The effects of an invasive habitat modifier on the biotic interactions between two native herbivorous species and benthic habitat in a subtidal rocky reef ecosystem

Range expanding species can have major impacts on marine ecosystems but experimental field based studies are often lacking. The urchin Centrostephanus rodgersii has recently undergone a southerly range expansion to the east coast of Tasmania, Australia. We manipulated densities of C. rodgersii and algal regrowth in urchin barrens habitat to test effects of the urchin on biotic interactions between two native herbivores, black-lip abalone (Haliotis rubra) and another urchin (Heliocidaris erythrogramma), and their benthic habitat. After 13 months, removals of only C. rodgersii resulted in overgrowth of barrens habitat by algae and sessile invertebrates. Densities of abalone increased (+92 %) only in patches from which C. rodgersii was removed and algal regrowth allowed. In contrast, densities of H. erythrogramma increased in all treatments (+45, +28, +25 %) in which C. rodgersii was removed, irrespective of the algal regrowth manipulations. These results suggest that C. rodgersii has a negative influence on the densities of abalone through competition for food and on densities of H. erythrogramma through competition for preferred habitat. Densities of abalone (+65 %) but not H. erythrogramma (+25 %), were lower in the patches from which C. rodgersii and canopy algae regrowth were removed relative to patches from which only C. rodgersii was removed (+92 and +28 %, respectively). These results suggest that C. rodgersii overgrazing of canopy-algae results in loss of structural complexity which could increase abalone susceptibility to predation, cause abalone to seek shelter in cryptic microhabitats and/or prevent their return to patches where canopy algae are absent. The ongoing spread of C. rodgersii and expansion of barrens habitat in eastern Tasmania will continue to negatively affect populations of these two native herbivores and their associated fisheries at a range of spatial scales. This example shows that habitat modifying species which become highly invasive can have disproportionate negative impacts on the structure and dynamics of the recipient community.     

Reproductive potential of a marine ecosystem engineer at the edge of a newly expanded range

Global climate change is leading to redistribution of marine species and altering ecosystem dynamics. Given recent poleward range extension of the barrens‐forming sea urchin Centrostephanus rodgersii (Diadematidae) from mainland Australia to Tasmania, there is a need to understand the population dynamics of this ecologically important species in the Tasmanian environment. This paper informs possible population dynamics of C. rodgersii in Tasmania by examining its reproductive ecology in this new environment. Reproductive periodicity (gonad index and propensity to spawn) was assessed bimonthly over 18 months at four sites in eastern Tasmania spanning ～2° in latitude. At all sites, C. rodgersii displayed a strong seasonal cycle in gonad production with major spawning occurring in winter (～August) at minimum annual water temperature. Gametes from Tasmanian C. rodgersii were viable as determined by fertilization and early development trials. However, development to the two‐arm stage at ～3 weeks was strongly dependent on water temperature across the 8–20 °C temperature range, with poor development occurring below 12 °C. The range of temperatures tolerated by Tasmanian C. rodgersii larvae was similar to that of larvae from its native New South Wales range, indicating that this species has not undergone an adaptive shift to the cooler Tasmanian environment. There was also no evidence for an adaptive shift in reproductive phenology. Importantly, coastal water temperatures in eastern Tasmania during the peak spawning in August fluctuate about the 12 °C larval development threshold. Recent warming of the eastern Tasmanian coast and further warming predicted by global climate change will result in an environment increasingly favourable for the reproduction and development of C. rodgersii.     

