No abstract

The utility of Sr/Ca ratios in otoliths as indicators of thermal history in fish was investigated for juvenile Girella elevata. There was no direct relationship between ratios of Sr/Ca and temperature of the water, as has been assumed in many previous studies. Sr/Ca ratios did not decrease when water temperature was elevated from 19 to 28 C. Elevation of ambient Sr levels in the sea water caused a significant increase in Sr/Ca ratios in otoliths, and there was a detectable increase in Sr/Ca ratios in otoliths of some individuals fed an Sr-enriched diet. Multiple factors may influence natural Sr/Ca ratios in otoliths of juvenile G. elevata and their interactions make it difficult to interpret the chronology of conditions experienced by an individual fish during early life in the pelagic or benthic environment. 1996 The Fisheries Society of the British Isles

Drifting macrophytic algae increased habitat complexity in coastal waters of California, USA, especially in convergence zones. Algae are large and abundant structures, especially drift Macrocystis pynfera (0.2 to 20 m long), and have been ignored in historical models of the pelagic environment. Drift plants redistribute small fish and invertebrates, and their movement (by wind and oceanographic features) can provide insight to the movements of meroplankton. The drift of whole M. pyrifera plants is also relevant to understanding the demography of kelp forests, whilst the droguelike qualities of plants can be used to study oceanographic features. The pelagic environment, therefore, is characterised by a hierarchy of structures (0.05 mm to > 10 m, marine snow to drift algae) and plankton, of different sizes.

Interrelations between zooplanktivorous fish and zooplankton were examined at the Poor Knights Islands 20 km off the east coast of Northland, New Zealand from 1980 to 1983. The pomacentrid Chromis dispilus was the most abundant planktivore at all locations; high densities of other planktivores were also found. The rankings of these species varied considerably among locations. These differences may have been due in part to Caprodon longimanus (Serranidae), Scorpis violaceus (Kyphosidae), and Decapterus koheru (Carangidae) malung forays for food away from the immedate vicinity of rocky reefs. The hypothesis that fish have a localised effect on zooplankton was investigated in detail within a small reef area (-2500 m') on 7 separate occasions. Distribution patterns of planktivorous fish changed according to current direction. Fish were always most abundant on the incurrent side of the reef and within an archway during the day. Large differences in densities of zooplankton were detected along a 200 m transect where samples were taken upcurrent, within, and downcurrent of the archway during the day. Lowest zooplankton densities were usually found in the archway where planktivorous fish were abundant. At night when fish were absent from the water column, there was a trend for highest abundances of plankton within the arch, relative to upcurrent and downcurrent sites. A similar 200 m transect parallel to the arch, but 1 km offshore where planktivorous fish were absent, showed no significant differences in density of plankton along its length during the day or night. Zooplankters that showed greatest reductions in density in the vicinity of feeding fish were most abundant in the guts of C. dispilus sampled from the arch. Estimates of removal rates of zooplankters by fish based on concurrent estimates of fish densities, plankton, feeding rates, diet of fish and current speeds suggest that fish were capable of causing the measured reductions in zooplankton concentrations through the archway. The diets of C. dispilus changed among sampling occasions and corresponded partly to changes in the composition of zooplankton captured in nets. Accordingly, any effect that fish have on zooplankton may change between times. Ecological consequences of predation by fish are discussed in terms of zooplankton communities, fish, and rocky reef environments.

Duration of presettlement phase was examined for the temperate reef fish Parika scaber. Information was also collected on seasonality, growth, development, and diet before settlement. Presettlement P. scaber associated with drift algae offshore of rocky reefs were of sizes 7 to 35 mm standard length (SL); highest abundances were found between November and January. Fish just prior to settlement were collected from algae tethered seaward of reefs. Fish associated with drift algae and fish captured around tethered algae had similar size-frequency relationships. Fish that associated with drift and tethered algae and settled on reefs were between 22 and 66 d old. Despite this wide range of ages and sizes, at any one time a large proportion of P. scaber around drift and tethered algae were of a similar size and age. However, among sampling times the mean value for these relations vaned.Hence, P. scaber have the capacity to settle at a variety of ages and sizes. Presettlement P. scaber (described from 3.5 mm) have a full adult fin-ray complement and a similar colouration to fish on the reef at 8 to 9 mm length. Development to the adult form correlated with a change from allometric to isometric growth. Reared and tetracycline-treated fish demonstrated that increments were deposited daily, after hatching, in the sagittal and lapillus otoliths. Assuming that the spacing of increments relates to the growth of fish, a growth curve was determined: After an initial period of slow growth there was a rapid acceleration in growth to 7 mm; growth remained relatively conztant in h g e : fish. Thc spacificj of inclements suggested that development rate vaned among samples of fish captured at different times. Growth rates, determined from age-size relations, showed a similar variation. T h~s is discussed in relation to the conditions fish may have experienced in the pelagic enviroment.