Algal Recruitment Research Articles

Contribution of benthic blue‐green algal recruitment to lake populations and phosphorus translocation

SUMMARY1. A two‐season investigation was undertaken to determine the contribution of benthic recruitment to the population development of several species of blue‐green algae.2. Gloevtrichia echinulata populations were shown to be heavily subsidized by benthic recruitment, deriving on average 40% of their planktonic colonies from the benthos.3. Benthic recruitment of Aphanizomenon flos‐aquae, Anabaena flos‐aquae and a second Anabaena species contributed less than 2% to planktonic increases, while Microcystis aeruginosa recruitment was negligible.4. Phosphorus translocation via migrating G. echinulata accounted for most of the phosphorus (P) in the planktonic colonies, and constituted a significant portion of the internal loading of the lake.5. Estimated P translocation via Aph. flos‐aquae was relatively minor, although there was evidence of luxury uptake in the benthos.

Gastropod grazers and algal colonization on a rocky shore in northern California: the importance of the body size of grazers

The effects of grazing by gastropods on algal colonization on a barnacle-dominated rocky shore in northern California were experimentally assessed by removing limpets [ Lottia ( = Cllissella) digitalis (Rathke) and C. scabra (Gould) or limpets and littorines ( Littorina plena Gould) from plots with barnacles ( Balanus glandula Darwin) and from cleared plots. Removal of limpets in the absence of barnacles resulted in increased algal cover. On cleared plots with limpets removed, littorines did not inhibit algal colonization. In contrast, on barnacle-covered plots, removal of limpets generally had little effect on algal recruitment, but additional removal of littorines resulted in increased algal cover. These results together suggest that L. plena are effective grazers primarily where barnacles are abundant, and that limpets are important where barnacles are scarce. The hypothesis that the body size of grazers influences the outcome of grazing on barnacle-covered substrata was tested. Algal colonization on barnacle-covered tiles, as indicated by Chl α biomass, was lowest in treatments with small (4 mm) littorines, and highest with large littorines (9 mm). The interaction of barnacle cover and littorine size significantly affected algal colonization.

An experimental evaluation of the influence of barnacles, crevices and seasonal patterns of grazing on algal diversity and cover in an intertidal barnacle zone

This investigation examines seasonal variations of the influence of a herbivorous limpet Patelloida latistrigata Angas, a barnacle Tesseropora rosea Krauss and potential refuges for algae (crevices between barnacles) on algal cover and diversity. While crevices had no effect on algae at any time, there were some periods (in ungrazed treatments) where more algae were found where barnacles were absent. Herbivores had a dramatic impact on the majority of algae. Most plants (ephemeral green algae) were heavily grazed, as were diatoms. The cover of other macroalgae ( Aphanothece pallida (Kutzing) Rabenhorst and Ralfsia verrucosa Aresch.), while very small, was unaffected by the grazing activities of the limpet. Patelloida initially reduced the mean number of algal species. The same species occurred in both grazed and ungrazed treatments but species were found more frequently in ungrazed treatments. As time progressed and algae (mainly Ulva lactuca L. and Enteromorpha intestrinalis (L.) Link) became established, the number of algal species in ungrazed treatments declined and was not significantly different from grazed treatments. Seasonal patterns in algal cover were more similar at one of the sites studied where the cover of algae (in ungrazed treatments) was much greater than at the other site. Ephemeral green algae occurred at all times of the year, although there was a decline in cover together with low recruitment during some seasons, while the blue-green alga Aphanothece exhibited no seasonal patterns in abundance. The abundance of diatoms appeared to be inversely related to the presence of ulvoids rather than a direct and independent seasonal influence. Algal recruitment in ungrazed areas responded differently in different seasons at both sites. Recruitment was fastest in summer and slowest during autumn. Recruitment during winter and spring was similar. Results of this study provide an insight into the various processes that contribute to the observed pattern in the algal community.

