The effects of trophic interactions and spatial competition on algal community composition on Hawaiian coral reefs

Much of coral reef ecology has focused on how human impacts change coral reefs to macroalgal reefs. However, macroalgae may not always be a good indicator of reef decline, especially on reefs with significant sea urchin populations, as found in Kenya and Hawaii. This study tests the effects of trophic interactions (i.e. herbivory by fishes and sea urchins) and spatial competition (between algae and coral) on algal community structure of reefs surrounding two Hawaiian Islands that vary in their level of human impacts. Reef‐building organisms (corals and crustose coralline algae) were less abundant and turf algae were more abundant on Maui as compared to Lanai, where human impacts are lower. In contrast to previous studies, we found no evidence that macroalgae increased with human impacts. Instead, low turf and macroalgal abundance were best explained by the interactive effects of coral cover and sea urchin abundance. Fishing sea urchin predators appeared to have cascading effects on the benthic community. The absence of sea urchin predators and high sea urchin densities correspond to a disproportionately high abundance of turf and crustose coralline algae. We propose that high turf algal abundance is a better indicator of reef decline in Hawaii than high macroalgal abundance because turf abundance was highest on reefs with low coral cover and few fish. The results of this study emphasize that understanding changes in community composition are context‐dependent and that not all degraded reefs look the same.     

Further refutation of the primary-secondary settlement hypothesis for the brown mussel Perna perna

The primary-secondary settlement hypothesis, that mussels first settle in algae and then move to mussel beds, was rejected as the only mode of recruitment for the brown mussel Perna perna in a previous study at one location over one year on the south coast of South Africa. We investigated recruitment of P. perna into mussel beds and algal turfs over a five-year period (1995–2000) at 3–4 sites at each of four locations on the South and East coasts. Attachment to the two substrata was significantly temporally synchronous at two of the four locations. The disparity among locations could be due to differences in the algal species present or to differences in the importance of turf algae as a facilitator of recruitment. At Zululand, on the East Coast, attachment to mussel beds and algae was measured monthly and found not to be temporally synchronous. At this location, primary settlement into algae was significantly correlated with an increase in the density of juveniles in the mussel beds 2–3 months later, indicating that turf algae can act as irregular but important facultative facilitators of mussel recruitment, supplementing direct input into the mussel beds. However, as amounts of settlers and recruits in mussel beds exceeded those found in algal turfs most years and places, the primary-secondary settlement hypothesis is inapplicable to P. perna under most circumstances.     

Feeding behavior in Caribbean surgeonfishes varies across fish size,algal abundance,and habitat characteristics

Feeding behavior of coral reef fishes often determines their species‐specific ecological roles. We studied the two most common Caribbean surgeonfishes (Acanthurus coeruleus and Acanthurus tractus) to examine their species‐specific grazing rates and feeding preferences and how these differed with environmental context. We quantified the feeding activity of both surgeonfishes at four spur and groove reefs in the Florida Keys, USA, that varied in fish abundance, rugosity, algal community composition, and sediment loading. Overall, A. tractus fed twice as fast as A. coeruleus. Both species selected for turf algae but avoided feeding on turf algae that had become laden with sediment. Selectivity for upright macroalgae was more complex with A. tractus targeting Dictyota spp., while A. coeruleus avoided Dictyota spp. relative to the alga's abundance. Both species selected for epiphytes growing on other organisms such as macroalgae and sponges. However, several of these feeding patterns changed with ontogeny. For example, larger individuals of both species fed more frequently on long, sediment‐laden algal turf and less frequently on Dictyota spp. compared to smaller sized individuals. In addition, A. tractus also increased its preference for upright calcareous algae as they attained larger sizes. Overall, the disparity in feeding preferences of surgeonfishes likely indicates subtle differences in species‐specific ecological roles. Both A. coeruleus and A. tractus likely prevent development of turf algae and thus maintain algal communities in the early stages of succession. Additionally, A. tractus may also help reduce macroalgal abundance by targeting common macroalgal species.     

