6. Reef fish and other major predators

Fish, like corals, have geographical patterns across regions and across individual reefs, being structured in the latter case by wave energy and depth. The thousands of species show a variety of feeding patterns. Detritus feeders are very abundant, feeding on the detritus on the seabed, especially in the fine, filamentous algal turf on apparently bare rock. Plankton feeders are common also, and herbivorous fishes show a large abundance, perhaps a quarter of the total species present, cropping algae that otherwise would grow unchecked and smother coral. Since turf algae also contain many micro-species and detritus, most herbivores also ingest much food other than simple plant material. Carnivores range from extreme specialists, such as polyp-picking butterflyfish, to generalists. Sharks and barracuda only consume other fish and generally are at the top of their food chains. The complicated ecological structure of the food webs can be clarified by analysing nitrogen isotope ratios in their tissues. Other important coral carnivores include the crown of thorns starfish, which can remove almost all living coral on a reef when it develops into plagues. Overfishing by humans greatly disturbs the equilibrium of a reef, and this is increasingly causing reef degradation.

ASPEK BIOLOGI HASIL TANGKAPAN PANCING ULUR PADA RUMPON PORTABLE

Rumpon portable merupakan rumpon yang tidak diletakkan secara tetap di perairan, tetapi diletakkan pada saat akan melakukan kegiatan penangkapan ikan. Tujuan dari penelitian ini adalah mengidentifikasi tingkat kematangan gonad, menganalisis hubungan isi perut hasil tangkapan dengan kelimpahan plankton yang tertarik pada rumpon portable, menganalisis indeks keanekaragaman, keseragaman, dan dominan plankton yang terdapat pada isi perut ikan dengan plankton yang terdapat pada perairan, menganalisis trofik level jenis ikan di sekitar rumpon portable. Metode penelitian dilakukan dengan cara experimental fishing dan uji laboratorium. Analisis data yang digunakan dalam penelitian ini yaitu analisis tingkat kematangan gonad, stomach content analysis, indeks keanekaragaman, indeks keseragaman dan indeks dominansi, serta analisis trofik level. Total hasil tangkapan ikan sebanyak 165 ekor didominasi oleh jenis ikan kembung dan ikan tongkol. Ikan-ikan lainnya yang tertangkap yaitu jenis ikan todak, barakuda dan selar kuning. Hasil analisis menunjukkan bahwa hasil tangkapan didominasi oleh ikan dengan TKG II sebanyak 53%, dan disusul ikan dengan TKG I sebanyak 38% dari total hasil tangkapan. Ikan-ikan yang tertangkap pada penelitian ini terdiri dari ikan pemakan plankton atau plankton feeders dan ikan karnivora. Organisme yang ditemukan dalam isi perut ikan yaitu ikan kecil, cumi-cumi, fitoplankton yang terdiri dari 7 genus, serta beberapa genus dari zooplankton. Hasil tangkapan ikan terbanyak ditangkap pada pengamatan hari ke-2 dengan jumlah tangkapan sebanyak 34 ekor.

Composition and Diversity of the Benthic Boundary Layer Macrofauna from the English Channel

The macrofauna of the benthic boundary layer (macrozooplankton and suprabenthos) was studied at six stations in May–June 1993 in the English Channel over sediments ranging from medium sand to pebble. The fauna collected consisted of 227 taxa in 30 suprabenthic sledge hauls. Numerically, the macrozooplankton was dominated by euphausids, chaetognaths, the holoplanktonic amphipod Apherusa spp. and fish larvae, and the suprabenthos by mysids (Anchialina agilis, Gastrosaccus spp.), amphipods (Stenothoe marina) and cumaceans at both medium sand stations. Suprabenthos species richness and diversity were significantly higher at western stations, in contrast to the pattern for macrozooplankton. The density of macrozooplankton was significantly higher, and suprabenthos significantly lower, at the western stations. The biomass of macrozooplankton was similar at the six stations, except in the middle of the Dover Strait which had a low biomass. The biomass of the suprabenthos was highest in the eastern part of the Channel. Two main assemblages were distinguished in relation to planktonic production and sediment composition: three western stations with two subgroups (stations 1 and 3 along the coasts of Brittany and station 2 off Plymouth); and the eastern stations also with two subgroups (station 4 in the Bay of Seine and stations 5 and 6 in the Dover Strait). For the macrozooplankton, two types of trophic structures could be distinguished: stations 1 and 4 where suspension-feeders dominated and the other stations (2, 3, 5 and 6) where carnivorous plankton feeders, omnivorous and scavengers predominate. For the suprabenthos, the plankton feeding, omnivorous and carnivorous trophic guilds dominated each station.

