Kelp Communities Research Articles

Organic carbon isotope ratios (δ 13 C) of Arctic Amerasian Continental shelf sediments

Organic matter origins are inferred from carbon isotope ratios (δ13C) in recent continental shelf sediments and major rivers from 465 locations from the north Bering-Chukchi-East Siberian-Beaufort Sea, Arctic Amerasia. Generally, there is a cross-shelf increase in δ13C, which is due to progressive increased contribution seaward of marine-derived organic carbon to surface sediments. This conclusion is supported by the correlations between sediment δ13C, OC/N, and δ15N. The sources of total organic carbon (TOC) to the Amerasian margin sediments are primarily from marine water-column phytoplankton and terrigenous C3 plants constituted of tundra taiga and angiosperms. In contrast to more temperate regions, the source of TOC from terrigenous C4 and CAM plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes. The input of carbon to the northern Alaskan shelf sediments from nearshore kelp community (Laminaria solidungula) is generally insignificant as indicated by the absence of high sediment δ13C values (–16.5 to –13.6‰) which are typical of the macrophytes. Our study suggests that the isotopic composition of sediment TOC has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial–interglacial changes in sea level and environments. Furthermore, recycling and advection of the extensive deposits of terrestrially derived organic matter from land, or the wide Amerasian margin, could be a mechanism for elevating total CO2 and pCO2 in the Arctic Basin halocline.

BIOGEOGRAPHY AND ECOLOGY OF THE KELP/RED ALGAL SYMBIOSIS

A kelp/red algal symbiosis is described from nature based on extensive collections from the San Juan Islands, Washington. Kelp gametophytes were found as endophytes in the cell walls of seventeen species of red algae in three different kelp communities. Host red algae were mostly filamentous (e.g., Pleonosporium vancouverianum) or polysiphonous (e.g. Polysiphonia paniculata). The kelp gametophytes completed vegetative and reproductive development in the hosts with gametangia formed at the host surface and with sporophytes up to several mm in height being produced while still attached to the host. To date, none of the kelp gametophytes from nature have been identified to genus or species, although the gametophyte of Nereocystis luetkeana is a potential candidate for the symbiosis. Preliminary observations from Nova Scotia and the Isle of Man have not found the association in the Atlantic Ocean. Laboratory studies in Korea successfully reconstructed the symbiosis in the red alga Aglaothamnion oosumiense using zoospores of Undaria pinnatifida but not Laminaria religiosa. Here we outline the development of the symbiosis and discuss the potential adaptive significance of the kelp/red algal interaction.

KELP ECOLOGY AND THE POINT LOMA KELP FOREST: A BLEND OF THE OLD AND THE NEW

The history of the Point Loma kelp forest parallels that of the earlier pioneers in Europe, with an early descriptive focus moving quickly toward mechanistic studies. At Point Loma, research was initiated because of large‐scale loss of kelps, so from the beginning there was an urgency to restore the kelp forest with a concomitant focus on sea urchin grazing. We review the evolving relationships between new questions and long‐term observations that emphasize both small and large‐scale events in time and space. For example, the early descriptive work grew into small‐scale experimental work that demonstrated problems of scaling up from experiments. As we repeated experiments over larger spatial and temporal scales we learned that the low frequency variation at both scales is extremely important and must be understood before small‐scale results are generalized. Regime shifts in the physical environment and the increasing effects of fishing represent continuing challenges to the kelp community structure that make it critically important to consider scaling problems.

