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Is Acropora palmata (elkhorn coral) making a comeback in the Virgin Islands?
White band disease (WBD) ravaged Acropora palmata (elkhorn coral) on many coral reefs in the Caribbean in the late 1970’s and 1980’s, including those around St. John and St. Croix, U. S. Virgin Islands—USVI (Gladfelter 1982, Rogers 1985). Quantitative data, photographs, and anecdotal observations indicate WBD killed large stands of elkhorn coral in the USVI from about 1976 until sometime in the late 1980’s. Branching Acroporid species, which are most susceptible to WBD, are also the most vulnerable to storm damage (Rogers et al. 1982). Since 1979, eight hurricanes have passed near or over the USVI. Because elkhorn coral contributed most of the living coral and determined the physical structure of many shallow reef zones, its demise dramatically altered many areas. But now, some of the reefs in the Virgin Islands once again have large, actively growing colonies of this important, reef-building species.
Dolomitization of Quaternary reef limestones, Aitutaki, Cook Islands
Six holes were drilled to depths of 30–69 m in the shallow lagoon of Aitutaki in the southern Cook Islands. One hole encountered pervasively dolomitized reef limestones at 36 m subbottom depth, which extended to the base of the drilled section at 69·3 m. This hole was drilled near the inner edge of the present barrier reef flat on the flank of a seismically defined subsurface ridge. Both the morphology and biofacies indicate that this ridge may represent an outer reef crest. Mineralogy, porosity and cementation change in concert downhole through three zones. Zone 1, 0–9 m, is composed of primary skeletal aragonite and calcite with minor void-filling aragonite and magnesian calcite cement of marine phreatic origin. Zone 2, 9–36 m, is composed of replacement calcite and calcite cement infilling intergranular, intragranular, mouldic and vuggy porosity. Stable isotopes (mean δ 18 O=—5·4‰ PDB for carbonate; δD =—50‰ SMOW for fluid inclusions) support the petrographic evidence indicating that sparry calcite cements formed in predominantly freshwater. Carbon isotope values of —4·0 to —11·0‰ for calcite indicate that organic matter and seawater were the sources of carbon. Zone 3, 36–69·3 m, is composed of replacement dolostone, consisting of protodolomite with, on average, 7 mol% excess CaCO 3 and broad and weak ordering X-ray reflections at 2·41 and 2·54 A. The fine-scale replacement of skeletal grains and freshwater void-filling cements by dolomite did not significantly reduce porosity. Stable isotopes (mean δ 18 O=+2·6‰ 0 PDB for dolomite; maximum δD =—27‰ SMOW for fluid inclusions) and chemical composition indicate that the dolomite probably formed from seawater, although formation in the lower part of a mixed freshwater-seawater zone, with up to 40% freshwater contribution, cannot be completely ruled out. The carbon (δ 13 C=2·7‰) and magnesium were derived from seawater. Low-temperature hydrothermal iron hydroxides and associated transition metals occur in void space in several narrow stratigraphic intervals in the limestone section that was replaced by dolomite. The entire section of dolomite is also enriched in these transition metals. The metals dispersed throughout the dolostone section were introduced at the time of dolomitization by a different and later episode of hydrothermal circulation than the one(s) that produced the localized deposits near the base of the section. The primary reef framework is considered to have been deposited during several highstands of sea level. Following partial to local recrystallization of the limestone, a single episode of dolomitization occurred. Both tidal and thermal pumping drove large quantities of seawater through the porous rocks and perhaps maintained a wide mixing zone. However, the isotopic, geochemical and petrographic data do not clearly indicate the extent of seawater mixing.
