Transcript Marshak Marine Ecol Overfishing and Climate Change Lecturex

Overfishing affects Marine Ecology
• Major top-down force which has led to major
depletion of top predators
• By removing species which exert control over
lower consumers, there are severe consequences
to marine ecosystems through trophic cascades
• Famous paper by Pauly et al. (1998) which spoke
of fishing down marine food webs
Pauly, D. et al. 1998. Fishing down marine
food webs. Science 279: 860-863
• Major decline in the mean trophic level of
commercial species taken by global fisheries
• Historical depletion of top predatory fishes has
led to fisheries now targeting lower trophic level
consumers and herbivorous fishes
• Generally, trophic levels range from 1 to 5
– Primary producers (lowest) to top predators (highest)
Pauly, D. et al. 1998. Fishing down marine
food webs. Science 279: 860-863
Trophic Level 4
Trophic Level 3
Trophic Level 2
Trophic Level 1
Pauly, D. et al. 1998. Fishing down marine
food webs. Science 279: 860-863
Figure 1A – Decline in average trophic
level due to importance of
planktivorous Peruvian anchoveta.
Fishery collapse and increase in
mean trophic level during early
1970s, and steady decline over time.
Figure 1B – Inland areas see steady
mean level up to mid 1970s and
decline afterward
Pauly, D. et al. 1998. Fishing down marine
food webs. Science 279: 860-863
Pauly, D. et al. 1998. Fishing down marine
food webs. Science 279: 860-863
• Trophic levels of fisheries landings declined in
recent decades at rate of 0.1 per decade
• Also declines in landings occurring compared to
historical values
• Suggest any rebuilding of fish populations will
have to focus on restoring food webs through
“no-take” Marine Protected Areas
Essington, T. et al. 2006. Fishing through
marine food webs. PNAS 103: 3171-3175
• Alternative view is fishing through food webs
where continue to fish for upper trophic levels
with sequential addition of lower trophic level
fisheries.
– E.g. Continue to fish for snapper and grouper
while concurrently targeting parrotfish and other
herbivores
A.) Sequential collapse/replacement
mode where mean trophic level
declines over time and old fisheries
are replaced with new ones at lower
trophic levels
B.) Sequential addition mode of
fishing down the food web where
continue to fish at all trophic levels
and introduce new fisheries as well
Essington, T. et al. 2006. Fishing through
marine food webs. PNAS 103: 3171-3175
• Essington et al. found that fishing down the food
web is very prevalent in marine ecosystems, and
the sequential addition model is occurring as
opposed to the collapse/replacement model
which was only found in N. Atlantic ecosystems
• Seeing fishing at all trophic levels which can have
major consequences for marine ecosystems AKA
fishing through marine food webs
Jackson, J.B.C. et al. 2001.
Historical Overfishing and the Recent Collapse
of Coastal Ecosystems. Science 293: 629-638
• Historical overfishing has altered coastal ecosystem
structure through targeting of top consumers, having
resulted in losses of previously abundant members of
the food web and increases in other members who
were once less abundant
• Analyzing historical and paleontological data allowed
for reconstruction of historical ecosystem structure
prior to the impacts of overfishing
Jackson, J.B.C. et al. 2001.
Historical Overfishing and the Recent Collapse of Coastal
Ecosystems. Science 293: 629-638
Once abundant sea otters and cod preyed on lobster and sea urchin to
allow kelp to thrive. After historical depletion, we see increased lobster
and sea urchin and less kelp, along with species hunted to extinction.
Jackson, J.B.C. et al. 2001.
Historical Overfishing and the Recent Collapse
of Coastal Ecosystems. Science 293: 629-638
Jackson, J.B.C. et al. 2001.
Historical Overfishing and the Recent Collapse
of Coastal Ecosystems. Science 293: 629-638
Regional warming and increased abundance of
tropical snappers & groupers in the nGOM
Could resident reef fishes be in hot water?
General distribution of most GOM snapper and grouper species
(From http://www.fishbase.org)
Regional warming is thought to result in a poleward shift in the species
distribution of marine fishes, which could alter community interactions
Fodrie, F.J. et al. 2009. Climate-related, decadal-scale
assemblage changes of seagrass-associated fishes in the
nGOM
• Increased abundance and new occurrence of tropically
associated fishes that were completely absent in the
region back in the 1970s
Fodrie, F.J. et al. 2009. Climate-related, decadal-scale
assemblage changes of seagrass-associated fishes in the
nGOM
Increased abundance - Lane snapper, Red grouper, Spotfin butterflyfish, Rock sea bass,
Bluespotted cornetfish, Yellowtail snapper, Bluehead wrasse, Surgeonfishes,
Stoplight parrotfish, Gray snapper, Gag grouper
Fodrie et al. (2009) recently detected increased numbers of tropical snappers
and groupers within inshore seagrass beds of the nGOM.
Also: Increasing rank of
abundance of gray, lane
snapper and gag, red
groupers in GOM landings
+
=?
So, does increased abundance of tropical snappers and groupers in the
northern Gulf of Mexico affect offshore resident reef fishes?
Areas of investigation
• Document if tropically associated snappers and groupers
have established larger offshore assemblages in nGOM
• Niche overlap between tropical/resident species?
– similar life history parameters and trophic roles in
snappers/groupers
– Does this mean increased resource competition?
– Could “invasives” be at a higher competitive advantage?
– Examine interactions within field and experimental mesocosms
• Do interactions vary within areas subject to differential
fishing pressure?
– Are “invasives” more prevalent in areas of lower red snapper
concentration, or vice-versa?