The Effects of Canopy Shadings on Algal Recruitment and Growth in a Giant Kelp Forest

The subtidal (10—15 m) assemblage in the relatively sheltered giant kelp forest at Stillwater Cove in Carmel Bay, California, consists of perennial species forming three major vertical layers: a Macrocystis pyrifera surface canopy, a dense subsurface canopy of another kelp, Pterygophora californica, and an understory of articulated and encrusting coralline algae. The kelp canopies alone or in combination can reduce bottom light to <30% (usually <1%) of surface influx. The effects of light reduction by these vegetation layers on algal recruitment and subsequent growth were determined by removing various combinations of canopies over a 2—yr period, and following subsequent changes relative to appropriate controls. Removing both M. pyrifera and P. californica canopies resulted in moderate recruitment of these species as well as of the annual brown alga Desmarestia ligulata var. ligulata. None of these algae recruited into control areas where one or both canopies were left intact. Highest brown and red algal recruitment occurred when both kelp canopies plus understory coralline branches were removed. Removal of the latter alone had no significant effect. The time of year when algal canopies were removed had little effect on the composition of subsequent algal colonization, as the recruitment of noncalcareous species occurred primarily during a short period in the spring. These results indicate that the relatively low levels of both physical and biological disturbance in Stillwater Cove allow the establishment of a few perennial algal species that inhibit their own recruitment, as well as invasion of other species, by shading. This contrasts with nearby kelp forests subjected to greater and more frequent disturbance, and characterized by a diverse assemblage of annual algal species.

Factors affecting the recruitment of algae in a midshore region dominated by barnacles

On New South Wales coasts, the barnacle Tesseropora rosea (Krauss) is often found in midshore areas that are exposed to moderate wave action. Two herbivorous gastropods, Littorina unifasciata Gray and Patelloida latistrigata (Angas) are common amongst the barnacles. Algae found in this zone consist of diatoms, ephemeral species (e.g. Ulva lactuca L. and Enteromorpha intestinalis (L.) Link) and perennial algae (e.g. Ralfsia verrucosa Aresch, Aphanothece pallida (Kutzing) Rabenhorst, and Gelidium pusillum (Stackhouse) Le Jolis). The distribution and abundance of algae is variable and patchy. This paper investigates the hypothesis that the patchy distribution and variable abundance of algae within this barnacle zone is due to factors affecting the germlings once settlement has occurred. Gastropods may consume the algae, and the barnacle shells may provide better sites for attachment of the plants than the bare rock. Crevices among barnacle shells may provide the algal spores (asexually or sexually derived propagules) with refuges from grazing and/or desiccation. Results of this study demonstrate that neither crevices between barnacle shells, nor barnacles themselves influenced algal recruitment. Grazing molluscs had a major impact on local algae. Herbivores may either reduce or have no effect on the mean number of algal species. The same algal species occurred in both grazed and ungrazed areas. Their abundance was, however, greater in ungrazed areas. The grazers in this system seem to be able to consume virtually all algal spores that settle in areas where the propagules can potentially survive. When a spore escapes being grazed it can grow and escape subsequent encounters as grazers feed primarily on microalgae (i.e. diatoms and propagules of macroalgae). Thus the distribution of algae reflects past escapes of the spores.

Latitudinal variation in intertidal algal community structure: the influence of grazing and vegetative propagation.

The hypothesis that sea urchin grazing and interactions with turf-forming red algae prevent large brown algae from forming an extensive canopy in the low intertidal zone of southern California was tested with field experiments at two study sites. Experimental removal of sea urchins resulted in rapid algal recruitment. Crustose coralline algae which typically dominate the substratum in areas with dense urchin populations were quickly overgrown by several species of short-lived green, brown and red algae. The removal of urchins also significantly increased the recruitment of two long-lived species of large brown algae (Egregia laevigata and Cystoseira osmundacea at one study site and E. laevigata and Halidrys dioica at the other). The experimental plots at both sites were eventually dominated by perennial red algae.A two-factorial experiment demonstrated that sea urchin grazing and preemption of space by red algae in areas where urchins are less abundant are responsible for the rarity of large brown algae in the low intertidal of southern California. The three dominant perennial red algae, Gigartina canaliculata, Laurencia pacifica and Gastroclonium coulteri, recruit seasonally from settled spores but can rapidly fill open space with vigorous vegetative growth throughout the year. These species encroach laterally into space created by the deaths of large brown algae or by other disturbances. Once extensive turfs of these red algae are established further invasion is inhibited. This interaction of algae which proliferate vegetatively with algae which recruit only from settled spores is analogous to those which occur between solitary and colonial marine invertebrates and between solitary and cloning terrestrial plants.It is suggested that a north-south gradient in the abundance of vegetatively propagating species, in grazing intensity and in the frequency of space-clearing disturbances, may account for latitudinal variation in intertidal algal community structure along the Pacific coast of North America.