Characterisation of microsatellite loci in the habitat-forming kelp, Ecklonia radiata (Phaeophyceae, Laminariales)

Habitat forming algae play an important role in the ecology of temperate reefs worldwide. Despite this, our understanding of levels of gene flow within and among populations of algae is largely limited to studies on intertidal species; we know comparatively little about important habitat-forming subtidal algae. Here, we develop eight polymorphic microsatellite markers for the characterisation of population genetic diversity and structure in the subtidal kelp, Ecklonia radiata. This large macroalga is the most abundant habitat-forming kelp on the subtidal rocky reefs of temperate Australia and New Zealand where it forms extensive forests that support an astounding diversity of associated taxa.     

Characterisation of microsatellite loci in the subtidal habitat-forming alga, Phyllospora comosa (Phaeophyceae, Fucales)

Habitat-forming macroalgae play a central role in the ecology of temperate reefs worldwide but there exists a critical lack of knowledge about important processes such as dispersal and gene flow. Understanding dispersal and gene flow of habitat-forming seaweeds is particularly pertinent given that loss of habitat-forming algae is an increasingly prevalent problem worldwide. Here, we develop 10 microsatellite markers for the monotypic Phyllospora comosa, an important habitat-forming macroalga that has undergone massive declines on urbanised coastlines of Sydney, Australia. We characterise population genetic diversity and structure and estimate levels of dispersal and gene flow between the geographically isolated northern and southern populations in this subtidal macroalga.     

Restoring seaweeds: does the declining fucoid Phyllospora comosa support different biodiversity than other habitats?

Degradation and loss of natural habitats due to human activities is a main cause of global biodiversity loss. In temperate systems, seaweeds are a main habitat former and support extremely diverse communities, including many economically important species. Coastal urbanisation is, however, causing significant declines of key habitat-forming seaweeds. To develop successful management strategies such as seaweed habitat restoration, it is necessary to first determine what additional ecosystem values are likely to be added through restoration and to provide baseline data against which goals can be established and success can be measured. The habitat-forming fucoid Phyllospora comosa was once common on shallow subtidal reefs around Sydney, Australia’s largest city, but disappeared in the 1980s, coincident with heavy sewage outfall discharges. To provide the baseline data necessary for restoring and managing Phyllospora in areas from where it has disappeared, we quantified the community composition and abundance of fish and large invertebrates (abalone and sea urchins) in healthy Phyllospora habitats and compared them to those in Ecklonia radiata (the other major habitat-forming kelp in the region) as well as other common shallow subtidal habitats. Fish assemblage structure was similar between Phyllospora vs Ecklonia beds, but Phyllospora supported much greater numbers of abalone and urchins than any other habitat. This suggests that, in terms of some components of the biodiversity it supports, Phyllospora is functionally unique and not a redundant species. Restoring this seaweed will, therefore, also contribute to biodiversity rehabilitation by restoring unique faunal assemblages that are supported by Phyllospora, including economically important species.     

Towards Restoration of Missing Underwater Forests

Degradation of natural habitats due to urbanization is a major cause of biodiversity loss. Anthropogenic impacts can drive phase shifts from productive, complex ecosystems to less desirable, less diverse systems that provide fewer services. Macroalgae are the dominant habitat-forming organisms on temperate coastlines, providing habitat and food to entire communities. In recent decades, there has been a decline in macroalgal cover along some urbanised shorelines, leading to a shift from diverse algal forests to more simple turf algae or barren habitats. Phyllospora comosa, a major habitat forming macroalga in south-eastern Australia, has disappeared from the urban shores of Sydney. Its disappearance is coincident with heavy sewage outfall discharges along the metropolitan coast during 1970s and 1980s. Despite significant improvements in water-quality since that time, Phyllospora has not re-established. We experimentally transplanted adult Phyllospora into two rocky reefs in the Sydney metropolitan region to examine the model that Sydney is now suitable for the survival and recruitment of Phyllospora and thus assess the possibility of restoring Phyllospora back onto reefs where it was once abundant. Survival of transplanted individuals was high overall, but also spatially variable: at one site most individuals were grazed, while at the other site survival was similar to undisturbed algae and procedural controls. Transplanted algae reproduced and recruitment rates were higher than in natural populations at one experimental site, with high survival of new recruits after almost 18 months. Low supply and settlement success of propagules in the absence of adults and herbivory (in some places) emerge as three potential processes that may have been preventing natural re-establishment of this alga. Understanding of the processes and interactions that shape this system are necessary to provide ecologically sensible goals and the information needed to successfully restore these underwater forests.     

