Preferred Algae Research Articles

Chironomus calligraphus Goeldi, 1905 (Diptera: Chironomidae) Larvae: Feeding Habits, Growth, and Maturation.

Chironomus calligraphus Goeldi, 1905 has a flexible life cycle with several generations per year, which can be modified by the quality and type of food. To categorize the functional feeding group of the species, food preference was evaluated in larval instars III and IV, through laboratory experiments and gut content analysis. To evaluate the influence of the type of food on the duration of the life cycle growth and maturation, experiments were carried out. Instar III preferred conditioned leaves and animal food, while instar IV preferred algae and fine particulate organic matter. Gut contents of instar IV collected from streams showed increased consumption of fine particulate organic matter than other items. All these observations allowed us to assign the species to the gatherer collector group. The duration of the life cycle varied between the different types of foods, being the conditioned leaves, animal food, and algae the items that caused a greater growth in the larvae and a faster passage to the pupal instar. Our results suggest that the opportunistic feeding behavior of C. calligraphus allows it to use several different foods, but the quality of the foods influences the length of the life cycle and this contributes to its plasticity.

Ecological Role of Cyprideis torosa and Heterocypris salina (Crustacea, Ostracoda) in Saline Rivers of the Lake Elton Basin: Abundance, Biomass, Production, Fatty Acids.

Saline rivers are highly productive ecosystems in arid regions. The meiobenthic community (bottom meiofauna) and its dominant representatives are one of the least studied components of these aquatic ecosystems. Ostracods Cyprideis torosa and Heterocypris salina are major consumers among the species of bottom meiofauna in saline rivers flowing into the hyperhaline Lake Elton (Volgograd Region, Russia). We estimated the abundance, biomass and production of C. torosa, the dominant species at the mouth of the polyhaline Chernavka River (average salinity is ~30 g l-1), and H. salina, the dominant species at the mouth of the mesohaline Bolshaya Samoroda River (~13 g l-1), in spring (May) and summer (August). Additionally, we studied the composition and content of fatty acids of the ostracods and their potential food sources (bottom sediments with bacterial-algal mats). We found that the abundance and biomass (wet weight with shells) of C. torosa in the Chernavka River and H. salina in the Bolshaya Samoroda River reached 3.5 × 106 ind. m-2 and 117 g m-2, and 1.1 × 105 ind. m-2 and 12 g m-2, respectively. The first species formed on average about 85% of the total abundance and 96% of the total biomass of the meiobenthos, and the second one, about 13% and 31%, respectively. The daily production of C. torosa and H. salina can reach 249 and 36 mg m-2 ash-free dry weight, respectively. The results indicate that these species may play an important role in the total flow of matter and energy in the studied habitats. Based on the fatty acid (FA) composition of the ostracods and their food sources, it was found that C. torosa mainly consumed diatoms, while H. salina preferred bacteria, cyanobacteria, and green algae. Differences between the species were greater than differences between the bottom sediments from the rivers. It may mean that the ostracods selectively consumed different food items that may be related to the different nutrient requirements of the species. Seasonal changes in the FA compositions of the ostracods were higher than in their food sources (bottom sediments), which also indicates selective feeding of the species.

Isolation of Chamigrene Sesquiterpenes and Absolute Configuration of Isoobtusadiene from the Brittle Star Ophionereis reticulata.

The chemical study of the Brazilian brittle star Ophionereis reticulata led to the isolation of three chamigrene sesquiterpenes, including the partially characterized isoobtusadiene (1), its unreported acetyl derivative (2), and the known (+)-elatol (3). The complete elucidation of the structures 1 and 2 was accomplished by 1D and 2D NMR spectroscopy. The first assignment of the absolute configuration of the isoobtusadiene skeleton is suggested as 6S,9R,10S on the basis of the NMR analysis of the Mosher's ester derivatives of 1 and the ECD study of the acetyl derivative 2. Chamigrenes are typical constituents of Laurencia red algae. O. reticulata is a predator with a preference for algae. Thus, the origin of these metabolites can be likely ascribed to diet.

