Reef Species Research Articles

Plutonium concentrations in fish and seawater from Kwajalein Atoll.

A follow-up study has been made to assess the concentrations of 239+240Pu and 137Cs in the marine environment of Kwajalein Atoll. Fish collected from the atoll in 1972 had body burdens of plutonium that were substantially higher than concentrations in similar species from locations contaminated only with global fallout. Our recent results, however, indicated that Kwajalein lagoon seawater contained levels of plutonium more similar to global fallout levels found in north equatorial Pacific surface waters. No satisfactory explanation for the reported plutonium levels in fish from Kwajalein collected in 1972 could be deduced from the available data. The highest plutonium concentrations reported for the 1972 reef species of fish could expose man, through ingestion of marine foods, to a dose rate as high as 25% of the proposed EPA guideline for annual total transuranic dose rate to bone (3 mrad/yr over 70 yr). Our present results show the dose rate from the marine food pathway is nearer to 0.005% of the recommended EPA value and is consistent with the view that Kwajalein Atoll contains plutonium concentrations that are expected from global fallout. The magnitude of the plutonium levels reported in fish collected from Kwajalein lagoon during 1972 was excessively high, and these results appear to be inconsistent with other environmental data from the lagoon. Our results also show that concentration factors for plutonium in fish muscle and bone tissues appear to be independent of species, trophic level and location, which leads us to believe that there is a great deal of validity in the concept of a concentration factor for estimating concentrations of plutonium in fish.

Physical and Biological Observations of the Northern Rim of the de Soto Canyon made from a Research Submersible

During June 1978, the research submersible DIAPHUS completed 27 dives in the north central Gulf of Mexico. Fourteen of these were concentrated on and around the high relief, northern ledge or rim of the De Soto Canyon, located at depths of 50-60 m, and approximately 25 km S of Navarre, Florida. The ledge is composed of limestone outcroppings. The invertebrate fauna is characterized as two principle assemblages, one associated with a sand-shell-coraline-algae slope and the other with a limestone block ledge. The ichthyofauna is dominated by deep water reef species, thirty of which are identified and their habitat and abundance described.

Offshore distributional patterns of Hawaiian fish larvae

An analysis of ichthyoplankton samples based on relative abundance reveals pronounced inshore/offshore distributional gradients for most Hawaiian fish larvae. Larvae of pelagic bay species are found almost exclusively in semi-enclosed bays and estuaries. Larvae of pelagic neritic species are more or less uniformly distributed with distance from shore. The larvae of reef species with non-pelagic eggs are most abundant close to shore, while those of reef species with pelagic eggs are most abundant offshore. Finally, the larvae of offshore (primarily mesopelagic) species show no clear pattern but frequently occur in high numbers nearshore. Within any group, variation in pattern was often evident; for example, although Hawaiian fishes of both the families Labridae and Mullidae spawn pelagic eggs, larvae of the former had not peaked in abundance 12 km from shore while larvae of the latter had peaked between 0.5 and 2 km. Some larvae which occur offshore are highly specialized morphologically for a pelagic existence (e.g. Chaetodontidae, which is illustrated) while others are little modified (e.g. Labridae). These findings indicate ichthyoplankton surveys in tropical areas must sample offshore areas in addition to the inshore adult habitat to obtain a complete picture.

Lethal limits and the zoogeography of the faunal assemblages of Coastal Carolina waters

The offshore waters of Cape Hatteras, North Carolina, USA, is an area of dynamic encounter between the northerly flowing, warm waters of the Gulf Stream and the southerly flowing, colder water of the Virginia coastal current. The faunal assemblages north of the Cape and those associated with a reeflike formation southe of the Cape in the Gulf Stream are distinct, each having predominantly cold- or warm-water affinities. To assess the zoogeographical significance of temperature, high and low thermal limits of both adult and larvae of species from these 2 regions were determined. Lethal salinity limits of the first stage zoeae of a few Crustacea were determined. In general, southern affinity species survived higher temperatures than northerly displanced species. In some cases, species with overlapping distributional limits had different thermal tolerances, which could be correlated with differential microhabitat selection. Many of the southern affinity species could not survive low temperatures which were characteristic of either the water mass northe of Cape Hatteras (4 °C) or the waters between the Gulf Stream and the shore (10 °C). A few species were able to seasonally acclimate to temperature extremes. Zoeae of reef species are the least resistant to both low temperature and low salinity.