Disturbance and organization of macroalgal assemblages in the Northwest Atlantic

Large seaweeds are often structurally dominant in subtidal and intertidal rocky shore benthic communities of the N.W. Atlantic. The mechanisms by which these algal assemblages are maintained are surprisingly different in the two habitats. In the subtidal community, kelps are dominant space competitors in the absence of strong grazing interactions. In contrast, the large perennial seaweeds of intertidal zones (fucoids and Chondrus crispus) are competitively inferior to both sessile filter feeders and ephemeral, pioneer algal species. Intertidal seaweed beds are maintained by carnivory of whelks, which reduces filter feeder populations, and by herbivorous periwinkles which reduce ephemeral algal populations. Through most of the intertidal zone, disturbance, both biological and physical, dictates which species shall compete and equilibrium conditions obtain subsequently.The roles of subtidal consumers are quite different. Sea urchins are the major algal herbivores and these voracious animals maintain an equilibrium state in which large tracts of subtidal coralline pavement are kept free of kelp forests. Urchins do not seem to play a successional facilitative role for kelps in the way that periwinkles do for fucoids in the intertidal. Control of herbivore populations is thus a key to the maintenance of subtidal foliose algal beds. It is clear that parasitic amoebas can decimate sea urchin populations so that kelp forest dominance is assured. However, the importance of carnivory in limiting urchins in the subtidal community is unclear in the absence of appropriate manipulation experiments. It is possible that carnivorous decapods and fin fish control sea urchin populations and hence foliose algal abundance, but this must remain speculative. The seaweed-dominated state of the subtidal system is an alternative equilibrium condition to the urchin/coralline alga configuration. The structure of the kelp beds is relatively uniform in responding to frequent small-scale, infrequent large-scale, or no, disturbance.     

ABSENCE OF A LARGE BROWN MACROALGA ON URBANIZED ROCKY REEFS AROUND SYDNEY,AUSTRALIA, AND EVIDENCE FOR HISTORICAL DECLINE1

Loss of habitat‐forming algae is increasingly prevalent in temperate marine ecosystems. Here, we document absence of an important habitat‐forming macroalga, Phyllospora comosa (Labill.) C. Agardh, along an urbanized coast in New South Wales (NSW), Australia. Dense Phyllospora canopies were common on shallow sublittoral reefs north and south of Sydney. In contrast, we did not find a single individual along ～70 km of rocky coastline in the Sydney metropolitan region, despite historical evidence to suggest that it was very common half a century ago. Recolonization of this important habitat‐forming alga has not occurred on Sydney reefs despite improved water quality, protection of its habitat, and frequent long‐distance dispersal of Phyllospora wrack. While there are obvious limitations, historical information can be useful for identifying potential shifts in community structure to increase our understanding of contemporary ecological patterns.     

Patterns in shallow subtidal marine assemblages along the coast of New South Wales

Shallow subtidal areas of rocky reefs in central and southern New South Wales may best be described as a mosaic of habitats, the distributions of which are seemingly related to depth, wave exposure and a number of biological processes, particularly herbivory. The Fringe habitat is generally found only in the most shallow waters. Forests of the laminarian alga Ecklonia radiata are often found at intermediate depths. In deeper, or more sheltered water, sponges, ascidians and red algae are more abundant and the abundances of sea urchins and other invertebrate grazers decline. Overlying this broad-brush pattern are patches of crustose coralline algae (the Barrens habitat), the distributions of which are not clearly related to depth. Invertebrate herbivores, and sea urchins in particular, are abundant in the Barrens habitat. The Barrens habitat was most represented at the more southern locations. At the two most northern locations, reefs were shorter in length and dominated by ascidians (Pyura species).     

