GLOBEC 2000: Gulf of Alaska copepod growth and reproduction
R. R. Hopcroft, K. Coyle & R. Gradingerb [all at University of Alaska]

Over the last few decades our knowledge of the zooplankton communities in the subarctic Pacific has improved considerably. We now appear to know the important players in the communities and their overall life histories. Nonetheless, our knowledge of copepod population dynamics is largely inferential through the examination of preserved collections (i.e. natural cohort analysis). There are few direct measurements of birth, growth or development for the dominant copepod species in the Gulf of Alaska (GoA). This is true not only for the region, but also for those species over their entire geographic range. A fundamental goal of the GLOBEC program is to understand the secondary production of the GoA and how the success of higher trophic levels, specifically salmon, are affected by the variability in the magnitude of secondary production seasonally, inter-annually, and at the decadal scale. Furthermore, because of the highly advective nature of the GoA, it will be necessary to establish the relative importance of local versus imported production. We cannot begin to address these questions without direct knowledge of the rates of development, growth and egg production, and how each is related to the environment.

This proposal seeks to undertake a comprehensive determination of rates of development, growth and egg production for the dominant copepod species in the GoA. It will determine the in situ rates inshore and offshore on LTOP cruises scheduled for 2000-2004 by incubation techniques employing artificial cohorts and individual females. Incubation techniques are the only appropriate methods for this region due to its highly advective nature. The proposed research will put the in situ rates in perspective by determining their maximal rates under food-saturated conditions in the laboratory. It will estimate the extent to which secondary production is food-limited in the field. It will determine the functional relationships of development, growth and egg production to body size, temperature and food regimes. Food regimes will be assessed in terms of chlorophyll and particulate organic carbon, plus the abundance and biomass of autotrophic and heterotrophic protists. It will estimate the rates of local copepod production, along with their temporal and spatial variability.

Thus, this proposal will provide half of the required information directed to the question of local versus advected production. At this point, it would be prohibitive to address the entire question in a single proposal. Other proposals address the other half of the question; establishing the rates of advection in this ecosystem. Still other proposals seek to understand the feeding or production of other groups. When all are complete, through synthesis it will be possible to establish the relative importance of each, and how their importance varies over space and time. The implications of these physical versus biological processes on the success of salmon recruitment can then be established and predicted.

DATA COLLECTION DETAILS AND TIME-LINE

Year 1

• After a brief period of organization, we will commence activities on the December 2000 GoA LTOP cruise. Realistically, this first cruise should be considered a 'shake-down' operation, although we do expect to generate usable data on cohorts at least in the smaller size-fractions. We expect to find females of many of the egg scattering species dormant, effort on egg production may therefore be relatively small. Sac-spawners will be active, and incubated. This cruise occurs at a time when zooplankton biomass and growth rates are near their seasonal minimums, thus any experimental difficulties will have minor impact on the overall data set. On this first cruise we will collect diapauing females of Neocalanus flemingeri and return them to the lab for incubation over the winter months to determine egg production. We will simultaneously collect deep diapausing late copepodites of Neocalanus cristatus and Neocalanus plumchrus to assess if they can be successfully cultured through to egg producing females.

• On subsequent LTOP cruises, March, April, May, July, and August 2001, we will be fully operational, running incubations to determine naupliar and copepodite growth, plus egg production for the dominant species encountered. It is hoped that a portion of the egg production experiments can be fully processed and quantified prior to the end of each cruise.

• It is essential that the processing of incubation experiments in Year 1 keeps up with the cruises so that we can quickly determine and implement any required modification to our methods (i.e., choice of mesh sizes used to create cohorts, duration of incubations).

• By year end we will know the ranges of development, growth and egg production rates to expect in subsequent years. We will assess if there is any further optimization of methods, or if any species require more intense targeting for rate estimates.

Year 2

• Activities will continue as described for Year 1. We will participate in 7 cruises, October, December, March, April, May, July, and August, determining naupliar and copepodite growth, plus egg production for the dominant species encountered.

• We will determine relationships between length and fresh weight (wet-weight, dry weight, carbon, and nitrogen) for the dominant species, and typical weight losses on preservation.

• Deep-collected Neocalanus species will again be incubated in the laboratory. In the laboratory we will begin systematic attempts to determine maximum food saturated rates of growth and development for selected species.

• By year end we should be able to make preliminary estimates putting bounds on the rates of secondary production for the GoA region examined in prior years.

Details for years 3-5 not shown.

This page was last updated on September 22, 2000.

Maintained by:
Hal Batchelder [hbatchelder@coas.oregonstate.edu
College of Oceanic & Atmospheric Sciences
Oregon State University
Corvallis, OR 97331-5503
phone: 541-737-4500; FAX 541-737-2064