Western Atlantic Coast Research Articles

Population Structure of Eastern Oysters (Crassostrea virginica) Inhabiting the Laguna Madre, Texas, and Adjacent Bay Systems

A survey of 16 enzyme systems and two structural proteins, among nine eastern oyster (Crassostrea virginica) populations in and adjacent to Laguna Madre, Texas, identified two genetically differentiated groups and the transition zone between them. The discontinuity in allele frequencies occurred between a reef in Corpus Christi Bay and reefs 26 km away in upper Laguna Madre. Although no fixed allelic differences were observed between populations from either side of the transition area, substantial frequency differences were observed at six gene loci, and both groups exhibited unique alleles. Spatial heterogeneity tests also suggested sizable allele frequency differences, as 8 of 15 polymorphic loci surveyed exhibited heterogeneity. Considerable genetic subdivision was observed, as 14 of 15 polymorphic loci surveyed exhibited significant fixation indices. The mean genetic similarity was 0.898 (range 0.813–0.977). Consequently, oysters inhabiting the Laguna Madre are genetically divergent from oysters inhabiting central and eastern Texas, the north-central and eastern Gulf of Mexico, and the western Atlantic coast. Thus, these groups should be considered as discrete management units, and the patterns of genetic exchange investigated. If eastern oysters inhabiting the Laguna Madre, Texas, are unique, they warrant protection.

New 'phantom' dinoflagellate is the causative agent of major estuarine fish kills.

A worldwide increase in toxic phytoplankton blooms over the past 20 years has coincided with increasing reports of fish diseases and deaths of unknown cause. Among estuaries that have been repeatedly associated with unexplained fish kills on the western Atlantic Coast are the Pamlico and Neuse Estuaries of the southeastern United States. Here we describe a new toxic dinoflagellate with 'phantom-like' behaviour that has been identified as the causative agent of a significant portion of the fish kills in these estuaries, and which may also be active in other geographic regions. The alga requires live finfish or their fresh excreta for excystment and release of a potent toxin. Low cell densities cause neurotoxic signs and fish death, followed by rapid algal encystment and dormancy unless live fish are added. This dinoflagellate was abundant in the water during major fish kills in local estuaries, but only while fish were dying; within several hours of death where carcasses were still present, the flagellated vegetative algal population had encysted and settled back to the sediments. Isolates from each event were highly lethal to finfish and shellfish in laboratory bioassays. Given its broad temperature and salinity tolerance, and its stimulation by phosphate enrichment, this toxic phytoplankter may be a widespread but undetected source of fish mortality in nutrient-enriched estuaries.

The external morphology of the parasitic copepod Holobomolochus confusus (Stock)

Holobomolochus confusus is reported for the first time from the western Atlantic coasts. The external morphology, especially that of the male, of specimens from the nasal cavities of cod, Gadus morhua, from the west coast of Sweden is described and discussed. Sexual dimorphism occurs in the maxillipeds, abdomen, first antenna and in the armature of the legs. The results indicate that the species has a good swimming ability and that this may allow the male especially to change hosts.

Macrozoobenthic community structure in the Lagoon of Albufeira, western coast of Portugal

A benthic survey of the Lagoon of Albufeira on the western Atlantic coast of Portugal, based on macrofaunal analyses from 50 subtidal sampling stations has provided initial data for a study of the benthic ecology of that system. The 126 species identified revealed that the overall faunal composition is characteristic of both Atlantic and Mediterranean lagoons, with the greatest proportion of the species occurring at low frequencies. A correspondence analysis of the distribution of species among sampling stations identified two areas characterized by different communities. In the vicinity of the lagoon mouth a coarse, clean sand community was delineated from a mixed inner lagoon community associated with mixed sediments, ranging from coarse and medium sand with variable percentages of silt, to mud with up to 90% silt content. In deeper areas this lagoon community was considerably impoverished, a condition attributable to intermittent stagnation of the bottom water. A coenotic model of the Lagoon of Albufeira is proposed and related to the hydrodynamics of the system and to the distribution of the superficial sediments.

Laboratory observations of the pattern of reproduction ofelasmopus levis(crustacea: Amphipoda)

Elasmopus levis is commonly found among shallow subtidal and intertidal macrofaunal assemblages along western Atlantic coasts, yet virtually nothing is known about its life history. The present study reports the results of laboratory observations of the key features of its pattern of reproduction. The observations show that the reproductive physiology of this species is similar to that of most amphipods studied to date, but it seems to spend much less energy on reproductive behaviors than others. No courtship or pair‐bonding behaviors were observed, and, although the male and female of heterosexual pairs were found in proximity more often at the time of the female molt than at other times, the frequency of these associations was lower than that of other species observed. It is hypothesized that the principal reproductive stimulus for this species may be an environmental factor, rather than a stimulus produced by the receptive female, as is the case in other species.

Osmoregulation and differential penetration of two grey mullets, Chelon labrosus (Risso) and Liza ramada (Risso) in estuarine fish ponds