English

The Mankessim Reservoir supports a thriving cichlid fishery that provides both financial gain and nutritional value to the people. Fish samples of Hemichromis fasciatus, Tilapia zillii and Sarotherodon melanotheron were obtained from artisanal fishermen by gill nets (10 m long and 1.5 m deep, 3, 6 and 12 mm mesh) and cast nets (25 mm mesh and 2.5 m radius) in the reservoir (5018''52.08'''N 1001''45.08'''W) from September 2011 to August 2012. Physicochemical parameters were measured in situ and nutrients level determined by the spectrophotometric method. Stomach contents were analyzed using the frequency of occurrence and “points” method and condition was evaluated by means of Fulton condition index. As a result, food resources exploited by T. zillii and S. melanotheron were highly similar. T. zillii fed more on plant material and benthic invertebrates with diatoms (Navicula spp., Pinnularia nobilis, Frustulia rohomboides, Stephanodiscus cymbella, Melosira spp., Gyrosigma spp., Tabellaria sp. and Diatoma sp.) blue green (mainly Ulothrix sp. Oscillatoria spp., Anabaena spp., and Microspora sp.) and desmids being the most preferred algae. S. melanotheron ingested more of debris, and fed on considerable amount of algae and benthic invertebrates mainly chironomid larvae and oligochaetes showing a high level of trophic flexibility. The three cichlids showed very good condition (1.75 ± 0.11 - 1.98 ± 0.40). This could probably be as a result of the observed favourable environmental conditions as all physicochemical parameters were within acceptable limits for their sustenance except for phosphates (1.68 ± 0.04 mg/L to 5.37 ± 0.02 mg/L).   Key words: Hemichromis fasciatus, Tilapia zillii, Sarotherodon melanotheron, Cichlids, Physicochemical parameters, Condition factor

Anatomical description of the Cortés damselfish Stegastes rectifraenum (Perciformes: Pomacentridae). Key structures for omnivore feeding

Pomacentridae is one of the most abundant fish families in coral and rocky reefs of tropical and temperate waters. Stegastes rectifraenum (Gill, 1862), as other members of the genus, is territorial and actively farm algae on its territory, helping in the regulation of the algal community structure and the reef productivity. It is endemic and one of the most abundant species along the Mexican Pacific coast. Even with its strong relationship with algae, this species is omnivorous. In this analysis, we present the first complete anatomical description of a species of Pomacentridae, focusing in one research question: which structures allow S. rectifraenum to have an omnivorous diet? Through the analysis of the skeletal, muscular and digestive systems, the anatomy of the species was described. The complex anatomy of S. rectifraenum shows a set of characters previously described for grazers (mandibular muscles), herbivorous (mandibular teeth), omnivorous with preference for algae (general skull osteology) and zooplanktivorous species (intestine shape and pharyngeal teeth). According to our results, S. rectifraenum is a grazer, omnivorous with preference for algae. Finally, the key character that facilitates S. rectifraenum access to a wider range of resources is the shape of the pharyngeal teeth, which can effectively grind, fasten and tear.

Preference of the herbivorous marine teleost Siganus canaliculatus for different macroalgae

The decomposition of a large amount of unexploited macroalgal resource along the coast of China often results in heavy environmental pollution. In order to pave a way of using macroalgae as the dietary ingredient of rabbitfish Siganus canaliculatus, one of a few farmed herbivorous marine teleosts in China, its preference (feeding selectivity) for different macroalgae was determined in this study. Seven seaweed species abundantly inhabiting the coast of east Guangdong Province were exposed simultaneously to rabbitfish juveniles in laboratory (multiple-choice feeding) with their content and absolute intake assayed. It was found that the most preferred algae were Ulva prolifera, Gracilaria lemaneiformis and Chaetomorpha linum, less preferred algae were U. pertusa and Porphyra haitanensis, and least preferred ones were Sargassum fusiforme and Corallina sessilis. Such an order did not change when one to four relatively preferred seaweeds were removed. The preferred seaweeds were richer in protein and soluble sugar thus higher in energy than the least preferred. In addition, this fish was found to favor filamentous and flat algae rather than calcified ones. Accordingly, the richness of nutrients and morphological characteristics determined the preference of S. canaliculatus for tested macroalgae.