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.

     

Reproductive ecology of the black reef leatherjacket, <Emphasis Type="Italic">Eubalichthys bucephalus</Emphasis> (Monacanthidae) in temperate Australia

Reproductive ecology of the black reef leatherjacket, Eubalichthys bucephalus (Monacanthidae), was studied in temperate Australia. The fish lived in the same heterosexual pairs, and each pair shared a home range composed of rocky reefs and boulders where they reproduced and fed on sponges. Spawnings were conducted in pairs, and fertilized eggs were attached to the algae-like Bryozoa species. Reproductive ecology of E. bucephalus was compared to other pair swimming fishes and confamilial species, and ecological features were discussed.     

The foraging ecology of two sympatric gobiid fishes: importance of behavior in prey type selection

Synopsis The foraging ecology of two temperate marine gobies (Pisces: Gobiidae) was studied in rocky subtidal habitats off Santa Catalina Island, California. The bluebanded goby, Lythrypnus dalli, foraged from exposed ledges and fed on planktonic and benthic prey, although planktonic prey were more important in diets by number and weight. The more cryptic zebra goby, Lythrypnus zebra, remained hidden under rocks and in crevices feeding on benthic prey almost exclusively. The active selection of particular prey taxa from the two prey sources (water column and substratum), mediated by species-specific differences in foraging behavior, resulted in interspecific differences in type, number, size and weight of prey consumed. Interspecific differences in foraging ecology reflect the selection of prey most readily available to these fishes that occupy specific and fixed microhabitats within rocky reefs.     

Taxonomic composition and distribution of the echinoderms associations in the littoral ecosystems from the Colombian Pacific

This paper examines published information and gray literature about taxonomy and ecology of echinoderm species of the Colombian Pacific Coast. Unpublished collection data of specimens kept in the Marine Sciences Museum of the University of Valle are also considered. Sixty-six species are found in coastal ecosystems and shallow bottoms of ten geographical, coastal and insular localities of the Pacific coast of Colombia. Main habitats having echinoderms are: rocky cliffs and shores, coral reefs, sand beaches, mud substrates, mangroves, and shallow bottoms of mud, sand, gravel and rocks. Regular Echinoidea and Asteroidea are the most diverse and abundant groups, mainly in subtidal rocky shallow bottoms and coral reefs. Ophiuroidea are abundant below rocky boulders. Irregular Echinoidea are abundant on sand beaches. The relatively high number of species shows that this geographical area presents a high diversity of echinoderms compared with other tropical shallow and littoral zones of the world. Rocky substrates and coral reefs are the ecosystems with the highest numbers of echinoderm species and individuals. A conservation status assessment is difficult because the lack of periodical sampling and few data about deep zones. In general, the species reported in the last 25 years, have not experimented important changes in their populations, although in some specific places, populations may decrease because human activities in coastal areas increase sedimentation rates change some rocky substrates to mud or sand.     

Disturbance and reef topography maintain high local diversity in Ecklonia radiata kelp forests

Disturbance of competitive‐dominant plant and algae canopies often lead to increased diversity of the assemblage. Kelp forests, particularly those of temperate Western Australia, are habitats with high alpha diversity. This study investigated the roles of broad‐scale canopy loss and local scale reef topography on structuring the kelp‐dominated macroalgal forests in Western Australia. Eighteen 314 m² circular areas were cleared of their Ecklonia radiata canopy and eighteen controls were established across three locations. The patterns of macroalgal recolonisation in replicate clearances were observed over a 34 month period. Macroalgal species richness initially increased after canopy removal with a turf of filamentous and foliose macroalgae dominating cleared areas for up to seven months. A dense Sargassum canopy dominated cleared areas from 11 to 22 months. By 34 months, partial recovery of the kelp canopy into cleared areas had occurred. Some cleared areas did not follow this trajectory but remained dominated by turfing, foliose and filamentous algae. As kelp canopies developed, the initial high species diversity declined but still remained elevated relative to undisturbed controls, even after 34 months. More complex reef topography was associated with greater variability in the algal assemblage between replicate quadrats suggesting colonising algae had a greater choice of microhabitats available to them on topographically complex reefs. Shading by canopies of either Sargassum spp. and E. radiata are proposed to highly influence the abundance of algae through competitive exclusion that is relaxed by disturbance of the canopy. Disturbance of the canopy in E. radiata kelp forests created a mosaic of different patch types (turf, Sargassum‐dominated, kelp‐dominated). These patch types were both transient and stable over the 34 months of this study, and are a potential contemporary process that maintains high species diversity in temperate kelp‐dominated reefs.     