Culture of larval spiny lobsters: a review of work done in northern Japan

The method developed over the past decade in northern Japan to culture phyllosoma larvae of five species of principally cool-temperate spiny lobsters combines the features of upwelling water, co- cultured microalgae, and use of mussel gonad as food. The feeding behaviour of the phyllosomas shows that they are primarily predators with the pereiopods and secondarily plankton feeders with the maxillipeds and maxillae. Recent work has shown that contamination of culture water by microorganisms such as the fouling protozoans Vorticellaspp. can greatly reduce phyllosoma survival. The significance of co-cultures of microalgae in maintaining water quality is not yet fully understood. Newly hatched lavae of sailfin sandfish (Arctoscopus japonicus) is an excellent food for late-stage phyllosomas of Jasus verreauxi. About 5% of J. verreauxi phyllosomas metamorphosed into pueruli. Mortality during the puerulus stage was reduced by increasing the capacity of the culture tanks from 30 L to 100 L. A single Palinurus elephas phyllosoma raised in co-culture with diatoms and fed mussel gonad and A. japonicus larvae metamorphosed into a puerulus in 65 days after seven moults.

Morphological and Ecological Divergence Within the Lake Whitefish (Coregonus clupeaformis) Species Complex in Yukon Territory

Two forms of lake whitefish (Coregonus clupeaformis species complex sensu McPhail and Lindsey [1970]) were found in each of five lakes in Yukon Territory. They are characterized by differences in gill raker counts. Low gill raker fish are benthic feeders and are found almost exclusively near the bottom while high raker fish are largely plankton feeders, being found throughout the lake water column. High raker fish have longer and more closely spaced gill rakers than low raker fish. They also have shorter life spans and mature earlier than low raker fish. Lakes supporting these sympatric populations of lake whitefish have no cisco populations. The low gill raker member of these sympatric populations seems to be equivalent to most other Yukon lake whitefish whereas the high raker member appears to be the unusual member of each sympatric pair. Key words: whitefish, lake, feeding, morphology, growth, divergence, Yukon Territory, sympatric populations

Trematode Populations in the Atlantic Argentine, Argentina silus, and Their Use as Biological Indicators

The trematode parasites Lecithophyllum botryophorum, Derogenes various, Hemiurus levinseni, and Lampritrema nipponicum were found in Argentina silus off Nova Scotia and Newfoundland. Changes in the length-frequency distribution in the population of L. botryophorum at different times of the year reflected changes in parasite recruitment and were used tentatively to estimate the life span of the parasite.Hemiurus levinseni had a high intensity and incidence in very young fish, decreasing to a low level in mature fish; L. botryophorum had the reciprocal relationship; and D. varicus was intermediate in incidence and had a low level of intensity in fish of all sizes. These results were related to the occurrence of the intermediate hosts of the parasites and to the movement of A. silus to deeper water as it increases in size. The intensity of infestation with L. botryophorum increased from south to north. Seasonal variation in recruitment, with a peak immediately after spawning, was reflected in the intensity of infestation, mean size, and percentage of immature specimens of L. botryophorum.The young A. silus are midwater plankton feeders and the mature fish change to a diet that incorporates a high proportion of the crustacean intermediate host of L. botryophorum, probably an amphipod. There is no parasitological evidence of separate populations of A. silus in the west Atlantic.

Basic Productivity of Trevor Channel and Alberni Inlet from Chemical Measurements

Chemical properties of the waters in Trevor Channel and Alberni Inlet during late summer have been applied for an estimate of basic productivity. Based on the assumptions that the deep water in the system is renewed once per year and that the observed conditions in September represent the state of the water just before renewal, the oxygen deficit and the phosphate surplus in the deep water have been used as a measure of the organisms decomposed during the year. Oxygen depletion gives 28 g/m2 of plankton per year as carbon; phosphate liberation gives 31 g/m2. From fishery statistics it was estimated that the herring in Barkley Sound consume about one-quarter of the available plankton and all plankton feeders consume about one-half of the total. This would increase the above figures of productivity to 56 g/m2 and 62 g/m2, respectively. These values are probably a minimum annual productivity inasmuch as basic assumptions may not be completely fulfilled. Regeneration of nutrients in the surface layer, and some renewal of deep water by mixing and circulation, probably occur throughout the year.