Feeding Preferences and the Nutritional Value of Tropical Algae for the Abalone Haliotis asinina

Understanding the feeding preferences of abalone (high-value marine herbivores) is integral to new species development in aquaculture because of the expected link between preference and performance. Performance relates directly to the nutritional value of algae – or any feedstock – which in turn is driven by the amino acid content and profile, and specifically the content of the limiting essential amino acids. However, the relationship between feeding preferences, consumption and amino acid content of algae have rarely been simultaneously investigated for abalone, and never for the emerging target species Haliotis asinina. Here we found that the tropical H. asinina had strong and consistent preferences for the red alga Hypnea pannosa and the green alga Ulva flexuosa, but no overarching relationship between protein content (sum of amino acids) and preference existed. For example, preferred Hypnea and Ulva had distinctly different protein contents (12.64 vs. 2.99 g 100 g−1) and the protein-rich Asparagopsis taxiformis (>15 g 100 g−1 of dry weight) was one of the least preferred algae. The limiting amino acid in all algae was methionine, followed by histidine or lysine. Furthermore we demonstrated that preferences can largely be removed using carrageenan as a binder for dried alga, most likely acting as a feeding attractant or stimulant. The apparent decoupling between feeding preference and algal nutritive values may be due to a trade off between nutritive values and grazing deterrence associated with physical and chemical properties.

Contribution of biofilm-dwelling consumers to pelagic-benthic coupling in a large river

1. Over the course of this 17-month study, we assessed the potential loss of plankton (bacteria, algae, heterotrophic flagellates) to consumers (ciliates and rotifers) within mature biofilms established on natural substrata exposed to the main current of the River Rhine (Germany). Once a month, in flow cells in a bypass system to the River Rhine, we measured the clearance rates of the biofilm-associated consumers on the different groups within the natural plankton. 2. Ciliates were the most dominant consumers, among which planktivorous groups, particularly peritrichs and (in spring and summer) heterotrichs dominated. Consumer biomass varied with season, with the highest density occurring directly after the appearance of the phytoplankton spring peak. 3. Clearance rates on plankton ranged from 96 to 565 L m−2 d−1 for bacteria and 66–749 L m−2 d−1 for algae, with a preference for algae in summer and for bacteria in winter. This pattern coincided with seasonal changes in the structures of the grazer communities. The consumers (both ciliates and rotifers with total standing stocks ranging between 19 and 572 mg C m−2) imported a substantial amount of organic matter (between 15 and 137 mg C m−2 d−1) into the biofilm. 4. These results highlight the potential importance of consumers in the biofilm as a trophic link between the plankton and the benthos, a function that has hitherto mostly been attributed to filter-feeding bivalves. In contrast to bivalves, the biofilm-dwelling consumers show a more dynamic response towards the plankton density and composition. Such dynamic components need to be considered when estimating total plankton consumption by the benthos.

Settlement behavior of cyphonautes larvae of the bryozoan Membranipora membranacea in response to two algal substrata

Abstract. Settlement is an important process in the biphasic life histories of many marine invertebrates. Little is known regarding the fine‐scale behavioral mechanisms for finding and attaching to a suitable substratum, particularly under conditions that may impose a potential challenge, such as flow. In this study, we examined the settlement behavior of cyphonautes larvae of the bryozoan, Membranipora membranacea, in response to two different algal substrata. Larvae showed a strong preference for settling on the kelp Nereocystis luetkeana over the red alga Mazzaella splendens. We then tested whether the behavioral mechanisms used by larvae to attach to these algae differed when presented with the challenge of flowing water during settlement. We found that larvae exhibited different behaviors on the two species of algae in flowing water. Larvae were more often observed in direct contact with the preferred alga (N. luetkeana) exhibiting fine‐scale active search behaviors. On the less preferred alga (M. splendens), larvae were less frequently observed in direct contact with the alga, and appeared to be exhibiting broad‐scale passive search behaviors along the surface of the blade. Our results suggest that cyphonautes larvae alter their behavior in response to their preferred settlement habitat.

