David R. Laur

Severe storm disturbances and reversal of community structure in a southern California kelp forest

Regular observations made over a period of 5 yr in four permanent transects provided data on plant, sea urchin, and fish densities which indicate that two unusually severe winter storms in 1980 (“Storm I”) and 1983 (“Storm II”) had different effects on a southern California kelp-forest community. Storm I removed all canopies of the giant kelp Macrocystis pyrifera, but spared most understory kelps, mainly Pterygophora californica. Hence, the previously large accumulation of detached drift kelp, mostly M. pyrifera, disappeared. Denied their preferred diet of drift kelp, the sea urchins Strongylocentrotus franciscanus and S. purpuratus then emerged from shelters to find alternative food. Without effective predators, they consumed most living plants, including the surviving understory kelps. This weakened the important detritus-based food chain, as indicated indirectly by declining abundances of algal turf and fish (Embiotocidae) that eat small animals living in turf. In 1983, Storm II reversed the process by eliminating exposed urchins, while clearing rock surfaces for widespread kelp settlement and growth. By summer 1984, the kelp grew to maturity to form extensive canopies despite elevated water temperatures during summer and fall of 1983. Thus, severe storms may have vastly different effects on community structure, depending on the state of the community before the disturbance.

Variation in Algal Dispersal and Recruitment: The Importance of Episodic Events

Spatial and temporal variation in dispersal and recruitment of the kelps Macrocystis pyrifera and Pterygophora californica and of filamentous brown algae (FBA) consisting primarily of Ectocarpus siliculosus were examined off southern California, USA. These three taxa of sublittoral brown algae show enormous differences in adult morphology and demography, but release propagules near the bottom that are similar in size, shape, and motility. Their weekly variation in recruitment was measured on replicate frosted glass slides placed at different distances from stands of fertile adults at three sites. For all taxa, significant temporal variation was observed in recruitment at the zoospore source as well as at distances out to 4000 m from the source. For the kelps, this variation was due to variable rates of both zoospore settlement and early postsettlement mortality. In general, recruitment density of both kelps rapidly declined with distance from the adult stand; significantly lower recruitment was observed at as little as 3 m away. In contrast, dispersal of FBA was much greater; no significant decrease in recruitment density was observed out to 500 m. The differences in dispersal between these two algal groups may result from behavioral differences of their zoospores. Unlike those of kelps, zoospores of FBA are positively phototatic. This enables FBA zoospores to remain in the water column longer, thus increasing the distances over which they disperse. The predominant pattern of limited dispersal in the two kelps, however, was not constant over time. Dispersal was greatly expanded during episodic periods of high recruitment that coincided with winter storms. Turbulent water flower associated with these storms may resuspend kelp zoospores normally occurring near the bottom and allow them to be transported greater distances by prevailing currents. Although species characteristics of the adult stand appeared to influence the distribution of recruits, the effect disappeared within 10 m of the stand. At a short—range study site, decreases in spatial variation in recruitment density between the zoospore source and 3 and 10 m away indicated that the distribution of zoospores became more uniform with distance. Likewise at a long—range site, recruitment out to 4000 m appeared to occur uniformly and coincided with recruitment at the zoospore source and at all intermediate distances. This uniformity and coincidence of recruitment indicated that dispersal over longer distances was probably via individual zoospores rather than via clumps of drifting plants or reproductive fragments as suggested in previous studies. Although episodic, such dispersal is probably essential in promoting the persistence of these plants in highly disturbed and unpredictable environments.

Community Recovery After Storm Damage: A Case of Facilitation in Primary Succession

Manipulations of early arriving, fast-growing algal stands, which appeared soon after a severe storm denuded a Southern California marine reef habiatat, indicated that the dense cover protected newly settled kelp plants from excessive damage by grazing fishes. This is an example of refuge facilitation in primary succession after a major natural disturbance, a mechanism that may contribute substantially to the regeneration of a kelp forest.

The influence of plant cover on surfperch abundance at an offshore temperate reef

SynopsisAt an offshore reef near Santa Barbara, southern California, young-of-year (‘young’) of five surfperch species (Embiotocidae: Embiotoca jacksoni, E. lateralis, Hypsurus caryi, Rhacochilus toxotes, Damalichthys vacca) once thrived in a dense kelp understory of Pterygophora californica and Laminaria farlowii, but disappeared after a severe storm in February, 1980 deforested their habitat. Measurements of fish density and kelp cover made before deforestation indicated that the young surfperch appeared in the spring and disappeared in the fall as cover increased and declined. Adult surfperch and large kelp bass (Paralabrax clathratus), which can eat young but not adult surfperch, remained all year. We tested to see if kelp cover was an essential refuge for the young by pruning back (‘thinning’) kelp blades from one of two transects. The thinning caused a significant redistribution of young which clearly avoided open spaces, but not of adults which are less vulnerable to predation. Measurements of fish density made after the storm-induced deforestation showed that adult surfperch and kelp bass still remained abundant even after the young surfperch were gone. Only after an abrupt reforestation in 1983, more than a year after the present study was terminated, were young once again seen on the reef. Although young surfperch may seek tiny prey living on kelp blades, most lines of evidence indicated that the distribution of the young is more a response to risk of predation. Hence the extent of kelp understory was probably the main determinant of the survival of young surfperch on the reef.