Ecology of marine algae on rocky shores and subtidal reefs in temperate Australia

Experiments in intertidal and subtidal rocky marine habitats in temperate Australia have identified the effects of various biological and physical factors on algal assemblages. In intertidal habitats, these involve micro- and macro-algae and grazing by gastropods. In subtidal habitats, interactions among micro- and macro-algae, echinoids, gastropods, micro-invertebrates and sessile invertebrates have been studied. Experimental studies on physical disturbances of algal assemblages have focussed on the effects of desiccation and storms. Most studies have not considered more than one spatial or temporal scale. Few have been concerned with seasonal influences and fewer have been concerned with variation from year to year. Most of the work lacks applicability to biogeographic comparisons. More experimental work across a variety of spatial and temporal scales is required to determine significant biological and physical processes affecting structure of algal assemblages across broad areas of temperate Australia.     

A subtidal transect in Jervis Bay,New South Wales

Long-term variations in the intertidal algal flora of the entire rock platform at Plantation Point, Jervis Bay, are described by May (1981). The study now reported presents similar long-term changes in the flora of a subtidal region of the same headland, observed within the same period of time. This first detailed report of subtidal macroalgal communities in New South Wales describes a several-year study of the benthic communities along a transect in the upper sublittoral region of a rocky headland at Plantation Point, Jervis Bay. Eighty-nine species of algae were recorded, five of which were previously unrecorded for New South Wales. The area studied is dominated by the large brown algae Ecklonia radiata and Phyllospora comosa, large areas of which were cleared periodically by storms. Turf, shade and crustose coralline algal communities also were present. Storms, seasonal variation and longer term changes all affected the abundance and distribution of the algal species growing along the transect and hence the floristic composition of the area.     

Identifying key habitats for the conservation of Bonelli's Eagle Aquila fasciata using radiotracking

Identifying the priority habitats of endangered species is crucial to implementing effective conservation actions. We characterize the key habitats used by Bonelli's Eagle Aquila fasciata, an umbrella and flagship species that is endangered in Mediterranean countries. We radiotracked 17 breeding individuals (10 males and seven females) in Catalonia (NE Iberian Peninsula) and used compositional analysis to determine the key habitats in home‐ranges of both sexes. The main habitats identified within the home‐range area were scrubland, coniferous forests, cropland, sclerophyllous forests, rock outcrops and urban areas, with little difference in habitat use between the sexes. Bonelli's Eagles preferred rocky habitats as breeding areas and scrubland as foraging areas, as these hold the highest abundance of their main prey, Rabbits Oryctolagus cuniculus and Red‐legged Partridges Alectoris rufa. Habitat selection varied seasonally in foraging areas: scrubland was the most preferred habitat type during the breeding season, whereas rocky areas were preferred during the non‐breeding season (although scrubland was also highly selected). Urban areas were avoided both as breeding and as foraging areas. Home‐range size was inversely correlated with the proportion of scrubland, suggesting that this is a key habitat for Bonelli's Eagle. To conserve this species effectively, policies that ensure the preservation of the cliffs used as breeding sites, as well as suitable management of the scrubland used for foraging, should be implemented in the areas inhabited by this species. The promotion of traditional land uses and management techniques that will enhance open areas in Mediterranean landscapes should in the future play an essential role in the conservation of Bonelli's Eagle in Mediterranean habitats.     