Response of reef corals on a fringing reef flat to elevated suspended-sediment concentrations: Moloka‘i, Hawai‘i
A long-term (10 month exposure) experiment on effects of suspended sediment on the mortality, growth, and recruitment of the reef corals Montipora capitata and Porites compressa was conducted on the shallow reef flat off south Molokaʻi, Hawaiʻi. Corals were grown on wire platforms with attached coral recruitment tiles along a suspended solid concentration (SSC) gradient that ranged from 37 mg l −1 (inshore) to 3 mg l −1 (offshore). Natural coral reef development on the reef flat is limited to areas with SSCs less than 10 mg l −1 as previously suggested in the scientific literature. However, the experimental corals held at much higher levels of turbidity showed surprisingly good survivorship and growth. High SSCs encountered on the reef flat reduced coral recruitment by one to three orders of magnitude compared to other sites throughout Hawaiʻi. There was a significant correlation between the biomass of macroalgae attached to the wire growth platforms at the end of the experiment and percentage of the corals showing mortality. We conclude that lack of suitable hard substrate, macroalgal competition, and blockage of recruitment on available substratum are major factors accounting for the low natural coral coverage in areas of high turbidity. The direct impact of high turbidity on growth and mortality is of lesser importance.
Using video survey to examine the effect of habitat on gag grouper encounter
Gag is a reef fish that was declared overfished in the Gulf of Mexico (GOM) in 2009. Although Gag are no longer listed as overfished, fisheries managers are concerned that stocks may not be recovering. Our objective was to identify habitat characteristics important to Gag, and their effect on the probability of Gag occurrence. We obtained data from three separate fisheries-independent video surveys that sampled in the eastern GOM from 2010-2017: the National Atmospheric and Oceanic Administration (NOAA) Panama City, FL Office, the NOAA Southeast Area Monitoring and Assessment Program, and the Florida Fish and Wildlife Research Institute. We ran a separate mixed effects logistic regression for each survey, and used Akaike’s Information Criteria to determine the best fitting models. Some variables - percent rock coverage, vertical relief, latitude, and depth - were present in all confidence models. Depth did not have the same relationship with Gag across all surveys, suggesting that shallower habitats (<50 m) might be more suitable for juveniles, whereas deeper habitats (>50 m) might be more suitable for adults. Managers may be able to help Gag and encourage their recovery by using these data to establish or expand protected areas throughout shallower waters.
Lake trout colonization of artificial reefs: Who’s interested, and how long does it take?
Restoring self-sustaining lake trout ( Salvelinus namaycush ) populations has been a major management objective for decades across the species’ native range. Reproduction has been observed but recruitment has been limited in many areas of the Laurentian Great Lakes. Reef restoration and construction have been proposed to increase recruitment, leading to the construction of experimental spawning reefs in Thunder Bay, Lake Huron, during 2009–2010. Research shortly after reef construction demonstrated lake trout quickly colonized those reefs during spawning. We revisited this site after 10 years to evaluate lake trout encounter rate and residency on each reef over time and relative to an adjacent historical, anthropogenic reef complex using fine-scale acoustic telemetry. Encounter frequency increased at most experimental reefs since reef construction, but changes in residency were dependent on lake trout origin (hatchery or wild). Hatchery-produced fish increased their residency on the experimental reefs and spent more time on these reefs collectively than the historical reef; wild lake trout continued to primarily use the historical reef. We expected younger wild fish to have increased residency on the experimental reefs assuming these individuals could have originated from those reefs and were therefore more likely to return to them; however, residency on experimental reefs remained low (< 50%) for these fish. These results indicate that reef construction provided additional habitat used by spawning lake trout, but wild individuals continue to prefer older habitat including naive wild fish born after reef construction.
Gross and microscopic pathology of hard and soft corals in New Caledonia
We surveyed the reefs of Grande Terre, New Caledonia, for coral diseases in 2010 and 2013. Lesions encountered in hard and soft corals were systematically described at the gross and microscopic level. We sampled paired and normal tissues from 101 and 65 colonies in 2010 and 2013, respectively, comprising 51 species of corals from 27 genera. Tissue loss was the most common gross lesion sampled (40%) followed by discoloration (28%), growth anomalies (13%), bleaching (10%), and flatworm infestation (1%). When grouped by gross lesions, the diversity of microscopic lesions as measured by Shannon–Wiener index was highest for tissue loss, followed by discoloration, bleaching, and growth anomaly. Our findings document an extension of the range of certain diseases such as Porites trematodiasis and endolithic hypermycosis (dark spots) to the Western Pacific as well as the presence of a putative cnidarian endosymbiont. We also expand the range of species infected by cell-associated microbial aggregates, and confirm the trend that these aggregates predominate in dominant genera of corals in the Indo-Pacific. This study highlights the importance of including histopathology as an integral component of baseline coral disease surveys, because a given gross lesion might be associated with multiple potential causative agents.