SCALE‐DEPENDENT PATTERNS OF DISTURBANCE AND RECOVERY IN GIANT KELP FORESTS

We studied spatial variability in giant kelp (Macrocystis pyrifera) forests at 84 sites along the west coast of North America in order to assess the impacts of the 1997–98 El Niño. Our sites spanned the geographic range of giant kelp in the Northern Hemisphere and were surveyed just before, immediately following, several months after, more than one year after, and nearly two years after the El Niño. Interspersion of sample units allowed us to compare the effects of this disturbance among spatial scales ranging from a few meters to more than a thousand kilometers. Variance components analyses revealed that El Niño shifted the relative importance of factors that regulate giant kelp communities from factors acting at the scale of a few meters (local control) to factors operating at hundreds of kilometers (regional control). Moreover, El Niño resulted in a near‐to‐complete loss of giant kelp populations throughout nearly two‐thirds of the species' range. Evaluation of these effects along with oceanographic data (at the “appropriate” spatial scales), along with closer examination of giant kelp populations in the most severely impacted region (Baja) suggested that the among‐region differences in giant kelp survival was due, at least in part, to El Niño‐induced differences in ocean climate. Giant kelp recovery following El Niño was also scale‐dependent, but driven by factors different from those of the disturbance. Here, we present results for several species of macroalgae in an attempt to relate the importance of El Niño to that of other processes in creating scale‐dependent patterns of variability.

Seasonal inhibitory effects of marine plants on sea urchins: structuring communities the algal way

Natural and manipulative experiments were used to evaluate the effect of algal cover on sea urchin (Strongylocentrotus polyacanthus) distribution on submarine pinnacles at Shemya Island in the western Aleutian Archipelago. In July, pinnacle tops had dense kelp stands with low densities of sea urchins. In subsequent months, urchin densities increased as annual algal cover declined. In the summer, removal of specific combinations of macroalgae from the pinnacle tops resulted in an increase in urchin density. Artificial structures that imitated certain common seaweeds were placed on pinnacle tops and inhibited urchin movement. Clod cards that were used to measure relative abrasion rates on vegetated and cleared pinnacles demonstrated that algae cause a significant amount of abrasion. This study showed that the physical structure of the dominant annual alga, Desmarestia viridis, is capable of limiting sea urchin distribution, movement, and grazing. In this study, a potential food source actively controlled herbivore distribution and was the primary cause for the persistence of isolated kelp communities surrounded by barrens dominated by sea urchin grazing.

Ecosystem effects of fishing in kelp forest communities

Kelp forests, highly diverse cold water communities organized around the primary productivity and physical structure provided by members of the Laminariales, support a variety of fisheries, and the kelp itself is harvested for alginates. Worldwide, these communities generally share susceptibility to destructive overgrazing by sea urchins. The impact of sea-urchin grazing is governed by the ratio between food availability and grazing pressure, thus factors affecting the abundance of both urchins and kelps are central to ecosystem integrity. Some kelp ecosystems share a second generality, the association of exploitation of various urchin predators with destructive levels of urchin grazing, leading to cascading implications for other species dependent on the productivity and habitat provided by the kelps. Competition between abalones and sea urchins also affects some kelp communities. These ecosystem-structuring processes are complicated by a variety of bottom-up and top-down factors, including variability in ocean climate affecting kelp productivity and recruitment of key species, and echinoid disease. Potential ecosystem effects of fisheries for predators, abalones, sea urchins, and kelps are reviewed biogeographically. Given the hundreds to thousands of years that many nearshore marine ecosystems have been exploited, no-take marine reserves may be the only way to determine the true ecosystem effects of fishing.

The Eastern Australian Region: a Dynamic Tropical/Temperate Biotone

Eastern Australia lies in an overlap of tropical Indo-Pacific and temperate bioregions because of the influence of the southward-flowing East Australian Current. It has a very high biodiversity, from tropical coral reef and seagrass in the north, to coastal lakes and kelp communities in the south. Offshore, Norfolk and Lord Howe Islands and Elizabeth and Middleton Reefs, are the highest latitude coral reefs in the world. The coastal region includes South-East Queensland and New South Wales (NSW) and supports almost half of Australia’s population. Catchments have been extensively cleared for agriculture and water quality in many rivers and estuaries is poor. There has been major loss of wetlands and acid soil runoff causes fish kills and diseases in estuaries. The coastline is exposed, and much has been mined for heavy minerals and is subject to erosion. Urbanization and industrialization, particularly in the Sydney area, has resulted in sewage and heavy metal pollution. Many of the coastal fisheries are declining, largely because of loss of water quality and wetlands habitats, and in some cases overfishing. Marine environmental management (the responsibility of the two states to the 3 mile limit, and the Commonwealth to the boundary of the 200 mile EEZ) is variable, and largely focused on the urban centres. Queensland has a system of marine protected areas (MPAs) while NSW has minimal protected areas. The major issues are declining water quality, loss of estuarine habitats, degradation of coastal lakes, and localized pollution from heavy metals and sewage in the Sydney area.