Feeding preferences of the sandhopper Orchestoidea tuberculata: the importance of algal traits

Factors such as nutritional quality and the secondary metabolite content of food resources have been shown to influence the feeding behavior of herbivores in many marine habitats. For intertidal macroalgae consumers on sandy beaches, the influence of these factors on feeding behavior and the consequences on their performance is poorly understood. In this study, we evaluated the relationships of nutritional quality, chemical defenses (phlorotannins), and the structure of three macroalgal species that form the bulk of imported wrack subsidies to beaches in southern Chile, with the feeding behavior, absorption efficiency, and growth rate of the talitrid amphipod Orchestoidea tuberculata, one of the most abundant organisms in this environment. The amphipods preferred Durvillaea antarctica over Lessonia nigrescens and Macrocystis pyrifera when simultaneously offered fresh pieces of each alga. Similar results were observed when artificial food made of dry powdered algae of each species was provided, suggesting that the structure of these three algae did not influence preference. The performance of amphipods when reared on a diet of a single algal species matched feeding preferences; higher growth rates were observed in treatments with the preferred alga, D. antarctica. These results imply that D. antarctica is a superior food item for O. tuberculata when compared to L. nigrescens or M. pyrifera, and also that the alga’s intrinsic quality (i.e., not structure) may influence dietary preference in these consumers. The higher content of proteins and carbohydrates found in D. antarctica may explain why this macroalga represents better quality food for O. tuberculata. Phlorotannin content did not have obvious negative effects on diet choice or growth, as D. antarctica, the alga with greater content of these secondary metabolites, was preferred and associated with higher growth rates of O. tuberculata. However, it is necessary to emphasize that the low phlorotannins concentrations registered in the three macroalgae species examined in this study, may not have been sufficient to deter O. tuberculata. When the amphipods were fed with each alga individually, they consumed significantly higher quantities of D. antarctica, which suggests that O. tuberculata did not eat more to compensate for the lower nutritional quality of the other algal species in order to maintain growth. Nor was compensation for lower food quality achieved by increasing absorption efficiency. Our results imply that the composition of the macroalgae arriving on the beach can significantly affect the performance and subsequent life history traits of O. tuberculata and by extension other amphipod species.

Feeding Choice and the Fate of Organic Materials Consumed by Sesarma CrabsPerisesarma bidens(De Haan) When Offered Different Diets

The feeding preference of the sesarmid crabPerisesarma bidenswas investigated when offered different diets:Enteromorpha intestinalis(algae),Kandelia obovataleaves, and propagules. Nutritional value of food, its assimilation, and fates were evaluated using a combination approach of the fatty acids (FAs) and C/N ratios. When offered a mixed diet, male crabs preferred algae than leaves and/or propagules, while a female preference was equally for leaves and algae but less than propagules. The nutritional value of algae was higher as indicated by low C : N ratios and highω3/ω6ratios than leaves and propagules. FAs comparison of tissues and faeces indicated that crabs efficiently assimilate essential fatty acids (EFAs) from a given diet in the order of algae greater than leaves and propagules. Despite of sesarmid crabs being a mangrove leaf-eater,E. intestinaliscan potentially be important source of nitrogen supplement forP. bidensunder mangrove forests.

Predation by the sea urchin Strongylocentrotus droebachiensis on capsular egg masses of the whelk Buccinum undatum

We evaluated sea urchin Strongylocentrotus droebachiensis predation on egg masses of the whelk Buccinum undatum. The urchin actively grazes on the egg masses, even as they are being deposited on the bottom. Whelks preferentially lay their egg masses on vertical areas where urchin densities are 4-fold less than on flat areas. This strategy is advantageous, as experimental trials showed that the loss in the mass of capsules was 4 fewer on walls than on flat areas. Nevertheless, a high proportion of egg masses on walls show damage from predation. Urchins provided with egg masses in the laboratory, ingested the capsules at a steady rate over a 9-d period (5 urchins ingested 2.8 g.d-1). Urchins provided agar discs that included a preferred alga and whelk capsule walls ingested the discs at a rate that was half that observed for discs that only included the alga. Discs that included the preferred alga and capsule contents were eaten at the same rate as discs that only included the alga. Thus, capsule walls, but not the capsule contents, provide a defence against urchin predation. Laying aggregate egg masses likely provides only a limited advantage, as the attachment surface does not increase with the number of egg masses deposited together, so the risk of detachment increases. Consideration of the interactions between urchins and whelks is important in managing the fisheries of the two species.

