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 1

Trophic Level 2

Trophic Level 3

Trophic Level 4

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.

So, does increased abundance of tropical snappers and groupers in the northern Gulf of Mexico affect offshore resident reef fishes?

Also: Increasing rank of abundance of gray, lane snapper and gag, red groupers in GOM landings

+ = ?

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?