of protruding tetra/bisporangial pore canal filaments, the presence of papillae lining the tetra/bisporangial pore canal, tetra/bisporangia distributed peripherally about a large central columella, tetra/bisporangial conceptacles low conical with a chamber that measures 220-400 μιη in diameter, the absence of a calcified pore dome and hyaline collar surrounding the tetra/bisporangial pore, and conceptacles that are shed on senescence. Pneophyllum conicum is the only non-geniculate coralline that we have observed to regularly and commonly overgrow and kill live coral, especially taxa with small polyps and relatively smooth colonies.

Two melobesioid coralline algae (Rhodophyta, Corallinales), Mesophyllum erubescens (Foslie) Lemoine and Mesophyllum funafutiense (Foslie) Verheij from Sodwana Bay, South Africa

Two species of the coralline red algal genus Mesophyllum (Corallinaceae, Melobesioideae) are reported from the southernmost coral reefs in the western Indian Ocean at Sodwana Bay, Natal, South Africa. Specimens attributed to Mesophyllum erubescens (Foslie) Lemoine were compared with the type specimens of Lithothamnion erubescens Foslie and L. erubescens f. madagascariensis Foslie [= M. madagascariensis (Foslie) Adey]. The comparison showed that the local material and the type specimens are all conspecific, confirming previous suggestions that M. madagascariensis should be subsumed in M. erubescens. Mesophyllum funafutiense (Foslie) Verheij was also recorded. These species are distinguishable on the basis of the structure of the roof and the pore of the tetrasporangial conceptacles, and on the size of tetrasporangial conceptacles and tetrasporangia.

A nocturnal inshore movement of juvenile cod Gadus morhua L. in eastern Newfoundland

Abstract Juvenile cod Gadus morhua L. (aged 1 + and 2 +) were counted, using an underwater scuba transect method, during the day and at night in shallow water at Newman Sound, Bonavista Bay, Newfoundland. They were 16 times more abundant during the night than during the day. Sampling at one site throughout a 24-h period showed that they arrive in shallow water at dusk, and leave again just before dawn. Much searching among algae and in crevices showed that the young cod are not simply hiding in cryptic habitats during the day. The hypothesis that they spend the day in deeper water is presented.

Refugial Laminaria Abundance and Reduction in Urchin Grazing in Communities in the North-West Atlantic

A literature review and new data are used to clarify geographical patterns of community response to release from heavy grazing by green sea urchins, Strongylocentrotus droebachiensis (O.F. Muller) within the north-west Atlantic region. Large geographical areas identified where urchin-removal experiments have not been conducted are the Passamaquoddy Bay area of the northern Bay of Fundy, the south and west coasts of Newfoundland, and southern Labrador. Within the north-west Atlantic region, there has been variation in the degree of domination by Laminaria species of post-urchin-removal communities. This is probably due, at least in part, to variation in the availability of Laminaria populations in refugia from urchin grazing. The following hypothesis is developed and given a preliminary test: in eastern Newfoundland, the absence of refugial Laminaria longicruris populations is due to periodic ice-scour. Despite the absence of significant Laminaria populations following short-term ( Laminaria spp. may be the natural, long-term community dominants in the absence of significant urchin grazing throughout the region. In view of the logistic problems involved in conducting long-term (6–15 years) urchin-removal experiments, it is suggested that urchin-removal/Laminaria-seeding experiments should be conducted within this region.

Factors Influencing the Growth Rates of Three Commercial Eucheumoids at Coastal Sites in Southern Kenya

As a possible means of improving the livelihoods of local villagers, off-bottom rope cultivation of commercial eucheumoids was investigated on the southern Kenyan coast at three sites, representative of the variety of environments. The morphotypes used were brown Eucheuma denticulatum and green and brown Kappaphycus alvarezii. The study was carried out over a 15 month period from August 2001 until October 2002. Relative growth rates were highest at a sandy flat in a mangrove system (Gazi; 5.6% d−1), and lowest in an intertidal reef flat (Kibuyuni; 3.2% d−1) with a lagoon being intermediate (Mkwiro; 4.8% d−1). The brown E. denticulatum had the highest growth rate of 4.7% d−1 compared to the green and brown K. alvarezii which were 4.3% d−1 and 4.2% d−1, respectively. Growth was more variable at Kibuyuni and Mkwiro. The growth was higher during the southeast monsoon (4.7% d−1) than during the northeast monsoon (4.0% d−1). This is part of a larger study and the effects of water motion, salinity, temperature, thallus nitrogen, and ‘ice-ice’ syndrome on growth of morphotypes is discussed. The water motion was observed to increase thallus nitrogen and hence the growth of eucheumoids. The ‘ice-ice’ condition affected both brown E. denticulatum and brown K. alvarezii but not green K. alvarezii. The results suggest that commercial cultivation of eucheumoids in Kenya will be feasible.

Three species of Hydrolithon (Rhodophyta: Corallinaceae): Hydrolithon onkodes (Heydrich) Penrose and Woelkerling, Hydrolithon superficiale sp. nov., and H. samoense (Foslie) comb. nov. from South Africa

Three species of Hydrolithon are reported from South Africa. Hydrolithon onkodes occurs on the southernmost coral reefs in the western Indian Ocean at Sodwana Bay, Natal. Hydrolithon superficiale sp. nov. is described on the basis of a distinctive layer of conceptacles that occur in a superficial layer of lightly calcified filaments with long, thin cells, that are sharply differentiated from the filaments of short cells in the thallus below. This species has been found only in the Sodwana Bay area of Natal Province. Lithophyllum samoense Foslie is transferred to Hydrolithon on the basis of the anatomy of the tetrasporangial pore. It was also determined that H. samoense (Foslie) comb. nov. is conspecific with Spongites wildpretti Afonso-Carrillo and Neogoniolithon illitus (Lemoine) Afonso-Carrillo. Hydrolithon samoense is known to occur throughout South Africa.

Leptophytum foveatum Chamberlain and Keats (Rhodophyta, Corallinales) retaliates against competitive overgrowth by other encrusting algae

Abstract The encrusting coralline alga, Leptophytum foveatum, is the most abundant crustose alga in the lower eulittoral zone at Yzerfontein and other exposed sites on the West Coast of South Africa. The surface of this species is usually imbricate (appears scaly) as a result of the aparently spontaneous regeneration of margins at the surface of the thallus. The thicker, fleshy, brown crustose alga, Ralfsia verrucosa, usually overgrows the margins of the thinner L. foveatum; however, L. foveatum counteracts this overgrowth by regenerating margins at the thallus surface, and these are able to grow up and over the encroaching margin of R. verrucosa. Experiments in which these regenerated margins were removed showed that the regenerated margins are able to slow or stop the encroachment of R. verrucosa. It is suggested that the regeneration of thallus margins at the surface, away from the primary thallus margin, allows L. foveatum to maintain the advantages of being thin (e.g. more rapid lateral growth), but also gain some of the advantages of being thick (e.g. improved competitive ability).