Purple Sea Urchin Barrens Nancy, Cassie and Jessica Pattern Sea Urchins existing in two stable states. Crevices along coastlines feeding on kelp litter that drifts by Emerged from the crevices creating urchin barrens Destroys kelp forests. Prevents new kelp recruitment Why? Low food availability because of storms and El Nino events Reduction of predators sea otters, spiny lobsters and sheep-head fish 1
Sites of Kelp Forest Destruction Goal To determine which factor, food availability or predation, has the most effect on the movement of urchins from the crevices near the shore to the kelp forest and the creation of barrens. 2
Hypotheses General 1: Predation is the main influence that keeps sea urchins in the crevices of the coastline. If sea otters are absent urchins will move away from the crevices of the coastline to feed directly on kelp. If spiny-lobsters are urchins will move away from the crevices of the coastline to feed directly on kelp. If sheep-head fish are absent urchins will move away from the crevices of the coastline to feed directly on kelp. General 2: Food availability is the main influence that keeps sea urchins in the crevices of the coastline. When there is low food availability because of kelp forest destruction urchins will move from the crevices of the coastline to feed directly on kelp. Strongylocentrotus purpuratus Commonly known as the purple urchin. 8mm test, 1mm spines Movement, protection, feeding. West coast of N. America from Canada to Baja. 3
Predators: Sea Otters Very few southern sea otters left from Point Conception to San Diego. Largest population : Half Moon Bay to Point Conception. Previously hunted for fur. Primarily killed by pollution such as agricultural runoff, sewage plants, marinas, and boat yards. Oil spills are a major threat. Keystone species of the kelp forest. Part of main diet is sea urchins. Predator: Spiny Lobster Live in the rock in and around kelp forests Prey on sea urchins and are eaten by a variety of fishes. Small localized fishery in southern California that focuses on spiny lobsters. Catching spiny lobsters is a recreational sport in southern California. 4
Predator: Sheep-head fish Species of rockfish. Their diet consists of barnacles, mussels, sea urchins, spiny lobsters. 1988 live-fish fishing started and one of the species targeted were the sheep-head fish. From 1981 to 1986, an average of 189 sheep-head per year was taken from the Point Loma kelp forest near San Diego; by 1994 9, the average number had dropped to 14. Destruction of the kelp forest Caused by episodically by storms and El Nino events Also caused by pollution Kelp forest biomass can range from 3-22kg/m 2 Limits food availability Urchins feed on the newly recruited kelp Prevents recovery of the kelp forest.
Experiments If sea otters are absent then urchins will move away from the crevices to feed on kelp directly. Chose 6 kelp forest sites from Half Moon Bay to Point conception. Net off 3 1m 2 sites to prevent otter predation. Allow otters to prey on urchins at 3 other sites. Measured bio mass of kelp forest and abundance of urchins every month. Counted number of urchins in crevices and number of urchins directly feeding on kelp. Continued for 1 year. Experiments If spiny-lobsters are absent urchins will move from crevices to feed on kelp directly. Chose 6 sites (separate from otter sites). Physical removal of all spiny lobsters within a 1m 2 area. Every month biomass of kelp and number of urchins measured. Number of urchins on crevices and directly feeding on kelp measured. Any new spiny lobsters removed. Continue monthly for 1 year. 6
Experiments If sheep-head fish are absent urchins will move away from the crevices to feed directly on the kelp. Chose 6 sites of 1m 2 area, physically remove all sheep-head fish from 3 sites. Measure bio mass of kelp and abundance of urchins every month. Count number of urchins present in the crevices and directly feeding on kelp. Continue monthly for 1 year. Experiments When there is low food availability because of kelp forest destruction urchins will move from the crevices of the coastline to create barrens. Chose 6 kelp forest sites of 1m2. Remove kelp to prevent kelp drift. Remove and measure biomass of any new kelp growth every month. Count number of urchins in crevices and number feeding directly on kelp out of the crevices. Continue monthly for one year. 7
Results 2 2 2 2 1 1 Crevices (#/m^2) 1 1 Urchins living in Crevices (#/m^2) on kelp directly (#/m^2) on kelp (#/m^2) Jan Mar May Jul Sept Nov Jan Mar May Jul Sept Nov Figure 1. Average effect of absence of sea otters on kelp biomass and the number and location of urchins. Figure 2: Null: Average effect of the absence of sea otters on kelp biomass and the number and location of urchins. Results 2 2 1 1 Kelp Forest Biomass Number of Sea Crevices Number of Sea on kelp 2 Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Figure 3. Average effect of absence of spiny lobster on biomass of kelp and number of urchins. 2 1 1 Kelp Forest Biomass Crevices (#/m^2) Urchins feeding on kelp (#/m^2) Jan Mar May Jul Sept Nov Figure 4. Null: Average effect of the absence spiny lobster on biomass of kelp and number of urchins. 8
Results 2 2 18 2 1 1 Jan Mar May Jul Sept Nov Crevices (#/m^2) Urchins feeding on kelp (#/m^2) 16 14 12 1 8 6 4 2 Jan Mar Jun Aug Oct Dec Crevices (#/m^2) on kelp (#/m^2) Figure. Average effect of the absence of sheep-head fish on kelp biomass and urchin abundance and location. Figure 6. Null: Average effect of the absence of sheep-head fish on kelp biomass and urchin abundance and location. Results 1 2 9 8 2 7 6 4 3 Kelp Bio Mass Crevices (#/m^2) on kelp (#/m^2) 1 1 crevices (#/m^2) Urchins feeding on kelp (#/m^2) 2 1 Figure 7. Average effect of the absence of kelp on the abundance and location of sea urchins. Jan Mar Jun Aug Oct Dec Jan Mar Jun Aug Oct Dec Figure 8. Null: Average effect of kelp on the abundance and location of sea urchins. 9