Growth and gonad production of the sea urchin Hemicentrotus pulcherrimus in the fucoid bed and algal turf in northern Japan

To clarify the differences in the growth and gonad size of the sea urchin Hemicentrotus pulcherrimus among algal sere, the study was conducted in June and July, and September 1998 at three fucoid beds in Oga and at three algal turfs in Hachimori, Akita Prefecture in northern Japan. The most rapid growth was observed in a large perennial fucoid bed at the climax stage. Growth in a small perennial Chondrus ocellatus‐dominated bed in algal turfs in the seral stage was then high. The slowest growth was observed in the small perennial Dictyopteris divaricata‐ and Laurencia spp.‐dominated beds which are known to possess chemicals which act as feeding deterrents against the sea urchins. The gonad index (gonad wet weight × 100/body wet weight) at a fucoid bed was high where standing crops exceeded 3 kg·m^?2. The gonad index in the Laurencia bed was lower than those at fucoid beds. These results suggest that growth and gonad production are affected by algal sere and differ among species of small perennial algae in the seral stage with or without chemical defense.     

Evaluating the effects of protection on two benthic habitats at Tavolara-Punta Coda Cavallo MPA (North-East Sardinia, Italy)

In this paper, two benthic habitats have been investigated in a fully protected site and two control sites at the Tavolara-Punta Coda Cavallo marine protected area (MPA) (NE Sardinia). Overall, a protection effect on the benthic assemblages was highlighted in the shallow subtidal (5 m deep) rather than at intertidal algal turf habitat. Structure of assemblages at the shallow subtidal habitat is different in the fully protected site vs. controls, while this was not true for the intertidal habitat. At the subtidal, this finding is probably linked to indirect effects due to an increase of consumers in the protected site (e.g., sea urchins), while the lack of direct impacts in the intertidal at control sites is indicative of very similar assemblages. Cover of encrusting algae was significantly higher at the subtidal protected site suggesting a possible higher grazing pressure. Possible causes underlying the inconsistency of results obtained between habitats include the possibility that trophic cascade effects have a different influence at different heights on the shore. The need to estimate the interconnection among benthic habitats through trophic links is also highlighted to provide an estimate of the vulnerability to protection of various habitats.     

宁波海岛潮阎带生态学研究──Ⅰ．种类组成与分布

本文研究了宁波海岛潮间带的生物种类组成与分布规律。生物种类以软体动物（１１３种）、甲壳动物（６５种）、多毛类（３６种）及藻类（３０种）为主。生物区系性质以广温广布种和亚热带种为主。不同底质潮间带中生物种类数不同，泥沙滩多于岩礁多于沙滩。岩礁潮间带生物种类数的水平分布为由近岸向外海增加。泥沙质潮间带生物种类数的水平分布为由北部向南部增加。沙质潮间带的生物种类数极其稀少。垂直分布与潮汐和底质有关。     

Population variations in the grazing turbinid Lunella smaragda (Mollusca: Gastropoda)

The grazing turbinid gastropod Lunella smaragda was sampled regularly over 3.5 y from precise sites of different microtopography and height on the platform shore at Goat Island Beach near Leigh, Northland, New Zealand. Growth is linear for over 3 y, and the year‐classes distinct. The position of the different size‐classes is related to both the shelter afforded by the microtopography, and to the height on the shore. The populations in the mid‐eulittoral turf flats, low eulittoral bare rock areas, and the sublittoral fringe are distinct, and there is a general movement down the shore with age and size. Wave action apparently dislodges the animals from higher areas when they grow to a critical size and transports them to sites lower on the shore, where wave disturbance is less. Field experiments with marked animals and laboratory studies with a wave tank confirm that the wave‐effected distribution is size related. However measurements showed that the ratio of foot attachment area to the shell area presented to the wave does not vary with animal size. The possible benefits of wave dislodgment and wave‐effected distribution are considered.     