Grazing rates of Elysia tomentosa on native and introduced Caulerpa taxifolia

The marine alga Caulerpa taxifolia Vahl (C. Agardh), recognized globally as one of the most prolific non-native species introductions, has been introduced to several temperate locations from where it has since rapidly expanded. C. taxifolia is protected by a toxin (terpenoid) in its tissues that limits grazing by native herbivores. Sacoglossan molluscs of the genus Elysia are among the few organisms that graze C. taxifolia; however, little is known about their feeding ecology. In the current study, we quantified the grazing rates of Elysia tomentosa on native C. taxifolia (Moreton Bay, Queensland) and introduced C. taxifolia (Botany Bay and Lake Conjola, New South Wales). Grazing rates were similar at Moreton Bay sites and Botany Bay; however, they were significantly lower in Lake Conjola. At the maximum observed grazing rate, slugs ate their body weight in C. taxifolia (dry weight) every 18–24 h. Differences in grazing rates between locations may be explained by differences in C. taxifolia morphology rather than native or introduced origin. Handling editor: J. Padisak     

Survival of kelp adjacent to areas grazed by sea urchins in New South Wales,Australia

Abstract The sea urchin Centrostephanus rodgersii grazes areas of reef free of large brown algae (the barrens habitat). Survival of the kelp Ecklonia radiata adjacent to patches of barrens habitat was compared to that in the centre of kelp forests (centre) and edges of forests not adjacent to patches of barrens habitat (ungrazed). Estimates of rates of instantaneous mortality for tagged plants, as described by the slope of a negative exponential model (± 95% CI) were: barrens, 0.078 ± 0.004; centre, 0.051 ± 0.004 and ungrazed edge, 0.065 ± 0.007. Survival of plants was greatest in the middle of forests and least on the margins of patches of barrens habitat. A significant proportion of mortality in the barrens and centre positions was caused by herbivorous fish. When these plants were excluded from analysis there were no significant differences in survival between the barrens and ungrazed positions. It is concluded that C. rodgersii has little impact on the abundance of Ecklonia outside sharply defined boundaries.     

Chemical composition of polysaccharides of the red alga <Emphasis Type="Italic">Tichocarpus crinitus</Emphasis> (Tichocarpaseae) from different sites of Peter the Great Bay,Sea of Japan

A comparative analysis of the quantitative and qualitative composition of polysaccharides in the red seaweed Tichocarpus crinitus, collected at different sites of Peter the Great Bay in the Japanese Sea (Sivuch’ya Bay, Risovaya Bay and Sobol’ Bay) was carried out. The sites differed in their biotopic and anthropogenic characteristics. The main monosaccharides of the investigated algal polysaccharides were galactose and 3.6-anhydrogalactose, which are structural components of carrageenan The highest contents of protein and glucose were found in the KCl-soluble fraction of algae from Sobol Bay that were experiencing increased anthropogenic pressure. Fourier transform infrared spectroscopy revealed that the KCl-insoluble polysaccharide fractions of all investigated algae had an identical structure corresponding to κ/β-carrageenan, while the KCl-soluble polysaccharide fractions had differences in their structures. The content of heavy metals and micro- and macroelements in polysaccharide fractions differed among algae growing in areas with different biotopic and anthropogenic conditions.     

Seawater temperature and sublethal coral bleaching in Jamaica

Permanent study sites were established at 6 m, 12 m and 18 m on the West Fore Reef at Discovery Bay, Jamaica. Colonies of Montastrea annularis, Porites astreoides, Porites porites and Agaricia spp. were assessed for presence and extent of bleached tissue at two month intervals between October 1986 and September 1987. In 98% of all corals exhibiting a bleaching response, less than 25% of the colony appeared pale. In the remaining 2%, more than 25% of the tissue appeared pale. M. annularis, P. astreoides and Agaricia spp. showed a significant positive correlation between the percent of colonies exhibiting a partial bleaching response and seawater temperature. There was no significant difference in the percentage of colonies bleached between the three depths. M. annularis and Agaricia spp. exhibited a significantly higher percentage of colonies bleached than P. astreoides and P. porites. For M. annularis 15% of coral colonies studied showed 1–2 cm² randomly seattered patches of pale tissue which remained constant throughout the study. The partial bleaching patterns observed in this study were never lethal and are considered, in part, to be a response to seasonal variations in seawater temperature. Study location: Discovery Bay Marine Laboratory, P.O. Box 35, Discovery Bay, Jamaica, W. Indies     

A comparative study of epiphytic algal communities on two common genera of sea-grasses in eastern Australia

Fifty-seven epiphytic species were found to occur on the two sea-grass hosts Zostera and Posidonia in Botany Bay and Jervis Bay, N.S.W. Among the algal epiphytes on Posidonia australis several indicator species were identified and it was found that their relative frequency of occurrence can be used to differentiate sites within the two bays. These indicator species can be used also to classify a collection from an unknown site within the region, and their relative occurrences may provide a useful index for early detection of changes in the bay environments.     