The role of terrestrial humic substances on the shift of kelp community to crustose coralline algae community of the southern Hokkaido Island in the Japan Sea

Crustose coralline algae dominates coastal rocky shores (crust-dominated community) in certain world coastal zones after the disappearance of kelp forest community. Local fisheries suffer greatly when this occurs. Well known ecological hypothese to explain this phenomenon such as sea urchin excessive grazing and anomalously high temperature events do not satisfactorily explain the shift in algal composition in the Japan Sea coast. Previously we have shown that coralline algae has a competitive edge over other algae under the extremely low iron levels associated with deforestation in the Japan Sea along the coast of the southern Hokkaido Island. In the present study we present direct evidence that forest-derived humic substances inhibit crustose coralline algal spore germination and also promote macroalgal oogonium formation. Our results strongly suggest that suburban development associated with deforestation in the Japan Sea coast watershed reduced the flux of humic substances into coastal water and in turn created an environment in which coralline algae dominate over other algae.

The Use of Aquatic Macrophyte Ecotoxicological Assays in Monitoring Coastal Effluent Discharges in Southern Australia

Germination inhibition of zoospores of the aquatic, brown algal macrophyte Ecklonia radiata was employed to assess the toxicity of sewage effluents under short to long term exposure and under modified salinity conditions. The rate of germination inhibition was determined for exposure times between 2 and 48 h in salinity modified and unmodified regimes and under reduced salinity conditions alone. The results indicated that rate of germination inhibition increased with duration of exposure to sewage effluents and to salinity reduction alone, and that response to the effluents may be enhanced under conditions of reduced salinity. Whilst the effect of primary treated effluent was primarily that of toxicity, secondary treated effluent effects appeared to be primarily that of reduced salinity although at a greater rate than would be expected for salinity reduction alone. The assay is suggested to provide a mechanism for monitoring sewage effluent quality and to monitor potential impacts of sewage effluent discharge on kelp communities in southern Australia.

The Effects of the Endicott Development Project on the Boulder Patch, an Arctic Kelp Community in Stefansson Sound, Alaska

The Boulder Patch in Stefansson Sound, Beaufort Sea, of Alaska harbors a diverse arctic kelp community in areas where rock cover exceeds 10%. In 1985, the Endicott Development Project, the first major offshore oil development in the Alaskan Arctic, was constructed shoreward of this community at the mouth of the Sagavanirktok River. A 7-year study was conducted to determine the effects of the development on kelp health and growth and taxa diversity of the overall community. No adverse effects were detected. The regional patterns of sediment transport served to protect the community from development-derived sediment loadings and discharges. Sediment transport patterns likely also contribute to the unusual presence of this community in the sound.Key words: Boulder Patch, kelp, Laminaria solidungula, Beaufort Sea, productivity, colonization, epilithic community, epilithic flora, epilithic fauna, benthic community, sediment transport

Caging experiments to examine the effects of fishes on understorey species in a sublittoral kelp community