大亚湾潮间带底栖生物种类组成与分布

于１９８８年９月－１９８９年１月在大亚湾潮间带采集底栖动物标本，经分类研究发现，共有５４７种，其中藻类９１种，多毛类１２０种，软体动物２０９种，甲壳动物８３种，棘皮动物１９种，其他动物２５种。研究表明，其区系性质以热带亚热带暖水种占多数，有许多热带种发展成优势种。在水平分布上，岩石相种类（３１６）＞沙滩种数（２２２）＞红树林泥滩（５１）；在垂直分布上，中潮区种数（３９８）＞低潮区（２２１）＞红树林     

A Comparison Among Assemblages in Areas Invaded by Caulerpa taxifolia and C. racemosa on a Subtidal Mediterranean Rocky Bottom

Abstract.  This study compares the structure of Mediterranean macroalgal assemblages invaded by Caulerpa taxifolia and C. racemosa . Assemblages in areas colonized by the two algae and in reference areas were sampled and analyzed for 2 years. Significant differences were recorded both between reference and invaded areas and between areas invaded by different Caulerpa species. Macroalgal assemblages colonized by C. racemosa were more separated from references than those colonized by C. taxifolia . Differences between assemblages colonized by C. racemosa and the others decreased during the alga's period of vegetative rest and increased at the last sampling date. While erect and turf species showed similar patterns in invaded areas, covers of encrusting algae were lower in C. racemosa areas than in C. taxifolia areas.     

Spatial Variation in the Structure of Kelp Forest Communities Along a Wave Exposure Gradient

Abstract. Four sites were sampled in kelp (Macrocysiis pyrifera) forests occupying rocky bottom habitats along a wave exposure gradient in central California. Consistent betwecn-site differences were found in the three major structural elements - the surface canopy, the undcrstory assemblage, and the ground cover/turf assemblage - of kelp forest communities. Macrocysiis pyrifera was found at all four sites. Nereucyslis tuelkeana only at the most exposed site. The understory kelps Laminaria setchellii and Pterygopltora californica were also characteristic of exposed sites. Articulated coralline algae were more abundant at exposed sites than protected, while fleshy red algae showed the opposite pattern. All four study sites were located along 8.5 km of coastline, and thus were assumed to have available to them the same species pool for colonization. The substrate composition was the same and the amount of unconsolidated substrate was similar at all four sites. We suggest that exposure to wave-generated water motion, through its influence on the surface canopy and therefore on the amount of light reaching the bottom, is responsible for these between-site differences.     

Design and performance of headland bays in Chesapeake Bay,USA

The use of headland-breakwater systems along the shore of Chesapeake Bay began in the early 1980s. Properly designed and installed headland breakwaters with beach fill and wetlands plantings provide shore protection and create a “full” coastal profile of beach/backshore/dune which enhances habitat. They create a tertiary buffer for upland runoff and groundwater and provide access and recreation. The wetland grasses also create an erosion resistant turf. The coastal profile accommodates environmental permitting requirements of habitat enhancement for shore protection structures.     

Fouling assemblages on offshore wind power plants and adjacent substrata

A significant expansion of offshore wind power is expected in the near future, with thousands of turbines in coastal waters, and various aspects of how this may influence the coastal ecology including disturbance effects from noise, shadows, electromagnetic fields, and changed hydrological conditions are accordingly of concern. Further, wind power plants constitute habitats for a number of organisms, and may locally alter assemblage composition and biomass of invertebrates, algae and fish. In this study, fouling assemblages on offshore wind turbines were compared to adjacent hard substrate. Influences of the structures on the seabed were also investigated. The turbines differed significantly from adjacent boulders in terms of assemblage composition of epibiota and motile invertebrates. Species number and Shannon–Wiener diversity were, also, significantly lower on the wind power plants. It was also indicated that the turbines might have affected assemblages of invertebrates and algae on adjacent boulders. Off shore wind power plant offer atypical substrates for fouling assemblages in terms of orientation, depth range, structure, and surface texture. Some potential ecological implications of the addition of these non-natural habitats for coastal ecology are discussed.     