Consistently outstanding recruitment of five species of fish to a seagrass bed in Botany Bay,NSW

Abstract Variability in abundance of fish associated with beds of the seagrass Zostera capricorni was documented at 16 sites in NSW. Samples were collected from each site by seine net every 3 months for 2.5 years. One site had significantly greater abundances of recruits of five species of economically important fish during all three recruitment seasons. This site was within a small, constructed harbour in Botany Bay. Between June and March of each year abundances of five species (Acanthopagrus australis, Rhabdosargus sarba, Girella tricuspidata, Achoerodus viridis and Meuschenia trachylepis) were up to 73 times greater than abundances at the other 15 sites. However, at other times during the year, there was no significant difference between this site and the 15 others. Understanding the processes that contribute to the success of this modified site as a recruitment sink should aid in increasing the potential of other areas as fish nursery habitat, and contribute to the management and productivity of fish populations.     

Invasion by a Japanese marine microorganism in western North America

The earliest record in western North America of Trochammina hadai Uchio, a benthic foraminifer common in Japanese estuaries, is from sediment collected in Puget Sound in 1971. It was first found in San Francisco Bay in sediment samples taken in 1983, and since 1986 has been collected at 91% of the sampled sites in the Bay, constituting up to 93% of the foraminiferal assemblage at individual sites. The species is also present in recent sediment samples from 12 other sites along the west coast of North America. The evidence indicates that T. hadai is a recent introduction to San Francisco Bay, and is probably also not native to the other North American sites. Trochammina hadai was probably transported from Japan in ships' ballast tanks, in mud associated with anchors, or in sediments associated with oysters imported for mariculture. Its remarkable invasion of San Francisco Bay suggests the potential for massive, rapid invasions by other marine microorganisms.     

Orchids with scarce occurrence records: The case of the endangered Botany Bay Bearded Greenhood

Poorly studied species are potentially under-prioritised by conservation programmes due to knowledge gaps presenting barriers to informing effective management strategies. The Botany Bay Bearded Greenhood, Pterostylis sp. Botany Bay, is an example of a poorly studied plant that is listed as endangered under both Commonwealth and New South Wales legislation. This study reports on archival surveys from 1998 to 2005 conducted at up to eight sites known to contain the Botany Bay Bearded Greenhood and follow-up surveys in 2022. The archival surveys found that the total population count ranged from 83 to 341 individuals. Mean numbers (± standard error) of seedlings, flowering individuals and individuals exhibiting capsule development recorded in the population were 43 ± 14, 33 ± 9 and 2 ± 1 respectively. The 2022 surveys did not detect the species. An area of potential habitat was derived from records in biodiversity databases, which determined a total historical extent of 1.38 ha restricted to the Kurnell Peninsula in Sydney, New South Wales. The priority next step is to gather contemporary data to confirm whether the Botany Bay Bearded Greenhood remains extant, which can be done by applied researchers, students, landholders and land managers, botanical practitioners and/or volunteers. For optimal species detection, we recommend undertaking formal surveys or opportunistic searches in historically known sites and replicating detection efforts across July–September periods to exploit seasonal flowering.     

