965 resultados para Primary contribution


Relevância:

20.00% 20.00%

Publicador:

Resumo:

The primary objective of this study was to predict the distribution of mesophotic hard corals in the Au‘au Channel in the Main Hawaiian Islands (MHI). Mesophotic hard corals are light-dependent corals adapted to the low light conditions at approximately 30 to 150 m in depth. Several physical factors potentially influence their spatial distribution, including aragonite saturation, alkalinity, pH, currents, water temperature, hard substrate availability and the availability of light at depth. Mesophotic corals and mesophotic coral ecosystems (MCEs) have increasingly been the subject of scientific study because they are being threatened by a growing number of anthropogenic stressors. They are the focus of this spatial modeling effort because the Hawaiian Islands Humpback Whale National Marine Sanctuary (HIHWNMS) is exploring the expansion of its scope—beyond the protection of the North Pacific Humpback Whale (Megaptera novaeangliae)—to include the conservation and management of these ecosystem components. The present study helps to address this need by examining the distribution of mesophotic corals in the Au‘au Channel region. This area is located between the islands of Maui, Lanai, Molokai and Kahoolawe, and includes parts of the Kealaikahiki, Alalākeiki and Kalohi Channels. It is unique, not only in terms of its geology, but also in terms of its physical oceanography and local weather patterns. Several physical conditions make it an ideal place for mesophotic hard corals, including consistently good water quality and clarity because it is flushed by tidal currents semi-diurnally; it has low amounts of rainfall and sediment run-off from the nearby land; and it is largely protected from seasonally strong wind and wave energy. Combined, these oceanographic and weather conditions create patches of comparatively warm, calm, clear waters that remain relatively stable through time. Freely available Maximum Entropy modeling software (MaxEnt 3.3.3e) was used to create four separate maps of predicted habitat suitability for: (1) all mesophotic hard corals combined, (2) Leptoseris, (3) Montipora and (4) Porites genera. MaxEnt works by analyzing the distribution of environmental variables where species are present, so it can find other areas that meet all of the same environmental constraints. Several steps (Figure 0.1) were required to produce and validate four ensemble predictive models (i.e., models with 10 replicates each). Approximately 2,000 georeferenced records containing information about mesophotic coral occurrence and 34 environmental predictors describing the seafloor’s depth, vertical structure, available light, surface temperature, currents and distance from shoreline at three spatial scales were used to train MaxEnt. Fifty percent of the 1,989 records were randomly chosen and set aside to assess each model replicate’s performance using Receiver Operating Characteristic (ROC), Area Under the Curve (AUC) values. An additional 1,646 records were also randomly chosen and set aside to independently assess the predictive accuracy of the four ensemble models. Suitability thresholds for these models (denoting where corals were predicted to be present/absent) were chosen by finding where the maximum number of correctly predicted presence and absence records intersected on each ROC curve. Permutation importance and jackknife analysis were used to quantify the contribution of each environmental variable to the four ensemble models.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Using a 10-yr time-series data set, we analyzed the effects of two severe droughts on water-quality and ecosystem processes in a temperate, eutrophic estuary (Neuse River Estuary, North Carolina). During the droughts, dissolved inorganic nitrogen concentrations were on average 46–68% lower than the long-term mean due to reduced riverine input. Phytoplankton productivity and biomass were slightly below average for most of the estuary during a spring–autumn drought in 2002, but were dramatically lower than average throughout the estuary during an autumn–winter drought in 2007–2008. Droughts affected upper trophic levels through alteration of both habitat condition (i.e., bottom-water dissolved oxygen levels) and food availability. Bottomwater dissolved oxygen levels were near or slightly above average during the 2002 drought and during summer 2007. Concomitant with these modest improvements in bottom-water oxygen condition, fish kills were greatly reduced relative to the long-term average. Low-oxygen bottom-water conditions were more pronounced during summer 2008 in the latter stages of the 2007–2008 drought, and mesozooplankton abundances were eight-fold lower in summer 2008 than during nondrought years. Below-average mesozooplankton abundances persisted for well over 1 yr beyond cessation of the drought. Significant fish kills were observed in summer 2008 and 2009, perhaps due to the synergistic effects of hypoxia and reduced food availability. These results indicate that droughts can exert both ephemeral and prolonged multiyear influence on estuarine ecosystem processes and provide a glimpse into the future, when many regions of the world are predicted to face increased drought frequency and severity due to climate change.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The food sources of the leptocephali of the teleostean superorder Elopomorpha have been controversial, yet observations on the leptocephali of the worm eels, Myrophis spp. (family Ophichthidae) collected in the northern Gulf of Mexico indicate active, not passive, feeding. Leptocephali had protists in their alimentary canals. Estimates of the physiological energetics of worm eels indicate that large aloricate protozoa including ciliates could provide substantial energy to these leptocephali toward the end of the premetamorphic and metamorphic stages, given the low energy requirements of metamorphosing leptocephali. Global ocean warming will likely force a shift in oceanic food webs; a shift away from large protozoa toward smaller protists is possible. Such a disruption of the oceanic food webs could further compromise the survival of leptocephali.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