REGULATION OF INTERTIDAL FOOD WEBS BY AVIAN PREDATORS ON NEW ENGLAND ROCKY SHORES

Although there is a large body of research on food webs in rocky intertidal communities, most of the emphasis has been on the marine benthic components. Effects of avian predation on highly mobile predators such as crabs, remains practically unstudied in rocky shore ecosystems. The crab, Cancer borealis, is an important component of the diet of gulls (Larus marinus, L. argentatus) at the Isles of Shoals, Maine, USA. C. borealis prey include the predatory gastropod Nucella lapillus L., the herbivore Littorina littorea, and mussels Mytilus edulis L. We hypothesized that gulls reduce abundance of C. borealis in the low intertidal and shallow subtidal, thereby allowing C. borealis prey to persist in high numbers. A study of crab tidal migration showed that C. borealis density nearly doubled at high tide compared to low tide; thus, crabs from a large subtidal source population migrate into the intertidal zone during high tides and either emigrate or are removed by gulls during low tides. Results from a small-scale (1 m2) predator caging experiment in the low intertidal zone indicated that enclosed crabs significantly reduced L. littorea abundance when protected from gull predation. In a much larger-scale gull exclusion experiment, densities of C. borealis increased significantly during low and high tides in exclosures relative to the controls. C. borealis density was inversely correlated with changes in the abundance of two mesopredators Carcinus maenas and Nucella lapillus, and with the space-occupier M. edulis. There was a similar negative correlation between abundance of C. borealis and the change in abundance of the herbivore L. littorea, but the trend was not significant. Mortality of tethered L. littorea was associated with C. borealis density across sites. However, preferred algae did not change in response to L. littorea density during the experiment. Thus, we found suggestive, but not conclusive, evidence for a three-level cascade involving gulls, crabs, and L. littorea. Our studies strongly suggest that gulls, as apex predators, generate three-level trophic cascades in rocky intertidal food webs by preventing the highly mobile subtidal predator, C. borealis, from establishing substantial populations in the low-mid intertidal zone thereby indirectly enhancing densities of two key mesopredators (N. lapillus, Carcinus) and blue mussels (M. edulis).

Resource use and impact of three herbivorous damselfishes on coral reef communities

Territorial damselfish are considered to be functionally important herbivores on coral reefs, promoting the abundance of preferred algae and depleting corals through a variety of ‘farming’ activities. However, the composition of algal and coral communities inside territories and patterns of feeding selectivity are known for only a few species. Here we compare substrata inside and next to territories of Plectroglyphidodon lacrymatus, P. dickii and Stegastes nigricans, 3 common damselfish in Papua New Guinea, and interpret patterns in relation to diets and patterns of feeding selectivity. The coral assemblages inside territories differed among fish species and also between defended and non-defended areas. Live corals dominated P. dickii territories, while those of P. lacrymatus and S. nigricans were primarily associated with algal substrata. Territories of P. lacrymatus were similar in coral composition to adjacent areas, while those of P. dickii and S. nigricans were associated with particular coral taxa. Territories of the 3 damselfish were similar in algal composition, with mixed turf algae (primarily blue-green algae Polysiphonia spp. and other filamentous red algae) more prominent inside territories and crustose coralline algae more prominent outside. Diets for the 3 species were also similar, as each species was primarily herbivorous and diets consisted of diatoms, blue-green algae, Polysiphonia spp. and other filamentous red algae. An experimental removal of P. lacrymatus showed that they promoted epiphyte loads without influencing macro-algal or coral cover. Our results suggest that while these 3 species of damselfish vary in their interactions with coral reef habitat, they selectively cultivate a similar range of epiphytic food algae on different substrata.