Effects of resuspension and eutrophication level on summer phytoplankton dynamics in two hypertrophic areas of Lake Taihu,China

The composition of summer phytoplankton communities in two highly eutrophic areas of Lake Taihu, a large, shallow water body in China (area 2,338 km²; mean depth 2.0 m), was studied in relation to selected environmental variables. Both areas have multiple uses, including drinking water supply, fisheries, and recreation. The first area, Meiliang Bay, is much closer to central lake and subjected to wind-driven sediment resuspension, while the second, at Wuli Lake, is less affected by wave action but is considered more nutrient-rich due to its proximity to human inhabitation. By comparing two lake areas, we attempt to advance the understanding and management of different regions of shallow lakes, mainly differing in resuspension levels and eutrophication levels. A comparison of these two lake areas indicated a higher standing crop of phytoplankton in Wuli Lake than in Meiliang Bay. Canonic Correspondence Analysis indicated that nutrient status and sediment resuspension were the principal factors influencing phytoplankton composition in both areas. The dominant algal group in Meiliang Bay comprised immobile R-type strategists (Reynolds in Growth and reproductive strategies of freshwater phytoplankton, 1988), including filamentous diatoms and green algae (Aulacoseira granulate and Planctonema lauterbornii), and recruitment-beneficial RS-type strategists, mainly the colonial cyanobacteria (Microcystis spp.). The community of Wuli Lake was dominated by S-strategists, principally motile flagellates (Cryptomonas spp.) and C-strategists including small nonmotile centric diatoms and chlorococcal green algae.     

Phytoplankton communities in navigation pool no. 7 of the Upper Mississippi River

A study of the phytoplankton community dynamics in Navigation Pool No. 7 of the Upper Mississippi River was conducted from May through October, 1982. The objectives of this study were to estimate total standing crops, determine the taxonomic composition and examine the seasonal succession of the phytoplankton community. Four sampling sites were established: two in Lake Onalaska, a large backwater lake on the Wisconsin side of the main channel; one in the main channel near Dakota, Minnesota; and one in the main channel just upstream from Lock and Dam No. 7.The phytoplankton communities at all sampling sites were dominated by diatoms except during July and August when a bloom of blue-green algae was observed. The dominant diatoms from May through mid-July were Melosira italica, Stephanodiscus niagarae, Stephanodiscus hantzschii, Stephanodiscus astrea, and Synedra ulna. Aphanizomenon flos-aquae and Microcystis aeruginosa were the most prevalent blue-green algae during the mid-summer bloom. The diatoms Melosira italica and Melosira granulata were dominant in September and October. Lesser amounts of green algae, cryptomonads and euglenoids were also observed at various times of the sampling period.Total standing crops based on cell volume were usually greatest at the Lock and Dam No. 7 site. The maximum standing crop (10.4 mm³ 1^–1) was observed at the Lock and Dam No. 7 site on 4 September; the minimum standing crop (0.4 mm³ 1^–1) was observed at the eastern Lake Onalaska site on the same date. Concentrations of nitrogen, phosphorus, and silica remained at high levels throughout the study period and did not appear to limit phytoplankton standing crops.     

The relative influence of hypoxia, anoxia, andassociated environmental factors as determinants ofmacrobenthic community structure in aNorthern Gulf of Mexico estuary

Seasonal patterns (i.e., December 1986, and April and October 1987) in benthic macroinfaunal abundance,distribution, and taxa composition at 19 sites in Perdido Bay, AL/FL, are evaluated to assess the relative importance of environmental factors as determinants of community structure. A total of 46 taxa from five phyla were collected with diver-held bottom corers. Polychaetes were numerically dominant followed by crustaceans. Seventeen taxa co-occurred in samples during all three study periods. Maximum animal densities and taxa richness showed no statistically significant bay-wide seasonal pattern,however, a bay-wide trend was detected where these response parameters tended to be greater in April than December or October. Deeper upper bay stations were depauperate during December and October. Low dissolved oxygen (DO) largely explained the depauperate pattern. Mean taxa richness per core(10 cm dia.) ranged from 0.0 to 5.0, 1.2 to 4.6, and0.0 to 4.4 in December, April and October,respectively. Mean densities ranged from zero to 368,0 to 960, and 0 to 430 individuals per 0.1 m² in December, April, and October, respectively. Results of a three-season statistical regression model indicated that DO deficiency was a primary determinant of taxa richness (partial R ²: 0.27) but was less important in explaining animal densities (partialR ²: 0.16). For December, when additional environmental variables were measured, DO was supplanted by weight loss on ignition (R ²: 0.24)and the sediment C:N ratio (R ²: 0.44) as highest explanatory factors for taxa richness and density,respectively. Application of a benthic index of environmental condition indicated wide-spread ecological stress on the benthic macroinfaunal assemblages. This revised version was published online in July 2006 with corrections to the Cover Date.     