The effects of predatory fish on the abundancesof understorey species in a sublittoral Ecklonia radiata kelp assemblage were examined using exclusion cages. Fish were excluded from replicate areas for comparison with uncaged controls and appropriate treatments to test for caging artifacts. Experiments were done under the kelp canopy and in areas cleared of kelp (simulating damage due to storms). The understorey assemblage was sampled using quadrats for macroscopic species, an underwater microscope for attached microscopic organisms, and an underwater suction sampler for mobile microscopic fauna. Significant caging artifacts were found to act on certain species early in the experiments and on most species after 8 wk. Caging led to increases in abundances of many microscopic invertibrates, microscopic silt and layers of sediment. Caging led to decreases in the abundances of encrusting algae as experimental plots became dominated by layers of sediment. For some encrusting algae, Zonaria-Lobophora, Myxilla sp. and juvenile Ecklonia radiata, caging negated natural increases in abundances, whilst for sessile animals, caging negated a natural decrease. The species richness of the assemblage was greater in areas with fish than in areas excluded from fish. More species appeared to be affected by predation by fish under the canopy than in clearings due to the greater number of species living under the canopy. Some species showed significant effects (an increase, decrease or the negation of a natural change in abundance) at all times of the year when fish were excluded, whilst others only showed effects at times when they were in large abundances. After removing certain cages, fishes quickly returned the assemblage to one dominated by encrusting species. The results are discussed in terms of alternative models and hypotheses to account for the observed patterns (particularly effects of fish predation and caging artifacts), problems with using predator-exclusion cages in such experiments, and the significance of these experiments for future studies of these interactions.

Earthquake-Caused Coastal Uplift and Its Effects on Rocky Intertidal Kelp Communities

The coastal uplift(approximately 40 to 60 centimeters) associated with the Chilean earthquake of 3 March 1985 caused extensive mortality of intertidal organisms at the Estación Costera de Investigaciones Marinas, Las Cruces. The kelp belt of the laminarian Lessonia nigrescens was particularly affected. Most of the primary space liberated at the upper border of this belt was invaded by species of barnacles, which showed an opportunistic colonization strategy. Drastic modifications in the environment such as coastal uplift, subsidence, or the effects of the El Niño phenomenon are characteristic of the southern Pacific. Modifications in the marine ecosystem that generate catastrophic and widespread mortalities of intertidal organisms can affect species composition, diversity, or local biogeography.

Diversity, Patterns of Adaptation, and Stability of Nova Scotian Kelp Beds

There are two alternate community states in the rocky subtidal of the Atlantic coast of Nova Scotia, an unproductive sea urchin/coralline alga community, and highly productive kelp beds dominated by Laminaria longicruris. Disease—induced mortality of the sea urchins (Strongylocentrotus droebachiensis) triggered a switch from the first state to the second and provided a unique opportunity to study (1) the ability of L. longicruris to recover its former dominant status, and (2) its stability when competing with other seaweeds and when perturbed by storms and grazers other than urchins. Rates of recolonization of L. longicruris depended on the proximity of a refugial source of spores. When reproductive plants were nearby, a closed canopy developed within 18 mo of urchin mortality. When a reproductive population was several kilometres away, there was sparse recolonization for 3 yr, then a massive recruitment occurred with closure of the canopy in the 4th yr. Laminaria is clearly the competitive dominant in the seaweed community. Manipulative experiments showed that the kelp limits the abundance of several understory species, but there was no evidence that the abundant annual seaweeds limited kelp recruitment. When sea urchins were rare, the density and growth rates of Laminaria were influenced mostly by intraspecific competition. When the canopy of adult plants was removed there was a dramatic increase in kelp recruitment, but the recruits that grew in dense patches in the clearings were significantly smaller than those of a similar age that grew more sparsely beneath the canopy. Once the kelp recovered from destructive grazing and formed a mature forest, it was able to maintain its dominance, even in habitats subject to severe nutrient stress for 8 mo of the year. For most of the year mortality and erosion of laminae outweighed the effects of recruitment and growth, and the canopy declined, especially during winter when storms were frequent. Erosion was exacerbated by grazing of the gastropod Lacuna vincta. However, in late winter and early spring, recruitment and rapid growth restored the canopy. When severe storm damage was simulated by completely removing Laminaria in patches, the kelp rapidly recolonized and soon outgrew other seaweeds. Unlike the competitive dominants in kelp bed systems in the northeast Pacific, L. longicruris in Nova Scotia manifests multiple patterns of adaptation that enable it to dominate early and late stages of succession in a range of habitats of different levels of nutrient stress and of disturbance from storms and grazers. The principal threat to the stability of the kelp beds is destructive grazing by sea urchins. We suggest that the considerable differences between the dynamics of kelp beds in Nova Scotia and those of the northeast Pacific, and the high degree of stability of L. longicruris stands in Nova Scotia, is attributable to the low diversity of kelps and therefore low levels of competition in Nova Scotia, and to the multiple adaptations of L. longicruris that enable it to tolerate several stresses and disturbances. We argue that the dynamics of community organization, and therefore the stability properties of this system are determined primarily by biological interactions and not by physical variables. This differs from the kelp communities in the northeast Pacific, in which both biological and physical factors influence dynamics significantly at a primary level. We offer a qualitative model of the dynamics of community structure in Nova Scotia that may be viewed as a set of deterministic "subroutines," in which each subroutine describes the outcome of a particular biological interaction. The subroutine(s) that predominate at one point in time and space are probably determined mostly by physical hydrographic variables that have a large stochastic component.