渔山列岛潮间带底栖海藻生态的初步研究

本文根据１９８７年１１月至１９８９年５月渔山列岛（２８°５３′Ｎ，１２２°１６′Ｅ）潮间带底栖海藻调查资料，分析了该海区潮间带的海藻种类、垂直分布及生物量的季节变化规律，并将本区海藻生态特点与临近海区作了比较。     

饵料对毛蚶(Scapharca subcrenata)不同发育期幼虫脂肪酸组成的影响

通过投喂不同藻类饵料,利用GC-MS法,研究饵料对毛蚶浮游幼虫体内脂肪酸组成变化的影响.结果表明,不同饵料对幼虫生长和附着变态速度的影响存在差异,混合饵料组效果最佳;饵料种类和脂肪酸含量对幼虫体内脂肪酸组成和其生长存在显著影响,且体内不饱和脂肪酸含量随着幼虫发育呈下降趋势.在众多脂肪酸中,DHA和EPA对幼虫存活有直接关系,而AA及饱和脂肪酸含量对幼虫生长存在显著影响,ω-3与ω-6脂肪酸含量比值也能反映幼虫生长和变态速度.     

Removal of intertidal algae by herbivores in experimental frames and on shores near Auckland

When grazing animals are excluded from any intertidal area algae grow unchecked. In screened frames on the shore where predation experiments are in progress such growth is undesirable. A number of shore herbivores were tested for their ability to remove such algal growth and prevent its reformation without interfering with the main experiments. Only the browsing species Lunella smaragda and Melagraphia aethiops were capable of removing large algal growths, and these species were acceptable food for some of the predatory species. The complex inter‐relationship between grazing species and shore zonation at several places near Auckland is discussed.     

Shore exposure affects mussel population structure and mediates the effect of epibiotic algae on mussel survival in SW Ireland

On rocky shores, the relative importance of abiotic and biotic processes that regulate community structure are thought to vary with levels of shore exposure. This can lead to characteristic features found on sheltered and exposed shores. This study identified differences in the population structure of mussels on exposed and sheltered rocky shores on Atlantic coasts of south-west Ireland. Direct interactions between epibiotic algae and their host mussels were also examined to test if potential effects varied with shore exposure. Mussel beds on sheltered shores were less dense and comprised larger mussels with greater rates of individual survival and growth than those on exposed shores. The results of a field experiment showed that algal epibionts had a negative effect on mussel survival on sheltered shores but not on exposed shores. Surprisingly, the presence of algal epibionts had no effect on mussel growth on either shore type. These findings contrast with those of previous studies. The effects of shore exposure and algal epibionts on mussels may be species-specific and may interact with other factors across different regions. This study shows that predictions of effects of exposure on mussel populations and their epibionts should only be based on specific experimental evidence and cannot be generalised across regions.     

Breeding biology and microhabitat utilization of the intertidal isopod Idotea granulosa Rathke,in the Irish Sea

The life history and distribution of the intertidal isopod Idotea granulosa were investigated at five rocky shore biotopes in the Isle of Man.I. granulosa breeds throughout the year in the Irish Sea. The breeding activity is highest in the early summer after the sexual maturation of the overwintered animals. At that period about 4% of the females were infested by Clypeoniscus sp. (Isopoda) which destroys the brood. A small proportion of the juveniles released in the early summer mature and breed in the autumn. In the winter Idotea populations consisted of juveniles, immature adults and old individuals which produce another brood. These large sized animals die off before the summer. Consequently, the age and size of the breeding I. granulosa fluctuates seasonally.The number of eggs is linearly related to the female length. The fecundity is highest in the spring and lowest in the autumn in all female size classes.I. granulosa inhabits an array of structurally different intertidal algae including the filamentous Cladophora rupestris, understory turfs Gigartina stellata, Laurencia pinnatifida and Corallina officinalis and the fucoids Fucus serratus and Ascophyllum nodosum. The distribution pattern of I. granulosa in examined intertidal communities is modified by the physiognomy of the algal microhabitats, by seasonal and spatial variation in wave agitation and by the breeding cycle of the population itself.Both the life history characteristics and distribution patterns are explained as adaptations to the spatially and temporally heterogeneous intertidal shores.