Herbivory and patch dynamics on rocky reefs in temperate Australasia: The roles of fish and sea urchins

Sea urchins are widely considered to be the major grazers in temperate subtidal systems, with herbivorous fish being browsers of minor importance. This paper reviews spatial and temporal patterns in these herbivores on rocky reels in temperate Australasia, with the aim of assessing their relative impacts on patch structure and dynamics. Herbivorous fishes are widespread and make up a significant numerical component the reel fish fauna. Sea urchins are also abundant, but not all geographic locations support actively grazing species. Both fish and sea urchins exhibit distinct patterns of distribution among depth strata. Within depth strata, all herbivores are restricted to (sea urchins) or forage preferentially in (fish) particular habitat patches, causing a mosaic of different feeding activities. These patches are either related to specific features of the habitat (e.g. Kelp patches, topography) or behavioural interactions. Foraging by sea urchins and demersal-nesting damselfishes is intense and persistent, whereas in the kelp-feeding fish Odax cyanomelas, foraging reaches greatest intensity at predictable locations during a few months of every year. Many fish and sea urchins consume some algae in preference to others. However, feeding preferences may determine the nature of the impact only in fishes. For sea urchins, preference may occasionally determine the order in which algae are consumed, but at high densities they consume all available macroalgae. Impacts of both types of herbivore on the abundance of algae have been recorded. Some sea urchins (e.g. Evechinus chloroticus, Centrostephanus rodgersii) appear to severely modify biogenic habitat structure by maintaining ‘barrens’ (areas devoid of macroalgae) over long periods. In contrast to this, the effects of fishes may be more transitory (e.g. seasonal impact of Odax cyanomelas on brown algae) or occur at smaller spatial scales (e.g. nest sites maintained by male Parma victoriae) Herbivorous and other fishes appear to respond to spatial patterns in algal distributions, rallier than having it major impact upon them. The relative effects of fish and sea urchins on the long-term dynamics of kelp forests are unknown, hut temporal patterns in herbivore abundance and behaviour, and algal demography arc urgent targets for research.     

Response of <Emphasis Type="Italic">Chrysaora quinquecirrha</Emphasis> medusae to low temperature

Because of their high abundance in Chesapeake Bay, Chrysaora quinquecirrha medusae may be an important reservoir of organic matter. The timing and location of the decomposition of biomass from medusae may have implications for carbon cycling in the bay. Our objective was to identify the cause of C. quinquecirrha medusa disappearance to better understand when and where decomposition occurs. A time series of visual surface counts and vertical net hauls in the Choptank River, a tributary of Chesapeake Bay, showed that as temperatures approached 15°C, C. quinquecirrha medusae disappeared from the surface, but persisted in net hauls until temperatures reached 10°C. In order to test whether medusae sink upon cooling, we exposed C. quinquecirrha medusae to low temperatures in large static tanks and measured their depth and pulsation rates twice daily for at least 6 days. This procedure was repeated three times through the 2008 jellyfish season. On average, individuals exposed to temperatures below 15°C were found deeper and pulsed slower than those in the warmer control tank. This suggests that low temperatures cause the medusae to sink before cooling to the limit of their physiological tolerance and may have implications for the deposition of organic matter associated with the seasonal disappearance of medusae from Chesapeake Bay.     

