Changes and Patterns of Biodiversity of the Intertidal Zone

Red Head sample site, Great Wass Island
Red Head sample site, Great Wass Island. Photo by Tom Trott.
Project Summary:

This study surveyed intertidal invertebrates along the coast of Maine, comparing current communities to those recorded from the same sites thirty years ago.

Location:

Coastal Maine, June – August 2004

Significance

Unraveling cause and effect in natural environments is extremely complex, but it begins with measuring change. Revisiting previously sampled sites and repeating biodiversity assessments elucidates the cumulative effect of human impact, climate and environmental change, and community dynamics.

  • Thomas Trott, Suffolk University and Friedman Field Station
  • Funded by: Gulf of Maine Area Program, and The Nature Conservancy, Maine Chapter
Project Detail:

We examined epibenthic macroinvertebrate communities at six rocky intertidal locations along the Maine shore spread between Sea Point in York, Maine at the southwest extreme and West Quoddy Head in Lubec, Maine, in the northeast (43º 5′ 3″ N, 70º 39′ 30″ W to 44º 58′ 28″ N, 67º 02′ 04″ W) (see figure below). All field sites chosen had been surveyed and designated Critical Marine Invertebrate Areas in the 1970s by the Maine State Planning Office Critical Areas Program (1970-1987).

We conducted our sampling of epibenthic macroinvertebrates by recording species observed on the surface and under rocks during a random walk through the intertidal zone. Sampling time and the frequency of rock flipping were proportionate to the size of the intertidal area.

With the exceptions of Sea Point and West Quoddy Head, we consistently found more species during the present investigation than were found during the original Critical Area evaluations. Excluding West Quoddy Head, this difference held for higher taxa as well. Molluscs were most numerous at all locations, a feature consistent with the original Critical Area evaluations. Arthropods were the next most common taxon found both historically and in our study, except in the original site evaluations for Red Head and West Quoddy Head where there were more species of annelids and echinoderms, respectively. Annelids and echinoderms were the next two most frequently encountered phyla in this study, followed by cnidarians. Poriferans, plathyheminths, nemerteans, ectoprocts, and chordates comprised minor portions of species assemblages at all locations.

Species richness decreased from 71 to 39 south to north with the greatest numbers of species found at Sea Point where habitats were most heterogeneous (bedrock, boulder, cobble, gravel, and sand are all present at this site). Average phylogenetic diversity increased and total phylogenetic diversity decreased south to north.

We also identified a geographic trend in β-diversity (the differences in diversity between sample sites). Specifically, species assemblages south of Penobscot Bay clustered together and were significantly different from communities sampled north of the bay, which also formed a distinct cluster. This study is the first to provide evidence from rocky intertidal habitats in support of the idea that Penobscot Bay represents a faunal break point. Coastal currents likely contribute to this distribution pattern.

Finally, we statistically compared the sampled species assemblage from each location to the historical master species list compiled by the Maine Critical Areas Program using average taxonomic distinctness. This analysis revealed that intertidal epibenthic macroinvertebrate diversity has changed significantly only at Sea Point and Bailey Island, the two southern-most locations. Comparisons made with original site descriptions and photographs did not show any detectable disturbances which could account for changes at these sites. While the causes for the measured changes are probably numerous, a trend of increasing sea water temperature may be a clue.

map of study area

Publications:

Trott, Thomas J. in preparation. Zoogeography and changes in macroinvertebrate community diversity of rocky intertidal habitats on the Maine Coast.

Trott, T.J. 2007. Can biodiversity be measured independent from sampling effort? In: Challenges in Environmental Management in the Bay of Fundy-Gulf of Maine. Proceedings of the 7th Bay of Fundy Science Workshop, St. Andrews, New Brunswick, 24–27 October 2006. Pohle, G. W., P.G. Wells, and S.J. Rolston (Eds). Bay of Fundy Ecosystem Partnership Technical Report No. 3. Bay of Fundy Ecosystem Partnership, Wolfville, NS. pp. 263-266. (PDF – 1005kb)

Trott, T.J. 2007. Zoogeography and changes in macroinvertebrate community diversity of rocky intertidal habitats on the Maine coast. In: Challenges in Environmental Management in the Bay of Fundy-Gulf of Maine. Proceedings of the 7th Bay of Fundy Science Workshop, St. Andrews, New Brunswick, 24–27 October 2006. Pohle, G.W., P.G.Wells, and S.J. Rolston (Eds). Bay of Fundy Ecosystem Partnership Technical Report No. 3. Bay of Fundy Ecosystem Partnership, Wolfville, NS. pp. 54-73. (PDF – 1008kb)