The Distribution of Nearshore Fishes in Kelp and Eelgrass Communities in Prince William Sound, Alaska: Associations with Vegetation and Physical Habitat Characteristics

The nearshore (less than 20 m depth) demersal fish community in Prince William Sound, Alaska, is dominated by Pacific cod, Gadus macrocephalus, pricklebacks (mostly Arctic shanny Stichaeus punctatus), gunnels (mostly crescent gunnels Pholis laeta), a variety of greenlings (Hexagrammidae) and sculpins (Cottidae). During summer, the spatial distribution of fishes, over scales of 100s of m to 10s of km, varied by habitats characterized by different vegetation types. Juvenile Pacific cod and greenlings were numerically dominant in eelgrass, Zostera marina, beds. Pricklebacks and sculpins were dominant in areas with an understory of the kelps Agarum cribrosum and Laminaria saccharina. Greenlings and sculpins were the most abundant demersal fishes in more exposed sites with a canopy of Nereocystis luetkeana and an understory of L. bongardiana. Measured habitat variables, including vegetation type, slope, vegetation biomass, and substratum type, explained a significant proportion of the variation in the presence or absence of most fishes. The relative importance of different habitat characteristics varied between taxonomic groups of fishes. Vegetation type explained a significant proportion of variation for cod, rockfishes, and ronquils. Juvenile cod were closely associated with eelgrass, while rockfish and ronquils were associated with kelps. Pricklebacks and rockfishes were more frequently observed on steeply sloped shorelines, while ronquils were more often found at sites with higher biomass of vegetation. Within A. cribrosum habitats, more greenlings and sculpins were present at sites where algal biomass was higher. Also, sculpins were more abundant in deeper water and gunnels were more abundant in shallow water within this habitat. These associations may not have been causative. However, evidence suggests that some differences between fish communities in eelgrass and Agarum beds may have been causally related to vegetation characteristics. The possible roles of different vegetation types as refugia from predators or as sources of prey are discussed.

Experimental evaluations of substrate types as barriers to sea urchin (Strongylocentrotus spp.) movement

Descriptive evidence that sandy surfaces and rock ledges inhibit progress of grazing sea urchins prompted an experimental investigation of physical obstacles to urchin movement in a subtidal area of reef and kelp off southern California in 1980. In laboratory experiments, we found that both red (Strongylocentrotus franciscanus) and purple (S. purpuratus) urchins can negotiate sand using their oral spines, although purple urchins are slower and more hesitant to do so. In field experiments, we observed the fates of starved red urchins transported to replicate plots within stands of sand-or rock-based understory kelp (Pterygophora californica). Urchins in rock plots retreated to nearby crevices from where they ate attached kelp. After finding kelp blades, urchins soon disappeared from sand plots because individuals in small groups may have difficulty holding and eating attached kelps on unconsolidated surfaces. In another experiment, red and purple urchins reached kelp on a rock ledge by mounting an artificial ramp. We conclude that by using their tube feet, individuals of both species move best over flat, hard surfaces, although soft substrate may constitute a major barrier only to purple urchins. In the absence of effective predator control, urchins can surmount most sand or rock barriers when water motion subsides. Hence, their ability to coordinate spine movements to negotiate soft substrates may be an adaptation to invade kelp refuges during quiet periods if preferred drift food is unavailable.

Effects of an oil spill on the soft-bottom macrofauna of Arthur Harbour, Antarctica compared with long-term natural change

The macroinfauna at depths 30–115 m was sampled in March–April 1989, c. two months after an oil spill that resulted from the grounding of the Bahia Paraiso. Stations consisted of the oil-spill site and a comparable control location, and two historical sites previously sampled in 1971. The historical sites were located at two distinct points along a known continuum of increasing physical stability with depth, attributed to disturbances from glacial calving. Macroinfaunal assemblages at most stations were characterized by very high densities and numbers of taxa. There were no significant differences ( P Bahia Paraiso. The assemblage at the shallower of the two historical sites, however, showed a substantial change over the 18-yr period between studies. This change consisted of a shift toward a more species-rich and abundant macroinfauna characteristic of the more physically stable parts of the harbour. This change may be related to the fact that the glacier face near this site has retreated c. 250 m over the last 20 yrs, resulting in less physical disturbance of the adjacent seafloor.

PURIFICATION OF SPECIES SPECIFIC ANTIBODIES TO CARBOHYDRATE COMPONENTS OF MACROCYSTIS PYRIFERA (PHAEOPHYTA)1

Polyclonal rabbit antibodies to cell wall components were produced against gametophytes of the giant kelp Macrocystis pyrifera (Linnaeus) C. Agardh. These antibodies were found to react with carbohydrates extracted from M. pyrifera and Pterygophora californica Ruprecht by carbohydrate based enzyme immunoassay (EIA). The antibodies reacted with carbohydrates from both species. After affinity purification on a column with M. pyrifera carbohydrate coupled to AH‐Sepharose, the eluted antibody was specific for M. pyrifera carbohydrate with little cross reactivity to P. californica carbohydrate in the EIA test. In experiments carried out to characterize the antigenic specificity of unfractionated antibody using commercially prepared carbohydrates in the EIA, the antibodies were shown to react primarily with fucoidan and to a lesser degree, alginate. The unfractionated antibody was also shown to bind to proteins from both M. pyrifera and P. californica. These results indicate that species specific carbohydrate determinants may be present in the kelp cell wall.