Marine reserves indirectly affect fine‐scale habitat associations,but not overall densities,of small benthic fishes

Many large, fishery‐targeted predatory species have attained very high relative densities as a direct result of protection by no‐take marine reserves. Indirect effects, via interactions with targeted species, may also occur for species that are not themselves targeted by fishing. In some temperate rocky reef ecosystems, indirect effects have caused profound changes in community structure, notably the restoration of predator–urchin–macroalgae trophic cascades. Yet, indirect effects on small benthic reef fishes remain poorly understood, perhaps because of behavioral associations with complex, refuge‐providing habitats. Few, if any, studies have evaluated any potential effects of marine reserves on habitat associations in small benthic fishes. We surveyed densities of small benthic fishes, including some endemic species of triplefin (Tripterygiidae), along with fine‐scale habitat features in kelp forests on rocky reefs in and around multiple marine reserves in northern New Zealand over 3 years. Bayesian generalized linear mixed models were used to evaluate evidence for (1) main effects of marine reserve protection, (2) associations with habitat gradients, including complexity, and (3) differences in habitat associations inside versus outside reserves. No evidence of overall main effects of marine reserves on species richness or densities of fishes was found. Both richness and densities showed strong associations with gradients in habitat features, particularly habitat complexity. In addition, some species exhibited reserve‐by‐habitat interactions, having different associations with habitat gradients inside versus outside marine reserves. Two species (Ruanoho whero and Forsterygion flavonigrum) showed stronger positive associations with habitat complexity inside reserves. These results are consistent with the presence of a behavioral risk effect, whereby prey fishes are more strongly attracted to habitats that provide refuge from predation in areas where predators are more abundant. This work highlights the importance of habitat structure and the potential for fishing to affect behavioral interactions and the interspecific dynamic attributes of community structure beyond simple predator–prey consumption and archetypal trophic cascades.     

Sponge community structure and anti-predator defenses on temperate reefs of the South Atlantic Bight

Predator–prey interactions can play a significant role in shaping the structure of both terrestrial and marine communities. Sponges are major contributors to benthic community structure on temperate reefs and although several studies have investigated how abiotic processes control sponge distributions on these reefs, the role of predation is less clear. We investigated the relationship between sponge predators and the distribution of sponges on temperate reefs in the South Atlantic Bight (SAB), off Georgia, USA. We documented sponge species richness and abundance, spongivorous fish density, and examined the ability of 19 sponge species to chemically and structurally deter predation by fishes. We also conducted reciprocal transplant experiments to determine if predation by fishes contributes to the observed zonation of sponge species on these reefs. Our surveys revealed two distinct sponge assemblages: one characterized by amorphous and encrusting sponge morphotypes colonizing the vertical, rocky outcroppings (scarp sponge community), while the other consisted of pedunculate, digitate, and arborescent growth forms occurring on the sediment-laden reef top (plateau sponge community). Spongivorous fishes were more abundant on the scarp than the plateau and scarp sponges were found to be more effective than plateau sponges at chemically deterring generalist fishes. In contrast, plateau sponges were more reliant on structural defenses: a result consistent with the higher spicule content of their skeletons. Transplant experiments confirmed that predators prevent some plateau sponges from colonizing the scarp even though they possess structural defenses. Thus, predation appears to play a role in shaping sponge community structure on SAB reefs by restricting those species lacking adequate chemical defenses to habitats where there is a paucity of spongivores.     

