Ocean Food Webs – One Ten East log

One Ten East Logs from the IIOE-2 voyage aboard RV Investigator will be posted on the WAMSI website during the month long voyage.

 

Today’s rousing trade winds were for perfect sailing across the Indian Ocean pond! If we hang up all the sheets, we’ll be there shortly Kiran and Satya!

– Captain Micheline Jenner 

 

 

Log from One Ten East

The RV Investigator is currently undertaking oceanographic research along the 110°E meridian off Western Australia as part of the second International Indian Ocean Expedition. The voyage is led by Professor Lynnath Beckley of Murdoch University and the research is supported by a grant of sea time on RV Investigator from the CSIRO Marine National Facility.

 

Date: June 02, 2019	Time:  1200 AWST
Latitude: 15.5°S	Longitude: 110°E
Wind direction: E	Wind speed: 17 knots
Swell direction: SE 2m, NE 0.5m, SW 2m	Depth: 5727 m
Air temperature: 27°C	Sea temperature: 27°C
Notes: At Station 17 of 20 on the 110°East line, we are in some of the deepest water so far.

 

Ocean Food Webs

By Prof Michael Landry

 

Food webs describe the feeding (trophic) relationships that exist among organisms in an ecosystem. If you have heard the old fisherman’s adage that “big bait catches big fish”, you may intuitively understand how ocean food webs operate, mainly on the basis of size, with larger consumers eating successively smaller prey down to where it all begins with microscopic phytoplankton. This is fundamentally different than food webs on land, where the plants are often much larger than their consumers (e.g., insects grazing on trees).

A further twist of ocean food webs is that different ocean conditions select for different sizes of phytoplankton. In the poorest (oligotrophic) environments, which occur over much of the tropical and subtropical open ocean, very small phytoplankton (photosynthetic bacteria) dominate because they are the most efficient competitors for nutrient uptake at low concentrations. In nutrient-rich coastal systems, large phytoplankton are dominant. One consequence of this difference is that open-ocean food webs lose most of their energy in transfers from tiny producers to tiny consumers on up, with little remaining in the end to support fisheries. In contrast, richer systems with large phytoplankton and larger consumers have fewer steps of intermediate consumers and can channel productivity more efficiently to fishes.

In this project (IN2019_V03), we are taking two approaches to compare food-web relationships along the stations and regions on the cruise track. One is experimental, involving measurements of community composition, productivity and grazing rates. The other utilizes information that resides in the isotopic composition of planktonic consumers to quantify their mean trophic positions in the food web relative to phytoplankton.

 

Claire Davies (IMOS/CSIRO) halves one of the filtered zooplankton samples for sonification and fluorometric analysis to ascertain grazing by copepods. Photo: Micheline Jenner AM.

 

Prof Raleigh Hood (University of Maryland Center for Environmental Science) shows the copepod material which was macerated with the sonicator (a low frequency sound emitted from the metal spike, in backgorund) prior to determination of the chlorophyll content. Photo: Micheline Jenner AM.

 

Claire Davies (IMOS/CSIRO) measures the chlorophyll content with the fluorometer to determine the extent of grazing on phytoplankton by copepods in the mesozooplankton samples collected with the oblique plankton tow. Photo: Micheline Jenner AM.

 

Be sure to follow our daily Log from One Ten East at https://iioe-2.incois.gov.in or www.wamsi.org.au
 

The natural mysteries of the Kimberley, one of Australia’s last pristine habitats, have been documented like never before thanks to a multi-million-dollar project.

 

Kimberley Marine Research Program

One Ten East Logs from the IIOE-2 voyage aboard RV Investigator will be posted on the WAMSI website during the month long voyage.

Today we are at Station 17. We are slowly creeping north with our studies and the pygmy blue whales are calling us northward too! – Captain Micheline Jenner 

Log from One Ten East

The RV Investigator is currently undertaking oceanographic research along the 110°E meridian off Western Australia as part of the second International Indian Ocean Expedition. The voyage is led by Professor Lynnath Beckley of Murdoch University and the research is supported by a grant of sea time on RV Investigator from the CSIRO Marine National Facility.

Date: June 03, 2019	Time:  1200 AWST
Latitude: 14°S	Longitude: 110°E
Wind direction: ESE	Wind speed: 17 knots
Swell direction: ENE 2m, ESE 2m	Depth: 5715 m
Air temperature: 27°C	Sea temperature: 28°C

Notes: Two crested terns flew around the ship today. With few seabird sightings in the last week, their fluttering was encouraging and welcome!

Isotopes in Food Web Studies

By Michael Landry

Direct measurements of phytoplankton growth and grazing by micro- and mesozooplankton are one way to look at variability in trophic structure in our study region (e.g., how many steps are mesozooplankton removed on average from phytoplankton). Analyses of bulk nitrogen and carbon isotopes from the size-fractioned mesozooplankton net tows will also provide an independent check on these estimates. Trophic information from isotopes comes from the fact that the lighter and more abundant isotope of nitrogen (¹⁴N) is selectively utilized by organisms when they metabolize, so the remaining proteins in animal tissues get enriched in the heavier isotope ¹⁵N. There’s a saying for this, “You are what you eat plus 3.4 parts per thousand ¹⁵N”, which captures the notion that this particular relationship has been widely applied in food web studies of both aquatic and land systems.

An additional important goal of our study is to use isotopes to determine how the food web may have changed over the five decades since the first International Indian Ocean Expedition (IIOE). This cannot be done by standard bulk isotope method which would require separate sampling for phytoplankton isotopes which vary substantially depending on whether the main source of N to the food web is nitrate mixed upward from deep water or fixed N₂ gas from the atmosphere (or some combination). Instead, we will use a relatively new technique called Compound-Specific Isotopic Composition of Amino Acids (CSIA-AA), which relies on differences in isotopic enrichment of individual amino acids to provide information. A group of source AAs retains ¹⁵N enrichment values similar to the baseline value of N. Another group of trophic AAs enriches very strongly with each trophic transfer step. The fact that N isotopic composition doesn’t change much with long-term preservation in formalin means we can use historical IIOE samples collected at the same stations and same time of year in the 1960s to compare N sources and trophic structure for the same dominant species sorted from the samples.

 

 

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