Effects of host injury on susceptibility of marine reef fishes to ectoparasitic gnathiid isopods
The importance of the role that parasites play in ecological communities is becoming increasingly apparent. However much about their impact on hosts and thus populations and communities remains poorly understood. A common observation in wild populations is high variation in levels of parasite infestation among hosts. While high variation could be due to chance encounter, there is increasing evidence to suggest that such patterns are due to a combination of environmental, host, and parasite factors. In order to examine the role of host condition on parasite infection, rates of Gnathia marleyi infestation were compared between experimentally injured and uninjured fish hosts. Experimental injuries were similar to the minor wounds commonly observed in nature. The presence of the injury significantly increased the probability of infestation by gnathiids. However, the level of infestation (i.e., total number of gnathiid parasites) for individual hosts, appeared to be unaffected by the treatment. The results from this study indicate that injuries obtained by fish in nature may carry the additional cost of increased parasite burden along with the costs typically associated with physical injury. These results suggest that host condition may be an important factor in determining the likelihood of infestation by a common coral reef fish ectoparasite, G. marleyi .
Impact of exploratory wells, offshore Florida: A biological assessment
Seven offshore exploratory oil well sites were examined in an effort to determine the ecological impact of exploratory drilling on the subtropical marine ecosystems of southern Florida, including seagrass beds and coral reefs. The time since drilling ranged from 2 to 29 years; water depths varied between 5 and 70 m. The major long-term ecological impact observed at these sites ranged from the creation of "artificial-reef" conditions to the physical destruction of hardbottom habitat that had not recovered in 29 years. Long-term ecological perturbation appeared to be limited to physical destruction and the deposition of drilling debris, which provided substratum for settling organisms. Significant deposits of drill muds or cuttings were not encountered at any of the sites, and there was no evidence of ecological damage from cuttings or drill muds. The results of this study pertain only to exploratory drilling that, unlike production wells that remain in place for tens of years, is a one-time perturbation to the habitat.
Geology and ground-water resources of the island of Niihau, Hawaii
Niihau lies 17 1 / 2 miles southwest of Kauai. Its area is 72 square miles, and its highest point has an altitude of 1,281 feet. The population is about 180, chiefly Hawaiians. The annual rainfall at Kiekie, the ranch headquarters, generally ranges between 18 and 26 inches. The chief industries are the raising of sheep and cattle and production of honey. The island is privately owned. The main mass of the island is composed of a deeply weathered remnant of a basalt dome of Tertiary age, cut by a dike complex trending NE-SW. These Tertiary rocks are herein named the Paniau volcanic series. The central vent lay about 2 miles out to sea to the east of the present island. The dome, after deep gulches were cut into it by stream erosion and it was cliffed all around by the sea, was partly submerged. During Pleistocene time a broad wave-cut platform on the north, west, and south sides was built above sea level and widened by the eruption of lavas and tuffs, from 9 vents now visible and other vents now buried, to form a low coastal plain. These Pleistocene volcanic rocks are named the Kiekie volcanic series. Ash from Lehua Island, a Pleistocene tuff cone, has been drifted into duties on the north end of Niihau. Lithified dunes that extend below sea level, and the small outcrops of emerged fossiliferous limestone above sea level, indicate the plus 100-foot, minus 60-foot, plus 25-foot, and plus 5-foot eustatic stands of the sea correlative with changes in the volume of the polar ice caps and concurrent changes in the configuration of ocean basins. Calcareous dune and beach deposits, short stretches of nullipore reef and beach rock, and playa and alluvial deposits constitute the Recent rocks. No perennial streams exist on the island but about a dozen playa lakes, fresh or brackish during rainy weather, lie on the plain. The domestic water supply is rain caught from roofs. Only three wells on the island yield water with less than 25 grains of salt per gallon (260 parts per million of chloride). Typically, water holes for stock are about 15 feet across, 5 feet deep, and 8 feet wide. They