Tropical Reef Corals: Tolerance of Low Temperatures on the North Carolina

Individual heads of two species of reef or herinatypic coral, Solenastrea hyades (Dana) and Siderastrea siderea (Ellis and Solander), occur on rock outcrops on the inner continental shelf off North Carolina in waters where winter bottom temperatures are as low as 10.6 degrees C. These temperatures are significantly lower than previously assumed minimum temperatures for the survival of tropical reef corals in their natural environment.

Sponge-feeding fishes of the West Indies

In an analysis of the stomach contents of 212 species of West Indian reef and inshore fishes, sponge remains were found in 21 species. In eleven of these, sponges comprised 6% or more of the stomach contents; it is assumed that these fishes feed intentionally on sponges. Sponges comprise over 95% of the food of angelfishes of the genus Holacanthus, over 70% of the food of species of the related genus Pomacanthus, and more than 85% of the food of the filefish, Cantherhines macrocerus. Lesser quantities of sponges are ingested by the remaining fish species. Fishes that feed on sponges belong to highly specialized teleost families, suggesting that this habit has evolved in geologically late time. The small number of fish species that concentrate on sponges as food suggests that the defensive characters of sponges—mineralized sclerites, noxious chemical substances, and tough fibrous components—are highly effective in discouraging predation. The two sponges most frequently eaten by fishes have a low percentage of siliceous spicules relative to organic matter, but among the 20 next most frequently consumed species no striking correlation occurs with respect to spicule content. Color and form of the sponge show no special correlation with frequency of occurrence in fish stomachs. Three species of fishes appear to concentrate on one species of sponge, but in these cases over 60% of the food taken consists of a variety of other organisms. Those fishes, more than half of whose diet consists of sponges, tend to sample a wide variety of species. No strong evidence is provided by our data that fish predation is a significant factor in limiting sponge distribution in the West Indian region.

The Biogeography of Queensland's Shallow-water Echinoderm Fauna (excluding Crinoidea), with a Rearrangement of the Faunistic Provinces of Tropical Australia

Analysis of Queensland's shallow-water echinoderm fauna reveals that approximately 44 per cent. of the 267 species recorded are confined to Queensland mainland waters and approximately 35 per cent, to Barrier Reef waters; the remainder are common to both environments. Marked faunistic attenuation with increasing latitude is exhibited by echinoderms occurring on the mainland north of lat. 25�S, and also by those found on the Great Barrier Reef. In both cases there are few substitutions. South of lat. 25�S Peronian species occur, but an apparently isolated population of tropical species is found in the Moreton Bay-Caloundra area. Queensland mainland echinoderms have strong affinities with those of the East Indies. The principal exchange route utilized by mainland species common to both areas seems to be via Torres Strait and the Arafura Sea. The Coral Sea appears to present a barrier to the spread of mainland species to the West Pacific area. On the other hand Barrier Reef echinoderms have strong ties with those of the latter region. Gene flow between populations of species common to the Barrier Reef and the West Pacific area probably occurs by way of the Coral Sea as a result of the transport of the pelagic larval stages of West Pacific populations by the Pacific south equatorial current. A dearth of coral structures immediately to the west of Torres Strait seems to have prevented the spread of Barrier Reef species to northern Australian waters. However, a few reef echinoderms appear to have entered north-western Australian waters from the East Indies, probably by way of atolls and reef platforms found on the Sahul and Rowley Shelfs. The echinoderm fauna of north-western Australia contains a large number of endemic species but has marked affinities with those of East Indian and Queensland mainland waters. The origin of the echinoderm fauna of tropical Australia is discussed in the light of palaeogeographic and zoogeographic findings. It is concluded that the present fauna of the area is derived predominantly from recent East Indian and West Pacific stocks. Also it is postulated that barriers between echinoderm populations present in tropical Australian waters were set up during the Pleistocene falls of sea-level and that this has resulted in the formation of closely allied sympatric and allopatric species. Available evidence indicates that the Solanderian Province should be restricted to the Great Barrier Reef area and, since Torres Strait does not present a barrier to the dispersal of echinoderms typically found in habitats in which terrigenous sediments predominate, the fauna of Queensland mainland waters and that of the Dampierian Province are grouped together tentatively in a single Tropical Australian Province.