On April 21st, Dr. Lindsay Green-Gavrielidis, Professor Austin Humphries, and I joined Russ Blank of Rome Point Oysters to take some final growth measurements of kelp before the upcoming harvest. Since the lines were seeded and planted out at the farms, Lindsay has been going back every month to monitor the growth of the kelp, which is kept track of using a hole-punch as a reference point. This may sound like a strange way to monitor growth, but it is actually a tried and true method of kelp ecologists.

 A Rome Point Oysters kelp line is pulled out of the water for growth measurements.  Photo credit: Austin Humphries

A Rome Point Oysters kelp line is pulled out of the water for growth measurements. Photo credit: Austin Humphries

The Hole-Punch Method

Hole punches are placed at a consistent 10 cm down the blade from the stipe (the stalk that supports the kelp blade). When we return a month later, the hole punch will have moved further away from the stipe along the blade and this can be measured to estimate elongation of the blade since it was hole punched.

Kelp Biomass Collection for Productivity Estimates

 Celeste cuts kelp off the line for productivity estimates.  Photo credit: Austin Humphries

Celeste cuts kelp off the line for productivity estimates. Photo credit: Austin Humphries

On this particular trip, we collected individuals from each of the lines that had been hole-punched the previous month and hole punched a new set of individuals. Since this was our last visit out to the site before harvest, we also selected a 10 cm segment of rope on each line and collected all the kelp from these sections as a way of ultimately being able to estimate overall productivity. It was challenging to cut all of the holdfast pieces that had grown tangled together around the rope. Austin did a great job with the camera catching all the weird facing I made through this process. On some of the lines, many of the kelp blades were taller than me (I’m 6’1”). Lastly, a trip out on Russ’s farm wouldn’t be complete without a visit from one of his friendly seagulls who like to hang around on the front of the boat in case there are scraps.

Kelp Morphometrics and Nutrient Analysis

Back in the lab, Dr. Lindsay Green-Gavrielidis takes length and width measurements of the hole punched blades. Other individual kelp blades are dried on foil sheets. Once these individuals are dry they are ground up for carbon and nitrogen content analysis. You have to be careful with the mortar and pestle, because the dry kelp is quite brittle and prone to jumping out of the mortar. There is a lot you could analyze in these samples, but we will measure nitrogen and carbon content because nitrogen is the main nutrient limiting kelp growth and carbohydrates are made in the central process of photosynthesis. I will be using the kelp data collected to fit an individual energy-based growth model called a dynamic energy budget model.

Written by: Celeste Venolia