This study provides an overview of the aquaculture sector in Ghana. It assesses the actual and potential contribution of aquaculture to poverty reduction and food security, and identifies enabling conditions for and drivers of the development of Ghana’s aquaculture sector. The study uses data collected from a variety of primary and secondary sources, including key informant interviews with actors within the aquaculture sector and relevant secondary literature.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Fluctuations in primary productivity at two subalpine lakes reveal both meteorological and biological influences. At Castle Lake, California, large-scale climate events such as the El Niño/Southern Oscillation affect total annual production and, combined with human fishing activity, modify the seasonal pattern of productivity. At Lake Tahoe, California-Nevada, local spring weather conditions modulate annual production and its seasonality by determining the depth of mixing and resulting internal nutrient load. Climatic conditions also contribute to deviations from the long-term trend in productivity by increasing the incidence of forest fires and through anomalous external nutrient loads during precipitation extremes. A 3-year cycle in productivity of as yet unknown origin has also been detected at Lake Tahoe.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Difference in zooplankton production in estuarine, coastal and oceanic realms of the Indian Ocean has been correlated to the fishery potential of the concerned area. In the estuarine habitat the estimated rate of secondary production can not sustain a fishery of the present magnitude. Direct correlation between fish landing and zooplankton is observed in the coastal waters. Compared to coastal waters zooplankton standing stock is low in the open ocean and this low production is compensated by a wider area. The estimated fishery potential of the ocean is much more than what is being exploited.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The rich zooplankton standing stock of Dharamtar Creek showed a variation of 8 to 5261 (av. 1032) mg C/100 m super(3)/d which led to a turnover of 29 tonnes C/km super(2)/y. The estimated fishery potential from zooplankton production was 0.079 tonnes C/km super(2) or 29.00 tonnes/km/y. The worked out yield in terms of wet weight of fish was 0.059 tonnes/km2u2/d. Experimental trawling within the creek showed a potential of 0.19 tonnes/km super(2)/d suggesting a transfer coefficient of only 31.4% form secondary to tertiary level. Fish eggs and larvae were very common in the area but contributed collectively only 1% to the total zooplankton population. On an average the outer zone sustained relatively higher population of fish eggs and larvae than the interior zone. The mean population density of larvae (334/100 m super(3)) was 3.5 times higher than fish eggs (93/100 m super(3)) suggesting the good survival rate and a congenial environment for larvae to thrive.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The coastal areas of Bombay are generally turbid and the euphotic zone in these waters hardly exceeds 6 m. Primary productivity is largely confined to surface layers. Nearshore polluted stations have low values of dissolved oxygen, salinity and pH. Nutrients, on the other hand, are high. Primary productivity in these areas was 16.86 mg C m super(-3) d super(-1) in October. Column production for all the 4 stations ranged from 10.32 to 2511.30 mg C m super(-2) d super(-1). A direct correlation was found between nutrients and productivity values.