have been dug in the lowlands where the depth to water is usually less than 5 feet. Forty-six dug wells and water holes exist, the water of some of which has become too salty for stock. Two or three deep wells were drilled 500 to 1,000 feet below sea level, but they encountered salty water. Three wells, not yet used, have been excavated in the Tertiary basalts. One of them has an infiltration tunnel at the bottom. Two seeps perched on vitric tuff beds more than 500 feet above sea level carry large quantities of salt leached from spray that falls on their recharge areas. Several sites are recommended for developing additional water for stock. The island, however, will always be short of domestic water because of aridity, unfavorable geologic structures, continuous deposition of salt spray, and abundant authigenic salts in the lake beds. Among the lavas of the Paniau volcanic series, of Tertiary age, olivine basalts probably predominate but ordinary basalts are abundant. Picrite-basalt of the primitive type, containing abundant olivine phenocrysts, also occurs. Andesites are probably present but are rare. Most of the lavas of the Kiekie volcanic series, of Pleistocene age, are olivine basalt, but one is transitional between olivine basalt and picrite-basalt. In many of the Pleistocene lavas the late-crystallized augite is titanian. A single occurrence of melilite-nepheline basalt has been reported. Chemical analyses of five rocks are listed.
Recent advances in life history of Gulf of Mexico sturgeon, Acipenser oxyrinchus desotoi, in the Suwannee River, Florida, USA: A synopsis
Gulf sturgeon spawn on portions of three sites in the upper Suwannee River, which may appropriately be described as spawning reefs. The same areas are utilized from year to year. Habitat factors important in spawning site determination include gravel/cobble substrate, the presence of eddy fields, a neutral to slightly alkaline pH, and an empirically observed range in calcium ion content (6-18 mg/L Ca++, corresponding to a conductivity range of 40-110??S). Eggs are deposited contagiously within a small area (< 10,000 m2) with very little scatter, suggesting little if any current drift. They are not found from samplers on immediately adjacent sand substrate. The broadcast spawner model does not seem to fit the Gulf sturgeon. Spawning begins 4-7 days after the March new moon, with water temperature above 17.0 oC, and extends for 9-23 days as discrete events involving individual females. Spawning may continue, if water temperature remains below 21-22oC. The total annual pool of spawning females in the Suwannee population is estimated at 80 individuals. Young of the year utilize open sand habitat away from shoreline and vegetated habitat. They disperse widely, and occur over freshwater reaches from rkm 10-237; no particular affinity with spring water habitat is evident. Larger Gulf sturgeon tend to congregate in deep holes serving as summer-fall holding areas. They fast and lose weight while remaining in freshwater, but more than compensate this loss during winter feeding in marine waters. The major downriver migration to the estuary takes place in October-November. After a period of river mouth staging, subadults and adults migrate into Gulf of Mexico nearshore mesohaline waters. They move further out and into deeper water (> 3 m) when water temperatures drop in mid-December, but final destinations in mid-winter remain unknown. Age-2 through 6 juveniles remain in the river mouth estuary over winter. In late January through early February YOY migrate downriver for the first time, joining larger juveniles to overwinter and feed. Tag and recapture data yield a Suwannee River population of Gulf sturgeon estimated at 7,650 individuals, with an annual turnover rate of 16%. Based on stability in cumulative recapture rates from 1991-1998, population size is stable with an effective balance between recruitment and mortality. However, population structure is dynamic, controlled by the juxtaposition, conjunction, and summation of successive strong and weak year classes. Length/age frequency distributions for 1995 and 1998 populations censuses are very different. The 1995 distribution is bimodal with a dominant mode of 9-14 year old subadults/adults, and a sub-dominant of mode of 2-4 year old juveniles. The 1998 distribution is trimodal, but overwhelmingly dominated by 6-9 year old subadults. Erosion by 1998 of the major subadult/adult mode from the 1995 census illustrates that large adults encounter the same high mortality as smaller fish. Ultimate adult size in the population has remained constant at 2.2 cm TL over 13 years, indicating a maximum life expectancy of 25 years for Suwannee River Gulf sturgeon.