Relationship of Live Shell to Dead "Brown" Shell

The relationship of live shell to dead “brown” shell in the oxic region above the sediment water interface can be viewed as a quantitative index of reef health in that shell encourages recruitment and growth of live oysters above the sediment water interface, although we are unaware of any such analysis in the published literature. The individual regions are presented below as volumetric plots with the live animal value being estimated from biomass. Linear fits, employing a y = m0 + m1 * x form, are added to each plot.  A summary of the descriptive fits is as follows:

(A) Pocomoke and Tangier Sounds: y = 5990.2 + 0.09x, r2 = 0.40

(B) Great Wicomico River: y = -13609 + 0.31x, r2 = 0.64

(C) Rappahannock River: y = 5079.7 + 0.07x, r2 = 0.33

(D) Piankatank River: y = 33.4 + 0.16x, r2 = 0.68

(E) Mobjack Bay: y = 5057.5 + 0.08x, r2 = 0.29

(F) York River: y = 31307 + 0.05x, r2 = 0.29

(G) James River: y = -69275 + 0.25x, r2 = 0.75 

(H) Elizabeth and Lafayette Rivers: y = 12409 + 0.04x, r2 = 0.29

Notable among the descriptors are the slopes for the Great Wicomico and James Rivers in the 0.247-0.281 range, higher than that for the Piankatank (0.156), but all with r2 values >0.60. The remaining locations exhibited both lower slopes (<0.1) and lower r2 values (<0.60).  The former grouping is generally considered to have the highest standing stock per unit area and consistent history of recruitment.  This relationship would appear to be anything but constant across the surveyed systems and is worthy of additional examination with respect to critical values for “healthy” versus challenged reef systems.

Brown shell volume (L) versus live shell volume (L) in Pocomoke and Tangier Sounds (region A). Brown shell volume (L) versus live shell volume (L) in the Great Wicomico River (region B).
Brown shell volume (L) versus live shell volume (L) in the Rappahannock River (region C). Brown shell volume (L) versus live shell volume (L) in the Piankatank River (region D).
Brown shell volume (L) versus live shell volume (L) in Mobjack Bay (region E). Brown shell volume (L) versus live shell volume (L) in the York River (region F).
Brown shell volume (L) versus live shell volume (L) in the James River (region G). Brown shell volume (L) versus live shell volume (L) in the Elizabeth and Lafayette Rivers (region H).

Link to Recruitment and Shell Substrate