Inhibition of kelp recruitment by turfing algae and consequences for an Australian kelp community

In the sublittoral kelp forests of New South Wales, dictyotalean turfing algae dominate the substratum in areas where kelp canopies have been removed by storms. The effects of the presence of these algae on the recruitment of kelp plants and the subsequent structure of the benthic community were determined. Areas of turfing algae in clearings were experimentally cleared of turf at a time of dense kelp settlement, and areas of the kelp canopy were also removed. These treatments were compared with unmanipulated areas of turf in clearings and areas under the kelp canopy. The number of kelp recruits in each replicate plot was recorded throughout time as were the abundances of most of the macroscopic and microscopic species living on the substratum. Kelp was found to recruit very quickly to areas of substratum which had the overlying kelp canopy removed, but few recruits appeared under the natural canopy, or in areas with turfing algae, or in clearings where turfing algae had been removed. The results showed that whilst the presence of a natural kelp canopy and/or turfing algae inhibited the recruitment of kelps, removal of turfing species from clearings did not facilitate kelp recruitment. This indicated that the presence of turf did not solely inhibit kelp recruitment, but some lingering influence of turf seems to affect the substratum in clearings such that kelp cannot recruit to such areas. Turfing species returned and dominated the substratum in clearings where turf had been removed. After an initial decline, encrusting species increased in abundances in clearings where kelp recruited as these recruits developed a canopy. Turf and encrusting species remained great in cover in the respective control treatments. The results are discussed in terms of alternate stable states within this community. Such concepts are concluded to be dependent upon the spatial and temporal scales of one's investigation.

Fish in Offshore Kelp Forests Affect Recruitment to Intertidal Barnacle Populations

Kelp forests along the coast of central California harbor juvenile rockfish that prey on the larvae of invertebrates from the rocky intertidal zone. This predation reduces recruitment to barnacle populations to 1/50 of the level in the absence of fish. The dynamics of the intertidal community are thus strongly coupled to the dynamics of the offshore kelp community.

Physical disturbances in an Australian kelp community. II. Effects on under-storey species due to differences in kelp cover

Physical disturbances in an Australian kelp community. II. Effects on under-storey species due to differences in kelp cover

Dependence of consumers on macroalgal (Laminaria solidungula) carbon in an arctic kelp community: ?13C evidence

Stable carbon isotope measurements (δ13C) were used to assess the importance of kelp carbon (-13.6 to-16.5‰) versus phytoplankton carbon (-25.5 to-26.5‰) to resident fauna of an isolated kelp bed community on Alaska's north arctic coast from 1979 to 1983. The predominant kelp, Laminaria solidungula, showed some seasonal variation in δ13C which was correlated with changes in the carbon content of the tissue. Animals that showed the greatest assimilation of kelp carbon (>=50%) included macroalgal herbivores (gastropods and chitons,-16.9 to-18.2‰), a nonselective suspension feeder (an ascidian,-19.0‰) and a predatory gastropod (-17.6‰). Animals that showed the least incorporation of kelp carbon into body tissues (<=7%) included selective suspension-feeders (hydroids, soft corals and bryozoans,-22.8 to-25.1‰). Sponges, and polychaete, gastropod and crustacean omnivores exhibited an intermediate dependence on kelp carbon (15 to 40%). Within some taxonomic groups, species exhibited a broad range in isotopic composition which was related to differences in feeding strategies. In the polychaete group alone, δ13C values identified four major feeding habits: deposit-feeders (-18.0‰), omnivores (-20.4‰), predators (-22.2‰) and microalgal herbivores (-23.0‰). Distinct seasonal changes in the δ13C values of several animals indicated an increased dependence on kelp carbon during the dark winter period when phytoplankton were absent. Up to 50% of the body carbon of mysid crustaceans, which are key prey species for birds, fishes and marine mammals, was composed of carbon derived from kelp detritus during the ice-covered period.