Production on burned and unburned sand prairies during drought and non-drought years

Biomass production was determined on burned and unburned sand prairie sites in Illinois during the 1986–89 growing seasons. Severe droughts characterized the 1988 and 1989 growing seasons with precipitation being at least 50% less in these two years than in 1985 and 1986. During the growing season following a fire, in drought and non-drought years, burned sites had higher total green biomass (all species), little bluestem (Schizachyrium scoparium) root and shoot biomass, and total grass and forb biomass production than the unburned sites. In 1988 and 1989, production on all sites was frequently significantly lower each month than it was in 1986 or 1987. The differences in productivity between burn and unburned sites were less pronounced during the drought years (1988–1989) than during the non-drought years (1986–87). Grass productivity (all species) declined considerably during drought years. In contrast, forb productivity did not vary significantly among years. Despite the drought, productivity of all species and little bluestem (root and shoot combined) was best predicted by the burn condition of the sites. Unlike many studies where drought alone can have significant effects on productivity, this study shows that on sand prairies the burn condition of sites, or burning regimes, and associated influences, can have a greater substantial impact on productivity than drought. Moisture deficits due to drought may, however, have longer term effects than those detected during the span of this study.     

Recovery of the coral Montastrea annularis in the Florida Keys after the 1987 Caribbean “bleaching event”

Many reef-building corals and other cnidarians lost photosynthetic pigments and symbiotic algae (zooxanthellae) during the coral bleaching event in the Caribbean in 1987. The Florida Reef Tract included some of the first documented cases, with widespread bleaching of the massive coral Montastrea annularis beginning in late August. Phototransects at Carysfort Reef showed discoloration of >90% of colonies of this species in March 1988 compared to 0% in July 1986; however no mortality was observed between 1986 and 1988. Samples of corals collected in February and June 1988 had zooxanthellae densities ranging from 0.1 in the most lightly colored corals, to 1.6x10⁶ cells/cm² in the darker corals. Minimum densities increased to 0.5x10⁶ cells/cm² by August 1989. Chlorophyll-a content of zooxanthellae and zooxanthellar mitotic indices were significantly higher in corals with lower densities of zooxanthellae, suggesting that zooxanthellar at low densities may be more nutrientsufficient than those in unbleached corals. Ash-free dry weight of coral tissue was positively correlated with zooxanthellae density at all sample times and was significantly lower in June 1988 compared to August 1989. Proteins and lipids per cm² were significantly higher in August 1989 than in February or June, 1988. Although recovery of zooxanthellae density and coral pigmentation to normal levels may occur in less than one year, regrowth of tissue biomass and energy stores lost during the period of low symbiont densities may take significantly longer.     

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.     

Abundance and Spread of the Invasive Red Algae, <Emphasis Type="Italic">Kappaphycus</Emphasis> spp., in Kane’ohe Bay,Hawai’i and an Experimental Assessment of Management Options

Several species of Kappaphycus were intentionally introduced into Kane’ohe Bay, Hawai’i in the 1970s. Subsequent research has demonstrated that these algae have spread rapidly throughout the bay and can be found in a variety of reef habitats overgrowing and killing corals. This study was conducted to (a) quantify Kappaphycus spp. abundance both spatially and temporally, and (b) investigate control options including manual removal and the use of biocontrol agents. Kappaphycus spp. distribution has increased in the bay over the period between surveys conducted in 1999 and 2002, with variation among reefs. The biomass of Kappaphycus spp. removed, and the amount of time required to manually remove them from the reef varied with habitat type, but in all cases amounted to at least 10 kg/m² requiring almost 2 person-hours to clear 1 m². Re-growth of the algae following their removal was rapid at most sites, likely due to the experimentally demonstrated ability of the algae to re-grow from minute attachment points and the low palatability of the algae to native herbivorous fishes. The native sea urchin, Tripneustes gratilla, reduced the biomass of Kappaphycus spp. in small experimental enclosures and may be a useful biocontrol agent. Because Kappaphycus spp. are still spreading in Kane’ohe Bay and can overgrow over 50% cover on some reefs, we recommend that rapid management action be taken to prevent further damage and spread to other Hawaiian coral reefs.