Water Column Communities

Understanding the impacts on ocean water column communities is even more complicated than predicting impacts on reefs. In 2002, the National Academies of Science produced a report summarizing the effect of oil on ocean communities (order the report), which states that “oil can kill marine organisms, reduce their fitness through sublethal effects, and disrupt the structure and function of marine communities and ecosystems.” The Gulf of Mexico is a critical region to many species of marine mammals and fishes that feed and use the Gulf as nursery grounds. The Harte Research Institute at Texas A&M produced a regional species inventory for the region. As they report in a short introduction to this work, “from that database, we know that the NNE octant of the Gulf (that area containing the Deep Horizon oil spill) contains 8332 species of plants and animals. Including only the major taxa of animals at all depths in the region of the spill, there are 1461 mollusks, 604 polychaetes, 1503 crustaceans, 1270 fishes, 4 sea turtles, 218 birds and 29 marine mammal species.”

Many of these species rely on the plant and animal plankton for food. Even less certain is how the amount of organic material being introduced into the Gulf will affect these microscopic species at the base of the Gulf ocean food chain. As reported by Dr. Nancy Rabalais, now leading the research effort for Louisiana Universities in the Gulf, in a 2003 article, “oil pollution also can have more subtle biological effects, caused by the toxicity of many of the compounds contained in petroleum or by the toxicity of compounds that form as the petroleum degrades over time. These effects may be of short duration and limited impact, or they may span long periods and affect entire populations or communities of organisms, depending on the timing and duration of the spill and the numbers and types of organisms exposed to the oil.”

Expedition Objective: Quantitative Assessment of Zooplankton
(P.I. Tamara Frank, Ph.D.)

Plankton are critical components all of the commercially important fisheries in the Gulf of Mexico. Many of the bottom dwelling species, like golden crab and rose shrimp, have planktonic larvae, as do valuable pelagic species like grouper and bluefin tuna. These plankton are particularly vulnerable to lethal and sub-lethal effects of oil: they may be poisoned by hydrocarbons in the spill plume, and oil has direct negative effects on their ability to swim and absorb enough oxygen from the water. Pre- and post-oil impact assessments of zooplankton in the water column will be done in shallow waters, over mesophotic (30-200 m) reef systems, and over deeper slope waters (>500m), to determine the distributions and abundances of the predominant zooplankton species. Pre-impact assessment will be used as a baseline against which to monitor the effects of oil intrusion into these areas, in order to determine if impacts at the plankton level play a role in changes in abundances of commercially important species in the next several years. Benthic species collected from each site will be examined for reproductive status and, if brooding, to document egg and larvae morphology to aid with identification of samples in zooplankton collections. A critical component of the benthic/pelagic coupling assessment is to determine when the dominant benthic species release larvae into the water column.