Physical disturbances in an Australian kelp community. I. Temporal effects

Physical disturbances in an Australian kelp community. I. Temporal effects

The Structure and Regulation of Some South American Kelp Communities

The main objective of this study was to evaluate how physical stress and herbivores influence the distribution, abundance, size frequency, and mortality of the giant kelp, Macrocystis pyrifera, in the southeast Pacific. These factors were studied for the kelp and the echinoid herbivore Loxechinus albus over a wide latitudinal range (56°—42° S) of South America on RV Hero cruises in 1972 and 1973. There were large kelp forests with many large plants in the southern Isla de los Estados and Tierra del Fuego sites. Sources of kelp mortality in these sites include entanglement with drift plants and heavy encrustation of bivalves. This resulted in a considerable amount of drifting kelp, and the sea urchins appeared to have abundant food and did not attack living kelp plants. Nevertheless, the urchin densities usually were relatively low and the Loxechinus size frequencies skewed to larger size classes, suggesting that their populations may be limited by larval availability in the Westwind Drift. There were also some large kelp forests in the northern Golfo Corcovado and Isla Chiloe areas, but here the kelp forests seemed relatively ephemeral and Loxechinus appeared to be harvested by humans. The intermediate latitudes (54°—46° S) in areas semiexposed to oceanic waves were characterized by situations in which Loxechinus overexploit the kelps and maintain urchin—coralline algae "barren grounds." In these areas kelps occur only where urchin access is restricted by wave exposure, ephemeral clumps of Desmarestia ligulata, and rarely, by a predator, the asteroid Meyenaster gelatinosus. In many areas the shallow distribution of Macrocystis was restricted by competition with the large fucoid Durvillaea antarctica. These relationships were evaluated by removal and addition experiments. Much more important than latitudinal relationships to both kelp and urchin distribution and abundance patterns were exposure gradients, from shores subject to strong oceanic swells to protected fjords. Transect data suggest that Loxechinus disappear from protected waters before Macrocystis. Thus in some semiprotected habitats there are very dense patches of kelps without grazers; kelp removal experiments in these habitats suggest strong density—dependent kelp interactions. In still more protected sites, the Macrocystis growth form changes, the plants appear to have low fertility, and there is very low recruitment. Summarizing, the Loxechinus population seems restricted by larval recruitment in the face of the Westwind Drift in the far south, perhaps by sedimentation or fresh water in protected fjords, and by human fishing in the north. The very low Loxechinus densities in the far south are correlated with large kelp forests in which the main kelp mortality results from drifting Macrocystis plants. The kelp populations appear limited by physical factors in the fjords and by Loxechinus grazing in most other areas.

Ecology of Kelp Communities

A taxonomic account of the world's kelps is far too complex for the scope of this review, but Mann (146) has characterized the world's kelp forests by their dominant genera. Laminaria species are found in many parts of the world but dominate both sides of the Atlantic and the coasts of China and Japan. Ecklonia dominates some kelp forests in Australia, New Zealand, South Africa, and a few other southern hemisphere localities. The giant kelp, Macrocystispyrifera, forms dense forests in many parts of the world including areas of the northeast Pacific, the southern shores of South America, many Southern Ocean islands, and isolated areas of South Africa, Australia, and New Zealand. Macrocystis pyrifera does not occur in the eastern Pacific area north of San Francisco, California; however, this northern region has the highest species diversity of kelps in the world (63), with Macrocystis integrifolia and Nereocystis, Alaria, Pterygophora, and Laminaria, among other conspicuous genera.