Grey mullet ponds situated in Arcachon Bay on the western Atlantic coast of France, display contrasting mixohaline habitats. The pattern of osmoregulation of Chelon labrosus and Liza ramada exhibiting differential penetration of fish ponds has been investigated. Key variables of salinity and temperature have been considered. The tolerances to low salinities and to fresh water have been determined. The dynamics of variation in plasma osmotic pressure and major plasma electrolytes (Na +, Cl −, K +) were studied in terms of: (1) gradual adaptation to a decreasing salinity gradient; (2) effects of a long-term adaptation in fresh water; (3) effects of low temperatures on sea water adapted fish. Both species can adapt to a wide range of salinities; however, while L. ramada show a good hypoosmotic regulation, with no alteration in plasma concentration over a wide range of salinity and after a long stay (5 months) in fresh water, C. labrosus cannot live for long periods of time in a wholly fresh water habitat. Both field samples obtained from thick-lipped grey mullets forced to stay in a freshwater pond and experimentally adapted fish showed, after 3 months, an unequivoqual decrease in plasma sodium and chloride, and plasma osmolality decreased to the same extent; this pattern of no compensation is bound, sooner or later, to end in death. The inability of C. labrosus to develop a long-term hypoosmoregulation in fresh water is referred to salinity preferences which probably limit the upstream penetration of this species. Plasma osmolality and major electrolytes (sodium and chloride) increased in cold (4 °C) sea water. This response might be due to a reduced ability of grey mullets to osmoregulate in cold waters. In the poly-mesohaline ponds, Winter drop in temperature (4–6 °C) causes grey mullets to migrate to the meso-oligohaline ponds where the mean temperature is more elevated (8 °C) and temperature changes less rapid (6–9 °C).

Some Adult Digenetic Trematodes in Striped Mullet from the Northern Gulf of Mexico

Morphological information is given on the adults of 4 trematodes from Mugil cephalus from estuarine waters of the northern Gulf of Mexico with complementary information from specimens from Georgia. Lasiotocus glebulentus sp. n., from the Gulf, possesses a submedian genital pore and apparently differs from all known species by containing several large concretions in the excretory vesicle. Data are presented for Hymenocotta manteri Overstreet, 1969, Saccocoelioides beauforti (Hunter and Thomas, 1961) comb. n., and Dicrogaster fastigatus Thatcher and Sparks, 1958. These 3 species are now known from both the Gulf of Mexico and the western Atlantic coast. Carassotrema mugilicola Shireman, 1964, is transferred to the genus Chalcinotrema Freitas, 1947. The striped mullet, Mugil cephalus Linnaeus, is a cosmopolitan marine fish found in both fresh and salt waters of the tropical and warm temperate zones. It is a host for a large number of trematodes, many of which were cited by Doss and Farr (1969). In fact, mullet have been theorized by Manter (1957) and others as serving as an ecological bridge between trematodes of freshwater and marine fishes of coastal waters. Four adult species from the northern Gulf of Mexico are discussed below. Two others, Carassotrema mugilicola Shireman, 1964, not recovered by me, and a new species of Lecithaster Liihe, 1901, which will be described by me in a future paper, are also found in striped mullet from the Gulf region. The trematodes were examined alive, fixed in hot AFA solution under minimal coverslip pressure, and stained with Van Cleave's hematoxylin. Figures, except those designated otherwise, were drawn from mounted material with the aid of a camera lucida. All except the first are of material from the Gulf of Mexico region. Measurements are given in microns. Family Haplosplanchnidae Hymenocotta manteri Overstreet, 1969

Microgeographical and Ecological Distribution of Colour Morphs of Botryllus schlosseri (Ascidiacea)

Botryllus schlosseri (Pallas), a compound ascidian widely distributed on European and western Atlantic coasts, is well known for its colour polymorphism, which has been shown to be under genetic control1–4. In the Venetian Lagoon Botryllus is found chiefly in two typical biotopes: the piles marking the navigable canals which cross the Lagoon, and the beds of Zostera which cover its bottom.

An Experimental Assessment of Some of the Characters Used for Specific Delimitation in the Genus Laminaria

The growth in culture of Laminaria saccharina (L.) Lamour. and a species from Nova Scotia, tentatively identified as L. agardhii Kjellm., has been compared. Several characters, normally used for specific distinction within the genus Laminaria, have been shown to be modified by environmental conditions. These all concern the lamina and include the following: general morphology and texture, the shape of the base, the anatomical construction and the presence or absence of mucilage canals.The question of the identity of L. agardhii from eastern and western Atlantic coasts is discussed.

Life of the Western Atlantic Coast

The Living Tide By N. J. Berrill. Pp. xi + 256 + 16 plates. (London: Victor Gollancz, Ltd., 1951.) 16s. 6d. net.

THE BIOLOGY OF OITHONA SIMILIS IN THE GULF OF MAINE AND BAY OF FUNDY

1. Oithona similis, although almost world-wide in distribution, is centered largely north of Cape Cod on the western Atlantic coast, and south from this point is gradually replaced by O. brevicornis. 2. The adult stock in the Gulf of Maine appears to approach the coast from offshore with rising temperatures in the spring. 3. Propagation begins in the Gulf in March and continues in a succession of generations until September. 4. Two breeding stocks are distinguishable, due to an average difference of about one month in the time of vernal propagation in the eastern and western parts of the region. This difference is reflected in subsequent generations after dispersal. 5. There appear to be four broods of the western stock, in March, May, July, and September, and three in the eastern, in April, June, and August. 6. A developmental period of two months during the early season and about six weeks in summer is indicated. 7. Oithona is at times far more prolific than either Calanus or Pseudocalanus, but mortality is relatively much higher, depletion being greatest in nauplius stages. 8. The western stock remained for the most part concentrated offshore, but the eastern, particularly in advanced stages, was more generally distributed, sometimes being more abundant inside than outside of the 100-meter contour. 9. There is some evidence that in June the local stock in the inner Gulf is supplemented by important contributions from another production area, probably in the vicinity of the outer banks. 10. There is no indication of successful propagation in the turbulent coastal region of the Gulf east of Mt. Desert or in the Bay of Fundy. 11. The larvæ of Oithona afford the most abundant source of food in the region in mid-summer for those animals feeding on larval planktonic organisms. Of added importance in the natural economy of the region is the fact that the seasonal maxima of the three numerically dominant species occur at successively later periods during the summer, Calanus in May, Pseudocalanus in June, and Oithona in August.