Age-dependent shift in response to food element composition in Collembola: contrasting effects of dietary nitrogen

We examined the effect of different food qualities, in terms of the C:N:P content, on the collembolan Hypogastrura viatica. We hypothesised that (faster growing) juveniles would have higher demands for P and N than adults; this, however, was rejected by our experiments. There was no difference between the elemental compositions of juveniles and adults. In food preference experiments, juveniles and adults were offered green algae Raphidocelis subcapitata with three different C:N:P ratios. There was a strong shift in dietary response with age; juveniles preferred algae with low or medium N contents over the most N-rich algae, whereas adults showed the opposite. No response was seen when the specific P content in the food was varied. Juveniles fed on algae with high N content showed lower growth rates and survival than those fed on algae with other food qualities. In contrast, adults had lowest growth rates when fed on algae with a low N content. The negative effect on juveniles of the most N-rich diet appeared to be a toxic response that was directly or indirectly related to the algal N content. Adults had higher tolerance for N-rich diets, but were also more likely to face dietary N-limitation. These animals face a stoichiometric trade-off scenario in the sense that adaptation to maximise retention of a limiting element may result in reduced physiological ability to cope with excessive elements when feeding on "richer" diets, and vice versa. This problem is partly solved in H. viatica by contrasting selective feeding and ontogenetic dietary shifts between juveniles and adults.

ALGAL MACRONUTRIENTS AND FOOD SELECTION BY THE OMNIVOROUS MARINE FISH GIRELLA TRICUSPIDATA

We used combined field and laboratory studies to investigate the relationships among foraging, food selection, and macronutrient intake and retention by the New Zealand marine reef fish, Girella tricuspidata (F. Girellidae). Gut analyses of field-caught fish revealed a diet comprising significant proportions both of algal and non-algal (copepods, hydroids, and organic detritus) foods, with the relative proportions of algal and non-algal food items varying from 65% of non-algal foods in the winter to 34% in autumn. Observations of the diurnal feeding pattern of free-ranging wild fish showed an increase in bite rate from sunrise to late afternoon, followed by a decrease toward sunset. In laboratory studies we recorded (a) gut throughput rates, (b) macronutrient intake, and (c) macronutrient assimilation by captive G. tricuspidata fed one of three algal species. The algae were Enteromorpha intestinalis and Ulva lactuca, both of which are preferred foods of G. tricuspidata, and Gracilaria chilensis, which has not been recorded in the stomach contents of the fish despite its co-occurrence in some habitats. The two species of preferred algae were found to have a higher starch and lower protein content than the non-dietary G. chilensis. The fish regulated their intake and utilization of the algae such that similar amounts of protein were ingested and assimilated from all three species, but less starch was ingested and assimilated from the non-dietary G. chilensis than from the preferred species. Gut throughput times correlated positively with starch availability in the algae but were lower for all treatments than previous studies would suggest are associated with fermentative digestion. The data suggest that omnivory in G. tricuspidata is likely based on complementarity, rather than substitutability of algal and animal foods.

Intra- and interspecific differences in palatability of Arctic macroalgae from Kongsfjorden (Spitsbergen) for two benthic sympatric invertebrates

Information on herbivore–macroalgae interactions is extremely scarce for Arctic habitats. In this study, the potential of 19 macroalgae as food source for herbivores was investigated for the first time in Arctic waters (Kongsfjorden, Spitsbergen) with emphasis on algal defense against grazing. Only two of the 19 tested macroalgae-associated invertebrates consumed macroalgae in measurable amounts, the locally abundant green sea urchin Strongylocentrotus droebachiensis (OF Müller) and the amphipod Gammarellus homari (JC Fabricius). In the inner basin of the fjord, the dense macroalgal stock represents a potential food source. However, in this area, herbivory plays only a minor role. In contrast, in the outer basin of Kongsfjorden S. droebachiensis exerts a strong top-down control on macroalgal assemblages. Laboratory feeding assays in the with the two herbivores showed grazer-specific feeding preferences. The amphipod G. homari exhibits a preference for delicate red algal species like Devaleraea ramentacea, whereas the sea urchin S. droebachiensis significantly preferred more leathery seaweeds like Laminaria and Alaria. The red alga Palmaria palmata is a very attractive food for both herbivores, while the brown alga Desmarestia viridis and the red alga Ptilota gunneri are among the least preferred algae. To distinguish between physical and tissue-specific plant properties, which have a deterring or stimulating effect on the grazing behaviour, both grazers were offered intact algal tissue and artificial food in separate feeding assays. While physical and tissue-specific plant properties–especially in the Laminariales–deterred G. homari, these properties did not deter S. droebachiensis. This study provides insights into herbivore consumption in the benthic food web of Kongsfjorden. As a general potential top-down factor controlling primary production, herbivory needs to be quantified further in Kongsfjorden to develop adequate carbon flow models for this important reference site for the study of climate change on high latitude marine ecosystems.