Effects of the El Niño southern oscillation on Turbo torquatus (Gastropoda) and their kelp habitat

Abstract Turbo torquatus (hereafter Turbo) were abundant and patchily distributed, especially in algal dominated habitats in shallow water (less then 10 metres) on rocky reefs in central New South Wales, Australia. Although the assemblage of algae was similar in barrens with and without crevices, Turbo were most abundant in crevices, suggesting that shelter was important. Experimental removal of the kelp canopy resulted in a great decrease in the number of Turbo. This was despite cleared patches containing more filamentous food algae, further highlighting the importance of shelter. The density of Turbo in kelp forests ranged from six to seven per square metre in times of abundance and less then one per square metre at other times over a 12‐year period. Variation in the resource base (i.e. food algae and kelp cover) was strongly linked to the abundance of Turbo. Abundance of Turbo was lowest when the density of adult kelp was low (less than 14 plants per square metre). The condition of kelp was severely affected during the 1997–1998 and 2002 El Niño events and was compromised 2–4 years after each event. These pulse events and related loss of shelter probably contributed to a decline in abundance of Turbo. This model was further supported when Turbo abundance increased with a subsequent increase in the density of kelp.     

The structure of a nearshore fish community of Western Australia: diel patterns and the habitat role of limestone reefs

Synopsis Extensive limestone reefs are a characteristic feature of much of the coastline of Western Australia, and potentially represent a major habitat feature influencing the structure of the coastal fish community. The structure and temporal dynamics of the fish fauna and its relationships to nearshore patch reefs and surrounding habitat near Dongara, Western Australia, were examined using (1) diel gill-netting and (2) quantitative rotenone sampling of enclosed areas of substratum. Long-term and day-to-day variability of the fauna was low. Dominant species of gill-net collections were either associated with reefs or occurred in similar abundances at both reefs and surrounding sand/seagrass flats. The overall abundance, number of species and biomass of netted fishes was higher around reefs. Rotenone collections of the more sedentary species showed a similar pattern, but suggested, however, that a simple reef versus surrounding sand and seagrass habitat comparison is complicated by the canopy-forming seagrass Amphibolis that occurs on reef tops. Time of day had an important effect on overall fish abundance and number of species, with peaks occurring at crepuscular periods. This reflected dusk and dawn activity peaks of a dominant species rather than overlapping activities of many diurnal and nocturnal species. Diel switches between reef-edge habitat and surrounding sand/seagrass flats were uncommon despite expectations (based on literature examples) that patch reefs would function primarily as sheltering habitats and surrounding non-reef areas act as foraging habitat. High catches at reef-edge sites suggest that the majority of fishes forage on or near limestone patch reefs. Fish densities of around 0.8 individuals per m^-2 of bottom on these Western Australian reefs are relatively high in comparison to visual census estimates obtained for temperate reef systems in South Australia and New Zealand, but similar to those obtained using comparable netting methods in temperate Australian seagrass systems.     

Ecological interactions in the provision of habitat by urban development: whelks and engineering by oysters on artificial seawalls

Abstract Increases in human population cause increased urbanization of most habitats, including the shoreline. This has many consequences for coastal environments, in particular the trend for artificial structures, such as seawalls, to replace natural habitats. Seawalls and natural shores support many of the common intertidal species, but others important on rocky shores are absent from or rare on many seawalls. The whelk Morula marginalba Blainville is an abundant and important predator on rocky shores of south‐eastern Australia, but is infrequently recorded on artificial substrata. In Sydney Harbour, where the Sydney rock oyster (Saccostrea glomerata Gould) was locally abundant, densities of M. marginalba on some seawalls appeared to be similar to those on rocky shores and to be larger than where there were few oysters. We sampled densities and sizes of whelks in four habitats, predicting and corroborating that: (i) on seawalls with many oysters, there would be more whelks than on seawalls with few oysters; (ii) where there are many oysters, densities of whelks would be similar on seawalls and rocky shores; and (iii) whelks would be larger where oysters were abundant. Growth and survival of whelks were measured to test hypotheses from the observed differences in size and density. Survival was greater in habitats with many oysters, which could explain differences in density, but size‐specific differences in survival could not explain differences in size among habitats. On seawalls but not on rocky shores, slower growth could explain the smaller size of whelks where there were few oysters. Seawalls provide important habitat for M. marginalba, but only via their indirect effects, mediated by oysters. These interactions cannot be predicted from those on natural rocky shores. Predicting how developed areas provide suitable habitat, either in management of conservation or in assessments of potential impacts clearly depends on understanding the roles of biogenic habitats.