Marine ecosystem management

Roughly 92% of the total volume of Earth's oceans is considered deep sea.
The eel species, Nemichthys scolopaceus, inhabits these waters, and little is known of
its diet, its place within pelagic food webs, and its overall ecological impact. In this
study we quantitatively estimate the abundance, feeding and predation impact of this
key predator. Specimens were collected in 2004 along Georges Bank as part of the
Census of Marine Life Gulf of Maine project. Gut contents were analyzed, revealing
thirteen prey types, primarily euphausiids and decapod crustaceans. Other potential
prey (i.e. fishes) were absent from the diet, suggesting a fairly selective feeding
preference. Of the 85 fish species collected, N scolopaceus ranked second in
abundance and first in total fish biomass. Therefore, this species is not only a large
biomass contributor, but perhaps cycles a great deal of macrocrustacean carbon
through deep-pelagic fishes in this, and likely other, ecosystems.

It can be difficult to disentangle the factors that determine population success in freshwater systems, particularly for organisms with disturbance-resistant life stages like aquatic invertebrates. Nevertheless, the effects of environmental variation and habitat structure on animal population success in wetlands are important for understanding both trophic interactions and biodiversity. I performed two experiments to determine the factors limiting crayfish (Procambarus fallax) and dragonfly (Family: Libellulidae) populations in wetland environments. A simulation of a dry-disturbance and subsequent sunfish (Family: Centrarchidae) re-colonization revealed that crayfish populations are sensitive to sunfish, while dragonfly naiads seemed to be limited by other drying-related factors. A second manipulation revealed that small-bodied fishes and habitat structure (submerged vegetation) shaped dragonfly communities primarily through postcolonization processes.

Fish predation can have structuring effects in aquatic communities, but the most important fish predators are not always immediately obvious. Generalist fish predators often occupy similar habitats and consume similar prey making determination of their consumptive impacts difficult. Understanding these consumptive impacts is important for understanding complex wetland food webs. I collected warmouth (Lepomis gulosus), bluespotted sunfish (Enneacanthus gloriosus), and dollar sunfish (Lepomis marginatus) in two seasons from sloughs for both diet and bioenergetics analysis. Macroinvertebrates dominated diets of the three species, and nonparametric analyses revealed evidence of diet ontogeny in warmouth and potential competition for prey items among gape-matched individuals. Bioenergetics modeling revealed high levels of macroinvertebrate comsumption by these species relative to macroinvertebrate reproductive output suggesting that when combined with other sources of mortality, consumptive pressures placed by sunfish on benthic macroinvertebrates may be quite large.

Two sympatric dolphin species, Stenella frontalis and Tursiops truncatus, resident to Little Bahama Bank, Bahamas were found to mostly forage independent of one another, but occasionally foraged in mixed groups. Analysis of over 20 years of data revealed the degree of overlap to be minimal with spatially distinct regions identified for both species, environmental segregation based on depth, bottom type, temperature, and time of day. Results based on observational data indicated significant differences in group size and selected prey. For S. frontalis, lactating females had the most distinct diet, which differed from that of non-reproductively active (NRA) females. Pregnant females had ambiguous prey use results, but diet differences were revealed through nutritional analysis. Lactating females had a higher intake of all nutrients (% moisture, % lipid, % protein, and calories) than pregnant females but lower than NRA females. Mother and calf pairs selected prey for caloric and moisture values. The influence of calves on foraging groups was reflected through discrete differences in all nutrients. Males and females appeared to select the same major prey, but female prey use was much more diverse.

A benthic environments classification system is devised from digital interpretations of multi-spectral IKONOS satellite imagery for 1,360 km2 of the carbonate platform and presented in a comprehensive digitized map. The classification scheme is designed as a 7th order hierarchical structure that integrates 5 Physiographic Realms, 24 Morphodynamic Zones, 11 Geoforms, 39 Landforms, 6 dominant surface sediment types, 9 dominant biological covers and 3 densities of biological covers for the description of benthic environments. Digital analysis of the high-resolution (4 m) IKONOS imagery employed ESRI's ArcMap to manually digitize 412 mapping units at a scale of 1:6,000 differentiated by spectral reflectance, color tones, and textures of seafloor topologies. The context of each morphodynamic zone is characterized by the content and areal distribution (in km2) of geomorphic forms and biological covers. Over 58% of the mapping area is occupied by sediment flats, and seagrasses are colonized in almost 80% of the topologies.

Trade-offs in traits conferring success in permanent and ephemeral habitats are often at odds with few species being able to persist in both types of environments. I examined the effect of sunfish predators on two species of south Florida crayfish to establish the mechanism that limits one species, Procambarus alleni, to short-hydroperiod environments. The crayfish assemblage response to a gradient of sunfish predators and the effect of predation on P. fallax alone was examined. I also examined the effects of sunfish on crayfish growth and quantified activity levels and risky behaviors of both crayfish species. P. alleni dominated at low sunfish densities but dominance shifted with increasing sunfish density. P. alleni was more active and likely to initiate risky behaviors, suggesting that sunfish predators remove the more active P. alleni, reducing their numbers disproportionally to those of P. fallax and allowing P. fallax to dominate crayfish assemblages in long-hydroperiod wetlands.

In estuaries, like the Indian River Lagoon, mesozooplankton have a vital role in the food web by connecting trophic levels. In this study, mesozooplankton abundance and species composition were monitored weekly on the incoming and outgoing tides from September 2006 to May 2009. For the incoming tide, the mean abundance was 2298.2 mesozooplankton/m3 (+/-325.2), and for the outgoing tide the mean abundance was 1180.0 mesozooplankton/m3 (+/-153.1). The mesozooplankton abundance on the incoming tide was significantly greater than on the outgoing tide. The most abundant type of mesozooplankton was the copepod Acartia tonsa, representing 35.0% and 52.1% of the individuals on the incoming and outgoing tides respectively. Mesozooplankton abundance values were compared with environmental data obtained from the South Florida Water Management District. The strongest positive correlation was found between chlorophyll a concentrations and A. tonsa abundance, likely due to phytoplankton being the primary food source for A. tonsa.