Ontogenetic and seasonal feeding habits of the annular seabream (Diplodus annularis L.) in Zostera sp. beds, eastern Adriatic Sea

Summary The ontogenetic and seasonal feeding habits of 489 individuals of Diplodus annularis L. in Zostera sp. beds were studied using frequency of occurrence, numeric percentage, percentage by weight and an index of relative importance (IRI). The Schoener overlap index was used to compare diets by fish size and seasons. Diet composition including 18 different prey taxa was evidently heterogenous among annular seabream size groups, with no significant dietary overlap. In relation to body size, juveniles were omnivorous and preferred algae and plants, while adults were omnivorous and preferred animals. Principal prey items by decreasing importance were Chlorophyta (dominant taxa Cladophora sp. and Enteromorpha flexuosa), Decapoda (dominant species Upogebia pusilla), Gastropoda (important species Rissoa ventricosa and Alvania sp.), Bivalvia and Spermatophyta, as well as other food items (mostly unidentified Crustacea and fish eggs). Differences in diets among seasons were not significant.

Food preferences of the sea urchin Diadema antillarum in Gran Canaria (Canary Islands, central-east Atlantic Ocean)

Preferences of the sea urchin Diadema antillarum (Echinodermata: Echinoidea) feeding on five species of brown macroalgae (Padina pavonica, Dyctiota dychotoma, Cystoseira abies-marina, Lobophora variegata and Halopteris filicina) have been studied using caging field experiments on Gran Canaria Island during August to October 2000. Results of three assays of both single and multiple diet experiments rejected the null hypothesis that Diadema does not feed selectively on the five selected algal species. In the multiple diet assays, Diadema consumed an average of 68–98 mg algae urchin−1 h−1 and 4–120 mg algae urchin−1 h−1 in the single diet experiments. On the basis of consumption, the five species of algae eaten can be divided into three groups. Thus Halopteris, Lobophora and Dyctiota were considered preferred algae, while Padina was considered an intermediate alga. Finally Cystoseira was significantly the less preferred and consumed seaweed in all sets of assays.

Resource allocation plasticity in sea urchins: rapid, diet induced, phenotypic changes in the green sea urchin, Strongylocentrotus droebachiensis (Müller)

The gonads of sea urchins have a dual function: reproduction and nutrient storage. In general, these animals are secondarily sessile and cannot easily migrate from areas of low resource availability to areas of high resource availability. Given these conditions, an experiment was performed to test the hypothesis that sea urchins ( Strongylocentrotus droebachiensis Müller) from an area of low food quality could rapidly increase gonadal tissue in response to a sudden increase of high quality food. Sea urchins were collected from a site that lacked preferred algae on Swans Island, Maine. Initially, animals were dissected to determine the percentage of the various body components. The remaining animals were distributed among four groups of equal number and size distribution. Each group was assigned randomly to 1 of 4 feeding treatments: Alaria esculenta, Laminaria digitata, Laminaria longicruris, and Ascophyllum nodosum. Animals were fed ad libitum during the experiment. Half of the sea urchins from each treatment were dissected after 3 weeks and the rest after 6 weeks. Significant differences were found among the treatments at both the 3 and 6 weeks dissections with A. esculenta producing the greatest increase in gonad wet weight. For the 6 weeks dissections there appeared to be a compensatory loss of perivisceral fluid in sea urchins that increased gonadal tissue. No differences among treatments were found for the body wall, Aristotle's lantern, or gut body components. Synthesizing these results with studies of other closely related species reveals a dynamic picture of resource allocation and phenotypic plasticity in sea urchins. Environmental variation can induce morphological change in sea urchins and these modifications have been described as graded reaction norms. The results presented here show that the temporal responses of the reaction norms of the various body components are graded and different components vary in response time.